Abstract
High concentrations of mercury (Hg) have been documented in deep-water fish species from some Norwegian fjords. In this study, tusk (Brosme brosme) was sampled from four locations in the innermost parts of Sognefjorden in Western Norway. Total Hg and methylmercury (MeHg) levels were measured in liver tissue. To search for potential sublethal effects of Hg, we characterized the hepatic transcriptome in tusk with high and low levels of Hg bioaccumulation using global transcriptomics analysis (RNA-seq). The results showed that there was a significant correlation between fish weight and accumulated concentrations of MeHg but not total Hg. MeHg accounted for 30–40% of total Hg in liver of most of the fish, although at concentrations above 2–3 mg Hg/kg wet weight the percentage of MeHg dropped considerably. Transcriptome analysis resulted in hundreds of differentially expressed genes in the liver of tusk with high Hg levels. Functional enrichment analysis suggested that the top affected pathways are associated with protein folding, adipogenesis, notch signaling, and lipid metabolism (beta-oxidation and phospholipids). Based on transcriptional responses pointing to well-known effects of Hg compounds in fish, the study suggests that tusk in Sognefjorden could be negatively impacted by Hg bioaccumulation.
Highlights
Mercury (Hg) is a globally distributed pollutant of great concern
By comparing transcriptomics profiles in fish with low and high levels of High concentrations of mercury (Hg) using RNA-seq, we explore molecular targets and identify potential biomarkers of environmental Hg exposure in tusk collected from a contaminated fjord
The enriched pathways using the different tools suggest that differentially expressed genes (DEGs) encoding proteins involved in protein stability and folding were differentially expressed
Summary
Mercury (Hg) is a globally distributed pollutant of great concern. Human activities such as mining and fossil fuel combustion have significantly increased the concentration of Hg worldwide (Lamborg et al, 2014). MeHg, which is more toxic than inorganic Hg, is bioaccumulative and biomagnifies in the aquatic food web (Wiener et al, 2003). Seafood such as fish is the main dietary source of MeHg exposure for humans. Many studies have documented a direct correlation between fish consumption and body burden of MeHg (Morel et al, 1998; Chapman and Chan, 2000; Cole et al, 2004; Bjornberg et al, 2005; Diez, 2009). It is of interest to study bioaccumulation and mechanistic impacts of Hg in wild fish
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