The Indispensable Role of Androgen in Follicular Development of Wild Female Ground Squirrels (Citellus dauricus Brandt) During Non-Breeding Season.

Abstract

In the female reproduction, androgen may exert its biological function mainly via two different ways: one way is to bind androgen receptor; the other way is to be catalyzed to estrogen or other metabolites and then bind estrogen receptors. The wild female ground squirrel (Citellus dauricus Brandt) is such a typical seasonal breeder, which has a breeding season from April to May after hibernation and then goes through a long period of sexual dormancy from June to March. The seasonal breeders may offer a useful model to study basic mechanisms on the regulation of follicular development in the breeding and the non-breeding seasons without any manipulations. The aim of this study was to elucidate the regulation mechanism of androgen on the follicular development in wild female ground squirrels. Histological observations of ovaries and the statistical number of follicles in different developmental stages were performed in wild female ground squirrels. The results showed that the number of primary follicles had no significantly difference between the breeding and non-breeding seasons, however, the number of secondary follicles, antral follicles, post-antral follicles and corpus luteum displayed a significantly decrease from the breeding season to the non-breeding season. Immunoactivities of steroidogenic enzymes P450c17 and P450arom were detected in the ovaries during the breeding and the non-breeding seasons. The results of immunohistochemistry showed that the positive staining of P450c17 was localized in the theca cells during the breeding and the non-breeding seasons; Immunostaining of P450arom was detected in granulose cells only in the breeding season. The results of Western blotting indicated the optical density of P450c17 in Western blotting was no difference between the breeding and the non-breeding seasons; meanwhile, the optical density of P450arom in Western blotting reduced significantly from the breeding season to the non-breeding season. These results suggested that the ratio of catalysis from androgen to estrogen decreased from breeding season to non-breeding season, and androgen might directly affect follicle development the non-breeding season. Based on all above findings, we hypothesized that androgen might play an important role mainly though binding its receptor in the process of developmental follicles of wild female ground squirrels during the non-breeding season. Therefore, the immunoactivities of androgen receptor (AR) and estrogen receptors (ERalpha and ERbeta) were also detected in the ovaries of wild female ground squirrels during the breeding and the non-breeding seasons. The results of Western blotting suggested the immunoactivity of AR was no significantly difference between the breeding season and non-breeding season; however, the immunoactivities of ERalpha and ERbeta were both significantly reduced from the breeding season to the non-breeding season. In conclusion, wild female ground squirrels offer a useful animal model to study the regulation pathway of androgen during the process of follicular development in ovary. Androgens may mainly transform into estrogen to regulate the follicular development via binding estrogen receptors during breeding season, whereas androgens may bind androgen receptors directly to regulate the follicular development during non-breeding season in the ovary of the wild female ground squirrel. This study is supported by Program for Changjiang Scholars and Innovative Research Team in Universities (IRT0607) from China. (poster)