SGK phosphorylates Cdc25 and Myt1 to trigger cyclin B-Cdk1 activation at the meiotic G2/M transition

The kinase cyclin B–Cdk1 complex is a master regulator of M-phase in both mitosis and meiosis. At the G2/M transition, cyclin B–Cdk1 activation is initiated by a trigger that reverses the balance of activities between Cdc25 and Wee1/Myt1 and is further accelerated by autoregulatory loops. In somatic cell mitosis, this trigger was recently proposed to be the cyclin A–Cdk1/Plk1 axis. However, in the oocyte meiotic G2/M transition, in which hormonal stimuli induce cyclin B–Cdk1 activation, cyclin A–Cdk1 is nonessential and hence the trigger remains elusive. Here, we show that SGK directly phosphorylates Cdc25 and Myt1 to trigger cyclin B–Cdk1 activation in starfish oocytes. Upon hormonal stimulation of the meiotic G2/M transition, SGK is activated by cooperation between the Gβ-PI3K pathway and an unidentified pathway downstream of Gβ, called the atypical Gβ pathway. These findings identify the trigger in oocyte meiosis and provide insights into the role and activation of SGK.

Source: Journal of Cell Biology - November 3, 2019 Category: Cytology Authors: Hiraoka, D., Hosoda, E., Chiba, K., Kishimoto, T. Tags: Cell Cycle and Division, Cell Signaling Articles Source Type: research