A second estrogen receptor from Japanese lamprey (Lethenteron japonicum) does not have activities for estrogen binding and transcription

Estrogens regulate many physiological responses in vertebrates by binding to the estrogen receptor (ER), a ligand-activated transcription factor. To understand the evolution of vertebrate ERs and to investigate how estrogen acts in a jawless vertebrate, we used degenerate primer sets and PCR to isolate DNA fragments encoding two distinct ER subtypes, Esrla and Esrlb from the Japanese lamprey, Lethenteron japonicum. Phylogenetic analysis indicates that these two ERs are the result of lineage-specific gene duplication within the jawless fishes, different from the previous duplication event of Esr1 (ER alpha) and Esr2 (ER beta) within the jawed vertebrates. Reporter gene assays show that lamprey Esrla displays both constitutive and estrogen-dependent activation of gene transcription. Domain swapping experiments indicate that constitutive activity resides in the A/B domain of lamprey Esrla. Unexpectedly, lamprey Esrlb does not bind estradiol and is not stimulated by other estrogens, androgens or corticosteroids. A 3D model of lamprey Esrlb suggests that although estradiol fits into the steroid binding site, some stabilizing contacts between the ligand and side chains that are found in human Esr1 and Esr2 are missing in lamprey Esrlb. (C) 2016 Elsevier Inc. All rights reserved.