Kinetics of meiotic progression, M-phase promoting factor (MPF) and mitogen-activated protein kinase (MAP kinase) activities during in vitro maturation of porcine and bovine oocytes: species specific differences in the length of the meiotic stages

The kinetics of nuclear maturation, M-phase promoting factor (MPF) and mitogen-activated protein kinase (MAP kinase) activities during in vitro maturation of porcine and bovine oocytes were examined. A further objective was to determine the duration of the meiotic stages during the maturation process. Porcine and bovine cumulus–oocyte complexes (COCs) were incubated in TCM 199 supplemented with 20% (v/v) heat inactivated fetal calf serum (FCS), 0.05 μg/ml gentamycin, 0.02 mg/ml insulin, 2.5 μg/ml FSH and 5 μg/ml LH. COCs were removed from the culture media in hourly intervals starting immediately after recovery from the follicle until 24 (bovine) or 48 h (porcine) of culture. Oocytes were either fixed to evaluate the maturation status or the activity of MPF, assessed by its histone H1 kinase activity, and MAP kinase were determined by a radioactive assay simultaneously. In oocytes of both species, the MPF activity oscillated during the culture period with two maxima corresponding with the two metaphases: between 27–32 and after 46 h (porcine) and between 6–9 and after 22 h (bovine). There was a temporary decline in activity after 33–38 (porcine) and after 19 h (bovine), which corresponded with anaphase I and telophase I. MAP kinase activity increased during the whole culture period and reached maximum levels after 47 (porcine) and after 22 h (bovine). In porcine oocytes, the MAP kinase was activated before GVBD and MPF activation. In bovine oocytes, MPF and MAP kinase were activated at approximately the same time as the GVBD (8–9 h of incubation). In average porcine, oocytes remain 23.4 h in the germinal vesicle (GV) stage (13 h in GV I, 5.7 h in GV II, 3.2 h in GV III and 1.5 h in GV IV), 0.9 h in diakinese, 9.6 h in the metaphase I, 2.8 h in anaphase I and 1.9 h in telophase I of the first meiotic division. In bovine oocytes, the temporal distribution of the meiotic stages were 8.5 h for the GV stage, 1.2 h for diakinese, 8.3 h for metaphase I, 1.6 h for anaphase I and 1.9 h for telophase I. These results indicate that the duration of the meiotic stages differs between the species and that MAP kinase is activated before MPF and GVBD in porcine oocytes.