In the mouse, the oocyte secretes a factor that enables cumulus cells to undergo expansion in response to epidermal growth factor (EGF) or FSH while expansion of the porcine cumulus oophorus has been shown to be independent of the oocyte. This study was undertaken to confirm independence of the porcine cumulus oophorus of the oocyte for its expansion and to determine if the porcine oocyte secretes the putative cumulus expansion-enabling factor that is required for FSH- stimulated mouse cumulus expansion. Porcine oocyte-cumulus cell complexes (P-OCC), oocytectomized oocyte-cumulus cell complexes (P-OOX) and intact clumps of cumulus cells (P-CCC) were cultured at 39 C in TCM-199 medium containing EGF (1 ng/ml) or FSH (1.5 μg/ml). After 24h culture periods, cumulus expansion was scored on an arbitrary scale of 0 to +4. EGF stimulated similar cumulus expansion (expansion score +3 compared to 0 for controls) in all the three groups. FSH stimulated cumulus expansion in significantly higher number of complexes in all groups compared to EGF. However, there was no difference in cumulus expansion among the three groups with EGF or FSH. To determine the production of the factor by the porcine oocyte, isolated clumps of cumulus cells of the mouse (M-CCC) were cocultured with porcine denuded oocytes (P-DO) in TCM-199 with or without 1.5 μg/ml FSH at 37 C for 24h. No expansion was observed when M-CCC were cultured alone in the presence of FSH or cocultured with P-DO in the absence of FSH. However, coculture of M-CCC with P-DO in the presence of FSH resulted in expansion of M-CCC similar to that observed in intact mouse oocyte-cumulus cell complexes (M-OCC) in response to FSH. These studies indicate that even though porcine cumulus expansion in vitro is not dependent on the oocyte, the porcine oocyte is capable of secreting cumulus expansion-enabling factor(s).
ASJC Scopus subject areas