Department of Biological Sciences, Dartmouth College, Hanover, NH, USA 03755.
Department of Molecular Biology, Princeton University, Princeton, NJ, USA 08544.
G3 (Bethesda). 2024 Aug 7;14(8). doi: 10.1093/g3journal/jkae123.
Accurate chromosome segregation during meiosis requires the maintenance of sister chromatid cohesion, initially established during premeiotic S phase. In human oocytes, DNA replication and cohesion establishment occur decades before chromosome segregation and deterioration of meiotic cohesion is one factor that leads to increased segregation errors as women age. Our previous work led us to propose that a cohesion rejuvenation program operates to establish new cohesive linkages during meiotic prophase in Drosophila oocytes and depends on the cohesin loader Nipped-B and the cohesion establishment factor Eco. In support of this model, we recently demonstrated that chromosome-associated cohesin turns over extensively during meiotic prophase and failure to load cohesin onto chromosomes after premeiotic S phase results in arm cohesion defects in Drosophila oocytes. To identify proteins required for prophase cohesion rejuvenation but not S phase establishment, we conducted a Gal4-UAS inducible RNAi screen that utilized two distinct germline drivers. Using this strategy, we identified 29 gene products for which hairpin expression during meiotic prophase, but not premeiotic S phase, significantly increased segregation errors. Prophase knockdown of Brahma or Pumilio, two positives with functional links to the cohesin loader, caused a significant elevation in the missegregation of recombinant homologs, a phenotype consistent with premature loss of arm cohesion. Moreover, fluorescence in situ hybridization confirmed that Brahma, Pumilio, and Nipped-B are required during meiotic prophase for the maintenance of arm cohesion. Our data support the model that Brahma and Pumilio regulate Nipped-B-dependent cohesin loading during rejuvenation. Future analyses will better define the mechanism(s) that govern meiotic cohesion rejuvenation and whether additional prophase-specific positives function in this process.
在减数分裂过程中准确地进行染色体分离需要维持姐妹染色单体的黏合，这种黏合最初是在减数分裂前期 S 期建立的。在人类卵母细胞中，DNA 复制和黏合建立发生在减数分裂分离的几十年前，减数分裂黏合的恶化是导致女性年龄增长时分离错误增加的一个因素。我们之前的工作使我们提出，在果蝇卵母细胞的减数分裂前期，存在一个黏合更新程序来建立新的黏合连接，该程序依赖于黏合加载器 Nipped-B 和黏合建立因子 Eco。支持该模型，我们最近证明，染色体相关的黏合在减数分裂前期会大量周转，如果在减数分裂前期 S 期之后未能将黏合加载到染色体上，则会导致果蝇卵母细胞的臂黏合缺陷。为了鉴定在减数分裂前期但不在减数分裂前期 S 期建立所需要的蛋白，我们进行了 Gal4-UAS 诱导 RNAi 筛选，该筛选利用了两种不同的生殖系驱动子。使用这种策略，我们鉴定出 29 种基因产物，这些基因产物在减数分裂前期而非减数分裂前期 S 期表达发夹 RNA，显著增加了分离错误。Brahma 或 Pumilio 的前期敲低，这两个蛋白与黏合加载器有功能联系，导致重组同源物的错误分离显著增加，这一表型与臂黏合的过早丢失一致。此外，荧光原位杂交证实，Brahma、Pumilio 和 Nipped-B 在减数分裂前期对于维持臂黏合是必需的。我们的数据支持 Brahma 和 Pumilio 在更新过程中调节 Nipped-B 依赖性黏合加载的模型。未来的分析将更好地定义调控减数分裂黏合更新的机制，以及是否有其他的前期特异性蛋白在此过程中发挥作用。
