Cdk1 activity during oocyte maturation. (A) Comparable Cdk1 activities during prometaphase I (3 h) and metaphase I (6 h) but delayed reduction in Cdk1 activity in OoMastl^−/− oocytes (9 h). Cdk1 activity cannot be increased after PBE (14 h) in OoMastl^−/− oocytes (bottom right). (B) Western blots showing the dynamics of p-Cdk1 (Y15) during oocyte maturation. Lysate from 100 oocytes was loaded in each lane. The levels of β-actin and Cdk1 were used as controls. The same β-actin panel is presented in Fig. 1 E, which shows the expression of other proteins of interest in the same cell lysates. (C) Comparable PP1 phosphorylation (indicating inhibition) at GVBD in OoMastl^−/− and OoMastl^+/+ oocytes. (D) Expression of Mastl, cyclin B1, p-Cdk1 (Y15), Cdk1, phospho–lamin A/C (S22), and lamin A/C in ovulated oocytes. β-Actin was used as the loading control. Lysate from 100 oocytes was loaded in each lane.