Search tips
Search criteria

Results 1-25 (63)

Clipboard (0)

Select a Filter Below

Year of Publication
more »
Document Types
1.  Deficiency of Capicua disrupts bile acid homeostasis 
Scientific Reports  2015;5:8272.
Capicua (CIC) has been implicated in pathogenesis of spinocerebellar ataxia type 1 and cancer in mammals; however, the in vivo physiological functions of CIC remain largely unknown. Here we show that Cic hypomorphic (Cic-L-/-) mice have impaired bile acid (BA) homeostasis associated with induction of proinflammatory cytokines. We discovered that several drug metabolism and BA transporter genes were down-regulated in Cic-L-/- liver, and that BA was increased in the liver and serum whereas bile was decreased within the gallbladder of Cic-L-/- mice. We also found that levels of proinflammatory cytokine genes were up-regulated in Cic-L-/- liver. Consistent with this finding, levels of hepatic transcriptional regulators, such as hepatic nuclear factor 1 alpha (HNF1α), CCAAT/enhancer-binding protein beta (C/EBPβ), forkhead box protein A2 (FOXA2), and retinoid X receptor alpha (RXRα), were markedly decreased in Cic-L-/- mice. Moreover, induction of tumor necrosis factor alpha (Tnfα) expression and decrease in the levels of FOXA2, C/EBPβ, and RXRα were found in Cic-L-/- liver before BA was accumulated, suggesting that inflammation might be the cause for the cholestasis in Cic-L-/- mice. Our findings indicate that CIC is a critical regulator of BA homeostasis, and that its dysfunction might be associated with chronic liver disease and metabolic disorders.
PMCID: PMC4317698  PMID: 25653040
2.  Mutations in NGLY1 Cause an Inherited Disorder of the Endoplasmic Reticulum-Associated Degradation (ERAD) Pathway 
The endoplasmic reticulum-associated degradation (ERAD) pathway is responsible for the translocation of misfolded proteins across the ER membrane into the cytosol for subsequent degradation by the proteasome. In order to understand the spectrum of clinical and molecular findings in a complex neurological syndrome, we studied a series of eight patients with inherited deficiency of N-glycanase 1 (NGLY1), a novel disorder of cytosolic ERAD dysfunction.
Whole-genome, whole-exome or standard Sanger sequencing techniques were employed. Retrospective chart reviews were performed in order to obtain clinical data.
All patients had global developmental delay, a movement disorder, and hypotonia. Other common findings included hypo- or alacrima (7/8), elevated liver transaminases (6/7), microcephaly (6/8), diminished reflexes (6/8), hepatocyte cytoplasmic storage material or vacuolization (5/6), and seizures (4/8). The nonsense mutation c.1201A>T (p.R401X) was the most common deleterious allele.
NGLY1 deficiency is a novel autosomal recessive disorder of the ERAD pathway associated with neurological dysfunction, abnormal tear production, and liver disease. The majority of patients detected to date carry a specific nonsense mutation that appears to be associated with severe disease. The phenotypic spectrum is likely to enlarge as cases with a more broad range of mutations are detected.
PMCID: PMC4243708  PMID: 24651605
NGLY1; alacrima; choreoathetosis; seizures; liver disease
3.  Rett-causing mutations reveal two domains critical for MeCP2 function and for toxicity in MECP2 duplication syndrome mice 
eLife  2014;3:e02676.
Loss of function of the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2) causes the progressive neurological disorder Rett syndrome (RTT). Conversely, duplication or triplication of Xq28 causes an equally wide-ranging progressive neurological disorder, MECP2 duplication syndrome, whose features overlap somewhat with RTT. To understand which MeCP2 functions cause toxicity in the duplication syndrome, we generated mouse models expressing endogenous Mecp2 along with a RTT-causing mutation in either the methyl-CpG binding domain (MBD) or the transcriptional repression domain (TRD). We determined that both the MBD and TRD must function for doubling MeCP2 to be toxic. Mutating the MBD reproduces the null phenotype and expressing the TRD mutant produces milder RTT phenotypes, yet both mutations are harmless when expressed with endogenous Mecp2. Surprisingly, mutating the TRD is more detrimental than deleting the entire C-terminus, indicating a dominant-negative effect on MeCP2 function, likely due to the disruption of a basic cluster.
eLife digest
Rett syndrome is a disorder that affects the development of the brain after birth. Infants with this condition develop as normal until they are 6–18 months old, when the development of their language and motor skills stops, or even regresses. Most cases of Rett syndrome are caused by mutations in a gene called MECP2.
If an individual mistakenly inherits an extra copy of the MECP2 gene, it can cause another developmental disorder called MECP2 duplication syndrome. This condition, which also affects the brain, gets worse over time and shares many features with Rett syndrome. The extra copy of the MECP2 gene leads to the production of too much MeCP2 protein. However, how doubling the level of this protein causes the syndrome and, in particular, which parts of the protein are involved are unknown.
Previously, researchers engineered mice that expressed a copy of the human MECP2 gene alongside their own version of the gene. These mice developed a condition similar to MECP2 duplication syndrome and many of these mice suffered from seizures and died within their first year.
Heckman et al. have now engineered mice that also have an extra human MECP2 gene but with one of two mutations that cause Rett syndrome in humans. Some mice had a mutation in a part of the MeCP2 protein that binds to DNA that is marked with small chemical tags called methyl groups. Other mice had a mutation in a domain of the protein that works to switch off genes. Heckman et al. found that mice with extra MeCP2 protein with either of these two mutations were as healthy as normal mice and showed none of the signs of MECP2 duplication syndrome. This indicates that both of these domains must be intact for doubling the levels of the MeCP2 protein to be harmful. Furthermore, Heckman et al. discovered that the mutation in the part of MeCP2 that works to switch genes off also reduces the protein's ability to bind to DNA.
The next challenge is to understand the mechanism by which doubling the levels of this protein causes harm to the brain. Further work is also needed to uncover why having too much MeCP2 protein or none at all cause syndromes that share many features.
PMCID: PMC4102243  PMID: 24970834
MeCP2; Rett syndrome; MECP2 duplication syndrome; neurobiology; genetics; mouse
4.  Dendritic Arborization and Spine Dynamics Are Abnormal in the Mouse Model of MECP2 Duplication Syndrome 
The Journal of Neuroscience  2013;33(50):19518-19533.
MECP2 duplication syndrome is a childhood neurological disorder characterized by intellectual disability, autism, motor abnormalities, and epilepsy. The disorder is caused by duplications spanning the gene encoding methyl-CpG-binding protein-2 (MeCP2), a protein involved in the modulation of chromatin and gene expression. MeCP2 is thought to play a role in maintaining the structural integrity of neuronal circuits. Loss of MeCP2 function causes Rett syndrome and results in abnormal dendritic spine morphology and decreased pyramidal dendritic arbor complexity and spine density. The consequences of MeCP2 overexpression on dendritic pathophysiology remain unclear. We used in vivo two-photon microscopy to characterize layer 5 pyramidal neuron spine turnover and dendritic arborization as a function of age in transgenic mice expressing the human MECP2 gene at twice the normal levels of MeCP2 (Tg1; Collins et al., 2004). We found that spine density in terminal dendritic branches is initially higher in young Tg1 mice but falls below control levels after postnatal week 12, approximately correlating with the onset of behavioral symptoms. Spontaneous spine turnover rates remain high in older Tg1 animals compared with controls, reflecting the persistence of an immature state. Both spine gain and loss rates are higher, with a net bias in favor of spine elimination. Apical dendritic arbors in both simple- and complex-tufted layer 5 Tg1 pyramidal neurons have more branches of higher order, indicating that MeCP2 overexpression induces dendritic overgrowth. P70S6K was hyperphosphorylated in Tg1 somatosensory cortex, suggesting that elevated mTOR signaling may underlie the observed increase in spine turnover and dendritic growth.
PMCID: PMC3858623  PMID: 24336718
5.  Atoh1-dependent rhombic lip neurons are required for temporal delay between independent respiratory oscillators in embryonic mice 
eLife  2014;3:e02265.
All motor behaviors require precise temporal coordination of different muscle groups. Breathing, for example, involves the sequential activation of numerous muscles hypothesized to be driven by a primary respiratory oscillator, the preBötzinger Complex, and at least one other as-yet unidentified rhythmogenic population. We tested the roles of Atoh1-, Phox2b-, and Dbx1-derived neurons (three groups that have known roles in respiration) in the generation and coordination of respiratory output. We found that Dbx1-derived neurons are necessary for all respiratory behaviors, whereas independent but coupled respiratory rhythms persist from at least three different motor pools after eliminating or silencing Phox2b- or Atoh1-expressing hindbrain neurons. Without Atoh1 neurons, however, the motor pools become temporally disorganized and coupling between independent respiratory oscillators decreases. We propose Atoh1 neurons tune the sequential activation of independent oscillators essential for the fine control of different muscles during breathing.
eLife digest
A healthy adult at rest will breathe in and out around 20 times per minute. Each breath requires a complex series of coordinated muscle activity. Inhalation begins with the opening of the airway followed by the contraction of the diaphragm and the intercostal muscles between the ribs, causing the chest cavity to expand. As the lungs increase in volume, the pressure inside them drops and air is drawn in. Relaxation of the diaphragm and intercostal muscles compresses the lungs, causing us to exhale.
Breathing is driven by the brainstem and it cannot be suppressed indefinitely: holding your breath eventually triggers a reflex that forces breathing to resume. The region of the brainstem that controls breathing is called the preBötzinger Complex. However, there is increasing evidence that a second region in the brainstem is also involved. This region, which is called the retrotrapezoid nucleus/parafacial respiratory group, consists of three types of excitatory neurons—Dbx1 neurons, Phox2b neurons, and Atoh1 neurons—but their roles had not been clear. Now, using multiple lines of genetically modified mice, Tupal et al. have teased apart the roles of these three cell types.
These experiments showed that the Dbx1 neurons—which are also found in the preBötzinger Complex—have an essential role in sending the signals from the brain that drive the different muscle activities needed to breathe. The Phox2b neurons modulate breathing based on the level of carbon dioxide in the blood. Atoh1 neurons help control the sequence of respiratory muscle activity during a breath, probably by selectively inhibiting different populations of Dbx1 neurons.
The work of Tupal et al. indicates that distinct populations of neurons within the brainstem independently control two different aspects of breathing: the generation of breathing rhythms, and the coordination of these rhythms. Given that many other physiological processes involve rhythmic activity patterns, this model may help us to understand how the brain generates and controls complex behaviors more generally.
PMCID: PMC4060005  PMID: 24842997
breathing; central pattern generator; PreBötzinger Complex; oscillator; transcription; mouse
6.  Genetic screens reveal RAS/MAPK/MSK1 modulate ataxin 1 protein levels and toxicity in SCA1 
Nature  2013;498(7454):325-331.
Many neurodegenerative disorders such as Alzheimer’s, Parkinson’s and polyglutamine diseases share a common pathogenic mechanism: the abnormal accumulation of disease-causing proteins, due to either the mutant protein’s resistance to degradation or overexpression of the wild-type protein. We developed a strategy to identify therapeutic entry points for such neurodegenerative disorders by screening for genetic networks that influence the levels of disease-driving proteins. We applied this approach, which integrates parallel cell-based and Drosophila genetic screens, to spinocerebellar ataxia type 1 (SCA1), a disease caused by expansion of a polyglutamine tract in ataxin 1 (ATXN1). Our approach revealed that downregulation of several components of the RAS–MAPK–MSK1 pathway decreases ATXN1 levels and suppresses neurodegeneration in Drosophila and mice. Importantly, pharmacologic inhibitors of components of this pathway also decrease ATXN1 levels, suggesting that these components represent new therapeutic targets in mitigating SCA1. Collectively, these data reveal new therapeutic entry points for SCA1 and provide a proof-of-principle for tackling other classes of intractable neurodegenerative diseases.
PMCID: PMC4020154  PMID: 23719381
7.  SHANK3 overexpression causes manic-like behavior with unique pharmacogenetic properties 
Nature  2013;503(7474):72-77.
Mutations in SHANK3 and large duplications of the region spanning SHANK3 both cause a spectrum of neuropsychiatric disorders, suggesting that proper SHANK3 dosage is critical for normal brain function. SHANK3 overexpression per se has not been established as a cause of human disorders, however, because 22q13 duplications involve several genes. Here we report that Shank3 transgenic mice modeling a human SHANK3 duplication exhibit manic-like behavior and seizures consistent with synaptic excitatory/inhibitory imbalance. We also identified two patients with hyperkinetic disorders carrying the smallest SHANK3-spanning duplications reported so far. These findings suggest SHANK3 overexpression causes a hyperkinetic neuropsychiatric disorder. To probe the mechanism underlying the phenotype, we generated a Shank3 in vivo interactome and found that Shank3 directly interacts with the Arp2/3 complex to increase F-actin levels in Shank3 transgenic mice. The mood-stabilizing drug valproate, but not lithium, rescues the manic-like behavior of Shank3 transgenic mice raising the possibility that this hyperkinetic disorder has a unique pharmacogenetic profile.
PMCID: PMC3923348  PMID: 24153177
8.  Synaptic Dysfunction in Neurodevelopmental Disorders Associated with Autism and Intellectual Disabilities 
The discovery of the genetic causes of syndromic autism spectrum disorders and intellectual disabilities has greatly informed our understanding of the molecular pathways critical for normal synaptic function. The top-down approaches using human phenotypes and genetics helped identify causative genes and uncovered the broad spectrum of neuropsychiatric features that can result from various mutations in the same gene. Importantly, the human studies unveiled the exquisite sensitivity of cognitive function to precise levels of many diverse proteins. Bottom-up approaches applying molecular, biochemical, and neurophysiological studies to genetic models of these disorders revealed unsuspected pathogenic mechanisms and identified potential therapeutic targets. Moreover, studies in model organisms showed that symptoms of these devastating disorders can be reversed, which brings hope that affected individuals might benefit from interventions even after symptoms set in. Scientists predict that insights gained from studying these rare syndromic disorders will have an impact on the more common nonsyndromic autism and mild cognitive deficits.
Approximately 1% of the human population has an autism spectrum disorder (ASD). Key insight into synaptic function has been gained by studying the many genetic alterations that cause ASD.
PMCID: PMC3282414  PMID: 22258914
9.  Female Mecp2+/− mice display robust behavioral deficits on two different genetic backgrounds providing a framework for pre-clinical studies 
Human Molecular Genetics  2012;22(1):96-109.
Rett syndrome (RTT) is an X-linked neurological disorder caused by mutations in the gene encoding the transcriptional modulator methyl-CpG-binding protein 2 (MeCP2). Typical RTT primarily affects girls and is characterized by a brief period of apparently normal development followed by the loss of purposeful hand skills and language, the onset of anxiety, hand stereotypies, autistic features, seizures and autonomic dysfunction. Mecp2 mouse models have extensively been studied to demonstrate the functional link between MeCP2 dysfunction and RTT pathogenesis. However, the majority of studies have focused primarily on the molecular and behavioral consequences of the complete absence of MeCP2 in male mice. Studies of female Mecp2+/− mice have been limited because of potential phenotypic variability due to X chromosome inactivation effects. To determine whether reproducible and reliable phenotypes can be detected Mecp2+/− mice, we analyzed Mecp2+/− mice of two different F1 hybrid isogenic backgrounds and at young and old ages using several neurobehavioral and physiological assays. Here, we report a multitude of phenotypes in female Mecp2+/− mice, some presenting as early as 5 weeks of life. We demonstrate that Mecp2+/− mice recapitulate several aspects of typical RTT and show that mosaic expression of MeCP2 does not preclude the use of female mice in behavioral and molecular studies. Importantly, we uncover several behavioral abnormalities that are present in two genetic backgrounds and report on phenotypes that are unique to one background. These findings provide a framework for pre-clinical studies aimed at improving the constellation of phenotypes in a mouse model of RTT.
PMCID: PMC3522402  PMID: 23026749
10.  Polyglutamine disease toxicity is regulated by Nemo-like kinase in spinocerebellar ataxia type 1 
Polyglutamine diseases are dominantly inherited neurodegenerative diseases caused by an expansion of a CAG trinucleotide repeat encoding a glutamine tract in the respective disease-causing proteins. Extensive studies have been performed to unravel disease pathogenesis and to develop therapeutics. Here, we report on several lines of evidence demonstrating that Nemo-like kinase (NLK) is a key molecule modulating disease toxicity in spinocerebellar ataxia type 1 (SCA1), a disease caused by a polyglutamine expansion in the protein ATAXIN1 (ATXN1). Specifically, we show that NLK, a serine/threonine kinase that interacts with ATXN1, modulates disease phenotypes of polyglutamine-expanded ATXN1 in a Drosophila model of SCA1. Importantly, the effect of NLK on SCA1 pathology is dependent upon NLK’s enzymatic activity. Consistent with this, reduced Nlk expression suppresses the behavioral and neuropathological phenotypes in SCA1 knock-in mice. These data clearly indicate that either reducing NLK enzymatic activity or decreasing NLK expression levels can have beneficial effects against the toxicity induced by polyglutamine-expanded ATXN1.
PMCID: PMC3710458  PMID: 23719801
11.  Purkinje Cell Ataxin-1 Modulates Climbing Fiber Synaptic Input in Developing and Adult Mouse Cerebellum 
Previous studies indicate that while transgenic mice with ATXN1[30Q]-D776-induced disease share pathological features caused by ATXN1[82Q] having an expanded polyglutamine tract, they fail to manifest the age-related progressive neurodegeneration seen in SCA1. The shared features include morphological alterations in climbing fiber (CF) innervation of Purkinje cells (PCs). To further investigate the ability of ATXN1 to impact CF/PC innervation, this study used morphological and functional approaches to examine CF/PC innervation during postnatal development in ATXN1[30Q]-D776 and ATXN1[82Q] cerebella. Notably, ATXN1[30Q]-D776 induced morphological alterations consistent with the development of the innervation of PCs by CFs being compromised, including a reduction of CF translocation along the PC dendritic tree, and decreased pruning of CF terminals from the PC soma. Like previously shown for ATXN1[82Q], ATXN1[30Q]-D776 must enter the nucleus of PCs to induce these alterations. Experiments using conditional ATXN1[30Q]-D776 mice demonstrate that both the levels and specific timing of mutant ATXN1expression are critical for alteration of the CF-PC synapse. Together these observations suggest that ATXN1, expressed exclusively in PCs, alters expression of a gene(s) in the postsynaptic PC that are critical for its innervation by CFs. To investigate whether ATXN1[30Q]-D776 curbs the progressive disease in ATXN1[82Q]-S776 mice, we crossed ATXN1[30Q]-D776 and ATXN1[82Q]-S776 mice and found that double transgenic mice developed progressive PC atrophy. Thus, the results also show that to develop progressive cerebellar degeneration requires expressing ATXN1 with an expanded polyglutamine tract.
PMCID: PMC3633086  PMID: 23536093
12.  A newly characterized AT-hook domain in MeCP2 determines clinical course of Rett syndrome and related disorders 
Cell  2013;152(5):984-996.
Mutations in the X-linked MECP2 cause Rett syndrome, a devastating neurological disorder typified by a period of apparently normal development followed by loss of cognitive and psychomotor skills. Data from rare male patients suggest symptom onset and severity can be influenced by the location of the mutation, with amino acids 270 and 273 marking the difference between neonatal encephalopathy and death, on the one hand, and survival with deficits on the other. We therefore generated two mouse models expressing either MeCP2-R270X or MeCP2-G273X. The mice developed phenotypes at strikingly different rates and showed differential ATRX nuclear localization within the nervous system, over time, coinciding with phenotypic progression. We discovered that MeCP2 contains three AT-hook-like domains over a stretch of 250 amino acids, like HMGA DNA-bending proteins; one conserved AT-hook is disrupted in MeCP2-R270X, lending further support to the notion that one of MeCP2’s key functions is to alter chromatin structure.
PMCID: PMC3641682  PMID: 23452848
13.  Pharmacometabolomic Signature of Ataxia SCA1 Mouse Model and Lithium Effects 
PLoS ONE  2013;8(8):e70610.
We have shown that lithium treatment improves motor coordination in a spinocerebellar ataxia type 1 (SCA1) disease mouse model (Sca1154Q/+). To learn more about disease pathogenesis and molecular contributions to the neuroprotective effects of lithium, we investigated metabolomic profiles of cerebellar tissue and plasma from SCA1-model treated and untreated mice. Metabolomic analyses of wild-type and Sca1154Q/+ mice, with and without lithium treatment, were performed using gas chromatography time-of-flight mass spectrometry and BinBase mass spectral annotations. We detected 416 metabolites, of which 130 were identified. We observed specific metabolic perturbations in Sca1154Q/+ mice and major effects of lithium on metabolism, centrally and peripherally. Compared to wild-type, Sca1154Q/+ cerebella metabolic profile revealed changes in glucose, lipids, and metabolites of the tricarboxylic acid cycle and purines. Fewer metabolic differences were noted in Sca1154Q/+ mouse plasma versus wild-type. In both genotypes, the major lithium responses in cerebellum involved energy metabolism, purines, unsaturated free fatty acids, and aromatic and sulphur-containing amino acids. The largest metabolic difference with lithium was a 10-fold increase in ascorbate levels in wild-type cerebella (p<0.002), with lower threonate levels, a major ascorbate catabolite. In contrast, Sca1154Q/+ mice that received lithium showed no elevated cerebellar ascorbate levels. Our data emphasize that lithium regulates a variety of metabolic pathways, including purine, oxidative stress and energy production pathways. The purine metabolite level, reduced in the Sca1154Q/+ mice and restored upon lithium treatment, might relate to lithium neuroprotective properties.
PMCID: PMC3732229  PMID: 23936457
14.  Overexpression of Methyl-CpG Binding Protein 2 Impairs TH1 Responses 
Science translational medicine  2012;4(163):163ra158.
The DNA binding protein methyl-CpG binding protein 2 (MeCP2) critically influences neuronal and brain function by modulating gene expression, and children with overexpression of the MECP2 gene exhibit postnatal neurological syndromes. We demonstrate that some children with MECP2 duplication also display variable immunological abnormalities that include reductions in memory T and B cells and natural killer cells and immunoglobulin assay responses. Moreover, whereas mice with MeCP2 overexpression were unable to control infection with the intra-macrophage parasite Leishmania major and secrete interferon-γ (IFN-γ) from involved lymph nodes, they were able to control airway fungal infection by Aspergillus niger and mount protective T helper cell type 2 (TH2)–dependent allergic responses. Relative to normal T cells, TH cells from children and mice with MECP2 duplication displayed similar impairments in IFN-γ secretion and TH1 responses that were due to both MeCP2-dependent suppression of IFN-γ transcription and sequestration of the IFN-γ locus as assessed by chromatin immunoprecipitation assay. Thus, overexpressed MeCP2 aberrantly suppresses IFN-γ secretion from TH cells, potentially leading to a partially immunodeficient state. Our findings establish a rational basis for identifying, treating, and preventing infectious complications potentially affecting children with MECP2 duplication.
PMCID: PMC3628825  PMID: 23220634
15.  Ataxin1L Is a Regulator of HSC Function Highlighting the Utility of Cross-Tissue Comparisons for Gene Discovery 
PLoS Genetics  2013;9(3):e1003359.
Hematopoietic stem cells (HSCs) are rare quiescent cells that continuously replenish the cellular components of the peripheral blood. Observing that the ataxia-associated gene Ataxin-1-like (Atxn1L) was highly expressed in HSCs, we examined its role in HSC function through in vitro and in vivo assays. Mice lacking Atxn1L had greater numbers of HSCs that regenerated the blood more quickly than their wild-type counterparts. Molecular analyses indicated Atxn1L null HSCs had gene expression changes that regulate a program consistent with their higher level of proliferation, suggesting that Atxn1L is a novel regulator of HSC quiescence. To determine if additional brain-associated genes were candidates for hematologic regulation, we examined genes encoding proteins from autism- and ataxia-associated protein–protein interaction networks for their representation in hematopoietic cell populations. The interactomes were found to be highly enriched for proteins encoded by genes specifically expressed in HSCs relative to their differentiated progeny. Our data suggest a heretofore unappreciated similarity between regulatory modules in the brain and HSCs, offering a new strategy for novel gene discovery in both systems.
Author Summary
Our labs, working separately on brain function and blood stem cells, noticed that a particular gene involved in movement disorders was also expressed in the blood system. We discovered through bone marrow transplantation experiments that this gene, called Ataxin-1-like, normally plays a role in restricting the number of blood-forming stem cells; stem cells lacking this gene were more numerous and more active. We wondered if this brain-blood similarity would hold for a larger number of genes, so we used bioinformatics approaches to compare large datasets our labs had generated from each system. We found that a surprising number of genes implicated in autism and ataxia by molecular studies were also highly expressed in blood-forming stem cells. We suggest that such cross-system comparisons could be used more widely to discover genes with important functions in brain and blood, but also perhaps other systems.
PMCID: PMC3610904  PMID: 23555280
16.  Atoh1 governs the migration of post-mitotic neurons that shape respiratory effectiveness at birth and chemoresponsiveness in adulthood 
Neuron  2012;75(5):799-809.
Hindbrain neuronal networks serving respiratory, proprioceptive, and arousal functions share a developmental requirement for the bHLH transcription factor Atoh1. Loss of Atoh1 in mice results in respiratory failure and neonatal lethality; however, the neuronal identity and mechanism by which Atoh1-dependent cells sustain newborn breathing remains unknown. We uncovered that selective loss of Atoh1 from the post-mitotic retrotrapezoid nucleus (RTN) neurons results in severely impaired inspiratory rhythm and pronounced neonatal death. Mice that escape neonatal death develop abnormal chemoresponsiveness as adults. Interestingly, the expression of Atoh1 in the RTN neurons is not required for their specification or maintenance, but is important for their proper localization and to establish essential connections with the preBötzinger Complex (preBötC). These results provide insights into the genetic regulation of neonatal breathing and shed light on the labile sites that might contribute to sudden death in newborn infants and altered chemoresponsiveness in adults.
PMCID: PMC3464459  PMID: 22958821
17.  Gcn5 loss-of-function accelerates cerebellar and retinal degeneration in a SCA7 mouse model 
Human Molecular Genetics  2011;21(2):394-405.
Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disease caused by expansion of a CAG repeat encoding a polyglutamine tract in ATXN7, a component of the SAGA histone acetyltransferase (HAT) complex. Previous studies provided conflicting evidence regarding the effects of polyQ–ATXN7 on the activity of Gcn5, the HAT catalytic subunit of SAGA. Here, we report that reducing Gcn5 expression accelerates both cerebellar and retinal degeneration in a mouse model of SCA7. Deletion of Gcn5 in Purkinje cells in mice expressing wild-type (wt) Atxn7, however, causes only mild ataxia and does not lead to the early lethality observed in SCA7 mice. Reduced Gcn5 expression strongly enhances retinopathy in SCA7 mice, but does not affect the known transcriptional targets of Atxn7, as expression of these genes is not further altered by Gcn5 depletion. These findings demonstrate that loss of Gcn5 functions can contribute to the time of onset and severity of SCA7 phenotypes, and suggest that non-transcriptional functions of SAGA may play a role in neurodegeneration in this disease.
PMCID: PMC3276287  PMID: 22002997
18.  Preclinical research in Rett syndrome: setting the foundation for translational success 
Disease Models & Mechanisms  2012;5(6):733-745.
In September of 2011, the National Institute of Neurological Disorders and Stroke (NINDS), the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the International Rett Syndrome Foundation (IRSF) and the Rett Syndrome Research Trust (RSRT) convened a workshop involving a broad cross-section of basic scientists, clinicians and representatives from the National Institutes of Health (NIH), the US Food and Drug Administration (FDA), the pharmaceutical industry and private foundations to assess the state of the art in animal studies of Rett syndrome (RTT). The aim of the workshop was to identify crucial knowledge gaps and to suggest scientific priorities and best practices for the use of animal models in preclinical evaluation of potential new RTT therapeutics. This review summarizes outcomes from the workshop and extensive follow-up discussions among participants, and includes: (1) a comprehensive summary of the physiological and behavioral phenotypes of RTT mouse models to date, and areas in which further phenotypic analyses are required to enhance the utility of these models for translational studies; (2) discussion of the impact of genetic differences among mouse models, and methodological differences among laboratories, on the expression and analysis, respectively, of phenotypic traits; and (3) definitions of the standards that the community of RTT researchers can implement for rigorous preclinical study design and transparent reporting to ensure that decisions to initiate costly clinical trials are grounded in reliable preclinical data.
PMCID: PMC3484856  PMID: 23115203
19.  Crh and Oprm1 mediate anxiety-related behavior and social approach in a mouse model of MECP2 duplication syndrome 
Nature genetics  2012;44(2):206-211.
Genomic duplications spanning Xq28 are associated with a spectrum of phenotypes including anxiety and autism. The minimal region shared among affected individuals includes MECP2 and IRAK1, however, it is unclear which gene, when overexpressed, causes anxiety and social behavior deficits. We report that doubling MeCP2 levels causes heightened anxiety and autism-like features in mice, and alters the expression of genes that influence anxiety and social behavior, such as Crh and Oprm1. To test the hypothesis that alterations in these two genes contribute to the heightened anxiety and social behavior deficits, we analyzed MECP2 duplication mice (MECP2-TG1) with reduced Crh and Oprm1 levels. In MECP2-TG1 animals, reducing Crh, or its receptor, Crhr1, suppresses anxiety-like behavior; in contrast, reducing Oprm1 improves abnormal social behavior. These data demonstrate that increased MeCP2 levels impact molecular pathways underlying anxiety and social behavior, and provide novel insight into potential therapies for MECP2-related disorders.
PMCID: PMC3267865  PMID: 22231481
20.  Exercise and Genetic Rescue of SCA1 via the Transcriptional Repressor Capicua* 
Science (New York, N.Y.)  2011;334(6056):690-693.
Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by expansion of a translated CAG repeat in Ataxin-1 (ATXN1). To determine the long-term effects of exercise, we implemented a mild exercise regimen in a mouse model of SCA1 and found a considerable improvement in survival accompanied by upregulation of epidermal growth factor and consequential downregulation of Capicua, an ATXN1 interactor. Offspring of Capicua mutant mice bred to SCA1 mice showed significant improvement of all disease phenotypes. Although polyglutamine-expanded Atxn1 caused some loss of Capicua function, further reducing Capicua levels, either genetically or by exercise, mitigated the disease phenotypes. Thus, exercise might have long-term beneficial effects in other ataxias and neurodegenerative diseases.
PMCID: PMC3232424  PMID: 22053053
21.  Inverted genomic segments and complex triplication rearrangements are mediated by inverted repeats in the human genome 
Nature Genetics  2011;43(11):1074-1081.
We identified complex genomic rearrangements consisting of intermixed duplications and triplications of genomic segments at both the MECP2 and PLP1 loci. These complex rearrangements were characterized by a triplicated segment embedded within a duplication in 12 unrelated subjects. Interestingly, only two novel breakpoint junctions were generated during each rearrangement formation. Remarkably, all the complex rearrangement products share the common genomic organization duplication-inverted triplication-duplication (DUP-TRP/INV-DUP) wherein the triplicated segment is inverted and located between directly oriented duplicated genomic segments. We provide evidence that the DUP-TRP/INV-DUP structures are mediated by inverted repeats that can be separated by over 300 kb; a genomic architecture that apparently leads to susceptibility to such complex rearrangements. A similar inverted repeat mediated mechanism may underlie structural variation in many other regions of the human genome. We propose a mechanism that involves both homology driven, via inverted repeats, and microhomologous/nonhomologous events.
PMCID: PMC3235474  PMID: 21964572
BIR; inversion; MMBIR; MECP2; PLP1; duplication; complex rearrangements
22.  Atxn1 protein family and Cic regulate extracellular matrix remodeling and lung alveolarization 
Developmental Cell  2011;21(4):746-757.
Although expansion of CAG repeats in ATAXIN1 (ATXN1) causes Spinocerebellar ataxia type 1, the functions of ATXN1 and ATAXIN1-Like (ATXN1L) remain poorly understood. To investigate the function of these proteins, we generated and characterized Atxn1L−/− and Atxn1−/−; Atxn1L−/− mice. Atxn1L−/− mice have hydrocephalus, omphalocoele and lung alveolarization defects. These phenotypes are more penetrant and severe in Atxn1−/−; Atxn1L−/− mice, suggesting that Atxn1 and Atxn1L are functionally redundant. Upon pursuing the molecular mechanism, we discovered that several Matrix metalloproteinase (Mmp) genes are overexpressed and that the transcriptional repressor Capicua (Cic) is destabilized in Atxn1L−/− lungs. Consistent with this, Cic deficiency causes lung alveolarization defect. Loss of either Atxn1L or Cic derepresses Etv4, an activator for Mmp genes, thereby mediating Mmp9 overexpression. These findings demonstrate a critical role of ATXN1/ATXN1L-CIC complexes in extracellular matrix (ECM) remodeling during development and their potential roles in pathogenesis of disorders affecting ECM remodeling.
PMCID: PMC3253850  PMID: 22014525
23.  In vivo neuronal subtype specific targets of Atoh1 (Math1) in dorsal spinal cord 
Neural basic helix-loop-helix (bHLH) transcription factors are crucial in regulating the differentiation and neuronal subtype specification of neurons. Precisely how these transcription factors direct such processes is largely unknown due to the lack of bona fide targets in vivo. Genetic evidence suggests that bHLH factors have shared targets in their common differentiation role, but unique targets with respect to their distinct roles in neuronal subtype specification. However, whether neuronal subtype specific targets exist remains an unsolved question. To address this question, we focused on Atoh1 (Math1), a bHLH transcription factor that specifies distinct neuronal subtypes of the proprioceptive pathway in mammals including the dorsal interneuron 1 (dI1) population of the developing spinal cord. We identified transcripts unique to the Atoh1-derived lineage using microarray analyses of specific bHLH-sorted populations from mouse. Chromatin immunoprecipitation-sequencing (ChIP-seq) experiments followed by enhancer reporter analyses identified five direct neuronal subtype specific targets of Atoh1 in vivo along with their Atoh1-responsive enhancers. These targets, Klf7, Rab15, Rassf4, Selm, and Smad7, have diverse functions that range from transcription factors to regulators of endocytosis and signaling pathways. Only Rab15 and Selm are expressed across several different Atoh1-specified neuronal subtypes including external granule cells (EGL) in the developing cerebellum, hair cells of the inner ear, and Merkel cells. Our work establishes on a molecular level that neuronal differentiation bHLH transcription factors have distinct lineage-specific targets.
PMCID: PMC3153066  PMID: 21795538
24.  Adult neural function requires MeCP2 
Science (New York, N.Y.)  2011;333(6039):186.
PMCID: PMC3150190  PMID: 21636743
25.  Protein interactome reveals converging molecular pathways among autism disorders 
Science translational medicine  2011;3(86):86ra49.
To uncover shared pathogenic mechanisms among the highly heterogeneous autism spectrum disorders (ASDs), we developed a protein interaction network that identified hundreds of new interactions among proteins encoded by ASD-associated genes. We discovered unexpectedly high connectivity between SHANK and TSC1, previously implicated in syndromic autism, suggesting that common molecular pathways underlie autistic phenotypes in distinct syndromes. ASD patients were more likely to harbor CNVs that encompass network genes than control subjects. We also identified, in patients with idiopathic ASD, three de novo lesions (deletions in 16q23.3 and 15q22 and one duplication in Xq28) that involve three network genes (NECAB2, PKM2, and FLNA). The protein interaction network thus provides a framework for identifying causes of idiopathic autism and for understanding molecular pathways that underpin both syndromic and idiopathic ASDs.
PMCID: PMC3169432  PMID: 21653829

Results 1-25 (63)