DNA Damage Response Pathways in Meiotic Sex Chromosome Inactivation

描述（由申请人提供）：本项目的目标是阐明生殖细胞中表观遗传编程的机制，特别关注DNA损伤反应途径在性染色体失活中的作用。生殖细胞能够进行有性生殖所需的独特的表观遗传编程。更好地了解生殖细胞中的表观遗传程序将阐明不孕症和出生缺陷背后的各种生殖问题。当生殖细胞经历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独特表观遗传程序。在减数分裂的粗线期阶段，X和Y上的基因在称为减数分裂性染色体失活（MSCI）的过程中被表观遗传学沉默。整个X和Y染色体形成一个染色质结构域，称为XY体，与常染色体区域不同。XY体以各种染色体范围的表观遗传修饰为标志，推测这些修饰维持了MSCI。我的博士后工作揭示了性染色体失活甚至在减数分裂后仍保持不变，并涉及精子发生和下一代胚胎发育中的表观遗传。在这个建议中，我们的目标是剖析性染色体的表观遗传沉默的分子基础。性染色体的表观遗传沉默与参与DNA损伤反应（DDR）途径的成分之间存在有趣的联系。细胞学证据显示，在MSCT开始时，DDR途径中涉及的各种组分在X和Y上积累。基于我们使用DDR途径缺陷的小鼠模型的初步研究，我们假设DDR途径适于启动和维持生殖细胞中性染色体的染色体范围沉默。我们将通过以下方式研究DDR途径在MSCI中的作用：（目的1）确定如何启动染色体范围的沉默;（目的2）解剖协调潜在下游途径的遗传途径;（目的3）确定如何建立性染色体上的表观遗传修饰以维持失活。在生殖细胞中进行的拟议研究将可能揭示DDR途径与可推广到体细胞的表观遗传编程之间的联系。

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.