Effects of exposure to oestrogenic compounds on aromatase gene expression are gender dependent in the rainbowfish, Melanotaenia fluviatilis

Abstract

This study investigated the influence of two endocrine disrupting chemicals (EDCs)—an exogenous oestrogen 17β-estradiol (E2) and the oestrogen mimic 4-n-nonylphenol (NP) on the expression of aromatase transcripts in both sexes of adult Murray river rainbowfish. Reproductively active mature fish were exposed to 1, 3, and 5μg/L E2 or 100 and 500μg/L NP for 24, 48, 72 and 96h. The results show a significant reduction in the expression of cyp19a1a isoform in ovarian tissues with complete inhibition at the higher concentrations (3 and 5μg/L E2; 500μg/L NP between 24 and 72h) and at all concentrations after 96h. There was no expression of the cyp19a1a isoform in female brain, male brain or testes in any treatment. E2 significantly increased expression of cyp19a1b in female brain except at 5μg/L after 24h exposure. In male brain tissue E2 exposure decreased cyp19a1b expression except at 1 and 5μg/L at 24h. NP significantly upregulated cyp19a1b in the female brain (except with 500μg/L at 72h) and in testes tissues. NP downregulated expression of cyp19a1b in the male brain tissue. Collectively, these observations support the hypothesis that the expression of cyp19a1b is regulated via both positive and negative feedback mechanisms, with differential modulation based on the type and concentration of the exposed oestrogens, duration of exposure, fish tissue and gender of the fish. The results also imply that exogenous oestrogens can have a disruptive effect on the steroidogenic pathway and may lead to effects on sex differentiation, sexual behaviour and reproductive cycles in this fish.