Isolation, sequence analysis, and characterization of androgen receptor in Southern catfish, Silurus meridionalis.

Androgen receptor (AR), the mediator of androgen, plays important roles in the androgen signal pathway. In the present study, we isolated and analyzed the cDNA sequence and tissue distribution of androgen receptor in Southern catfish (scAR). The full-length cDNA of scAR contains 3,116 bp with an open reading frame (ORF) of 2,415 bp, encoding a protein of 804 amino acids (aa). Tissue distribution analysis of scAR revealed that it was expressed in all tissues examined, with no sexual dimorphism in the ovary and testis. Phylogenetic analysis and multiple amino acids sequence alignment indicated the close relationship and high similarity of scAR with ARs from cypriniform species. In addition, partial sequences of ARs from 7 other siluriform species were also isolated. Comparison of catfish ARs with those from other vertebrates revealed that an extra C-terminal tail of about 20aa exists in all the ARs from siluriform fishes investigated, but not in other ARs. The extra sequence was resulted from a 4-bp insertion before the stop codon of other vertebrate ARs, and it was identical in ARs from siluriform species of the same genus but different among ARs from species of different genera. We report here for the first time that the ARs from siluriform species are longer in C-terminal than those from other vertebrates and it might be useful in reconstruction of the phylogenetic relationship among siluriform fishes. The significance of the extra C-terminal tail for AR function remains elusive.