Gene Expression Changes Related to Endocrine Function and Decline in Reproduction in Fathead Minnow ( Pimephales promelas ) after Dietary Methylmercury Exposure

Abstract

BackgroundMethylmercury (MeHg) is a known neurotoxic agent, but the mechanisms by which MeHg may act on reproductive pathways are relatively unknown. Several studies have indicated potential changes in hormone levels as well as declines in vertebrates with increasing dietary MeHg exposure.ObjectivesThe purpose of this study was to identify alterations in gene expression associated with MeHg exposure, specifically those associated with previously observed changes in reproduction and reproductive biomarkers. Fathead minnows, Pimephales promelas, were fed one of three diets that were similar to documented concentrations of MeHg in the diets of wild invertivorous and piscivorous fish. We used a commercial macroarray in conjunction with quantitative polymerase chain reaction to examine gene expression in fish in relation to exposure to these environmentally relevant doses of MeHg.ResultsExpression of genes commonly associated with endocrine disruption was altered with Hg exposure. Specifically, we observed a marked up-regulation in vitellogenin mRNA in individual Hg-exposed males and a significant decline in vitellogenin gene expression in female fish with increasing Hg concentrations. Other genes identified by the macroarray experiment included those associated with egg fertilization and development, sugar metabolism, apoptosis, and electron transport. We also observed differences in expression patterns between male and female fish not related to genes specifically associated with reproduction, indicating a potential physiological difference in the reaction of males and females to MeHg.ConclusionGene expression data may provide insight into the mechanisms by which MeHg affects reproduction in fish and indicate how MeHg differs in its effect from other heavy metals and endocrine-disrupting compounds.

Characteristics, functions, and applications of metallothionein in aquatic vertebrates

“…In previous studies, exposure to environmentally related concentrations of MeHg suppressed gonadal development and estrogen production in female FHM and testosterone in male FHM (Drevnick and Sandheinrich, 2003). Therefore, MeHg may function as an endocrine disruptor by binding to estrogen receptors and acting virtually as an estrogen mimic (Klaper et al, 2006). In addition, MeHg appears to affect bone cells, inducing hypercalcemia in goldfish and interferes with calcium homeostasis (Suzuki et al, 2004).…”

What are the toxicological effects of mercury in Arctic biota?

“…In a controlled feeding study, Webber and Haines (2003) reported that golden shiners (Notemigonuscryso leucas), with whole-body Hg concentrations averaging 0.52 μg/g ww, were hyperactive and had altered shoaling behavior relative to fish with lower Hg concentrations. Other negative effects of Hg exposure reported in fish include impacts on reproductive parameters, such as impaired spawning behavior, mediated through a disruption of normal neuroendocrine function (Hammerschmidt et al, 2002;Drevnick and Sandheinrich, 2003;Klaper et al, 2006;Sandheinrich and Miller, 2006;Crump and Trudeau, 2009). In a critical review of the recent literature, Sandheinrich and Wiener (2010) concluded that changes in biochemical processes, damage to cells and tissues, and reduced reproduction in fish occur at MeHg concentrations of about 0.5 to 1.2 μg Hg/g ww in axial muscle.…”

Sexual Variation in Fisheries Research and Management: When Does Sex Matter?

“…Due to the speed with which physiological status can change when perturbed by abiotic stress, multiple studies have focused on the sex-specific physiological responses of fish to environmental contaminants (Aaltonen et al, 2000;Afonso et al, 2003;Klaper et al, 2006). Exposure to methylmercury (MeHg) has been shown to elicit sex-related responses in fish (Klaper et al, 2006).…”

“…Exposure to methylmercury (MeHg) has been shown to elicit sex-related responses in fish (Klaper et al, 2006). Male fathead minnows (Pimephales promelas) respond by an up-regulation of vittelogenin mRNA, while females show the opposite (i.e., down-regulation).…”