Genomic structure and embryonic expression of estrogen receptor beta a (ERβa) in zebrafish (Danio rerio)

Abstract

Estrogenic steroid hormones mediate complex actions important in both embryonic and adult life. The hormones signal through ligand-inducible transcription factors known as estrogen receptors (ERs). In this study, we have isolated a zebrafish estrogen receptor with homology to human estrogen receptor beta (ERβ). This zebrafish ERβ (ERβa) has a conserved genomic structure of eight coding exons with boundaries similar to those of human ERβ. The coding exon structures of two other zebrafish estrogen receptors (ERα and ERβb) are presented as well. We also analyzed 3.3 kb of the promoter region and identified numerous putative transcription factor binding sites, including SP1 and ER half sites. Zebrafish ERβa message RNA is maternally loaded, but quickly degraded after fertilization, as detected by reverse transcriptase polymerase chain reaction. ERβa transcripts are detected again between 24 and 48 h post fertilization. These results indicate that ERβ has been highly conserved during evolution and is likely used during later embryogenesis in zebrafish. Future identification of the expression levels and patterns of this and other estrogen receptors in zebrafish will allow a better understanding of estrogen signaling during embryogenesis.