Characterization of a testicular 17alpha, 20beta-dihydroxy-4-pregnen-3-one (a spermiation-inducing steroid in fish) receptor from a teleost, Japanese eel (Anguilla japonica).

A cDNA encoding a nuclear 17alpha,20beta-dihydroxy-4-pregnen-3-one (17alpha,20beta-DP, spermiation-inducing hormone in fish) receptor (DPR) was, for the first time, isolated from an eel testis cDNA library. The amino acid sequence of DPR shows high homology with those of human and chicken progesterone receptors. The affinity of the bacterial recombinant DPR ligand binding domain protein for 17alpha,20beta-DP is higher than that of progesterone. In transfection experiments using COS7 cells, the DPR showed progestin-dependent activation of transcription. 17alpha,20beta-DP was the most effective activator of transcription. These results indicate that the cDNA encodes a functional eel DPR, and show that 17alpha,20beta-DP has a nuclear receptor-mediated action in eel testes.