Epimutation at the CD4 locus: induction, propagation and repair

描述（由申请人提供）：上皮突变是由短暂暴露于环境因素（如饮食和吸烟）引起的自我维持的染色质畸变，发育中的胚胎特别容易受到影响。生殖细胞诱导的增殖可以遗传给后代，具有深远的临床、生物学和进化意义。上皮突变远比经典的DNA突变更常见，是多种人类疾病的基础。尽管表观突变具有稳定性，但它们在本质上是可逆的，这推动了表观遗传治疗的概念，即利用靶向相关酶的“表观遗传药物”来修复表观突变。目前对表观遗传变异的诱导和繁殖机制知之甚少，且表观遗传药物毒性较大。我们开发了一种新的动物模型来解决这些问题。具体来说，我们已经修改了CD4基因座，以便对其表观遗传状态进行实验操作；CD4是一种抗原辅助受体，表达于CD4 T细胞表面，但在CD8 T细胞中受到抑制。我们发现子宫内CD4位点的短暂激活会破坏CD8 T细胞在随后成年小鼠甚至其后代中的CD4抑制，这表明我们已经成功地诱导了CD4位点的增殖。在这里，我们建议使用该系统来解决诱导和传递细胞增殖的机制，利用CD4调节已被广泛研究的事实。为此，我们将定义CD8细胞中与上皮化相关的染色质缺陷，剖析胎儿发育过程中导致上皮化建立的过程，并表征精子中的染色质缺陷（am1）。此外，我们将测试一种新的策略，用于选择性地修复CD4位点的增殖（目的2）。我们的研究将提供人们期待已久的关于上皮细胞的见解，并为研究和修复上皮细胞建立一个新的范式。

DESCRIPTION (provided by applicant): Epimutations are self-sustaining chromatin aberrations induced by transient exposures to environmental factors such as diet and smoking, with developing embryos particularly susceptible. Epimutations induced in the germ cells can be transmitted to the offspring, which has profound clinical, biological and evolutionary implications. Epimutations are far more common than classical DNA mutations, and underlie diverse human diseases. Despite their stability, epimutations are intrinsically reversible, which has fueled the concept of epigenetic therapy that seeks to repair epimutations using "epigenetic drugs" targeting relevant enzymes. At present, little is known about the mechanisms of induction and propagation of epimutations, and the epigenetic drugs are rather toxic. We have developed a novel animal model to address these problems. Specifically, we have modified the CD4 locus to allow for experimental manipulation of its epigenetic states; CD4 is an antigen coreceptor expressed on the surface of CD4 T cells but repressed in CD8 T cells. We found that transient activation of the CD4 locus in utero destabilizes CD4 repression in CD8 T cells in the ensuing adult mice and even their offspring, indicating that we have successfully induced an epimutation at the CD4 locus. Here we propose to use this system to address the mechanisms of the induction and transmission of an epimutation, taking advantage of the fact that CD4 regulation has been extensively studied. To this end, we will define the chromatin defects associated with the epimutation in CD8 cells, dissect the process leading to the establishment of the epimutation during fetal development, and characterize the chromatin defects in sperm (Am 1). In addition, we will test a novel strategy for selectively repairing the epimutation at the CD4 locus (Aim 2). Our study will provide long-awaited insights into epimutations, and establish a new paradigm for studying and repairing epimutations. PUBLIC HEALTH RELEVANCE: Adverse environmental conditions can stably changes gene functions without mutating DNA, and such changes underlie many human diseases. We will study the mechanisms of this remarkable phenomenon and seek to reverse the aberrant changes using a new approach.)