PMCCPMCCPMCC

Search tips
Search criteria 

Advanced

 
 
CNS Neurol Disord Drug Targets. 2010 August; 9(4): 504–523.
PMCID: PMC2992341

Drosophila melanogaster in the Study of Human Neurodegeneration

Abstract

Human neurodegenerative diseases are devastating illnesses that predominantly affect elderly people. The majority of the diseases are associated with pathogenic oligomers from misfolded proteins, eventually causing the formation of aggregates and the progressive loss of neurons in the brain and nervous system. Several of these proteinopathies are sporadic and the cause of pathogenesis remains elusive. Heritable forms are associated with genetic defects, suggesting that the affected protein is causally related to disease formation and/or progression. The limitations of human genetics, however, make it necessary to use model systems to analyse affected genes and pathways in more detail. During the last two decades, research using the genetically amenable fruitfly has established Drosophila melanogaster as a valuable model system in the study of human neurodegeneration. These studies offer reliable models for Alzheimer’s, Parkinson’s, and motor neuron diseases, as well as models for trinucleotide repeat expansion diseases, including ataxias and Huntington’s disease. As a result of these studies, several signalling pathways including phosphatidylinositol 3-kinase (PI3K)/Akt and target of rapamycin (TOR), c-Jun N-terminal kinase (JNK) and bone morphogenetic protein (BMP) signalling, have been shown to be deregulated in models of proteinopathies, suggesting that two or more initiating events may trigger disease formation in an age-related manner. Moreover, these studies also demonstrate that the fruitfly can be used to screen chemical compounds for their potential to prevent or ameliorate the disease, which in turn can directly guide clinical research and the development of novel therapeutic strategies for the treatment of human neurodegenerative diseases.

Keywords: Alzheimer’s disease, Parkinson’s disease, motor neuron disease, trinucleotide repeat expansion disease, c-Jun N-terminal kinase, bone morphogenetic protein, neurodegeneration, Drosophila.

INTRODUCTION

Human neurodegenerative diseases describe a clinical condition characterised by the selective and progressive loss of neurons, eventually leading to cognitive, behavioural and physical defects that can cause the death of the patient [1]. Neurodegenerative diseases are categorised by clinical appearance and pathology, such as movement disorders (e.g. Parkinson’s (PD), Huntington’s (HD), motor neuron diseases (MND)) and dementias (e.g. Alzheimer’s disease (AD), fronto-temporal dementia (FTD)); by the type(s) of neurons affected, such as dopaminergic (PD), GABAergic (HD) or motor neurons (MND); and by means of origin as to whether the form of disease is heritable (familial cases) or not (sporadic cases). Age is the greatest risk factor and adult-onset neurodegenerative diseases present a growing socio-economic burden for developed societies because of increased life expectancy. Current estimates for the number of individuals suffering, for example, from AD are as high as 16 million across the United States, France, Germany, Italy, Spain, United Kingdom, and Japan, and the prevalence of AD is estimated to exceed 21 million patients by 2010 [2].

For the vast majority of neurodegenerative diseases, the causes are unclear and effective treatments are lacking. At its best, prescribed treatments such as acetylcholinesterase inhibitors (AD treatment) [3] or levodopa (PD treatment) [4] provide modest symptomatic relief in a proportion of patients. To date, no drug has been identified that does more than improve symptoms. This is particularly exigent for those 95% of patients that suffer from a sporadic form of disease. In those sporadic cases, no indication allows a decided inference about the underlying causes as well as the pathogenic mechanisms involved, apart from age as the main risk factor. This lack of mechanistic insights has been challenged over the last two decades by two different but mutually overlapping approaches.

The first approach addresses the nature and content of proteinaceous inclusions that are typical pathological features of the majority of neurodegenerative diseases, including AD, PD, FTD, several trinucleotide repeat expansion diseases (TRED) and MND. These inclusions are characterised by protein aggregates that accumulate in the extracellular milieu or intracellular compartments of affected neurons. The proteins are usually modified (fragmented, phosphorylated, ubiquitinated) and their identification provides a mechanistic link to the potential aberrant pathway mediating pathogenesis. Textbook examples are amyloid plaques in AD that comprise fragments of aberrantly cleaved amyloid precursor protein (APP) [5-8], Lewy bodies in PD that comprise forms of alpha-synuclein (ASYN) [9], tangles in AD, FTD, PD and MND that comprise forms of tau [10-14], and more recently TAR DNA binding protein 43 (TDP-43) containing aggregates in MND, FTD, AD and PD [15, 16]. It is a striking mystery, however, that comparable inclusions can be observed in several diseases, such as tangles in AD and MND, although present in different neuronal cell types. This enigma as well as clinical evidence suggesting that neurodegeneration can occur even in the absence of inclusion formation continues to fuel the debate as to whether aggregate formation is a cause of disease or rather an attempt of the cell to protect itself. In any case, the identification of the nature and content of proteinaceous inclusions alone has not revealed a major breakthrough in understanding disease formation. However, in conjunction with information generated by the second approach, these data led to the identification of key pathogenic pathways operant in human neurodegeneration.

The second approach addresses familial forms of neurodegene-rative diseases, even though they represent only the minority of about 5% of all cases. Familial cases show clinical features similar to sporadic cases but at the same time are heritable, substantiating the reasonable quest to identify the origin, cause and underlying mechanisms of disease. Accordingly, large-scale pedigree analyses and genome-wide association studies have been and are still carried out in order to identify genes and loci that are affected in neurodegenerative diseases [see recent example, 17, 18]. These efforts led to the identification of APP, tau, ASYN, Huntingtin (HTT), and TDP-43 as the major culprits involved in AD, FTD, PD, HD, and MND, respectively. The genetic data corroborate earlier observations that proteinaceous inclusions harbour Abeta fragments derived from aberrant APP cleavage (amyloid plaques), tau (tangles), ASYN (Lewy bodies), polyglutamine expanded HTT and TDP-43. The fact that inclusion content and a mutant allele converge on the same defective protein unifies familial and sporadic cases and strongly suggests that the affected protein is causally related to disease formation and/or progression.

The limitations of human genetic studies however, often make it difficult to analyse genes and pathways in any further detail, because of complex patterns of inheritance, lack of sufficient family pedigree data and population-based genetic heterogeneity. Therefore, model systems are used to study specific functional aspects of the genes/proteins identified in neurodegenerative diseases. These models range from yeast [19] and C. elegans [20] to mammals and human cell culture systems. But yet, in most of the cases, these models fulfil only some of the criteria expected to apply in the study of human neurodegeneration. Essential criteria include: cognitive, behavioural and physical dysfunction caused by cell type-specific neurodegeneration; cellular pathophysiology including aggregate formation; clear pattern of inheritance; pedigree data covering three and more generations; population-based genetic homogeneity. In addition, an ideal model system would provide further detailed information: case-specific data spanning a whole life from conception to age-related death, which would allow the study of disease formation and progression in relation to age as the major risk factor; knowledge about the focus of disease, its time and site of origin, which in turn would allow the visualisation and eventually manipulation of disease formation and progression; and large numbers of genetically identical individuals, like multiple twins, that would allow strong power calculations to deduce quantitative traits as well as insights into pathogenic mechanisms in a statistically significant manner. An organism that meets all these criteria in a formidable way is the fruitfly Drosophila melanogaster.

DROSOPHILA MELANOGASTER

The protostomian, ecdysozoan arthropod Drosophila melanogaster belongs to a sub-species of the Drosophilidae, dipteran insects that are found all over the globe. During the course of evolution, the arthropod lineage already separated from the vertebrate lineage more than 600 million years ago [21, 22], suggesting that Drosophila might be completely unrelated to humans. However, genetic, molecular and behavioural analyses over more than a century suggest otherwise, and Drosophila has been used as a prime model organism for experimental studies of multi-cellular eukaryotic biology. This led to the discovery of fundamental biological principles, such as validation of the chromosomal theory of inheritance and the first experimental description of the gene as a functional unit [23].

Apart from tradition, the reasons for using the fruitfly as a study object are manifold: Drosophila is cheap and easy to maintain in the laboratory (Fig. 1a1a); it can give rise to a large number of genetically identical progeny; it has a rather short life span ranging from 40 to 120 days (Fig. 1b1b) depending on diet and stress [24, 25]; it shows complex behaviour, including learning and memory [26, 27], driven by a sophisticated brain (Fig. 22) and nervous system [28]. The entire Drosophila genome is encoded by roughly 13,600 genes as compared to 27,000 human genes, located on only four pairs of chromosomes as compared to 23 pairs in human [29]. Thanks to very well-described anatomy and development [30, 31], and the availability of molecular genetic tools [32-34], Drosophila is one of the most extensively used genetic model organisms to study complex biological processes. In comparison to other organisms like C. elegans and the mouse, the fly provides a very powerful genetic model system for the analysis of brain and behavioural disorders related to human disease: its brain is complex enough (as compared to C. elegans) to make fly behaviour highly interesting and relevant to humans but it is still small enough (as compared to mouse) for an in-depth structural and functional analysis [35].

Fig. (1)
Drosophila as a model organism in the study of age-related neurodegeneration. (a) The arthropod Drosophila melanogaster belongs to a subspecies of the Drosophilidae, dipteran insects that fit on a pencil tip and can be easily kept en masse in the laboratory. ...
Fig. (2)
Adult brain of Drosophila. (a) Confocal image of a parafin cross-section through the adult Drosophila head; auto-immunofluorescence visualises the ommatidia of the compound eye (CE), the optic lobe (OL) and the central brain (CB). Note that cell bodies ...

The value of Drosophila as a model system has been amply demonstrated by the fact that many genes and processes first discovered in the fly have proven to be conserved in other organisms, including humans. Comparative analysis of whole genome sequencing revealed striking similarities in the structural composition of individual genes of Homo sapiens and Drosophila [36]. Moreover, the molecules and mechanisms underlying core modules of cell biology are conserved as well: homologous genes mediate homologous pathways such as cyclin/cdk modules regulating the eukaryotic cell cycle [37-39], or insulin signalling regulating metazoan cell growth [40, 41]. These data provide compelling evidence for the structural conservation of genes due to common origin; they elucidate a deep homology underlying cell biological mechanisms that extends beyond gene structure to patterned protein expression and function. This notion is further supported by experiments demonstrating that Drosophila and human genes can substitute each other in species-specific but evolutionarily conserved mechanisms underlying brain development in insects and mammals [42-45].

Based on these observations, it is obvious that Drosophila can offer unique opportunities in the study of human neurodegeneration: Most of the genes implicated in familial forms of disease have at least one fly homolog [46] (see Tables 11--44); fundamental cellular processes related to neurobiology are similar in Drosophila and humans, including synapse formation, neuronal communication, membrane trafficking and cell death; the neurobiological bases of behaviour are of the same kind in flies and humans, including sensory perception, integration and motor output, as well as aspects of learning and memory formation. These features make Drosophila a prime model organism in the study of adult-onset, age-related neurodegeneration.

Table 1
Alzheimer’s Disease-Associated Genes
Table 4
Motor Neuron Disease-Associated Genes

DROSOPHILA IN THE STUDY OF NEURODEGENERATION

The fundamental aims in the study of neurodegeneration are to elucidate underlying pathogenic pathway(s) and in turn the development and successful application of targeted treatment(s) to stop or at least ameliorate the disease. The genetic dissection of disease pathways is therefore a reasonable means to address these aims and three mutually interrelated approaches are utilised in Drosophila:

  1. mis-expression of a human disease gene, in its wild-type or mutant form;
  2. loss and gain of function of the Drosophila homolog of a human disease gene;
  3. genetic screens to identify enhancers and suppressors that are able to modify a phenotype caused by (i) and (ii).

Mis-expression of a human gene is used to investigate its functional properties in a neurodegenerative process and to elucidate its interactions with other Drosophila proteins. This is usually achieved by using the Gal4/ upstream activating sequence (UAS) system that allows time- and tissue-specific mis-expression of any gene of interest in Drosophila [47]. Most robust models have been established using nervous system-specific Gal4 drivers, thereby corresponding to the human condition. However, several other tissues are also used as a phenotypic read-out system, including the compound eyes, wings and bristles, because a degenerative phenotype can be revealed without affecting the survival of the fly. Especially the compound eye is predominantly used because it allows the generation of a neurodegenerative phenotype (rough eye phenotype) that can be easily scored under a standard light microscope [see, for example, 48], and in turn can be utilised for genetic enhancer/suppressor screens.

There are, however, serious drawbacks to this approach: (i) degeneration can occur by excess Gal4 protein itself [49], thereby causing a rough eye phenotype unrelated to the disease gene under investigation; (ii) a rough eye phenotype can occur by degeneration of accessory cells unrelated to neurodegeneration; (iii) the severity of a degenerative phenotype may not relate to the amount of protein expressed because of the way the UAS construct (harbouring the human disease gene) has been integrated into the fly genome (position effect). The latter can and should be avoided by site-specific genomic integration of the UAS construct (for details, see [50]) so that the same levels of protein expression are achieved. In comparison to wild-type protein expression, only this will permit meaningful conclusions about the impact of mis-expressing a human mutant protein or its post-translational modifications that frequently occur in neurodegeneration, such as hyperphosphorylation or ubiquitination.

The second approach applies standard analytical techniques available to study the function of a Drosophila gene/protein. These include mutational inactivation for a loss-of-function analysis, and Gal4/UAS-mediated RNA interference for a knockdown or over-expression for gain-of-function analyses, with several modifications and more sophisticated possibilities available [28, 51-55]. The ultimate goal is to gain insights into the role and function of a Drosophila homologue of a human disease gene. By way of homology between the fly and human protein, a reasonable inference can be made on the function of the human protein, and hypotheses and predictions can be deduced about the potential pathogenic pathway(s). Following this approach, it has been shown first in Drosophila that mitochondrial dysfunction can result from defective PINK1/Parkin signalling which appears to be one of the pathogenic pathways underlying PD [56-58].

A third approach is utilised once a neurodegenerative phenotype is established. Drosophila offers the advantage of performing unbiased genetic screens to identify enhancers and suppressors on a genome-wide basis. Several labs have used the ease and accessibility of the compound eye to carry out such modifier screens, and targeted genes that either suppress or enhance the rough eye phenotype, thereby signifiyng the candidate genes as members of a common pathogenic pathway. These attempts have identified several ‘key’ interacting partners of tau, Abeta and ASYN [59-65]. However, in only very few cases [62, 66], the results obtained in Drosophila led to the identification of a human homologue that is similarly involved in the corresponding human disease. The potential reason(s) for such a meagre yield are phenotypic screens predominantly based on eye-specific Gal4 drivers that are already active during development, thereby generating a rough eye phenotype in the newly hatched adult fly - a situation that does not mimic nor model adult-onset neurodegeneration in an age-related manner.

In addition to these genetic approaches, a fourth one uses established fly models of neurodegeneration in order to screen compound collections for their potential to prevent or ameliorate the “disease”. A Drosophila compound screen is achieved by simply feeding flies with their usual food to which a defined concentration of the compound has been added (Fig. 33). There are obvious drawbacks to such screens, especially when used for adult onset, age-related neurodegeneration phenotypes, as these screens are time-consuming and far from being “high-throughput”. In addition, compound screens have been ineffective when based on a rough eye phenotype that is generated during development and detectable in the newly hatched adult fly [Luz and Hirth, unpublished]. This is because flies can be easily raised on drug-treated food but ingestion stops during puparium formation and the subsequent pupal stage, which lasts four days until the adult fly hatches. Moreover, this final stage of development is characterised by a high metabolic rate related to metamorphosis, during which a previously incorporated drug loses its efficacy.

Fig. (3)
Drug treatment in Drosophila. (a) Four vials with flies are kept on cornmeal food each of which has been supplemented with a different concentration of the same drug. The applied drug is screened for its potential to either enhance or suppress a given ...

Despite all these limitations, Drosophila has been used successfully to identify compounds that not only improve symptoms, but also modify the course of the “disease”. These successful cases are mainly (but not only) based on fly models of adult-onset, age-related neurodegeneration, and resulted in improvements relevant to human disease, including extended life-span in models of AD [67] and prolonged survival of dopaminergic neurons in models of PD [68, 69] as well as the complete rescue of disease-related phenotypes [70]. The relevance and impact of such small-scale compound screens in Drosophila cannot be rated highly enough because of their potential for translational research: the fruitfly is a complex behaving animal with a sophisticated, centralised nervous system including a blood-brain barrier [71], and therefore superior to cell cultures and C. elegans, but still inexpensive and short-lived as compared to mice. Accordingly, Drosophila drug screens in cancer research [72] have already identified compounds that are now in phase I and II clinical trials, illustrating the enormous potential for its application in the study of human diseases.

The above mentioned experimental approaches have established Drosophila as an excellent model organism in the study of human neurodegeneration. Numerous reviews have covered detailed aspects of this topic and are highly recommended to the reader [73-85]. In the following article, key and novel findings as well as their implications are summarized and reviewed. A special emphasis is given to Drosophila models of AD, PD, TREDs and MNDs.

ALZHEIMER’S DISEASE

Alzheimer’s disease is the most common neurodegenerative disease affecting primarily elderly people. Over 95% of the known cases are sporadic, whereas less than 5% account for familial cases [86, 87]. These heritable cases led to the identification of genes that, when mutated appear to be involved in AD pathogenesis, including APP, presenilins 1 and 2 (PSN-1/2) and tau (Table 11). In addition, Apolipoprotein E isoform epsilon4 has been identified as a risk factor [88]. AD is characterized by progressive memory loss and the subsequent degeneration of large areas of the brain [89, 90]. Microscopically, AD pathology reveals neuritic plaques, composed mainly of Abeta peptides, and neurofibrillary tangles, composed of abnormal tau protein [86, 91, 92]. Abeta peptides are produced by proteolytic cleavage of the APP transmembrane receptor at the beta and gamma sites. Familial mutations (familial AD, FAD) in APP result in increased production of Abeta42 peptide, the amyloidogenic form of the two Abeta species, Abeta40 and Abeta42. Abeta42 forms protofibrils and fibrils much more readily than Abeta40 and is the predominant form of the peptide found in plaques. The membrane-tethered aspartyl protease beta-site APP-cleaving enzyme (BACE) cleaves APP at the beta site, and the presenilins, PS1 and PS2, participate in APP cleavage at the gamma site along with the genes nicastrin, Aph-1 and Pen-2. These data led to the amyloid cascade hypothesis as the main culprit of AD formation [93, 94]. Drosophila carries homologues of AD-related genes, including APP, presenilin, and tau (Table 11), which has made it a model system in AD research.

APP AND ABETA

The Drosophila homologue of APP, β-amyloid protein precursor-like (Appl, CG7727), is expressed in the central nervous system; however, mutational inactivation of Appl does not cause a neurodegenerative phenotype [95]. Flies deleted for the Appl gene are viable, fertile, and morphologically normal, yet they exhibit subtle behavioural deficits: a fast phototaxis defect can be observed which is partially rescued by wild-type, but not mutant APPL. There is functional homology between APPL and human APP, as transgenes expressing human APP show a similar level of rescue as the fly protein. Drosophila APPL lacks homology to APP within the Abeta peptide region, and thus is not cleaved like mammalian APP, and Abeta deposition does not occur in Drosophila. Interestingly, however, a recent report identified a beta-secretase-like cleavage site in APPL [96], but further proof is required to show that this is a functional site leading to Abeta-like deposition. Accordingly, Drosophila models of APP-mediated AD have used the GAL4/UAS-system to over-express human forms of Abeta.

These models recapitulate, at least to some extent, aspects of human AD pathology, including Abeta plaque deposition [97, 98], defective axonal transport [99, 100] and axonopathies [101], mitochondrial mislocalisation [102], defects in synaptic plasticity [103] and progressive locomotor deficits [98], affected life-span [97, 98, 104], and age-dependent neurodegeneration including vacuolization of the brain [97, 98, 105]. The severity of these phenotypes is related to Abeta toxicity, with the Abeta 42 arctic mutation being the most toxic form.

Drosophila Abeta models were subsequently utilised to target modifiers of AD pathology by genetic or pharmacological interference. Genetic experiments showed that secretase inhibitors and neprilysin can ameliorate Abeta42 phenotypes, by either reducing Abeta production [67, 104, 106] or by increasing Abeta degradation [107, 108]. In addition, a recent study identified FKBP52, a prolyl-isomerase of the immunophilin/FK506 binding protein family as a modifier of Abeta toxicity. This study also showed that mutations in the copper transporter Atox1 which interacts with FKBP52 enhance Abeta pathology which can be suppressed in FKBP52 mutant flies raised on a copper chelator diet [109]. Pharmacological interference identified Congo Red [104] and glutaminyl cyclase inhibitors [110] as effective suppressors of Abeta deposition and amyloid plaque formation.

Resulting from these studies, several signalling pathways have been identified as potential mediators of Abeta pathogenesis. These include altered Toll->NFkappaB signalling [65], age-dependent autophagic-lysosomal injury [111], and the Abelson tyrosine kinase/JNK stress kinase cascades [112]. Autophagy and JNK signalling have been shown to be altered in human AD [113, 114]. However, it is not clear whether these pathways are activated because of a causal relationship to disease formation/progression or because of a cellular protection attempt. In any case, these studies not only corroborate the amyloid cascade hypothesis, but also support recent data indicating that Abeta oligomerization, rather than plaque formation, is the toxic event that acts as a seed for Abeta aggregation [110, 115, 116]. Yet, it is unknown how Abeta oligomerization causes neuronal cell death.

PRESENILIN AND FAD

FAD mutations in PS1 and PS2 alter proteolytic processing of APP to generate more toxic Abeta42 peptides which accelerates amyloid plaque formation in brain tissues. PS mutations also contribute to neurodegeneration and cognitive decline through amyloid-independent mechanisms, involving altered regulation of receptor signalling and intracellular kinase activity. Drosophila Presenilin (Psn, CG18803) represents the only fly homologue of the mammalian PSN1 and PSN2 genes. Functional studies in Drosophila showed that it is involved in various biological processes: cytoskeleton organization and biogenesis; cell fate commitment; nervous system development; Notch receptor processing; membrane protein ectodomain proteolysis; cell-cell adhesion and intracellular signalling cascades. With regard to neurodegeneration, Drosophila Psn is not involved in Abeta42 production because APPL lacks homology to APP within the Abeta peptide region, and thus is not cleaved like mammalian APP. Accordingly, a more suitable substrate to monitor Psn FAD mutant activity in Drosophila is the Notch receptor, the most extensively characterized fly gamma-secretase substrate [117]. Psn is required throughout Drosophila development for Notch signalling, and a wide variety of Notch-related phenotypes exist that range from severe embryonic lethality to specific defects in adult tissues [118].

As is the case for Abeta models, Psn1/2 wild-type and mutant forms have been mis-expressed in Drosophila. These studies reveal that PSN FAD mutant activities are tightly linked to the age-of-onset of degeneration, suggesting that disease severity primarily reflects differences in PSN mutant lesions [119]. Most recent studies relate PSN-mediated pathogenesis to ubiquilin dysfunction [120, 121] and defective calcium storage that can be suppressed by calmodulin loss-of-function mutations [122]. The latter model underscores earlier findings suggesting that perturbed neuronal Ca2+ homeostasis is implicated in PSN and APP-mediated AD pathogenesis, whereby the resulting toxic forms of Abeta can induce Ca2+ influx into neurons. This occurs by Abeta forming an oligomeric pore in the membrane which in turn renders neurons vulnerable to excitotoxicity and apoptosis (for review see [123]). However, as is the case for Abeta models, the actual cause(s) of cell death are currently unknown, although defects in axonal transport and synaptic dysfunction refer to cytoskeletal abnormalities that are the major culprit of AD-related tauopathy.

TAU AND TAUOPATHY

Pathological aggregation of the microtubule-associated protein tau [124] is a defining feature not only of AD but also of other neurodegenerative diseases collectively called tauopathies [91, 92, 125]. The process of tau accumulation, paired helical filament assembly, and aggregation is incompletely understood. While tau hyper-phosphorylation clearly accelerates neurodegeneration, the role of other posttranslational modifications, including proteolysis, ubiquitination, nitration, and glycosylation, as well as the function of the tau amino terminus in this process, remain unclear.

The Drosophila homologue of MAPtau, tau (CG31057) exhibits 46% identity and 66% similarity with the human protein. However, the fly protein does not contain the N-terminal repeats found in several human isoforms of tau [126]. To date, Drosophila models of tauopathy rely on the over-expression of wild-type or mutant forms of human tau, including the FTD-related P301L, V337M and R406W mutants. The resulting phenotypes mimic, at least to some extent, the human disease condition, including learning and memory deficits [127], phosphorylation–dependent tau toxicity [128, 129], correlation between FTD-related mutant forms and enhanced toxicity [130, 131], tangle formation in some [132] but not all cases [see, f.e. 130], synergistic interaction with Abeta leading to Hirano body formation [131], and altered life-span as well as region-specific neurodegeneration in the adult brain [130-132].

Subsequent genetic interaction studies showed that kinase-dependent phosphorylation increases tau toxicity and identified Shaggy/glycogen synthase kinase-3 [132] and MARK/Par-1 [129, 133] as key players in this process. In addition, genetic modifier screens identified targets and signalling pathways as potential mediators of tau toxicity, including puromycin-sensitive aminopeptidase [134], altered Wingless [132] and JNK [135] signalling, as well as TOR-mediated cell cycle activation [136]. Although it is still unclear whether aberrant cell cycle activation is directly causing tauopathy/neurodegeneration (see, for example, [137]), a potential role of defective TOR signalling has been further substantiated by pharmacological interference. These data show that rapamycin targeting TOR is able to reduce wild-type or mutant tau-induced toxicity by reducing insoluble tau [138]. Yet, the relevance of puromycin-sensitive aminopeptidase and TOR signalling in human AD pathogenesis remains to be established. In contrast, pathological tau phosphorylation has been shown to be involved in human disease progression [139], and there is at least circumstantial evidence that altered JNK signalling may contribute to AD formation and/or progression [114].

PARKINSON’S DISEASE

Parkinson’s disease is the most common neurodegenerative movement disorder characterized by severe motor symptoms, including uncontrollable tremor, imbalance, slowness of movement and rigidity. Among the exemplary pathological changes observed in PD is the progressive loss of dopamine (DA) neurons in the substantia nigra pars compacta of the ventral midbrain, although neuropathology is not limited to this region [89]. DA neurons of the substantia nigra pars compacta innervate the putamen and caudate via the nigrostriatal pathway and thereby exert a stimulating function to the striatum regulating motor control. Loss of DA neurons and the subsequent degeneration of the nigrostriatal pathway are a primary cause for movement disorders observed in PD cases. DA cell loss is usually associated with the presence of intraneuronal inclusions known as Lewy bodies, which are composed principally of ASYN [9].

PD prevalence increases with age, with a mean age of onset around 70 years, although 4% of patients develop early-onset disease before the age of 50 [140]. The mean disease duration from diagnosis to death is 15 years, but the precise mode of death is often difficult to determine. Males appear to be 1.5 times more likely to develop PD than females, although the underlying causes are not known [141]. PD is progressive and current treatment is symptomatic only with DA (levodopa) replacement as the major therapy. The majority of PD cases are sporadic, likely to be caused by a combination of risk factors, the most evident being age. However, there are also rare familial disease forms caused by gene mutations which show similar clinical and neuropathological features. Although these inherited forms account for 5% of all PD cases only, studies of the function of the affected genes have provided insights into PD pathogenesis.

Several genetic loci have been identified that are affected in familial forms of PD or have been identified as being associated with PD. These include (see Table 22): alpha-synuclein (asyn), parkin, ubiquitin carboxy-terminal hydrolase L1 (UCHL1), phosphatase and tensin homologue (PTEN)-induced kinase 1, (PINK1), DJ-1, leucine-rich-repeat kinase 2 (LRRK2), high temperature requirement protein A2 (HTRA2), glucocerebrosidase, polymerase gamma and tau [141-146]. Based on pathophysiology as well as genetic defects, three types of cellular dysfunction are currently implicated in the pathogenesis of PD: abnormal protein aggregation, oxidative damage, and mitochondrial dysfunction [142, 143, 145, 147, 148]. Homologues for PD genes exist in Drosophila, with the interesting exception of ASYN (see Table 22). Accordingly, Drosophila models of PD have been established based on the experimental approaches outlined above. Rather than listing them gene by gene, I consider it more reasonable to summarise the prerequisites, main findings and resulting insights into PD pathogenesis.

Table 2
Parkinson’s Disease-Associated Genes

PARKINSONISM IN DROSOPHILA

Synthesis of the neurotransmitter DA is conserved between Drosophila and human and distinct clusters of DA neurons are detectable in the developing and adult fly brain [149]. Comparable to the human condition, the Drosophila DA system is also involved in locomotor control [150, 151], although the details of the underlying neural circuit(s) are unknown. It is therefore reasonable to assume that loss of DA neurons can affect locomotion in Drosophila comparable to the situation in PD. Indeed, loss of subsets of DA neurons in the brain as well as locomotion defects are the two principal parkinsonian-like phenotypes used to characterise fly models of PD. Both phenotypes have been induced by mis-expression of wild-type and/or mutant forms of human PD genes, including ASYN [152-160], PINK1 [159, 161, 162], Parkin [154-156, 163, 164] and LRRK2 [165-169].

Loss-of-function mutations or DA neuron-specific inactivation of the respective Drosophila homologues of PINK1 [161, 170-173], Parkin [61, 174-176], DJ-1 [69, 177-182], LRRK2 [165, 166, 173, 183], and HtrA2 [184-186] can also lead to parkinsonism-like DA cell loss and locomotor defects. However, it should be noted that in several cases loss of the Drosophila homologue of a human PD gene causes a much weaker phenotype than mis-expression of the corresponding human protein. Moreover, for some models including LRRK2 and HtrA2 there are conflicting data as to whether loss of the Drosophila homologue causes a parkinsonian-like phenotype or not [166, 183, 185, 186]. These discrepancies might be attributable, at least to some extent, to the inherent artificial situation of Gal4-mediated protein overload added to the endogenous protein level. In addition, the total number of DA neurons per cluster varies between individual wild-type flies [White and Hirth, unpublished] and the methods used to measure DA cell loss can substantially impact on the phenotypic read-out [187].

In addition to these genetic modifications, pharmacological insults also cause parkinsonian-like phenotypes in Drosophila, thereby modelling sporadic cases of PD. The pesticide rotenone as well as paraquat-induced oxidative damage cause cluster-specific DA neuron loss together with motor deficits that can be ameliorated by levodopa added to the food [188, 189]. In contrast, a Drosophila model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism [for review see 142] has not been established so far.

It should be noted, however, that in Drosophila the majority of these genetic and pharmacological models do not reveal Lewy body formation, which is a predominant pathological feature of both familial and sporadic cases of PD. As noted above, a Drosophila homologue of ASYN is missing which may account for the lack of Lewy body formation, except for those cases where human ASYN is mis-expressed in the fly [152, 153, 157, 160, 190]. Nevertheless, Drosophila models of PD have revealed valuable insights into potential pathogenic mechanisms and identified targets of ASYN and other PD-related genes.

MECHANISMS AND TARGETS OF PARKINSONISM

ASYN is the principal component of Lewy bodies found in the majority of PD cases and therefore represents a prime target for PD research. Although a role in synapse homeostasis is suggested, its wild-type function remains elusive [191]. Insights into ASYN-mediated pathogenesis come from studies showing that phosphorylation and enhanced oligomer formation are the major culprits of ASYN toxicity in Drosophila [157, 190-193]. Thus, phosphorylation at residue serine 129 can ameliorate [190] whereas phospho tyrosine 125 can exacerbate soluble oligomer formation and toxicity [193]. Moreover, a recent elegant study addressing the in vivo impact of biophysically defined pre-fibrillar variants of ASYN showed that the increasing potential to form fibrils and soluble oligomers correlates with increasing neurodegeneration, not only in Drosophila but also in C. elegans and human cell culture models [192]. These data suggest that soluble oligomers are the most toxic species in PD-like pathogenesis, which is further supported by the fact that an ASYN mutant lacking residues 71-82 and unable to form oligomers and fibrils, is also unable to induce DA neurotoxicity in the fly [157].

Drosophila ASYN models have been used to target modifiers of PD pathology by genetic or pharmacological interference. Genetic experiments showed that calpain cleavage [194] and superoxide dismutase (SOD) activity [158] affect ASYN, whereas inhibition of Silent information regulator 2 (Sir2), a nicotinamide adenine dinucleotide–dependent histone deacetylase rescues ASYN toxicity [66]. Moreover, ASYN inhibits histone acetylases and its neurotoxic effects can be rescued by histone deacetylase inhibitors [195], further supporting a link between ASYN-mediated pathogenesis and histone acetylation. Pharmacological interference identified nicotinamide which can improve motor deficits [196]; as does dietary supplementation of S-methyl-L-cysteine, a substrate in the catalytic antioxidant system mediated by methionine sulfoxide reductases [197]. In addition, geldanamycin can suppress ASYN toxicity, a process that appears to be mediated by heat shock protein 70 chaperone activity [68].

The latter studies strongly suggest that ASYN-mediated pathogenesis is accompanied, if not accelerated by a stress response, which can be also found in other Drosophila models of PD. Loss of PINK1 function in the fly eye can be suppressed by SOD1 as well as with vitamine E [161]. Loss of parkin leads to oxidative stress [175] and in both ASYN and parkin models, neuronal cell loss can be overcome by genetic or pharmacological interventions increasing glutathione synthesis or glutathione conjugation activity [198]. This detox activity of parkin might be mediated by glutathione S-transferase S1 [61]. Parkin also associates with parkin-associated endothelin receptor-like receptor, which by itself can cause parkinsonism in Drosophila [154, 199]. Similar to ASYN and parkin, DJ-1 has been shown to be involved in an oxidative stress response [69, 177-179, 181, 182]. Some of these screens also indentified signalling pathways that mediate PD-like pathogenesis. Among those involved in Parkin-mediated pathogenesis are PI3K/Akt [180, 200], JNK [176] as well as TOR signalling [167, 173]. Interestingly, both Parkin and LRRK2-mediated pathogenesis can be ameliorated with rapamycin targeting 4E-BP activity [173], a situation comparable to its application in Drosophila models of tauopathy [138].

PD-RELATED MITOCHONDRIAL DYSFUNCTION

A surprising and equally promising finding of these interaction studies in Drosophila was the discovery that LRRK2, PINK1 and Parkin genetically interact with each other [168, 173] as does DJ-1 [169]. PINK1 is able to phosphorylate Parkin, which is a requirement for its mitochondrial localisation [201]. PINK1 and Parkin loss-of-function genotypes phenocopy each other as both affect mitochondrial morphology. Subsequent epistatic analyses demonstrated that the mitochondrial phenotype caused by PINK1 loss-of-function can be rescued by Parkin [170-172]. Moreover, over-expression of human Parkin mutant R275W but not wild-type or G328E mutant can cause mitochondrial abnormalities similar to Parkin loss-of-function mutants [163]. These data strongly suggest that at least PINK1 and Parkin act together in a common pathway regulating mitochondrial function [57, 58].

Mitochondria are endosymbiontic organelles found in all eukaryotic cells required for ATP production as well calcium buffering and apoptotic signals [202]; they encode their own DNA (mtDNA) in up to 1000 copies per cell, and undergo frequent morphological changes through fission and fusion, thereby retaining mtDNA integrity and essential neuronal function, such as synaptic transmission, plasticity, and ultimately cell survival [203, 204]. The PD model studies in Drosophila showed that PINK1 and Parkin regulate mitochondrial morphology [162, 205, 206], potentially by acting on Drp-1 [207] and other factors mediating mitochondrial fission/fusion. It should be noted, however, that the majority of these interactions have been discovered and described using the fly muscle as a model, and not in DA neurons of the fly brain itself. Moreover, it is currently not known whether PINK1 and/or Parkin act directly or indirectly on genes regulating fission/fusion and mtDNA integrity. PINK1 and Parkin loss-of function increases Drp-1 dependent mitochondrial fragmentation, suggesting that at least a feedback loop exists between PINK1/Parkin signalling and mitochondrial fission/fusion. It remains to be shown whether this feedback loop requires other mediators regulating mtDNA maintenance and/or fission/fusion.

In summary, these examples of Drosophila research into human PD corroborate and extend current hypotheses suggesting that abnormal protein aggregation, oxidative damage and mitochondrial dysfunction are causally related to PD pathogenesis. The results obtained in Drosophila led to the identification of homologues and homologous pathways involved in the formation and progression of parkinsonism. Thus, despite some heterogeneity, these models identify oligomer formation of ASYN and histone acetylation, as well as altered PINK1/Parkin signalling and mitochondrial dysfunction as two distinguishable pathogenic pathways underlying PD-like neurodegeneration – a situation corresponding to the human disease condition [145]. These data from Drosophila also identify JNK as well as PI3K/Akt and TOR signalling as contributors to disease progression, whereas detox pathways reducing oxidative stress, either genetically or pharmacologically, can ameliorate it. Significantly, these pathways parallel some of those involved in AD pathogenesis, indicating that common disease mechanisms may underlie AD and PD-like neurodegeneration.

TRINUCLEOTIDE REPEAT EXPANSION DISEASES

TREDs account for more than 16 neurological disorders that are caused by aberrant expansion of triplet reiterations in either coding or non-coding regions of disease-specific genetic loci that result in dysfunction of the respective protein, eventually leading to neurodegeneration and, ultimately, patient death (for review see [208]). The majority of TREDs are diseases caused by expansion of CAG repeats coding for glutamine (polyglutamine, PolyQ), including HD, spinal bulbar muscular atrophy (SBMA, also Kennedy disease), spinocerebellar ataxias (SCA) 1, 2, 3 (also known as Machado-Joseph disease), 6, 7, and 17, and dentatorubral-pallidoluysian atrophy (DRPLA). Other TREDs include Fragile X syndrome (FRX, CGGn repeats) and Friedreich’s ataxia (FRDA, GAAn repeats). Apart from codon reiteration as a common denominator, TREDs differ in disease-related length of expanded repeats, age of onset, clinical features and neuropathology. The reader is referred to reviews addressing each TRED in more detail [208-210] The genetic loci affected by the expansion of unstable trinucleotide repeats have been identified and with the exception of the androgen receptor, there is a fly homologue known for each of them (see Table 33), which in turn led to the establishment of Drosophila models of PolyQ diseases, FRX and FRDA.

Table 3
Trinucleotide Repeat Expansion Disease-Associated Genes

POLYQ-RELATED NEURODEGENERATION

HD, SBMA, SCA1/2/3/6/7/17 and DRPLA are predominantly inherited diseases where polyQ expansions confer structural changes to the disease-related protein, leading to oligomeric species and protofibril forms rich in beta-sheets [211]. The resulting mutant proteins become dominantly toxic and can lead to intra-nuclear inclusions in neurons and glial cells, ultimately causing neuronal dysfunction and cellular degeneration. The direct causes of degenerative cell death still remain elusive but there is an inverse correlation between repeat length and disease severity, with expansions of 40 glutamines and more being a general threshold for disease formation [212].

As is the case for AD and PD, fly models have been generated by mis-expression of mutant forms of human polyQ genes as well as loss- and gain-of-function of Drosophila homologues. In all of these cases, Gal4 specific mis-expression can cause pronounced neurodegenerative phenotypes in the eye or central nervous system that can be accompanied by aggregated formation and reduced life-span [for recent review, see 82, 208, 213]. Several studies established that toxicity is due to polyQ tracts [214, 215]. However, the protein context around the pathogenic expansion strongly modulates dominant toxicity, suggesting that the resulting aberrant protein conformation may trigger an amyloid-like cascade [216-218], and that protein-protein interactions are a major culprit of polyQ-related neurodegeneration. These protein-protein interactions occur even between polyQ-related disease proteins, at least for some of the proteins involved in SCA, thereby promoting neurodegeneration. For example, nuclear accumulation of ataxin-2 contributes to SCA1-related neurodegenerative phenotypes caused by ataxin-1[82Q], probably by direct interaction [219]. Ataxin-2 can also modify SCA3-induced neurodegeneration by accelerating the onset of nuclear inclusion formation associated with SCA3. Ataxin-2 activity depends on a conserved protein interaction domain, the PAM2 motif, which mediates binding of cytoplasmic poly(A)-binding protein which itself can influence SCA3-associated neurodegeneration [220].

Based on available fly models of polyQ-induced neurode-generation, numerous genetic and pharmacological modifier screens identified targets affecting protein folding and oligomerization [221-228], as well as RNA [229], microRNA [230] and RNA processing [228] as mediators of polyQ toxicity. These data suggest that altered protein conformation is only one of the causes underlying polyQ-induced neurodegeneration. However, the actual cause(s) of cell death are currently unknown. Apoptotic signalling [228, 231] has been involved, as well as the retinoblastoma pathway [232]; sumoylation and ubiquitination [233, 234], as well as PI3K/Akt [235] and TOR signalling affecting macroautophagy [236]. It is not clear whether these pathways are activated as a cause or consequence, but they do provide a target for therapeutic intervention. This is particularly evident for histone deacetylase (HDAC) inhibitors, which protect against polyQ toxicity [237, 238]. Interestingly, this effect can be modulated by simultaneous inhibition of two HDACs leading to enhanced neuroprotection [239], suggesting that HDACs may propagate/accelerate toxicity in Drosophila models of PolyQ-mediated neurodegeneration.

FRAGILE X SYNDROME AND FRIEDREICH ATAXIA

Trinucleotide repeat expansion can also occur in non-coding regions, as is the case for FRX and FRDA. In both cases, single gene loci are affected and repeat expansion of >200 inversely correlates with age of onset. FRX occurs in 1/4000 males and 1/8000 females, leading to mental retardation and behavioural abnormalities due to expansion of unstable non-coding CGG repeats in the 5 prime untranslated region of fragile X mental retardation 1 (FMR1). These excess repeats cause aberrant methylation of CpG islands and decreased histone acetylation in the 5 prime regulatory region of FMR1, leading to loss of FMR1 and its encoded protein FMRP. FMRP is a selective RNA-binding protein that shuttles between nucleus and cytoplasm and controls local protein synthesis by suppressing mRNA translation (for review see [208]). This function of FMRP appears to be evolutionary conserved, as both mammalian FMRP and its Drosophila homologue dfmr1 target the microtubule-associated protein 1B/Drosophila futsch [240]. Local regulation of protein synthesis is an essential function in synaptic terminals, and several studies in Drosophila identified related targets of dfmr1, including rac1, pick pocket [241, 242], discs overgrown and polyA-binding protein [243], all of which are implicated in synaptic function. Moreover, several loss- and gain-of-function studies demonstrated that dfmr1 regulates synaptic structure [244] by associating physically and functionally with the microRNA pathway, thereby regulating the translation of synaptic mRNAs [for review see 245].

FRDA is an autosomal recessive disorder that occurs in 1/50,000 individuals characterised by gait ataxia due to progressive atrophy of dorsal columns, and spinocerebellar and corticospinal tracts. Unstable GAA repeats in the first intron of FRDA encoding frataxin inhibit transcriptional elongation, leading to decreased protein levels. Frataxin localises to the inner mitochondrial membrane and is involved in the regulation of iron levels and free radical protection. Similar functions have been identified for the only Drosophila homologue, dfh [246-248], suggesting that oxidative stress and impaired biosynthesis of Fe-S cluster containing proteins in the mitochondrial respiratory chain might be causally related to disease. However, as is the case for PD, it is still unclear whether and how oxidative stress can cause cell death, or whether it is merely a potentiator of mitochondrial dysfunction, ultimately leading to neurodegeneration. The available Drosophila model of FRDA will certainly allow rigorous testing of several hypotheses, including the possibility that impaired oxidative phosphorylation due to frataxin deficiency might be the major culprit underlying FRDA pathogenesis.

MOTOR NEURON DISEASES

MND is a common denominator for several etiologically heterogeneous diseases affecting upper motor neurons located principally in the primary motor cortex and/or lower motor neurons located in the anterior horn of the spinal cord and the brainstem. MNDs include amyotrophic lateral sclerosis (ALS), some forms of FTD and fronto-temporal lobar degeneration (FTLD), as well as spinal muscular atrophy (SMA), hereditary spastic paraplegia (HSP), and others [249-254]. The most prevalent cases are SMA (1/6,000-10,000), HSP (3-10/100,000), and ALS (4-6/100,000). MNDs vary in severity and can affect all ages from infancy (SMA) to late onset (FTD and FTLD). However, in every case, the degeneration of motor neurons causes neuronal dysfunction and muscle wasting, leading to various locomotor disabilities, such as inability to use arms and/or legs, to speak or to swallow, and ultimately can cause the death of the patient when breathing muscles become involved.

To date, there is no effective therapy or cure for MND. As is the case for AD and PD, the majority of MND cases are sporadic and the causes are unknown. However, the identification of protein aggregates (fragmented, phosphorylated, ubiquitinated) in intracellular inclusions as well as the analyses of heritable, familial cases led to the identification of genes involved in MND pathogenesis (Table 44). In some cases motor neuron death is caused by mutations in a single gene, such as survival of motor neurons (SMN) causing SMA [255]. For the majority of these disease-related genes, Drosophila homologues are present (Table 44) and movement disorders can be easily monitored in the fly (Fig. 44). Thus, loss- and gain-of-function analyses or mis-expression of the human disease gene have been used to establish fly models of MND.

Fig. (4)
Experimental study of Drosophila locomotor behaviour. (a) An adult wild-type fly (wt, arrow) is kept in an arena which can be a converted petri dish. The fly’s activity and movement is recorded with a high-speed video camera and a computer programme ...

AMYOTROPHIC LATERAL SCLEROSIS

ALS is the most common adult-onset MND affecting upper and lower motor neurons, with an age of onset between 40 and 60 years. The majority of ALS cases are sporadic with currently unknown causes whereas 5-10% are familial cases (FALS), for which several disease-related genes have been identified [253, 254]. Most prominent among them are mutations of the Cu/Zn superoxide dismutase SOD1 which account for 15-20% of autosomal dominant FALS cases and 1-2% of all ALS cases. Although implicated in anti-oxidative activity, the precise role of SOD1 dysfunction in ALS is incompletely understood [256]. Drosophila models of SOD1 include mis-expression of human FALS forms as well as loss-and gain-of-function of the Drosophila SOD1 homologue [257-261].

Surprisingly and in contrast to the human condition, initial studies in Drosophila showed that expression of either Drosophila or human SOD1 results in increased lifespan without affecting locomotion or motor neuron survival [258-260], whereas loss of Drosophila SOD1 decreases lifespan [260] and causes necrotic cell death in the fly eye [257]. Yet, a recent study suggests that motor neuron-specific expression of wild-type or disease-linked (A4V, G85R) mutants of human SOD1 do not affect lifespan but induce progressive climbing defects that are accompanied by impaired neural circuit physiology and a stress response in surrounding glial cells [261]. The observed phenotypes occurred without loss of motor neurons but were accompanied with an age-related accumulation of mutant human SOD1-specific aggregates. These data, together with earlier results [257] raise the interesting possibility that SOD1 mutations leading to soluble oligomers rather than aggregate formation confer cellular toxicity – as seen for Abeta in AD and for ASYN in PD.

In addition to SOD1, TDP-43 was recently identified as a major player in the pathogenesis of ALS and probably other neurodegenerative diseases. TDP-43 encodes a primarily nuclear protein with so far unknown function(s) in the nervous system [262]. Phosphorylated and ubiquitinated C-terminal fragments of TDP-43 are found as cytoplasmic inclusions not only in ALS and FTLD [15, 16], but also in AD and PD [263]. Significantly, TDP-43 mutations affecting the C-terminal part of the protein have been found in both sporadic ALS and FALS (for review, see [264]), suggesting that cytoplasmic accumulation and/or nuclear loss-of-function of TDP-43 is causally related to MND formation. Drosophila encodes two homologues of TDP-43 (Table 44) and three recent publications provide initial insights into the function of one of these homologues [265-267]. Two of these studies show that hypomorhpic TBPH alleles lead to reduced lifespan and locomotor defects [265,266]. As potential causes, changes in the number of synapses at the larval neuromuscular junction (NMJ) [265] and defective dendritic pruning of larval sensory neurons [266] are reported. A third study describes a TBPH deletion which causes larval lethality accompanied by reduced HDAC6 levels, a molecular phenotype also seen in HEK293E cells depleted for TDP-43 [267]. In addition, a recent study over-expressed human forms of wild-type and mutant TDP-43 that where C-terminally tagged with red fluorescent protein (RFP). Mis-expression of these constructs led to degenerative phenotypes in the eye and central brain [268], but it remains to be seen whether these phenotypes are attributable to gain of TDP-43 function or rather to RFP. Moreover, insights into tissue-specific gene expression or potential pathogenic mechanisms underlying TDP-43-related adult-onset, age-related MND are still lacking.

Fly models of ALS also exist for vesicle-associated membrane protein B (VAPB) which is involved in rare cases of late-onset ALS. The VAPB P56S mutation is nevertheless of interest because it was found in ALS and SMA cases, indicating a potential common pathogenic mechanism underlying both MNDs. Mis-expression of wild-type or mutant forms of human VAPB as well as loss-of-function of the corresponding Drosophila homologue VAP33-1 [269, 270] affect synapse formation and maintenance [269-271] and can lead to aggregate formation, motor neuron loss and locomotion defects. The underlying pathogenic mechanisms are only beginning to emerge. A recent study suggests that VAP33/VAPB leads to defective bone morphogenetic protein (BMP) signalling at the NMJ, eventually causing motor neurodegeneration [270], whereas another study demonstrated that VAPB is involved in Eph receptor signalling [272].

SPINAL MUSCULAR ATROPHY

SMA is, after cystic fibrosis, the most common autosomal recessive disorder in humans and is characterised by loss of lower motor neurons and progressive muscular atrophy in the limbs and trunk, eventually leading to respiratory failure and death [250]. SMA is caused by recessive mutations of SMN1 which, together with SMN2 provides functional SMN required for motor neuron survival. Disease severity is inversely proportional to levels of SMN; however, the mechanistic details of a motor neuron requirement of SMN are incompletely understood [255]. Drosophila encodes a homologue of SMN and loss-of-function of dSMN results in recessive larval lethality and NMJ defects [273, 274] which appear to be due to a bidirectional function of dSMN in both muscles and neurons [275]. A subsequent genomic screen characterised enhancers and suppressors of dSMN and identified altered BMP signalling as a potential pathogenic pathway – a situation strikingly similar to the ALS-related VAP33/VAPB phenotype [270].

HEREDITARY SPASTIC PARAPLEGIA

HSP describes a heterogeneous group of genetic disorders that are characterised by retrograde axonal degeneration of the corticospinal tracts and posterior columns in the spinal cord, leading to the loss of lower motor neurons and subsequent progressive spasticity and weakness of the lower limbs [276]. Several genetic loci have been identified that are causally related to HSP formation (for a recent update see [254]). The majority of cases are caused by mutations in Spastin which account for 40% of autosomal dominant HSP [277]. A Drosophila homologue has been identified [278] and several studies addressing dSpastin loss-of-function phenotypes as well as over-expression of human mutant forms established a role in microtubule organisation/stability, synapse morphology and neurotransmitter release at the NMJ [279-283]. Insights into the underlying pathogenic pathway(s) are coming from studies addressing the function of two other HSP-related genes, Atlastin-1 (Atl-1) and non-imprinted in Prader-Willi/Angelman syndrome 1 (NIPA1).

Drosophila Atl localizes to endoplasmic reticulum membranes and mediates membrane tethering and fusion [284]; it is also expressed in muscles and functions with Spastin in microtubule organisation/stability [285]. Genetic analyses revealed that Drosophila Atl is required for normal growth of muscles and synapses at the NMJ as loss-of-function mutations lead to reduced muscle size and increased numbers of synaptic boutons. Defects are accompanied by altered expression levels of synaptic proteins Dlg and alpha-spectrin and can be rescued by muscle but not neuron-specific Atl expression [285], suggesting that Atl and Spastin regulate synapse morphology at the NMJ via microtubule organisation/stability. Loss-and gain-of-function mutations of Spichthyin (Spict), the Drosophila homologue of human NIPA1, revealed that Spict regulates microtubule maintenance and morphology of presynaptic NMJs by way of BMP signalling, where it interacts with BMP receptors and promotes their internalization from the plasma membrane [286]. A recent follow-up study showed that mammalian NIPA1 also interacts with BMP type II receptor and similarly inhibits BMP signalling by regulating BMP receptor traffic [287]. Moreover, this study also provides evidence that spastin and another HSP-related gene spartin are also inhibitors of BMP signalling [287], indicating an evolutionary conserved role of Spast, Spict/NIPA1 and other HSP-related proteins in the regulation of BMP-mediated synapse morphology at the NMJ.

It is becoming apparent from these Drosophila studies into human MND that mutations of fly homologues of VAPB [270], SMN [275], NIPA1 and Spastin [286, 287] all seem to activate the same pathogenic pathway, suggesting that de-regulated BMP type II receptor signalling may unify ALS, SMA and HSP. This would make sense because all three MNDs affect lower motor neurons and BMP activity has been shown to play a significant role in the development and function of the NMJ [for review see 288, 289]. It will be interesting to see whether other MND-related genes also impinge on BMP signalling and whether its alteration is a cause or consequence of progressive motor neuron degeneration.

CONCLUDING REMARKS AND OUTLOOK

The above mentioned studies exemplify Drosophila research over the past two decades in the study of human neurodegeneration which led to the establishment of reliable models for Alzheimer’s, Parkinson’s, and motor neuron diseases, as well as models for Trinucleotide repeat expansion diseases. These studies made valuable contributions to our understanding of the molecular, genetic, and cellular aspects of neurodegeneration from genes to brain and behaviour. However, three major aspects still remain elusive and further efforts are required to address them.

WHAT CAUSES CELLULAR DEGENERATION?

The majority of neurodegenerative diseases are associated with the accumulation of misfolded proteins into aggregates that contain fibrillar structures. Although still debated, the prevalent hypothesis is that aggregates represent a cellular protection mechanism against toxic aggregation intermediates, whereas soluble oligomers and pre-fibrillar species most probably are the major cause of toxicity [115, 290, 291]. Several studies in Drosophila support this hypothesis [192, 193, 216, 257, 261]. However, the exact nature of the toxic species and how they exert their pathogenic function is still unclear. Thus, potential toxic species need to be tested in available Drosophila models (see [192]), followed by unbiased genome-wide modifier screens to identify molecular pathways executing cellular toxicity. In addition, there is mounting evidence suggesting that several of these toxic species, including forms of Abeta, Tau, ASYN, and HTT may harbour prion-like features that can trigger cell-to-cell transmission [292], thereby acting both as seeds of disease formation and propagators of disease progression. These features are compatible with permissive templating [293] and provide an explanation for the spread of disease from initially local foci to major regions of the brain, as seen for example in AD and PD [89,90]. Significantly, permissive templating represents an experimentally testable hypothesis in the search for additional prionogenic proteins [294] that may propagate disease progression. It remains to be tested whether cell-to-cell transmission of proteinopathies can be modelled in Drosophila, but a combination of bioinformatic and genetic modifier screens may provide powerful tools for experimental analyses.

WHAT MEDIATES AGE-RELATED PATHOGENESIS?

The vast majority of patients suffering from neurodegenerative diseases represent sporadic cases. The post-mortem brain of such patients is usually characterised by inclusions composed of misfolded but non-mutated proteins where the cause of pathogenesis remains elusive. Several risk factors have been implicated in disease formation and progression, including environmental and genetic risk factor(s), but age remains the dominant, overarching one. Yet, almost nothing is known about age-related pathogenic mechansims and how they impact on neurodegeneration. Obvious suspects are genetic instability, decline in protein quality control and mitochondrial dysfunction [202, 203]. However, these age-related phenotypes may explain some but not all of the sporadic cases observed in neurodegenerative diseases. Thus, comparable to the multi-hit hypothesis on cancer [295], one has to postulate at least two or more initiating events that trigger disease formation in an age-related manner. This seems to be the case in Drosophila, where deregulation of two or more conserved signalling pathways is seen in models of genetically-induced proteinopathies. These include PI3K/Akt and TOR signalling in AD and PD, JNK signalling in AD and PD, histone acetylation in PD, MNDs and TREDs, as well as BMP signalling in MNDs. It is currently not clear whether de-regulated signalling represents a cause or consequence of disease, nor is it clear whether non-canonical pathway components are involved. However, the available genetic tools make it possible to investigate disease formation and progression in an adult onset, age-related manner in Drosophila, and to screen for unknown pathway components at a systematic genome-wide level (see [228]). This will allow genetic dissection of pathogenic pathways related to age as the main risk factor and to determine the causative roles of individual pathway components.

WHAT PREVENTS DISEASE FORMATION?

An increased life expectancy in developed countries will steadily increase the number of individuals suffering from age-related neurodegenerative diseases. This represents an enormous socio-economic burden, and will intensify the demand to identify and develop new drugs and compounds that can be used for targeted treatment(s) in order to prevent or at least ameliorate disease symptoms. As part of these efforts, compounds need to be screened and tested in reliable models. Drosophila can make a significant contribution in this direction, and several successful examples have already shown that pharmacological intervention can ameliorate the disease, as demonstrated for example by the first description of geldanamycin and chaperone treatment of ASYN toxicity [68, 153]. Examples like this can directly guide clinical research and the development of novel therapeutic strategies for the treatment of these debilitating diseases. Considering previous work over the last two decades, it is reasonable to assume that Drosophila research will continue to make significant contributions in the study of human neurodegeneration.

ACKNOWLEDGEMENTS

The author thanks Beate Haege for comments on the manuscript, past and present members of his lab for their contributions, and especially Seong Ha Jeon, Sophia Luz, Katherine White, Zoe Ludlow, and Dickon Humphrey for image material. Work in the author’s lab is supported by grants from the UK Medical Research Council (G070149), the Royal Society (Hirth/2007/R2), the Parkinson’s Disease Society (G-0714), the Wellcome Trust, the Motor Neurone Disease Association (Hirth/Oct07/6233), and King’s College NHS Medical Research Trust (JRC19/2007). The author declares that he has no competing financial interests.

ABBREVIATIONS

AD
 = Alzheimer’s disease
ALS
 = Amyotrophic lateral sclerosis
APOe4
 = Apolipoprotein e4
APP
 = Amyloid precursor protein
Appl
 = Amyloid precursor protein-like
AR
 = Androgen receptor
ASYN
 = Alpha-synuclein
ATL-1
 = Atlastin-1
ATP
 = Adenosin tri-phosphate
ATN1
 = Atrophin -1
ATXN-1/2/3/7
 = Ataxin-1/2/3/7
BACE
 = Beta-site APP-cleaving enzyme
BMP
 = Bone morphogenetic protein
CACNA1A
 = Calcium channel, voltage-dependent, P/Q type, alpha 1A subunit
Caz
 = Cabeza
CHMP2B
 = Charged multivesicular body protein 2B
CNS
 = Central Nervous System
DA
 = Dopamine
DNA
 = Desoxy ribonucleic acid
DRPLA
 = Dentatorubropallidoluysian Atrophy
ER
 = Endoplasmatic reticulum
FAD
 = Familial AD
FALS
 = Familial ALS
Fh
 = Frataxin homolog
FMR1/2
 = Fragile X mental retardation 1
FRDA
 = Friedreich’s ataxia
FRX
 = Fragile X syndrome
FTD
 = Fronto-temporal dementia
FTLD
 = Fronto-temporal lobar degeneration
FUS/TLS
 = Fused in sarcoma/translocated in liposarcoma
FXN
 = Frataxin
GABA
 = Gamma-aminobutyric acid
GFP
 = Green Fluorescent Protein
Gug
 = Grunge
HD
 = Huntington’s disease
HDAC
 = Histone deacetylase
HSP
 = Hereditary spastic paraplegia
Hsp70
 = Heat shock protein 70
HtrA2
 = High temperature requirement protein A2
HTT
 = Huntingtin
JNK
 = c-Jun N-terminal kinase
LRRK2
 = Leucine-rich repeat kinase 2
MND
 = Motor neuron diseases
MPTP
 = 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine
mtDNA
 = Mitochondrial DNA
NIPA1
 = Non-imprinted in Prader-Willi/Angelman syndrome 1
NMJ
 = Neuromuscular junction
PD
 = Parkinson’s disease
PI3K
 = Phosphatidylinositol 3-kinase
PINK1
 = Phosphatase and tensin homologue (PTEN)- induced kinase 1
POLG
 = Polymerase gamma
PolyQ
 = Polyglutamine
PSN-1/2
 = Presenilin-1/2
RFP
 = Red Fluorescent Protein
RNA
 = Ribonucleic Acid
SBMA
 = Spinal Bulbar Muscular Atrophy
SCA
 = Spinocerebellar ataxias
SETX
 = Senataxin
SMA
 = Spinal muscular atrophy
SMN-1/2
 = Survival of motor neuron protein 1/2
SOD1
 = Cu/Zn superoxide dismutase 1
SPAST
 = Spastin
Spict
 = Spichthyin
TBP
 = TATA box binding protein
TBPH
 = Transactive response DNA-binding protein homologue
TDP-43
 = TAR DNA binding protein 43
TOR
 = Target of rapamycin
TRED
 = Trinucleotide repeat expansion diseases
UAS
 = Upstream activating sequence
Vap-33-1
 = Vesicle-associated membrane protein 33-1
VAPB
 = Vesicle-associated membrane protein B

REFERENCES

1. Beal MF, Lang AE, Ludolph AC. Neurodegenerative Diseases: Neurobiology, Pathogenesis and Therapeutics. UK: Cambridge University Press; 2005.
2. Bio Portfolio. New molecular target identified for the prevention of Alzheimer's disease. http://www.bioportfolio.com/news/DailyUpda tes_63.htm .
3. Pepeu G, Giovannini MG. Cholinesterase inhibitors and beyond. Curr. Alzheimer Res. 2009;6:86–96. [PubMed]
4. Schapira AH, Emre M, Jenner P, Poewe W. Levodopa in the treatment of Parkinson's disease. Eur. J. Neurol. 2009;16:982–989. [PubMed]
5. Glenner GG, Wong CW. Alzheimer's disease: initial report of the purification and characterization of a novel cerebrovascular amyloid protein. Biochem. Biophys. Res. Commun. 1984;120:885–890. [PubMed]
6. Masters CL, Simms G, Weinman NA, Multhaup G, McDonald BL, Beyreuther K. Amyloid plaque core protein in Alzheimer disease and Down syndrome. Proc. Natl. Acad. Sci. USA. . 1985;82:4245–4249. [PubMed]
7. Masters CL, Multhaup G, Simms G, Pottgiesser J, Martins RN, Beyreuther K. Neuronal origin of a cerebral amyloid: neurofibrillary tangles of Alzheimer's disease contain the same protein as the amyloid of plaque cores and blood vessels. EMBO J. 985b;4:2757–2763. [PubMed]
8. Tanzi RE, McClatchey AI, Lamperti ED, Villa-Komaroff L, Gusella JF, Neve RL. Protease inhibitor domain encoded by an amyloid protein precursor mRNA associated with Alzheimer's disease. Nature. 1988;331:528–530. [PubMed]
9. Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M. Alpha-synuclein in Lewy bodies. Nature. 1997;388:839–840. [PubMed]
10. Wolozin BL, Pruchnicki A, Dickson DW, Davies P. A neuronal antigen in the brains of Alzheimer patients. Science. 1986;232:648–650. [PubMed]
11. Grundke-Iqbal I, Iqbal K, Quinlan M, Tung YC, Zaidi MS, Wisniewski HM. Microtubule-associated protein tau. A component of Alzheimer paired helical filaments. J. Biol. Chem. 1986;261:6084–6089. [PubMed]
12. Wood JG, Mirra SS, Pollock NJ, Binder LI. Neurofibrillary tangles of Alzheimer disease share antigenic determinants with the axonal microtubule-associated protein tau (tau) Proc. Natl. Acad. Sci. USA. 1986;83:4040–4043. [PubMed]
13. Kosik KS, Joachim CL, Selkoe DJ. Microtubule-associated protein tau (tau) is a major antigenic component of paired helical filaments in Alzheimer disease. Proc. Natl. Acad. Sci. USA. 1986;83:4044–4048. [PubMed]
14. Ihara Y, Nukina N, Miura R, Ogawara M. Phosphorylated tau protein is integrated into paired helical filaments in Alzheimer's disease. J. Biochem. 1986;99:1807–1810. [PubMed]
15. Neumann M, Sampathu DM, Kwong LK, Truax AC, Micsenyi MC, Chou TT, Bruce J, Schuck T, Grossman M, Clark CM, McCluskey LF, Miller BL, Masliah E, Mackenzie IR, Feldman H, Feiden W, Kretzschmar HA, Trojanowski JQ, Lee VM. Ubiquitinated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Science. 2006;314:130–133. [PubMed]
16. Arai T, Hasegawa M, Akiyama H, Ikeda K, Nonaka T, Mori H, Mann D, Tsuchiya K, Yoshida M, Hashizume Y, Oda T. TDP-43 is a component of ubiquitin-positive tau-negative inclusions in frontotemporal lobar degeneration and amyotrophic lateral sclerosis. Biochem. Biophys. Res. Commun. 2006;351:602–611. [PubMed]
17. Satake W, Nakabayashi Y, Mizuta I, Hirota Y, Ito C, Kubo M, Kawaguchi T, Tsunoda T, Watanabe M, Takeda A, Tomiyama H, Nakashima K, Hasegawa K, Obata F, Yoshikawa T, Kawakami H, Sakoda S, Yamamoto M, Hattori N, Murata M, Nakamura Y, Toda T. Genome-wide association study identifies common variants at four loci as genetic risk factors for Parkinson's disease. Nat. Genet. 2009;41:1303–1307. [PubMed]
18. Simón-Sánchez J, Schulte C, Bras JM, Sharma M, Gibbs JR, Berg D, Paisan-Ruiz C, Lichtner P, Scholz SW, Hernandez DG, Krüger R, Federoff M, Klein C, Goate A, Perlmutter J, Bonin M, Nalls MA, Illig T, Gieger C, Houlden H, Steffens M, Okun MS, Racette BA, Cookson MR, Foote KD, Fernandez HH, Traynor BJ, Schreiber S, Arepalli S, Zonozi R, Gwinn K, van der Brug M, Lopez G, Chanock SJ, Schatzkin A, Park Y, Hollenbeck A, Gao J, Huang X, Wood NW, Lorenz D, Deuschl G, Chen H, Riess O, Hardy JA, Singleton AB, Gasser T. Genome-wide association study reveals genetic risk underlying Parkinson's disease. Nat. Genet. 2009;41:1308–1312. [PMC free article] [PubMed]
19. Winderickx J, Delay C, De Vos A, Klinger H, Pellens K, Vanhelmont T, Van Leuven F, Zabrocki P. Protein folding diseases and neurodegeneration: lessons learned from yeast. Biochim. Biophys. Acta. 2008;1783:1381–1395. [PubMed]
20. Teschendorf D, Link CD. What have worm models told us about the mechanisms of neuronal dysfunction in human neurodegenerative diseases? Mol. Neurodegener. 2009;4:38. [PMC free article] [PubMed]
21. Adoutte A, Balavoine G, Lartillot N, Lespinet O, Prud’homme B, de Rosa R. The new animal phylogeny: Reliability and implications. Proc. Natl. Acad. Sci. USA. 2000;97:4453–4465. [PubMed]
22. Peterson KJ, Lyons JB, Nowak KS, Takacs CM, Wargo MJ, McPeek MA. Estimating metazoan divergence times with a molecular clock. Proc. Natl. Acad. Sci. USA. 2004;101:6536–6541. [PubMed]
23. Sturtevant AE, Lewis EB. A History of Genetics. USA: Cold Spring Harbor Laboratory Press; 2001.
24. Piper MD, Skorupa D, Partridge L. Diet, metabolism and lifespan in Drosophila. Exp. Gerontol. 2005;40:857–862. [PubMed]
25. Pletcher SD, Libert S, Skorupa D. Flies and their golden apples: the effect of dietary restriction on Drosophila aging and age-dependent gene expression. Ageing Res. Rev. 2005;4:451–480. [PubMed]
26. McGuire SE, Deshazer M, Davis RL. Thirty years of olfactory learning and memory research in Drosophila melanogaster. Prog. Neurobiol. 2005;76:328–347. [PubMed]
27. Margulies C, Tully T, Dubnau J. Deconstructing memory in Drosophila. Curr. Biol. 2005;15:R700–R713. [PMC free article] [PubMed]
28. Nichols CD. Drosophila melanogaster neurobiology, neuropharmacology, and how the fly can inform central nervous system drug discovery. Pharmacol. Ther. 2006;112:677–700. [PubMed]
29. Adams MD, Celniker SE, Holt RA, Evans CA, Gocayne JD, Amanatides PG, Scherer SE, Li PW, Hoskins RA, Galle RF, George RA, Lewis SE, Richards S, Ashburner M, Henderson SN, Sutton GG, Wortman JR, Yandell MD, Zhang Q, Chen LX, Brandon RC, Rogers YH, Blazej RG, Champe M, Pfeiffer BD, Wan KH, Doyle C, Baxter EG, Helt G, Nelson CR, Gabor GL, Abril JF, Agbayani A, An HJ, Andrews-Pfannkoch C, Baldwin D, Ballew RM, Basu A, Baxendale J, Bayraktaroglu L, Beasley EM, Beeson KY, Benos PV, Berman P, Bhandari D, Bolshakov S, Borkova D, Botchan MR, Bouck J, Brokstein P, Brottier P, Burtis KC, Busam DA, Butler H, Cadieu E, Center A, Chandra I, Cherry JM, Cawley S, Dahlke C, Davenport LB, Davies P, de Pablos B, Delcher A, Deng Z, Mays AD, Dew I, Dietz SM, Dodson K, Doup LE, Downes M, Dugan-Rocha S, Dunkov BC, Dunn P, Durbin KJ, Evangelista CC, Ferraz C, Ferriera S, Fleischmann W, Fosler C, Gabrielian AE, Garg NS, Gelbart WM, Glasser K, Glodek A, Gong F, Gorrell JH, Gu Z, Guan P, Harris M, Harris NL, Harvey D, Heiman TJ, Hernandez JR, Houck J, Hostin D, Houston KA, Howland TJ, Wei MH, Ibegwam C, Jalali M, Kalush F, Karpen GH, Ke Z, Kennison JA, Ketchum KA, Kimmel BE, Kodira CD, Kraft C, Kravitz S, Kulp D, Lai Z, Lasko P, Lei Y, Levitsky AA, Li J, Li Z, Liang Y, Lin X, Liu X, Mattei B, McIntosh TC, McLeod MP, McPherson D, Merkulov G, Milshina NV, Mobarry C, Morris J, Moshrefi A, Mount SM, Moy M, Murphy B, Murphy L, Muzny DM, Nelson DL, Nelson DR, Nelson KA, Nixon K, Nusskern DR, Pacleb JM, Palazzolo M, Pittman GS, Pan S, Pollard J, Puri V, Reese MG, Reinert K, Remington K, Saunders RD, Scheeler F, Shen H, Shue BC, Sidén-Kiamos I, Simpson M, Skupski MP, Smith T, Spier E, Spradling AC, Stapleton M, Strong R, Sun E, Svirskas R, Tector C, Turner R, Venter E, Wang AH, Wang X, Wang ZY, Wassarman DA, Weinstock GM, Weissenbach J, Williams SM, Woodage T, Worley KC, Wu D, Yang S, Yao QA, Ye J, Yeh RF, Zaveri JS, Zhan M, Zhang G, Zhao Q, Zheng L, Zheng XH, Zhong FN, Zhong W, Zhou X, Zhu S, Zhu X, Smith HO, Gibbs RA, Myers EW, Rubin GM, Venter JC. The genome sequence of Drosophila melanogaster. Science. 2000;287:2185–2195. [PubMed]
30. Campos-Ortega JA, Hartenstein V. The Embryonic Development of Drosophila Melanogaster. Berlin and Heidelberg: Springer Verlag; 1997.
31. Technau GM. Brain Development in Drosophila Melanogaster. Berlin: Springer Verlag; 2008.
32. Ashburner M, Golic K, Hawley S. Drosophila: A Laboratory Handbook. New Jersey: Cold Spring Harbor Laboratory Press; 2004.
33. Greenspan RJ. Fly Pushing: The Theory and Practice of Drosophila Genetics. New Jersey: Cold Spring Harbor Laboratory Press; 2004.
34. Dahmann C. Drosophila: Methods and Protocols. New York: Humana Press; 2008.
35. Heisenberg M. Genetic approaches to neuroethology. Bioessays. 1997;19:1065–1073. [PubMed]
36. Rubin GM, Yandell MD, Wortman JR, Gabor Miklos GL, Nelson CR, Hariharan IK, Fortini ME, Li PW, Apweiler R, Fleischmann W, Cherry JM, Henikoff S, Skupski MP, Misra S, Ashburner M, Birney E, Boguski MS, Brody T, Brokstein P, Celniker SE, Chervitz SA, Coates D, Cravchik A, Gabrielian A, Galle RF, Gelbart WM, George RA, Goldstein LS, Gong F, Guan P, Harris NL, Hay BA, Hoskins RA, Li J, Li Z, Hynes RO, Jones SJ, Kuehl PM, Lemaitre B, Littleton JT, Morrison DK, Mungall C, O'Farrell PH, Pickeral OK, Shue C, Vosshall LB, Zhang J, Zhao Q, Zheng XH, Lewis S. Comparative genomics of the eukaryotes. Science. 2000;287:2204–2215. [PMC free article] [PubMed]
37. Edgar BA, Lehner CF. Developmental control of cell cycle regulators: a fly's perspective. Science. 1996;274:1646–1652. [PubMed]
38. Bähler J. Cell-cycle control of gene expression in budding and fission yeast. Annu. Rev. Genet. 2005;39:69–94. [PubMed]
39. Sánchez I, Dynlacht BD. New insights into cyclins, CDKs, and cell cycle control. Semin. Cell Dev. Biol. 2005;16:311–321. [PubMed]
40. Stocker H, Hafen E. Genetic control of cell size. Curr. Opin. Genet. Dev. 2000;10:529–535. [PubMed]
41. Hietakangas V, Cohen SM. Regulation of tissue growth through nutrient sensing. Annu. Rev. Genet. 2009;43:389–410. [PubMed]
42. Leuzinger S, Hirth F, Gerlich D, Acampora D, Simeone A, Gehring WJ, Finkelstein R, Furukubo-Tokunaga K, Reichert H. Equivalence of the fly orthodenticle gene and the human OTX genes in embryonic brain development of Drosophila. Development. 1998;125:1703–1710. [PubMed]
43. Nagao T, Leuzinger S, Acampora D, Simeone A, Finkelstein R, Reichert H, Furukubo-Tokunaga K. Developmental rescue of Drosophila cephalic defects by the human Otx genes. Proc. Natl. Acad. Sci. USA. 1998;95:3737–3742. [PubMed]
44. Hanks MC, Loomis CA, Harris E, Tong CX, Anson-Cartwright L, Auerbach A, Joyner A. Drosophila engrailed can substitute for mouse Engrailed1 function in mid-hindbrain, but not limb development. Development. 1998;125:4521–4530. [PubMed]
45. Hirth F, Reichert H. Conserved genetic programs in insect and mammalian brain development. Bioessays. 1999;21:677–84. [PubMed]
46. Reiter LT, Potocki L, Chien S, Gribskov M, Bier E. A systematic analysis of human disease-associated gene sequences in Drosophila melanogaster. Genome Res. 2001;11:1114–1125. [PubMed]
47. Brand AH, Perrimon N. Targeted gene expression as a means of altering cell fates and generating dominant phenotypes. Development. 1993;118:401–15. [PubMed]
48. Sang TK, Jackson GR. Drosophila models of neurodegenerative disease. NeuroRx. 2005;2:438–46. [PubMed]
49. Kramer JM, Staveley BE. GAL4 causes developmental defects and apoptosis when expressed in the developing eye of Drosophila melanogaster. Genet. Mol. Res. 2003;2:43–47. [PubMed]
50. Bischof J, Basler K. Recombinases and their use in gene activation, gene inactivation, and transgenesis. Methods Mol. Biol. 2008;420:175–195. [PubMed]
51. Leung B, Waddell S. Four-dimensional gene expression control: memories on the fly. Trends Neurosci. 2004;27:511–513. [PubMed]
52. Bier E. Drosophila, the golden bug, emerges as a tool for human genetics. Nat. Rev. Genet. 2005;6:9–23. [PubMed]
53. Venken KJ, Bellen HJ. Transgenesis upgrades for Drosophila melanogaster. Development. 2007;134:3571–3584. [PubMed]
54. Venken KJ, Bellen HJ. Emerging technologies for gene manipulation in Drosophila melanogaster. Nat. Rev. Genet. 2005;6:167–178. [PubMed]
55. Dietzl G, Chen D, Schnorrer F, Su KC, Barinova Y, Fellner M, Gasser B, Kinsey K, Oppel S, Scheiblauer S, Couto A, Marra V, Keleman K, Dickson BJ. A genome-wide transgenic RNAi library for conditional gene inactivation in Drosophila. Nature. 2007;448:151–156. [PubMed]
56. Dodson MW, Guo M. Pink1 Parkin DJ-1 and mitochondrial dysfunction in Parkinson’s disease. Curr. Opin. Neurobiol. 2007;17:331–337. [PubMed]
57. Park J, Kim Y, Chung J. Mitochondrial dysfunction and Parkinson's disease genes: insights from Drosophila. Dis. Model Mech. 2009;2:336–340. [PubMed]
58. Van Laar VS, Berman SB. Mitochondrial dynamics in Parkinson’s disease. Exp. Neurol. 2009;218:247–256. [PMC free article] [PubMed]
59. Shulman JM, Feany MB. Genetic modifiers of tauopathy in Drosophila. Genetics. 2003;165:1233–1242. [PubMed]
60. Scherzer CR, Jensen RV, Gullans SR, Feany MB. Gene expression changes presage neurodegeneration in a Drosophila model of Parkinson's disease. Hum. Mol. Genet. 2003;12:2457–2466. [PubMed]
61. Whitworth AJ, Theodore DA, Greene JC, Benes H, Wes PD, Pallanck LJ. Increased glutathione S-transferase activity rescues dopaminergic neuron loss in a Drosophila model of Parkinson's disease. Proc. Natl. Acad. Sci. USA. 2005;102:8024–8029. [PubMed]
62. Karsten SL, Sang TK, Gehman LT, Chatterjee S, Liu J, Lawless GM, Sengupta S, Berry RW, Pomakian J, Oh HS, Schulz C, Hui KS, Wiedau-Pazos M, Vinters HV, Binder LI, Geschwind DH, Jackson GR. A genomic screen for modifiers of tauopathy identifies puromycin-sensitive aminopeptidase as an inhibitor of tau-induced neurodegeneration. Neuron. 2006;51:549–560. [PubMed]
63. Cooper AA, Gitler AD, Cashikar A, Haynes CM, Hill KJ, Bhullar B, Liu K, Xu K, Strathearn KE, Liu F, Cao S, Caldwell KA, Caldwell GA, Marsischky G, Kolodner RD, Labaer J, Rochet JC, Bonini NM, Lindquist S. Alpha-synuclein blocks ER-Golgi traffic and Rab1 rescues neuron loss in Parkinson's models. Science. 2006;313:324–328. [PMC free article] [PubMed]
64. Blard O, Feuillette S, Bou J, Chaumette B, Frébourg T, Campion D, Lecourtois M. Cytoskeleton proteins are modulators of mutant tau-induced neurodegeneration in Drosophila. Hum. Mol. Genet. 2007;16:555–566. [PubMed]
65. Tan L, Schedl P, Song HJ, Garza D, Konsolaki M. The Toll-->NFkappaB signaling pathway mediates the neuropatho-logical effects of the human Alzheimer's Abeta42 polypeptide in Drosophila. PLoS One. 2008;3:e3966. [PMC free article] [PubMed]
66. Outeiro TF, Kontopoulos E, Altmann SM, Kufareva I, Strathearn KE, Amore AM, Volk CB, Maxwell MM, Rochet JC, McLean PJ, Young AB, Abagyan R, Feany MB, Hyman BT, Kazantsev AG. Sirtuin 2 inhibitors rescue alpha-synuclein-mediated toxicity in models of Parkinson's disease. Science. 2007;317:516–519. [PubMed]
67. Rajendran L, Schneider A, Schlechtingen G, Weidlich S, Ries J, Braxmeier T, Schwille P, Schulz JB, Schroeder C, Simons M, Jennings G, Knölker HJ, Simons K. Efficient inhibition of the Alzheimer's disease beta-secretase by membrane targeting. Science. 2008;320:520–523. [PubMed]
68. Auluck PK, Meulener MC, Bonini NM. Mechanisms of Suppression of {alpha}-Synuclein Neurotoxicity by Geldanamycin in Drosophila. J. Biol. Chem. 2005;280:2873–2878. [PubMed]
69. Faust K, Gehrke S, Yang Y, Yang L, Beal MF, Lu B. Neuroprotective effects of compounds with antioxidant and anti-inflammatory properties in a Drosophila model of Parkinson's disease. BMC Neurosci. 2009;10:109. [PMC free article] [PubMed]
70. Chang S, Bray SM, Li Z, Zarnescu CD, He C, Jin C, Warren ST. Identification of small molecules rescuing fragile X syndrome phenotypes in Drosophila. Nat. Chem. Biol. 2008;4:256–263. [PubMed]
71. Stork T, Engelen D, Krudewig A, Silies M, Bainton RJ, Klambt C. Organization and function of the blood-brain barrier in Drosophila. J. Neurosci. 2008;28:587–597. [PubMed]
72. Vidal M, Cagan RL. Drosophila models for cancer research. Curr. Opin. Genet. Dev. 2006;16:10–16. [PubMed]
73. Zoghbi HY, Botas J. Mouse and fly models of neurodegeneration. Trends Genet. 2002;18:463–471. [PubMed]
74. Bonini NM, Fortini ME. Human neurodegenerative disease modeling using Drosophila. Annu. Rev. Neurosci. 2003;26:627–659. [PubMed]
75. O'Kane CJ. Modelling human diseases in Drosophila and Caenorhabditis. Semin Cell Dev. Biol. 2003;14:3–10. [PubMed]
76. Driscoll M, Gerstbrein B. Dying for a cause: invertebrate genetics takes on human neurodegeneration. Nat. Rev. Genet. 2003;4:181–194. [PubMed]
77. Shulman JM, Shulman LM, Weiner WJ, Feany MB. From fruit fly to bedside: translating lessons from Drosophila models of neurodegenerative disease. Curr. Opin. Neurol. 2003;16:443–449. [PubMed]
78. Marsh JL, Thompson LM. Can flies help humans treat neurodegenerative diseases? Bioessays. 2004;26:485–496. [PubMed]
79. Cauchi RJ, van den Heuvel M. The fly as a model for neurodegenerative diseases: is it worth the jump? Neurodegener. Dis. 2006;3:338–356. [PubMed]
80. Iijima K, Iijima-Ando K. Drosophila models of Alzheimer's amyloidosis: the challenge of dissecting the complex mechanisms of toxicity of amyloid-beta 42. J. Alzheimers Dis. 2008;15:523–540. [PubMed]
81. Khurana V. Modeling Tauopathy in the fruit fly Drosophila melanogaster. J. Alzheimers Dis. 2008;15:541–553. [PubMed]
82. Lu B, Vogel H. Drosophila models of neurodegenerative diseases. Annu. Rev. Pathol. Mech. Dis. 2009;4:315–342.
83. Lu B. Recent advances in using Drosophila to model neurodegenerative diseases. Apoptosis. 2009;14:1008–1020. [PMC free article] [PubMed]
84. McPhee CK, Baehrecke EH. Autophagy in Drosophila melanogaster. Biochim. Biophys. Acta. 2009;1793:1452–1460. [PMC free article] [PubMed]
85. Lessing D, Bonini NM. Maintaining the brain: insight into human neurodegeneration from Drosophila melanogaster mutants. Nat. Rev. Genet. 2009;10:359–370. [PMC free article] [PubMed]
86. Goedert M, Spillantini MG. A century of Alzheimer’s disease. Science. 2006;314:777–781. [PubMed]
87. Hardy J. A hundred years of Alzheimer's disease research. Neuron. 2006;52:3–13. [PubMed]
88. Bu G. Apolipoprotein E and its receptors in Alzheimer’s disease: pathways, pathogenesis and therapy. Nat. Rev. Neurosci. 2009;10:333–344. [PMC free article] [PubMed]
89. Braak H, Del Tredici K. Invited Article: Nervous system pathology in sporadic Parkinson disease. Neurology. 2008;70:1916–1925. [PubMed]
90. Nelson PT, Braak H, Markesbery WR. Neuropathology and cognitive impairment in Alzheimer disease: a complex but coherent relationship. J. Neuropathol. Exp. Neurol. 2009;68:1–14. [PMC free article] [PubMed]
91. Lee V, Goedert M, Trojanowski JQ. Neurodegenerative Tauopathies. Annu. Rev. Neurosci. 2001;24:1121–1159. [PubMed]
92. Ballatore C, Lee VM, Trojanowski JQ. Tau-mediated neurodegeneration in Alzheimer’s disease and related disorders. Nat. Rev. Neurosci. 2007;8:663–672. [PubMed]
93. Hardy J, Selkoe DJ. The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science. 2002;297:353–356. [PubMed]
94. Hardy J. The amyloid hypothesis for Alzheimer’s disease: a critical reappraisal. J. Neurochem. 2009;110:1129–1134. [PubMed]
95. Luo L, Tully T, White K. Human amyloid precursor protein ameliorates behavioral deficit of flies deleted for Appl gene. Neuron. 1992;9:595–605. [PubMed]
96. Carmine-Simmen K, Proctor T, Tschäpe J, Poeck B, Triphan T, Strauss R, Kretzschmar D. Neurotoxic effects induced by the Drosophila amyloid-beta peptide suggest a conserved toxic function. Neurobiol. Dis. 2009;33:274–281. [PubMed]
97. Greeve I, Kretzschmar D, Tschape JA, Beyn A, Brellinger C, Schweizer M, Nitsch RM, Reifegerste R. Age-dependent neurodegeneration and Alzheimer-amyloid plaque formation in transgenic Drosophila. J. Neurosci. 2004;24:3899–3906. [PubMed]
98. Iijima K, Liu HP, Chiang AS, Hearn SA, Konsolaki M, Zhong Y. Dissecting the pathological effects of human Abeta40 and Abeta42 in Drosophila: a potential model for Alzheimer's disease. Proc. Natl. Acad. Sci. USA. 2004;101:6623–6628. [PubMed]
99. Torroja L, Chu H, Kotovsky I, White K. Neuronal overexpression of APPL, the Drosophila homologue of the amyloid precursor protein (APP), disrupts axonal transport. Curr. Biol. 1999;9:489–492. [PubMed]
100. Gunawardena S, Goldstein LS. Disruption of axonal transport and neuronal viability by amyloid precursor protein mutations in Drosophila. Neuron. 2001;32:389–401. [PubMed]
101. Stokin GB, Almenar-Queralt A, Gunawardena S, Rodrigues EM, Falzone T, Kim J, Lillo C, Mount SL, Roberts EA, McGowan E, Williams DS, Goldstein LS. Amyloid precursor protein-induced axonopathies are independent of amyloid-beta peptides. Hum. Mol. Genet. 2008;17:3474–3486. [PMC free article] [PubMed]
102. Iijima-Ando K, Hearn SA, Shenton C, Gatt A, Zhao L, Iijima K. Mitochondrial mislocalization underlies abeta42-induced neuronal dysfunction in a Drosophila model of Alzheimer's disease. PLoS One. 2009;4:e8310. [PMC free article] [PubMed]
103. Rusu P, Jansen A, Soba P, Kirsch J, Löwer A, Merdes G, Kuan YH, Jung A, Beyreuther K, Kjaerulff O, Kins S. Axonal accumulation of synaptic markers in APP transgenic Drosophila depends on the NPTY motif and is paralleled by defects in synaptic plasticity. Eur. J. Neurosci. 2007;25:1079–1086. [PubMed]
104. Crowther DC, Kinghorn KJ, Miranda E, Page R, Curry JA, Duthie FA, Gubb DC, Lomas DA. Intraneuronal Abeta, non-amyloid aggregates and neurodegeneration in a Drosophila model of Alzheimer's disease. Neuroscience. 2005;132:123–135. [PubMed]
105. Iijima K, Chiang HC, Hearn SA, Hakker I, Gatt A, Shenton C, Granger L, Leung A, Iijima-Ando K, Zhong Y. Abeta42 mutants with different aggregation profiles induce distinct pathologies in Drosophila. PLoS One. 2008;3:e1703. [PMC free article] [PubMed]
106. van de Hoef DL, Hughes J, Livne-Bar I, Garza D, Konsolaki M, Boulianne GL. Identifying genes that interact with Drosophila presenilin and amyloid precursor protein. Genesis. 2009;47:246–260. [PubMed]
107. Finelli A, Kelkar A, Song HJ, Yang H, Konsolaki M. A model for studying Alzheimer's Abeta42-induced toxicity in Drosophila melanogaster. Mol. Cell. Neurosci. 2004;26:365–375. [PubMed]
108. Iijima-Ando K, Hearn SA, Granger L, Shenton C, Gatt A, Chiang HC, Hakker I, Zhong Y, Iijima K. Overexpression of neprilysin reduces alzheimer amyloid-beta42 (Abeta42)-induced neuron loss and intraneuronal Abeta42 deposits but causes a reduction in cAMP-responsive element-binding protein-mediated transcription, age-dependent axon pathology, and premature death in Drosophila. J. Biol. Chem. 2008;283:19066–19076. [PMC free article] [PubMed]
109. Sanokawa-Akakura R, Cao W, Allan K, Patel K, Ganesh A, Heiman G, Burke R, Kemp FW, Bogden JD, Camakaris J, Birge RB, Konsolaki M. Control of Alzheimer's amyloid beta toxicity by the high molecular weight immunophilin FKBP52 and copper homeostasis in Drosophila. PLoS One. 2010;5:e8626. [PMC free article] [PubMed]
110. Schilling S, Zeitschel U, Hoffmann T, Heiser U, Francke M, Kehlen A, Holzer M, Hutter-Paier B, Prokesch M, Windisch M, Jagla W, Schlenzig D, Lindner C, Rudolph T, Reuter G, Cynis H, Montag D, Demuth HU, Rossner S. Glutaminyl cyclase inhibition attenuates pyroglutamate Abeta and Alzheimer's disease-like pathology. Nat. Med. 2008;14:1106–1111. [PubMed]
111. Ling D, Song HJ, Garza D, Neufeld TP, Salvaterra PM. Abeta42-induced neurodegeneration via an age-dependent autophagic-lysosomal injury in Drosophila. PLoS One. 2009;4:e4201. [PMC free article] [PubMed]
112. Leyssen M, Ayaz D, Hébert SS, Reeve S, De Strooper B, Hassan BA. Amyloid precursor protein promotes post-developmental neurite arborization in the Drosophila brain. EMBO J. 2005;24:2944–2955. [PubMed]
113. Nixon RA. Autophagy, amyloidogenesis and Alzheimer disease. J. Cell. Sci. 2007;120:4081–4091. [PubMed]
114. Erol A. Unraveling the molecular mechanisms behind the metabolic basis of sporadic Alzheimer's disease. J. Alzheimers Dis. 2009;17:267–276. [PubMed]
115. Haass C, Selkoe DJ. Soluble protein oligomers in neurodegeneration: lessons from the Alzheimer’s amyloid beta-peptide. Nat. Rev. Mol. Cell. Biol. 2007;8:101–112. [PubMed]
116. Harmeier A, Wozny C, Rost BR, Munter LM, Hua H, Georgiev O, Beyermann M, Hildebrand PW, Weise C, Schaffner W, Schmitz D, Multhaup G. Role of amyloid-beta glycine 33 in oligomerization, toxicity, and neuronal plasticity. J. Neurosci. 2009;29:7582–7590. [PubMed]
117. Ye Y, Lukinova N, Fortini ME. Neurogenic phenotypes and altered Notch processing in Drosophila Presenilin mutants. Nature. 1999;398:525–529. [PubMed]
118. Fiúza UM, Arias AM. Cell and molecular biology of Notch. J. Endocrinol. 2007;194:459–474. [PubMed]
119. Seidner GA, Ye Y, Faraday MM, Alvrod WG, Fortini ME. Modeling clinically heterogenous presenilin mutations with transgenic Drosophila. Curr. Biol. 2006;16:1026–1033. [PubMed]
120. Li A, Xie Z, Dong Y, McKay KM, McKee ML, Tanzi RE. Isolation and characterization of the Drosophila ubiquilin ortholog dUbqln: in vivo interaction with early-onset Alzheimer disease genes. Hum. Mol. Genet. 2007;16:2626–2639. [PubMed]
121. Ganguly A, Feldman RM, Guo M. ubiquilin antagonizes presenilin and promotes neurodegeneration in Drosophila. Hum. Mol. Genet. 2008;17:293–302. [PubMed]
122. Michno K, Knight D, Campusano JM, van de Hoef D, Boulianne GL. Intracellular calcium deficits in Drosophila cholinergic neurons expressing wild type or FAD-mutant presenilin. PLoS One. 2008;4:e6904. [PMC free article] [PubMed]
123. Bezprozvanny I, Mattson MP. Neuronal calcium mishandling and the pathogenesis of Alzheimer's disease. Trends Neurosci. 2008;31:454–463. [PMC free article] [PubMed]
124. Dehmelt L, Halpain S. The MAP2/Tau family of microtubule-associated proteins. Genome Biol. 2005;6:204. [PMC free article] [PubMed]
125. Gasparini L, Terni B, Spillantini MG. Frontotemporal dementia with Tau pathology. Neurodegen. Dis. 2007;4:236–253.
126. Heidary G, Fortini ME. Identification and characterization of the Drosophila tau homolog. Mech. Dev. 2001;108:171–178. [PubMed]
127. Mershin A, Pavlopoulos E, Fitch O, Braden BC, Nanopoulos DV, Skoulakis EM. Learning and memory deficits upon TAU accumulation in Drosophila mushroom body neurons. Learn. Mem. 2004;11:277–287. [PubMed]
128. Steinhilb ML, Dias-Santagata D, Fulga TA, Felch DL, Feany MB. Tau phosphorylation sites work in concert to promote neurotoxicity in vivo. Mol. Biol. Cell. 2007;18:5060–5068. [PMC free article] [PubMed]
129. Chatterjee S, Sang TK, Lawless GM, Jackson GR. Dissociation of tau toxicity and phosphorylation: role of GSK-3beta, MARK and Cdk5 in a Drosophila model. Hum. Mol. Genet. 2009;18:164–77. [PMC free article] [PubMed]
130. Wittmann CW, Wszolek MF, Shulman JM, Salvaterra PM, Lewis J, Hutton M, Feany MB. Tauopathy in Drosophila: neurodegeneration without neurofibrillary tangles. Science. 2001;293:711–714. [PubMed]
131. Fulga TA, Elson-Schwab I, Khurana V, Steinhilb ML, Spires TL, Hyman BT, Feany MB. Abnormal bundling and accumulation of F-actin mediates tau-induced neuronal degeneration in vivo. Nat. Cell Biol. 2007;9:139–148. [PubMed]
132. Jackson GR, Wiedau-Pazos M, Sang T-K, Wagle N, Brown CA, Massachi S, Geschwind DH. Human wild-type tau interacts with wingless pathway components and produces neurofibrillary pathology in Drosophila. Neuron. 2002;34:509–519. [PubMed]
133. Wang JW, Imai Y, Lu B. Activation of PAR-1 kinase and stimulation of tau phosphorylation by diverse signals require the tumor suppressor protein LKB1. J. Neurosci. 2007;27:574–581. [PubMed]
134. Karsten SL, Sang TK, Gehman LT, Chatterjee S, Liu J, Lawless GM, Sengupta S, Berry RW, Pomakian J, Oh HS, Schulz C, Hui KS, Wiedau-Pazos M, Vinters HV, Binder LI, Geschwind DH, Jackson GR. A genomic screen for modifiers of tauopathy identifies puromycin-sensitive aminopeptidase as an inhibitor of tau-induced neurodegeneration. Neuron. 2006;51:549–60. [PubMed]
135. Dias-Santagata D, Fulga TA, Duttaroy A, Feany MB. Oxidative stress mediates tau-induced neurodegeneration in Drosophila. J. Clin. Invest. 2007;117:236–245. [PMC free article] [PubMed]
136. Khurana V, Lu Y, Steinhilb ML, Oldham S, Shulman JM, Feany MB. TOR-mediated cell-cycle activation causes neurodegeneration in a Drosophila tauopathy model. Curr. Biol. 2006;16:230–241. [PubMed]
137. Kim D, Tsai LH. Linking cell cycle reentry and DNA damage in neurodegeneration. Ann. NY Acad. Sci. 2009;1170:674–679. [PubMed]
138. Berger Z, Ravikumar B, Menzies FM, Oroz LG, Underwood BR, Pangalos MN, Schmitt I, Wullner U, Evert BO, O'Kane CJ, Rubinsztein DC. Rapamycin alleviates toxicity of different aggregate-prone proteins. Hum. Mol. Genet. 2006;15:433–442. [PubMed]
139. Hanger DP, Anderton BH, Noble W. Tau phosphorylation: the therapeutic challenge for neurodegenerative disease. Trends Mol. Med. 2009;15:112–119. [PubMed]
140. Farrer MJ. Genetics of Parkinson disease: Paradigm shifts and future prospects. Nat. Rev. Genet. 2006;7:303–318.
141. Lees AJ, Hardy J, Revesz T. Parkinson’s disease. The Lancet. 2009;373:2055–2066.
142. Dauer W, Przedborski S. Parkinson’s disease: mechanisms and models. Neuron. 2003;39:889–909. [PubMed]
143. Moore DJ, West AB, Dawson VL, Dawson TM. Molecular pathophysiology of Parkinson's disease. Annu. Rev. Neurosci. 2005;28:57–87. [PubMed]
144. Thomas B, Beal MF. Parkinson's disease. Hum. Mol. Genet. 2007;16(Spec No. 2):R183–194. [PubMed]
145. Hardy J, Lewis P, Revesz T, Lees A, Paisan-Ruiz C. The genetics of Parkinson's syndromes: a critical review. Curr. Opin. Genet. Dev. 2009;19:254–265. [PubMed]
146. Shulman JM, de Jager PL. Evidence for a common pathway linking neurodegenerative diseases. Nat. Genet. 2009;41:1261–1262. [PubMed]
147. Bogaerts V, Theuns J, van Broeckhoven C. Genetic findings in Parkinson’s disease and translation into treatment: a leading role for mitochondria? Genes Brain Behav. 2008;7:129–151. [PMC free article] [PubMed]
148. Wood-Kaczmar A, Gandhi S, Wood NW. Understanding the molecular causes of Parkinson's disease. Trends Mol. Med. 2006;12:521–528. [PubMed]
149. Monastirioti M. Biogenic amine systems in the fruit fly Drosophila melanogaster. Microsc. Res. Tech. 1999;45:106–121. [PubMed]
150. Yellman C, Tao H, He B, Hirsh J. Conserved and sexually dimorphic behavioral responses to biogenic amines in decapitated Drosophila. Proc. Natl. Acad. Sci. USA. 1997;94:4131–4136. [PubMed]
151. Lima SQ, Miesenböck G. Remote control of behavior through genetically targeted photostimulation of neurons. Cell. 2005;121:141–152. [PubMed]
152. Feany MB, Bender W. A Drosophila model of Parkinson’s disease. Nature. 2000;404:394–398. [PubMed]
153. Auluck PK, Chan HY, Trojanowski JQ, Lee VM, Bonini NM. Chaperone suppression of alpha-synuclein toxicity in a Drosophila model for Parkinson’s disease. Science. 2002;295:865–868. [PubMed]
154. Yang Y, Nishimura I, Imai Y, Takahashi R, Lu B. Parkin suppresses dopaminergic neuron-selective neurotoxicity induced by Pael-R in Drosophila. Neuron. 2003;37:911–924. [PubMed]
155. Haywood AF, Staveley BE. Parkin counteracts symptoms in a Drosophila model of Parkinson's disease. BMC Neurosci. 2004;5:14. [PMC free article] [PubMed]
156. Haywood AF, Staveley BE. Mutant alpha-synuclein-induced degeneration is reduced by parkin in a fly model of Parkinson's disease. Genome. 2006;49:505–510. [PubMed]
157. Periquet M, Fulga T, Myllykangas L, Schlossmacher MG, Feany MB. Aggregated alpha-synuclein mediates dopaminergic neurotoxicity in vivo. J. Neurosci. 2007;27:3338–3346. [PubMed]
158. Botella JA, Bayersdorfer F, Schneuwly S. Superoxide dismutase overexpression protects dopaminergic neurons in a Drosophila model of Parkinson's disease. Neurobiol. Dis. 2008;30:65–73. [PubMed]
159. Todd AM, Staveley BE. Pink1 suppresses alpha-synuclein-induced phenotypes in a Drosophila model of Parkinson's disease. Genome. 2008;51:1040–1046. [PubMed]
160. Seugnet L, Galvin JE, Suzuki Y, Gottschalk L, Shaw PJ. Persistent short-term memory defects following sleep deprivation in a drosophila model of Parkinson disease. Sleep. 2009;32:984–992. [PubMed]
161. Wang D, Qian L, Xiong H, Liu J, Neckameyer WS, Oldham S, Xia K, Wang J, Bodmer R, Zhang Z. Antioxidants protect PINK1-dependent dopaminergic neurons in Drosophila. Proc. Natl. Acad. Sci. USA. 2006;103:13520–13525. [PubMed]
162. Yang Y, Ouyang Y, Yang L, Beal MF, McQuibban A, Vogel H, Lu B. Pink1 regulates mitochondrial dynamics through interaction with the fission/fusion machinery. Proc. Natl. Acad. Sci. USA. 2008;105:7070–7075. [PubMed]
163. Wang C, Lu R, Ouyang X, Ho MW, Chia W, Yu F, Lim KL. Drosophila overexpressing parkin R275W mutant exhibits dopaminergic neuron degeneration and mitochondrial abnormalities. J. Neurosci. 2007;27:8563–8570. [PubMed]
164. Sang TK, Chang HY, Lawless GM, Ratnaparkhi A, Mee L, Ackerson LC, Maidment NT, Krantz DE, Jackson GR. A Drosophila model of mutant human parkin-induced toxicity demonstrates selective loss of dopaminergic neurons and dependence on cellular dopamine. J. Neurosci. 2007;27:981–992. [PubMed]
165. Lee SB, Kim W, Lee S, Chung J. Loss of LRRK2/PARK8 induces degeneration of dopaminergic neurons in Drosophila. Biochem. Biophys. Res. Commun. 2007;358:534–539. [PubMed]
166. Liu Z, Wang X, Yu Y, Li X, Wang T, Jiang H, Ren Q, Jiao Y, Sawa A, Moran T, Ross CA, Montell C, Smith WW. A Drosophila model for LRRK2-linked parkinsonism. Proc. Natl. Acad. Sci. USA. 2008;105:2693–2698. [PubMed]
167. Imai Y, Gehrke S, Wang HQ, Takahashi R, Hasegawa K, Oota E, Lu B. Phosphorylation of 4E-BP by LRRK2 affects the maintenance of dopaminergic neurons in Drosophila. EMBO J. 2008;27:2432–2443. [PubMed]
168. Ng CH, Mok SZ, Koh C, Ouyang X, Fivaz ML, Tan EK, Dawson VL, Dawson TM, Yu F, Lim KL. Parkin protects against LRRK2 G2019S mutant-induced dopaminergic neurodegeneration in Drosophila. J. Neurosci. 2009;29:11257–11262. [PMC free article] [PubMed]
169. Venderova K, Kabbach G, Abdel-Messih E, Zhang Y, Parks RJ, Imai Y, Gehrke S, Ngsee J, Lavoie MJ, Slack RS, Rao Y, Zhang Z, Lu B, Haque ME, Park DS. Leucine-Rich Repeat Kinase 2 interacts with Parkin, DJ-1 and PINK-1 in a Drosophila melanogaster model of Parkinson's disease. Hum. Mol. Genet. 2009;18:4390–4404. [PubMed]
170. Clark IE, Dodson MW, Jiang C, Cao JH, Huh JR, Seol JH, Yoo SJ, Hay BA, Guo M. Drosophila pink1 is required for mitochondrial function and interacts genetically with parkin. Nature. 2006;441:1162–116. [PubMed]
171. Park J, Lee SB, Lee S, Kim Y, Song S, Kim S, Bae E, Kim J, Shong M, Kim JM, Chung J. Mitochondrial dysfunction in Drosophila PINK1 mutants is complemented by parkin. Nature. 2006;441:1157–1161. [PubMed]
172. Yang Y, Gehrke S, Imai Y, Huang Z, Ouyang Y, Wang JW, Yang L, Beal MF, Vogel H, Lu B. Mitochondrial pathology and muscle and dopaminergic neuron degeneration caused by inactivation of Drosophila Pink1 is rescued by Parkin. Proc. Natl. Acad. Sci. USA. 2006;103:10793–10798. [PubMed]
173. Tain LS, Mortiboys H, Tao RN, Ziviani E, Bandmann O, Whitworth AJ. Rapamycin activation of 4E-BP prevents parkinsonian dopaminergic neuron loss. Nat. Neurosci. 2009;12:1129–1135. [PMC free article] [PubMed]
174. Greene JC, Whitworth AJ, Kuo I, Andrews LA, Feany MB, Pallanck LJ. Mitochondrial pathology and apoptotic muscle degeneration in Drosophila parkin mutants. Proc. Natl. Acad. Sci. USA. 2003;100:4078–4083. [PubMed]
175. Greene JC, Whitworth AJ, Andrews LA, Parker TJ, Pallanck LJ. Genetic and genomic studies of Drosophila parkin mutants implicate oxidative stress and innate immune responses in pathogenesis. Hum. Mol. Genet. 2005;14:799–811. [PubMed]
176. Cha GH, Kim S, Park J, Lee E, Kim M, Lee SB, Kim JM, Chung J, Cho KS. Parkin negatively regulates JNK pathway in the dopaminergic neurons of Drosophila. Proc. Natl. Acad. Sci. USA. 2005;102:10345–10350. [PubMed]
177. Meulener M, Whitworth AJ, Armstrong-Gold CE, Rizzu P, Heutink P, Wes PD, Pallanck LJ, Bonini NM. Drosophila DJ-1 mutants are selectively sensitive to environmental toxins associated with Parkinson's disease. Curr. Biol. 2005;15:1572–1577. [PubMed]
178. Park J, Kim SY, Cha GH, Lee SB, Kim S, Chung J. Drosophila DJ-1 mutants show oxidative stress-sensitive locomotive dysfunction. Gene. 2005;361:133–139. [PubMed]
179. Menzies FM, Yenisetti SC, Min KT. Roles of Drosophila DJ-1 in survival of dopaminergic neurons and oxidative stress. Curr. Biol. 2005;15:1578–1582. [PubMed]
180. Yang Y, Gehrke S, Haque ME, Imai Y, Kosek J, Yang L, Beal MF, Nishimura I, Wakamatsu K, Ito S, Takahashi R, Lu B. Inactivation of Drosophila DJ-1 leads to impairments of oxidative stress response and phosphatidylinositol 3-kinase/Akt signaling. Proc. Natl. Acad. Sci. USA. 2005;102:13670–13675. [PubMed]
181. Meulener MC, Xu K, Thomson L, Ischiropoulos H, Bonini NM. Mutational analysis of DJ-1 in Drosophila implicates functional inactivation by oxidative damage and aging. Proc. Natl. Acad. Sci. USA. 2006;103:12517–12522. [PubMed]
182. Lavara-Culebras E, Paricio N. Drosophila DJ-1 mutants are sensitive to oxidative stress and show reduced lifespan and motor deficits. Gene. 2007;400:158–165. [PubMed]
183. Wang D, Tang B, Zhao G, Pan Q, Xia K, Bodmer R, Zhang Z. Dispensable role of Drosophila ortholog of LRRK2 kinase activity in survival of dopaminergic neurons. Mol. Neurodegener. 2008;8:33.
184. Whitworth AJ, Lee JR, Ho VM, Flick R, Chowdhury R, McQuibban GA. Rhomboid-7 and HtrA2/Omi act in a common pathway with the Parkinson's disease factors Pink1 and Parkin. Dis. Model Mech. 2008;1:168–174. [PubMed]
185. Yun J, Cao JH, Dodson MW, Clark IE, Kapahi P, Chowdhury RB, Guo M. Loss-of-function analysis suggests that Omi/HtrA2 is not an essential component of the PINK1/PARKIN pathway in vivo. J. Neurosci. 2008;28:14500–10. [PMC free article] [PubMed]
186. Tain LS, Chowdhury RB, Tao RN, Plun-Favreau H, Moisoi N, Martins LM, Downward J, Whitworth AJ, Tapon N. Drosophila HtrA2 is dispensable for apoptosis but acts downstream of PINK1 independently from Parkin. Cell Death Differ. 2009;16:1118–1125. [PMC free article] [PubMed]
187. Pesah Y, Burgess H, Middlebrooks B, Ronningen K, Prosser J, Tirunagaru V, Zysk J, Mardon G. Whole-mount analysis reveals normal numbers of dopaminergic neurons following misexpression of alpha-Synuclein in Drosophila. Genesis. 2005;41:154–159. [PubMed]
188. Coulom H, Birman S. Chronic exposure to rotenone models sporadic Parkinson's disease in Drosophila melanogaster. J. Neurosci. 2004;24:10993–8. [PubMed]
189. Chaudhuri A, Bowling K, Funderburk C, Lawal H, Inamdar A, Wang Z, O'Donnell JM. Interaction of genetic and environmental factors in a Drosophila parkinsonism model. J. Neurosci. 2007;27:2457–67. [PubMed]
190. Chen L, Feany MB. Alpha-synuclein phosphorylation controls neurotoxicity and inclusion formation in a Drosophila model of Parkinson disease. Nat. Neurosci. 2005;8:657–663. [PubMed]
191. Sidhu A, Wersinger C, Vernier P. Does alpha-synuclein modulate dopaminergic synaptic content and tone at the synapse? FASEB J. 2004;18:637–47. [PubMed]
192. Karpinar DP, Balija MB, Kügler S, Opazo F, Rezaei-Ghaleh N, Wender N, Kim HY, Taschenberger G, Falkenburger BH, Heise H, Kumar A, Riedel D, Fichtner L, Voigt A, Braus GH, Giller K, Becker S, Herzig A, Baldus M, Jäckle H, Eimer S, Schulz JB, Griesinger C, Zweckstetter M. Pre-fibrillar alpha-synuclein variants with impaired beta-structure increase neurotoxicity in Parkinson's disease models. EMBO J. 2009;28:3256–3268. [PubMed]
193. Chen L, Periquet M, Wang X, Negro A, McLean PJ, Hyman BT, Feany MB. Tyrosine and serine phosphorylation of alpha-synuclein have opposing effects on neurotoxicity and soluble oligomer formation. J. Clin. Invest. 2009;119:3257–3265. [PMC free article] [PubMed]
194. Dufty BM, Warner LR, Hou ST, Jiang SX, Gomez-Isla T, Leenhouts KM, Oxford JT, Feany MB, Masliah E, Rohn TT. Calpain-cleavage of alpha-synuclein: connecting proteolytic processing to disease-linked aggregation. Am. J. Pathol. 2007;170:1725–1738. [PubMed]
195. Kontopoulos E, Parvin JD, Feany MB. Alpha-synuclein acts in the nucleus to inhibit histone acetylation and promote neurotoxicity. Hum. Mol. Genet. 2006;15:3012–3023. [PubMed]
196. Jia H, Li X, Gao H, Feng Z, Li X, Zhao L, Jia X, Zhang H, Liu J. High doses of nicotinamide prevent oxidative mitochondrial dysfunction in a cellular model and improve motor deficit in a Drosophila model of Parkinson's disease. J. Neurosci. Res. 2008;86:2083–2090. [PubMed]
197. Wassef R, Haenold R, Hansel A, Brot N, Heinemann SH, Hoshi T. Methionine sulfoxide reductase A and a dietary supplement S-methyl-L-cysteine prevent Parkinson's-like symptoms. J. Neurosci. 2007;27:12808–12816. [PubMed]
198. Trinh K, Moore K, Wes PD, Muchowski PJ, Dey J, Andrews L, Pallanck LJ. Induction of the phase II detoxification pathway suppresses neuron loss in Drosophila models of Parkinson's disease. J. Neurosci. 2008;28:465–472. [PubMed]
199. Umeda-Kameyama Y, Tsuda M, Ohkura C, Matsuo T, Namba Y, Ohuchi Y, Aigaki T. Thioredoxin suppresses Parkin-associated endothelin receptor-like receptor-induced neurotoxicity and extends longevity in Drosophila. J. Biol. Chem. 2007;282:11180–11187. [PubMed]
200. van der Brug MP, Blackinton J, Chandran J, Hao LY, Lal A, Mazan-Mamczarz K, Martindale J, Xie C, Ahmad R, Thomas KJ, Beilina A, Gibbs JR, Ding J, Myers AJ, Zhan M, Cai H, Bonini NM, Gorospe M, Cookson MR. RNA binding activity of the recessive parkinsonism protein DJ-1 supports involvement in multiple cellular pathways. Proc. Natl. Acad. Sci. USA. 2008;105:10244–10249. [PubMed]
201. Kim Y, Park J, Kim S, Song S, Kwon SK, Lee SH, Kitada T, Kim JM, Chung J. PINK1 controls mitochondrial localization of Parkin through direct phosphorylation. Biochem. Biophys. Res. Commun. 2008;377:975–980. [PubMed]
202. Wallace DC. A mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine. Annu. Rev. Genet. 2005;39:359–407. [PMC free article] [PubMed]
203. Krishnan KJ, Greaves LC, Reeve AK, Turnbull DM. Mitochondrial DNA mutations and aging. Ann. N. Y. Acad. Sci. 2007;1100:227–240. [PubMed]
204. Mattson MP, Gleichmann M, Cheng A. Mitochondria in neuroplasticity and neurological disorders. Neuron. 2008;60:748–766. [PMC free article] [PubMed]
205. Poole AC, Thomas RE, Andrews LA, McBride HM, Whitworth AJ, Pallanck LJ. The PINK1/Parkin pathway regulates mitochondrial morphology. Proc. Natl. Acad. Sci. USA. 2008;105:1638–1643. [PubMed]
206. Deng H, Dodson MW, Huang H, Guo M. The Parkinson's disease genes pink1 and parkin promote mitochondrial fission and/or inhibit fusion in Drosophila. Proc. Natl. Acad. Sci. USA. 2008;105:14503–14508. [PubMed]
207. Lutz AK, Exner N, Fett ME, Schlehe JS, Kloos K, Lämmermann K, Brunner B, Kurz-Drexler A, Vogel F, Reichert AS, Bouman L, Vogt-Weisenhorn D, Wurst W, Tatzelt J, Haass C, Winklhofer KF. Loss of parkin or PINK1 function increases Drp1-dependent mitochondrial fragmentation. J. Biol. Chem. 2009;284:22938–22951. [PMC free article] [PubMed]
208. Orr HT, Zoghbi HY. Trinucleotide repeat disorders. Annu. Rev. Neurosci. 2007;30:575–621. [PubMed]
209. Yamada M, Sato T, Tsuji S, Takahashi H. CAG repeat disorder models and human neuropathology: similarities and differences. Acta Neuropathol. 2008;115:71–86. [PubMed]
210. Hands S, Sinadinos C, Wyttenbach A. Polyglutamine gene function and dysfunction in the ageing brain. Biochim. Biophys. Acta. 2008;1779:507–521. [PubMed]
211. Perutz MF. Glutamine repeats and neurodegenerative diseases: molecular aspects. Trends Biochem. Sci. 1999;24:58–63. [PubMed]
212. Gusella JF, MacDonald ME. Molecular genetics: unmasking polyglutamine triggers in neurodegenerative disease. Nat. Rev. Neurosci. 2000;1:109–15. [PubMed]
213. Bettencourt BR, Hogan CC, Nimali M. Polyglutamine expansion in Drosophila: thermal stress and Hsp70 as selective agents. J. Biosci. 2007;32:537–547. [PubMed]
214. Marsh JL, Walker H, Theisen H, Zhu YZ, Fielder T, Purcell J, Thompson LM. Expanded polyglutamine peptides alone are intrinsically cytotoxic and cause neurodegeneration in Drosophila. Hum. Mol. Genet. 2000;9:13–25. [PubMed]
215. Slepko N, Bhattacharyya AM, Jackson GR, Steffan JS, Marsh JL, Thompson LM, Wetzel R. Normal-repeat-length polyglutamine peptides accelerate aggregation nucleation and cytotoxicity of expanded polyglutamine proteins. Proc. Natl. Acad. Sci. USA. 2006;103:14367–14372. [PubMed]
216. Li LB, Xu K, Bonini NM. Suppression of polyglutamine toxicity by the yeast Sup35 prion domain in Drosophila. J. Biol. Chem. 2007;282:37694–37701. [PubMed]
217. Romero E, Cha GH, Verstreken P, Ly CV, Hughes RE, Bellen HJ, Botas J. Suppression of neurodegeneration and increased neurotransmission caused by expanded full-length huntingtin accumulating in the cytoplasm. Neuron. 2008;57:27–40. [PMC free article] [PubMed]
218. Zhang S, Feany MB, Saraswati S, Littleton JT, Perrimon N. Inactivation of Drosophila Huntingtin affects long-term adult functioning and the pathogenesis of a Huntington's disease model. Dis. Model Mech. 2009;2:247–266. [PubMed]
219. Al-Ramahi I, Pérez AM, Lim J, Zhang M, Sorensen R, de Haro M, Branco J, Pulst SM, Zoghbi HY, Botas J. dAtaxin-2 mediates expanded Ataxin-1-induced neurodegeneration in a Drosophila model of SCA1. PLoS Genet. 2007;3:e234. [PMC free article] [PubMed]
220. Lessing D, Bonini NM. Polyglutamine genes interact to modulate the severity and progression of neurodegeneration in Drosophila. PLoS Biol. 2008;6:e29. [PMC free article] [PubMed]
221. Fernandez-Funez P, Nino-Rosales ML, de Gouyon B, She WC, Luchak JM, Martinez P, Turiegano E, Benito J, Capovilla M, Skinner PJ, McCall A, Canal I, Orr HT, Zoghbi HY, Botas J. Identification of genes that modify ataxin-1-induced neurodegeneration. Nature. 2000;408:101–106. [PubMed]
222. Kazemi-Esfarjani P, Benzer S. Genetic suppression of polyglutamine toxicity in Drosophila. Science. 2000;287:1837–1840. [PubMed]
223. Agrawal N, Pallos J, Slepko N, Apostol BL, Bodai L, Chang LW, Chiang AS, Thompson LM, Marsh JL. Identification of combinatorial drug regimens for treatment of Huntington's disease using Drosophila. Proc. Natl. Acad. Sci. USA. 2005;102:3777–3781. [PubMed]
224. Ehrnhoefer DE, Duennwald M, Markovic P, Wacker JL, Engemann S, Roark M, Legleiter J, Marsh JL, Thompson LM, Lindquist S, Muchowski PJ, Wanker EE. Green tea (-)-epigallocatechin-gallate modulates early events in huntingtin misfolding and reduces toxicity in Huntington's disease models. Hum. Mol. Genet. 2006;15:2743–2751. [PubMed]
225. Desai UA, Pallos J, Ma AA, Stockwell BR, Thompson LM, Marsh JL, Diamond MI. Biologically active molecules that reduce polyglutamine aggregation and toxicity. Hum. Mol. Genet. 2006;15:2114–2124. [PubMed]
226. Kaltenbach LS, Romero E, Becklin RR, Chettier R, Bell R, Phansalkar A, Strand A, Torcassi C, Savage J, Hurlburt A, Cha GH, Ukani L, Chepanoske CL, Zhen Y, Sahasrabudhe S, Olson J, Kurschner C, Ellerby LM, Peltier JM, Botas J, Hughes RE. Huntingtin interacting proteins are genetic modifiers of neurodegeneration. PLoS Genet. 2007;3:e82. [PubMed]
227. Bilen J, Bonini NM. Genome-wide screen for modifiers of ataxin-3 neurodegeneration in Drosophila. PLoS Genet. 2007;3:1950–1964. [PubMed]
228. Latouche M, Lasbleiz C, Martin E, Monnier V, Debeir T, Mouatt-Prigent A, Muriel MP, Morel L, Ruberg M, Brice A, Stevanin G, Tricoire H. A conditional pan-neuronal Drosophila model of spinocerebellar ataxia 7 with a reversible adult phenotype suitable for identifying modifier genes. J. Neurosci. 2007;27:2483–2492. [PubMed]
229. Li LB, Yu Z, Teng X, Bonini NM. RNA toxicity is a component of ataxin-3 degeneration in Drosophila. Nature. 2008;453:1107–1111. [PMC free article] [PubMed]
230. Bilen J, Liu N, Burnett BG, Pittman RN, Bonini NM. MicroRNA pathways modulate polyglutamine-induced neurodegeneration. Mol. Cell. 2006;24:157–63. [PubMed]
231. Sang TK, Li C, Liu W, Rodriguez A, Abrams JM, Zipursky SL, Jackson GR. Inactivation of Drosophila Apaf-1 related killer suppresses formation of polyglutamine aggregates and blocks polyglutamine pathogenesis. Hum. Mol. Genet. 2005;14:357–372. [PubMed]
232. Suzuki E, Zhao Y, Ito S, Sawatsubashi S, Murata T, Furutani T, Shirode Y, Yamagata K, Tanabe M, Kimura S, Ueda T, Fujiyama S, Lim J, Matsukawa H, Kouzmenko AP, Aigaki T, Tabata T, Takeyama K, Kato S. Aberrant E2F activation by polyglutamine expansion of androgen receptor in SBMA neurotoxicity. Proc. Natl. Acad. Sci. USA. 2009;106:3818–3822. [PubMed]
233. Chan HY, Warrick JM, Andriola I, Merry D, Bonini NM. Genetic modulation of polyglutamine toxicity by protein conjugation pathways in Drosophila. Hum. Mol. Genet. 2002;11:2895–2904. [PubMed]
234. Steffan JS, Agrawal N, Pallos J, Rockabrand E, Trotman LC, Slepko N, Illes K, Lukacsovich T, Zhu YZ, Cattaneo E, Pandolfi PP, Thompson LM, Marsh JL. SUMO modification of Huntingtin and Huntington's disease pathology. Science. 2004;304:100–104. [PubMed]
235. Chen HK, Fernandez-Funez P, Acevedo SF, Lam YC, Kaytor MD, Fernandez MH, Aitken A, Skoulakis EM, Orr HT, Botas J, Zoghbi HY. Interaction of Akt-phosphorylated ataxin-1 with 14-3-3 mediates neurodegeneration in spinocerebellar ataxia type 1. Cell. 2003;113:457–468. [PubMed]
236. Sarkar S, Krishna G, Imarisio S, Saiki S, O'Kane CJ, Rubinsztein DC. A rational mechanism for combination treatment of Huntington's disease using lithium and rapamycin. Hum. Mol. Genet. 2008;17:170–178. [PubMed]
237. Steffan JS, Bodai L, Pallos J, Poelman M, McCampbell A, Apostol BL, Kazantsev A, Schmidt E, Zhu YZ, Greenwald M, Kurokawa R, Housman DE, Jackson GR, Marsh JL, Thompson LM. Histone deacetylase inhibitors arrest polyglutamine-dependent neurodegeneration in Drosophila. Nature. 2001;413:739–743. [PubMed]
238. Pandey UB, Nie Z, Batlevi Y, McCray BA, Ritson GP, Nedelsky NB, Schwartz SL, DiProspero NA, Knight MA, Schuldiner O, Padmanabhan R, Hild M, Berry DL, Garza D, Hubbert CC, Yao TP, Baehrecke EH, Taylor JP. HDAC6 rescues neurodegeneration and provides an essential link between autophagy and the UPS. Nature. 2007;447:859–863. [PubMed]
239. Pallos J, Bodai L, Lukacsovich T, Purcell JM, Steffan JS, Thompson LM, Marsh JL. Inhibition of specific HDACs and sirtuins suppresses pathogenesis in a Drosophila model of Huntington's disease. Hum. Mol. Genet. 2008;17:3767–3775. [PubMed]
240. Pan L, Zhang YQ, Woodruff E, Broadie K. The Drosophila fragile X gene negatively regulates neuronal elaboration and synaptic differentiation. Curr. Biol. 2004;14:1863–1870. [PubMed]
241. Lee A, Li W, Xu K, Bogert BA, Su K, Gao FB. Control of dendritic development by the Drosophila fragile X-related gene involves the small GTPase Rac1. Development. 2003;130:5543–5552. [PubMed]
242. Xu K, Bogert BA, Li W, Su K, Lee A, Gao FB. The fragile X-related gene affects the crawling behavior of Drosophila larvae by regulating the mRNA level of the DEG/ENaC protein pickpocket1. Curr. Biol. 2004;14:1025–1034. [PubMed]
243. Cziko AM, McCann CT, Howlett IC, Barbee SA, Duncan RP, Luedemann R, Zarnescu D, Zinsmaier KE, Parker RR, Ramaswami M. Genetic modifiers of dFMR1 encode RNA granule components in Drosophila. Genetics. 2009;182:1051–1060. [PubMed]
244. Gatto CL, Broadie K. Temporal requirements of the fragile X mental retardation protein in the regulation of synaptic structure. Development. 2008;135:2637–2648. [PMC free article] [PubMed]
245. Cheever A, Ceman S. Translation regulation of mRNAs by the fragile X family of proteins through the microRNA pathway. RNA Biol. 2009;6:175–178. [PubMed]
246. Anderson PR, Kirby K, Hilliker AJ, Phillips JP. RNAi-mediated suppression of the mitochondrial iron chaperone, frataxin, in Drosophila. Hum. Mol. Genet. 2005;14:3397–405. [PubMed]
247. Anderson PR, Kirby K, Orr WC, Hilliker AJ, Phillips JP. Hydrogen peroxide scavenging rescues frataxin deficiency in a Drosophila model of Friedreich's ataxia. Proc. Natl. Acad. Sci. USA. 2008;105:611–616. [PubMed]
248. Llorens JV, Navarro JA, Martínez-Sebastián MJ, Baylies MK, Schneuwly S, Botella JA, Moltó MD. Causative role of oxidative stress in a Drosophila model of Friedreich ataxia. FASEB J. 2007;21:333–344. [PubMed]
249. Donaghy M. Classification and clinical features of motor neurone diseases and motor neuropathies in adults. J. Neurol. 1999;246:331–333. [PubMed]
250. Monani UR. Spinal Muscular Atrophy: a deficiency in a ubiquitous protein; a motor neuron-specific disease. Neuron. 2005;48:885–896. [PubMed]
251. Pasinelli P, Brown RH. Molecular biology of amyotrophic lateral sclerosis: insights from genetics. Nat. Rev. Neurosci. 2006;7:710–723. [PubMed]
252. Forman MS, Trojanowski JQ, Lee VM. TDP-43: a novel neurodegenerative proteinopathy. Curr. Opin. Neurobiol. 2007;17:1–8.
253. Van Damme P, Robberecht W. Recent advances in motor neuron disease. Curr. Opin. Neurol. 2009;22:486–492. [PubMed]
254. Dion PA, Daoud H, Rouleau GA. Genetics of motor neuron disorders: new insights into pathogenic mechanisms. Nat. Rev. Genet. 2009;10:769–782. [PubMed]
255. Burghes AH, Beattie CE. Spinal muscular atrophy: why do low levels of survival motor neuron protein make motor neurons sick? Nat. Rev. Neurosci. 2009;10:597–609. [PMC free article] [PubMed]
256. Rothstein JD. Current hypotheses for the underlying biology of amyotrophic lateral sclerosis. Ann. Neurol. 2009;65(Suppl 1):S3–9. [PubMed]
257. Phillips JP, Tainer JA, Getzoff ED, Boulianne GL, Kirby K, Hilliker AJ. Subunit-destabilizing mutations in Drosophila copper/zinc superoxide dismutase: neuropathology and a model of dimer dysequilibrium. Proc. Natl. Acad. Sci. USA. 1995;92:8574–8578. [PubMed]
258. Parkes TL, Elia AJ, Dickinson D, Hilliker AJ, Phillips JP, Boulianne GL. Extension of Drosophila lifespan by overexpression of human SOD1 in motorneurons. Nat. Genet. 1998;19:171–174. [PubMed]
259. Elia AJ, Parkes TL, Kirby K St, George-Hyslop P, Boulianne GL, Phillips JP, Hilliker AJ. Expression of human FALS SOD in motorneurons of Drosophila. Free Radic. Biol. Med. 1999;26:1332–1338. [PubMed]
260. Mockett RJ, Radyuk SN, Benes JJ, Orr WC, Sohal RS. Phenotypic effects of familial amyotrophic lateral sclerosis mutant Sod alleles in transgenic Drosophila. Proc. Natl. Acad. Sci. USA. 2003;100:301–306. [PubMed]
261. Watson MR, Lagow RD, Xu K, Zhang B, Bonini NM. A Drosophila model for amyotrophic lateral sclerosis reveals motor neuron damage by human SOD1. J. Biol. Chem. 2008;283:24972–24981. [PMC free article] [PubMed]
262. Buratti E, Baralle FE. Multiple roles of TDP-43 in gene expression, splicing regulation, and human disease. Front. Biosci. 2008;13:867–878. [PubMed]
263. Wang IF, Wu LS, Shen CK. TDP-43: an emerging new player in neurodegenerative diseases. Trends Mol. Med. 2008;14:479–485. [PubMed]
264. Neumann M. Molecular Neuropathology of TDP-43 Proteinopathies. Int. J. Mol. Sci. 2009;10:232–246. [PMC free article] [PubMed]
265. Feiguin F, Godena VK, Romano G, D'Ambrogio A, Klima R, Baralle FE. Depletion of TDP-43 affects Drosophila motoneurons terminal synapsis and locomotive behavior. FEBS Lett. 2009;583:1586–1592. [PubMed]
266. Lu Y, Ferris J, Gao FB. Frontotemporal dementia and amyotrophic lateral sclerosis-associated disease protein TDP-43 promotes dendritic branching. Mol. Brain. 2009;2:30. [PMC free article] [PubMed]
267. Fiesel FC, Voigt A, Weber SS, Van den Haute C, Waldenmaier A, Görner K, Walter M, Anderson ML, Kern JV, Rasse TM, Schmidt T, Springer W, Kirchner R, Bonin M, Neumann M, Baekelandt V, Alunni-Fabbroni M, Schulz JB, Kahle PJ. Knockdown of transactive response DNA-binding protein (TDP-43) downregulates histone deacetylase 6. EMBO J. 2009;29:209–221. [PubMed]
268. Li Y, Ray P, Rao EJ, Shi C, Guo W, Chen X, Woodruff EA, Fushimi K, Wu JY. A Drosophila model for TDP-43 proteinopathy. Proc. Natl. Acad. Sci. USA. 2010;00:0.
269. Pennetta G, Hiesinger PR, Fabian-Fine R, Meinertzhagen IA, Bellen HJ. Drosophila VAP-33A directs bouton formation at neuromuscular junctions in a dosage-dependent manner. Neuron. 2002;35:291–306. [PubMed]
270. Ratnaparkhi A, Lawless GM, Schweizer FE, Golshani P, Jackson GR. A Drosophila model of ALS: human ALS-associated mutation in VAP33A suggests a dominant negative mechanism. PLoS One. 2008;3:e2334. [PMC free article] [PubMed]
271. Chai A, Withers J, Koh YH, Parry K, Bao H, Zhang B, Budnik V, Pennetta G. hVAPB, the causative gene of a heterogeneous group of motor neuron diseases in humans, is functionally interchangeable with its Drosophila homologue DVAP-33A at the neuromuscular junction. Hum. Mol. Genet. 2008;17:266–280. [PubMed]
272. Tsuda H, Han SM, Yang Y, Tong C, Lin YQ, Mohan K, Haueter C, Zoghbi A, Harati Y, Kwan J, Miller MA, Bellen HJ. The amyotrophic lateral sclerosis 8 protein VAPB is cleaved, secreted, and acts as a ligand for Eph receptors. Cell. 2008;133:963–977. [PMC free article] [PubMed]
273. Chan YB, Miguel-Aliaga I, Franks C, Thomas N, Trülzsch B, Sattelle DB, Davies KE, van den Heuvel M. Neuromuscular defects in a Drosophila survival motor neuron gene mutant. Hum. Mol. Genet. 2003;12:1367–1376. [PubMed]
274. Rajendra TK, Gonsalvez GB, Walker MP, Shpargel KB, Salz HK, Matera AG. A Drosophila melanogaster model of spinal muscular atrophy reveals a function for SMN in striated muscle. J. Cell Biol. 2007;176:831–841. [PMC free article] [PubMed]
275. Chang HC, Dimlich DN, Yokokura T, Mukherjee A, Kankel MW, Sen A, Sridhar V, Fulga TA, Hart AC, Van Vactor D, Artavanis-Tsakonas S. Modeling spinal muscular atrophy in Drosophila. PLoS One. 2008;3:e3209. [PMC free article] [PubMed]
276. Salinas S, Proukakis C, Crosby A, Warner TT. Hereditary spastic paraplegia: clinical features and pathogenetic mechanisms. Lancet Neurol. 2008;7:1127–1138. [PubMed]
277. Hazan J, Fonknechten N, Mavel D, Paternotte C, Samson D, Artiguenave F, Davoine CS, Cruaud C, Dürr A, Wincker P, Brottier P, Cattolico L, Barbe V, Burgunder JM, Prud'homme JF, Brice A, Fontaine B, Heilig B, Weissenbach J. Spastin, a new AAA protein, is altered in the most frequent form of autosomal dominant spastic paraplegia. Nat. Genet. 1999;23:296–303. [PubMed]
278. Kammermeier L, Spring J, Stierwald M, Burgunder JM, Reichert H. Identification of the Drosophila melanogaster homolog of the human spastin gene. Dev. Genes Evol. 2003;213:412–415. [PubMed]
279. Trotta N, Orso G, Rossetto MG, Daga A, Broadie K. The hereditary spastic paraplegia gene, spastin, regulates microtubule stability to modulate synaptic structure and function. Curr. Biol. 2004;14:1135–1147. [PubMed]
280. Sherwood NT, Sun Q, Xue M, Zhang B, Zinn K. Drosophila spastin regulates synaptic microtubule networks and is required for normal motor function. PLoS Biol. 2004;2:e429. [PMC free article] [PubMed]
281. Roll-Mecak A, Vale RD. The Drosophila homologue of the hereditary spastic paraplegia protein, spastin, severs and disassembles microtubules. Curr. Biol. 2005;15:650–655. [PubMed]
282. Orso G, Martinuzzi A, Rossetto MG, Sartori E, Feany M, Daga A. Disease-related phenotypes in a Drosophila model of hereditary spastic paraplegia are ameliorated by treatment with vinblastine. J. Clin. Invest. 2005;115:3026–3034. [PMC free article] [PubMed]
283. Wang X, O'Kane CJ. Hereditary spastic paraplegia genes in Drosophila: dissecting their roles in axonal degeneration and intracellular traffic. SEB Exp. Biol. Ser. 2008;60:161–182. [PubMed]
284. Orso G, Pendin D, Liu S, Tosetto J, Moss TJ, Faust JE, Micaroni M, Egorova A, Martinuzzi A, McNew JA, Daga A. Homotypic fusion of ER membranes requires the dynamin-like GTPase atlastin. Nature. 2009;460:978–983. [PubMed]
285. Lee M, Paik SK, Lee MJ, Kim YJ, Kim S, Nahm M, Oh SJ, Kim HM, Yim J, Lee CJ, Bae YC, Lee S. Drosophila Atlastin regulates the stability of muscle microtubules and is required for synapse development. Dev. Biol. 2009;330:250–262. [PubMed]
286. Wang X, Shaw WR, Tsang HT, Reid E, O'Kane CJ. Drosophila spichthyin inhibits BMP signaling and regulates synaptic growth and axonal microtubules. Nat. Neurosci. 2007;10:177–185. [PMC free article] [PubMed]
287. Tsang HT, Edwards TL, Wang X, Connell JW, Davies RJ, Durrington HJ, O'Kane CJ, Luzio JP, Reid E. The hereditary spastic paraplegia proteins NIPA1, spastin and spartin are inhibitors of mammalian BMP signalling. Hum. Mol. Genet. 2009;18:3805–3821. [PMC free article] [PubMed]
288. Keshishian H, Kim YS. Orchestrating development and function: retrograde BMP signaling in the Drosophila nervous system. Trends Neurosci. 2004;27:143–147. [PubMed]
289. Tsuchida K. The role of myostatin and bone morphogenetic proteins in muscular disorders. Expert Opin. Biol. Ther. 2006;6:147–54. [PubMed]
290. Lansbury PT, Lashuel HA. A century-old debate on protein aggregation and neurodegeneration enters the clinic. Nature. 2006;443:774–9. [PubMed]
291. Gunther EC, Strittmatter SM. Beta-amyloid oligomers and cellular prion protein in Alzheimer’s disease. J. Mol. Med. 2010;88:331–338. [PMC free article] [PubMed]
292. Aguzzi A, Rajendran L. The transcellular spread of cytosolic amyloids, prions, and prionoids. Neuron. 2009;64:783–90. [PubMed]
293. Hardy J. Expression of normal sequence pathogenic proteins for neurodegenerative disease contributes to disease risk: 'permissive templating' as a general mechanism underlying neurodegeneration. Biochem. Soc. Trans. 2005;33:578–81. [PubMed]
294. Alberti S, Halfmann R, King O, Kapila A, Lindquist S. A systematic survey identifies prions and illuminates sequence features of prionogenic proteins. Cell. 2009;137:146–158. [PMC free article] [PubMed]
295. Nordling CO. A new theory on cancer-inducing mechanism. Br. J. Cancer. 1953;7:68–72. [PMC free article] [PubMed]

Articles from Bentham Open Access are provided here courtesy of Bentham Science Publishers