Transcriptional response of stress genes to metal exposure in zebra mussel larvae and adults

Transcriptome Analysis and Identification of Cadmium-Induced Oxidative Stress Response Genes in Different Meretrix meretrix Developmental Stages

Cadmium (Cd) is one of the major pollutants in the aquatic environment, and it can easily accumulate in aquatic animals and result in toxic effects by changing the metabolism of the body, causing a serious impact on the immune system, reproductive system, and the development of offspring. The clam Meretrix meretrix is one of the commercially important species that is cultivated in large-scale aquaculture in China. To elucidate the underlying molecular mechanisms of Cd2+ in the developmental processes, fertilized eggs and larvae of M. meretrix at different developmental stages were exposed to Cd2+ (27.2 mg L-1 in natural seawater) or just natural seawater without Cd2+ (control), and high-throughput transcriptome sequencing and immunohistochemistry techniques were used to analyze the toxic effects of Cd on larvae at different early developmental stages. The results revealed 31,914 genes were differentially expressed in the different stages of M. meretrix development upon treatment with Cd2+. Ten of these genes were differentially expressed in all stages of development examined, but they comprised only six unigenes (CCO, Ndh, HPX, A2M, STF, and pro-C3), all of which were related to the oxidative stress response. Under Cd exposure, the expression levels of CCO and Ndh were significantly upregulated in D-shaped and pediveliger larvae, while pro-C3 expression was significantly upregulated in the fertilized egg, D-shaped larva, and pediveliger. Moreover, HPX, A2M, and STF expression levels in the fertilized egg and pediveliger larvae were also significantly upregulated. In contrast, CCO, Ndh, HPX, A2M, STF, and pro-C3 expression levels in the postlarva were all downregulated under Cd exposure. Besides the genes with changes in expression identified by the transcriptome, the expression of two other oxidative stress-related genes (MT and Nfr2) was also found to change significantly in the different developmental stages of M. meretrix upon Cd exposure, confirming their roles in combating oxidative stress. Overall, the findings of this study indicated that Cd would interfere with cellular respiration, ion transport, and immune response through inducing oxidative stress, and changes in the expression of oxidative stress-related genes might be an important step for M. meretrix to deal with the adverse effects of Cd at different stages of its development.

Dreissena polymorpha responses under thermal and hypoxic stress: New insights in the tolerance of this freshwater sentinel species

Dreissena polymorpha is a sentinel freshwater mussel providing key functional ecosystemic services like nutrient recycling and suspended matter filtration. Global warming and especially extreme events imply rapid fluctuations of environmental parameters that sessile organisms could not escape. The increase occurrence of heat waves and the subsequent expansion of hypoxic areas could challenge the survival of mussels. This study provided a deeper knowledge of energy management and cellular function during thermal (+15 °C) or hypoxic (30% of dissolved oxygen saturation) stress for 7 days. A potential metabolic rate depression was highlighted in D. polymorpha under hypoxia through a decline in the mitochondrial activity and a constant AMP content over time. A contrasted pattern of response was observed in thermal-stressed mussels between 24 h and 7 days of exposure. A global increase of metabolic activity was noticed in mussels after 24 h while a return to control level was noticed at the end of the experiment. Although D. polymorpha is considered as a temperature tolerant species, a significant increase of ADP:ATP ratio, related to a decrease of mitochondrial activity and density, suggested an overwhelming of organisms. This study pointed to the importance of considering time of exposure to natural factor variations in tolerance window of organisms in a long-term changing environment. The apparent short-term tolerance of D. polymorpha could hide much more deleterious consequences, i.e. mortality, if abiotic stresses persist, as suggested by climate change models.

Metal Contamination and Biomarkers in Cerastoderma glaucum: A Multi-level Approach

In this study, we focused on evaluating the responses of the cockle, Cerastoderma glaucum to in situ exposures to metals at three sites in the Gulf of Gabes in the coastal zone of Tunisia differing in levels of metal contamination. Firstly, we examined the general physiological state of the organisms. Secondly, we evaluated the bioaccumulation of several metals (Cd, Cu, Zn, Ni) in the cockles. Thirdly, we focused on evaluating histologically changes in gametogenesis and sexual maturity of the organisms. Finally, we determined the expression of seven key genes encoding enzymes or proteins involved in responses to different types of environmental stressors. Results showed a decrease in the general physiological status of the cockles, including a reduced condition index, sex ratios skewed to females (70% and 80% females in the intermediate and the contaminated site, respectively) and greater mortalities in tests under anoxic conditions (i.e., stress on stress test) in cockles collected from the most contaminated site (LT50 = 2.88 days) compared to the cockles from the intermediate site (LT50 = 5 days) and the less contaminated site (LT50 = 6 days). Results for metal bioaccumulation showed that the levels of Cd, Cu, Zn and Ni in cockles were consistent with the contaminant gradient, with the highest levels in cockles from the most contaminated site (1.04; 4.92; 52.76 and 13.81 µg/g dw, respectively), followed by those from the intermediate site (0.34; 2.94; 36.94; 17.40 µg/g dw, respectively) and then the less contaminated site (0.065; 1.27; 21.62 and 5.40 µg/g dw, respectively). Results from the gametogenesis and maturity index showed few differences in the reproductive cycle of cockles collected from the three study sites. There were different patterns of gene expression that were divided into three groups in terms of responses: (1) expression of genes involved in metal detoxification, ATP Binding Cassette Subfamily B Member 1 (ABCB1) and metallothionein MT) and genes for superoxide dismutases (i.e., Mn SOD and CuZn SOD), which did not show any difference in their levels of expression; (2) heat shock protein 70 (HSP70) gene expression, which decreased in cockles according to the pollution gradient, and (3) expression of catalase (CAT) and cytochrome oxidase subunit 1 (COI) genes was threefold and 1000-fold higher in cockles from intermediate and most contaminated sites compared to the less contaminated site. Therefore, changes in overall physiological condition, sex ratios and expression of HSP70, CAT and COI genes may be appropriate biomarkers for in situ studies of the impacts of metals in cockles. However, these biomarkers should be coupled to proteomics studies.

Transcriptional Responses as Biomarkers of General Toxicity: A Systematic Review and Meta-analysis on Metal-Exposed Bivalves

Through a systematic review and a series of meta-analyses, we evaluated the general responsiveness of putative transcriptional biomarkers of general toxicity and chemical stress. We targeted metal exposures performed on bivalves under controlled laboratory conditions and selected six transcripts associated with general toxicity for evaluation: catalase, glutathione-S-transferase, heat shock proteins 70 and 90, metallothionein, and superoxide dismutase. Transcriptional responses (n = 396) were extracted from published scientific articles (k = 22) and converted to log response ratios (lnRRs). By estimating toxic units, we normalized different metal exposures to a common scale, as a proxy of concentration. Using Bayesian hierarchical random effect models, we then tested the effects of metal exposure on lnRR, both for metal exposure in general and in meta-regressions using toxic unit and exposure time as independent variables. Corresponding analyses were also repeated with transcript and tissue as additional moderators. Observed patterns were similar for general and for transcript- and tissue-specific responses. The expected overall response to arbitrary metal exposure was an lnRR of 0.50, corresponding to a 65% increase relative to a nonexposed control. However, when accounting for publication bias, the estimated "true" response showed no such effect. Furthermore, expected response magnitude increased slightly with exposure time, but there was little support for general monotonic concentration dependence with regard to toxic unit. Altogether, the present study reveals potential limitations that need consideration prior to applying the selected transcripts as biomarkers in environmental risk assessment. Environ Toxicol Chem 2023;42:628-641. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A global synthesis of ecosystem services provided and disrupted by freshwater bivalve molluscs

Identification of ecosystem services, i.e. the contributions that ecosystems make to human well-being, has proven instrumental in galvanising public and political support for safeguarding biodiversity and its benefits to people. Here we synthesise the global evidence on ecosystem services provided and disrupted by freshwater bivalves, a heterogenous group of >1200 species, including some of the most threatened (in Unionida) and invasive (e.g. Dreissena polymorpha) taxa globally. Our systematic literature review resulted in a data set of 904 records from 69 countries relating to 24 classes of provisioning (N = 189), cultural (N = 491) and regulating (N = 224) services following the Common International Classification of Ecosystem Services (CICES). Prominent ecosystem services included (i) the provisioning of food, materials and medicinal products, (ii) knowledge acquisition (e.g. on water quality, past environments and historical societies), ornamental and other cultural contributions, and (iii) the filtration, sequestration, storage and/or transformation of biological and physico-chemical water properties. About 9% of records provided evidence for the disruption rather than provision of ecosystem services. Synergies and trade-offs of ecosystem services were observed. For instance, water filtration by freshwater bivalves can be beneficial for the cultural service 'biomonitoring', while negatively or positively affecting food consumption or human recreation. Our evidence base spanned a total of 91 genera and 191 species, dominated by Unionida (55% of records, 76% of species), Veneroida (21 and 9%, respectively; mainly Corbicula spp.) and Myoida (20 and 4%, respectively; mainly Dreissena spp.). About one third of records, predominantly from Europe and the Americas, related to species that were non-native to the country of study. The majority of records originated from Asia (35%), with available evidence for 23 CICES classes, as well as Europe (29%) and North America (23%), where research was largely focused on 'biomonitoring'. Whilst the earliest record (from 1949) originated from North America, since 2000, annual output of records has increased rapidly in Asia and Europe. Future research should focus on filling gaps in knowledge in lesser-studied regions, including Africa and South America, and should look to provide a quantitative valuation of the socio-economic costs and benefits of ecosystem services shaped by freshwater bivalves.

Metabolic, cellular and defense responses to single and co-exposure to carbamazepine and methylmercury in Dreissena polymorpha

Carbamazepine (CBZ) and Hg are widespread and persistent micropollutants in aquatic environments. Both pollutants are known to trigger similar toxicity mechanisms, e.g. reactive oxygen species (ROS) production. Here, their effects were assessed in the zebra mussel Dreissena polymorpha, frequently used as a freshwater model in ecotoxicology and biomonitoring. Single and co-exposures to CBZ (3.9 μg L^-1) and MeHg (280 ng L^-1) were performed for 1 and 7 days. Metabolomics analyses evidenced that the co-exposure was the most disturbing after 7 days, reducing the amount of 25 metabolites involved in protein synthesis, energy metabolism, antioxidant response and osmoregulation, and significantly altering cells and organelles' structure supporting a reduction of functions of gills and digestive glands. CBZ alone after 7 days decreased the amount of α-aminobutyric acid and had a moderate effect on the structure of mitochondria in digestive glands. MeHg alone had no effect on mussels' metabolome, but caused a significant alteration of cells and organelles' structure in gills and digestive glands. Single exposures and the co-exposure increased antioxidant responses vs control in gills and digestive glands, without resulting in lipid peroxidation, suggesting an increased ROS production caused by both pollutants. Data globally supported that a higher number of hyperactive cells compensated cellular alterations in the digestive gland of mussels exposed to CBZ or MeHg alone, while CBZ + MeHg co-exposure overwhelmed this compensation after 7 days. Those effects were unpredictable based on cellular responses to CBZ and MeHg alone, highlighting the need to consider molecular toxicity pathways for a better anticipation of effects of pollutants in biota in complex environmental conditions.

Evaluation of transcriptional biomarkers using a high-resolution regression approach: Concentration-dependence of selected transcripts in copper-exposed freshwater mussels (Anodonta anatina)

We tested concentration-dependence of selected gene transcripts (cat, gst, hsp70, hsp90, mt and sod) for evaluation as biomarkers of chemical stress. Contrary to the common approach of factorial designs and few exposure concentrations, we used regression across a high-resolution concentration series. Specifically, freshwater mussels (Anodonta anatina) were acutely (96 h) exposed to Cu (13 nominal concentrations, measuring 0.13-1 600 µg/L), and transcripts were measured by RT-qPCR. In digestive glands, cat, hsp90 and mt decreased with water Cu (p < 0.05), but response magnitudes saturated at < 2-fold decreases. In gills, gst, hsp70, hsp90 and mt increased with water Cu (p < 0.05). While hsp70, hsp90 and mt exceeded 2-fold increases within the exposure range, high Cu concentrations were required (38-160 µg/L). Although gill responses were generally more robust compared to digestive glands, overall small response magnitudes and moderate sensitivity may set limit for potential application as general biomarkers of chemical stress.

Coping with stress in a warming Gulf: the postlarval American lobster's cellular stress response under future warming scenarios

The Gulf of the Maine (GoM) is one of the fastest warming bodies of water in the world, posing serious physiological challenges to its marine inhabitants. Marine organisms can cope with the cellular and molecular stresses created by climate change through changes in gene expression. We used transcriptomics to examine how exposure to current summer temperatures (16 °C) or temperature regimes reflective of projected moderate and severe warming conditions (18 °C and 22 °C, respectively) during larval development alters expression of transcripts affiliated with the cellular stress response (CSR) in postlarval American lobsters (Homarus americanus). We identified 26 significantly differentially expressed (DE) transcripts annotated to CSR proteins. Specifically, transcripts for proteins affiliated with heat shock, the ubiquitin family, DNA repair, and apoptosis were significantly over-expressed in lobsters reared at higher temperatures relative to current conditions. Substantial variation in the CSR expression between postlarvae reared at 18 °C and those reared at 22 °C suggests that postlarvae reared under severe warming may have a hindered ability to cope with the physiological and molecular challenges of ocean warming. These results highlight that postlarval American lobsters may experience significant heat stress as rapid warming in the GoM continues, potentially compromising their ability to prevent cellular damage and inhibiting the reallocation of cellular energy towards other physiological functions beyond activation of the CSR. Moreover, this study establishes additional American lobster stress markers and addresses various knowledge gaps in crustacean biology, where sufficient 'omics research is lacking.

Integrated biomarker responses in oysters Crassostrea gasar as an approach for assessing aquatic pollution of a Brazilian estuary

The Laguna Estuarine System (LES), southern Brazil, suffers impacts from anthropogenic activities, releasing contaminants into the ecosystem. This study evaluated changes in biochemical and molecular biomarkers and contaminants concentrations in oysters Crassostrea gasar transplanted and kept for 1.5 and 7 days at three potentially contaminated sites (S1, S2, and S3) at LES. Metals varied spatiotemporally; S1 exhibited higher Ag and Pb concentrations, whereas Cd was present in S3. S2 was a transition site, impacted by Ag, Pb, or Cd, depending on the period. Organic contaminants concentrations were higher before transplantation, resulting in the downregulation of biotransformation genes transcripts levels. Phase II-related genes transcripts and metals showed positive correlations. Decreased levels of HSP90-like transcripts and antioxidant enzymes activity were related to increased pollutant loads. Integrated biomarker response index (IBR) analysis showed S1 and S3 as the most impacted sites after 1.5 and 7 days, respectively. Regardless of the scenario, LES contaminants pose a significant threat to aquatic biota.

Gene Expression Changes after Parental Exposure to Metals in the Sea Urchin Affect Timing of Genetic Programme of Embryo Development

It is widely accepted that phenotypic traits can be modulated at the epigenetic level so that some conditions can affect the progeny of exposed individuals. To assess if the exposure of adult animals could result in effects on the offspring, the Mediterranean sea urchin and its well-characterized gene regulatory networks (GRNs) was chosen as a model. Adult animals were exposed to known concentrations of zinc and cadmium (both individually and in combination) for 10 days, and the resulting embryos were followed during the development. The oxidative stress occurring in parental gonads, embryo phenotypes and mortality, and the expression level of a set of selected genes, including members of the skeletogenic and endodermal GRNs, were evaluated. Increased oxidative stress at F₀, high rates of developmental aberration with impaired gastrulation, in association to deregulation of genes involved in skeletogenesis (dri, hex, sm50, p16, p19, msp130), endodermal specification (foxa, hox11/13b, wnt8) and epigenetic regulation (kat2A, hdac1, ehmt2, phf8 and UBE2a) occurred either at 24 or 48 hpf. Results strongly indicate that exposure to environmental pollutants can affect not only directly challenged animals but also their progeny (at least F₁), influencing optimal timing of genetic programme of embryo development, resulting in an overall impairment of developmental success.

Resilience of Dreissena polymorpha in wastewater effluent: Use as a bioremediation tool?

Nowadays, it is necessary to improve the efficiency of wastewater treatment plant treatments. In this context the use of biofilter species, like Dreissena polymorpha, as a bioremediation tool in wastewater is increasingly highlighted. The innovative aim of this study is to evaluate the zebra mussel survival in the outlet channel of a conventional WWTP to use them as bioremediation tool. For this, mussels were transplanted in the outlet channel for 28 days and different biomarkers were monitored. D. polymorpha is able to maintain itself in good physiological conditions until 21 days, yet at 28 days a high mortality rate (24%), a decrease in filtration efficiency (8/15 mussels filtered and 17.0% of filtration rate) and antioxidant system activation (CAT activity et gpx gene expression increase) suggest an exhaustion. Some biomarkers suggested a hypoxic stress. Despite the unfavourable conditions, bivalves have bioaccumulated pathogenic protozoa (Toxoplasma gondii and Giardia duodenalis) during the exposure. Zebra mussel seems to be a promising tool for bioremediation in wastewater.

Effect of reproduction cycle stage on energy metabolism responses in a sentinel species (Dreissena polymorpha) exposed to cadmium: What consequences for biomonitoring?

Metal trace elements such as cadmium (Cd) are commonly present in ecosystems and could lead to impairment of mitochondrial functions and energy imbalance in aquatic organisms including molluscs. Combined exposure to increasing temperatures and Cd could enhance such an impact on animals. Seasonal fluctuations, such as temperature, and the corresponding reproduction cycle can affect biomarker responses. However, the reproduction cycle stage is rarely taken into account in ecotoxicological studies. Thus, this work aimed at understanding energy metabolism responses in a sentinel species, Dreissena polymorpha. Mussels were collected during the rest and the reproduction periods and were exposed to 10 μg.L^-1 of cadmium (Cd) at two temperatures (in situ temperature and in situ temperature + 5°C) during 7 days. Energy metabolism was monitored by measuring reserves and energy nucleotides charge and by assessing aerobic and anaerobic metabolism markers, and upstream regulation pathways. Markers related to OXPHOS activity revealed seasonal variations under laboratory conditions. Conversely, adenylate nucleotides, glycogen, lipid and transcript levels of AMP-activated protein kinase, citrate synthase, ATP synthase and cytochrome b encoding genes remained steady after the acclimation period. No evident effect of Cd on energy metabolism markers was noticed for both exposures although the transcript level of succinate dehydrogenase and citrate synthase encoding genes decreased with Cd during the rest period. Cellular stress, revealed by lipid peroxidation and catalase mRNA levels, only occurred in Cd and warming co-exposed mussels during the reproduction period. These results suggest that contaminant impact might differ according to the reproduction cycle stage. The effect of confounding factors on biomarker variations should be further investigated to have a deeper knowledge of metabolism responses under laboratory conditions.

Spatial Distribution of Toxic Metal(loid)s and Microbial Community Analysis in Soil Vertical Profile at an Abandoned Nonferrous Metal Smelting Site

In this study soils at different depths were collected in a Zn smelting site located in Zhuzhou City, China, in order to understand toxic metal(loid)s distribution and microbial community in vertical soil profile at a smelting site. Except Soil properties and metal(loid)s content, the richness and diversity of microbial communities in soil samples were analyzed via high-throughput Illumina sequencing of 16s rRNA gene amplicons. The results showed that the content of As, Pb, Cu, Cd, Zn, and Mn was relatively high in top soil in comparison to subsoil, while the concentration of Cr in subsoil was comparable with that in top soil due to its relative high background value in this soil layer. The bioavailability of Cd, Mn, Zn, and Pb was relative higher than that of As, Cr, and Cu. The diversity of soil microbial communities decreased with increasing depth, which might be ascribed to the decrease in evenness with increase in depth duo to the influence by environmental conditions, such as pH, TK (total potassium), CEC (cation exchange capacity), ORP (oxidation reduction potential), and Bio-Cu (bioavailable copper). The results also found Acidobacteria, Proteobacteria, Firmicutes, and Chloroflexi were dominant phyla in soil samples. At the genus level, Acinetobacter, Pseudomonas, and Gp7 were dominant soil microorganism. Besides, Environmental factors, such as SOM (soil organic matter), pH, Bio-Cu, Bio-Cd (bioavailable cadmium), and Bio-Pb (bioavailable lead), greatly impacted microbial community in surface soil (1-3 m), while ORP, TK, and AN concentration influenced microbial community in the subsoil (4-10 m).

Seasonal monitoring of cellular energy metabolism in a sentinel species, Dreissena polymorpha (bivalve): Effect of global change?

Aquatic organisms such as bivalves are particularly sensitive to seasonal fluctuations associated with climate changes. Energy metabolism management is also closely related to environmental fluctuations. Changes in both biotic and abiotic conditions, such as the reproduction status and temperature respectively, may affect the organism energy status. A bivalve sentinel species, Dreissena polymorpha was sampled along its one-year reproduction cycle in situ (2018-2019) to study natural modulations on several markers of energy metabolism regarding seasonal variations in situ. A panel of different processes involved in energy metabolism was monitored through different functions such as energy balance regulation, mitochondrial density, and aerobic/anaerobic metabolism. The typical schema expected was observed in a major part of measured responses. However, the monitored population of D. polymorpha showed signs of metabolism disturbances caused by an external stressor from April 2019. Targeting a major part of energy metabolism functions, a global analysis of responses suggested a putative impact on the mitochondrial respiratory chain due to potential pollution. This study highlighted also the particular relevance of in situ monitoring to investigate the impacts of environmental change on sentinel species.

New Insights into Cellular Impacts of Metals in Aquatic Animals

Toxic metals remain a current important threat to aquatic ecosystems, despite regulatory efforts to reduce their release. Several toxic metals already appear in the list of priority substances polluting surface waters, while concerns arise from the increasing use of technology-critical metals such as metallic nanoparticles, rare-earth, and platinum group metals. In aquatic environments, various chemical, biological and physical processes determine the impact of metals on the biota. This review provides insights into responses to toxic metals recently reported in freshwater and marine animals. The specific emphasis is on: (i) common cellular and molecular responses; (ii) stress proteins; (iii) redox homeostasis; (iv) cytoskeleton rearrangement; (v) metabolism reshuffle; (vi) free cellular energy and mitochondrial metabolism; and (vi) immunity. These endpoints are promising, notably in multi-biomarker approaches to identify precise cellular toxicity pathways and anticipate the impact of environmental metal pollution.

Effects of waterborne exposure to cadmium on biochemical responses in the freshwater gastropod, Bellamya aeruginosa

The biochemical responses of Bellamya aeruginosa as a dominant and widespread freshwater gastropod throughout China to waterborne cadmium (Cd) were investigated to explore the impacts of exposure concentration and duration in this potential sentinel species. After the 7 days' test of dosage-mortality relationship, gastropods were exposed for either 7 days at the LC₅₀ (1.7 mg/L), the LC₁₀ (0.7 mg/L) and 0.02 mg/L Cd, or 28 days at 0.02 mg/L Cd. A suite of biochemical indicators including metallothionein-like protein (MTLP), reduced glutathione (GSH), catalase (CAT), contents of tissue metal (Cd, Fe, Mn, Cu, Zn), and the compartments of these metals bound to MTLP were examined. The treatment of 0.02 mg/L Cd led to the increase of Cd bound to MTLP (Cd-MTLP) levels, the decrease of GSH content, and the upregulation of CAT activity, but no induction of MTLP, indicating that the intrinsic MTLP and GSH worked together for the detoxification of Cd at the low exposure. When the exposure concentration increased, GSH was depleted severely and synthesis of MTLP was triggered, leading to a strong and significant relationship between MTLP level and Cd accumulation. At the lethal concentrations (1.7 mg/L), both MTLP induction and CAT activity were inhibited while the proportion of Cd-MTLP to total Cd were increased, suggesting more intrinsic MTLP were utilized to sequester free Cd ions. Therefore, the content of Cd-MTLP in digestive glands of B. aeruginosa was recommended as a reliable biomarker for Cd contamination.

Short-term spatiotemporal biomarker changes in oysters transplanted to an anthropized estuary in Southern Brazil

Estuarine ecosystems are increasingly being affected by pollution caused by anthropogenic activities. In this study, Crassostrea gasar oysters were transplanted and maintained for seven days at three sites (S1, S2, and S3) in the Laguna Estuarine System (LES)-situated in southern Brazil-that has been exposed to multiple anthropic stresses. On the basis of the concentrations of metal and organic pollutants in oysters, we identified marked spatial variations in pollutant levels, with S3 showing the highest concentration of Ag, Fe, Ni, Zn, and total polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and linear alkylbenzenes (LABs), followed by S2 and S1. Along with the concentrations of pollutants, a set of biomarkers was analyzed. Oysters maintained at S3 showed enhanced protective defenses in gills, as observed by the increased levels of superoxide dismutase (SOD-like) and heat shock protein 90 (HSP90-like) transcripts and catalase (CAT) activity, concomitant with reduced lipid peroxidation (MDA) levels. Decreased antioxidant activities together with increased MDA levels are indicative of the digestive gland being more susceptible to pollutant-induced oxidative damage. Oysters transplanted into LES showed lower levels of cytochrome P450 transcripts (CYP356A1-like and CYP2AU1), and decreased glutathione S-transferase (GST) enzyme activity, suggesting lower biotransformation capacity. By integrating information regarding the concentration of metal and organic pollutants with that of molecular as well as biochemical biomarkers, our study provides novel insights into pollutant exposure and the potential biological impacts of such exposure on estuarine organisms in southern Brazil.

Effects of cadmium on the gene transcription of the liver in the freshwater turtle (Chinemys reevesii)

This study investigated the related gene transcription of liver in freshwater turtle Chinemys reevesii exposed to cadmium (Cd). After acclimation, healthy turtles were selected for experiments. They were randomly divided into four experimental groups and each group had 5 animals. The turtles were treated with 0 mg/kg, 7.5 mg/kg, 15 mg/kg, and 30 mg/kg Cd chloride separately by intraperitoneal injection. Liver samples were collected for examination of the transcription of related genes at 2 weeks after Cd exposure. The transcription of mRNA of MT, SOD, CAT, PNKP, and GPX4 genes in turtle liver cells were analyzed. Results showed that Cd promoted MT mRNA transcription in turtle's liver at low dose (7.5 mg/kg) and inhibited MT mRNA transcription in turtle's liver at middle dose (15 mg/kg) and high dose (30 mg/kg). Cd inhibited the transcription of SOD, CAT, and PNKP mRNA in turtle's liver, and the inhibition was obvious at high dose (30 mg/kg). Cd promoted GPX4 mRNA transcription in turtle's liver, especially at low dose (7.5 mg/kg). In conclusion, Cd had different effects on the mRNA transcription of liver cells in the freshwater turtle Chinemys reevesii exposed to Cd.

Transcriptional and biochemical biomarker responses in a freshwater mussel (Anodonta anatina) under environmentally relevant Cu exposure

Molecular biomarkers, like gene transcripts or enzyme activities, are potentially powerful tools for early warning assessment of pollution. However, a thorough understanding of response and baseline variation is required to distinguish actual effects from pollution. Here, we assess the freshwater mussel Anodonta anatina as a biomarker model species for freshwater ecosystems, by testing responses of six transcriptional (cat, gst, hsp70, hsp90, mt, and sod) and two biochemical (AChE and GST) biomarkers to environmentally relevant Cu water concentrations. Mussels (n = 20), collected from a stream free from point source pollution, were exposed in the laboratory, for 96 h, to Cu treatments (< 0.2 μg/L, 0.77 ± 0.87 μg/L, and 6.3 ± 5.4 μg/L). Gills and digestive glands were extracted and analyzed for transcriptional and biochemical responses. Biological and statistical effect sizes from Cu treatments were in general small (mean log₂ fold-change ≤ 0.80 and Cohen's f ≤ 0.69, respectively), and no significant treatment effects were observed. In contrast, four out of eight biomarkers (cat, gst, hsp70, and GST) showed a significant sex:tissue interaction, and additionally one (sod) showed significant overall effects from sex. Specifically, three markers in gills (cat, mt, GST) and one in digestive gland (AChE) displayed significant sex differences, independent of treatment. Results suggest that sex or tissue effects might obscure low-magnitude biomarker responses and potential early warnings. Thus, variation in biomarker baselines and response patterns needs to be further addressed for the future use of A. anatina as a biomarker model species.

Corbicula fluminea gene expression modulated by CeO2 nanomaterials and salinity

Cerium dioxide nanomaterials (CeO₂ NMs) are used in different fields and incorporated in daily products. Several studies highlighted their effects on organism physiology, although molecular studies remain scarce. NM behavior is strongly dependent on the environment but few data are available using complex exposure media, raising the question of its environmental impacts. The aim of the present work was to assess the toxic potential of three CeO₂ NMs in Corbicula fluminea at a molecular level by RT-qPCR under a more realistic scenario of exposure, in a multistress context at two different salinities (1.5 and 15 psu). C. fluminea was exposed for 28 days to pulses of the three selected NMs (reference, manufactured, and aged manufactured). In bivalves, the gills and digestive gland are two key organs used for ecotoxicological studies. The expression change of 12 genes was measured in control organisms after 28 days in both organs, allowing us to clearly separate the responses for both organs and salinities. As gills come in contact with the environment first, we monitored gene the expression at intermediate time points (7, 14, and 21 days) for this organ in order to highlight clams responses to NM and salinity. Two genes (Se-GPx, MnSOD) had a salinity-dependent level of expression. HSP70, Se-GPx, and Trxr mRNAs presented significant changes in their expressions in the presence of NM. This study was completed using an integrated statistical approach. The exposed organisms differed more from control at field salinity than those exposed to hyper-saline conditions. At 15 psu, salinity pressure seems to cause the first molecular impact. At 1.5 psu, gene expression patterns allowed the effect of each NM to separate clearly. These results confirmed the usefulness of gene expression studies. Moreover, we highlighted the necessity to assess the environmental toxicity of the different forms of manufactured NM.

Aberrant gene expression profiles in Mediterranean sea urchin reproductive tissues after metal exposures

Marine organisms are simultaneously exposed to numerous pollutants, among which metals probably represent the most abundant in marine environments. In order to evaluate the effects of metal exposure at molecular level in reproductive tissues, we profiled the sea urchin transcriptional response after non-lethal exposures using pathway-focused mRNA expression analyses. Herein, we show that exposures to relatively high concentrations of both essential and toxic metals hugely affected the gonadic expression of several genes involved in stress-response, detoxification, transcriptional and post-transcriptional regulation, without significant changes in gonadosomatic indices. Even though treatments did not result in reproductive tissues visible alterations, metal exposures negatively affected the main mechanisms of stress-response, detoxification and survival of adult P. lividus. Additionally, transcriptional changes observed in P. lividus gonads may cause altered gametogenesis and maintenance of heritable aberrant epigenetic effects. This study leads to the conclusion that exposures to metals, as usually occurs in polluted coastal areas, may affect sea urchin gametogenesis, thus supporting the hypothesis that parental exposure to environmental stressors affects the phenotype of the offspring.

Neonicotinoid insecticides are potential substrates of the multixenobiotic resistance (MXR) mechanism in the non-target invertebrate, Dreissena sp

Mussels are among the most frequently used invertebrate animals in aquatic toxicology to detect toxic exposure in the environment. The presence and activity of a cellular defence system, the multixenobiotic resistance (MXR) mechanism, was also established in these organisms. In isolated gill tissues of dreissenid mussels (D. bugensis) the MXR activity was assayed after treatment by commercially available insecticides (formulated products) which contain neonicotinoids as their active ingredients: Actara (thiamethoxam), Apacs (clothianidin), Calypso (thiacloprid) and Kohinor (imidacloprid), respectively. While applying the accumulation assay method, 0.5 μM rhodamine B was used as model substrate and 20 μM verapamil as model inhibitor of the MXR mechanism. In acute (in vitro) experiments when isolated gills were co-incubated in graded concentrations of insecticides and rhodamine B simultaneously, Calypso and Kohinor treatment resulted increasing rhodamine accumulation. Chemical analysis of gills in vitro incubated in insecticides demonstrated higher tissue concentrations of thiamethoxam, clothianidin and thiacloprid in the presence of verapamil suggesting that the active ingredients of Actara, Apacs and Calypso are potential substrates of the MXR mediated cellular efflux. In contrast, verapamil did significantly alter the accumulated imidacloprid concentrations in gills, suggesting that the active component of Kohinor is not transported by the MXR mechanism. Chronic (in vivo) exposures of the intact animals in lower, 1, 10 mg/L concentration of neonicotinoid products, resulted in a decreased level of both rhodamine accumulation and verapamil inhibition by the 12th-14th days of treatment. These results suggest an enhancement of MXR activity (chemostimulation), building up gradually in the animals exposed to Actara, Apacs and Kohinor, respectively. Neonicotinoid-type insecticides are generally considered as selective neurotoxins for insects, targeting the nicotinic type acetylcholine receptors (nAChRs) in their central nervous system. Our present results provide the first evidences that neonicotinoid insecticides are also able to alter the transmembrane transport mechanisms related to the MXR system.

BaP-metals co-exposure induced tissue-specific antioxidant defense in marine mussels Mytilus coruscus

Both benzo(α)pyrene (BaP) and metals are frequently found in marine ecosystem and can cause detrimental effects in marine organism, especially the filter feeder-marine mussels. Although the biological responses in mussels have been well-studied upon the single metal or BaP exposure, the information about antioxidant defense, especially in different tissues of mussels, are still limited. Considering the variety of contaminants existing in the actual marine environment, single BaP (56 μg/L) and the co-exposure with Cu, Cd and Pb (50 μg/L, 50 μg/L and 3 mg/L respectively) were applied in a 6 days exposure followed by 6 days depuration experiment. The alterations of superoxide dismutase (SOD), catalase (CAT) activities and total antioxidant capacity (TAC) level were assessed in haemolymph, gills and digestive glands of marine mussels, Mytilus coruscus. An unparalleled change in antioxidant biomarkers was observed in all cells/tissues, with the SOD activity showing higher sensitivity to exposure. A tissue-specific response showing unique alteration in gill was investigated, indicating the different function of tissues during stress responses. Depressed antioxidant effects were induced by BaP-metals co-exposure, indicating the interaction may alter the intact properties of BaP. To our knowledge, this is the first research to explore the antioxidant defense induced by combined exposure of BaP-metals regarding to tissue-specific responses in marine mussels. The results and experimental model will provide valuable information and can be utilized in the investigation of stress response mechanisms, especially in relation to tissue functions in marine organism in the future.

Differentiation of sympatric zebra and quagga mussels in ecotoxicological studies: A comparison of morphometric data, gene expression, and body metal concentrations

The zebra mussel is among the best studied freshwater molluscs in ecotoxicology, but information on the quagga mussel is lacking. Considering its potential spread, we selected a river in France in which zebra and quagga mussels coexisted, and then we used genetic markers to differentiate the two species and compared morphological parameters. cDNA sequencing assays of ten genes already used in zebra mussels were performed on quagga mussels to obtain functional specific primers. Then we analyzed the expression of genes involved in cellular metabolic activities (Cytochrome-c-oxidase - cox, and ATP synthase - atp), detoxification processes (Glutathione-S-Transferase - gst), oxidative stress (Catalase - cat), and digestive functions (Amylase - amy) on the two species. Whereas morphometric analysis underlined similarities in shape between the two species, relative gene expression profiles and metal concentrations evidenced strong differences. Quagga mussels notably presented half as high concentrations in Cd and Pb, two particularly toxic elements, as zebra mussels. These results imply that i) particular attention should be paid to properly distinguish the two species considering their similar external appearance, and ii) zebra mussels cannot be replaced by quagga mussels in ecotoxicological studies without preliminary investigations on biomarker response patterns. To our knowledge, this study is the first to have undertaken such an approach in gene expression analysis in quagga mussels, and more generally to have compared such biomarker responses of zebra and quagga mussels in the field.

Effects of Hg sublethal exposure in the brain of peacock blennies Salaria pavo: Molecular, physiological and histopathological analysis

Marine environments are affected by large amounts of toxicants among those mercury (Hg). The aim of this study was to assess potential neurotoxic effects of Hg in the peacock blenny Salaria pavo. A sublethal contamination to 66 μg HgCl₂ L^-1 over periods of 1, 4, 10 and 15 days was performed. Total Hg concentrations measured in the brain highlighted the detection of Hg at days 1 and 4 following the exposure but no concentration of the metal was further detected. Partial-length cDNA of genes coding ABC transporters (abcb1, abcc1, abcc2, abcg2) and acetylcholinesterase (ache) were characterized. Results from mRNA expression levels displayed an up-regulation of abcb1 mRNA while a down-regulation of abcc1 and abcc2 mRNA was observed. No change in abcg2 and ache mRNA expression was noted throughout the experiment. At each sampling time, Hg exposure did not affect the activity of the AChE enzyme. The histological analysis indicated that fish exhibited several damages in the optic tectum and the cerebellum and 3 reaction patterns were identified for each organ: circulatory disturbances, regressive and progressive changes. Molecular, physiological and histological biomarkers assessed in the present study highlighted that peacock blennies were able to detoxify Hg from the brain tissue by developing defense mechanisms. More globally, neurotoxic effects of a sublethal Hg exposure in the brain of peacock blennies and the adaptation capacity of this species were evaluated.

Transcriptomic approach: A promising tool for rapid screening nanomaterial-mediated toxicity in the marine bivalve Mytilus edulis-Application to copper oxide nanoparticles

The extensive development of nanotechnologies will inevitably lead to the release of nanomaterials (NMs) in the environment. As the aquatic environments represent the ultimate sink for various contaminants, it is highly probable that they also constitute a reservoir for NMs and hence aquatic animals represent potential targets. In a regulatory perspective, it is necessary to develop tools to rapidly screen the impact of NMs on model organisms, given that the number of NMs on the market will be increasing. In this context High Throughput Screening approaches represent relevant tools for the investigation of NM-mediated toxicity. The objective of this work was to study the effects of copper oxide nanoparticles (CuONPs) in the marine bivalve Mytilus edulis, using a transcriptomic approach. Mussels were exposed in vivo to CuONPs (10 μg·L^-1CuO NPs) for 24 h and analysis of mRNA expression levels of genes implicated in immune response, antioxidant activities, cell metabolism, cell transport and cytoskeleton was investigated by qPCR on hemocytes and gills. Results showed common effects of CuONPs and its ionic counterpart. However, greater effects of CuONPs on GST, SOD, MT, Actin, ATP synthase gene expressions were observed compared to ionic form indicating that toxicity of CuONPs is not solely due to the release of Cu²⁺. Even though M. edulis genome is not fully characterized, this study provides additional knowledge on the signaling pathways implicated in CuONP-mediated toxicity and demonstrates the reliability of using a qPCR approach to go further in the cellular aspects implicated in response to NPs in marine bivalves.

Signaling pathways involved in metal-based nanomaterial toxicity towards aquatic organisms

Environmental risk assessment of engineered nanomaterials (ENMs) is an emergent field since nanotechnology industry is rapidly growing due to the interesting physicochemical properties of nanomaterials. Metal-based nanomaterials are among the most rapidly commercialized materials and their toxicity towards aquatic animals has been investigated at different levels of the biological organization. The objective of this synthesis review is to give an overview of the signaling molecules that have a key role in metal-based NM mediated cytotoxicity in both marine and freshwater organisms. Since toxicity of metal-based NMs could be (partly) due to metal dissolution, this review only highlights studies that showed a specific nano-effect. From this bibliographic study, three mechanisms (detoxification, immunomodulation and genotoxicity) have been selected as they represent the major cell defense mechanisms and the most studied ones following ENM exposure. This better understanding of NM-mediated cytotoxicity may provide a sound basis for designing environmentally safer nanomaterials.

Variations in gene expression levels in four European zebra mussel, Dreissena polymorpha, populations in relation to metal bioaccumulation: A field study

The present study was performed to validate the suitability of using gene expression in zebra mussels, Dreissena polymorpha, for biomonitoring of freshwater environment. Mussels were collected in four French rivers (Meuse, Moselle, Oise and Vilaine) in spring and autumn. Relative gene expression of 9 candidate genes involved in cellular metabolic activities (Cytochrome-c-oxidase - cox, and ATP synthase - atp), detoxification process (Metallothionein - mt and Glutathion-S-Transferase - gst), oxidative stress (Catalase - cat, Superoxyde Dismutase - sod and Glutathion peroxidase - gpx) and digestive functions (Amylase - amy and Cellulase - ghf) were measured in digestive gland. Metal bioaccumulation in tissues and morphometric parameters were also analyzed to interpret molecular responses. All our results are consistent with different physiological reactions to environmental condition between zebra mussel populations. In spring, the levels of mt, sod, gpx, cat, atp, amy and ghf relative expression were significantly higher in mussels with the lowest metal bioaccumulation (the Meuse) compared to at least one of the other sites. In autumn, this higher expression levels in Meuse River were still observed for gpx, cat, atp and amy. This study has also pointed out different sources of variability in gene expression (individual size, season, trophic resources and origin of mussels) which are inevitable in natural fluctuant environment. This underlines the importance to take them into account in field study to propose a correct interpretation of biomarker responses.

Ecological relevance of biomarkers in monitoring studies of macro-invertebrates and fish in Mediterranean rivers

Mediterranean rivers are probably one of the most singular and endangered ecosystems worldwide due to the presence of many endemic species and a long history of anthropogenic impacts. Besides a conservation value per se, biodiversity is related to the services that ecosystems provide to society and the ability of these to cope with stressors, including climate change. Using macro-invertebrates and fish as sentinel organisms, this overview presents a synthesis of the state of the art in the application of biomarkers (stress and enzymatic responses, endocrine disruptors, trophic tracers, energy and bile metabolites, genotoxic indicators, histopathological and behavioural alterations, and genetic and cutting edge omic markers) to determine the causes and effects of anthropogenic stressors on the biodiversity of European Mediterranean rivers. We also discuss how a careful selection of sentinel species according to their ecological traits and the food-web structure of Mediterranean rivers could increase the ecological relevance of biomarker responses. Further, we provide suggestions to better harmonise ecological realism with experimental design in biomarker studies, including statistical analyses, which may also deliver a more comprehensible message to managers and policy makers. By keeping on the safe side the health status of populations of multiple-species in a community, we advocate to increase the resilience of fluvial ecosystems to face present and forecasted stressors. In conclusion, this review provides evidence that multi-biomarker approaches detect early signs of impairment in populations, and supports their incorporation in the standardised procedures of the Water Frame Work Directive to better appraise the status of European water bodies.

Impacts of BDE209 addition on Pb uptake, subcellular partitioning and gene toxicity in earthworm (Eisenia fetida)

Lead (Pb) and decabromodiphenyl ether (BDE209) are the mainly co-existed contaminants at e-waste recycling sites. The potential toxicity of Pb (250 μg g(-1)) to earthworm Eisenia fetida in the presence of BDE209 (1, 10 and 100 μg g(-1)) was determined during 14-d incubation period. Compared to Pb treatment alone, the co-exposure with 1 μg g(-1) BDE209 barely affected Pb uptake, subcellular partitioning and gene expression; however, histopathological changes in earthworms' body wall (epidermal, circular and longitudinal muscles) demonstrated that 10 and 100 μg g(-1) BDE209 additions enhanced Pb uptake and altered its subcellular partitioning, indicating that Pb redistributed from fractions E (cell debris) and D (metal-rich granules) to fraction C (cytosols); Additionally, BDE209 supply significantly inhibited (p<0.05) the induction of SOD (superoxide dismutase) and CAT (catalase) gene expressions (maximum down-regulation 59% for SOD gene at Pb+100 μg g(-1) BDE209 and 89% for CAT gene at Pb+10 μg g(-1) BDE209), while facilitated (p<0.05) Hsp90 (heat shock protein 90) gene expression with maximum induction rate of 120% after exposure to Pb+10 μg g(-1) BDE209. These findings illustrate the importance of considering environmental BDE209 co-exposure when assessing Pb bioaccumulation and toxicity in multi-contaminated soil ecosystems.

Transcriptional response of stress-regulated genes to industrial effluent exposure in the cockle Cerastoderma glaucum

This study assessed the responses of molecular biomarkers and heavy metal levels in Cerastoderma glaucum exposed for 1 week to two industrial effluents (1%) discharged into the Tunisian coastal area, F1 and F2, produced by different units of production of a phosphate treatment plant. A significant uptake of metals (Cd, Cu, Zn, and Ni) was observed in exposed cockles compared to controls, with an uptake higher for F1 than for F2. A decrease in LT50 (stress on stress test) was also observed after an exposure to the effluent F1. Treatments resulted in different patterns of messenger RNA (mRNA) expression of the different genes tested in this report. Gene transcription monitoring performed on seven genes potentially involved in the tolerance to metal exposure showed that for both exposures, mechanisms are rapidly and synchronically settled down to prevent damage to cellular components, by (1) handling and exporting out metal ions through the up-regulation of ATP-binding cassette xenobiotic transporter (ABCB1) and metallothionein (MT), (2) increasing the mRNA expression of antioxidant enzymes (catalase (CAT), superoxide dismutases, CuZnSOD and MnSOD), (3) protecting and/or repairing proteins through the expression of heat shock protein 70 (HSP70) mRNAs, and (4) increasing ATP production (through the up-regulation of cytochrome c oxidase 1 (CO1)) to provide energy for cells to tolerate stress exposure. The tools developed may be useful both for future control strategies and for the use of the cockle C. glaucum as a sentinel species.

Transcriptional response of stress-regulated genes to cadmium exposure in the cockle Cerastoderma glaucum from the gulf of Gabès area (Tunisia)

This study investigates cadmium effects on key messenger RNA (mRNA) expression (MT, MnSOD, CuZnSOD, CAT, ABCB1, HSP70, and CO1) by qPCR in the cockle Cerastoderma glaucum after chronic exposure to two high but environmentally relevant concentrations of CdCl2 (50 μg/L and 5 mg/L) for 12 h to 18 days. Cd accumulation measured in cockles' tissues is significantly higher in both treatment conditions compared to controls and in a dose-dependent manner. Stress on stress tests performed at different times of the experiment clearly demonstrated that exposure to both concentrations of Cd significantly affects cockle survival time in air. Important changes in gene transcription were also highlighted. In particular, MT, HSP70, CAT, and CuZnSOD seem to be relevant biomarkers of Cd exposure because (1) their mRNA levels increase upon exposure and (2) they are highly correlated to Cd accumulation in tissues. Results may be useful for control strategies and for the use of cockles as sentinel organisms.

qRT-PCR evaluation of the transcriptional response of zebra mussel to heavy metals

Background

The transcriptional response of adult zebra mussels (Dreissena polymorpha) to heavy metals (mercury, copper, and cadmium) was analyzed by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) to study the coordinated regulation of different metal-, oxidative stress- and xenobiotic defence-related genes in gills and digestive gland. Regulatory network analyses allowed the comparison of this response between different species and taxa.

Results

Chemometric analyses allowed identifying the effects of these metals clearly separating control and treated samples of both tissues. Interactions between the different genes, either in the same or between both tissues, were analysed to identify correlations and to propose stress-related genes’ regulatory networks. These networks were finally compared with existing data from human, mouse, zebrafish, Drosophila and the roundworm to evaluate their mechanistically-known response to metals (and to stressors in general) with the correlations observed in the still poorly-known, invasive zebra mussel.

Conclusions

Our analyses found a general conservation of regulation genes and of their interactions among the different considered species, and may serve as a guide to extrapolate regulatory data from model species to lesser-known environmentally (or medically) relevant species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1567-4) contains supplementary material, which is available to authorized users.

Genotoxicity and activation of cellular defenses in transplanted zebra mussels Dreissena polymorpha along the Seine river

The aim of the present study was to confirm the relevance of studying DNA adduct formation in a field study. In that context, freshwater mussels Dreissena polymorpha, collected in a reference station, were transplanted in different sites with a pollution gradient. After one and two months, mussels were collected and DNA adduct formation was analyzed using the (32)P post labelling technique on both gills and digestive glands. In addition, the expression of genes involved in the detoxification system (catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), HSP70, aryl hydrocarbon receptor (AHR), P glycoprotein (PgP), metallothionein (MT)) was assessed by RT-PCR. DNA adducts were observed at amount comparable to data from literature. Increase of DNA adducts after two months of transplantation could be correlated with strong modulation of gene expression implicated in detoxification processes. Indeed, PgP and HSP70 gene expressions were similarly induced in gills and digestive glands while SOD and CAT expressions were down regulated in both tissues. AHR, GST and MT genes were differently regulated depending upon the tissue studied and the level of contamination in the different sites. We demonstrated that mussels transplanted in the different stations with pollution gradient were able to biotransform PAHs, assessed by DNA adduct formation and the high decrease of detoxification genes. Specific DNA adducts pattern obtained after one and two month mussel transplantations demonstrated the relevance of DNA adduct as biomarker of environmental pollution.

Transcriptional and biochemical effects of cadmium and manganese on the defense system of Octopus vulgaris paralarvae

Due to anthropogenic activities the relative concentrations of cadmium and manganese have increased in the marine environment. Cephalopods are able to accumulate such metals and, as inhabitant of coastal waters, Octopus vulgaris is continuously exposed to anthropogenic activities. Since no study is available on the effects of heavy metals at molecular level in developing octopuses, herein we exposed 1-day-old paralarvae for 24 h to 10, 100, and 1000 μg/L of CdCl2 or MnCl2. Cd exerted a concentration-dependent inhibition of survival and a reduction in growth rate was shown while Mn exposure did not affect the survival rate even at the highest concentrations. Gene expression profiles of hsp70, sod, cat, and gst genes were analyzed by quantitative real-time PCR and defined patterns of transcription were observed. Moreover posttranscriptional analyses were also performed suggesting the impairment of metabolic functions, under strong oxidative conditions (as occurred in paralarvae exposed to Cd) or the complete detoxification events (as occurred in paralarvae exposed to Mn).

Does zebra mussel (Dreissena polymorpha) represent the freshwater counterpart of Mytilus in ecotoxicological studies? A critical review

One of the fundamentals in the ecotoxicological studies is the need of data comparison, which can be easily reached with the help of a standardized biological model. In this context, any biological model has been still proposed for the biomonitoring and risk evaluation of freshwaters until now. The aim of this review is to illustrate the ecotoxicological studies carried out with the zebra mussel Dreissena polymorpha in order to suggest this bivalve species as possible reference organism for inland waters. In detail,we showed its application in biomonitoring, as well as for the evaluation of adverse effects induced by several pollutants, using both in vitro and in vivo experiments. We discussed the advantages by the use of D. polymorpha for ecotoxicological studies, but also the possible limitations due to its invasive nature.

Sublethal Cd-induced cellular damage and metabolic changes in the freshwater crab Sinopotamon henanense

To explore whether sublethal cadmium (Cd) exposure causes branchial cellular damages and affects the metabolic activity in brachyuran crustaceans, the freshwater crab Sinopotamon henanense was exposed to 0.71, 1.43, and 2.86 mg/L Cd(2+) for 3 weeks. Gill morphology, metabolic activity (activities of isocitrate dehydrogenase (IDH), cytochrome c oxidase (CCO) and lactate dehydrogenase (LDH), mRNA expression of CCO active subunit 1 (cco-1) and ldh, as well as ATP levels) in crab muscle were investigated. The results showed that sublethal Cd exposure caused profound morphological damages in the gills. The branchial epithelial cells were disorganized and vacuolized. Ultrastructurally, a decrease in number of apical microvilli, vacuolized mitochondria, and condensed chromatin were observed in gill epithelial cells. Correspondingly, the Cd exposure also induced downregulations of cco-1 and ldh mRNA expression and reduced activities of IDH, CCO, and LDH, in accordance with the lower ATP level in crab muscle. These results led to the conclusion that gill damage caused by sublethal Cd exposure could lead to an impairment of oxygen uptake of S. henanense, and the inhibition of metabolic activity decreases the oxygen demand of the crab and assists them to survive under the condition of lower oxygen availability. These effects add to our understanding on toxic effects of Cd and survival management of S. henanense subchronically exposed to sublethal Cd.

Biochemical biomarker responses of green-lipped mussel, Perna canaliculus, to acute and subchronic waterborne cadmium toxicity

The biochemical responses of the green-lipped mussel, Perna canaliculus, to waterborne cadmium (Cd) were investigated in order to delineate toxic mechanisms, and the impacts of exposure dose and duration, of this important toxicant in a potential sentinel species. Mussels were exposed for either 96 h (acute: 0, 2000, 4000 μgL(-1) Cd) or for 28 d (subchronic: 0, 200, 2000 μgL(-1) Cd), and the digestive gland, gill and haemolymph were examined for impacts. Biochemical responses measured included those associated with metal detoxification (metallothionein-like protein; MTLP), oxidative stress (catalase, lipid peroxidation), cellular homeostasis (alkaline phosphatase, Na(+), K(+)-ATPase; NKA), and energy utilisation (glycogen, haemolymph protein). Following acute exposure, digestive gland glycogen and gill NKA activity were significantly altered by Cd exposure relative to levels in mussels exposed to Cd-free seawater. Subchronic Cd exposure resulted in a significant increase in MTLP levels in both the gill and the digestive gland. This increase was correlated strongly with the levels of Cd accumulation measured in these tissues (R=0.957 for gill, 0.964 for digestive gland). Catalase activity followed a similar pattern, although the correlation with tissue Cd accumulation was not as strong (R=0.907 for gill, 0.708 for digestive gland) as that for MTLP. Lipid peroxidation increased in the digestive gland at Days 7 and 14 at both subchronic Cd levels tested, but this effect had largely dissipated by Days 21 and 28 (with the exception of the 2,000 μgL(-1) group at Day 28). Alkaline phosphatase activity decreased significantly with Cd exposure in both tissues. This effect was observed at both tested concentrations in the gill, but only at the highest concentration for digestive gland. A decrease in digestive gland glycogen levels was observed in Cd-exposed mussels (Days 14 and 21 at 2,000 μgL(-1)), while haemolymph protein levels increased as a result of subchronic Cd exposure. These findings indicated that biochemical responses in Cd-exposed mussels were tissue-specific, dose- and time-dependent, with duration of exposure being the predominant effect. This study shows that biochemical changes in Cd-exposed green-lipped mussels can be linked to tissue metal accumulation and are consistent with previously reported physiological effects. It also suggests that green-lipped mussels are amenable to a multiple biomarker approach and may be of use as a bioindicator species for monitoring coastal metal pollution.

Genetic and phenoptypic differentiation of zebra mussel populations colonizing Spanish river basins

Zebra mussel populations in Ebro and Mijares Rivers (northern Spain) were analyzed to study the mechanisms by which this aquatic species deals with pollution. Variability analyses of mitochondrial cytochrome oxidase I gene and of one nuclear microsatellite were performed for ten populations from the Ebro River and one from the Mijares River. Comparison of these results with those from five additional European populations indicated that the Spanish populations constitute a homogeneous gene pool. Transcriptome analyses of gill samples from a subset of the Spanish populations showed changes on expression levels that correlated with variations in general fitness and loads of heavy metals. The less polluted upstream Ebro populations showed overexpression of mitochondrial and cell proliferation-related genes compared to the more polluted, downstream Ebro populations. Our data indicate that heavy metals were the main factors explaining these transcriptomic patterns, and that zebra mussel is resilient to pollutants (like mercury and organochlorine compounds) proved to be extremely toxic to vertebrates. We propose that zebra mussel populations sharing a common gene pool may acclimate to different levels and forms of pollution through modulations in their transcriptomic profile, although direct selection on genes showing differential expression patterns cannot be ruled out.

Transcriptomic seasonal variations in a natural population of zebra mussel (Dreissena polymorpha)

The zebra mussel Dreissena polymorpha is a Caspian Sea bivalve that colonized freshwater bodies worldwide during the XX century. To analyze the impact of seasonal and environmental variations on the physiology and metabolism of this invasive species, we developed a custom microarray using 4057 publicly available DNA sequences from Dreissena and other related genera. Transcriptome profiles were analyzed using half-body samples from a relatively clean site (Riba-Roja, low Ebro River, N.E. Spain), at three different stages of the annual cycle: Pre-spawning (February), spawning (June), and gonad resorption (September). Transcripts from a total of 745 unique sequences showed significant changes among these three groups of samples. Functional characterization of these transcripts based on their closest known homologues showed that genes involved in stress defense (oxidative and infection) were overrepresented in September, whereas genes related to reproductive functions were overrepresented in the spawning and pre-spawning periods. This transcriptomic information can help to identify developmental stages at which the organism is more vulnerable for future control strategies. These data will also contribute to the implementation of gene expression-based assays for pollution monitoring in water bodies harboring stable zebra mussel populations.

Cadmium-induced apoptosis in primary rat cerebral cortical neurons culture is mediated by a calcium signaling pathway

Cadmium (Cd) is an extremely toxic metal, capable of severely damaging several organs, including the brain. Studies have shown that Cd disrupts intracellular free calcium ([Ca²⁺]_i) homeostasis, leading to apoptosis in a variety of cells including primary murine neurons. Calcium is a ubiquitous intracellular ion which acts as a signaling mediator in numerous cellular processes including cell proliferation, differentiation, and survival/death. However, little is known about the role of calcium signaling in Cd-induced apoptosis in neuronal cells. Thus we investigated the role of calcium signaling in Cd-induced apoptosis in primary rat cerebral cortical neurons. Consistent with known toxic properties of Cd, exposure of cerebral cortical neurons to Cd caused morphological changes indicative of apoptosis and cell death. It also induced elevation of [Ca²⁺]_i and inhibition of Na⁺/K⁺-ATPase and Ca²⁺/Mg²⁺-ATPase activities. This Cd-induced elevation of [Ca²⁺]_i was suppressed by an IP₃R inhibitor, 2-APB, suggesting that ER-regulated Ca²⁺ is involved. In addition, we observed elevation of reactive oxygen species (ROS) levels, dysfunction of cytochrome oxidase subunits (COX-I/II/III), depletion of mitochondrial membrane potential (ΔΨm), and cleavage of caspase-9, caspase-3 and poly (ADP-ribose) polymerase (PARP) during Cd exposure. Z-VAD-fmk, a pan caspase inhibitor, partially prevented Cd-induced apoptosis and cell death. Interestingly, apoptosis, cell death and these cellular events induced by Cd were blocked by BAPTA-AM, a specific intracellular Ca²⁺ chelator. Furthermore, western blot analysis revealed an up-regulated expression of Bcl-2 and down-regulated expression of Bax. However, these were not blocked by BAPTA-AM. Thus Cd toxicity is in part due to its disruption of intracellular Ca²⁺ homeostasis, by compromising ATPases activities and ER-regulated Ca²⁺, and this elevation in Ca²⁺ triggers the activation of the Ca²⁺-mitochondria apoptotic signaling pathway. This study clarifies the signaling events underlying Cd neurotoxicity, and suggests that regulation of Cd-disrupted [Ca²⁺]_i homeostasis may be a new strategy for prevention of Cd-induced neurodegenerative diseases.

Oxygen consumption and metabolic responses of freshwater crab Sinopotamon henanense to acute and sub-chronic cadmium exposure

To explore the respiratory and metabolic responses of the freshwater crab (Sinopotamon henanense) to Cd exposure, crabs were acutely exposed to 7.14, 14.28, 28.55 mg/L Cd for 96 h and subchronically exposed to 0.71, 1.43, 2.86 mg/L for three weeks. The oxygen consumption, concentrations of oxyhemocyanin, hemolymph protein, the activities of respiratory enzymes, i.e. lactate dehydrogenase (LDH), NAD-isocitrate dehydrogenase (IDH), cytochrome c oxidase (CCO), as well as cco-1(CCO active subunit 1) and ldh mRNA expression level and adenosine triphosphate (ATP) content in crab heart were assessed. Oxygen consumption, concentration of oxyhemocyanin and oxyhemocyanin/blood protein proportion were increased during acute exposure and decreased during sub-chronic exposure. Both exposure schemes induced downregulation of cco-1 gene expression and lowered CCO activity. For acute exposure, tissue ATP level was increased, in association with increased IDH activity and decreased LDH activity, whereas subchronic exposure caused decreased IDH activity accompanied with increased ldh gene expression and LDH activity, resulting in lowered ATP level. By coupling gene expression to biochemical and physiological endpoints, this work provides new insights into the mechanisms involved in metal stress and the differential respiratory and metabolic responses of S. henanense to acute and subchronic Cd exposure.

Sublethal effects of silver nanoparticles and dissolved silver in freshwater mussels

The increasing application of silver nanoparticles (nAg) in various consumer products has raised concerns regarding toxicological impacts in the environment. It is unclear at present whether the toxicity of nAg is mainly the result of the release of ionic Ag(+) in mussels. The freshwater mussel Elliptio complanata was exposed to increasing concentrations of 20-nm nAg, 80-nm nAg, and dissolved Ag(+) for 48 h at 15°C. The following biomarkers were used to determine the mode of action of nAg-induced adverse effects: metallothioneins (MT) (ionic Ag(+) release), lipid peroxidation (LPO) (ionic Ag(+) and nanosurface interactions), heat-shock proteins (HSP) (size-related effects), protein-ubiquitin levels (size-related effects), and DNA strand breaks (ionic Ag(+) and size effects). Results revealed that the response pattern of 80 nm nAg was more closely related to ionic Ag(+) than 20 nm nAg, suggesting a more important release of dissolved Ag from 80 nm nAg. Data showed that all forms of Ag were able to increase the levels of MT and LPO, which suggests the presence of ionic Ag(+) leads to oxidative stress. However, nanoparticles were also able to induce changes in protein-ubiquitin and to a lesser extent actinomyosin-ATPase, MT, and DNA strand breaks in the digestive gland in a manner different from Ag(+), which permitted discrimination of the forms of Ag. Moreover, LPO was closely associated with DNA strand breaks in the digestive gland and was not entirely explained by induction of MT, suggesting another type of toxic interaction. It was concluded that the presence of nAg not only increases the toxic loadings of released Ag ions but also generates other and perhaps cumulative effects of nanoparticle-induced toxicity related to size and surface properties.

Abcb and Abcc transporter homologs are expressed and active in larvae and adults of zebra mussel and induced by chemical stress

Multixenobiotic resistance (MXR) of aquatic invertebrates has so far been associated with cellular efflux activity mediated by P-glycoprotein (ABCB1) and MRP (multidrug resistance protein; ABCC) type ABC (ATP binding cassette) transporters. Expression and activity of an abcb1/Abcb1 homolog has been shown in eggs and larvae of the zebra mussel Dreissena polymorpha. Here we report identification of a partial cDNA sequence of an abcc/Abcc homolog from zebra mussel that is transcribed and active as a cellular efflux transporter in embryos and gill tissue of adult mussels. Transcript expression levels were comparatively low in eggs and sharply increased after fertilization, then maintaining high expression levels in 1 and 2 dpf (days post fertilization) larvae. MK571, a known inhibitor of mammalian ABCC transporters, blocks efflux of calcein-am in larvae and gill tissue as indicated by elevated calcein fluorescence; this indicates the presence of active Abcc protein in cells of the larvae and gills. Dacthal and mercury used as chemical stressors both induced expression of abcb1 and abcc mRNAs in larvae; accordingly, assays with calcein-am and ABCB1 inhibitor reversin 205 and ABCC inhibitor MK571 indicated enhanced Abcb1 and Abcc efflux activities. Responses to chemicals were different in gills, where abcb1 transcript abundances were enhanced in dacthal and mercury treatments, whereas abcc mRNA was only increased with mercury. Abcb1 and Abcc activities did not in all cases show increases that were according to respective mRNA levels; thus, Abcc activity was significantly higher with dacthal, whereas Abcb1 activity was unchanged with mercury. Our data indicate that abcb1/Abcb1 and abcc/Abcc transporters are expressed and active in larvae and adult stages of zebra mussel. Expression of both genes is induced as cellular stress response, but regulation appears to differ in larvae and tissue of adult stages.

The involvement of metallothionein in the development of aquatic invertebrate

The many documents on metallothioneins (MTs) in aquatic organisms focus especially on their use as biomarkers in environmental monitoring programs, but there are a few papers that summarize the physiological role of MTs in aquatic organisms especially in their development. The multifaceted role of MTs include involvement in homeostasis, protection against heavy metals and oxidant damage, metabolic regulation, sequestration and/or redox control. MTs could be induced by heavy metals which are able to hinder gametogenesis, suppress embryogenesis, and hamper development. Here we pay more attention on the non-essential metal cadmium, which is the most studied heavy metal regarding MTs, and its effects on the development of aquatic invertebrates. In this paper, we have collected published information on MTs in aquatic organisms - mollusks, crustaceans, etc., and summarize its functions in aquatic invertebrates, especially those related to their development.