Meiotic Centromere Behavior in Yeast

描述（由申请人提供）：在过去的三十年中，文献中有零星的报道，在减数分裂的两个不同阶段，同源和非同源染色体的着丝粒之间配对。首先，对各种生物（洋葱、小麦、芽殖酵母、小鼠）的研究表明，在减数分裂的早期，DNA复制之后，着丝粒会成对排列。这种配对主要发生在非同源的着丝粒之间。这种非同源的，早期的，减数分裂的着丝粒配对溶解，同源染色体在后期的减数分裂前期变得对齐。其次，着丝粒也可以在减数分裂的后期积极配对。例如，对芽殖酵母和雌性果蝇的研究表明，未能重组的伴侣染色体（非交换染色体）在后期前期的着丝粒（或臂间异染色质）配对，此时同源染色体完全突触。这种非交换伴侣之间的晚减数分裂着丝粒配对促进了它们在第一次减数分裂时的分离。在芽殖酵母中，着丝粒配对的早期和晚期都依赖于联会复合体（SC）蛋白Zip1。该项目旨在描述减数分裂中着丝粒配对的两个阶段，测试它们是否在机制上相关或不同，并确定它们如何影响减数分裂I中染色体的分离。由于减数分裂着丝粒配对的观察已经从这样一个不同的实验生物体中收集，拟议的实验可能会揭示一个保守的细节，但在很大程度上未被认识到，减数分裂染色体行为的方面。该项目分为五组实验。第一组实验确定了Zip1的区域，该区域在早期减数分裂中与着丝粒相关，并使用亲和纯化方法来鉴定参与着丝粒配对早期阶段的蛋白质。很少有人知道从早期到后期着丝粒配对的过渡。第二组实验将探索这种转变，并阐明这两个阶段的关系。在减数分裂Ⅰ开始时排列非同源着丝粒的目的是什么？减数分裂Ⅰ的最终目的是配对然后分离同源染色体。第三组实验检验了非同源着丝粒配对阻止着丝粒附近交叉形成的假设。已知这种交换会破坏许多生物体中减数分裂I染色体分离的保真度。最后两组实验将探讨第一，如何Zip1促进配对的着丝粒在后期减数分裂前期，第二，将测试的假设，这后期着丝粒配对促进附件的着丝粒对两极的减数分裂I纺锤体，并在这样做，有助于减数分裂I分离的保真度在重要的方面。 公共卫生相关性：染色体分配到配子过程中的错误是出生缺陷的主要原因。该项目使用芽殖酵母来识别未被发现的方式，其中染色体的一个组成部分，称为着丝粒，可能有助于指导染色体运动，这样做有助于防止导致出生缺陷的错误。

DESCRIPTION (provided by applicant): Over the past thirty years there have been sporadic reports in the literature of pairing between the centromeres of both homologous and non-homologous chromosomes at two different stages of meiosis. First, studies in a variety of organisms (onions, wheat, budding yeast, mice) have revealed that early in meiosis, just after DNA replication, centromeres arrange themselves in pairs. This pairing is primarily between non-homologous centromeres. This non-homologous, early, meiotic centromere pairing dissolves as homologous chromosomes become aligned in later meiotic prophase. Second, centromeres can also actively pair at a later stage of meiosis. For example, studies with budding yeast and female Drosophila have shown that partner chromosomes that have failed to recombine (non-exchange chromosomes) pair at their centromeres (or pericentric heterochromatin) in late prophase, when homologous chromosomes are completely synapsed. This late meiotic centromere pairing between non-exchange partners promotes their disjunction at the first meiotic division. In budding yeast, both the early and late stages of centromere pairing depend upon the synaptonemal complex (SC) protein, Zip1. This project aims to characterize the two phases of centromere pairing in meiosis, test whether they are mechanistically related, or distinct, and determine how they impact the segregation of chromosomes in meiosis I. Because observations of meiotic centromere pairing have been gathered from such a diverse range of experimental organisms, the proposed experiments may reveal the details of a conserved, but largely unrecognized, aspect of meiotic chromosome behavior. The project is organized into five groups of experiments. The first group of experiments determines the region of Zip1 that is involved in association with the centromere in early meiosis and uses affinity purification methods to identify proteins that are involved in the early phase of centromere pairing. Little is known about the transition from early to later centromere pairing. A second group of experiments will explore this transition and shed light on the relationship of the two stages. What is the purpose of aligning non-homologous centromeres at the beginning of a process (meiosis I) that is ultimately intended to pair then separate homologous chromosomes? A third group of experiments tests the hypothesis that non-homologous centromere pairing blocks the formation of crossovers near to centromeres. Such crossovers are known to disrupt meiosis I chromosome segregation fidelity in many organisms. The final two groups of experiments will explore first, how Zip1 promotes the pairing of centromeres in later meiotic prophase, and second, will test the hypothesis that this late centromere pairing promotes the attachment of centromeres to opposite poles of the meiosis I spindle, and in doing so, contributing to meiosis I segregation fidelity in important ways. PUBLIC HEALTH RELEVANCE: Errors in the process of distributing chromosomes to the gametes is the major cause of birth defects. This project uses budding yeast to identify undiscovered ways in which a component of the chromosome, called the centromere, might help direct chromosomes movements, in doing so helping to prevent the errors that lead to birth defects.