Application of a yeast estrogen screen in non-biomarker species Varicorhinus barbatulus fish with two estrogen receptor subtypes to assess xenoestrogens.

Xenoestrogens can interfere with normal estrogen signaling by competitively binding to the estrogen receptor (ER) and activating transcription of target genes. In this study, we cloned the estrogen receptor alpha (vbERalpha) and beta 2 (vbERbeta2) genes from liver of the indigenous Taiwanese cyprinid fish Varicorhinus barbatulus and tested the direct impact of several xenoestrogens on these ERs. Transcriptional activity of xenoestrogens was measured by the enzymatic activity of estrogen responsive element (ERE)-containing beta-galactosidase in a yeast reporter system. The xenoestrogens tested were phenol derivatives, DDT-related substances, phthalic acid esters, and polychlorinated biphenyls, with 17beta-estradiol (E2) as a subjective standard. The phenol derivatives [4-nonylphenol (4-NP), 4-t-octylphenol (4-t-OP) and bisphenol A (BPA)] exhibited significant dose-dependent responses in both ligand potency and ligand efficiency. Consistent with yeast assays using human or rainbow trout ERs, we observed a general subtype preference in that vbERalpha displayed higher relative potencies and efficiencies than vbERbeta2, although our assays induced a stronger response for xenoestrogens than did human or trout ERs. Whereas 4-NP and 4-t-OP have similar EC50 values relative to E2 for both ER subtypes, the strong estrogenic response of BPA markedly differentiates vbERalpha from vbERbeta2, suggesting possible species-specific BPA sensitivity. We report that the ameliorative yeast tool is readily applicable for indigenous wildlife studies of the bio-toxic influence of xenoestrogens with wildlife-specific estrogen receptors.