DNA Damage Response Pathways in Meiotic Sex Chromosome Inactivation

描述（申请人提供）：本项目旨在阐明生殖细胞表观遗传编程的机制，重点研究DNA损伤反应途径在性染色体失活中的作用。生殖细胞能够进行独特的表观遗传编程，这是有性生殖所必需的。更好地了解生殖细胞的表观遗传程序将阐明不育和出生缺陷背后的各种生殖问题。当生殖细胞进行雄性减数分裂产生单倍体精子时，X和Y染色体经历了一个不同于常染色体的独特的表观遗传程序。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）的过程中被表观遗传沉默。整个X和Y染色体形成一个染色质结构域，称为XY体，与常染色体区域不同。XY体被各种染色体范围的表观遗传修饰所标记，这些修饰可能维持了MSCI。我的博士后工作揭示了性染色体失活在减数分裂后仍能维持，并涉及精子发生和下一代胚胎发育的表观遗传。在这个提议中，我们的目的是剖析性染色体表观遗传沉默的分子基础。性染色体的表观遗传沉默与DNA损伤反应（DDR）途径相关成分之间存在有趣的联系。细胞学证据表明，在MSCI发病时，参与DDR通路的各种成分在X和Y上积累。基于我们对DDR通路缺陷小鼠模型的初步研究，我们假设DDR通路适合于启动和维持生殖细胞中性染色体的全染色体沉默。我们将通过以下方式研究DDR通路在MSCI中的作用：（目的1）确定染色体范围沉默是如何启动的；（目的2）剖析协调潜在下游途径的遗传途径；（目标3）确定性染色体上的表观遗传修饰是如何建立以维持失活的。在生殖细胞中提出的研究将潜在地揭示DDR通路和表观遗传编程之间的联系，这种联系可以推广到体细胞。公共卫生相关性：在拟议的研究中，小鼠模型表现出雄性生殖失败，表明该研究将确定与雄性不育相关的机制。由于生殖细胞的表观遗传缺陷可能影响胚胎发育，因此提出的研究与出生缺陷的原因具有重要的相关性。此外，确定男性减数分裂期间性染色体的表观遗传沉默的步骤将导致对性连锁非整倍体的遗传原因的理解，这导致了特纳综合征（XO）和Klinefelter综合征（XXY）。

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. PUBLIC HEALTH RELEVANCE: The mouse models in the proposed study exhibit male reproductive failure, indicating this research will identify mechanisms associated with male infertility. Because epigenetic defects in germ cells may affect embryonic development, the proposed study has significant relevance to the causes of birth defects. Also, identifying steps involved in the epigenetic silencing of sex chromosomes during male meiosis will lead to an understanding of the genetic cause of sex-linked aneuploidy, which results in Turner syndrome (XO) and Klinefelter's syndrome (XXY). PUBLIC HEALTH RELEVANCE: Epigenetic programming in germ cells is required for mammalian reproduction. We aim to investigate this process by dissecting the molecular mechanisms underlying sex chromosome inactivation. Our central hypothesis is that DNA damage response pathways are adapted to initiate and maintain epigenetic silencing on sex chromosomes. The mouse models in the proposed study exhibit male reproductive failure, indicating this research will identify mechanisms associated with male infertility.