Analysis of the estrogen regulation of the zebrafish estrogen receptor (ER) reveals distinct effects of ERalpha, ERbeta1 and ERbeta2

Abstract

We have previously cloned and characterized three estrogen receptors (ER) in the zebrafish (zfERalpha, zfERbeta1 and zfERbeta2). 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 zfERalpha gene expression while zfERbeta1 gene expression was markedly reduced and zfERbeta2 remained virtually unchanged. To establish the potential implication of each zfER in the E2 upregulation of the zfERalpha 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 zfERalpha gene requires ERalpha 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 zfERalpha was the most potent at inducing the expression of its own gene, the effect of E2 mediated by zfERbeta2 represented 50% of the zfERalpha activity. In contrast, zfERbeta1 was unable to upregulate the zfERalpha 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 ERbeta forms recently characterized in teleost fish could have partially distinct and not redundant functions.

Effects of steroid hormones on reproduction- and detoxification-related gene expression in adult male mosquitofish, Gambusia affinis

“…It has been shown that ERα plays a dominant role in the up-regulation of Vtg mRNA expression in the liver of female mosquitofish (Huang et al, 2012) and other fish (Sabo-Attwood et al, 2004;Davis et al, 2007) by E2. The lack of significant changes found in ERβ mRNA expression levels in the liver of male mosquitofish in response to E2 is consistent with other studies in which E2 treatment had no effects on zebrafish (Menuet et al, 2004) and male goldfish (Pomatto et al, 2011), suggesting that ERβ is unlikely to be the primary mediator of E2 actions on the liver associated with the induction of Vtg mRNA expression. It has been previously shown that the presence of an estrogen-responsive element (ERE) in the promoter of ERα in the rainbow trout may be a major cis-acting element involved in the regulation of the gene by E2 (Le Dréan et al, 1995).…”

“…It has been previously shown that the presence of an estrogen-responsive element (ERE) in the promoter of ERα in the rainbow trout may be a major cis-acting element involved in the regulation of the gene by E2 (Le Dréan et al, 1995). In addition, an imperfect ERE in the promoter of ERα has been demonstrated in the zebrafish along with ERE half sites with no consensus EREs in the promoter of ERβ (Lassiter et al, 2002;Menuet et al, 2004). It is still unclear whether the presence of different EREs in the promoters of different ER genes instructs their response to E2.…”

Effects of fluoxetine on the reproductive axis of female goldfish (Carassius auratus)

“…Accompanying the decrease in blood E 2 was a decrease in ER␣ mRNA levels in the goldfish hypothalamus and telencephalon. The promoter of the teleost ER␣ contains one full estrogen response element (ERE) and one half-ERE, which have been shown to contribute to E 2 -stimulated ER␣ expression in vitro (37). Therefore, the decrease in circulating E 2 may have resulted in the decreased transcription of ER␣ observed in our study.…”

Regeneration of breeding tubercles on zebrafish pectoral fins requires androgens and two waves of revascularization

“…Males and females were treated with E2 (1 μg/l), which binds to all zebrafish estrogen receptors (Menuet et al, 2004). After 16 dot, no changes are observed in the intact and regenerating female pectoral fins (n=6; Fig.…”