Cloning and expression of two carbonyl reductase-like 20β-hydroxysteroid dehydrogenase cDNAs in ovarian follicles of rainbow trout (Oncorhynchus mykiss)

In salmonid fish, 20β-hydroxysteroid dehydrogenase (20β-HSD) is a key enzyme involved in the production of oocyte maturation-inducing hormone (MIH), 17α,20β-dihydroxy-4-pregnen-3-one. Here we report the isolation of two cDNAs which encode proteins with high homology to carbonyl reductase-like 20β-HSD (CR/20β-HSD) from rainbow trout (Oncorhynchus mykiss) ovarian follicles. Genomic DNA analysis showed that the two CR/20β-HSD cDNAs are derived from two different genes. Northern blot and RT PCR analysis demonstrated that trout CR/20β-HSDs are broadly expressed in various tissues. Enzymatic characterization using recombinant CR/20β-HSD proteins produced in E. coli showed that the product of one of the two cDNAs had both 20β-HSD and CR activity, but the other had neither activity. Although the functional significance of the two genes remains unresolved, these results clearly demonstrate the presence of two distinct CR/20β-HSD transcripts in the trout ovary.