Maturation/M-phase promoting factor: A regulator of aging in porcine oocytes

Deterioration in the quality of mammalian oocytes during the metaphase-II a rrest period is well known as "oocyte aging." Oocytes in which aging has oc curred are called aged oocytes, and these oocytes show enhanced activation and higher fragmentation rates after parthenogenetic activation. Previously we showed that porcine aged oocytes had low maturation/M-phase promoting f actor (MPF) activity, and we suggested that this low MPF activity contribut ed at least in part to the aging phenomena. In the present study, we examin ed the relationship between MPF activity and these aging phenomena by artif icially regulating MPF activity in porcine metaphase-II-arrested oocytes. S ince we have shown recently that aged porcine oocytes contain abundant phos phorylated inactive MPF, so-called pre-MPF, we used vanadate and caffeine, which affect the phosphorylation status of MPF, to regulate MPF activity. I ncubation of 48-h-matured oocytes with vanadate for 1 h increased the phosp horylation of MPF and decreased MPF activity. The parthenogenetic activatio n and fragmentation rates were significantly increased compared with those of control oocytes. Conversely, treatment of 72-h-cultured aged oocytes wit h caffeine (last 10 h of culture) decreased the level of pre-MPF and elevat ed MPF activity. These oocytes revealed significantly lower parthenogenetic activation rates and a lower percentage of fragmentation than did untreate d aged oocytes. These results indicate that not only the increased ability for parthenogenetic activation but also the increased fragmentation rate ob served in porcine aged oocytes may be attributable in part to the gradual d ecrease in MPF activity during prolonged culture. Control of MPF phosphoryl ation with these agents may allow for some degree of manipulation of oocyte aging.