A novel piscine vitellogenin gene: Structural and functional analyses of estrogen-inducible promoter

The Oreochromis aureus vitellogenin, OaVtg, gene spans 9 kb and contains 34 exons. Its transcription start site is located 15 bp upstream of the translational start codon. Although the OaVtg promoter has a nonconsensus TATA, transient transfection assay showed that this promoter is capable of driving basal transcription. Two imperfect estrogen response elements: ERE(p) (proximal) and ERE(d) (distal) are located in the promoter at - 532 and - 1352, respectively. In competition gel mobility-shift assays, only ERE(p) exhibited specific binding of the recombinant estrogen receptor protein, GST- C/D OaER. Another imperfect ERE (ERE(exon2)) was detected within exon 2 of the OaVtg gene. This is a novel finding for a vitellogenin (Vtg) gene. ERE(exon2) similarly showed specific recognition of GST-C/D OaER. Both EREp and ERE(exon2) showed comparable binding affinities as consensus ERE. In transient transfections, the OaVtg promoter, ERE(p) and ERE(d) elicited significant increase in estrogen-dependent synthesis of CAT protein. Hence, we propose that the non-consensus OaVtg EREs contribute to the estrogen- dependent regulation of the OaVtg gene in vivo.