Seasonal Changes In Immunoreactivity Of C-kit/SCF And Testicular Function In The Wild Male Ground Squirrel (Citellus Dauricus Brandt)

Seasonal breeding is a kind of special reproductive mode which is suitable for the adaption of the wild environment. It is a common phenomenon in the wildlife rather than experimental animals. The wild ground squirrel (Citellus dauricus Brandt), a widely-spread rodent, offers an ideal model for the study of the seasonal breeding mechanisms. The wild ground squirrels are seasonal breeder with a breeding season from April to May.c-kit is a kind of proto-oncogene which encodes a transmemberane tyrosine kinase receptor. The binding with its ligand SCF (stem cell factor) functions in several major cell systems, including hematopoiesis, melanogenesis, the gastrointestinal tract, and gametogenesis. In gametogenesis, c-kit/SCF system plays a regulate role in the migration and proliferation of primordial germ cells during embryogenesis development, post-natal germ cells and spermatogenesis.The objectives of this study were to determine whether there were seasonal changes in spermatogenesis and immunoreactivity of c-kit/SCF system, and to correlate these changes with testicular steroidogenesis. Testes of 41 the wild ground squirrels were captured in the breeding period (May), the non-breeding period (July) and pre-hibernation (September) of 2009, histological and immunohistochemical observations of testicular tissues were performed in wild male ground squirrels. Total proteins were extracted from testicular tissue were used for Western blotting analysis. Histologically, all types of spermatogenic cells including mature spermatozoa were found in the breeding season, only spermatogonia and primary spermatocytes were identified in the non-breeding season, while spermatogonia, primary spermatocytes and second spermatocytes were observed in pre-hibernation. Immunolocalization of SCF and FSH receptor were detected in Sertoli cells during the breeding season and pre-hibernation. The positive signal of the c-kit receptor correlated to PCNA was observed in spermatogonia and Leydig cells during the breeding season and pre-hibernation. Proto-oncogenes c-fos and c-jun were also observed in different seasons in the testis of wild ground squirrels and the mean level is higher in breeding season than in non-breeding and pre-hibernation season. The highest immunoreactivity for P450scc,3βHSD and P450c17 were also observed in testes during the breeding season. In additional, the mean level of SCF and the c-kit receptor protein in the breeding season and pre-hibernation were significantly higher than those in the non-breeding season, In conclusion, the present studies provided new evidences, that seasonal changes in testicular activity are correlated with changes in immunoreactivity of c-kit/SCF system in the wild ground squirrel; SCF and the c-kit receptors interactions might contribute to events either steroidogenesis or spermatogenesis; as the intrinsic regulator, the c-kit receptor may act as a marker of seasonal change of spermatogenesis in the wild ground squirrels.