Molecular cloning and characterization of Japanese eel estrogen receptor cDNA

A cDNA encoding the Japanese eel, Anguilla japonica, estrogen receptor (ER) was isolated and sequenced. This cDNA contains a complete open reading frame encoding 573 amino acid residues, and the molecular weight of this protein is calculated to be 63417. The amino acid sequence of the eel ER shows high homology of the DNA binding (80%) and ligand binding (55%) domains with those of other species. However, the other domains show greatly reduced homology (10-20%). When the cDNA was ligated to the pSVL vector and transfected into COS7 cells, a protein was produced that had high affinity for estradiol-17 beta (E2) and specifically bound estrogens. Northern analysis showed that three ER mRNAs with lengths of 5.6, 3.8 and 1.2 kb were expressed in eel liver. Their expression was E2 inducible, with the 5.6 kb mRNA being strongly dependent on E2 stimulation.