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, EE(2) , 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 EE(2) 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 EE(2) decreased body sizes. There was a significant increase in the frequency of abnormalities (mostly edema) in larvae exposed to all concentrations of EE(2), and high ZEAR, and EE(2) + 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 EE(2) and luteinizing hormone expression increased significantly in response to all treatments tested. As expected, EE(2) induced vitellogenin expression; however, ZEAR also induced expression of this gene to similar levels compared to EE(2). Overall, exposure to EE(2) + 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.

Characterization of ontogenetic changes in gene expression in the fathead minnow (Pimephales promelas).

Recently, researchers have begun looking at changes in gene expression in the fathead minnow (Pimephales promelas) after contaminant exposure as a way to develop biomarkers of exposure and effects. However, the bulk of this research has been conducted on adults, with few studies focusing on early life stages. Expression of selected genes important in growth, development, and reproduction in teleosts was quantified by quantitative polymerase chain reaction during different developmental time periods (from 0 to 28 d postfertilization [dpf]). Over the developmental period studied, there was a significant up-regulation of growth hormone mRNA and no significant changes in the expression of insulin-like growth factor 1. Thyroid hormone receptors A and B were detected in 4 dpf embryos and their expression stayed relatively constant. The variation in cytochrome P45019A mRNA expression was large during the first week of development, returning to 0 dpf expression levels thereafter. Estrogen receptor 2B was up-regulated during the first three weeks postfertilization, returning to prehatch values by 28 dpf. Expression of hydroxysteroid dehydrogenase 3B and steroidogenic acute regulatory protein increased after the third or fourth week postfertilization, respectively. Vitellogenin exhibited a large degree of variation within time points, especially after day 15, and a significant up-regulation for this gene was observed at 7 and 10 dpf. Knowledge of the normal changes in gene expression during embryo and larval development will allow for better experimental design and selection of suitable biomarkers when testing the potential toxicological effects of contaminants in this model fish species.