Exposure to estrogenic chemicals induces ectopic expression of vtg in the testis of rainbowfish, Melanotaenia fluviatilis.

Vitellogenin (Vtg) is the major egg-yolk precursor protein in oviparous organisms normally synthesised only in mature females. In males and juveniles, the vtg gene, although present, is silent, but its hepatic expression may be activated by xenoestrogens. Surprisingly, its induction and potential consequences in non-hepatic tissues remain unexplored. Here we test the hepatic and testicular response of vtg expression in adult male rainbowfish Melanotaenia fluviatilis exposed to either 1, 3, 5 μg/L 17β-estradiol or 100, 500 μg/L 4-n-nonylphenol for 24-96 h. Significant increase in the expression level of vtg mRNA in the liver and testes of exposed males was observed. The early (24 h), sensitive and reliable detection of the vtg induction using qPCR demonstrates the assay's robustness to monitor xenobiotic exposure particularly in smaller fish like rainbowfish, an emerging indicator species. Whilst, the ectopic induction of vtg mRNA in testes suggests a more complex Vtg pathway.