DNA Damage Response Pathways in Meiotic Sex Chromosome Inactivation

摘要 本项目的目的是阐明该蛋白的调节机制和生物学意义。 雄性生殖系中性染色体的表观遗传编程。在男性减数分裂过程中，无突触的性行为 染色体在一种称为减数分裂性染色体失活(MSCI)的过程中表观遗传沉默， 这是精子发生所必需的。在上一笔拨款的有效期内，我们澄清了 MSCI的机制，并证明了DNA损伤反应(DDR)因子的作用是必不可少的 监管者。MSCI的建立需要组蛋白变异体H_2AX(γH_2AX)的磷酸化才能扩散 从性染色体的轴到整个染色体的区域。这一过程由mdc1、 粗线期开始时，γH_2AX的结合伙伴。在MDC1，SCML2下游，一个生殖系- 特定的多梳蛋白，被招募到含有γH_2AX的核小体中，是表观遗传学所必需的 编程。在上一个项目期间，我们意外地发现，MSCI的发起与 活跃的DNA去甲基化。最初，DNA去甲基化是由mdc1指导的，在 静默组蛋白修饰的建立。在此续订申请中，我们将测试以下中心假设 DDR途径调节活跃的DNA去甲基化，使性的表观遗传编程成为可能 雄性生殖所必需的染色体。而DNA甲基化通常与基因有关 沉默，我们认为DNA去甲基化与MSCI中的基因沉默有关。我们的数据表明 MSCI中的去甲基化包括两个主要阶段：初始阶段由DDR途径介导，在 粗线期早期(目标1)和后期由SCML2介导的DDR下游在中期 粗线期(目标2)。本研究将在DDR信号和活性DNA之间建立一种新的联系 去甲基化，并将进一步阐明性别表观遗传编程的生物学意义 染色体，这是男性生殖所必需的。

ABSTRACT The objective of this project is to elucidate the regulatory mechanisms and biological significance of the epigenetic programming of the sex chromosomes in the male germline. During male meiosis, unsynapsed sex chromosomes are epigenetically silenced in a process called meiotic sex chromosome inactivation (MSCI), which is necessary for spermatogenesis. During the term of the previous grant, we elucidated the underlying mechanisms of MSCI and demonstrated the role of DNA damage response (DDR) factors as essential regulators. Establishment of MSCI requires phosphorylation of the histone variant H2AX (γH2AX) to spread from the axes to the chromosome-wide domain of the sex chromosomes. This process is directed by MDC1, a binding partner of γH2AX, at the onset of the pachytene stage. Downstream of MDC1, SCML2, a germline- specific Polycomb protein, is recruited to γH2AX-containing nucleosomes and required for epigenetic programming. During the last project period, we unexpectedly found that initiation of MSCI is tightly coupled to active DNA demethylation. Initially the DNA demethylation is directed by MDC1 and precedes the establishment of silent histone modifications. In this renewal application, we will test the central hypothesis that the DDR pathway regulates active DNA demethylation, enabling the epigenetic programming of sex chromosomes necessary for male reproduction. While DNA methylation is generally associated with gene silencing, we propose that DNA demethylation is linked to gene silencing in MSCI. Our data suggest that demethylation in MSCI involves two major phases: the initial phase is mediated by the DDR pathway at the early pachytene stage (Aim 1) and the later phase is mediated by SCML2 downstream of the DDR at the mid- pachytene stage (Aim 2). This study will establish a novel link between DDR signaling and active DNA demethylation, and will further elucidate the biological significance of the epigenetic programming of the sex chromosomes, which is essential for male reproduction.