DNA Damage Response Pathways in Meiotic Sex Chromosome Inactivation

描述(申请人提供)：这个项目的目标是阐明生殖细胞中表观遗传编程的机制，特别是DNA损伤反应通路在性染色体失活中的作用。生殖细胞能够进行独特的表观遗传编程，这是有性繁殖所必需的。更好地理解生殖细胞的表观遗传程序将阐明不孕不育和出生缺陷背后的各种生殖问题。当生殖细胞经过雄性减数分裂产生单倍体精子时，X和Y染色体经历不同于常染色体的不同的表观遗传程序。在减数分裂的粗线期，X和Y上的基因在一个称为减数分裂性染色体失活(MSCI)的过程中表观遗传沉默。整个X和Y染色体形成一个染色质结构域，称为XY小体，它不同于常染色体区域。XY小体以各种染色体范围的表观遗传修饰为标志，推测这可能维持了MSCI。我的博士后工作揭示，性染色体失活即使在减数分裂后仍保持不变，这与精子发生和下一代胚胎发育有关。在这项建议中，我们旨在剖析性染色体表观遗传沉默的分子基础。在性染色体的表观遗传沉默和参与DNA损伤反应(DDR)途径的成分之间存在着有趣的联系。细胞学证据表明，在MSCI开始时，参与DDR通路的各种成分在X和Y处积聚。基于我们使用DDR通路缺陷小鼠模型的初步研究，我们假设DDR通路适用于启动和维持生殖细胞性染色体的染色体范围内的沉默。我们将通过以下几个方面研究DDR通路在MSCI中的作用：(目的1)确定如何启动整个染色体范围的沉默；(目的2)剖析协调潜在下游通路的遗传途径；(目的3)确定如何建立性染色体的表观遗传修饰以维持失活。这项拟议的生殖细胞研究可能会揭示DDR途径和表观遗传编程之间的联系，这一联系可以推广到体细胞。

DESCRIPTION (provided by applicant): The goal of this project is to elucidate the mechanism of epigenetic programming in germ cells, especially focusing on the roles of DNA damage response pathways in sex chromosome inactivation. Germ cells are capable of unique epigenetic programming which is required for sexual reproduction. A better understanding of the epigenetic program in germ cells will illuminate various reproductive issues underlying infertility and birth defects. When germ cells undergo male meiosis to generate haploid sperm, X and Y chromosomes go through a distinct epigenetic program different from autosomes. At the pachytene stage of meiosis, the genes on the X and Y are epigenetically silenced in a process called meiotic sex chromosome inactivation (MSCI). The entire X and Y chromosomes form a chromatin domain, known as the XY body, which is distinct from autosome regions. The XY body is marked by various chromosome-wide epigenetic modifications, which presumably maintain MSCI. My postdoctoral work revealed that sex chromosome inactivation is maintained even after meiosis, and implicated epigenetic inheritance in spermiogenesis and the embryonic development of the next generation. In this proposal, we aim to dissect the molecular basis of epigenetic silencing of sex chromosomes. An intriguing link between epigenetic silencing of sex chromosomes and components involved in DNA damage response (DDR) pathways has been suggested. Cytological evidence shows that various components involved in DDR pathways accumulate on the X and Y at the onset of MSCI. Based on our preliminary studies using mouse models defective for DDR pathways, we hypothesize that DDR pathways are adapted to initiate and maintain chromosome-wide silencing of sex chromosomes in germ cells. We will investigate the role of DDR pathways in MSCI by: (Aim 1) determining how chromosome-wide silencing is initiated; (Aim 2) dissecting the genetic pathways that coordinate potential downstream pathways; and (Aim 3) determining how epigenetic modifications on sex chromosomes are established to maintain inactivation. The proposed study in germ cells will potentially reveal a link between DDR pathways and epigenetic programming that can be generalized to somatic cells.