Role of epigenetic crosstalks in directing locus sensitivity to arsenic

项目摘要 本申请中提出的研究的首要目标是了解是什么使一些 基因座比其他基因座更易受环境化学扰动的影响。使用无机砷 (iAs)作为一种与人类高度相关的模式环境毒物，我们将寻求机械地研究 表观遗传串扰如何决定基因座对砷的敏感性。 iAs是一种典型的表观遗传毒物，因为它对整体DNA低甲基化的影响已得到充分描述 与用于DNA和组蛋白的通用甲基供体SAM的水平降低相一致 甲基化然而，这种iAs表观遗传机制的模型在很大程度上被认为是 这是不令人满意的，因为（1）即使在整体DNA低甲基化的背景下，一些基因座也显示出高甲基化 而其他组蛋白甲基化没有变化;（2）对组蛋白甲基化的影响是不均匀的， 组蛋白标记显示增加，而其他标记显示减少。在这里，我们建议建立在令人信服的基础上， 通过高定量质谱和代谢组学研究获得的初步数据表明， 小鼠胚胎干细胞，在亚砷酸钠不会引起ROS水平显著增加的水平下， SAM、DNA甲基化和几种组蛋白标记（如H3 K36 me 2/3）的显著减少， 观察然而，H3 K27 me 3水平增加，而H3 K9 me 3水平不变。此外，委员会认为， RNA-seq研究显示，即使在深刻的转录变化的背景下， 沉积抑制的H3 K9 me 3在亚砷酸钠暴露后仍然保持转录沉默。 因此，我们假设，表观遗传串扰可以差异竞争减少SAM池 由iAs暴露引起，从而驱动轨迹敏感性。 为了检验这一假设，我们将使用小鼠胚胎干细胞，其中串扰得到很好的表征。在目标1中， 表征DNA甲基化和3种不同组蛋白PTM的全基因组变化。我们还将测试 这些由iAs引起的表观遗传改变是否需要砷的代谢活性 甲基转移酶AS 3 MT。在aim 2中，我们将使用敲除，过表达和分析的组合 在砷暴露的背景下，机械地询问表征良好的 在不同的基因组位点，DNA甲基化和组蛋白PTM之间的串扰。最后，在目标3中，我们将 研究砷诱导的表观遗传改变的可重编程性，因为ESCs分化为早期 阶段生殖细胞并经历深刻的表观遗传重塑。 在完成这些目标时，我们将建立DNA变化的全面概况 甲基化和4组蛋白PTM。我们还将确定表观遗传学 crosstalk介导基因座对砷的特异性敏感性及其在PGCs中重编程的能力。这项工作 将坚定地确立表观遗传串扰在应对环境侮辱中的核心作用。

PROJECT SUMMARY The overarching goal of the research presented in this application is to understand what make some genomic loci more susceptible than others to environmental chemical perturbation. Using inorganic arsenic (iAs) as a model environmental toxicant of high human relevance, we will seek to mechanistically investigate how epigenetic crosstalks dictate locus-specific sensitivity to arsenic. iAs is a model epigenetic toxicant owing to its well described impact on global DNA hypomethylation coinciding with a reduction in the levels of the universal methyl donor SAM, used towards DNA and histone methylation. However, this model of epigenetic mechanism of iAs has been acknowledged as largely unsatisfactory since (1) even in the context of global DNA hypomethylation, some loci show hypermethylation while others show no change, and (2) the effect on histone methylation are non-uniform with many methylated histone marks showing increases while others show a decrease. Here, we propose to build on compelling preliminary data obtained through highly quantitative Mass Spec and metabolomic studies that show that in mouse ESCs, at levels where sodium arsenite does not cause a significant increase in ROS levels, a pronounced decrease in SAM, DNA methylation, and in several histone marks, such as H3K36me2/3, are observed. However, H3K27me3 levels are increased while H3K9me3 levels are unchanged. Furthermore, RNA-seq studies revealed even in the context of profound transcriptional changes, repetitive elements that are repressed by deposition of H3K9me3 remain transcriptionally silenced following sodium arsenite exposure. Thus, we hypothesize that epigenetic crosstalks can differentially compete for the reduced SAM pool caused by iAs exposure, thereby driving locus sensitivity. To test this hypothesis, we will use mouse ESCs where crosstalks are well characterized. In aim 1, we will characterize the genome-wide changes in DNA methylation and in 3 distinct histone PTMs. We will also test whether these epigenetic alterations caused by iAs require the metabolic activity of the arsenic methyltransferase AS3MT. In aim 2, we will use a combination of knock-down, over-expression, and profiling approaches to mechanistically interrogate in the context of arsenic exposure the role of the well-characterized crosstalks between DNA methylation and histone PTMs at distinct genomic loci. Finally, in aim 3, we will examine the reprogrammability of arsenic-induced epigenetic alterations as ESCs are differentiated into early stage germ cells and go through profound waves of epigenetic remodeling. At the completion of these aims, we will have established the comprehensive profile of changes in DNA methylation and 4 histone PTMs following arsenic exposure. We will also have determined how epigenetic crosstalks mediate locus-specific sensitivity to arsenic and their ability to be reprogrammed in PGCs. This work will firmly establish the central role of epigenetic crosstalks in the response to environmental insults.