Regulation of vitellogenin (vtg1) and estrogen receptor (er) gene expression in zebrafish (Danio rerio) following the administration of Cd2+ and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

• Combined effects of Cd and TCDD on vtg1 gene expression was studied.
• In vitro study showed that ERα in important in mediating the inhibitory effects of Cd on vtg1 gene transcription.
• In vivo gene expression study confirmed similar effects in embryo, larvae, and male liver tissues.
• Male fish gave sensitive response to TCDD induction of vtg1 and such induction was inhibited by Cd.

We evaluated the individual and joint estrogenic effects of cadmium (Cd2+) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the zebrafish liver (ZFL) cell line, zebrafish embryo, larvae and the liver of adult zebrafish. The mRNA expression of vtg1 was inhibited by Cd2+, but unaffected by TCDD in ZFL cells. Similar changes in the mRNA levels of ERα, ERβ1, ERβ2 and GPER (G protein coupled estrogen receptor) in ZFL cells were also observed. Deletion mutants of vtg1 gene promoters were constructed to investigate transcriptional regulation, and we found that all of the constructs failed to respond to TCDD or Cd2+. However, after co-transfection with a vtg1 promoter-luciferase construct to the ERα, ERβ1, ERβ2 and GPER expression vectors, decreased luciferase activity was observed in the ERα co-transfection group after treatment with Cd2+, suggesting that ERα participates in vtg1 transcriptional regulation and is affected by Cd2+. Differences in the regulation of the mRNA levels of these genes were also observed between different developmental stages and between the livers of male and female zebrafish.

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