Histone H1 and MAP kinase activities in bovine oocytes following protein synthesis inhibition

In vitro nuclear maturation is associated with known activity profiles of the M-phase promoting factor (MPF) and the mitogen-activated protein (MAP) kinases, which are two key regulators of mitotic and meiotic cell cycles. Initiation of meiotic resumption in vitro can be prevented by cycloheximide treatment and after removal of the inhibitor germinal vesicle breakdown takes place nearly twice as fast as in untreated controls. In this study experiments were conducted in order to examine the chromosome condensation status and the dynamics of MPF and MAP kinase activities after cycloheximide treatment (10 microg/ml) of cumulus-enclosed oocytes for 17 and 24 h, respectively, and subsequent culture in inhibitor-free medium for various times. Bovine oocytes displayed variations in the degree of chromosome condensation at the end of the inhibitor treatment phase. Following removal of the inhibitor germinal vesicle breakdown occurred after 4-5 h of subsequent culture in inhibitor-free medium. MPF and MAP kinase exhibited low activities during the first 1-3 h following cycloheximide treatment. Increasing levels of enzyme activities were detected 4-7 h following cycloheximide treatment for 17 and 24 h, respectively, and subsequent culture in inhibitor-free medium. The patterns of enzyme activities corresponded with the accelerated nuclear maturation process. It can be concluded that cycloheximide treatment does not lead to a more synchronous course of nuclear maturation and that the activities of both, MPF and MAP kinase are initiated at least 2-5 h earlier in comparison with untreated oocytes.