Abstract. After reaching metaphase II, in vitro matured oocytes undergo the complex processes referred to as oocyte aging. Under our culture conditions, some aged oocytes remained at the stage of metaphase II, some underwent spontaneous parthenogenetic activation and others underwent cellular death, either through apoptosis (fragmentation) or lysis. We investigated the effect of c-Jun N-terminal kinases (JNK) and p38 Mitogen-activated protein kinase (p38 MAPK) inhibition on pig oocyte aging and the activity of JNK and p38 MAPK during the aging period. Inhibition of JNK protected the oocytes from fragmentation (0% fragmented oocytes under JNK inhibition vs. 26% fragmented oocytes in the control group). Inhibition of p38 MAPK had no effect on fragmentation. Inhibition of JNK also had an influence on spontaneous parthenogenetic activation of aged oocytes. The ratio of activated JNK to total JNK decreased during aging of oocytes. However, exit from MII had no effect on it. The ratio of activated p38 MAPK to total p38 MAPK did not change significantly. The phosphorylated form of JNK is present in fragmented and activated oocytes, while lysed oocytes lack the active form of JNK. Based on our data, we can conclude that JNK plays an active role in fragmentation of pig oocytes and that p38 MAPK is not involved in this process.

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ABSTRACT:The objective of the study was to verify the hypothesis that GEN (genistein -phytoestrogen and an inhibitor of tyrosine protein kinase -TPK) effects on pig oocyte maturation and cumular cell expansion under in vitro conditions are connected with its estrogenic activity. Oocytes were cultivated for 24 hours up to the stage of the first meiotic metaphase (MI). Three different doses of GEN (13, 40, 80 µg/ml of medium) and also three doses of GIN, genistin, an analogue of GEN without effects on TPK, (80, 160 and 240 µg/ml of medium) were tested. To verify the reversibility of GEN effects, the oocytes were first cultivated for 24 hours with 80 µg of GEN per 1 ml of medium and then for another 24 hours without any GEN. GEN blocked pig oocyte maturation at the stage of the germinal vesicle (GV), depending on the dose. After rinsing out the GEN the oocyte maturation recovered, but with abnormalities (32%). GIN in a concentration of 80 µg/ml of medium induced a significant blockage at the GV stage (18%). With an increase in the GIN concentration, the number of oocytes blocked at the GV stage significantly decreased, but the abnormal maturation increased (up to 31%). GEN inhibited the cumular cell expansion in proportion to its dose. GIN had a less pronounced effect. As GEN and GIN effects demonstrate similar patterns, it is probable that estrogenic activity is involved.