Mechanism and regulation of meiotic recombination

 描述(由申请人提供)：减数分裂期间的同源重组对生殖系基因组的完整性是必不可少的，但也是基因组多样性、进化和(当错误发生时)不稳定性的强大决定因素。减数分裂重组是由Spo11蛋白引起的双链断裂(DSB)启动的。双链断裂对成功的减数分裂很重要，但也是危险的病变，可以变异或杀死，因此细胞确保只在正确的时间、地点和数量制造双链断裂。DSB处理和重组也受到控制，以最大限度地提高修复效率，并将有害结果的风险降至最低。生殖生物学和基因组完整性的一个基本问题是了解DSB形成的分子机制和 规范DSB和重组。老鼠和萌芽酵母将被用来探索染色体生物学的这些关键方面。具体的调查领域包括：*最近的工作发现了一个复杂的电路网络，它控制着DSB的数量、定时和分布。一个重要的回路涉及依赖于DSB的DNA损伤反应激酶ATM的激活，它反馈抑制额外的断裂形成。第二个不同的反馈电路在同源染色体彼此成功接合的地方抑制DSB的形成。这个网络的轮廓只能用粗略的笔画来理解；现在的一个重要挑战是定义详细的机制和不同调控电路之间的相互作用。DSB的非随机分布对遗传性和基因组进化有重要影响，但影响DSB格局的因素仍然知之甚少。这种基本信息的缺乏将被用最近开发的以核苷酸分辨率绘制全基因组DSB分布的强大方法来修饰。DSB末端必须由核酸外切酶处理才能进行重组，但人们对其机制知之甚少。一种新的用于DSB切除的全基因组分析已经被设计出来，它将允许对这一重要但未被研究的重组方面进行前所未有的探索。重复序列的分散拷贝之间的重组是生殖系突变的一个重要来源。现在的重要挑战是了解这种非等位基因同源重组的机制，并了解细胞利用哪些途径将这种风险降至最低。性染色体分离在哺乳动物雄性减数分裂中尤其令人担忧，因为X和Y染色体只共享一个小的同源区域(伪常染色体区域，或PAR)，在这个区域内必须发生重组。PAR重组缺陷会导致不育或性染色体错误分离。关键问题将涉及PAR和精母细胞的属性，以确保性染色体分离的保真度。

 DESCRIPTION (provided by applicant): Homologous recombination during meiosis is essential for genome integrity in the germ line, but is also a powerful determinant of genome diversity, evolution, and (when mistakes occur) instability. Meiotic recombination is initiated by double-strand breaks (DSBs) made by the Spo11 protein. DSBs are important for successful meiosis, but are also dangerous lesions that can mutate or kill, so cells ensure that DSBs are made only at the right times, places, and amounts. DSB processing and recombination are also controlled to maximize repair efficiency and minimize risks of deleterious outcomes. A fundamental problem in reproductive biology and genome integrity is to understand the molecular mechanisms of DSB formation and of the processes that regulate DSBs and recombination. Mouse and the budding yeast S. cerevisiae will be used to explore these critical aspects of chromosome biology. Specific areas of inquiry include the following: * Recent work uncovered a complex network of circuits that control the number, timing, and distribution of DSBs. One important circuit involves DSB-dependent activation of the DNA damage-response kinase ATM, which feeds back to inhibit additional break formation. A second, distinct feedback circuit suppresses DSB formation in places where homologous chromosomes have successfully engaged one another. The outlines of this network are understood in only broad strokes; an important challenge now is to define detailed mechanisms and interactions between different regulatory circuits. The nonrandom distribution of DSBs has important consequences for heritability and genome evolution, but factors shaping the DSB landscape remain poorly understood. This lack of essential information will be ad- dressed using powerful methods that were recently developed to map DSB distributions genome-wide at nucleotide resolution. DSB ends must be processed by exonucleases to allow recombination, but little is known about the mechanism. A novel whole-genome assay for DSB resection has been devised that will permit unprecedented exploration of this important, but understudied, aspect of recombination. Recombination between dispersed copies of repetitive sequences is a potent source of germ line mutations. Important challenges now are to understand the mechanisms of this non-allelic homologous recombination and to understand the pathways cells exploit to minimize this risk. Sex chromosome segregation is particularly fraught in mammalian male meiosis because the X and Y chromosomes share only a small region of homology (the pseudoautosomal region, or PAR) within which re- combination must occur. Defects in PAR recombination cause sterility or sex chromosome missegregation. Key questions will be addressed concerning the properties of the PAR and of spermatocytes that ensure the fidelity of sex chromosome segregation.