INHIBITION OF PROTEIN-SYNTHESIS AFFECTS HISTONE H1 KINASE, BUT NOT CHROMOSOME CONDENSATION ACTIVITY, DURING THE FIRST MEIOTIC DIVISION OF PIG OOCYTES

The influence of protein synthesis on the regulation of the first meio tic division was studied in pig oocytes. We show that histone H1 kinas e activity gradually increases during in vitro culture of pig oocytes, reaching maximum in metaphase I stage after 24 hr of culture. However , in the presence of the protein synthesis inhibitor cycloheximide, hi stone H1 kinase is not activated during the whole culture period, and after 24 hr it is approximately at the same level as in prophase-stage oocytes. The gradual increase in phosphorylation of six proteins of m olecular weights 39, 48, 53, 66, 96, and 120 kDa, observed during the first 24 hr of culture, was not detected when cycloheximide was added to the culture medium. Similarly, the decrease in phosphorylation of a 90-kDa protein was not seen in cycloheximide-treated oocytes. On the other hand, the levels of both MPF components, p34(cdc2) and cyclin B, which were found to be nearly constant during the first meiotic divis ion, were not influenced by cycloheximide treatment as revealed by Wes tern blotting. The process of germinal vesicle breakdown (GVBD) was to tally blocked by cycloheximide. The condensation of chromatin, however , was not influenced, suggesting that GVBD and chromosome condensation could be regulated independently. The different degrees of MPF activa tion involved in these processes, as well as the nature of the protein (s) which must be synthesized for triggering GVBD, are discussed. (C) 1995 Wiley-Liss, Inc.