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

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 (ERbeta). This zebrafish ERbeta (ERbetaa) has a conserved genomic structure of eight coding exons with boundaries similar to those of human ERbeta. The coding exon structures of two other zebrafish estrogen receptors (ERalpha and ERbetab) 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 ERbetaa message RNA is maternally loaded, but quickly degraded after fertilization, as detected by reverse transcriptase polymerase chain reaction. ERbetaa transcripts are detected again between 24 and 48 h post fertilization. These results indicate that ERbeta 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.