Studies on cell cycle regulatory mechanism which prevents production of aneuploid gametes due to chromosome mis-segregation during meiosis

后期促进复合体/环体(APC/C)通过泛素化促进细胞周期调节因子的蛋白降解。CDH1调节亚基从晚期到G1激活APC/C。裂解酵母中的CDH1(Ste9)失活会导致G1期停滞和营养限制导致的不育症。然而，当交配信息素强烈激活Ras-MAP激酶途径时，在ste9突变体中Rnesis会恢复。在正常减数分裂中，同源染色体在第一次“还原”分裂中彼此分离。相反，在Ste9细胞中，由于每个姐妹染色体在第一次减数分裂中分离，所以发生了等距分裂。结果，在减数分裂过程中，染色体在该突变体中经常错误分离。在缺乏减数分裂粘附素亚基Rec8的细胞中也观察到了类似的缺陷，但GFP-Rec8蛋白似乎定位于正在进行减数分裂的Ste9细胞的染色质区域，因此Rec8的表达和定位不是该突变体异常的原因。此前，我们向…报道更多的研究表明，在营养剥夺导致细胞周期停滞时，Ste9负责降解APC/C的代表底物M期细胞周期蛋白(CDC13)。用免疫印迹法检测细胞减数分裂过程中CDc13的蛋白水平。在野生型菌株中，Cdc13首先在01期停滞时消失，然后在减数分裂进入减数分裂进入减数分裂阶段后重新出现。与之形成鲜明对比的是，在Ste9细胞中，细胞周期停滞主要发生在G2期，而不是G1期，CDc13在整个细胞周期中都保持在高水平。在这个突变体中，即使在激活Ras-MAP激酶通路后，DNA合成也没有发生，但令人惊讶的是，减数分裂直接从G2期开始。在这种异常的G2-出口减数分裂中，最初没有发生CDC13水平的下调，减数分裂直接从高CDC13状态开始。我们的结论是，通过促进Cdc13的降解，Ste9在防止G2期败育的减数分裂和确保从G1期开始减数分裂方面发挥了重要作用，而G1期减数分裂是染色体正确分离所必需的。较少

The anaphase-promoting complex/cyclosome (APC/C) promotes proteolysis of cell cycle regulators by ubiquitylating them. Cdh1 regulatory subunit activates APC/C from late anaphase to G1. Inactivation of Cdh1 (Ste9) in fission yeast causes inability of G1 arrest and sterility upon nutrient limitation. However, rneiosis restores in ste9 mutant when Ras-MAP kinase pathway is strongly activated by mating pheromone. In normal meiosis, homologous chromosomes segregate each other in first "reductional" division. In contrast, equational division occurs thus each sister chromosome segregates in first meiotic division in ste9 cells. As a result, chromosomes frequently mis-segregate in this mutant in meiosis. Similar defect is observed in cells lacking meiotic cohesin subunit Rec8, but GFP-Rec8 protein seems to localize in a chromatin region in ste9 cells undergoing meiosis, therefore inability of expression and localization of Rec8 is not a cause of aberrancy in this mutant. Previously, we reporte … More d that Ste9 is responsible for degradation of M phase cyclin (Cdc13), a representative substrate of APC/C, upon cell cycle arrest by nutrient deprivation. Protein levels of Cdc13 were monitored during meiosis by western blotting. In wild type strain; Cdc13 firstly disappeared during arrest in 01 phase, then re-appeared upon meiotic entry after premebtic DNA synthesis. In marked contrast, Cdc13 was kept at high levels throughout cell cycle arrest which mostly occurs in G2 phase, not in G1 in ste9 cells. In this mutant, DNA synthesis did not occur even after activation of Ras-MAP kinase pathway but surprisingly, meiotic nuclear division directly initiates from G2 phase. In this aberrant G2-exit meiosis, initial down-regulation of Cdc13 levels did not occur and meiosis directly started from high Cdc13 state. We concluded that by promoting Cdc13 degradation Ste9 plays an important role to prevent abortive meiosis from G2 phase and ensures initiation of meiosis from G1 that is necessary for proper chromosome segregation. Less