Seasonal Expression Of Androgen Receptor Estrogen Receptor And Hormone Synthesis Enzyme In The Ovaries Of Wild Female Ground Squirrels(Citellus Dauricus Brandt)

Seasonal breeding is a special reproductive characteristic and strategy of wild animals to adapt to the environment and ensure their offspring survive in the long-term evolutionary process. It is common in the wildlife rather than experimental animals. Wild ground squirrels are typical seasonal breeders. The breeding season is April to May, the nonbreeding season is June to October, the hibernation season is October to March the next year. The wild female ground squirrel provided us with a useful model to study the role of androgen in follicular development during the breeding and nonbreeding seasons. The aim of this study was to elucidate the immunoreactivities of androgen receptor (AR), estrogen receptor (ERa and ERb) and hormone synthesis enzyme (P450c17and P450arom) and the regulatory role of androgen in the follicular development of wild female ground squirrels. Morphological observation was utilized to detect the size and weight of ovaries during the breeding and the nonbreeding seasons. Histological observations of follicular in the ovary were performed in wild female ground squirrels. And immunolocalization of FSHR, LHR, P450c17, P450arom, AR and ERs were executed in ovaries of wild ground squirrels between breeding and non-breeding season. The results of morphology showed that there were significantly reduced in the size and weight of ovaries of wild female ground squirrels from the breeding to the nonbreeding seasons. According to the results of histological observation, Follicles were observed at every different stage of the follicular development in the ovaries of the breeding season, including primary follicle, secondary follicle, antral follicle, dominant follicle and corpus luteum. Only primary follicles and secondary follicles were found in the ovaries of the nonbreeding season. Immunohistochemical staining of FSHR, LHR, P450c17, P450arom, androgen receptor, estrogen receptors were executed in ovaries of female ground squirrels from both breeding and nonbreeding seasons. In addition, total ovarian proteins were extracted from the ovaries of squirrels from breeding and nonbreeding seasons, and Western blot analysis were performed in order to probe for FSHR,LHR, P450c17. P450arom,AR, ERa and ERb. The results of immunohistochemical staining and Western blotting of P450cl7showed that there was no significant difference between the breeding and nonbreeding seasons. It was found that granulosa cells expressed P450arom during the breeding season. In contrast, there was no positive staining of P450arom in the nonbreeding season. There was no significant difference in immunoreactivity of AR between the breeding and nonbreeding seasons. However, the immunoreactivities of ERa and ERb were both significantly reduced in the nonbreeding season compared to the breeding season. The positive stains of FSHR and LHR were found in the granulosa cells and theca cells of the ovaries of the breeding and nonbreeding seasons. In addition, the Western blotting results of FSHR and LHR showed a significant reduction in the nonbreeding season compared with the breeding season. These findings suggested that androgen might be predominantly converted into estrogen in order to regulate the follicular development via binding of estrogen receptors during the breeding season, whereas androgen might predominantly directly bind androgen receptor to regulate the follicular development during the nonbreeding season in the ovaries of wild female ground squirrels.