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

项目摘要/摘要 在减数分裂过程中，同源基因之间的互换有助于准确的染色体分离，并防止 非整倍体，这反过来又防止流产和唐氏综合症等染色体疾病。这个 减数分裂交叉的调节和放置是防止年龄相关减数分裂的重要保障 缺陷和不孕症，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，减数分裂交叉(CoS)形成 同源重组。然而，只有一部分DSB被修复以形成CoS；其余的被修复为 非交叉(NCO)。尽管减数分裂DSB分布在整个染色体上，但CO的位置是 受到三种图案化现象的错综复杂的调控。其中之一，着丝粒效应(CE)，确保了 在着丝粒-近端区域排除CoS，这对作为着丝粒-近端的减数分裂细胞至关重要 COS增加了NDJ的风险。此外，母亲年龄的增加已被证明削弱了行政长官， 这可能解释了为什么NDJ在老年女性中的发病率增加。虽然首次在果蝇中观察到 1932年，行政长官背后的机制至今仍不为人所知。这里提出的实验旨在 解决关于防止错误分离事件的关键细胞过程的知识差距， 特别是在产妇年龄较大的人群中。最近，我们的实验室显示，行政长官是不同的 建立在果蝇包着丝点的两类异染色质中。在高度重复的 与着丝粒相邻的α异染色质，观察到Cos被完全排除，而 与近端常染色质相邻的重复率较低的β异染色质显示出距离依赖的CO 压制。我会在这些结果的基础上，调查行政长官的设立机制 在这两类着丝粒周围异染色质中。关于CE机制的一个突出问题 主要集中在着丝粒周围的异染色质和着丝粒本身对CE的贡献。为数不多的 在过去的一个世纪里，关于中心周围交叉的研究试图将其中之一建立为 在果蝇中比其他更重要，但未能达成共识。因此，着丝粒周围的异染色质 从在相邻时间间隔内积极参与降低CO，到什么都不做，都被考虑 而不是常染色质和着丝粒之间的被动间隔物。通过本文件中概述的实验 建议，我将询问着丝粒周围异染色质和着丝粒对CE有何贡献 相互独立，特别是高度重复的阿尔法异染色质。 研究α异染色质与着丝粒周围异染色质作为整体的分离作用 在如何设立行政长官这一更广泛的问题中，体现行政长官是一个新的研究领域。在……里面 综上所述，这项建议将增加我们对防止衰老的机制的理解- 通过揭示减数分裂交叉模式与非整倍体和不育性相关。

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.