Résumé
Transgenic fish are powerful models that can provide mechanistic information regarding the endocrine activity of test chemicals. In this study our objective was to refine the OECD Fish Short Term Reproduction Assay (TG229) using a new transgenic zebrafish line expressing GFP under the control of the cyp19a1a promoter, to provide additional mechanistic information. For this purpose, we exposed this zebrafish line using prochloraz (PCZ), one of the TG229 reference molecule, at 3, 30 and 300 µg/L. In addition to “classical” endpoints, the fluorescence intensity of the ovaries was monitored at 4 different times of exposure using in vivo imaging. At the end of the experiment, we found that PCZ significantly decreased the number of eggs laid per female per day at 300 µg/L and the concentrations of vitellogenin in females, most probably reflecting the decreasing E2 synthesis due to inhibition of the ovarian aromatase activities. Additional information on the mode of action of PCZ were provided through the measurement of GFP intensities. At 7 and 14 days, GFP intensities in ovaries were similar over the treatment groups but significantly increased after 21 days at 30 and 300 µg/L. A similar profile was observed for cyp19a1a expression (qPCR) thereby confirming the reliability of the GFP measurement for assessing aromatase gene expression. The overexpression of the cyp19a1a gene likely reflects a compensatory response to the inhibitory action of PCZ on aromatase enzymatic activities. Overall, this study illustrates the feasibility of using the cyp19a1a-GFP transgenic line for assessing the effect of PCZ in an OECD test guideline while providing complementary information of the time- and concentration-dependent effect on a key target gene through in vivo GFP imaging without increasing the number of individuals or costs of the experiments.