Molecular Mechanisms of Genetic Recombination in Mammals

描述(申请人提供)：非整倍体--个体染色体数目错误--是导致人类出生缺陷的主要原因。这是由于配子发生过程中同源染色体(同源染色体)分离错误所致。减数分裂重组保证了适当的分离。它从引入DNA双链断裂(DSB)开始，然后以同源染色体的完整DNA为模板进行修复。这导致了通过交换(CoS)稳定的同系物的时间关联。这种成对的排列确保了同源染色体有序地分离到分裂核的相反两极，从而每个配子接收到每对同源染色体的一个同源。未能配对的同源基因随机分离，有50%的机会进入同一子细胞。伴随着CO的缺失，CO的位置效应也是导致非整倍体的原因之一。重组事件的空间分布在不同的水平上受到控制，定义这种调控的机制对于理解为什么一些事件逃脱这种控制是必要的。我们的长期目标是阐明导致哺乳动物非整倍体的减数分裂错误重组背后的机制。在这项研究中，我们将采用全基因组的方法来确定一氧化碳在小鼠体内的放置机制。(I)通过对小鼠减数分裂染色体的细胞学评估，我们将确定减数分裂DSB的放置是随机的还是显示干扰的，即一个DSB的形成抑制了相邻区域第二个DSB的形成。这将有助于阐明施加CO干扰的机制。(Ii)使用染色质免疫沉淀和直接高通量测序，我们将绘制小鼠基因组中倾向于发生减数分裂双链断裂的区域(减数分裂双链断裂的热点)。重组并不均匀地分布在整个基因组中，定义与重组热点相关的特定特征将为它们形成的机制提供线索。(Iii)我们将采用类似的方法绘制COS减数分裂热点图。对这两个图谱的对比分析将有助于阐明CO形成的途径，以及CO/NCO指定的机制。总体而言，我们的研究结果将阐明CO定位机制的几个重要方面，并将为未来描述减数分裂重组控制机制的研究开辟新的途径。减少或取消重组的突变总是与减数分裂停滞或染色体分离错误有关，从而导致不孕或非整倍体。在制定预防措施和治疗方法之前，有必要了解推动重组的力量。 公共卫生相关性：这项研究的目标是阐明基因重组所涉及的机制。减少或取消重组的突变总是与不孕不育或非整倍体有关，在开发预防措施和治疗方法之前，了解推动重组的力量是必要的。

DESCRIPTION (provided by applicant): Aneuploidy - the wrong number of chromosomes in an individual - is the leading cause of birth defects in humans. It results from errors in the segregation of homologous chromosomes (homologs) during gametogenesis. The proper segregation is ensured by meiotic recombination. It begins with the introduction of DNA double stranded breaks (DSBs) followed by their repair using the intact DNA of a homologous chromosome as a template. This leads to a temporal association of the homologs stabilized by crossing-overs (COs). Such an arrangement into pairs ensures orderly segregation of the homologous chromosomes to the opposite poles of dividing nuclei so that each gamete receives one homolog of each pair. The homologs that fail to pair segregate randomly, and have a 50% chance to go into the same daughter cell. Along with the lack of COs, positional effects of CO placement also contribute to aneuploidy. Spatial distribution of recombination events is controlled at different levels and defining the mechanisms of this regulation is necessary to understand why some of the events escape this control. Our long-term goal is to elucidate the mechanisms behind faulty meiotic recombination resulting in aneuploidy in mammals. In this study we will take a genome-wide approach to define the mechanisms of CO placement in the mouse. (i) By cytological evaluation of the mouse meiotic chromosomes we will determine whether placement of meiotic DSBs is random or displays interference, i.e. the formation of one DSB suppresses the formation of a second one in adjacent regions. This will help to clarify the mechanisms involved in imposition of CO interference. (ii) Using chromatin immunoprecipitation followed by direct high-throughput sequencing we will map the regions of mouse genome where meiotic DSBs tend to occur (hotspots of meiotic DSBs). Recombination is not evenly distributed throughout the genome and defining the particular features associated with recombination hotspots will provide the cues to the mechanism behind their formation. (iii) We will map the hotspots of meiotic COs using the similar approach. Comparative analysis of these two maps will help to elucidate the pathways leading to CO formation, and the mechanisms involved in CO/NCO designation. Overall, the results from our studies will illuminate several important aspects of the mechanisms involved in CO placement, and will also create new avenues for future research in delineating the mechanism of meiotic recombination control. Mutations that reduce or abolish recombination are invariably associated with meiotic arrest or chromosome segregation errors leading to infertility or aneuploidy. Understanding the forces driving recombination is necessary before preventive measures and therapeutic approaches can be developed. PUBLIC HEALTH RELEVANCE: The goal of this study is to elucidate the mechanisms involved in genetic recombination. Mutations that reduce or abolish recombination are invariably associated with infertility or aneuploidy, and understanding the forces driving recombination is necessary before preventive measures and therapeutic approaches can be developed.