Mortality and transcriptional effects of inorganic mercury in the marine copepod Calanus finmarchicus

ABSTRACT

Inorganic mercury (Hg) is highly toxic to organisms including crustaceans and displays multiple toxic modes of action (MoA). The main aim of this investigation was to assess the acute and sublethal toxicity mediated by mercury chloride (HgCl₂) in the marine copepod Calanus finmarchicus. A combination of short-term static studies to determine acute toxicity and a transcriptional investigation to characterize the sublethal MoA of HgCl₂ were conducted with an in-house continuous culture of C. finmarchicus. Transcriptional changes were determined by a custom 6.6 k C. finmarchicus Agilent oligonucleotide microarray and quantitative RT-PCR analysis. Data demonstrate that HgCl₂ produced a concentration- and time-dependent reduction in survival (NOEC_{48 h} = 6.9 μg/L [Hg²⁺] and LC₅₀ of 279, 73, 48, and 34 µg/L [Hg²⁺] after 24, 48, 72, and 96 h, respectively) and that exposure to sublethal concentrations of HgCl₂ (5 μg/L [Hg2⁺]) induced differential expression of 98 features (probes) on the microarray. Gene ontology (GO) and toxicological pathway analyses suggested that the main MOA were (1) uncoupling of mitochondrial oxidative phosphorylation (OXPHOS) and ATP production, (2) oxidative stress and macromolecular damage, (3) inactivation of cellular enzymes, (4) induction of cellular apoptosis and autophagocytosis, (5) over-excitation of glutamate receptors (neurotoxicity), (6) disruption of calcium homeostasis and signaling, and (7) modulation of nuclear receptor activity involved in vitamin D receptor signaling. Quantitative RT-PCR analysis verified that oligoarray performed reliably in terms of specificity and response, thus demonstrating that Hg²⁺ exerts multiple potential MoA in C. finmarchicus.

Acknowledgments

Authors would like to thank Stine Kooyman (NIVA/NMBU, Norway) and Kenneth Macrae (NIVA/Norwegian Environment Agency, Norway) for RNA extraction, Mie L. Jareid (NIVA/NMBU) for running the microarray analysis and Ann M. Tarrant (Woods Hole Oceanographic Institution, USA) for providing annotation information on the Calanus finmarchicus de novo transcriptome assembly.

Funding

Authors gratefully acknowledge financial support from the Norwegian Research Council (project no. 196711, 268294, 223268), the Norwegian Institute for Water Research (NIVA) and SINTEF Materials and Chemistry (Calanomics project).

Supplemental Material

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Additional information

Funding

Authors gratefully acknowledge financial support from the Norwegian Research Council (project no. 196711, 268294, 223268), the Norwegian Institute for Water Research (NIVA) and SINTEF Materials and Chemistry (Calanomics project).