Characterization of estrogen receptor βb in sea bream (Sparus auratus): Phylogeny, ligand-binding, and comparative analysis of expression

Estrogens control many physiological processes in both female and male vertebrates, mostly mediated by specific nuclear estrogen receptors (ER). Two ER subtypes (ERα and ERβ) are present in most vertebrates, including the sea bream (Sparus auratus) a hermaphrodite teleost fish. In the present study several variant cDNAs encoding a second sea bream ERβ (sbERβb) is reported. Phylogenetic and Southern blot analysis indicate that sbERβb and the previously cloned sbERβa (formerly sbERβ) are encoded by different genes, which may have arisen by duplication of an ancestral ERβ gene. Competitive binding assays show that sbERβb has high affinity for 17β-estradiol (Kd = 1 nM) and specifically binds estrogen agonists (diethylstilbestrol and ethynylestradiol) and antagonists (ICI 182,780). In Northern blot sbERα, sbERβa, sbERβb produce several different transcripts in a variety of tissues. RT-PCR showed a partially overlapping but differential tissue distribution in both male and female sea bream.