Molecular cloning and expression analysis of 17β-hydroxysteroid dehydrogenase 1 and 12 during gonadal development, recrudescence and after in vivo hCG induction in catfish, Clarias batrachus

Abstract

In teleosts, the levels of steroids during critical period of sex differentiation are critical for gonadogenesis. Hence, steroidogenesis and expression of steroidogenic enzyme genes are very critical for gonadal development and function. In this regard, 17β-HSDs are important as they are involved in both 17β-estradiol (E2) and testosterone (T) biosynthesis. Full length cDNAs of 17β-HSD 1 (1791bp) and 12 (1073bp) were cloned from catfish gonads which encodes a protein of 295 and 317 amino acids, respectively. To understand the importance of these enzymes in teleost reproduction, mRNA expression was analyzed during gonadal development, seasonal reproductive cycle and after human chorionic gonadotropin (hCG) induction. Phylogenetic analysis revealed that the 17β-HSD 1 and 12 share high homology with their respective 17β-HSD forms from other teleosts and both the 17β-HSD forms belong to short chain dehydrogenase/reductase family. Tissue distribution analysis showed that the 17β-HSD 1 expression was higher in ovary and gills, while 17β-HSD 12 was higher expressed in testis, ovary, brain, intestine and head kidney compared to other tissues analyzed. Developing and mature ovary showed higher expression of 17β-HSD 1, while 17β-HSD 12 was higher in testis than the ovary of corresponding stages. Further, 17β-HSD 1 and 12 transcripts together with E2 and T levels were found to be modulated during different phases of the seasonal reproductive cycle. Expression of 17β-HSD 1 and 12 was upregulated after hCG induction which shows possible regulation by gonadotropin. Our findings suggest that 17β-HSD 1 and 12 might play important role in regulating gonadal development and gametogenesis through modulation of sex steroid levels.