Second-site genetic modifiers of CTG/CAG microsatellite stability

描述（由申请人提供）： 简单DNA序列重复（DNA微卫星）的基因组不稳定性是30多种人类神经系统疾病的原因。在强直性肌营养不良1型（DM 1）（一种在其他器官中具有多种表型的骨骼肌的常染色体显性疾病）的情况下，疾病的分子触发因素是DMPK基因的3' UTR中CTG/CAG三核苷酸重复序列的数量增加。显著增加的CTG/CAG拷贝数可以在代际上发生，或者更适度的扩增可以在整个生命中在体细胞上发生，并且在组织之间存在显著差异。CTG/CAG扩增的程度与疾病严重程度的增加和症状发作的早期年龄有关，但DM 1的表达率变化很大。这表明，其他遗传位点（第二个网站的基因）显着影响的稳定性CTG/CAG重复反式。本项目的目标是表征第二个网站的基因，有助于CTG/CAG微卫星不稳定性。我们将采用候选基因的方法来实现本研究的目的：（i）通过shRNA敲除、小池PCR和PAGE技术来鉴定DMPK（CTG/CAG）重复序列不稳定性所需的基因;（ii）确定基因敲除对CTG/CAG不稳定性的时间过程和长度依赖性的影响，以及对其他疾病相关微卫星的影响;（iii）鉴定体内CTG/CAG不稳定性的DNA发夹途径。这项工作的长期目标是了解人类CTG/CAG微卫星在体内不稳定性的机制基础，以及第二位点基因表达水平与DM 1表型的相关性。我们已经改造了人培养细胞，其中不同长度的DMPK CTG/CAG微卫星重复DNA已插入在一个独特的染色体位置;该模型测定系统模拟DM 1患者细胞中观察到的CTG/CAG不稳定性。重要的是，我们已经表明，敲低DNA代谢途径中的第二位点基因促进CTG/CAG重复不稳定性。该项目的第一个结果将是编辑一系列基因，其表达水平可用于预测家族或患者特定组织中的CTG/CAG不稳定性。我们还将进行第二位点基因敲除对体内不稳定DNA发夹中间体形成的影响的分子表征，不稳定率，突变前CTG/CAG重复的不稳定性，以及这些遗传修饰剂对其他微卫星稳定性的影响。这些危险因素的临床价值包括难以通过定期筛查预测的散发症状的预后，以及治疗方案的个体化。目前，超过7500名医生和90，000名患者正在使用类似的基因表达水平测试来预测乳腺癌和结肠癌的化疗益处和疾病复发。我们的数据产生到目前为止，使用该检测系统作为传感器的DNA代谢表明，参与CTG/CAG重复不稳定性的基因的鉴定将深入了解基因组稳定性和微卫星扩增在多种神经退行性疾病的基本机制。

DESCRIPTION (provided by applicant): Genomic instability of simple DNA sequence repeats (DNA microsatellites) is the cause of more than 30 human neurological diseases. In the case of myotonic dystrophy type 1 (DM1), an autosomal dominant disease of skeletal muscle with multiple phenotypes in other organs, the molecular trigger of disease is an increase in the number of CTG/CAG trinucleotide repeats in the 3' UTR of the DMPK gene. Dramatically increased CTG/CAG copy numbers can occur intergenerationally, or more modest expansions can occur somatically throughout life and differ substantially between tissues. The extent of CTG/CAG expansion is linked to increased disease severity and earlier age of onset of symptoms, but the penetrance of DM1 varies widely. This suggests that other genetic loci (second site genes) significantly affect the stability of CTG/CAG repeats in trans. The goal of this project is to characterize second site genes that contribute to CTG/CAG microsatellite instability. We will take a candidate gene approach to carry out the Aims of this work: (i) to identify genes required for the instability of DMPK (CTG/CAG) repeats by shRNA knockdown, small pool PCR and PAGE; (ii) to determine the effect of gene knockdown on the time course and length dependence of CTG/CAG instability, and effects on other disease-related microsatellites; (iii) to identify DNA hairpin pathways of CTG/CAG instability in vivo. The long term goals of this work are to understand the mechanistic basis for human CTG/CAG microsatellite instability in vivo, and the correlation of second site gene expression levels with DM1 phenotypes. We have engineered human cultured cells in which different lengths of DMPK CTG/CAG microsatellite repeat DNA have been inserted at a unique chromosomal location; this model assay system mimics the CTG/CAG instability observed in DM1 patient cells. Importantly, we have shown that knockdown of second site genes in DNA metabolic pathways promotes CTG/CAG repeat instability. The first result of this project will be the compilation of a list of genes whose expression levels could be used to predict CTG/CAG instability in a family, or in specific tissues of a patient. We will also perform molecular characterization of the effect of second site gene knockdown on the formation of unstable DNA hairpin intermediates in vivo, the rate of instability, the instability of pre-mutation CTG/CAG repeats, and the effects of these genetic modifiers on the stability of other microsatellites. The clinical value of these risk factors would include the prognosis of sporadic symptoms that are difficult to predict by periodic screening, and the individualization of treatment regimens. Similar tests of gene expression levels are currently in use by more than 7500 physicians and 90,000 patients to predict chemotherapy benefit and disease recurrence in breast and colon cancer. Our data generated thus far using this assay system as a sensor of DNA metabolism show that the identification of genes involved in CTG/CAG repeat instability will give insight into the basic mechanisms of genome stability and microsatellite expansion in multiple neurodegenerative disorders.