Abstract
Aiming at an integrated and mechanistic view of the early biological effects of selected metals in the marine sentinel organism Mytilus galloprovincialis, we exposed mussels for 48 hours to 50, 100 and 200 nM solutions of equimolar Cd, Cu and Hg salts and measured cytological and molecular biomarkers in parallel. Focusing on the mussel gills, first target of toxic water contaminants and actively proliferating tissue, we detected significant dose-related increases of cells with micronuclei and other nuclear abnormalities in the treated mussels, with differences in the bioconcentration of the three metals determined in the mussel flesh by atomic absorption spectrometry. Gene expression profiles, determined in the same individual gills in parallel, revealed some transcriptional changes at the 50 nM dose, and substantial increases of differentially expressed genes at the 100 and 200 nM doses, with roughly similar amounts of up- and down-regulated genes. The functional annotation of gill transcripts with consistent expression trends and significantly altered at least in one dose point disclosed the complexity of the induced cell response. The most evident transcriptional changes concerned protein synthesis and turnover, ion homeostasis, cell cycle regulation and apoptosis, and intracellular trafficking (transcript sequences denoting heat shock proteins, metal binding thioneins, sequestosome 1 and proteasome subunits, and GADD45 exemplify up-regulated genes while transcript sequences denoting actin, tubulins and the apoptosis inhibitor 1 exemplify down-regulated genes). Overall, nanomolar doses of co-occurring free metal ions have induced significant structural and functional changes in the mussel gills: the intensity of response to the stimulus measured in laboratory supports the additional validation of molecular markers of metal exposure to be used in Mussel Watch programs.
Highlights
Edible marine bivalves of the genus Mytilus have a long history as biosensors of coastal water pollution [1] but they are attractive for genetic selection [2], biotechnological applications [3] and functional ecology studies [4,5,6,7].Both the levels of contaminants accumulated by filter-feeding in the mussel tissues and related biological effects are widely documented, and used to assess the quality of the coastal marine waters and health risks [8,9]
We used offshore mussels collected in late Spring to test the effects of the same metal mixture previously chosen to investigate the transcriptional response of the Mediterranean mussels to cooccurring metal contaminants [32]
The triplicate analysis of selected metal elements performed by atomic spectrometry on the pooled flesh of mussels exposed to the 200 nM metal dose for 48 h indicated mean concentration values of 1.42 (Pb), 1.56 (Cd), 0.24 (Cr), 2.85 (As), 3.08 (Cu), 31.38 (Zn) and 22.52 (Hg) mg/g ww (Table 3)
Summary
Edible marine bivalves of the genus Mytilus have a long history as biosensors of coastal water pollution [1] but they are attractive for genetic selection [2], biotechnological applications [3] and functional ecology studies [4,5,6,7]. Both the levels of contaminants accumulated by filter-feeding in the mussel tissues and related biological effects are widely documented, and used to assess the quality of the coastal marine waters and health risks [8,9]. Careful evaluation of the cause-effect relationships and identification of reliable biomarkers in various exposure sceneries are crucial for advancing in environmental toxicology and risk assessment
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