The roles of Hop2 and Mndl in mouse meiotic homologous recombination

项目总结(见说明)： 同源重组是修复DNA双链断裂的唯一无差错系统。在减数分裂中，同源重组还提供了同源染色体对之间的时间关联，使它们有序地分离到分裂核的相反两极。这对一个基因组的忠实单倍化与非整倍体的产生有直接的影响。事实上，正确的同源染色体分离失败会导致不孕和严重的基于非整倍体的出生缺陷，如唐氏综合症、克林菲尔特综合征、爱德华兹综合征和特纳综合征。在同源重组途径的中心是由普遍存在的RAD51和减数分裂特异的DmCL重组酶催化的链侵袭步骤。重组酶的正常功能需要与辅助蛋白相互作用。我们的中心假设是两个辅助蛋白，Hop2和MNDL，对于哺乳动物减数分裂中同源重组和同源染色体分离的正常进行是必不可少的。这可能部分是由于Hop2和MNDL形成了一种异源二聚体，刺激了DmCL和RAD51促进的链侵袭。在这个提案中，我们将使用遗传学和生物化学的方法来验证这一假说，并解决高等真核生物中关于Mnd1和Hop2的基本问题：Hop2/Mnd1-Dmc1/RAD51合作的结构决定因素是什么，以及MNDL和Hop2何时以及如何调控哺乳动物减数分裂细胞中同源重组的进程？此外，一个重要的目标是确定Hop2本身是否可以作为重组酶发挥作用。如果我们的结果得到证实，我们的结果将使Hop2成为唯一的不依赖于ATP的减数分裂重组酶，并定义一条不同于DmCL和RAD51启动的DSB修复的新途径。通过定义辅助蛋白的作用，我们研究的更广泛的意义是了解同源重组在防止人类同源染色体分离缺陷导致不孕和非整倍体方面的贡献。

PROJECT SUMMARY (See instructions): Homologous recombination is the only error-free system to repair DNA double-strand breaks. In meiosis, homologous recombination also provides temporal association between pairs of homologous chromosomes allowing their orderly segregation to opposite poles of dividing nuclei. This has a direct impact on faithful haploidization of a genome versus generation of aneuploidy. Indeed, failure of proper homologous chromosome segregation leads to infertility and severe aneuploid-based birth defects such as Down, Klinefelter, Edwards and Turner syndromes. At the center of the homologous recombination pathway is the step of strand invasion catalyzed by the ubiquitous Rad51 and the meiotic specific Dmcl recombinases. The proper functions of the recombinases require interaction with accessory proteins. Our central hypothesis is that two accessory proteins, Hop2 and Mndl, are essential for normal progression of homologous recombination and homologous chromosome segregation in mammalian meiosis. In part this may be explained by Hop2 and Mndl forming a heterodimer that stimulates strand invasion promoted by Dmcl and Rad51. In this proposal, we will use genetic and biochemical approaches to test this hypothesis and address fundamental questions about Mnd1 and Hop2 in higher eukaryotes: what are the structural determinants of the Hop2/Mnd1-Dmc1/Rad51 cooperation, and when and how do Mndl and Hop2 regulate the progression of homologous recombination in mammalian meiotic cells? Additionally, an important goal is to determine whether Hop2 by itself can function as a recombinase. If confirmed, our results will position Hop2 as the only ATP-independent meiotic recombinase and define a new pathway of DSB repair distinct from those promoted by Dmcl and Rad51. Through defining the roles of accessory proteins, the broader implication of our studies is to understand the contribution of homologous recombination in preventing homologous chromosome segregation defects leading to infertility and aneuploidy in humans.