Preventing Age-Associated Oocyte Aneuploidy: Mechanisms Behind the Drosophila melanogaster Centromere Effect

项目概要/摘要 在减数分裂过程中，同源物之间的交叉有利于染色体的准确分离并防止 非整倍体，从而预防流产和唐氏综合症等染色体疾病。的 减数分裂交叉的调节和放置是防止与年龄相关的减数分裂的重要保障 缺陷和不孕不育，因为不分离（NDJ）的风险随着母亲年龄的增加而增加。 当程序性双链断裂 (DSB) 被修复时，就会形成减数分裂交叉 (CO) 同源重组。然而，只有一部分 DSB 被修复形成 CO；其余的修复为 非交叉（NCO）。尽管减数分裂 DSB 分布在整个染色体上，CO 的放置是 受三种类型的图案现象的复杂调节。其中之一，着丝粒效应（CE），确保 近端着丝粒区域中 CO 的排除，对于减数分裂细胞作为近端着丝粒至关重要 CO 会增加 NDJ 的风险。此外，母亲年龄的增加已被证明会削弱CE， 可能解释为什么老年女性 NDJ 发病率增加。尽管首先在果蝇中观察到 1932 年，CE 背后的机制至今仍不得而知。这里提出的实验旨在 解决有关防止错误分离事件的重要细胞过程的知识空白， 尤其是高龄产妇。最近，我们的实验室表明 CE 是有差异的 在果蝇着丝粒周围发现的两类异染色质中建立。在高度重复的情况下 α异染色质紧邻着丝粒，观察到CO完全排除，而 与近端常染色质相邻的重复性较低的 β 异染色质显示出距离依赖性 CO 镇压。我将在这些结果的基础上研究 CE 的建立机制 在这两类中心周异染色质中。关于CE机制的一个突出问题 围绕着丝粒周围异染色质和着丝粒本身如何对 CE 做出贡献。少数人 在过去的一个世纪里，针对中心周交叉问题的研究试图将其建立为 在果蝇中比另一个更重要，但未能达成共识。因此，中心周异染色质 已被考虑为从相邻时间间隔内积极参与二氧化碳减排到仅此而已的一切 而非常染色质和着丝粒之间的被动间隔区。通过本文概述的实验 提案，我会问中心周围异染色质和着丝粒如何对CE做出贡献 彼此独立，特别关注高度重复的α异染色质。 研究 α 异染色质与整个中心周异染色质的作用分开的情况 在如何建立 CE 的更广泛问题中，体现 CE 是一个新颖的研究领域。在 总之，该提案将增加我们对防止年龄增长的机制的理解 通过揭示减数分裂交叉模式来研究相关的非整倍性和不孕症。

Project Summary/Abstract During meiosis, crossing-over between homologs facilitates accurate chromosome segregation and prevents aneuploidy, which in turn forestalls miscarriages and chromosomal disorders such as Down syndrome. The regulation and placement of meiotic crossovers acts as a vital safeguard against age-associated meiotic defects and infertility, as the risk of non-disjunction (NDJ) increases with increasing maternal age. Meiotic crossovers (COs) are formed when programmed double-strand breaks (DSBs) are repaired through homologous recombination. However, only a subset of DSBs are repaired to form COs; the rest are repaired as non-crossovers (NCOs). Despite meiotic DSBs being distributed throughout the chromosome, CO placement is intricately regulated by three types of patterning phenomena. One of these, the centromere effect (CE), ensures the exclusion of COs in centromere-proximal regions and is crucial to the meiotic cell as centromere-proximal COs increase the risk of NDJ. Furthermore, increasing maternal age has been shown to weaken the CE, potentially explaining why NDJ incidence increases in older women. Although first observed in Drosophila in 1932, the mechanisms behind the CE remain unknown even today. The experiments proposed here aim to address this gap in knowledge regarding a vital cellular process that prevents mis-segregation events, especially in those with advanced maternal age. Recently, our lab showed that the CE is differentially established in the two classes of heterochromatin found at the Drosophila pericentromere. In the highly repetitive alpha heterochromatin immediately adjacent to the centromere, a complete exclusion of COs is observed, while the less repetitive beta heterochromatin adjacent to proximal euchromatin shows a distance dependent CO suppression. I will build on these results by investigating the mechanisms of how the CE is established in these two classes of pericentric heterochromatin. A prominent question regarding CE mechanisms centers around how pericentromeric heterochromatin and the centromere itself contribute to the CE. The few studies that have addressed pericentric crossing-over in the past century have attempted to establish one as more important than the other in Drosophila but failed to arrive at a consensus. Thus, pericentric heterochromatin has been considered everything from an active participant in CO reduction in adjacent intervals to nothing more than a passive spacer between euchromatin and the centromere. Through the experiments outlined in this proposal, I will ask how pericentric heterochromatin and the centromere contribute to the CE independently of each other, particularly focusing on highly repetitive alpha heterochromatin. Investigating the role of alpha heterochromatin as separate from that of pericentric heterochromatin as a whole in manifesting the CE is a novel area of research within the broader question of how the CE is established. In summary, this proposal will increase our understanding of the mechanisms that safeguard against age- related aneuploidy and infertility through shedding light on meiotic crossover patterning.