Epigenetic control of sex chromosome behavior in meiosis.

描述(申请人提供)：减数分裂是一种特殊类型的细胞分裂，产生用于有性繁殖的单倍体配子。在减数分裂过程中，染色体配对、联会和交换依赖于父本和母本同源染色体之间的同源性，以确保适当的分离和形成具有正确数目的染色体的配子。交叉是由同源重组诱导的双链断裂(DSB)的形成和修复启动的。染色体配对的缺陷扰乱了DSB修复，导致检查点激活，导致细胞凋亡或形成非整倍体配子。在男性中，性染色体主要是半合子的(即，缺乏同源染色体)，这对修复DSB提出了特殊的挑战，而且还提出了逃避检查点激活的挑战。我们的初步结果表明，DSB修复和检查点抑制发生在一种仅在男性X染色体上发现的特殊染色质结构的背景下。我们的总体假设是，性染色体的表观遗传格局和雄性减数分裂的其他方面改变了与DSB修复和检查点机制的相互作用，以确保通过减数分裂准确地传递雄性基因组。为了验证这一假说，我们建议使用秀丽线虫的后生动物模型来阐明男性减数分裂过程中染色体行为的保守机制，该模型特别适合于遗传学、细胞生物学和分子方法。在目标1中，我们将通过对野生型和修复缺陷突变体的减数分裂和工程DSB的修复进行细胞学、分子和功能上的分析，确定在性染色体半合子区域介导DSB修复的途径。在目标2中，我们将通过分析染色质改变的生殖系中DSB加工因子和检查点蛋白对DSB的招募来阐明特定的组蛋白修饰在DSB修复和检查点沉默中的作用。在这里，我们还将探讨染色质、染色质修饰物、DNA修复和检查点蛋白之间的物理相互作用。在目标3中，我们将定义雄性生殖系和雌性生殖系在DSB处理方面的全球差异。总而言之，对这一遗传易控系统中这些过程的理解将为如何修改减数分裂程序以促进成功的雄性减数分裂提供新的和重要的见解。这些研究直接关系到性染色体非整倍体频率的增加与人类减数分裂导致的发育障碍，包括Turner和Klinefelter综合征。重要的是，这些研究还将阐明DNA修复和检查点信号的一般机制，这些机制在监测和维持所有细胞的基因组完整性方面发挥着关键作用。

DESCRIPTION (provided by applicant): Meiosis is a special type of cell division that produces haploid gametes for sexual reproduction. During meiosis, chromosome pairing, synapsis and crossing over rely on homology between the paternal and maternal homologous chromosomes to ensure proper segregation and formation of gametes with the correct number of chromosomes. Crossovers are initiated by the formation and repair of induced double-strand breaks (DSBs) by homologous recombination. Defects in chromosome pairing disrupt DSB repair and result in checkpoint activation, leading to either apoptosis or the formation of aneuploid gametes. In males, sex chromosomes are largely hemizygous (i.e., lack a homologous chromosome), which presents a special challenge to repair DSBs and, moreover, to evade checkpoint activation. Our preliminary results show that DSB repair and checkpoint suppression occur in the context of a specialized chromatin structure found only on the X chromosome of males. Our overall hypothesis is that the epigenetic landscape of sex chromosomes and other aspects of male meiosis alter interactions with DSB repair and checkpoint machinery to ensure accurate transmission of the male genome through meiosis. To test this hypothesis we propose to elucidate the conserved mechanisms underlying chromosome behavior during male meiosis using the metazoan animal model Caenorhabditis elegans, which is particularly amenable to genetic, cell biological and molecular approaches. In Aim 1 we will define the pathways that mediate DSB repair on hemizygous regions of sex chromosomes by analyzing repair of both meiotic and engineered DSBs cytologically, molecularly and functionally in wild type and repair-defective mutants. In Aim 2 we will elucidate the role of specific histone modifications on DSB repair and checkpoint silencing by analyzing the recruitment of DSB processing factors and checkpoint proteins to DSBs in germ lines with altered chromatin. Here we will also probe the physical interactions between chromatin, chromatin modifiers, DNA repair and checkpoint proteins. In Aim 3 we will define global differences in DSB processing in the male versus female germ line. Together, an understanding of these processes in this genetically tractable system will provide novel and important insights into how the meiotic program is modified to promote successful male meiosis. These studies have direct relevance to understanding the increased frequency of sex chromosome aneuploidy associated with human meiosis resulting in developmental disorders including Turner and Klinefelter's Syndromes. Importantly, these studies will also elucidate general mechanisms of DNA repair and checkpoint signaling, which play critical roles in monitoring and maintaining genome integrity in all cells.