Sox3 binds to 11β-hydroxysteroid dehydrogenase gene promoter suggesting transcriptional interaction in catfish

In fishes, the expression of steroidogenic enzyme genes and their related transcription factors (TFs) are critical for the regulation of steroidogenesis and gonadal development. 11-KT is the potent androgen and hence, 11β-hsd, enzyme involved in 11-KT production is important. Regulation of 11β-hsd gene was never studied in any fishes. At first 11β-hsd was cloned and recombinant protein was tested for enzyme activity prior to expression and promoter motif analysis. Expression changes revealed stage- and sex-dependent increase in the ontogenic studies. Further, 11β-hsd expression was higher during spawning phase of reproductive cycle and was found to be gonadotropin inducible both in vivo and in vitro. ∼2kb of 5' upstream region of 11β-hsd, was cloned from catfish genomic DNA library and in silico promoter analysis revealed putative TF binding sites such as Sox3, Wt1, Pax2, Dmrt1 and Ad4BP/SF-1. Luciferase reporter assay using the sequential deletion constructs in human embryonic kidney and Chinese hamster ovary cells revealed considerable promoter activity of the constructs containing Sox3, but not with other motifs largely. Site-directed mutagenesis, Sox3 over expression, electrophoretic mobility shift and chromatin immunoprecipitation assays further substantiated the binding of Sox3 to its corresponding cis-acting element in the upstream promoter motif of 11β-hsd. This is the first report to show that Sox3 binds to the 11β-hsd gene promoter and transactivates to regulate male reproduction in a teleost.