Utilizing well-characterized models for gonadotropin stimulation, withdrawal in the rat ovary, and porcine oogenesis, we report here, to our knowledge for the first time, the cellular localization and modulation of prohibitin expression during rat follicular maturation, atresia, and porcine oocyte/embryo development.
We have demonstrated that prohibitin expression in granulosa cells is not uniform across all stages of follicular development and that it follows two distinct expression patterns: one with a low prohibitin expression level in follicles within which cell proliferation dominates, and another with a high prohibitin expression in cells exhibiting differentiated functions typical of antral follicles. These two distinctive patterns suggest that prohibitin may be involved in granulosa proliferation as well as differentiation depending on the intensity of pro-hibitin signaling. Furthermore, the high immunoreactivity of prohibitin in theca-interstitial cells is consistent with the notion that their functions may also be mediated, in part, by prohibitin. Additionally, the presence of prohibitin in both differentiated and atretic follicles suggests that expression of this protein may be modulated by gonadotropin and that it is important in follicular maturation and atresia. Moreover, the observation that prohibitin is localized in both the cytoplasm and the nucleus of some cells in atretic follicles suggests that translocation of prohibitin from the cytoplasm to the nucleus may be associated with granulosa cell apoptosis and follicular atresia. Interestingly, this observation was similar to that seen in defective oocytes, defective fertilized eggs, and defective blastocysts.