cDNA cloning of a novel androgen receptor subtype

There has been general acceptance that only one type of androgen receptor (AR) exists in an individual. This contrasts with other members of the nuclear receptor superfamily where multiple forms have been reported (e.g. estrogen receptor alpha/beta, thyroid hormone receptor alpha/beta, etc.). We have previously identified 11-ketotestosterone (a potent androgen in teleosts) as the spermatogenesis-inducing hormone of the Japanese eel and have cloned its receptor (eAR1) cDNA from eel testis. Here we report on the cloning of a cDNA encoding a second type of AR (eAR2) from the eel testis and the functional characterization of the encoded protein. This cDNA contains a complete open reading frame encoding 797 amino acid residues. The amino acid sequence of eAR2 shows high homology with other ARs, including eAR1, in the DNA-binding (98-88%) and ligand-binding (59-85%) domains, whereas the other domains show low homology (<35%). In transient transfection assays of mammalian cells, the eAR2 protein displayed androgen-dependent activation of transcription from the androgen-responsive murine mammary tumor virus promoter. Tissue distribution of its mRNA was different from that of eAR1. We conclude that eAR2 is a novel AR in the eel, which we suggest should be named eel ARbeta to distinguish it from eAR1 (eARalpha).