ENHANCEMENT OF CUMULUS EXPANSION AND NUCLEAR MATURATION DURING BOVINEOOCYTE MATURATION IN-VITRO BY THE ADDITION OF EPIDERMAL GROWTH-FACTORAND INSULIN-LIKE GROWTH-FACTOR-I

This study was carried out to identify the possible effects of epiderm al growth factor (EGF) and insulin-like growth factor-I (IGF-I) on cum ulus expansion and nuclear maturation in bovine oocytes matured in vit ro in serum-free media. Bovine follicular oocytes were matured in vitr o and were then classified as cumulus cell-enclosed oocytes or denuded oocytes. They were then cultured for 24 h in TCM-199 (tissue culture medium-199) with EGF (50 ng ml(-1)), IGF-I (100 ng ml(-1)) and EGF plu s IGF-I (50 and 100 ng ml(-1), respectively). At the end of the cultur e period, the morphology of oocytes was evaluated for cumulus expansio n and nuclear stage of maturation. In Expt 1, percentages of oocytes r eaching maximum cumulus expansion were: 12.5% (control), 46.5% (EGF), 15.2% (IGF-I) and 52.8% (EGF plus IGF-I). In Expt 2, the respective ra tes of nuclear maturation were: 35.6%, 52.1%, 45.5% and 61.4% for cumu lus cell-enclosed oocytes, and 35.5%, 46.6%, 45.4% and 42.5% for denud ed oocytes; the same growth factor treatments were used in both cases. There was no significant effect of IGF-I on cumulus expansion. Maximu m rates of cumulus expansion and nuclear maturation were obtained in t he presence of both growth factors. These results lead to the followin g conclusions: (i) EGF, either alone or together with IGF-I, stimulate s cumulus expansion; and (ii) both growth factors, acting alone or tog ether, enhance nuclear maturation in oocytes surrounded by compact cum ulus cells.