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

项目摘要 真核生物的有性生殖包括产生单倍体配子（在人类，精子和卵子 细胞）减数分裂，随后两个配子融合产生二倍体后代。在减数分裂中，同源的 染色体相互识别，并通过修饰的同源 重组DNA修复途径，以及由此产生的交叉，使准确的同源物分离，在 减数分裂I分裂以降低倍性。在包括人类在内的大多数真核生物中， 由一个高度保守的称为染色体轴的结构排列的染色质环。染色体轴 还募集和控制DNA切割和重组因子以介导交叉的形成， 在控制重组水平的关键反馈途径中交叉形成后被重塑。 在这里，我们建议将S.联合收割机的生物化学、结构和遗传学结合起来。酿酒酵母和小鼠， 确定染色体轴如何组装，组织染色体，并介导交叉形成。 我们将确定S的结构。酿酒酵母Red 1和哺乳动物SYCP 2：SYCP 3，功能相关 我们发现的染色体轴“基础”蛋白具有保守的结构域结构和倾向 自我组装成细丝接下来我们将确定这些蛋白质如何与减数分裂粘附素相互作用 复合物，以了解轴介导的染色体组织的结构基础。接下来我们就 剖析由S介导的相互作用网络。酿酒酵母Hop1是保守的HORMAD家族的一员 家族和减数分裂重组的主调节器，并研究这种相互作用网络如何在 减数分裂前期Hop1最终从染色体轴上移除，这是一个重要的反馈途径 控制重组水平，是由AAA + ATP酶Pch2介导的。我们将测试我们的假设， 直接识别特定的Hop1构象，并部分展开其HORMA结构域，以介导其 从轴上移开。最后，我们将研究两个分子的结构、DNA结合特异性和相互作用。 减数分裂特异性蛋白复合物，Msh4：Msh5和Zip2：Zip4：Spo16，以了解它们如何稳定特定的DNA 重组中间体和协调的交叉形成与染色体轴形态的变化。 总的来说，这里提出的工作将导致一个全面的分子图片，染色体轴如何 组装，协调交叉形成，然后随着重组的进行而分解。 了解染色体轴和相关因子的分子机制， 人类健康，因为减数分裂染色体分离中的错误是人类流产的主要原因， 并且是唐氏综合症和特纳综合症等“非整倍性疾病”的根源。而且很多 癌症类型显示减数分裂染色体轴蛋白的错误表达，包括TRIP 13，HORMAD 1， SYCP 2.更好地理解这些蛋白质在其天然环境中的机制将是至关重要的， 确定它们的错误表达如何导致基因组不稳定和癌症。

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, structure, and genetics in S. cerevisiae and the mouse to determine how the chromosome axis assembles, organizes chromosomes, and mediates crossover formation. We will 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 and a master regulator of meiotic recombination, and study how this interaction network changes during meiotic prophase. 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.