Molecular and morphological analyses of the initiation of cyclin B translation during oocyte maturation

卵母细胞成熟是由成熟促进因子（也称为m期促进因子）（MPF）触发的，MPF由Cdc2和Cyclin B组成。通过翻译激活卵母细胞中储存的休眠mRNA合成Cyclin B是正常成熟进程所必需的。在本研究中，我们研究了cyclin B翻译的信号转导途径、翻译激活机制以及MPF的作用机制。我们研究了磷脂酰肌醇3-激酶（PI3K）和蛋白激酶B （PKB）在黄体酮诱导的Rana卵母细胞成熟中的作用。结果表明，PI3K而非PKB在信号转导通路中起作用。为了了解细胞周期蛋白B翻译的启动机制，我们研究了Pumilio和细胞质多聚腺苷化元件结合蛋白（CPEB），并提出Pumilio作为一种特异性调节剂，通过其在卵母细胞成熟过程中释放更多磷酸化的CPEB来决定细胞周期蛋白B mRNA的翻译激活时间。利用Rana卵母细胞对细胞周期蛋白B1和B2的功能进行的研究表明，尽管细胞周期蛋白B1或B2在诱导生发囊泡破裂和染色体凝聚方面是多余的，但在组织双极纺锤体方面需要细胞周期蛋白B2，而不是细胞周期蛋白B1。MPF和丝裂原活化蛋白激酶（MAPK）参与了成熟过程中发生的形态变化，但它们的确切作用尚不清楚。利用Rana卵母细胞，我们明确了MPF和MAPK在卵母细胞成熟过程中顺序形态变化的各个过程中的作用。γ -微管蛋白对中心体微管的成核至关重要，但对其在卵母细胞纺锤体形成过程中的作用知之甚少。我们观察了γ -微管蛋白在爪蟾卵母细胞纺锤体形成过程中的行为，发现γ -微管蛋白可能通过动力蛋白易位来调节导致纺锤体形成的微管组织。γ -微管蛋白在纺锤极形成中的作用也通过过表达实验得到证实。少

Oocyte maturation is triggered by the maturation-promoting factor (also known as the M-phase-promoting factor) (MPF) that consists of Cdc2 and Cyclin B. Synthesis of Cyclin B by translational activation of the dormant mRNA stored in oocytes is required for normal progression of maturation. In this study, we investigated the signal transduction pathways to cyclin B translation, the mechanisms of translational activation, and the action mechanisms of MPF.We examined the involvement of phosphatidylinositol 3-kinase (PI3K) and protein kinase B (PKB) in progesterone-induced Rana oocyte maturation. The obtained results suggest that PI3K, but not PKB, functions during the signal transduction pathway. To know the initiation mechanisms of cyclin B translation, we investigated Pumilio and cytoplasmic polyadenylation element-binding protein (CPEB), and suggested that Pumilio acts as a specific regulator that determines the timing of translational activation of cyclin B mRNA by its release from ph … More osphorylated CPEB during oocyte maturation.Investigations into the functions of Cyclins B1 and B2 using Rana oocytes provide evidence of the requirement of Cyclin B2, but not Cyclin B1, for organizing the bipolar spindle, though either Cyclin B1 or B2 is redundant for inducing germinal vesicle breakdown and chromosome condensation. MPF and mitogen-activated protein kinase (MAPK) are involved in the morphological changes that occur during maturation, but their precise roles are unknown. Using Rana oocytes, we clarified the functions of MPF and MAPK in each process of sequential morphological changes during oocyte maturation.Gamma-tubulin is essential for nucleation of microtubules at centrosomes, but little is known about its role during spindle formation in oocytes. We observed the behavior of gamma-tubulin during spindle formation in Xenopus oocytes, and found that gamma-tubulin is probably translocated by dynein to regulate microtubule organization leading to spindle formation. Significance of gamma-tubulin in spindle pole formation is also demonstrated by overexpression experiments. Less