Effects of Follicle Cells on in vitro Penetration of Pig Oocytes by Cryopreserved, Ejaculated Spermatozoa.

Cumulus-enclosed or denuded pig oocytes before and after maturation were inseminated with cryopreserved ejaculated spermatozoa in modified TCM-199. High proportions (79-94%) of cumulus-enclosed mature oocytes, but none of immature oocytes, were penetrated regardless of the presence of extra granulosa cells. However, significantly (P<0.001) higher penetration rates were always obtained in denuded mature and immature oocytes in the presence than in the absence of granulosa cells. All of the penetrated immature oocytes had decondensed sperm nuclei and remained at the germinal vesicle (GV) or condensed GV stage. The ability of granulosa cells to induce sperm capacitation and/or acrosome reaction was acquired fully when they were cultured for 36h at 39C. Frozen-thawed granulosa cell masses could support penetration of denuded mature oocytes in spite of complete loss in cell viability indicating that intercellular matrix and possibly cytosolic components liberated from damaged cells rather than components secreted from living cells may play an important role for inducing sperm capacitation and/or acrosome reaction and penetration of oocytes. The activity of the granulosa cell masses was completely lost by treatment of them at 60C for 30 min.