Epigenetics of Down Syndrome

更好地了解唐氏综合征（DS; 21三体）的发病机制对于 改善DS患者的生活质量，并了解主要表型，包括智力 残疾，自身免疫，心脏缺陷，阿尔茨海默病，癌症易感性和抵抗力， 在DS中很突出，也与一般人群高度相关。最近我们进行了表观遗传学 分析，重点是DNA甲基化，在灰质和纯化的神经元和神经胶质细胞从尸检的大脑， 以及T淋巴细胞，从个人与DS与匹配的正常对照。我们发现， 甲基化模式（DS-DM）的DS特异性差异，以及观察到的DS-DM的组织特异性， 在胎儿阶段改变的甲基化模式，和改变的mRNA表达（DS-DE），只有一个子集， 受影响的基因。我们发现，在特定类别的转录因子结合位点（TFBS）的CpG是 优先受影响，暗示改变TFBS占用作为形成DS-DM模式的机制。 此外，我们对DS小鼠模型的脑进行了全基因组亚硫酸氢盐测序（WGBS）， 与野生型同窝仔相比，发现甲基化模式的改变， 那些在人类大脑中。受这些发现的启发，我们现在试图回答三个问题-所有使用 携带染色体三倍体的DS的良好对照小鼠模型。首先，要了解分子 我们将在小鼠模型中鉴定DM基因，并确定其中哪些基因具有 差异mRNA表达我们将在纯化的细胞类型中解决这个问题：T细胞和GABA能 神经元第二，我们将测试两个假设的反式作用机制的DS-DM：（i）异常 甲基化是由于甲基化途径基因的过度表达，包括Dnmt 3l和其他基因， 三重染色体区域，和/或（ii）甲基化的异常模式通过过表达形成 在三重区的特定TF基因，导致改变TFBS占用，然后改变CpG 在这些位点内和周围的甲基化。我们将转移片段缺失和/或敲除等位基因， 将单个基因导入DS小鼠模型中以标准化基因剂量，并使用WGBS和表型分析来询问 后代中DM的特定组分和特定表型是否分别受到影响 携带着复合突变第三，我们将应用最先进的基因组分析来询问是否 细胞核内的染色质结构因额外遗传物质的存在而改变， 这种改变是否反过来影响DNA甲基化、基因表达和表型。成功的 该项目将确定DS-DM的效应基因和靶基因，并阐明DS-DM的潜在机制。我们 预计这些数据将大大提高我们对DS发病机制的理解，并具有广泛的应用前景。 在其他人类发育和肿瘤中的反式作用遗传表观遗传相互作用的意义 与染色体非整倍性相关的疾病。

Achieving a better understanding of the pathogenesis of Down syndrome (DS; trisomy 21) is important for improving the quality of life of people with DS and for understanding major phenotypes, including intellectual disability, autoimmunity, cardiac defects, Alzheimer’s disease, and cancer susceptibility and resistance, which are prominent in DS and are also highly relevant to the general population. Recently we carried out epigenetic profiling, focusing on DNA methylation, in grey matter and purified neurons and glial cells from autopsy brains, as well as T-lymphocytes, from individuals with DS vs. matched normal controls. We found highly recurrent DS-specific differences in methylation patterns (DS-DM), and observed tissue-specificity of the DS-DM, onset of the altered methylation patterns at the fetal stage, and altered mRNA expression (DS-DE) of only a subset of the affected genes. We found that CpGs in specific classes of transcription factor binding sites (TFBS) were preferentially affected, implicating altered TFBS occupancy as a mechanism in shaping the patterns of DS-DM. Additionally, we carried out whole genome bisulfite sequencing (WGBS) on brains from mouse models of DS, compared to wild-type littermates, and found alterations in methylation patterns that significantly paralleled those in the human brains. Motivated by these findings, we now seek to answer three questions – all using well-controlled mouse models of DS carrying chromosomal triplications. First, to understand the molecular consequences of DS-DM we will identify DM genes in the mouse models and determine which of them have differential mRNA expression. We will address this question in purified cell types: T cells and GABAergic neurons. Second, we will test two hypotheses for the trans-acting mechanisms of DS-DM: (i) the abnormal methylation is due to over-expression of methylation pathway genes, including Dnmt3l and others, in the triplicated chromosome regions, and/or (ii) the abnormal patterns of methylation are shaped by overexpression of specific TF genes in the triplicated regions, leading to altered TFBS occupancy followed by altered CpG methylation in and around these sites. We will transfer segmental deletions and/or knockout alleles of individual genes into the DS mouse models to normalize gene dosage, and use WGBS and phenotyping to ask whether specific components of the DM and specific phenotypes are affected, respectively, in the offspring carrying the compound mutations. Third, we will apply state-of-the-art genomic assays to ask whether chromatin architecture within the cell nucleus is altered by the presence of the extra genetic material, and whether this alteration in turn affects DNA methylation, gene expression and phenotypes. Success of our project will identify effector and target genes for DS-DM and unravel the mechanisms underlying DS-DM. We expect that these data will significantly improve our understanding of DS pathogenesis and have broad implications for trans-acting genetic epigenetic interactions in other human developmental and neoplastic disorders that are associated with chromosomal aneuploidies.