Choriogenin mRNA as a sensitive molecular biomarker for estrogenic chemicals in developing brackish medaka (Oryzias melastigma)

Teleost choriogenins, precursors of the inner layer subunits of the egg envelope, are regarded as sensitive biomarkers for estrogenic pollutants. In this study, two full-length cDNAs, omChgH and omChgL, which encode the choriogenin H and L forms, respectively, were isolated from a brackish medaka, Oryzias melastigma. 17β-Estradiol (E2; 10 μg/L)-dependent expression of omChgH and omChgL was observed starting at embryonic stage 34 and restricted exclusively to the liver. In hatchlings, E2 induction of omChgH was stronger than that of omChgL. Static exposure of adult fish to E2 (0, 1, 10, 100, and 500 ng/L), 17α-ethinylestradiol (EE2; 0, 1, 10, 100 and 500 ng/L), 4-nonylphenol (NP; 0, 1, 10, 100, and 200 μg/L), and bisphenol A (BPA; 0, 1, 10, 100, and 200 μg/L) in artificial seawater for 7 days resulted in dose-dependent induction of both genes in the liver. In the male livers, the sensitivity of omChgH to these estrogenic compounds was higher than that of omChgL; the lowest-observed-effect concentrations (LOECs) of E2, EE2, NP, and BPA on omChgH were 10 ng/L, 10 ng/L, 100 μg/L and 100 μg/L, respectively, and on omChgL were 100 ng/L, 100 ng/L, 100 μg/L, and 200 μg/L, respectively. All these suggest that omChgH can be used as a highly sensitive biomarker for monitoring estrogenic chemicals in the marine environment.