Cloning and expression of 3β-hydroxysteroid dehydrogenase during gonadal recrudescence and after hCG induction in the air-breathing catfish, Clarias gariepinus

Abstract

3β-hydroxysteroid dehydrogenase (3β-hsd) plays an important role in biosynthesis of both androgens and estrogens during steroidogenesis. In this study, we report the cloning of a full-length cDNA of 3β-hsd from gonads of the air-breathing catfish, Clarias gariepinus a seasonally reproducing teleost fish. We studied the expression pattern of 3β-hsd during gonadal ontogeny and recrudescence (flanking two years of reproductive cycle) using real-time PCR. We also examined the influence of gonadotropin on 3β-hsd expression in gonads of catfish by human chorionic gonadotropin (hCG) induction. The real-time PCR results revealed that 3β-hsd transcript was detectable much earlier in undifferentiated gonads i.e. before the sex differentiation and later on its expression was seen in both male and female gonads throughout the development. The expression analysis during subsequent seasonal reproductive cycle in catfish (older than one year) showed that in adult males, the transcripts were significantly high during prespawning phase (spermatogenesis) and declined during spermiation. In adult females, the transcripts were abundantly expressed in the ovarian follicles both at prespawning and spawning phases. Furthermore, the 3β-hsd mRNA levels in different follicular stages were markedly high in vitellogenic follicles (maturing oocytes; stage III) compared to other stages. Treatment of hCG in recrudescing female fish, in vivo as well as in testicular slices, in vitro resulted in the up-regulation of gonadal 3β-hsd mRNA indicating that it is under the regulation of gonadotropins. These results together suggest that 3β-hsd gene plays an important role during spermatogenesis and oogenesis as well as in the gonadal recrudescence of catfish.