Localization of Five Steroidogenic Enzyme mRNAs in Japanese Black Bear (Ursus thibetanus japonicus) Testes During the Mating Season by In Situ Hybridization

The Japanese black bear (Ursus thibetanus japonicus) is a typical seasonal breeder that has a mating season in early summer. Spermatogenesis and testicular steroidogenesis are known to develop and regress annually; however, its molecular mechanism has not yet been investigated. In the present study, we clarified the mRNA sequence of 5 steroidogenic enzymes (P450scc, 3 beta HSD, P450c17, 17 beta HSD3 and P450arom) using RT-PCR and RACE methods and the localization of these gene expressions in the bear testis using an in situ hybridization technique. The amino acid sequence deduced from each mRNA sequence had high homology with the corresponding sequences of other species and possessed a motif typical of the P450 family or short chain alcohol dehydrogenase family. Expression of P450scc, 3 beta HSD and P450c17 mRNA in interstitial tissue indicated that conversion from cholesterol to androstenedione occurs in Leydig cells. On the other hand, the mRNA of 17 beta HSD3, which plays a central role in synthesizing testosterone, was detected not only in the interstitium but also inside the seminiferous tubules, along the basement membrane. P450arom mRNAs were distributed in the seminiferous tubules. These results suggest the possibility of testosterone and estradiol-17 beta synthesis inside the seminiferous tubules in the bear testis. We expect that the results of this study will be useful for further investigation of the molecular mechanism of steroidogenic seasonality in the bear testis.