The Japanese eel (Anguilla japonica) and Nile tilapia (Oreochromis niloticus) 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) cDNAs were isolated from their respective testes cDNA libraries. The cDNAs predict two peptides of 436 and 406 amino acid residues that share about 42% homology with mammalian 11beta-HSD type 2 proteins. Analysis of the tissue distribution pattern by RT-PCR reveals that 11beta-HSD2 is expressed in a wide variety of tissues in tilapia, with higher expression in kidney and gill of both sexes, and with the highest expression in testis. 11beta-Dehydrogenase activity of the eel 11beta-HSD2 was confirmed by demonstrating the conversion of cortisol to cortisone by the recombinant protein after transient expression of this cDNA clone in COS-1 cells. Bands of approximately 2.7 and approximately 3.8 Kb were detected in Northern blot of eel and tilapia testes respectively, which is consistent with the cloned cDNA sizes of the two species. Northern blot analysis also revealed that the expression of the eel testis 11beta-HSD2 gene could be induced by human chorionic gonadotropin (hCG) injection, implying a role of 11beta-HSD2 in hCG-induced 11-ketotestosterone production and spermatogenesis in the Japanese eel.

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