Fig. 1. Expression of the regulators of Cdc2 activation in stage IV oocytes. Prophase oocytes at stage IV (750-800 µm), stage V₁ (900-1000 µm), stage V₂ (1000-1100 µm) and stage VI (1200 µm) were incubated or not in the presence of progesterone and collected 18 hours afterwards. Occurrence of GVBD is indicated by (+). Oocyte extracts were either assayed for H1 kinase activity of Cdc2 (A) or western blotted (B) with antibodies against Cdc2, cyclin B1, cyclin B2, Cdc25, Plx1 and the Tyr15-phosphorylated form of Cdc2 (P-Tyr-Cdc2).