Effect of Igf-i, Leptin, Ghrelin and Mapk-erk on the Nuclear Maturation of Bovine Oocytes

The aim of the study was to examine the involvement of insulin-like growth factor-I (IGF-I), leptin, ghrelin and mitogen-activated protein kinase (MAPK)-ERK1/2 in control of nuclear maturation of bovine oocytes. The oocytes isolated from bovine ovaries were cultured in TCM199 medium with or without IGF-I, leptin and ghrelin supplementation in a humidified atmosphere at 39°C during 24 h (5% CO2). The stage of meiosis and the presence of MAPK/ERK within the oocyte were analysed by immunocytochemistry, DAPI staining and evaluated by fluorescent microscope. Preliminary analysis showed that the matured metaphase II stage oocytes after culture contained less MAPK, than the immature ones (64% vs 100%, respectively). The addition of IGF-I stimulated meiosis (90% vs 76%), but not the expression of MAPK (82% vs 100%). The treatment with leptin did not influence nuclear maturation (73% vs 76%), but increased the proportion of cells containing MAPK (up to 91%). Ghrelin addition did not influence meiosis (85%), but increased the expression of MAPK (up to 89%). The obtained preliminary results suggest that (1) the culture of bovine oocytes induces their nuclear maturation, which is associated with the reduction of accumulation of MAPK, (2) IGF-I, but not leptin or ghrelin, promotes bovine oocyte nuclear maturation, and that (3) leptin and ghrelin, but not IGF-I, increase the expression of MAPK within the oocytes. These observations suggest that MAPK, IGF-I, leptin and ghrelin may be involved in the control of oocyte nuclear maturation, although the interrelationships between these signaling substances require further studies.