Distinct Roles of Estrogen Receptors in the Regulation of Vitellogenin Expression in Orange-Spotted Grouper ().

During their breeding season, estrogen induces vitellogenin (VTG) production in the liver of teleost fish through estrogen receptors (ERs) that support oocyte vitellogenesis. There are at least three ER subtypes in teleost fish, but their roles in mediating E-induced VTG expression have yet to be ascertained. In this study, we investigated the expression of and in the liver of orange-spotted grouper (). Their expression levels were significantly increased in the breeding season and were upregulated by an estradiol (E) injection in female fish, except for the expression of . The upregulation of , and by E was also observed in primary hepatocytes, but these stimulatory effects could be abolished by ER antagonist ICI182780 treatment. Subsequent studies showed that ERβ antagonist Cyclofenil downregulated the E-induced expression of , , and , while the ERβ agonist DPN simulated their expression. Knockdown of by siRNA further confirmed that ERβ2 mediated the E-induced expression of and . To reveal the mechanism of ERβ2 in the regulation of expression, the promoter was cloned, and its activity was examined in cells. E treatment simulated the activity of the promoter in the presence of ERβ2. Deletions and site-directed mutations showed that the E up-regulated transcriptional activity of occurs through a classical half-estrogen response element- (ERE) dependent pathway. This study reveals the roles of ER subtypes in VTG expression in orange-spotted grouper and provides a possible explanation for the rapid and efficient VTG production in this species during the breeding season.