Fish Androgen Receptor: cDNA Cloning, Steroid Activation of Transcription in Transfected Mammalian Cells, and Tissue mRNA Levels

We have previously identified 11-ketotestosterone (11KT, a portent androgen in teleosts) as the spermatogenesis-inducing hormone of the Japanese eel. In this study, a cDNA encoding the eel androgen receptor (AR) was isolated from the Japanese eel testis. This cDNA contains a complete open reading frame encoding 848 amino residues. The amino acid sequence of the eel AR shows high homology with other ARs. In transient transfection assays of mammalian cells, the eel AR showed androgen-dependent activation of transcription from the androgen-responsive MMTV promoter. Of the endogenous androgens found in the Japanese eel, 11KT was the most effective activator of transcription. These results indicate that the cloned cDNA encodes a functional eel AR, and its major native ligand is 11KT. This is the first isolation of an AR molecule from fish, and is the first evidence that 11KT acts via a nuclear receptor.