MSBR1在减数分裂特异DSB修复中的募集及作用机制研究

Meiosis is a specialized cell division to generate haploid gametes in organisms with sexual reproduction. The recognition，pairing, synapsis and recombination between homologous chromosomes is the basic feature of meiosis, which is based on the formation and repair of programmed DNA double-strand breaks (DSBs). The progression of DSB repair include 5’ –end resection, ssDNA protection by meiosis specific RPA complex, the substitution of RPA complex with RAD51/DMC1 mediated by BRCA2, the single-strand invasion mediated by RAD51/DMC1 as well as the procession of DSB repair intermediates into crossovers or non-crossovers. Among all these progressions, the substitution of RPA complex with RAD51/DMC1 mediated by BRCA2 serves as a precondition for DSB repair. In our former research, we found MSBR1, a protein highly expressed in testes, interacts with BRCA2. Further experiments also showed that MSBR1 interacts with MEIOB, a component of meiosis specific RPA complex. We then made Msbr1 mutant mice and found MSBR1 is essential for the recruitment of RAD51/DMC1 in spermatocytes. In this program, we will further explore the mechanism of MSBR1 recruitment and function based on its interaction with BRCA2 and MEIOB，which will provide us new sights into the understanding of regulatory mechanism under meiotic recombination.

减数分裂是有性生殖生物配子发生的必需过程，而减数分裂前期程序性DNA双链断裂（DSB）的产生和修复是减数分裂正常进行的基础。BRCA2介导的重组蛋白RAD51/DMC1对RPA复合物的取代是程序性DSB正常修复的前提。在前期研究中，我们发现睾丸高表达蛋白MSBR1可以和BRCA2以及减数分裂特异的RPA复合物中的MEIOB互作，MSBR1 C端缺失小鼠（Msbr1 m/m）精母细胞中RAD51/DMC1不能募集。本项目将从MSBR1与BRCA2和MEIOB的互作入手，研究MSBR1如何在减数分裂中被募集到DSB位点，以及MSBR1如何减数分裂特异地募集RAD51/DMC1，以期阐明MSBR1在减数分裂重组中的作用和机制，为深入理解减数分裂重组调控提供新思维。

减数分裂是有性生殖生物配子发生的必需过程，而减数分裂前期程序性DNA双链断裂（DSB）的产生和修复是减数分裂正常进行的基础。BRCA2介导的重组蛋白RAD51/DMC1对RPA复合物的取代是程序性DSB正常修复的前提。在前期工作中，我们发现睾丸高表达蛋白MSBR1和RPA complex共定位且募集RAD51和DMC1. 因此，在本项目中，我们对MSBR1的募集和作用机制进行了探索，发现MSBR1通过与SPATA22的互作被募集。酵母双杂交结果显示，MSBR1可以通过其N端和SPATA22互作，其中间部分和C端则是与MEIOB和BRCA2互作所必须的。通过制作MSBR1 C末端截短突变的小鼠，我们发现，在仅保留与SPATA22互作的情况下，MSBR1依然可以被募集，但是不能发挥功能。而在MEIOB敲除小鼠中对MSBR1进行染色显示，在MEIOB和SPATA22不能被募集的情况下，MSBR1同样不能被募集到DSB位点。以上结果提示：MSBR1通过和SPATA22互作被募集到DSB位点。考虑到MEIOB敲除小鼠中，RAD51与DMC1可以正常募集，我们的结果提示：MEIOB和SPATA22的存在抑制了BRCA2介导的RAD51和DMC1对RPA complex的取代，而MSBR1则帮助了MEIOB和SPATA22被替换。