In this study, the effects of U0126 that inhibits the activity of mitogen-activated protein (MAP) kinase kinase (MEK), and LY294002, which is a phosphatidylinositol (PI) 3-kinase inhibitor, on meiotic progression beyond the metaphase I (MI) stage in porcine oocytes were examined. Cumulus-oocyte complexes (COCs) were cultured for 22 h with 50 μM LY294002 or 10 μM U0126 following cultivation for the initial 22 h. MAP kinase activity in oocytes cultured with LY294002 or U0126 was significantly lower than that in control oocytes cultured for up to 44 h. U0126 and LY294002 significantly decreased p34cdc2 kinase activity and the proportion of oocytes reaching the MII stage compared to those in control oocytes. Oocytes denuded after COCs had been cultured for 22 h were cultured further for 22 h with U0126 or LY294002. In the denuded oocytes, U0126 suppressed MAP kinase activity, p34cdc2 kinase activity, and meiotic progression to the MII stage; however, LY294002 did not significantly affect the activity of these kinases and meiotic progression. These results suggest that increasing MAP kinase activity in oocytes via the PI 3-kinase signaling pathway in cumulus cells is involved in the stimulation of maturation promoting factor, leading to meiotic progression beyond the MI to MII stage in porcine oocytes.
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