The functions of a previously uncharacterized meiotic protein, MCMDC2, that is crucial for meiotic recombination and fertility in mouse.

有性繁殖关键依赖于通过减数分裂的特殊细胞分裂过程从二倍体细胞产生单倍体细胞。在减数分裂过程中，染色体的有序分离和倍性的减少需要同源染色体找到彼此，并在第一次减数分裂前期通过交叉形成联系。这项艰巨的任务需要经过特殊修改的同源重组过程，这需要：(1)大量DNA双链断裂的活跃产生，(2)使用所得到的DNA末端进行同源性搜索，以及(3)DNA断裂的修复，优先使用同源染色体而不是姐妹染色单体作为修复模板。尽管进行了广泛的研究，但减数分裂重组的关键问题仍未得到解答。减数分裂和有丝分裂重组之间的关键分子差异是什么？这些差异如何有助于确保即使在大量重复序列丰富的哺乳动物基因组中，同源染色体也能高保真地找到彼此？回答这些问题的一个关键障碍是对减数分裂重组工具包的不完全了解。在一次筛选中，我们确定了一个未知的潜在DNA解旋酶MCMDC2，它在减数分裂中优先表达。重要的是，我们发现MCMDC2对于减数分裂同源性搜索是必不可少的。因此，我建议研究MCMDC2以获得对减数分裂重组的分子基础的新见解。简而言之，涉及McMDC2敲除分析的广泛的小鼠遗传学将被用来定义减数分裂重组中需要MCMDC2的步骤，并检验MCMDC2主要用于同系物间重组而不是姐妹间重组的假设。作为对这一方法的补充，我们将研究MCMDC2相对于其他重组蛋白在野生型和各种减数分裂重组缺陷突变小鼠中的定位和行为。此外，我们将尝试使用生物化学和酵母双杂交试验来定位MCMDC2的S相互作用伙伴。这些方法的结合将使我们能够定义MCMDC2在减数分裂中的生物学功能，并将为未来解决MCMDC2在重组中的机制作用的实验铺平道路。鉴于MCMDC2的重要性，我预计拟议的工作将为减数分裂重组的关键问题提供新的答案，并将大大有助于理解同源染色体如何相互识别，以及如何在生殖系减数分裂过程中保持基因组完整性。关键的减数分裂重组基因是生育和基因组健康的核心，它们的错误表达和突变是一些癌症的促成因素。因此，这项拟议的工作也具有明显的医学意义。

Sexual reproduction crucially depends on the generation of haploid cells from diploid cells by the specialized cell-division process of meiosis. Orderly segregation of chromosomes and the reduction of ploidy during meiosis require that homologous chromosomes find each other and become linked through the formation of crossovers in the first meiotic prophase. This demanding task requires a specially modified homologous recombination process that entails: (1) the active generation of large numbers of DNA double strand breaks, (2) the use of resulting DNA ends for homology search, and (3) the repair of the DNA breaks with the preferential use of homologous chromosomes, as opposed to sister chromatids, as repair templates. Despite extensive research, key questions of meiotic recombination are unanswered. What are the key molecular differences between meiotic and mitotic recombination, and how do these differences help to ensure that homologous chromosomes find each other with high fidelity even in large repeat-rich mammalian genomes?One key impediment to answering these questions has been the incomplete knowledge of the tool-kit of meiotic recombination. In a screen, we identified an uncharacterized potential DNA helicase, MCMDC2, that is preferentially expressed in meiosis. Importantly, we found that MCMDC2 is essential for meiotic homology search. Hence, I propose to study MCMDC2 to gain novel insight into the molecular basis of meiotic recombination.In brief, extensive mouse genetics involving Mcmdc2 knockout analysis will be used to define the steps in meiotic recombination that require MCMDC2, and to test the hypothesis that MCMDC2 is primarily needed for inter-homologue recombination as opposed to inter-sister recombination. Complementing this approach, we will examine the localization and the behaviour of MCMDC2 relative to other recombination proteins both in wild-type and various meiotic recombination defective mutant mice. Additionally, we will attempt to map MCMDC2´s interacting partners using biochemistry and yeast two-hybrid assay. The combination of these approaches will allow us to define the biological function of MCMDC2 in meiosis, and will pave the way for future experiments addressing the mechanistic role of MCMDC2 in recombination. Given the importance of MCMDC2, I expect that the proposed work will provide new answers to key questions of meiotic recombination, and will significantly contribute to the understanding of how homologous chromosomes recognize each other, and how genome integrity is maintained during meiosis in the germline. Key meiotic recombination genes are central to fertility and genome health, and their misexpression and mutations are contributing factors in some cancers. Hence, the proposed work has obvious medical implication too.