Regulation of M phase exit

CDK/Cyclin复合体驱动真核细胞周期的进展。 进入有丝分裂是由CDK1(Cdc2)/Cyclin B复合体触发的，而M 阶段退出需要Cyclin B的降解和有丝分裂的去磷酸化 磷蛋白。周期B在M期出口的破坏是由 APC(后期促进复合体)，是一种多蛋白E3泛素连接酶，它 泛素化Cyclin B并促进其蛋白酶体的降解。多重因素 合作防止过早激活，并确保及时停用 APC。在脊椎动物的卵中，它们在M期停留了很长一段时间 时间上，APC受到一种称为细胞抑制因子(CSF)的活动的抑制。 最近在非洲爪哇和小鼠卵子中的发现与Emi2有很强的相关性 蛋白质作为脑脊液活性的关键成分，负责直接抑制 APC。我们并不确切地了解Emi2是如何影响APC抑制的， 虽然我们最近发现Emi2似乎是催化作用的，但 而不是人们普遍认为的化学计量学。此外，我们的数据表明， Emi2功能被抑制，至少部分是通过直接的cdc2介导的。 磷酸化，尽管磷酸酶复合体的性质是对抗 这对激活Emi2功能是未知的。这项提议的目的是 阐明Emi2抑制APC的机制(S)并确定其机制 Emi2受脑脊液调节。这种理解是至关重要的，因为这是不恰当的 APC在减数分裂退出时的激活可导致染色体错误分离和 一系列出生缺陷背后的严重发育异常。

Cdk/Cyclin complexes drive progression through the eukaryotic cell cycle. Entry into mitosis is triggered by Cdk1 (Cdc2)/Cyclin B complexes, while M phase exit requires Cyclin B degradation and dephosphorylation of mitotic phosphoproteins. The destruction of Cyclin B at M phase exit is driven by the APC (anaphase promoting complex), a multi-protein E3 ubiquitin ligase, which ubiquitylates Cyclin B and promotes its proteasomal degradation. Multiple factors cooperate to prevent premature activation and ensure timely inactivation of the APC. In vertebrate eggs, which are arrested in M phase for prolonged periods of time, the APC is restrained by an activity known as Cytostatic Factor (CSF). Recent findings in both Xenopus and mouse eggs have strongly implicated Emi2 protein as a critical component of CSF activity, responsible for direct inhibition of the APC. We do not understand precisely how Emi2 effects APC inhibition, though we have recently found that Emi2 appears to act catalytically, rather than stoichiometrically, as is generally believed. Moreover, our data indicate that Emi2 function is inhibited, at least in part, through direct Cdc2-mediated phosphorylation, though the nature of the phosphatase complexes that counter this to activate Emi2 function are unknown. The aims of this proposal are to elucidate the mechanism(s) of APC inhibition by Emi2 and to determine how Emi2 is regulated by CSF. This understanding is critical in that inappropriate APC activation at meiotic exit can lead to errors in chromosome segregation and severe developmental abnormalities underlying a range of birth defects.