Molecular mechanisms of chromosome organization and recombination control by the meiotic chromosome axis

项目总结 真核生物的有性繁殖涉及减数分裂过程中单倍体配子(人类、精子和卵细胞)的产生， 然后两个配子融合产生二倍体后代。在减数分裂中，同源染色体识别一个 另一个通过修改的同源重组DNA修复途径成为物理连接，以及由此产生的 杂交可以在减数分裂I分裂中准确地分离同源基因，以减少倍性。在大多数真核生物中，包括 人类的染色体是由一种被称为染色体的高度保守的结构组成的染色质环阵列 轴心。染色体轴还招募和控制DNA裂解和重组因子，以调节 交叉，并在控制重组水平的关键反馈路径中交叉形成后被重塑。 在这里，我们建议将酿酒酵母和小鼠的生物化学、大分子结构和遗传学结合起来，以 确定染色体轴如何组装、组织染色体和调节交叉形成。我们将首先 酿酒酵母Red1和哺乳动物SYCP2的结构确定：SYCP3，功能相关的染色体轴 我们发现的“基础”蛋白具有保守的结构域结构和自组装成细丝的倾向。 接下来，我们将确定这些蛋白质如何与减数分裂粘连蛋白复合体相互作用，以了解 轴介导的染色体组织。接下来，我们将剖析酿酒酵母Hop1，a介导的相互作用网络。 HORMAD家族中保守的AXIS蛋白家族成员，是减数分裂重组的主要调节者，并研究如何 随着减数分裂前期的进展，这种相互作用网络发生了变化。S最终从染色体轴上移走， AAA ATPase Pch2是控制重组水平的重要反馈途径。我们将测试我们的 假设Pch2直接识别特定的Hop1构象并部分展开其Horma结构域以调节 它从轴上移走。最后，我们将研究两个减数分裂的结构、DNA结合特异性和相互作用。 特定的蛋白质复合体，Msh4：Msh5和Zip2：ZIP4：Spo16，以了解它们如何稳定特定的DNA重组 中间体与染色体轴形态的变化协调交叉形成。 总体而言，这里提出的工作将产生染色体轴如何组装的全面分子图， 坐标交叉编队，然后随着重组的进行而分解。理解分子 染色体轴和相关因素的机制与人类健康高度相关，因为减数分裂中的错误 染色体分离是人类流产的主要原因，也是“非整倍体疾病”的根源 唐氏综合征和特纳综合征。此外，许多癌症类型都表现出减数分裂染色体轴的错误表达。 蛋白质，包括TRIP13、HORMAD1和SYCP2。更好地了解这些蛋白质在其天然体内的作用机制 环境将是决定它们的错误表达如何可能导致基因组不稳定和癌症的关键。

PROJECT SUMMARY Sexual reproduction in eukaryotes involves the generation of haploid gametes (in humans, sperm and egg cells) in meiosis, followed by the fusion of two gametes to produce diploid offspring. In meiosis, homologous chromosomes recognize one another and become physically linked through a modified homologous recombination DNA repair pathway, and the resulting crossovers enable accurate homolog segregation in the meiosis I division to reduce ploidy. In most eukaryotes including humans, chromosomes are organized as an array of chromatin loops by a highly conserved structure called the chromosome axis. The chromosome axis also recruits and controls DNA cleavage and recombination factors to mediate the formation of crossovers, and is remodeled after crossover formation in a key feedback pathway controlling recombination levels. Here, we propose to combine biochemistry, macromolecular structure, and genetics in both S. cerevisiae and the mouse to determine how the chromosome axis assembles, organizes chromosomes, and mediates crossover formation. We will first determine the structures of S. cerevisiae Red1 and mammalian SYCP2:SYCP3, functionally-related chromosome axis “foundation” proteins that we have found share a conserved domain structure and propensity to self-assemble into filaments. We will next determine how these proteins interact with meiotic cohesin complexes, to understand the structural basis for axis-mediated chromosome organization. Next, we will dissect the network of interactions mediated by S. cerevisiae Hop1, a member of the conserved HORMAD family of axis proteins and a master regulator of meiotic recombination, and study how this interaction network changes during as meiotic prophase progresses. Hop1's eventual removal from the chromosome axis, an important feedback pathway controlling recombination levels, is mediated by the AAA+ ATPase Pch2. We will test our hypothesis that Pch2 directly recognizes a specific Hop1 conformation and partially unfolds its HORMA domain to mediate its removal from the axis. Finally, we will examine the structures, DNA binding specificity, and interactions of two meiosis- specific protein complexes, Msh4:Msh5 and Zip2:Zip4:Spo16, to learn how they stabilize specific DNA recombination intermediates and coordinate crossover formation with chromosome axis morphology changes. Overall, the work proposed here will result in a comprehensive molecular picture of how the chromosome axis assembles, coordinates crossover formation, and is then disassembled as recombination proceeds. Understanding the molecular mechanisms of the chromosome axis and associated factors is highly relevant to human health, as errors in meiotic chromosome segregation are a principal cause of miscarriage in humans, and are the source of “aneuploidy disorders” like Down syndrome and Turner syndrome. Moreover, many cancer types show mis-expression of meiotic chromosome axis proteins, including TRIP13, HORMAD1, and SYCP2. A better understanding of these proteins' mechanisms in their native environment will be critical to determine how their mis-expression might lead to genome instability and cancer.