Effects of estrogens and antiestrogens on gene expression of fathead minnow (Pimephales promelas) early life stages

Endocrine disrupting chemicals (EDCs) are known to contaminate aquatic environments and alter the growth and reproduction of organisms. The objective of this study was to evaluate the sensitivity and utility of fathead minnow (Pimephales promelas) early life-stages as a model to measure effects of estrogenic and antiestrogenic EDCs on physiological and gene expression endpoints relative to growth and reproduction. Embryos (<24-h postfertilization, hpf) were exposed to a potent estrogen (17α-ethinyl estradiol, EE₂, 2, 10, and 50 ng L^-1); a weak estrogen (mycotoxin zearalenone, ZEAR, same concentrations as above); an antiestrogen (ZM 189, 154; 40, 250, and 1000 ng L^-1); and to mixtures of EE₂ and ZM until swim-up stage (∼170 hpf). Exposure to all concentrations of ZEAR and to the lowest concentration of ZM resulted in increased body sizes, whereas high concentrations of EE₂ decreased body sizes. There was a significant increase in the frequency of abnormalities (mostly edema) in larvae exposed to all concentrations of EE₂, and high ZEAR, and EE₂ + ZM mixture groups. Expression of growth hormone was upregulated by most of the conditions tested. Exposure to 50 ng L^-1 ZEAR caused an induction of insulin-like growth factor 1, whereas exposure to 40 ng L^-1 ZM caused a downregulation of this gene. Expression of steroidogenic acute regulatory protein gene was significantly upregulated after exposure to all concentrations of EE₂ and luteinizing hormone expression increased significantly in response to all treatments tested. As expected, EE₂ induced vitellogenin expression; however, ZEAR also induced expression of this gene to similar levels compared to EE₂. Overall, exposure to EE₂ + ZM mixture resulted in a different expression pattern compared to single exposures. The results of this study suggest that an early life stage 7-day exposure is sufficient to recognize and evaluate effects of estrogenic compounds on gene expression in this fish model.