Impact of environmental estrogens on nucleotide excision repair gene expression in embryonic zebrafish

Estrogens and estrogen mimics are aquatic contaminants that can elicit a variety of deleterious effects in exposed fauna. One of the most potent xenoestrogens found in the aquatic environment is 17α-ethinylestradiol (EE(2)), the pharmaceutically derived semi-synthetic hormone found in oral contraceptives and hormone replacement therapies. Exposure to 100 ng/L EE(2) has previously been shown to profoundly decrease functional hepatic nucleotide excision repair (NER) processes in adult zebrafish in correlation with dramatic decreases in the abundance of hepatic XPC and XPA transcripts; however, its effects on these processes in embryos are currently unknown. Because developing organisms are known to have increased sensitivities to endocrine disrupting compounds such as EE(2), the goal of this study was to examine the impacts of estrogen exposure on mRNA expression of these two key NER genes in zebrafish embryos during the first 4 days of development. Embryos were exposed from 0 h post fertilization (hpf) to waterborne EE(2), its major metabolite, estrone (E(1)), or combinations of the two compounds and sampled at 12, 24, 48, 72 and 96 hpf. Increased abundance of vitellogenin-1 (VTG1) mRNA, a bioindicator of estrogen exposure, was evident as early as 24 hpf in embryos that were co-exposed to EE(2) and E(1) and this effect was sustained throughout 96 hpf. Embryos exposed to EE(2) alone exhibited elevated VTG1 beginning at 72 hpf. In contrast to observations from adult zebrafish exposed to EE(2), embryos did not show any change in mRNA abundance of the excision repair gene, XPC, during the first 4 days of development. However, co-exposure to EE(2) and E(1) elicited an increase in XPA mRNA abundance at 48 and 72 hpf, which was the opposite response as that observed in exposed adults where hepatic XPA mRNA abundance decreased after EE(2) exposure. These differences between embryos and adults suggest that alteration of NER gene transcription by EE(2) is operating under different stimuli during development.