Detection of endocrine disrupting chemicals, in particular, environmental estrogens with living organisms, has many advantages if compared to chemical analysis. The screening of novel pollutants with meaningful endpoints, the integration of uptake, bioconcentration, and excretion as well as the evaluation of endocrine disrupting effects with respect to toxicity require in vivo biotests for estrogen-like substances (ELSs). Critical disadvantages of whole organism biotests are their low sensitivity and the need for laborious and time-consuming work. To overcome these problems, we have developed a transgenic medaka strain harboring the green fluorescence protein (GFP) gene driven by choriogenin H gene regulatory elements. Choriogenin H is an egg envelope protein induced by estrogens in the liver. With yolk sac larvae of this strain, GFP induction in liver was observed 24 h after onset of aqueous exposure to 0.63 nM 17beta-estradiol (E2), 0.34 nM ethynylestradiol, or 14.8 nM estrone. Furthermore, concentrated sewage treatment effluent induced GFP expression. Comparison of E2 equivalents estimated by GFP-induction in transgenic medaka, a YES assay, and GC/MS showed detection limits in the same order of magnitude. These results indicated that the sensitivity of the transgenic medaka strain was sufficient for application as an alternative model in monitoring environmental water samples for ELSs.
TheChgH-GFP strain of the teleost medaka contains a regulatory region of the estrogen-responsive choriogenin H (chgH) gene fussed to the green fluorescent protein (GFP) gene. The strain was developed for the identification of environmental estrogens by noninvasive analysis of GFP fluorescence. In the present study, a quantification method for GFP by image analysis was establishedand applied to the analysis of time- and concentration-dependent GFP fluorescence in juvenile fish. Concentration-response analyses were performed with fish exposed for 14 d to 17beta-estradiol (0.37-367 pM), genistein (0.37-367 nM), or p-nonylphenol (0.367-1,835 nM). By means of image analysis, it was shown that ChgH-GFP was induced at 183.5 pM or greater 17beta-estradiol. Time-course and recovery experiments indicated a strong accumulation of GFP in the liver. Results of reverse transcriptase-polymerase chain reaction analysis of choriogenin H and vitellogenin demonstrated induction of gene expression for the same rangeof concentrations as that for GFP analysis. Neither expression of these genes nor GFP fluorescence was induced by genistein and p-nonylphenol. Although the ChgH-GFP strain failed to detect these weakly estrogenic compounds, the simplicity of the GFP quantification during early life stages of fish offers promising possibilities for further developments of transgenic strains using different target regulatory sequences.
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