Follicle somatic cells influence pig oocyte penetrability and cortical granule distribution

The influence of somatic cells on oocyte penetrability was studied during in vitro maturation. Four experiments were carried out. In the first, pig oocytes were fertilized in vitro immediately after collection (immature oocytes) or after being cultured for 44 hr with cumulus cells connected to the whole wall of the extroverted follicle (follicle oocytes) or without cumulus cells (denuded oocytes) (Mattioli et al.: Gamete Res 20:177-183, 1988a). In follicle and immature oocytes, 12 hr after insemination, the sperm were equally distributed between zona and ooplasm; in denuded oocytes, the majority (90.5%) of the sperm were located in the zona. In the second experiment, zonae pellucidae of follicle and denuded oocytes, obtained after 44 hr of culture, were incubated with a sperm suspension for 2 hr at 39 degrees C to evaluate the zona binding. The different number of sperm found on the zona pellucida of follicle or denuded oocytes (49.3 +/- 2.97 vs. 37.8 +/- 1.77) did not achieve statistical significance (P greater than 0.05). In the third experiment, follicle and denuded oocytes were denuded of their zonae after maturation and then fertilized in vitro. The number of sperm recorded in the ooplasm of zona-free follicle oocytes was significantly higher than that recorded in zona-free denuded oocytes (9.2 +/- 0.93 vs 1.19 +/- 0.28) (P less than 0.01). In the last experiment the influence of somatic cells on the distribution of cortical granules was evaluated. Pig oocytes were denuded at different stages of culture and, after completion of maturation, processed for electron microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)