Katsu Y, Yamashita M, Hirai T, Tokumoto T, Kajiura H, Nagahama Y
Department of Molecular Biomechanics, Graduate University for Advanced Studies, Sapporo, Japan.
Dev Biol. 1995 Aug;170(2):616-25. doi: 10.1006/dbio.1995.1241.
Cyclin A belongs to a family of proteins involved in the regulation of the eukaryotic cell cycle. Although cyclin A is thought to be involved in the regulation of both S and M phase, its exact role in the cell cycle, especially in the meiotic cycle (oocyte maturation), is uncertain. We isolated cyclin A cDNA clones from a goldfish oocyte cDNA library. Monoclonal antibody raised against bacterially produced goldfish cyclin A recognized a 47-kDa protein that disappeared after egg activation. Unlike goldfish cyclin B, which is absent in immature oocytes, cyclin A was already present in immature oocytes and its protein level did not change remarkably during oocyte maturation. These results differ from the finding in Xenopus, in which cyclin A is absent, but cyclin B is present, in immature oocytes. Goldfish cyclin A was associated with cdc2 kinase in mature oocytes, but not with cdk2. Recombinant cyclin A bound to and activated cdc2 in a cell-free system, but cyclin A and cdk2 binding was not observed. The kinase activity of cyclin A-cdc2 was undetectable in immature oocytes and first appeared at about the time of germinal vesicle breakdown (GVBD). In contrast to the cyclin B-cdc2 activity that corresponded to the occurrence of GVBD, cyclin A-cdc2 activity increased only slightly until GVBD was completed and increased drastically after the completion of the first meiotic division. Furthermore, microinjection of cyclin A mRNA into immature oocytes did not cause GVBD; however, microinjection of cyclin B mRNA did. These results suggest that cyclin A-cdc2 kinase and cyclin B-cdc2 kinase play different roles in controlling oocyte maturation. The roles of cyclin A in the rapid activation of cyclin B-cdc2 kinase at meiosis I and II transition and in the maintenance of high maturation-promoting factor activity in mature unfertilized eggs are discussed.
细胞周期蛋白A属于参与真核细胞周期调控的蛋白质家族。尽管细胞周期蛋白A被认为参与S期和M期的调控，但其在细胞周期中的确切作用，尤其是在减数分裂周期（卵母细胞成熟）中的作用尚不确定。我们从金鱼卵母细胞cDNA文库中分离出细胞周期蛋白A的cDNA克隆。针对细菌产生的金鱼细胞周期蛋白A制备的单克隆抗体识别出一种47 kDa的蛋白质，该蛋白质在卵子激活后消失。与未成熟卵母细胞中不存在的金鱼细胞周期蛋白B不同，细胞周期蛋白A在未成熟卵母细胞中已经存在，并且其蛋白质水平在卵母细胞成熟过程中没有显著变化。这些结果与非洲爪蟾的发现不同，在非洲爪蟾的未成熟卵母细胞中不存在细胞周期蛋白A，但存在细胞周期蛋白B。金鱼细胞周期蛋白A在成熟卵母细胞中与cdc2激酶相关，但与cdk2不相关。重组细胞周期蛋白A在无细胞系统中与cdc2结合并激活cdc2，但未观察到细胞周期蛋白A与cdk2的结合。细胞周期蛋白A - cdc2的激酶活性在未成熟卵母细胞中无法检测到，并且在生发泡破裂（GVBD）时首次出现。与对应于GVBD发生的细胞周期蛋白B - cdc2活性相反，细胞周期蛋白A - cdc2活性在GVBD完成之前仅略有增加，而在第一次减数分裂完成后急剧增加。此外，将细胞周期蛋白A的mRNA显微注射到未成熟卵母细胞中不会导致GVBD；然而，注射细胞周期蛋白B的mRNA则会导致GVBD。这些结果表明，细胞周期蛋白A - cdc2激酶和细胞周期蛋白B - cdc2激酶在控制卵母细胞成熟中发挥不同作用。本文讨论了细胞周期蛋白A在减数分裂I和II转换时对细胞周期蛋白B - cdc2激酶的快速激活以及在成熟未受精卵中维持高成熟促进因子活性方面的作用。
