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Influence of growth factors on the time-dependent meiotic progression of the bovine oocytes during their in vitro maturation.

The present study examines the effects of epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), and the presence of cumulus cells on the meiotic progression of the bovine oocyte maturation. Oocytes were aspirated from 2-8 mm ovarian follicles, and the cumulus-oocyte complexes (COC) obtained (n = 2,729) were divided into COC or denuded oocytes. They were then cultured in four defined treatments comprising TCM-199 and growth-factors: control (no growth factor), IGF-I, EGF, and EGF+IGF-I. Each treatment group of oocytes was cultured during 6, 12, 18, 24, and 30 h; the oocytes were fixed and stained at the end of each 6 hour interval from 0 to 30-h, and were assessed for their nuclear maturation stage. Germinal vesicle (GV) and metaphase II (MII) stages present were used as the final parameters for data analysis. The results indicate that treatments with growth factors enhanced the incidence of GV activation and MII stage in all the culture periods. Maximal stimulation for nuclear maturation occurred with EGF+IGF-I. As regards the denuded oocytes, no positive effects on nuclear maturation rates were observed for any treatment. These results suggest that EGF and IGF-I, singly and combined, stimulate the meiotic progression significantly, and this effect can be induced by a positive signal which is transferred from cumulus cells to oocyte.