Vg mRNA induction in an endangered fish species (Anguilla anguilla) from the Loire estuary (France)
Résumé
Estuarine zones are extremely fragile due to increasing stress from anthropogenic activities. Among
those, the Loire estuary (France) is potentially exposed to various contaminants including Endocrine
Disruptors Compounds (EDCs) able to impact the reproduction physiology of fish. The European eel
(Anguilla anguilla), endangered fish species, is apparently not relevant, in its yellow stage, to monitor the
effects of endocrine disruption. Despite this weakly responsiveness, this study aimed to investigate
whether European eel from the Loire estuary may still be the subject of estrogenic disruption quantifying
the hepatic Vg gene expression according to gender and sexual stage. Vitellogenin (Vg) appears as a
valuable biomarker of EDCs, as well as for exposure and effects. Quantitative real-time Reverse
Transcription Polymerase Chain Reaction (q RT PCR) was used in this study to amplify responses of
hepatic Vg transcripts. European eels were sampled in May 2009 (N¼57) and November 2010 (during
the downstream migration, N¼10) in two sites of the Loire estuary with different ecological conditions
and contamination pressures (upstream: Varades; downstream: Nantes). Reproductive (gender, sexual
maturity stage) and biometric parameters of collected eels were determined. A laboratory exposure of
silver male to steroid hormones (Testosterone (T), 11-KetoTestosterone (11-KT), Estradiol (E2)) was
conducted in parallel to validate the q RT PCR approach on hepatic Vg mRNA. Results demonstrated the
responsiveness of exposed silver male eels, since hepatic mRNA Vg induction was observed in E2 treated
males compared to control specimens. In the field, results of female silver eels reflected large interindividual differences in the activation of hepatic Vg at silvering. However, while only female silver eels
should express hepatic Vg mRNA, quantifiable levels were also detected in a proportion of 38% of the
other individuals sampled, normally not inclined to express it, those being undifferentiated eels, yellow
females, yellow and silver males. According to each sexual stage, no difference of expression was
observed between eels from the two sampling sites. Histological results as well as low Vg mRNA levels
detected do not permit a conclusion as to a potential effect of endocrine disruption.