Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disease mainly characterized by motor incoordination and visual impairment due to progressive cerebellar and retinal degeneration.Alteration of other nervous tissues also contributes to symptoms. The mechanisms underlying motor incoordination of SCA7 remain to be characterized. SCA7 is caused by a polyglutamine (polyQ) expansion in ATXN7, a member of the transcriptional coactivator SAGA complex, which harbors histone modi cation activities. PolyQ expansion in other proteins is responsible for 5 other SCAs (SCA1-3, 6 and 17). However, the converging and diverging pathophysiological points remain poorly understood. Using a new SCA7 knock-in model carrying 140 glutamines in ATXN7, we analyzed cell-type speci c gene expression in the cerebellum. We show that gene deregulation affects all cerebellar cell types, although at variable degree, and correlates with alterations of SAGA-dependent epigenetic marks histone H3 acetylation and H2B ubiquitination. Our results further show that Purkinje cells (PCs) are far the most affected neurons: unlike other cerebellar cell types, PCs show reduced expression of 83 cell-type identity genes, critical for their spontaneous ring activity and synaptic functions. PC gene downregulation precedes morphological alterations, pacemaker dysfunction and motor incoordination. Strikingly, most PC identity genes downregulated in SCA7 mice are also decreased in early symptomatic SCA1 and SCA2 mice, revealing a common signature of early PC pathology involving cGMP-PKG and phosphatidylinositol signaling pathways and long-term depression. Our study thus points out molecular targets for therapeutic development which may prove bene cial for several SCAs. Finally, we show that unlike previous SCA7 mouse models, SCA7 140Q/5Q mice exhibit the major disease features observed in patients, including cerebellar damage, cerebral atrophy, peripheral nerves pathology and photoreceptor dystrophy, which account for progressive impairment of behavior, motor and vision functions. Therefore, SCA7 140Q/5Q mice represent an accurate model for the investigation of different aspects of SCA7 pathogenesis.Page 5/52 [42]. While SCA proteins do not share any domain and have different cellular functions, changes in gene expression are central features in most polyQ SCAs. Therefore, the comparison of differentially expressed genes should provide insight into converging disease mechanisms.To get insight into the mechanisms underlying motor incoordination and cerebellar degeneration, we used a new SCA7 knock-in mice line carrying 140 CAG repeats. A comprehensive and longitudinal characterization of this model using a battery of analyses (motor and behavioral tests, retina imaging, MRI, electrophysiology, neuropathology) indicates that SCA7140Q/5Q mice remarkably recapitulate the major clinical features observed in patients, including cerebellar damage, speci c cerebral atrophy, peripheral nerves pathology and photoreceptor dystrophy, which account for prog...

Polyglutamine spinocerebellar ataxias (polyQ SCAs) include SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 and constitute a group of adult onset neurodegenerative disorders caused by the expansion of a CAG repeat sequence located within the coding region of specific genes, which translates into polyglutamine tract in the corresponding proteins. PolyQ SCAs are characterized by degeneration of the cerebellum and its associated structures and lead to progressive ataxia and other diverse symptoms. In recent years, gene and epigenetic deregulations have been shown to play a critical role in the pathogenesis of polyQ SCAs. Here, we provide an overview of the functions of wild type and pathogenic polyQ SCA proteins in gene regulation, describe the extent and nature of gene expression changes and their pathological consequences in diseases, and discuss potential avenues to further investigate converging and distinct disease pathways and to develop therapeutic strategies.

Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disease mainly characterized by motor incoordination and visual impairment due to progressive cerebellar and retinal degeneration. Alteration of other nervous tissues also contributes to symptoms. The mechanisms underlying motor incoordination of SCA7 remain to be characterized. SCA7 is caused by a polyglutamine (polyQ) expansion in ATXN7, a member of the transcriptional coactivator SAGA complex, which harbors histone modification activities. PolyQ expansion in other proteins is responsible for 5 other SCAs (SCA1-3, 6 and 17). However, the converging and diverging pathophysiological points remain poorly understood. Using a new SCA7 knock-in model carrying 140 glutamines in ATXN7, we analyzed cell-type specific gene expression in the cerebellum. We show that gene deregulation affects all cerebellar cell types, although at variable degree, and correlates with alterations of SAGA-dependent epigenetic marks histone H3 acetylation and H2B ubiquitination. Our results further show that Purkinje cells (PCs) are far the most affected neurons: unlike other cerebellar cell types, PCs show reduced expression of 83 cell-type identity genes, critical for their spontaneous firing activity and synaptic functions. PC gene downregulation precedes morphological alterations, pacemaker dysfunction and motor incoordination. Strikingly, most PC identity genes downregulated in SCA7 mice are also decreased in early symptomatic SCA1 and SCA2 mice, revealing a common signature of early PC pathology involving cGMP-PKG and phosphatidylinositol signaling pathways and long-term depression. Our study thus points out molecular targets for therapeutic development which may prove beneficial for several SCAs. Finally, we show that unlike previous SCA7 mouse models, SCA7140Q/5Q mice exhibit the major disease features observed in patients, including cerebellar damage, cerebral atrophy, peripheral nerves pathology and photoreceptor dystrophy, which account for progressive impairment of behavior, motor and vision functions. Therefore, SCA7140Q/5Q mice represent an accurate model for the investigation of different aspects of SCA7 pathogenesis.

Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progressive cerebellar degeneration with major alteration of Purkinje cells (PC) due to polyglutamine expansion in ATXN7, a subunit of SAGA transcriptional co-regulator complex. Additional neural tissues are affected and contribute to diverse symptoms. Current animal models were insufficient to recapitulate the broad spectrum of SCA7 pathology and the mechanisms of PC degeneration remain poorly explored. Methods: To delineate spatio-temporal features of SCA7, we performed a longitudinal characterization of a new knock-in mice line expressing ATXN7 with 140 glutamines (SCA7 140Q/5Q ) using a battery of analyses including motor tests, brain and retina imaging, morphometry, electrophysiology, electron microscopy and immunohistochemistry of disease tissues. We also determined the cerebellar transcriptome and cell-type specific gene deregulation. Results: Here we describe the first SCA7 knock-in mice that combine most cardinal features of SCA7, including retinal, cerebellar, cerebral and peripheral nerves pathologies, which account for progressive impairment of behavior, motor and vision functions. MRI and brain morphometry reveal atrophy of grey and white matter of specific cerebral regions, while peripheral nerves and photoreceptors show functional and morphological alterations. We show that cerebellar pathology is characterized by gene deregulation in all cerebellar cell types and alterations of SAGA-dependent epigenetic marks. Intranuclear accumulation of mutant ATXN7 and gene downregulation precede the onset of PC pacemaker dysfunction. Interestingly, PC show loss of expression of 83 PC-specific genes coding for ion channels, receptors and signaling proteins involved in pacemaker function and long-term depression, which are causal factors of many type of ataxias. Comparison of cerebellar transcriptome with other SCAs reveals a subset of 67 PC-specific genes downregulated in SCA1, SCA2 and SCA7, providing a common signature of early PC dysfunction. Conclusions: The SCA7 140Q/5Q mice represent a promising model for the investigation of different aspects of SCA7 pathogenesis, and offers opportunities for translational development of therapeutic strategies by targeting the brain, retina, peripheral nerve or whole body. Our results also provide insight into converging mechanisms of PC degeneration in polyglutamine SCAs and point out molecular targets for therapeutic development w hich may prove beneficial for several SCAs.

Background Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder that primarily affects the cerebellum and retina. SCA7 is caused by a polyglutamine expansion in the ATXN7 protein, a subunit of the transcriptional coactivator SAGA that acetylates histone H3 to deposit narrow H3K9ac mark at DNA regulatory elements of active genes. Defective histone acetylation has been presented as a possible cause for gene deregulation in SCA7 mouse models. However, the topography of acetylation defects at the whole genome level and its relationship to changes in gene expression remain to be determined. Methods We performed deep RNA-sequencing and chromatin immunoprecipitation coupled to high-throughput sequencing to examine the genome-wide correlation between gene deregulation and alteration of the active transcription marks, e.g. SAGA-related H3K9ac, CBP-related H3K27ac and RNA polymerase II (RNAPII), in a SCA7 mouse retinopathy model. Results Our analyses revealed that active transcription marks are reduced at most gene promoters in SCA7 retina, while a limited number of genes show changes in expression. We found that SCA7 retinopathy is caused by preferential downregulation of hundreds of highly expressed genes that define morphological and physiological identities of mature photoreceptors. We further uncovered that these photoreceptor genes harbor unusually broad H3K9ac profiles spanning the entire gene bodies and have a low RNAPII pausing. This broad H3K9ac signature co-occurs with other features that delineate superenhancers, including broad H3K27ac, binding sites for photoreceptor specific transcription factors and expression of enhancer-related non-coding RNAs (eRNAs). In SCA7 retina, downregulated photoreceptor genes show decreased H3K9 and H3K27 acetylation and eRNA expression as well as increased RNAPII pausing, suggesting that superenhancer-related features are altered. Conclusions Our study thus provides evidence that distinctive epigenetic configurations underlying high expression of cell-type specific genes are preferentially impaired in SCA7, resulting in a defect in the maintenance of identity features of mature photoreceptors. Our results also suggest that continuous SAGA-driven acetylation plays a role in preserving post-mitotic neuronal identity.