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1.  Loss of β-III spectrin leads to Purkinje cell dysfunction recapitulating the behaviour and neuropathology of SCA5 in humans 
Mutations in SPTBN2, the gene encoding β-III spectrin, cause spinocerebellar ataxia type 5 in humans (SCA5), a neurodegenerative disorder resulting in loss of motor coordination. How these mutations give rise to progressive ataxia and what the precise role β-III spectrin plays in normal cerebellar physiology are unknown. We developed a mouse lacking full length β-III spectrin and found that homozygous mice reproduced features of SCA5 including gait abnormalities, tremor, deteriorating motor coordination, Purkinje cell loss and cerebellar atrophy (molecular layer thinning). In vivo analysis reveals an age-related reduction in simple spike firing rate in surviving β-III−/− Purkinje cells while in vitro studies show these neurons to have reduced spontaneous firing, smaller sodium currents and dysregulation of glutamatergic neurotransmission. Our data suggest an early loss of EAAT4- (protein interactor of β-III spectrin) and subsequent loss of GLAST-mediated uptake may play a role in neuronal pathology. These findings implicate a loss of β-III spectrin function in SCA5 pathogenesis and indicate there are at least two physiological effects of β-III spectrin loss that underpin a progressive loss of inhibitory cerebellar output, namely an intrinsic Purkinje cell membrane defect due to reduced sodium currents and alterations in glutamate signaling.
doi:10.1523/JNEUROSCI.6065-09.2010
PMCID: PMC2857506  PMID: 20371805
ataxia; cerebellum; motor coordination; glutamate transporters; excitotoxicity; neurodegeneration
2.  β-III spectrin underpins ankyrin R function in Purkinje cell dendritic trees: protein complex critical for sodium channel activity is impaired by SCA5-associated mutations 
Human Molecular Genetics  2014;23(14):3875-3882.
Beta III spectrin is present throughout the elaborate dendritic tree of cerebellar Purkinje cells and is required for normal neuronal morphology and cell survival. Spinocerebellar ataxia type 5 (SCA5) and spectrin associated autosomal recessive cerebellar ataxia type 1 are human neurodegenerative diseases involving progressive gait ataxia and cerebellar atrophy. Both disorders appear to result from loss of β-III spectrin function. Further elucidation of β-III spectrin function is therefore needed to understand disease mechanisms and identify potential therapeutic options. Here, we report that β-III spectrin is essential for the recruitment and maintenance of ankyrin R at the plasma membrane of Purkinje cell dendrites. Two SCA5-associated mutations of β-III spectrin both reduce ankyrin R levels at the cell membrane. Moreover, a wild-type β-III spectrin/ankyrin-R complex increases sodium channel levels and activity in cell culture, whereas mutant β-III spectrin complexes fail to enhance sodium currents. This suggests impaired ability to form stable complexes between the adaptor protein ankyrin R and its interacting partners in the Purkinje cell dendritic tree is a key mechanism by which mutant forms of β-III spectrin cause ataxia, initially by Purkinje cell dysfunction and exacerbated by subsequent cell death.
doi:10.1093/hmg/ddu103
PMCID: PMC4065159  PMID: 24603075
3.  Mutant β-III Spectrin Causes mGluR1α Mislocalization and Functional Deficits in a Mouse Model of Spinocerebellar Ataxia Type 5 
The Journal of Neuroscience  2014;34(30):9891-9904.
Spinocerebellar ataxia type 5 (SCA5), a dominant neurodegenerative disease characterized by profound Purkinje cell loss, is caused by mutations in SPTBN2, a gene that encodes β-III spectrin. SCA5 is the first neurodegenerative disorder reported to be caused by mutations in a cytoskeletal spectrin gene. We have developed a mouse model to understand the mechanistic basis for this disease and show that expression of mutant but not wild-type β-III spectrin causes progressive motor deficits and cerebellar degeneration. We show that endogenous β-III spectrin interacts with the metabotropic glutamate receptor 1α (mGluR1α) and that mice expressing mutant β-III spectrin have cerebellar dysfunction with altered mGluR1α localization at Purkinje cell dendritic spines, decreased mGluR1-mediated responses, and deficient mGluR1-mediated long-term potentiation. These results indicate that mutant β-III spectrin causes mislocalization and dysfunction of mGluR1α at dendritic spines and connects SCA5 with other disorders involving glutamatergic dysfunction and synaptic plasticity abnormalities.
doi:10.1523/JNEUROSCI.0876-14.2014
PMCID: PMC4107406  PMID: 25057192
long term potentiation; mGluR1α; mouse model; neurodegeneration; Purkinje cells; spinocerebellar ataxia type 5
4.  Remodeling of Monoplanar Purkinje Cell Dendrites during Cerebellar Circuit Formation 
PLoS ONE  2011;6(5):e20108.
Dendrite arborization patterns are critical determinants of neuronal connectivity and integration. Planar and highly branched dendrites of the cerebellar Purkinje cell receive specific topographical projections from two major afferent pathways; a single climbing fiber axon from the inferior olive that extend along Purkinje dendrites, and parallel fiber axons of granule cells that contact vertically to the plane of dendrites. It has been believed that murine Purkinje cell dendrites extend in a single parasagittal plane in the molecular layer after the cell polarity is determined during the early postnatal development. By three-dimensional confocal analysis of growing Purkinje cells, we observed that mouse Purkinje cells underwent dynamic dendritic remodeling during circuit maturation in the third postnatal week. After dendrites were polarized and flattened in the early second postnatal week, dendritic arbors gradually expanded in multiple sagittal planes in the molecular layer by intensive growth and branching by the third postnatal week. Dendrites then became confined to a single plane in the fourth postnatal week. Multiplanar Purkinje cells in the third week were often associated by ectopic climbing fibers innervating nearby Purkinje cells in distinct sagittal planes. The mature monoplanar arborization was disrupted in mutant mice with abnormal Purkinje cell connectivity and motor discoordination. The dendrite remodeling was also impaired by pharmacological disruption of normal afferent activity during the second or third postnatal week. Our results suggest that the monoplanar arborization of Purkinje cells is coupled with functional development of the cerebellar circuitry.
doi:10.1371/journal.pone.0020108
PMCID: PMC3105010  PMID: 21655286
5.  Genome-wide mRNA sequencing of a single canine cerebellar cortical degeneration case leads to the identification of a disease associated SPTBN2 mutation 
BMC Genetics  2012;13:55.
Background
Neonatal cerebellar cortical degeneration is a neurodegenerative disease described in several canine breeds including the Beagle. Affected Beagles are unable to ambulate normally from the onset of walking and the main pathological findings include Purkinje cell loss with swollen dendritic processes. Previous reports suggest an autosomal recessive mode of inheritance. The development of massively parallel sequencing techniques has presented the opportunity to investigate individual clinical cases using genome-wide sequencing approaches. We used genome-wide mRNA sequencing (mRNA-seq) of cerebellum tissue from a single Beagle with neonatal cerebellar cortical degeneration as a method of candidate gene sequencing, with the aim of identifying the causal mutation.
Results
A four-week old Beagle dog presented with progressive signs of cerebellar ataxia and the owner elected euthanasia. Histopathology revealed findings consistent with cerebellar cortical degeneration. Genome-wide mRNA sequencing (mRNA-seq) of RNA from cerebellum tissue was used as a method of candidate gene sequencing. After analysis of the canine orthologues of human spinocerebellar ataxia associated genes, we identified a homozygous 8 bp deletion in the β-III spectrin gene, SPTBN2, associated with spinocerebellar type 5 in humans. Genotype analysis of the sire, dam, ten clinically unaffected siblings, and an affected sibling from a previous litter, showed the mutation to fully segregate with the disorder. Previous studies have shown that β-III spectrin is critical for Purkinje cell development, and the absence of this protein can lead to cell damage through excitotoxicity, consistent with the observed Purkinje cell loss, degeneration of dendritic processes and associated neurological dysfunction in this Beagle.
Conclusions
An 8 bp deletion in the SPTBN2 gene encoding β-III spectrin is associated with neonatal cerebellar cortical degeneration in Beagle dogs. This study shows that mRNA-seq is a feasible method of screening candidate genes for mutations associated with rare diseases when a suitable tissue resource is available.
doi:10.1186/1471-2156-13-55
PMCID: PMC3413603  PMID: 22781464
Beta-III spectrin; Beagle dogs; Cerebellar cortical degeneration; Spinocerebellar ataxia type 5; Genome-wide mRNA sequencing; Cerebellum; mRNA-seq; SPTBN2; Canine; Next generation sequencing
6.  Recessive Mutations in SPTBN2 Implicate β-III Spectrin in Both Cognitive and Motor Development 
PLoS Genetics  2012;8(12):e1003074.
β-III spectrin is present in the brain and is known to be important in the function of the cerebellum. Heterozygous mutations in SPTBN2, the gene encoding β-III spectrin, cause Spinocerebellar Ataxia Type 5 (SCA5), an adult-onset, slowly progressive, autosomal-dominant pure cerebellar ataxia. SCA5 is sometimes known as “Lincoln ataxia,” because the largest known family is descended from relatives of the United States President Abraham Lincoln. Using targeted capture and next-generation sequencing, we identified a homozygous stop codon in SPTBN2 in a consanguineous family in which childhood developmental ataxia co-segregates with cognitive impairment. The cognitive impairment could result from mutations in a second gene, but further analysis using whole-genome sequencing combined with SNP array analysis did not reveal any evidence of other mutations. We also examined a mouse knockout of β-III spectrin in which ataxia and progressive degeneration of cerebellar Purkinje cells has been previously reported and found morphological abnormalities in neurons from prefrontal cortex and deficits in object recognition tasks, consistent with the human cognitive phenotype. These data provide the first evidence that β-III spectrin plays an important role in cortical brain development and cognition, in addition to its function in the cerebellum; and we conclude that cognitive impairment is an integral part of this novel recessive ataxic syndrome, Spectrin-associated Autosomal Recessive Cerebellar Ataxia type 1 (SPARCA1). In addition, the identification of SPARCA1 and normal heterozygous carriers of the stop codon in SPTBN2 provides insights into the mechanism of molecular dominance in SCA5 and demonstrates that the cell-specific repertoire of spectrin subunits underlies a novel group of disorders, the neuronal spectrinopathies, which includes SCA5, SPARCA1, and a form of West syndrome.
Author Summary
β-III spectrin is present in the brain and is known to be important in the function of the cerebellum. Mutations in β-III spectrin cause spinocerebellar ataxia type 5 (SCA5), sometimes called Lincoln ataxia because it was first described in the relatives of United States President Abraham Lincoln. This is generally an adult-onset progressive cerebellar disorder. Recessive mutations have not previously been described in any of the brain spectrins. We identified a homozygous mutation in SPTBN2, which causes a more severe disorder than SCA5, with a developmental cerebellar ataxia, which is present from childhood; in addition there is marked cognitive impairment. We call this novel condition SPARCA1 (Spectrin-associated Autosomal Recessive Cerebellar Ataxia type 1). This condition could be caused by two separate gene mutations; but we show, using a combination of genome-wide mapping, whole-genome sequencing, and detailed behavioural and neuropathological analysis of a β-III spectrin mouse knockout, that both the ataxia and cognitive impairment are caused by the recessive mutations in β-III spectrin. SPARCA1 is one of a family of neuronal spectrinopathies and illustrates the importance of spectrins in brain development and function.
doi:10.1371/journal.pgen.1003074
PMCID: PMC3516553  PMID: 23236289
7.  β-III spectrin mutation L253P associated with spinocerebellar ataxia type 5 interferes with binding to Arp1 and protein trafficking from the Golgi 
Human Molecular Genetics  2010;19(18):3634-3641.
Spinocerebellar ataxia type 5 (SCA5) is an autosomal dominant neurodegenerative disorder caused by mutations in β-III spectrin. A mouse lacking full-length β-III spectrin has a phenotype closely mirroring symptoms of SCA5 patients. Here we report the analysis of heterozygous animals, which show no signs of ataxia or cerebellar degeneration up to 2 years of age. This argues against haploinsufficiency as a disease mechanism and points towards human mutations having a dominant-negative effect on wild-type (WT) β-III spectrin function. Cell culture studies using β-III spectrin with a mutation associated with SCA5 (L253P) reveal that mutant protein, instead of being found at the cell membrane, appears trapped in the cytoplasm associated with the Golgi apparatus. Furthermore, L253P β-III spectrin prevents correct localization of WT β-III spectrin and prevents EAAT4, a protein known to interact with β-III spectrin, from reaching the plasma membrane. Interaction of β-III spectrin with Arp1, a subunit of the dynactin–dynein complex, is also lost with the L253P substitution. Despite intracellular accumulation of proteins, this cellular stress does not induce the unfolded protein response, implying the importance of membrane protein loss in disease pathogenesis. Incubation at lower temperature (25°C) rescues L253P β-III spectrin interaction with Arp1 and normal protein trafficking to the membrane. These data provide evidence for a dominant-negative effect of an SCA5 mutation and show for the first time that trafficking of both β-III spectrin and EAAT4 from the Golgi is disrupted through failure of the L253P mutation to interact with Arp1.
doi:10.1093/hmg/ddq279
PMCID: PMC2928133  PMID: 20603325
8.  Spectrin mutations that cause spinocerebellar ataxia type 5 impair axonal transport and induce neurodegeneration in Drosophila 
The Journal of Cell Biology  2010;189(1):143-158.
How spectrin mutations caused Purkinje cell death becomes clearer following studies that examined the effect of expressing mutant SCA5 in the fly eye. Mutant spectrin causes deficits in synapse formation at the neuromuscular junction and disrupts vesicular trafficking.
Spinocerebellar ataxia type 5 (SCA5) is an autosomal dominant neurodegenerative disorder caused by mutations in the SPBTN2 gene encoding β-III–spectrin. To investigate the molecular basis of SCA5, we established a series of transgenic Drosophila models that express human β-III–spectrin or fly β-spectrin proteins containing SCA5 mutations. Expression of the SCA5 mutant spectrin in the eye causes a progressive neurodegenerative phenotype, and expression in larval neurons results in posterior paralysis, reduced synaptic terminal growth, and axonal transport deficits. These phenotypes are genetically enhanced by both dynein and dynactin loss-of-function mutations. In summary, we demonstrate that SCA5 mutant spectrin causes adult-onset neurodegeneration in the fly eye and disrupts fundamental intracellular transport processes that are likely to contribute to this progressive neurodegenerative disease.
doi:10.1083/jcb.200905158
PMCID: PMC2854382  PMID: 20368622
9.  Pharmacological enhancement of mGlu1 metabotropic glutamate receptors causes a prolonged symptomatic benefit in a mouse model of spinocerebellar ataxia type 1 
Molecular Brain  2013;6:48.
Background
Spinocerebellar ataxia type 1 (SCA1) is a genetic disorder characterized by severe ataxia associated with progressive loss of cerebellar Purkinje cells. The mGlu1 metabotropic glutamate receptor plays a key role in mechanisms of activity-dependent synaptic plasticity in the cerebellum, and its dysfunction is linked to the pathophysiology of motor symptoms associated with SCA1. We used SCA1 heterozygous transgenic mice (Q154/Q2) as a model for testing the hypothesis that drugs that enhance mGlu1 receptor function may be good candidates for the medical treatment of SCA1.
Results
Symptomatic 30-week old SCA1 mice showed reduced mGlu1 receptor mRNA and protein levels in the cerebellum. Interestingly, these mice also showed an intense expression of mGlu5 receptors in cerebellar Purkinje cells, which normally lack these receptors. Systemic treatment of SCA1 mice with the mGlu1 receptor positive allosteric modulator (PAM), Ro0711401 (10 mg/kg, s.c.), caused a prolonged improvement of motor performance on the rotarod and the paw-print tests. A single injection of Ro0711401 improved motor symptoms for several days, and no tolerance developed to the drug. In contrast, the mGlu5 receptor PAM, VU0360172 (10 mg/kg, s.c.), caused only a short-lasting improvement of motor symptoms, whereas the mGlu1 receptor antagonist, JNJ16259685 (2.5 mg/kg, i.p.), further impaired motor performance in SCA1 mice. The prolonged symptomatic benefit caused by Ro0711401 outlasted the time of drug clearance from the cerebellum, and was associated with neuroadaptive changes in the cerebellum, such as a striking reduction of the ectopically expressed mGlu5 receptors in Purkinje cells, increases in levels of total and Ser880-phosphorylated GluA2 subunit of AMPA receptors, and changes in the length of spines in the distal dendrites of Purkinje cells.
Conclusions
These data demonstrate that pharmacological enhancement of mGlu1 receptors causes a robust and sustained motor improvement in SCA1 mice, and lay the groundwork for the development of mGlu1 receptor PAMs as novel “cerebellum-specific”, effective, and safe symptomatic drugs for the treatment of SCA1 in humans.
doi:10.1186/1756-6606-6-48
PMCID: PMC4225515  PMID: 24252411
mGlu1 receptor; Ro0711401; mGlu5 receptor; VU0360172; JNJ16259685; Spinocerebellar ataxia type 1; Purkinje cell; Motor coordination
10.  Progress in pathogenesis studies of spinocerebellar ataxia type 1. 
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited disorder characterized by progressive loss of coordination, motor impairment and the degeneration of cerebellar Purkinje cells, spinocerebellar tracts and brainstem nuclei. Many dominantly inherited neurodegenerative diseases share the mutational basis of SCA1: the expansion of a translated CAG repeat coding for glutamine. Mice lacking ataxin-1 display learning deficits and altered hippocampal synaptic plasticity but none of the abnormalities seen in human SCA1; mice expressing ataxin-1 with an expanded CAG tract (82 glutamine residues), however, develop Purkinje cell pathology and ataxia. These results suggest that mutant ataxin-1 gains a novel function that leads to neuronal degeneration. This novel function might involve aberrant interaction(s) with cell-specific protein(s), which in turn might explain the selective neuronal pathology. Mutant ataxin-1 interacts preferentially with a leucine-rich acidic nuclear protein that is abundantly expressed in cerebellar Purkinje cells and other brain regions affected in SCA1. Immunolocalization studies in affected neurons of patients and SCA1 transgenic mice showed that mutant ataxin-1 localizes to a single, ubiquitin-positive nuclear inclusion (NI) that alters the distribution of the proteasome and certain chaperones. Further analysis of NIs in transfected HeLa cells established that the proteasome and chaperone proteins co-localize with ataxin-1 aggregates. Moreover, overexpression of the chaperone HDJ-2/HSDJ in HeLa cells decreased ataxin-1 aggregation, suggesting that protein misfolding might underlie NI formation. To assess the importance of the nuclear localization of ataxin-1 and its role in SCA1 pathogenesis, two lines of transgenic mice were generated. In the first line, the nuclear localization signal was mutated so that full-length mutant ataxin-1 would remain in the cytoplasm; mice from this line did not develop any ataxia or pathology. This suggests that mutant ataxin-1 is pathogenic only in the nucleus. To assess the role of the aggregates, transgenic mice were generated with mutant ataxin-1 without the self-association domain (SAD) essential for aggregate formation. These mice developed ataxia and Purkinje cell abnormalities similar to those seen in SCA1 transgenic mice carrying full-length mutant ataxin-1, but lacked NIs. The nuclear milieu is thus a critical factor in SCA1 pathogenesis, but large NIs are not needed to initiate pathogenesis. They might instead be downstream of the primary pathogenic steps. Given the accumulated evidence, we propose the following model for SCA1 pathogenesis: expansion of the polyglutamine tract alters the conformation of ataxin-1, causing it to misfold. This in turn leads to aberrant protein interactions. Cell specificity is determined by the cell-specific proteins interacting with ataxin-1. Submicroscopic protein aggregation might occur because of protein misfolding, and those aggregates become detectable as NIs as the disease advances. Proteasome redistribution to the NI might contribute to disease progression by disturbing proteolysis and subsequent vital cellular functions.
PMCID: PMC1692607  PMID: 10434309
11.  Abnormal dendrite and spine morphology in primary visual cortex in the CGG knock-in mouse model of the fragile X premutation 
Epilepsia  2012;53(0 1):150-160.
Summary
The fragile X mental retardation 1 gene (Fmr1) is polymorphic for CGG trinucleotide repeat number in the 5′-untranslated region, with repeat lengths <45 associated with typical development and repeat lengths >200 resulting in hypermethylation and transcriptional silencing of the gene and mental retardation in the fragile X Syndrome (FXS). Individuals with CGG repeat expansions between 55 and 200 are carriers of the fragile X premutation (PM). PM carriers show a phenotype that can include anxiety, depression, social phobia, and memory deficits. They are also at risk for developing fragile X–associated tremor/ataxia syndrome (FXTAS), a late onset neurodegenerative disorder characterized by tremor, ataxia, cognitive impairment, and neuropathologic features including intranuclear inclusions in neurons and astrocytes, loss of Purkinje cells, and white matter disease. However, very little is known about dendritic morphology in PM or in FXTAS. Therefore, we carried out a Golgi study of dendritic complexity and dendritic spine morphology in layer II/III pyramidal neurons in primary visual cortex in a knock-in (KI) mouse model of the PM. These CGG KI mice carry an expanded CGG trinucleotide repeat on Fmr1, and model many features of the PM and FXTAS. Compared to wild-type (WT) mice, CGG KI mice showed fewer dendritic branches proximal to the soma, reduced total dendritic length, and a higher frequency of longer dendritic spines. The distribution of morphologic spine types (e.g., stubby, mushroom, filopodial) did not differ between WT and KI mice. These findings demonstrate that synaptic circuitry is abnormal in visual cortex of mice used to model the PM, and suggest that such changes may underlie neurologic features found in individuals carrying the PM as well as in individuals with FXTAS.
doi:10.1111/j.1528-1167.2012.03486.x
PMCID: PMC4316681  PMID: 22612820
Golgi impregnation; Pyramidal neurons; Visual cortex; Dendritic spines; Fragile X; Fragile X mental retardation protein; Fragile X premutation; FXTAS; Synapse; Circuitry
12.  Altered Dendritic Morphology of Purkinje cells in Dyt1 ΔGAG Knock-In and Purkinje Cell-Specific Dyt1 Conditional Knockout Mice 
PLoS ONE  2011;6(3):e18357.
Background
DYT1 early-onset generalized dystonia is a neurological movement disorder characterized by involuntary muscle contractions. It is caused by a trinucleotide deletion of a GAG (ΔGAG) in the DYT1 (TOR1A) gene encoding torsinA; the mouse homolog of this gene is Dyt1 (Tor1a). Although structural and functional alterations in the cerebellum have been reported in DYT1 dystonia, neuronal morphology has not been examined in vivo.
Methodology/Principal Findings
In this study, we examined the morphology of the cerebellum in Dyt1 ΔGAG knock-in (KI) mice. Golgi staining of the cerebellum revealed a reduction in the length of primary dendrites and a decrease in the number of spines on the distal dendrites of Purkinje cells. To determine if this phenomenon was cell autonomous and mediated by a loss of torsinA function in Purkinje cells, we created a knockout of the Dyt1 gene only in Purkinje cells of mice. We found the Purkinje-cell specific Dyt1 conditional knockout (Dyt1 pKO) mice have similar alterations in Purkinje cell morphology, with shortened primary dendrites and decreased spines on the distal dendrites.
Conclusion/Significance
These results suggest that the torsinA is important for the proper development of the cerebellum and a loss of this function in the Purkinje cells results in an alteration in dendritic structure.
doi:10.1371/journal.pone.0018357
PMCID: PMC3066238  PMID: 21479250
13.  Mitochondrial Morphogenesis, Dendrite Development, and Synapse Formation in Cerebellum Require both Bcl-w and the Glutamate Receptor δ2 
PLoS Genetics  2008;4(6):e1000097.
Bcl-w belongs to the prosurvival group of the Bcl-2 family, while the glutamate receptor δ2 (Grid2) is an excitatory receptor that is specifically expressed in Purkinje cells, and required for Purkinje cell synapse formation. A recently published result as well as our own findings have shown that Bcl-w can physically interact with an autophagy protein, Beclin1, which in turn has been shown previously to form a protein complex with the intracellular domain of Grid2 and an adaptor protein, nPIST. This suggests that Bcl-w and Grid2 might interact genetically to regulate mitochondria, autophagy, and neuronal function. In this study, we investigated this genetic interaction of Bcl-w and Grid2 through analysis of single and double mutant mice of these two proteins using a combination of histological and behavior tests. It was found that Bcl-w does not control the cell number in mouse brain, but promotes what is likely to be the mitochondrial fission in Purkinje cell dendrites, and is required for synapse formation and motor learning in cerebellum, and that Grid2 has similar phenotypes. Mice carrying the double mutations of these two genes had synergistic effects including extremely long mitochondria in Purkinje cell dendrites, and strongly aberrant Purkinje cell dendrites, spines, and synapses, and severely ataxic behavior. Bcl-w and Grid2 mutations were not found to influence the basal autophagy that is required for Purkinje cell survival, thus resulting in these phenotypes. Our results demonstrate that Bcl-w and Grid2 are two critical proteins acting in distinct pathways to regulate mitochondrial morphogenesis and control Purkinje cell dendrite development and synapse formation. We propose that the mitochondrial fission occurring during neuronal growth might be critically important for dendrite development and synapse formation, and that it can be regulated coordinately by multiple pathways including Bcl-2 and glutamate receptor family members.
Author Summary
A neuron cell is composed of cell body, axons, and dendrites. Dendritic spines on dendrites form synapses with axons of other neurons, establishing communication between neuron cells. Dendrite development and synapse formation are therefore important for neuronal function. Although many genes have been previously identified as affecting the development of dendrites and synapses, the apoptosis Bcl-2 family members have not yet been shown to regulate these processes. In this study, a Bcl-2 family survival member, Bcl-w, was found not to affect cell death, but to be required for synapse formation and motor learning in mouse cerebellum. Bcl-w also appears to control dendrite development as double null mutant mice of Bcl-w and the glutamate receptor δ2 (Grid2) have severe defects in Purkinje cell dendrites, spines, and synapses. In addition, Bcl-w and Grid2 act synergistically to promote what is likely to be mitochondrial fission in Purkinje cells. Neither the survival members of the Bcl-2 family nor the excitatory receptors have been demonstrated previously to regulate mitochondrial morphogenesis in brain. We conclude that neuronal dendrite development and synapse formation require perhaps mitochondrial fission that can be controlled by two critical pathways including Bcl-w and Grid2.
doi:10.1371/journal.pgen.1000097
PMCID: PMC2405952  PMID: 18551174
14.  Lithium Therapy Improves Neurological Function and Hippocampal Dendritic Arborization in a Spinocerebellar Ataxia Type 1 Mouse Model 
PLoS Medicine  2007;4(5):e182.
Background
Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disorder characterized by progressive motor and cognitive dysfunction. Caused by an expanded polyglutamine tract in ataxin 1 (ATXN1), SCA1 pathogenesis involves a multifactorial process that likely begins with misfolding of ATXN1, which has functional consequences on its interactions, leading to transcriptional dysregulation. Because lithium has been shown to exert neuroprotective effects in a variety of conditions, possibly by affecting gene expression, we tested the efficacy of lithium treatment in a knock-in mouse model of SCA1 (Sca1154Q/2Q mice) that replicates many features of the human disease.
Methods and Findings
Sca1154Q/2Q mice and their wild-type littermates were fed either regular chow or chow that contained 0.2% lithium carbonate. Dietary lithium carbonate supplementation resulted in improvement of motor coordination, learning, and memory in Sca1154Q/2Q mice. Importantly, motor improvement was seen when treatment was initiated both presymptomatically and after symptom onset. Neuropathologically, lithium treatment attenuated the reduction of dendritic branching in mutant hippocampal pyramidal neurons. We also report that lithium treatment restored the levels of isoprenylcysteine carboxyl methyltransferase (Icmt; alternatively, Pccmt), down-regulation of which is an early marker of mutant ATXN1 toxicity.
Conclusions
The effect of lithium on a marker altered early in the course of SCA1 pathogenesis, coupled with its positive effect on multiple behavioral measures and hippocampal neuropathology in an authentic disease model, make it an excellent candidate treatment for human SCA1 patients.
Huda Zoghbi and colleagues show that lithium treatment initiated before or after disease onset improves multiple symptoms of neurodegeneration in a mouse model of spinocerebellar ataxia.
Editors' Summary
Background.
Spinocerebellar ataxia type 1 (SCA1) is an inherited, incurable neurodegenerative disease in which the neurons (cells that transmit information between the brain and body) in the cerebellum (the brain region that coordinates movement) gradually die. Symptoms of the disease, which usually begins in early adult life, include poor coordination of movement (ataxia), slurred speech, and cognitive (learning and memory) problems. As more neurons die, these symptoms get worse until breathing difficulties eventually cause death. SCA1 is a “triplet repeat disease.” Information for making proteins is stored in DNA as groups of three nucleotides (codons), each specifying a different amino acid (the building blocks of proteins). In triplet repeat diseases, patients inherit a mutant gene containing abnormally long stretches of repeated codons. In SCA1, the repeated codon is CAG, which specifies glutamine. Consequently, SCA1 is a “polyglutamine disease,” a group of neurodegenerative disorders in which an abnormal protein (a different one for each disease) containing a long stretch of glutamine forms nuclear inclusions (insoluble lumps of protein) in neurons that, possibly by trapping essential proteins, cause neuronal death. In SCA1, the abnormal protein is ataxin 1, which is made in many neurons including the cerebellar neurons (Purkinje cells) that coordinate movement.
Why Was This Study Done?
Early in SCA1, the production of several messenger RNAs (the templates for protein production) decreases, possibly because transcription factors (proteins that control gene expression) interact with the mutant protein. Could the progression of SCA1 be slowed, therefore, by using an agent that affects gene expression? In this study, the researchers have investigated whether lithium can slow disease progression in an animal model of SCA1. They chose lithium for their study because this drug (best known for stabilizing mood in people with bipolar [manic] depression) affects gene expression, is neuroprotective, and has beneficial effects in animal models of Huntington disease, another polyglutamine disease.
What Did the Researchers Do and Find?
The researchers bred mice carrying one mutant gene for ataxin 1 containing a very long CAG repeat and one normal gene (Sca1154Q/2Q mice; genes come in pairs). These mice develop symptoms similar to those seen in people with SCA1. After weaning, the mice and their normal littermates were fed normal food or food supplemented with lithium for several weeks before assessing their ability to coordinate their movements and testing their cognitive skills. Dietary lithium (given before or after symptoms appeared) improved both coordination and learning and memory in the Sca1154Q/2Q mice but had little effect in the normal mice. Lithium did not change the overall appearance of the cerebellum in the Sca1154Q/2Q mice nor reduce the occurrence of nuclear inclusions, but it did partly reverse hippocampal neuron degeneration in these animals. The researchers discovered this effect by examining the shape of the hippocampal neurons in detail. These neurons normally have extensive dendrites—branch-like projections that make contact with other cells—but these gradually disappear in Sca1154Q/2Q mice; lithium partly reversed this loss. Finally, lithium also restored the level of Icmt/Pccmt mRNA in the cerebellum to near normal in the Sca1154Q/2Q mice—this mRNA is one of the first to be reduced by ataxin 1 toxicity.
What Do These Findings Mean?
These findings show that treatment with lithium slows neurodegeneration in a mouse model of SCA1, even when it is given only after the first symptoms of the disease have appeared. Unfortunately, lithium did not improve the life span of the Sca1154Q/2Q mice (although this could be because the mutant SCA1 protein has some deleterious effects outside the brain). Thus, lithium is unlikely to cure SCA1, but it could provide some help to people with this devastating disease, even if (as is usual), their condition is not diagnosed until the disease is quite advanced. However, because drugs that work in animal models of diseases do not necessarily work in people, patients with SCA1 (or other polyglutamine diseases, which might also benefit from lithium supplementation) should not be treated with lithium until human trials of this approach have been completed.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040182.
The US National Ataxia Foundation provides information for patients
International Network of Ataxia Friends has information for patients and carergivers on ataxias, including SCA1
GeneTests provides information for health care providers and researchers about SCA1
Online Mendelian Inheritance in Man (OMIM) has detailed scientific information on SCA1
Huntington's Outreach Project for Education offers information for lay people from Stanford University on trinucleotide repeat disorders including SCA1
doi:10.1371/journal.pmed.0040182
PMCID: PMC1880853  PMID: 17535104
15.  Glial S100B protein modulates mutant ataxin-1 aggregation and toxicity: TRTK12 peptide, a potential candidate for SCA1 therapy 
Cerebellum (London, England)  2011;10(2):254-266.
Non-cell autonomous involvement of glial cells in the pathogenesis of polyglutamine diseases is gaining recognition in the ataxia field. We previously demonstrated that Purkinje cells (PCs) in polyglutamine disease spinocerebellar ataxia-1 (SCA1) contain cytoplasmic vacuoles rich in Bergmann glial (BG) protein S100B. The vacuolar formation in SCA1 PCs is accompanied with an abnormal morphology of dendritic spines. In addition, S100B mRNA expression levels are significantly high in the cerebella of asymptomatic SCA1 transgenic (Tg) mice and increase further with age when compared with the age-matched wildtype animals. This higher S100B mRNA expression positively correlates with an increase in the number of vacuoles. To further characterize the function of S100B in SCA1 pathology, we explored the effects of S100B protein on GFP-ataxin-1 (ATXN1) with expanded polyglutamines [82Q] in HEK stable cell line. Externally added S100B protein to these cells induced S100B positive vacuoles similar to those seen in SCA1 PCs in vivo. Further, we found that both externally added and internally expressed S100B significantly reduced GFP-ATXN1[82Q] inclusion body formation. In contrast, the addition of S100B inhibitory peptide TRTK12 reversed S100B mediated effects. Interestingly, in SCA1 Tg mice, PCs containing S100B vacuoles also showed the lack of nuclear inclusions, whereas, PCs without vacuoles contained nuclear inclusions. Additionally, TRTK12 treatment reduced abnormal dendritic growth and morphology of PCs in cerebellar slice cultures prepared from SCA1 Tg mice. Moreover, intranasal administration of TRTK12 to SCA1 Tg mice reduced cerebellar S100B levels in the particulate fractions and these mice displayed a significant improvement in their performance deficit on the Rotarod test. Taken together our results suggest that glial S100B may augment degenerative changes in SCA1 PCs by modulating mutant ataxin-1 toxicity/solubility through an unknown signaling pathway.
doi:10.1007/s12311-011-0262-5
PMCID: PMC3142943  PMID: 21384195
Purkinje cells; S100B; ataxin-1; spinocerebellar ataxia-1; cerebellum; vacuoles; neurodegeneration; Bergmann glia
16.  Patterned Neuroprotection in the Inpp4awbl Mutant Mouse Cerebellum Correlates with the Expression of Eaat4 
PLoS ONE  2009;4(12):e8270.
The weeble mutant mouse has a frame shift mutation in inositol polyphosphate 4-phosphatase type I (Inpp4a). The phenotype is characterized by an early onset cerebellar ataxia and neurodegeneration, especially apparent in the Purkinje cells. Purkinje cell loss is a common pathological finding in many human and mouse ataxic disorders. Here we show that in the Inpp4awbl mutant, Purkinje cells are lost in a specific temporal and spatial pattern. Loss occurs early in postnatal development; however, prior to the appearance of climbing fibers in the developing molecular layer, the mutant has a normal complement of Purkinje cells and they are properly positioned. Degeneration and reactive gliosis are present at postnatal day 5 and progress rapidly in a defined pattern of patches; however, Inpp4a is expressed uniformly across Purkinje cells. In late stage mutants, patches of surviving Purkinje cells appear remarkably normal with the exception that the climbing fibers have been excessively eliminated. Surviving Purkinje cells express Eaat4, a glutamate transporter that is differentially expressed in subsets of Purkinje cells during development and into adult stages. Prior to Purkinje cell loss, reactive gliosis and dendritic atrophy can be seen in Eaat4 negative stripes. Our data suggest that Purkinje cell loss in the Inpp4awbl mutant is due to glutamate excitotoxicity initiated by the climbing fiber, and that Eaat4 may exert a protective effect.
doi:10.1371/journal.pone.0008270
PMCID: PMC2788419  PMID: 20011524
17.  Differential regulation of Purkinje cell dendritic spines in rolling mouse Nagoya (tgrol/tgrol), P/Q type calcium channel (α1A/Cav2.1) mutant 
Anatomy & Cell Biology  2010;43(3):211-217.
Voltage dependent calcium channels (VDCC) participate in regulation of neuronal Ca2+. The Rolling mouse Nagoya (Cacna1atg-rol) is a spontaneous P/Q type VDCC mutant, which has been suggested as an animal model for some human neurological diseases such as autosomal dominant cerebellar ataxia (SCA6), familial hemiplegic migraine and episodic ataxia type-2. Morphology of Purkinje cell (PC) dendritic spine is suggested to be regulated by signal molecules such as Ca2+ and by interactions with afferent inputs. The amplitude of excitatory postsynaptic current was decreased in parallel fiber (PF) to PC synapses, whereas apparently increased in climbing fiber (CF) to PC synapses in rolling mice Nagoya. We have studied synaptic morphology changes in cerebella of this mutant strain. We previously found altered synapses between PF varicosity and PC dendritic spines. To study dendritic spine plasticity of PC in the condition of insufficient P/Q type VDCC function, we used high voltage electron microscopy (HVEM). We measured the density and length of PC dendritic spines at tertiary braches. We observed statistically a significant decrease in spine density as well as shorter spine length in rolling mice compared to wild type mice at tertiary dendritic braches. In proximal PC dendrites, however, there were more numerous dendritic spines in rolling mice Nagoya. The differential regulation of rolling PC spines at tertiary and proximal dendrites in rolling mice Nagoya suggests that two major excitatory afferent systems may be regulated reciprocally in the cerebellum of rolling mouse Nagoya.
doi:10.5115/acb.2010.43.3.211
PMCID: PMC3015039  PMID: 21212861
Ataxia; Dendritic spine; High voltage electron microscope; Purkinje cell; Voltage dependent calcium channel
18.  Cerebellar Expression of Copper Chaperone for Superoxide, Cytosolic Cu/Zn-Superoxide Dismutase, 4-Hydroxy-2-Nonenal, Acrolein and Heat Shock Protein 32 in Patients with Menkes Kinky Hair Disease: Immunohistochemical Study 
Yonago Acta Medica  2014;57(1):23-35.
Background
To clarify the pathogenesis of cerebellar Purkinje cell death in patients with Menkes kinky hair disease (MD), a disorder of copper absorption, we investigated the morphological and functional abnormalities of residual Purkinje cells in MD patients and the mechanism of cell death.
Methods
Seven MD patients and 39 neurologically normal autopsy cases were studied. We performed histopathological and quantitative analyses of the Purkinje cells. In addition, we used immunohistochemistry to detect copper-dependent enzymes [cytosolic Cu/Zn-superoxide dismutase (SOD1) and copper chaperone for superoxide dismutase (CCS)], oxidative stress markers [4-hydroxy-2-nonenal (HNE) and acrolein] and heat shock protein 32 (hsp 32).
Results
The surviving MD Purkinje cells showed abnormal development, such as somatic sprouts and heterotopic location. Due to maldevelopment and degeneration, dendrites showed the cactus and weeping willow patterns. Axonal degeneration led to the formation of torpedoes. Quantitative analysis revealed loss of approximately 50% of the Purkinje cells in MD patients. Almost all of the normal Purkinje cells were positive for immunostaining by anti-CCS and anti-SOD1 antibodies, with staining of the cell bodies, dendrites and axons. Normal Purkinje cells were not stained by antibodies for HNE, acrolein or hsp 32. In MD patients, the majority of Purkinje cells were positive for CCS, but the positive rate for SOD1 was only about 23%. Approximately 56%, 42% and 40% of the Purkinje cells of MD patients were positive for HNE, acrolein and hsp 32, respectively.
Conclusion
In MD patients, about 50% of the Purkinje cells have been lost due to maldevelopment and degeneration. In the residual Purkinje cells, CCS expression seems to be nearly normal as a protective response to decreased SOD1 activity due to copper deficiency. Because oxidative stress is elevated secondary to decreased SOD1 activity, hsp 32 is induced as another protective mechanism.
PMCID: PMC4110693  PMID: 25067875
copper chaperone for superoxide dismutase; cytosolic Cu/Zn-superoxide dismutase; immunohistochemistry; Menkes kinky hair disease; Purkinje cell
19.  Pinceau Organization in the Cerebellum Requires Distinct Functions of Neurofascin in Purkinje and Basket Neurons During Postnatal Development 
The Journal of Neuroscience  2012;32(14):4724-4742.
Basket axon collaterals synapse onto the Purkinje soma/axon initial segment (AIS) area to form specialized structures, the pinceau, which are critical for normal cerebellar function. Mechanistic details of how the pinceau become organized during cerebellar development are poorly understood. Loss of cytoskeletal adaptor protein Ankyrin G (AnkG) results in mislocalization of the cell adhesion molecule Neurofascin (Nfasc) at the Purkinje AIS and abnormal organization of the pinceau. Loss of Nfasc in adult Purkinje neurons leads to slow disorganization of the Purkinje AIS and pinceau morphology. Here we utilized mouse conditional knockout techniques to show that selective loss of Nfasc specifically in Purkinje neurons during early development prevented maturation of the AIS and resulted in loss of Purkinje neuron spontaneous activity and pinceau disorganization. Loss of Nfasc in both Purkinje and basket neurons caused abnormal basket axon collateral branching and targeting to Purkinje soma/AIS, leading to extensive pinceau disorganization, Purkinje neuron degeneration and severe ataxia. Our studies reveal that the Purkinje Nfasc is required for AIS maturation and for maintaining stable contacts between basket axon terminals and the Purkinje AIS during pinceau organization, while the basket neuron Nfasc in combination with Purkinje Nfasc is required for proper basket axon collateral outgrowth and targeting to Purkinje soma/AIS. Thus, cerebellar pinceau organization requires coordinated mechanisms involving specific Nfasc functions in both Purkinje and basket neurons.
doi:10.1523/JNEUROSCI.5602-11.2012
PMCID: PMC3337041  PMID: 22492029
20.  MOLECULAR ALTERATIONS IN THE CEREBELLUM OF THE PLASMA MEMBRANE CALCIUM ATPASE 2 (PMCA2)-NULL MOUSE INDICATE ABNORMALITIES IN PURKINJE NEURONS 
PMCA2, a major calcium pump, is expressed at particularly high levels in Purkinje neurons. Accordingly, PMCA2-null mice exhibit ataxia suggesting cerebellar pathology. It is not yet known how changes in PMCA2 expression or activity affect molecular pathways in Purkinje neurons. We now report that the levels of metabotropic glutamate receptor 1 (mGluR1), which plays essential roles in motor coordination, synaptic plasticity, and associative learning, are reduced in the cerebellum of PMCA2-null mice as compared to wild type littermates. The levels of inositol 1,4,5-triphosphate receptor type 1 (IP3R1), an effector downstream to mGluR1, which mediates intracellular calcium signaling, and the expression of Homer 1b/c and Homer 3, scaffold proteins that couple mGluR1 to IP3R1, are also reduced in somata and dendrites of some Purkinje cell subpopulations. In contrast, no alterations occur in the levels of mGluR1 and its downstream effectors in the hippocampus, indicating that the effects are region specific. The reduction in cerebellar mGluR1, IP3R1 and Homer 3 levels are neither due to a generic decrease in Purkinje proteins nor extensive dendritic loss as immunoreactivity to total and non-phosphorylated neurofilament H (NFH) is increased in Purkinje dendrites and microtubule associated protein 2 (MAP2) staining reveals a dense dendritic network in the molecular layer of the PMCA2-null mouse cerebellum. PMCA2 coimmunoprecipitates with mGluR1, Homer 3 and IP3R1, suggesting that the calcium pump is a constituent of the mGluR1 signaling complex. Our results suggest that the decrease in the expression of mGluR1 and its downstream effectors and perturbations in the mGluR1 signaling complex in the absence of PMCA2 may cumulatively result in aberrant metabotropic glutamate receptor signaling in Purkinje neurons leading to cerebellar deficits in the PMCA2-null mouse.
doi:10.1016/j.mcn.2006.10.010
PMCID: PMC2561181  PMID: 17150372
21.  Purkinje Cell-Specific Ablation of CaV2.1 Channels is Sufficient to Cause Cerebellar Ataxia in Mice 
Cerebellum (London, England)  2011;11(1):246-258.
The Cacna1a gene encodes the α1A subunit of voltage-gated CaV2.1 Ca2+ channels that are involved in neurotransmission at central synapses. CaV2.1-α1-knockout (α1KO) mice, which lack CaV2.1 channels in all neurons, have a very severe phenotype of cerebellar ataxia and dystonia, and usually die around postnatal day 20. This early lethality, combined with the wide expression of CaV2.1 channels throughout the cerebellar cortex and nuclei, prohibited determination of the contribution of particular cerebellar cell types to the development of the severe neurobiological phenotype in Cacna1a mutant mice. Here, we crossed conditional Cacna1a mice with transgenic mice expressing Cre recombinase, driven by the Purkinje cell-specific Pcp2 promoter, to specifically ablate the CaV2.1-α1A subunit and thereby CaV2.1 channels in Purkinje cells. Purkinje cell CaV2.1-α1A-knockout (PCα1KO) mice aged without difficulties, rescuing the lethal phenotype seen in α1KO mice. PCα1KO mice exhibited cerebellar ataxia starting around P12, much earlier than the first signs of progressive Purkinje cell loss, which appears in these mice between P30 and P45. Secondary cell loss was observed in the granular and molecular layers of the cerebellum and the volume of all individual cerebellar nuclei was reduced. In this mouse model with a cell type-specific ablation of CaV2.1 channels, we show that ablation of CaV2.1 channels restricted to Purkinje cells is sufficient to cause cerebellar ataxia. We demonstrate that spatial ablation of CaV2.1 channels may help in unraveling mechanisms of human disease.
Electronic supplementary material
The online version of this article (doi:10.1007/s12311-011-0302-1) contains supplementary material, which is available to authorized users.
doi:10.1007/s12311-011-0302-1
PMCID: PMC3311848  PMID: 21870131
P/Q-type Ca2+ channels; Conditional; Cell-specific knockout; Cacna1a; Ataxia
22.  Early changes in cerebellar physiology accompany motor dysfunction in the polyglutamine disease, Spinocerebellar Ataxia type 3 
The relationship between cerebellar dysfunction, motor symptoms and neuronal loss in the inherited ataxias, including the polyglutamine disease Spinocerebellar Ataxia type 3 (SCA3), remains poorly understood. We demonstrate that prior to neurodegeneration, Purkinje neurons in a mouse model of SCA3 exhibit increased intrinsic excitability resulting in depolarization block and the loss of the ability to sustain spontaneous repetitive firing. These alterations in intrinsic firing are associated with increased inactivation of voltage-activated potassium currents. Administration of an activator of calcium-activated potassium channels, SKA-31, partially corrects abnormal Purkinje cell firing and improves motor function in SCA3 mice. Finally, expression of the disease protein, ataxin-3, in transfected cells increases the inactivation of Kv3.1 channels and shifts the activation of Kv1.2 channels to more depolarized potentials. Our results suggest that in SCA3, early Purkinje neuron dysfunction is associated with altered physiology of voltage-activated potassium channels. We further suggest that the observed changes in Purkinje neuron physiology contribute to disease pathogenesis, underlie at least some motor symptoms, and represent a promising therapeutic target in SCA3.
doi:10.1523/JNEUROSCI.2789-11.2011
PMCID: PMC3170039  PMID: 21900579
23.  Morphine inhibits Purkinje cell survival and dendritic differentiation in organotypic cultures of the mouse cerebellum 
Experimental neurology  1994;130(1):95-105.
The effects of morphine on the morphogenesis and survival of calbindin-D28kimmunoreactive Purkinje cells was studied in organotypic explant cultures isolated from 1- or 7-day-old mouse cerebella. To reduce experimental variability, bilaterally matched pairs of organotypic cultures were used to compare the effects of opiate drug treatment. One explant within each pair was untreated, while the remaining explant was continuously treated for 7 to 10 days with morphine, morphine plus naloxone, or naloxone alone. In explants derived from 1-day-old mice, morphine treatment significantly reduced Purkinje cell dendritic length compared to symmetrically-matched untreated control explants. The concentration of morphine estimated to cause a half-maximal reduction (EC50) in dendritic length was 4.9 × 10−8 M. At higher concentrations (EC50 = 3.6 × 10−6 M), morphine also significantly decreased the number of Purkinje cells in explants from 1-day-old mice compared to untreated explants. Electron microscopy identified increased numbers of degenerating Purkinje cells in explants derived from 1-day-old mice. This showed that high concentrations (10−5 M) of morphine reduced Purkinje cell numbers by decreasing their rate of survival. In explants derived from 7-day-old mice, morphine (10−5 M) neither affected Purkinje cell dendritic length nor cell numbers compared to symmetrically-matched untreated (control) explants. Collectively, these findings suggest that morphine per se, through a direct action on the cerebellum, can affect Purkinje cell differentiation and survival. The results additionally suggest there is a critical period during development when Purkinje cells are especially vulnerable to the effects of morphine.
doi:10.1006/exnr.1994.1188
PMCID: PMC4306355  PMID: 7821399
Endogenous opioid systems; Calbindin-D28k; Cerebellar development; Cell death; Drug abuse; Critical period; Neurotoxicity
24.  Bergmann Glia and the Recognition Molecule CHL1 Organize GABAergic Axons and Direct Innervation of Purkinje Cell Dendrites 
PLoS Biology  2008;6(4):e103.
The geometric and subcellular organization of axon arbors distributes and regulates electrical signaling in neurons and networks, but the underlying mechanisms have remained elusive. In rodent cerebellar cortex, stellate interneurons elaborate characteristic axon arbors that selectively innervate Purkinje cell dendrites and likely regulate dendritic integration. We used GFP BAC transgenic reporter mice to examine the cellular processes and molecular mechanisms underlying the development of stellate cell axons and their innervation pattern. We show that stellate axons are organized and guided towards Purkinje cell dendrites by an intermediate scaffold of Bergmann glial (BG) fibers. The L1 family immunoglobulin protein Close Homologue of L1 (CHL1) is localized to apical BG fibers and stellate cells during the development of stellate axon arbors. In the absence of CHL1, stellate axons deviate from BG fibers and show aberrant branching and orientation. Furthermore, synapse formation between aberrant stellate axons and Purkinje dendrites is reduced and cannot be maintained, leading to progressive atrophy of axon terminals. These results establish BG fibers as a guiding scaffold and CHL1 a molecular signal in the organization of stellate axon arbors and in directing their dendritic innervation.
Author Summary
Large principal neurons in vertebrate neural circuits often consist of distinct anatomical and physiological compartments, which allow distributed and compartmentalized signaling and greatly increase the computational power of single neurons. Superimposed upon this intrinsic compartmental architecture is the subcellular organization of synaptic inputs, which exert local control over the biophysical properties and differentially regulate the input, integration, and output of principal neurons. In the cerebellar cortex, Purkinje neurons are innervated by GABA inhibitory synapses from the stellate and basket cells at dendrites and soma-axon initial (AIS) segments, respectively. Previous studies have shown that an L1 family immunoglobulin cell adhesion molecule (neurofascin186) is distributed as a subcellular gradient and directs basket cell axons to innervate Purkinje cell AIS. Here, we examine the mechanisms underlying the innervation of Purkinje cell dendrites by stellate axons. We found that stellate axons are organized into characteristic trajectories and guided towards Purkinje dendrites by an intermediate scaffold of astroglia—the Bergmann glial (BG) fibers. Another member of L1 family, Close Homologue of L1 (CHL1), is localized to BG fibers and stellate cells, and contributes to the organization of stellate axons along BG fibers and to the innervation of Purkinje cell dendrites.
Subcellular synapse organization regulates the input, integration, and output of target neurons. An astroglial scaffold and an L1 family cell adhesion molecule contribute to dendritic innervation by GABA inhibitory synapses.
doi:10.1371/journal.pbio.0060103
PMCID: PMC2689695  PMID: 18447583
25.  Cadm1-Expressing Synapses on Purkinje Cell Dendrites Are Involved in Mouse Ultrasonic Vocalization Activity 
PLoS ONE  2012;7(1):e30151.
Foxp2(R552H) knock-in (KI) mouse pups with a mutation related to human speech–language disorders exhibit poor development of cerebellar Purkinje cells and impaired ultrasonic vocalization (USV), a communication tool for mother-offspring interactions. Thus, human speech and mouse USV appear to have a Foxp2-mediated common molecular basis in the cerebellum. Mutations in the gene encoding the synaptic adhesion molecule CADM1 (RA175/Necl2/SynCAM1/Cadm1) have been identified in people with autism spectrum disorder (ASD) who have impaired speech and language. In the present study, we show that both Cadm1-deficient knockout (KO) pups and Foxp2(R552H) KI pups exhibit impaired USV and smaller cerebellums. Cadm1 was preferentially localized to the apical–distal portion of the dendritic arbor of Purkinje cells in the molecular layer of wild-type pups, and VGluT1 level decreased in the cerebellum of Cadm1 KO mice. In addition, we detected reduced immunoreactivity of Cadm1 and VGluT1 on the poorly developed dendritic arbor of Purkinje cells in the Foxp2(R552H) KI pups. However, Cadm1 mRNA expression was not altered in the Foxp2(R552H) KI pups. These results suggest that although the Foxp2 transcription factor does not target Cadm1, Cadm1 at the synapses of Purkinje cells and parallel fibers is necessary for USV function. The loss of Cadm1-expressing synapses on the dendrites of Purkinje cells may be associated with the USV impairment that Cadm1 KO and Foxp2(R552H) KI mice exhibit.
doi:10.1371/journal.pone.0030151
PMCID: PMC3260241  PMID: 22272290

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