The control of meiotic DNA break formation by key chromosome axis components, IHO1 and HORMAD1, in mammals.

单倍体配子的产生需要二倍体生殖细胞的同源染色体（同系物）在减数分裂的第一次分裂期间分离。 同源物的分离需要它们之间的物理联系，这种联系通过交叉发生。杂交是由一个专门的重组过程产生的，该过程始于第一次减数分裂前期DNA双链断裂（DSB）的程序化产生。沿着每条染色体的蛋白质核心/轴沿着产生多个DSB。DSB驱动同源物的配对，这导致同源物之间的突触。DSB的修复也产生同源物间的交叉。鉴于交叉的重要性和DSB的潜在遗传毒性，对DSB的形成进行严格控制。因此，DSB只允许在非突触轴上形成，在那里DSB需要促进同源突触。我们最近的工作确定IHO 1是一种与非突触轴相关的蛋白质，对DSB的形成至关重要。根据我们的模型，IHO 1向轴的募集在很大程度上取决于IHO 1与非突触轴传感器HORMAD 1的相互作用。因此，我们假设IHO 1-HORMAD 1相互作用是限制DSB形成于非突触轴的机制的关键。我们的数据表明，IHO 1-HORMAD 1相互作用的调节和由此产生的IHO 1轴定位的调节有助于抑制DSB形成（1）在突触染色体上，（2）在现有的DSB断裂附近和（3）在同源性搜索终止的晚期前期阶段。因此，IHO 1似乎是保护生殖细胞免于过度DNA断裂形成的机制的核心。我们将测试我们的DSB形成模型和IHO 1在其中的功能，我们将讨论靶向IHO 1的调节机制的分子基础。其中一个主要目的是解决IHO 1-HORMAD 1相互作用和IHO 1轴关联在DSB形成中的重要性。因此，我们使用CRISPR/Cas9来产生具有IHO 1-HORMAD 1相互作用和IHO 1轴关联选择性缺陷的突变IHO 1版本的小鼠。我建议对这些小鼠进行表型分析，并对影响IHO 1和HORMAD 1功能和调节的其他减数分裂突变体进行表型分析。我们将联合收割机与IHO 1的相互作用研究相结合，以更深入地了解IHO 1的功能和调节。拟议的实验将为DSB形成的时空控制的逻辑和分子基础提供重要的新见解。考虑到需要正确控制重组以维持生殖系中的基因组完整性，并且受损的重组会导致人类非整倍性，预期结果将具有与人类生殖健康明显相关的高度影响。

Generation of haploid gametes requires that homologous chromosomes (homologues) of diploid germ cells segregate during the first division of meiosis. Segregation of homologues requires physical links between them, which occur via crossovers. Crossovers are generated by a specialized recombination process that starts with programmed generation of DNA double strand breaks (DSBs) in the first meiotic prophase. Multiple DSBs are generated along the proteinaceous core/axis of each chromosome. DSBs drive the pairing of homologues, which results in synapsis between homologues. The repair of DSBs also generates the inter-homologue crossovers. Given the importance of crossovers and the potential genotoxicity of DSBs, tight control is exerted on DSB formation. Hence, DSBs are allowed to form only on unsynpased axes, where DSBs are needed to promote homologue synapsis. Our recent work identified IHO1 as a protein that associates with unsynapsed axis and is crucial for DSB formation. According to our model, IHO1 recruitment to axes largely depends on IHO1´s interaction with an unsynapsed-axis-sensor, HORMAD1. Thus, we hypothesize that IHO1-HORMAD1 interaction is key to the mechanism that limits DSB formation to unsynapsed axes. Our data suggest that regulation of IHO1-HORMAD1 interaction and the resulting modulation of IHO1 axis-localization contribute to the inhibition of DSB formation (1) on synapsed chromosomes, (2) in the vicinity of existing DSB breaks and (3) in advanced prophase stages where homology search is terminated. Thus, IHO1 appears central to mechanisms that protect the germ line from excessive DNA break formation.We will test our model of DSB formation and IHO1 function within it, and we will address the molecular basis of the regulatory mechanisms that target IHO1. One of the key aims is to address the importance of IHO1-HORMAD1 interaction and IHO1 axis association in DSB formation. Hence, we used CRISPR/Cas9 to generate mice with mutant IHO1 versions that are selectively defective in IHO1-HORMAD1 interaction and IHO1 axis association. I propose phenotypic analysis of these mice and that of additional meiotic mutants affecting IHO1 and HORMAD1 functions and regulation. We will combine this with interaction studies of IHO1 to gain deeper understanding of IHO1 functions and regulation.The proposed experiments will provide major new insights into the logic and the molecular basis of the spatiotemporal control of DSB formation. Given that correct control of recombination is needed to maintain genome integrity in the germ line, and that impaired recombination causes human aneuploidies, the expected results will have high impact with a clear relevance to human reproductive health.