Cloning of 17β-hydroxysteroid dehydrogenase-1 cDNAs from Japanese eel ovary

17 beta -hydroxysteroid dehydrogenase-I (17 beta -HSD-I) is a key steroidogenic enzyme for estradiol-17 beta (E-2) production, cDNAs encoding 17 beta -HSD-I were cloned for the first time in lower vertebrates from the ovary of a teleost, the Japanese eel. The deduced amino acid sequence from these cDNAs was approximately 50% identical to mammalian 17 beta -HSD-Is. 17 beta -HSD-I mRNA was not detected in previtellogenic ovaries by Northern blotting. However, transcript abundance increased in early vitellogenic ovaries obtained from fish artificially matured by gonadotropic treatment, but thereafter did not appear to change further. Recombinant 17 beta -HSD-I expressed in human kidney 293 cells selectively converted estrone to E-2, but androstenedione, testosterone, or E-2 were not converted to any other steroids. Although it is widely accepted that E-2 is produced from testosterone in other species of teleosts, the substrate specificity of eel 17 beta -HSD-I suggests that a steroidogenic pathway for production of E-2 from androstenedione via estrone exists in the Japanese eel ovary. (C) 2000 Academic Press.