Effects of transforming growth factors and activin-A on in vitro porcine oocyte maturation.

Growth factors are known to regulate ovarian function. In the present study, effects of these growth factors, TGF-alpha, TGF-beta, and activin-A were tested on spontaneous porcine oocyte maturation. Cumulus-oocyte complexes (COC) were cultured in the presence of TGF-alpha, TGF-beta, and activin-A for 48 hr. Stages of meiotic maturation were assessed by staining with acetic orcein. Among these factors, only TGF-alpha significantly enhanced the maturation rate, whereas TGF-beta suppressed the spontaneous maturation rate. The site of action of TGF-alpha on COC and the interaction between TGF-alpha and EGF receptor was also examined. Denuded oocytes, alone or in coculture with cumulus cells, were cultured in the presence of TGF-alpha for 48 hr. TGF-alpha did not have any significant effect on denuded oocyte maturation. Heptanol was employed to investigate the role of gap junctions on TGF-alpha-induced oocyte maturation in COC. Although heptanol did not have any significant effect in the control medium, heptanol reversed the stimulatory effect of TGF-alpha on porcine oocyte maturation. TGF-alpha was able to displace 125I-EGF binding on COC. In conclusion, TGF-alpha enhances the spontaneous maturation of porcine oocytes by generating positive signal(s) in cumulus cells that are transferred to the oocyte via gap junctions. TGF-alpha shares the same receptor with EGF on porcine COC. TGF-beta, in contrast, inhibits porcine oocyte maturation.