Meiotic Maturation of Bovine Oocytes Cultured In Vitro with EGF and Wortmannin.

Abstract

This study was designed to examine the effect of EGF on meiotic maturation of bovine oocytes and to evaluate the ability of wortmannin, a specific PI 3-kinase inhibitor, to modulate EGF-induced oocyte maturation. EGF significantly improved meiotic maturation of both cumulus-intact and denuded oocytes. Wortmannin effectively and irreversibly blocked oocytes from progressing to the MII stage. When oocytes were transferred to wortmannin-treated medium after being cultured for 2 h in wortmannin-free medium, 36% of them progressed to the MII stage. By delaying the time of transfer to 4 h, 64% of the oocytes developed to MII, and by further delaying to 6 h, the rate of MII formation was almost similar to that of oocytes cultured without wortmannin supplementation. Culturing of the oocytes with EGF for 2 h did not improve their meiotic maturation. Increasing the incubation period with EGF for 4 or 6 h resulted in a maturation rate similar to that of those cultured with EGF for the total period of incubation. Data suggest that EGF is capable of stimulating bovine oocyte meiotic maturation regardless of the presence of cumulus cells, and that PI 3-kinase is involved in this process. Results also show that inhibition of PI 3-kinase from 6 h after the onset of culture does not block meiotic progression, and that EGF induces its positive maturation signal during the first 4 h of culture period.