Expression of epiregulin and amphiregulin in the rat ovary.

We have previously reported that the epidermal growth factor (EGF) family growth factor, epiregulin, is expressed in rat ovarian granulosa cells by induction with pregnant mare serum gonadotropin (PMSG). In this study, we report that amphiregulin, another member of the EGF family, was also induced in the rat ovary by gonadotropin treatment. Northern blot analysis revealed that PMSG treatment induced the expression of both epiregulin and amphiregulin mRNA after 24 h, but the expression then decreased 48 h after treatment. Further treatment with human chorionic gonadotropin (hCG) rapidly induced the expression of both epiregulin and amphiregulin genes and maximal levels were reached 4 h after hCG treatment. A marginal increase in amphiregulin mRNA levels was also observed 6 h after PMSG treatment. In situ hybridization revealed that epiregulin and amphiregulin mRNAs were localized in the granulosa cells of large antral follicles. These spatio-temporal expression patterns were similar to those of cyclo-oxygenase-2 (COX-2) and progesterone receptor (PR). In adult cycling rats, epiregulin and amphiregulin were strongly induced at 1800 and 2000 h on proestrus coinciding with the preovulatory LH surge. An in situ hybridization study also showed that epiregulin and amphiregulin mRNAs were detectable in the granulosa cells of preovulatory ovarian follicles at 2000 h on proestrus, where transcripts of COX-2 and PR were co-localized with those of epiregulin and amphiregulin. These observations suggested that the EGF family members, epiregulin and amphiregulin, may play a role in the ovulatory process of cycling rats as well as in the induction of ovulation in immature rats.