EFFECTS OF THE PROTEIN-PHOSPHORYLATION INHIBITOR GENISTEIN ON MATURATION OF PIG OOCYTES IN-VITRO

In vitro maturation of cumulus enclosed and denuded pig oocytes was re versibly inhibited by the protein kinase inhibitor genistein. The half -maximal effect on maturation was observed at 40 mug ml-1. Genistein i nhibited total protein phosphorylation and synthesis with the same dos e-response relationship (ED50: 40 mug ml-1). Protein phosphorylation a nd synthesis patterns were changed by effective concentrations of geni stein. Pig oocytes were sensitive to genistein during the first 12 h o f in vitro maturation. This genistein sensitive period corresponds clo sely with the period of sensitivity to the protein synthesis inhibitor cycloheximide. Whereas the inhibition of protein synthesis affects on ly nuclear membrane breakdown and not chromatin condensation, genistei n inhibits both events. The results of these experiments suggest that protein phosphorylation and synthesis play major roles during pig oocy te maturation in vitro. It is concluded that genistein inhibited prote in phosphorylation is a regulator of chromatin condensation, whereas b oth new protein synthesis and phosphorylation appear to be required fo r nuclear membrane disassembly. Caution about this second conclusion i s, however, necessary because of the dual action of genistein on both protein phosphorylation and indirectly on protein synthesis.