Huntington's Disease Repeat Instability and Pathogenesis

描述(由申请人提供)：亨廷顿病(HD)是一种致命的神经退行性疾病，由CAG重复序列的多态扩展超过阈值~36个单位引起。扩大的CAG重复序列被翻译成亨廷顿蛋白氨基末端的聚谷氨酰胺延伸，引发纹状体和皮质中神经元的子集细胞死亡。扩增的CAG重复序列在生殖系和体细胞组织中也表现出极大的不稳定性。这项研究的长期目标是阐明HD CAG重复序列不稳定的分子途径以及由突变的Huntingtin引发的特异性神经退行性变。在HD敲入小鼠中，Msh2基因是重复不稳定的修饰物和早期纹状体的表型，它准确地概括了人类HD突变。在这项研究中，我们将检验Msh2在错配修复途径中作用的假设，以改变HD敲入小鼠的CAG重复不稳定和早期表型。我们将与特定错配修复基因缺失的小鼠和携带Msh2‘S ATPase结构域突变的小鼠进行遗传杂交。这些实验将为Msh2的S在CAG重复不稳定性和突变的HD等位基因的表型表达中所起的作用提供机制方面的见解。为了确定候选DNA修复基因是否是人类HD发病年龄的修饰者，我们将对发病年龄与CAG重复大小预测值相背离的极端个体进行遗传关联研究。为了进一步了解Msh2改变小鼠重复不稳定和早期纹状体疾病的机制，我们将使用Cre-loxP系统产生Msh2基因的条件敲除。我们将使用Camclla驱动的Cre转基因来特异性地灭活前脑神经元中的Msh2，以验证Msh2在纹状体神经元中作用于改变不稳定和早期表型的假设。总之，这些研究将提供对重复不稳定性和发病机制的洞察，导致旨在减缓或阻止这种毁灭性疾病的合理治疗策略。

DESCRIPTION (provided by applicant): Huntington's disease (HD) is a fatal neurodegenerative disorder caused by the expansion of a polymorphic CAG repeat tract beyond a threshold of ~ 36 units. The expanded CAG repeat is translated into a polyglutamine stretch at the amino-terminus of the huntingtin protein, triggering cell death in a subset of neurons in the striatum and cortex. The expanded CAG repeat also exhibits dramatic instability in the germline and in somatic tissues. The long-term goals of this research are to elucidate the molecular pathways that underlie the instability of the HD CAG repeat and the specific neurodegeneration triggered by mutant huntingtin. In HD knock-in mice, which accurately recapitulate the human HD mutation, the Msh2 gene is a modifier of repeat instability and an early striatal phenotype. In this study, we will test the hypothesis that Msh2 acts in the mismatch repair pathway to modify CAG repeat instability and early phenotypes in HD knock-in mice. We will perform genetic crosses with mice deficient in specific mismatch repair genes and mouse line carrying a mutation in Msh2's ATPase domain. These experiments will provide mechanistic insight into Msh2's role in CAG repeat instability and phenotypic expression of the mutant HD allele. To determine whether candidate DNA repair genes are modifiers of the age of onset of HD in humans genetic association studies will be performed using 'extreme' individuals with onset ages deviating from values predicted by CAG repeat size. To gain further insight into the mechanism by which Msh2 modifies repeat instability and early striatal disease in the mouse we will generate a conditional knockout of the Msh2 gene using the Cre-loxP system. We will specifically inactivate Msh2 in forebrain neurons using a Camklla-driven Cre transgene to test the hypothesis that Msh2 acts in striatal neurons to modify instability and early phenotypes. Together, these studies will provide insight into mechanisms of repeat instability and pathogenesis, leading to rational therapeutic strategies aimed at slowing or halting this devastating disease.