Analysis of the estrogen regulation of the zebrafish estrogen receptor (ER) reveals distinct effects of ERα, ERβ1 and ERβ2

Abstract

We have previously cloned and characterized three estrogen receptors (ER) in the zebrafish (zfERα, zfERβ1 and zfERβ2). We have also shown that they are functional in vitro and exhibit a distinct expression pattern, although partially overlapping, in the brain of zebrafish. In this paper, we have shown that the hepatic expression of these zfER genes responds differently to estradiol (E2). In fact, a 48-h direct exposure of zebrafish to E2 resulted in a strong stimulation of zfERα gene expression while zf ERβ1 gene expression was markedly reduced and zfERβ2 remained virtually unchanged. To establish the potential implication of each zfER in the E2 upregulation of the zfERα gene, the promoter region of this gene was isolated and characterized. Transfection experiments with promoter-luciferase reporter constructs together with different zfER expression vectors were carried out in different cell contexts. The data showed that in vivo E2 upregulation of the zfERα gene requires ERα itself and a conserved transcription unit sequence including at least an imperfect estrogen-responsive element (ERE) and an AP-1/ERE half site at the proximal transcription initiation site. Interestingly, although in the presence of E2 zfERα was the most potent at inducing the expression of its own gene, the effect of E2 mediated by zfERβ2 represented 50% of the zfERα activity. In contrast, zfERβ1 was unable to upregulate the zfERα gene whereas this receptor form was able to tightly bind E2 and activate a reporter plasmid containing a consensus ERE. Altogether, these results indicated that the two ERβ forms recently characterized in teleost fish could have partially distinct and not redundant functions. © 2004 Society for Endocrinology.