Abstract
In the present study, a regulation mechanism of porcine oocyte maturation was examined with special focus on maturation promoting factor (MPF), a crucial regulator of cell division cycle composed of catalytic subunit, p34cdc2 and regulatory subunit, cyclin B, and Mitogen-activated protein kinase (MAPK). At first, an in vitro maturation system using porcine follicular fluid as maturation medium was established in order to mature the oocytes physiologically normal. The oocytes in the germinal vesicle stage (GV) had a significant amount of p34cdc2 and MAPK, which concentrations were not changed throughout maturation. An extremely small amount of cyclin B was present in GV oocytes and cyclin B was not synthesised during GV. The extremely small amount of cyclin B associated p34cdc2 was inactivated by tyrosine phosphorylation and MAPK is also inactive during GV. Germinal vesicle breakdown (GVBD) was induced by tyrosine dephosphorylation of p34cdc2. After GVBD, cyclin B synthesis was started and the amount of cyclin B associated p34cdc2 and MPF activity were increased dramatically. MAPK was also activated by phosphorylation and maintained the high activity until the second metaphase (Met2). MPF activity was decreased transiently after the first metaphase (Merl) then reactivated at Met2 without tyrosine dephosphorylation. The amount of cyclin B associated p34cdc2 in Met2 was greater than that in Metl and most of them were stored as pre-MPF. These results suggest that the regulation of porcine oocyte maturation is essentially similar with other reported species but have some modifications specific for porcine oocytes.
