Cdc2 regulation for the meiotic transition from M phase to M phase

为了研究细胞周期在减数分裂周期中从M期向M期转变的调控机制，开发了一种执行M/M期转变的非洲爪哇卵母细胞提取物。利用减数分裂提取液，我们发现由于细胞周期蛋白B的不完全降解，在减数分裂I(MI)的出口处仍有较低水平的Cdc2活性。剩余的Cdc2活性的失活导致进入S期以及在MII后Cdc2上的酪氨酸磷酸化。定量分析表明，在MI出口处存在相当数量的Weel，在此期间，Cdc2的抑制磷酸化被抑制。在提取物中加入超过临界量的Weel可诱导Cdc2抑制磷酸化，将M/M转变为M/S/M转变。因此，在M/M减数分裂过渡期，保持在MI出口的Cdc2活性是抑制进入S相所必需的。

To investigate the regulatory mechanisms for the cell cycle transition from M phase to M phase in meiotic cycles, a Xenopus oocyte extract that performs the M/M transition has been developed. Using the meiotic extract, we found that a low level of Cdc2 activity remained at the exit of meiosis I (MI), due to incomplete degradation of cyclin B.The inactivation of the residual Cdc2 activity induced both entry into S phase and tyrosine-phosphorylation on Cdc2 after MI.Quantitative analysis demonstrated that a considerable amount of Weel was present at the MI exit and Cdc2 inhibitory phosphorylation during this period was suppressed by the dominance of Cdc2 over Weel. Consistently, the addition of more than a critical amount of Weel to the extract induced Cdc2 inhibitory phosphorylation, changing the M/M transition into an M/S/M transition. Thus, the Cdc2 activity remaining at the MI exit is required for suppressing entry into S phase during the meiotic M/M transition period.