Mouse cumulus-oocyte complexes from in vitro-cultured preantral follicles suggest an anti-luteinizing role for the EGF cascade in the cumulus cells.

The mammalian ovulatory process is a fairly complex succession of events that leads to the release of a competent oocyte. The luteinizing hormone triggers the cascade of events which starts with the production of secondary messengers in the follicular wall and ends with the release of a fertilizable oocyte. Most of these events can be reproduced in in vitro models which offer a wide range of possibilities for study strategies. Although it is accepted that EGFR activation is required for the transmission of the LH initiated signal, we hypothesized that LH receptor activation might also play a role on oocyte meiotic resumption and cumulus cell response as the current mouse preantral follicle in vitro model express functional LH receptor. In order to separate the LH-mediated response and the EGF-mediated response (following LH stimulus), in vitro-grown mouse ovarian follicles were stimulated for ovulation with a combination of hCG + galardin (inhibitor for the release of endogenous EGF-like factors) and hCG + galardin + EGF. Results suggest that the stimulation provided by LH (hCG) is insufficient to induce a maximum oocyte meiotic resumption and that EGF receptor activation is also required. Analysis of transcript levels of Egfr, Ereg, Cyp19a1, Hsd3b1, Adamts1, and Has2 in cumulus cells further indicated that the triggers for the EGF receptor cascade preserve the expression profile of the studied transcripts. Therefore, it is proposed that within this in vitro mouse model, EGF signaling during ovulation might protect the cumulus cells from the potential luteinizing effects of LH.