Molecular bases that ensure genomic inheritance through successive generations

点击翻译按钮获取中文摘要

Based on the cell cycle control and the nuclear formation, molecular mechanisms that ensure genomic inheritance through successive generations have been studied in oocytes and eggs of starfish and frog.1. Meiotic reinitiation : We had previously showed that the signaling pathway that leads to meiotic reinitiation in starfish oocytes is composed of the putative receptor for maturation-inducing hormone, 1-MeAde/hetero-trimeric G-protein/PI3-kinase/Akt/cyclin B-Cdc2/Plk1. Here, we tried to isolate the 1-MeAde receptor using affinity ferrite beads. Three peptides of 42, 92 and 97 kDa which should possibly consitute the receptor were identified. In addition, we found that activation of Aurora, a mitotic kinase, completely depends on activation of cyclin B-Cdc2 at meiotic reinitiation in starfish oocytes ; and that a single type of starfish Aurora exhibits both functions of Aurora A and B, each of which has distinct functions in HeLa cells.2. Meiotic metaphase-II arrest and its release : In Xenopus oocytes, we demonstrated that meta-II arrest is induced by direct phosphorylation of Erp1 with p9ORsk, which enhances both stability of Erp1 and its inhibitory activity against APC/C, thereby preventing the APC/C-mediated degradation of cyclin B.At release from meta-II arrest, we showed that in addition to previously known CaMKII, transient activation of calcineurin is required for Erp1 degradation and restart of the cell cycle.3. Formation of male and female pronuclei : In immature Xenopus oocytes, we found that importin α-mediated nuclear transport is suppressed due to its trapping into annulate lamellae, and that the trapping is cancelled at meiotic reinitiation. This should contribute to acqusition of the pronuclear formation ability during meiotic maturation. Further, we showed in starfish eggs that pronuclear congression and fusion after fertilization do not depend on the cell cycle progression.