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

17 beta -hydroxysteroid dehydrogenase-I (17 beta -HSD-I) is a key steroidog enic 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 o f a teleost, the Japanese eel. The deduced amino acid sequence from these c DNAs was approximately 50% identical to mammalian 17 beta -HSD-Is. 17 beta -HSD-I mRNA was not detected in previtellogenic ovaries by Northern blottin g. However, transcript abundance increased in early vitellogenic ovaries ob tained from fish artificially matured by gonadotropic treatment, but therea fter did not appear to change further. Recombinant 17 beta -HSD-I expressed in human kidney 293 cells selectively converted estrone to E-2, but andros tenedione, testosterone, or E-2 were not converted to any other steroids. A lthough it is widely accepted that E-2 is produced from testosterone in oth er species of teleosts, the substrate specificity of eel 17 beta -HSD-I sug gests that a steroidogenic pathway for production of E-2 from androstenedio ne via estrone exists in the Japanese eel ovary. (C) 2000 Academic Press.