We followed the immediate effect of sensorimotor training on postural stability in patients with spinocerebellar ataxia (SCA). We have tried to explain the possible mechanisms of adaptation to change COP, motor learning and neuroplasticity in the field of neurodegenerative changes in the cerebellum. Research Methods: A total of 10 patients with spinocerebellar ataxia (6 men, 4 women) aged 34-71 years, with an average disease duration of 11.6 years participated in the measurement of postural stability. First, we measured the patients with SCA before and after a 15-minute sensorimotor-training exercise, then this group underwent another day of the same measurement without sensorimotor training. As a second control group of 10 healthy subjects served a similar age, who also underwent sensorimotor training. Then we compared the results of posturographic measurement. Results: In the group of SCA patients, sensorimotor training was found significantly lower values in the monitored parameters LENGTH (t stat = 3,537731 > t krit = 2,262157), VELOCITY (t stat = 3,537731 > t krit = 2,262157) and energy to sustain COP (t stat = 2,715085 > t krit = 2,262157), measured on a foam pad with eyes closed. Measurement without making sensorimotor training produced no significant improvement in the results of monitored...

The 14-3-3 family of proteins are important signalling proteins involved in a number of cellular processes. These include cell cycle regulation, apoptosis, signal transduction and cell signalling. There is also considerable evidence in the literature that 14-3-3 proteins play a vital role in the pathology of neurodegenerative diseases, including Alzheimer’s, Parkinson’s, Huntington’s and Prion disease. The neurodegenerative disease of focus in this research is Spinocerebellar Ataxia Type 1 (SCA1). SCA1 is a polyglutamine-repeat disease and the interaction of the disease protein ataxin-1 with 14-3-3 proteins leads to the toxic accumulation and subsequent protein aggregation which is characteristic of this disease. This study focused on attempting to elucidate the structure of various domains of the disease protein and also in identifying potential inhibitors of this deleterious interaction. Unfortunately, structural studies were not successful due to a number of caveats encountered in the expression and purification of the ataxin-1 protein domains. By utilising computational methods and small molecule inhibitors, a number of potential lead compounds which possess the ability to at least partly disrupt the interaction of 14- 3-3ζ have been identified. As 14-3-3 proteins play roles in other neurodegenerative diseases, successful identification of potential drug lead treatments can have far reaching benefits in a number of neurodegenerative diseases including SCA1. Lipid rafts are also involved in neurodegenerative disease pathology. Lipid rafts are cholesterol and sphingolipid rich domains which organise the plasma membrane into discrete microdomains and act as signalling platforms and processing centres which attach specific proteins and lipids. A number of disease proteins are processed at these membrane regions, including those involved in Alzheimer’s, Parkinson’s and Prion disease. This processing is a step which is critical in the pathology of disease and abnormal processing leads to the formation of toxic protein aggregates. Previous research in the lab identified the association of low levels of the five main brain isoforms of 14-3-3 proteins with rafts. This study expanded on this to positively identify the presence of the two phospho-forms of 14-3-3, α and δ. The mechanism by which 14-3-3 proteins associate with rafts was also investigated, indicating that 14-3-3 associates with rafts via an unidentified raftbound protein(s). In addition, the phosphorylation status and quaternary structure of 14-3-3 in the presence of sphingolipids has been explored.

Introdução: A doença de Machado-Joseph, também conhecida como ataxia espinocerebelar tipo 3 (DMJ/SCA3), é de inicio na vida adulta, uma doença neurodegenerativa autossômica dominante causada por uma expansão CAG no gene ATXN3. A DMJ/SCA3 pertence ao grupo de doenças chamado de poliglutaminopatias (PoliQ). A redução do risco de câncer em indivíduos com PolyQ tais como a doença de Huntington foi previamente relatada em um população diferente. Nenhum estudo buscando essa associação em DMJ/SCA3 já foi realizada.Objetivos: comparar os 15 anos de incidência cumulativa de câncer (ICC) e a proporção de câncer como causa de morte em portadores de DMJ/SCA3 sintomáticos observados e nos controles. Métodos: Indivíduos com DMJ/SCA3 pertencentes ao Rio Grande do Sul em uma coorte de 2000 a 2015 foram identificados. Entrevistas estruturadas foram feitas com indivíduos afetados e com controles não relacionados. A CIC conforme publicado pelo Instituto Nacional de Câncer (INCA), do Brasil, foi usado como um controle populacional. As causas de morte entre as famílias com DMJ/SCA3 e controles não relacionados pareados também foram obtidos pelo Sistema de Informações sobre Mortalidade Pública. Foram entrevistados 154 pacientes com DMJ/SCA3 e 80 controles não relacionados: Resultados: A CIC foi de 7/154 (4,5%) e 5/80 (6,3%) entre DMJ/SCA3 e nos indivíduos controles não relacionados, respectivamente. Para obter uma redução do risco absoluto de 1,8 entre os casos e controles, seriam necessários 1.938 indivíduos por grupo para detectar uma diferença significativa entre os grupos. A população total de sintomáticos com DMJ/SCA3 igualou-se a 625 indivíduos em 2015, esse estudo foi interrompido. O câncer foi a causa da morte em 9/101 (8,9%) DMJ/SCA3 e em 52/202 (26,2%) controles, com uma redução do risco absoluto de 17,3% no grupo DMJ/SCA3 (χ² = 12,421; p = 0,001 ; OR 0,27, IC 95% 0,13-0,58). Indivíduos com DMJ/SCA3 que morreram de câncer eram mais velhos e tinham uma menor CAGexp que os casos que faleceram de outras causas.Discussão: Devido à raridade da DMJ/SCA3, estudos de CIC em indivíduos vivos com poder estatístico são inviáveis. No entanto, uma redução significativa de câncer como uma causa de morte foi detectada em DMJ/SCA3. Estes dados confirmam a associação de polyQ com proteção contra o câncer e sugerem que polyQ de fato são doenças de multissistemas. / Introduction: Machado-Joseph disease, also known as Spinocerebellar Ataxia type 3 (MJD/SCA3), is an adult-onset autosomal dominant neurodegenerative disease caused by an expanded CAG repeat in the ATXN3 gene. MJD/SCA3 belongs to the so-called group of polyglutamine disorders (PolyQ). Reduced risk of câncer in individuals with PolyQ such as Huntington disease was previously reported in different population. No study searching for this association in MJD/SCA3 was already performed. Objectives: We aimed to compare the 15 years cumulative incidence of câncer (ICC) and the proportion of câncer as a cause of death in symptomatic SCA3/MJD carriers with those observed in controls. Methods: SCA3/MJD individuals belonging to the Rio Grande do Sul cohort from 2000 to 2015 were identified. A structured interview was done with affected individuals and with unrelated controls. CIC as published by the National Institute of Câncer (INCA), Brazil, was used as a population control. Causes of death among SCA3/MJD families and paired unrelated controls were also obtained from the Public Information System on Mortality. Results: 154 SCA3/MJD patients and 80 unrelated controls were interviewed. CIC were 7/154 (4.5%) and 5/80 (6.3%) among SCA3/MJD and unrelated control individuals, respectively. For an absolute risk reduction of 1.8 between cases and controls, 1,938 individuals per group would be needed to detect a significant difference between groups. Since the total symptomatic SCA3/MJD population equaled 625 individuals in 2015, this study was interrupted. Câncer was a cause of death in 9/101 (8.9%) SCA3/MJD and in 52/202 (26.2%) controls, with an absolute reduction risk of 17.3% in the SCA3/MJD group (χ²=12.421; p=0.001; OR 0.27, IC95% 0.13 to 0.58). SCA3/MJD individuals who died from câncer were older and carried shorter CAGexp than those SCA3/MJD cases who died from other causes. Discussion: Due to the rarity of SCA3/MJD, CIC studies in living individuals with statistical power are unfeasible. However, a significant reduction of câncer as a cause of death was detected in SCA3/MJD. This data confirm the association of PolyQ with protection against câncer and suggest that PolyQ are indeed multisystem disorders.

Les maladies par expansion de polyglutamines sont des maladies neurodégénératives dues à l’expansion du trinucléotide cytosine-adénine-guanine (CAG) dans les gènes correspondants codant pour une expansion d’homopolymère de glutamine dans les protéines mutées. Ce projet concerne les formes les plus courantes qui sont la maladie de Huntington (MH) et les ataxies spinocérébelleuses (SCA) types 1, 2, 3 et 7. Ce sont des maladies autosomiques dominantes, responsables de troubles graves de la motricité partageant des voies physiopathologiques communes, avec un effet notable sur la dysfonction métabolique. La disponibilité des tests génétiques et le fait que la plupart du temps la maladie débute à l’âge adulte offre la possibilité d’une intervention thérapeutique avant l’apparition de symptômes. Toutefois, les échelles cliniques ne sont pas assez sensibles et ne peuvent effectivement être utilisés pour évaluer les personnes au stade présymptomatique de la maladie. Les techniques d’imagerie par résonance magnétique (IRM) et de spectroscopie (SRM) sont des approches non invasives qui permettent de recueillir des informations pertinentes et sensibles. Ainsi, dans ce travail, nous présentons une combinaison de différentes techniques d’IRM et SRM afin d’identifier de robustes biomarqueurs de la MH et des SCA. Nous présentons aussi des approches thérapeutiques prometteuses dans la MH. De la même manière, nous voulons démontrer que des biomarqueurs d’imagerie sont plus sensibles que des échelles cliniques. Pour conclure, nous combinons des données multimodales – volumétrie, SRM, métabolomique et lipidomique – à partir de SCA dans un modèle qui explique mieux la pathologie. / Mutations in different gene loci that lead to the encoding of the unstable and expanded glutamine-encoding cytosine-adenine-guanine (CAG) repeats results in the group of diseases known as the polyglutamine diseases. This project focuses on the most common forms which are Huntington disease (HD) and spinocerebellar ataxia (SCA) types 1, 2, 3 and 7. These are autosomal dominant diseases responsible for severe movement disorders and are thought to share common pathophysiological pathways with a major emphasis on metabolic dysfunction. The availability of genetic testing and their predominantly adult onset opens a window for therapeutic intervention before symptoms onset. However, current clinical scales are not sensitive and cannot effectively be used to evaluate individuals at the presymptomatic stage of the diseases. This prompts the need for biomarkers that are sensitive to macroscopic and microscopic changes that may occur prior to disease onset. Magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques present non-invasive approaches to extract pertinent information that otherwise would not be possible with clinical scales. In this work therefore, we present a combination of different MRI and MRS techniques to identify robust biomarkers in HD and SCA. We also present therapeutic approaches that hold promise in HD. Likewise, we show that imaging biomarkers have higher effect sizes than clinical scales. Finally, we combine multimodal data – volumetry, MRS, metabolomics and lipidomic – from SCA into a model that best explains the pathology.

Spinocerebellar ataxia type 7 (SCA7) is a hereditary neurodegenerative disorder affecting the cerebellum, pons and retina. SCA7 patients present with gait ataxia and visual impairment as the main symptoms. Anticipation, commonly observed in SCA7 families, is a phenomenon where an earlier age at onset and a more severe progression of disease is seen in successive generations. In order to identify the gene responsible for SCA7, we performed linkage analysis on a Swedish SCA7 kindred. Evidence for linkage of the SCA7 disease locus to a 32 cM region on chromosome 3p12-21.1, between markers D3S1547 and D3S1274, was established. A number of neurodegenerative disorders associated with anticipation are caused by expanded (CAG)n repeats in their respective disease genes. In order to isolate the SCA7 disease gene we, therefore, screened a human infant brain stem cDNA library for CAG repeat containing clones, mapping to chromosome 3. Four candidate clones were isolated and analysed, but could all be excluded as the SCA7 disease gene. In 1997, the SCA7 disease gene was identified and, as expected, shown to harbour a CAG repeat, expanded in SCA7 patients. Analysis of the SCA7 CAG repeat region in Swedish SCA7 patients demonstrated that CAG repeat size was negatively correlated to age at onset of disease. Furthermore, patients with larger repeats presented with visual impairment, whereas patients with smaller repeats presented with ataxia as the initial symptom. SCA7 is the most common autosomal dominant cerebellar ataxia in Sweden and Finland, but rare in other populations. In order to investigate if the relatively high frequency of SCA7 in these countries is the result of a founder effect in the region, a haplotype analysis was performed on all SCA7 families available. All 7 families shared a common haplotype of at least 1.9 cM surrounding the SCA7 locus. In addition, strong linkage disequilibrium was demonstrated for marker D3S1287 closely linked to the SCA7 gene, suggesting a founder effect for the SCA7 mutation in Sweden and Finland. The function of the SCA7 protein, ataxin-7, is not known and it does not show significant homologies to any previously known proteins. In order to gain insight into the function of ataxin-7 we analysed the expression of ataxin-7 in brain and peripheral tissue from SCA7 patients and controls. In brain, expression was found to be mainly neuronal with a nuclear subcellular localisation. Ataxin-7 expression was found throughout the CNS, not restricted to sites of pathology. We also confirmed previously reported findings of neuronal intranuclear inclusions (NIls) in the brains of SCA7 patients. Based on our findings, we conclude that the cell type specific neurodegeneration in SCA7 is not due to differences in expression pattern in affected and non-affected tissue or the distribution pattern of aggregated protein.

Introdução: A doença de Machado-Joseph, também conhecida como ataxia espinocerebelar tipo 3 (DMJ/SCA3), é de inicio na vida adulta, uma doença neurodegenerativa autossômica dominante causada por uma expansão CAG no gene ATXN3. A DMJ/SCA3 pertence ao grupo de doenças chamado de poliglutaminopatias (PoliQ). A redução do risco de câncer em indivíduos com PolyQ tais como a doença de Huntington foi previamente relatada em um população diferente. Nenhum estudo buscando essa associação em DMJ/SCA3 já foi realizada.Objetivos: comparar os 15 anos de incidência cumulativa de câncer (ICC) e a proporção de câncer como causa de morte em portadores de DMJ/SCA3 sintomáticos observados e nos controles. Métodos: Indivíduos com DMJ/SCA3 pertencentes ao Rio Grande do Sul em uma coorte de 2000 a 2015 foram identificados. Entrevistas estruturadas foram feitas com indivíduos afetados e com controles não relacionados. A CIC conforme publicado pelo Instituto Nacional de Câncer (INCA), do Brasil, foi usado como um controle populacional. As causas de morte entre as famílias com DMJ/SCA3 e controles não relacionados pareados também foram obtidos pelo Sistema de Informações sobre Mortalidade Pública. Foram entrevistados 154 pacientes com DMJ/SCA3 e 80 controles não relacionados: Resultados: A CIC foi de 7/154 (4,5%) e 5/80 (6,3%) entre DMJ/SCA3 e nos indivíduos controles não relacionados, respectivamente. Para obter uma redução do risco absoluto de 1,8 entre os casos e controles, seriam necessários 1.938 indivíduos por grupo para detectar uma diferença significativa entre os grupos. A população total de sintomáticos com DMJ/SCA3 igualou-se a 625 indivíduos em 2015, esse estudo foi interrompido. O câncer foi a causa da morte em 9/101 (8,9%) DMJ/SCA3 e em 52/202 (26,2%) controles, com uma redução do risco absoluto de 17,3% no grupo DMJ/SCA3 (χ² = 12,421; p = 0,001 ; OR 0,27, IC 95% 0,13-0,58). Indivíduos com DMJ/SCA3 que morreram de câncer eram mais velhos e tinham uma menor CAGexp que os casos que faleceram de outras causas.Discussão: Devido à raridade da DMJ/SCA3, estudos de CIC em indivíduos vivos com poder estatístico são inviáveis. No entanto, uma redução significativa de câncer como uma causa de morte foi detectada em DMJ/SCA3. Estes dados confirmam a associação de polyQ com proteção contra o câncer e sugerem que polyQ de fato são doenças de multissistemas. / Introduction: Machado-Joseph disease, also known as Spinocerebellar Ataxia type 3 (MJD/SCA3), is an adult-onset autosomal dominant neurodegenerative disease caused by an expanded CAG repeat in the ATXN3 gene. MJD/SCA3 belongs to the so-called group of polyglutamine disorders (PolyQ). Reduced risk of câncer in individuals with PolyQ such as Huntington disease was previously reported in different population. No study searching for this association in MJD/SCA3 was already performed. Objectives: We aimed to compare the 15 years cumulative incidence of câncer (ICC) and the proportion of câncer as a cause of death in symptomatic SCA3/MJD carriers with those observed in controls. Methods: SCA3/MJD individuals belonging to the Rio Grande do Sul cohort from 2000 to 2015 were identified. A structured interview was done with affected individuals and with unrelated controls. CIC as published by the National Institute of Câncer (INCA), Brazil, was used as a population control. Causes of death among SCA3/MJD families and paired unrelated controls were also obtained from the Public Information System on Mortality. Results: 154 SCA3/MJD patients and 80 unrelated controls were interviewed. CIC were 7/154 (4.5%) and 5/80 (6.3%) among SCA3/MJD and unrelated control individuals, respectively. For an absolute risk reduction of 1.8 between cases and controls, 1,938 individuals per group would be needed to detect a significant difference between groups. Since the total symptomatic SCA3/MJD population equaled 625 individuals in 2015, this study was interrupted. Câncer was a cause of death in 9/101 (8.9%) SCA3/MJD and in 52/202 (26.2%) controls, with an absolute reduction risk of 17.3% in the SCA3/MJD group (χ²=12.421; p=0.001; OR 0.27, IC95% 0.13 to 0.58). SCA3/MJD individuals who died from câncer were older and carried shorter CAGexp than those SCA3/MJD cases who died from other causes. Discussion: Due to the rarity of SCA3/MJD, CIC studies in living individuals with statistical power are unfeasible. However, a significant reduction of câncer as a cause of death was detected in SCA3/MJD. This data confirm the association of PolyQ with protection against câncer and suggest that PolyQ are indeed multisystem disorders.

Introdução: A doença de Machado-Joseph, também conhecida como ataxia espinocerebelar tipo 3 (DMJ/SCA3), é de inicio na vida adulta, uma doença neurodegenerativa autossômica dominante causada por uma expansão CAG no gene ATXN3. A DMJ/SCA3 pertence ao grupo de doenças chamado de poliglutaminopatias (PoliQ). A redução do risco de câncer em indivíduos com PolyQ tais como a doença de Huntington foi previamente relatada em um população diferente. Nenhum estudo buscando essa associação em DMJ/SCA3 já foi realizada.Objetivos: comparar os 15 anos de incidência cumulativa de câncer (ICC) e a proporção de câncer como causa de morte em portadores de DMJ/SCA3 sintomáticos observados e nos controles. Métodos: Indivíduos com DMJ/SCA3 pertencentes ao Rio Grande do Sul em uma coorte de 2000 a 2015 foram identificados. Entrevistas estruturadas foram feitas com indivíduos afetados e com controles não relacionados. A CIC conforme publicado pelo Instituto Nacional de Câncer (INCA), do Brasil, foi usado como um controle populacional. As causas de morte entre as famílias com DMJ/SCA3 e controles não relacionados pareados também foram obtidos pelo Sistema de Informações sobre Mortalidade Pública. Foram entrevistados 154 pacientes com DMJ/SCA3 e 80 controles não relacionados: Resultados: A CIC foi de 7/154 (4,5%) e 5/80 (6,3%) entre DMJ/SCA3 e nos indivíduos controles não relacionados, respectivamente. Para obter uma redução do risco absoluto de 1,8 entre os casos e controles, seriam necessários 1.938 indivíduos por grupo para detectar uma diferença significativa entre os grupos. A população total de sintomáticos com DMJ/SCA3 igualou-se a 625 indivíduos em 2015, esse estudo foi interrompido. O câncer foi a causa da morte em 9/101 (8,9%) DMJ/SCA3 e em 52/202 (26,2%) controles, com uma redução do risco absoluto de 17,3% no grupo DMJ/SCA3 (χ² = 12,421; p = 0,001 ; OR 0,27, IC 95% 0,13-0,58). Indivíduos com DMJ/SCA3 que morreram de câncer eram mais velhos e tinham uma menor CAGexp que os casos que faleceram de outras causas.Discussão: Devido à raridade da DMJ/SCA3, estudos de CIC em indivíduos vivos com poder estatístico são inviáveis. No entanto, uma redução significativa de câncer como uma causa de morte foi detectada em DMJ/SCA3. Estes dados confirmam a associação de polyQ com proteção contra o câncer e sugerem que polyQ de fato são doenças de multissistemas. / Introduction: Machado-Joseph disease, also known as Spinocerebellar Ataxia type 3 (MJD/SCA3), is an adult-onset autosomal dominant neurodegenerative disease caused by an expanded CAG repeat in the ATXN3 gene. MJD/SCA3 belongs to the so-called group of polyglutamine disorders (PolyQ). Reduced risk of câncer in individuals with PolyQ such as Huntington disease was previously reported in different population. No study searching for this association in MJD/SCA3 was already performed. Objectives: We aimed to compare the 15 years cumulative incidence of câncer (ICC) and the proportion of câncer as a cause of death in symptomatic SCA3/MJD carriers with those observed in controls. Methods: SCA3/MJD individuals belonging to the Rio Grande do Sul cohort from 2000 to 2015 were identified. A structured interview was done with affected individuals and with unrelated controls. CIC as published by the National Institute of Câncer (INCA), Brazil, was used as a population control. Causes of death among SCA3/MJD families and paired unrelated controls were also obtained from the Public Information System on Mortality. Results: 154 SCA3/MJD patients and 80 unrelated controls were interviewed. CIC were 7/154 (4.5%) and 5/80 (6.3%) among SCA3/MJD and unrelated control individuals, respectively. For an absolute risk reduction of 1.8 between cases and controls, 1,938 individuals per group would be needed to detect a significant difference between groups. Since the total symptomatic SCA3/MJD population equaled 625 individuals in 2015, this study was interrupted. Câncer was a cause of death in 9/101 (8.9%) SCA3/MJD and in 52/202 (26.2%) controls, with an absolute reduction risk of 17.3% in the SCA3/MJD group (χ²=12.421; p=0.001; OR 0.27, IC95% 0.13 to 0.58). SCA3/MJD individuals who died from câncer were older and carried shorter CAGexp than those SCA3/MJD cases who died from other causes. Discussion: Due to the rarity of SCA3/MJD, CIC studies in living individuals with statistical power are unfeasible. However, a significant reduction of câncer as a cause of death was detected in SCA3/MJD. This data confirm the association of PolyQ with protection against câncer and suggest that PolyQ are indeed multisystem disorders.

Les maladies à polyglutamines (polyQ) sont des maladies neurodégénératives héréditaires dominantes causées par une expansion de CAG traduite en longue expansion de polyglutamine dans la protéine correspondante. Ces maladies comprennent l’ataxie spinocérébélleuse 7 (SCA7) et la maladie de Huntington (MH) causées par une expansion de polyQ dans les protéines ataxine-7 (ATXN7) et huntingtine (htt), respectivement. Les souris SCA7 et MH développent des rétinopathies similaires suggérant des pathomécanismes communs toujours inexpliqués. Durant ma thèse, j’ai trouvé qu’en réponse à la toxicité des polyQ, les photorécépteurs (PR) perdent leur différenciation alors que d’autres migrent ou meurent. De plus, cette mortalité cellulaire active la prolifération des cellules gliales de Müller et leur différenciation en PR. Récemment, j’ai trouvé que l’ATXN7 et la htt se trouvent dans le cil primaire et leur mutation mène à une perte des protéines endogènes des cils associée à des défauts du cil. / Polyglutamine (polyQ) disorders are dominantly inherited neurodegenerative disorders caused by the expansion of CAG repeats translated into long polyQ tracts in the corresponding proteins. These diseases include Spinocerebellar ataxia 7(SCA7) and Huntington’s Disease (HD), caused by polyQ expansion ataxin-7 (ATXN7) and huntingtin (htt), respectively. SCA7 and HD mouse models develop similar retinopathies suggesting common pathomechanisms. In my thesis, I found that, in response to polyQ toxicity, SCA7 photoreceptors (PR) undergo several cell fates ranging from their deconstruction, to their migration and their death. Moreover, this cell death activates the proliferation of Müller glial cells and their differentiation into PR like cells. The pathomechanisms underlying HD and SCA7 are still unknown. Recently, I found that ATXN7 and htt are localized to the PR cilia and that the mutant proteins lead to a progressive loss of the wild-type proteins that correlates with defects in the PR cilia.

L’ataxie spinocérébelleuse de type 7 (SCA7) est une maladie neurodégénérative à transmission autosomale dominante, causée par une expansion toxique de polyglutamine (polyQ) dans la protéine Ataxine-7. Elle se caractérise par une dégénérescence des photorécepteurs en cônes et en bâtonnets, ainsi que des cellules cérébelleuses de Purkinje et granuleuses. La nature sélective de cette dégénérescence reste peu claire, l’expression d’Ataxine-7 étant ubiquitaire. Dans ce contexte, nous avons exploré la fonction de l’orthologue d’Ataxine-7 chez le poisson-zèbre au cours du développement de l’œil. L’inactivation d’atxn7 chez le poisson-zèbre – par des approches utilisant des oligonucléotides anti-sens ou par CRISPR/Cas9 – résulte principalement en un colobome, malformation structurelle de l’œil causée par un défaut de fermeture de la fissure choroïde. Les morphants atxn7 présentent une altération du motif proximo-distal de la vésicule optique causée par une élévation de la signalisation Hedgehog (Hh). Une étude minutieuse des photorécepteurs révèle un défaut de la morphogénèse des segments externes. La sensibilité de l’œil aux variations de fonction d’atxn7 pourrait expliquer la phyiopathologie SCA7. Notre étude suggère également qu’une perte de fonction d’atxn7 contribuerait au développement du colobome chez l’Homme. / Spinocerebellar ataxia type 7 (SCA7) is an autosomal-dominant neurodegenerative disorder caused by a toxic polyglutamine (polyQ) expansion in Ataxin-7 which leads to degeneration of cone and rod photoreceptors. The selective nature of degeneration remains unclear since Ataxin-7 is ubiquitously expressed. Here, we have explored the function of the Ataxin-7 ortholog in zebrafish during eye development. Inactivation of atxn7 in zebrafish primarily resulted in a coloboma defect, a structural malformation of the eye caused by failure of the choroid fissure to close. atxn7 morphants displayed altered proximo-distal patterning of the optic vesicle, caused by elevated Hedgehog (Hh) signaling. Careful examination of the photoreceptors reveals a defect in the morphogenesis of the outer segments. The eye sensitivity to variations in atxn7 function could account for SCA7 physiopathology. Our study also suggests that atxn7 loss of function may contribute to the development of human coloboma.

For many dominant diseases, conventional treatment options are limited. This makes them attractive candidates for gene therapy, which may be directed to specifically silence a disease-causing allele. However, many mutations are not easily amenable to this technique, including nucleotide repeat expansions, which cause numerous neurodegenerative diseases such as Huntington’s disease and several Spinocerebellar Ataxias. Combined gene knockdown and replacement (K&R) may present a more practical approach for such conditions, whereby the gene of interest is subject to mutation-independent non-allele-specific silencing and concurrently replaced with a functional copy. Artificial mimics of naturally occurring intronic microRNAs are theoretically ideal for this purpose, since they can be nested within the replacement gene. This thesis investigates the development of mimics of two different intronic miRNA systems (mirtron miR-1224 and the miR-106b cluster) to silence Ataxin-7 and to be incorporated into novel single K&R constructs for testing in vitro. Artificial mirtrons and intronic miRNAs were successfully developed and shown to silence Ataxin-7 mRNA in numerous cell lines. An RNAi-resistant gene was developed and mirtrons could be successfully incorporated as introns. Patient-derived fibroblasts and iPSC-derived neuronal cells were investigated as models for testing of gene silencing therapies. This work suggests that mirtron-based K&R is achievable, and warrants further investigation.