Effects of wortmannin on the kinetics of GVBD and the activities of the maturation-promoting factor and mitogen-activated protein kinase during bovine oocyte maturation in vitro

The present study was conducted with the objective of examining the effect of wortmanin, a specific PI 3-kinase inhibitor, on the kinetic of GVBD, and on the activities of the maturation-promoting factor (MPF) and mitogen-activated protein (MAP) kinase during bovine oocyte maturation. The time sequence for GVBD was not different between oocytes cultured with or without wortmannin. Most of the cultured oocytes were at the filamentous bivalents stage after 4 h of culture. Six hours after the start of culture, most of the oocytes possessed germinal vesicles with condensed bivalent, and by 10 h of culture nearly all of the cultured oocytes underwent GVBD. A gradual increase in MPF activity until 12 h of culture was observed in the presence and absence of wortmannin. A sharp decrease in MPF activity in oocytes cultured without wortmannin treatment was recorded at 14 h of culture. Thereafter, MPF regained activity, reaching a maximum level at 20 to 24 h of culture. For oocytes cultured with wortmannin, no decline in the activity of MPF was observed during the interval from 12 to 24 h of culture. For these oocytes the MPF activity remained nearly stable during this transition until the end of incubation. The presence of wortmannin in the maturation medium did not alter MAP kinase activity. Taken together, these observations indicate that inhibition of PI 3-kinase does not modulate the time sequence of GVBD or the pattern of MAP kinase activity in bovine oocytes. However, PI 3-kinase might be one of the molecules that regulate the sharp reduction in the activity of MPF during the MI/MII transition.