Fig. 4.

Molecular circuitry of the Cdk1 positive feedback loop. In G2-arrested oocytes, Cdk1-Cyclin B is stockpiled in an inactive state, with Cdk1 phosphorylated at T14 and Y15 by Myt1, while Cdc25 is inactive. PP2A-B55δ maintains Cdc25 and Myt1 under a dephosphorylated state. The first active molecules of Cdk1 reverse the balance by phosphorylating Myt1 and Cdc25. They also recruit other kinases that facilitate further phosphorylation of Myt1 and Cdc25. Finally, Cdk1 indirectly inactivates PP2A-B55δ through Gwl and S67-phosphorylated Arpp19