Proteomic profiling of cytosolic glutathione transferases from three bivalve species: Corbicula fluminea, Mytilus galloprovincialis and Anodonta cygnea

microRNA-mRNA Analysis Reveals Tissue-Specific Regulation of microRNA in Mangrove Clam (Geloina erosa)

Geloina erosa is an important benthic animal in the mangrove, serving as an indicator organism for coastal environmental pollution. This study aimed to investigate the tissue-specific expression of miRNAs and their regulatory roles in predicted targets in G. erosa. Through miRNA sequencing and co-expression network analysis, we extensively studied the miRNA expression in three tissues: gills, hepatopancreas, and muscle. The results revealed a total of 1412 miRNAs, comprising 1047 known miRNAs, and 365 newly predicted miRNAs. These miRNAs exhibited distinct tissue-specific expression patterns. In the miRNA target gene prediction, a total of 7404 potential predicted targets were identified, representing approximately 33% of all unique transcripts associated with miRNAs. Further co-expression network analysis revealed nine modules, each showing a positive correlation with specific tissues (gills, hepatopancreas, or muscle). The blue module showed a significant correlation with gills (r = 0.83, p-value = 0.006), the black module was significantly related to the hepatopancreas (r = 0.78, p-value = 0.01), and the purple module was significantly correlated with muscle (r = 0.83, p-value = 0.006). Within these modules, related miRNAs tended to cluster together, while their correlations with other modules were relatively weak. Functional enrichment analysis was performed on miRNAs and their predicted targets in each tissue. In the gills, miRNAs primarily regulate immune-related genes, substance transport, and cytoskeletal organization. In the hepatopancreas, miRNAs suppressed genes involved in shell formation and played a role in cellular motor activity and metabolism. In muscle, miRNAs participate in metabolism and photoreceptive processes, as well as immune regulation. In summary, this study provides valuable insights into the tissue-specific regulation of miRNAs in G. erosa, highlighting their potential roles in immune response, metabolism, and environmental adaptation. These findings offer important clues for understanding the molecular mechanisms and biological processes in G. erosa, laying the foundation for further validation and elucidation of these regulatory relationships.

Combined effect of microplastic, salinomycin and heating on Unio tumidus

Microplastic (MP) and heating (T) suspected to modulate biological effects of aquatic contaminants. Salinomycin (Sal) is veterinary antibiotic and anticancer agent. The goal of this study was to examine the multistress effect of MP, Sal and T on the bioindicator bivalve mollusc. The Unio tumidus were treated with MP (1 mg L^-1), Sal (0.6 µg L^-1), their combination under 18° C (Mix) and 25° C (MixT) for 14 days. The digestive glands were analyzed. MP and Sal did not cause changes of Mn- and Cu,Zn-SOD, lipid peroxidation and Cyp-450-depended EROD levels, whereas catalase, GST and protein carbonyls (Sal-group) increased compared to control. In the Mix-group, enzymes, particularly EROD and GST (by 34% and 115% respectively) were up-regulated. However, in the MixT-group, they were corresponding to control or lesser (EROD, catalase). Our findings emphasize the need to take into account multistress interactions in the MP environmental risk assessment.

Biochemical characterization and peptide mass fingerprinting of two glutathione transferases from Biomphalaria alexandrina snails (Gastropoda: Planorbidae)

Background

The freshwater snails Biomphalaria alexandrina (Gastropoda: Planorbidae) has public health importance of being an intermediate host of Schistosoma mansoni, the parasite species that causes intestinal schistosomiasis in humans. Glutathione transferases (GSTs) play an important role in detoxification of a broad range of compounds including secondary metabolites and exogenous compounds. Studying GSTs in snails may clarify their role in detoxification of molluscicides.

Results

Two glutathione transferases (BaGST2 and BaGST3) were purified and characterized from B. alexandrina snails. BaGST2 and BaGST3 were electrophoretically homogeneous preparations with subunit molecular weight of 23.6 kDa and molecular weight of 45 kDa. Isoelectric focusing of BaGST2 revealed the presence of two components at pI 4.47 and 4.67, while BaGST3 showed one band at pI 4.17. The specific activity of BaGST2 and BaGST3 toward 1-chloro-2,4-dinitrobenzene (CDNB) was 19.0 and 45.2 μmol/min/mg protein following 146- and 346-fold purification, respectively. The catalytic pH optima, km values, and the activation energies for BaGST2 and BaGST3 were determined. BaGST2 and BaGST3 were significantly inhibited by hematin and Cibacron Blue and to a less extent by bromosulfophthalein, S-butyl-GSH, S-hexyl-GSH, and S-P-bromobenzyl-GSH. BaGST2 and BaGST3 showed high activity against ethacrynic acid as substrate, and they also exhibited peroxidase activity on cumene hydroperoxide. The two enzymes showed identical patterns of lysine-C digestion after high-performance liquid chromatography. The amino acid sequences of three peptide fragments and peptide mass fingerprinting of fourteen peptides were used to predict the primary structure of BaGST2. A polypeptide of 206 amino acids (with 7 gaps, 3 of which could not identified) was predicted for BaGST2. The theoretical subunit molecular weight of BaGST2 is 22.6 kDa, with pI of 8.58. BaGST2 has 65% sequence identity and 78% positive with Biomphalaria glabrata GST7. The overall structure of BaGST2 at the N-terminal domain is identical to the canonical GST N-terminal domain, having the typical thioredoxin-like fold with a βαβ-α-ββα motif, whereas the C-terminal domain is made from 6 α-helices. A conservative GST-N-domain includes glutathione binding sites Y11, L17, Q53, M54, Q65, and S66, while a variable GST-C domain contains electrophilic substrate binding site H99, R102, A103, F106, K107, L161, and Y167. Phylogenetic tree showed that BaGST2 was clustered in the sigma group with GSTs sigma class from invertebrates and vertebrates.

Conclusions

We have purified and characterized two GSTs from B. alexandrina snails. Our study broadens the biochemical information on freshwater snail GSTs by demonstrating the role of BaGSTs in defense mechanisms against structurally different electrophilic compounds. BaGST2 and BaGST3 have Se-independent peroxidase activity, which indicates their role in cellular antioxidant defense by reducing organic hydroperoxides in B. alexandrina. A polypeptide chain of 206 amino acids was predicted. The primary structure of BaGST2 showed 65% sequence identity with Biomphalaria glabrata GST7. Sequence analysis indicates that BaGST2 is a GST-N-sigma-like with a thioredoxin-like superfamily. Phylogenetic tree confirms that BaGST2 belongs to the sigma class of GSTs superfamily.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-022-00372-x.

Identification and characterization of the novel genes encoding glutathione S-transferases in Mytilus galloprovincialis

The superfamily of glutathione S-transferases (GST) plays an essential role in the xenobiotic metabolism, binding compounds to the glutathione, and is like a cell protector during the influence of various negative external factors. Nevertheless, there are very few works devoted to the investigation of these genes in marine invertebrates. Up to this time, only three classes of cytosolic GSTs for one of the leading commercial molluscs Mytilus galloprovincialis were described. We sequenced the whole transcriptome from the gill tissues and, using bioinformatic analysis, detected ten classes of glutathione S-transferases, which are expressed in the mussel M. galloprovincialis. For the first time, two subfamilies were described: mitochondrial GST (kappa class) and microsomal (MAPEG), as well as five classes of the family of cytosolic GSTs (mu, omega, rho, tau, theta). Omega and sigma GST classes might be rapidly regulated genes due to the lack of introns and this assumption was confirmed by the investigation of short-term hypoxia on M. galloprovincialis. Seven new classes of GST revealed a greater gene variety of this detoxifying enzyme in mussels than expected. The obtained nucleotide sequences are necessary for future investigations of GSTs expression in response to various external factors (pollution, oxygen starvation, infection, etc.).

Review on Cyanobacterial Studies in Portugal: Current Impacts and Research Needs

Cyanobacteria have long been associated with harmful effects on humans, animals and aquatic biota. Cyanotoxins are their most toxic metabolite. This review summarizes the current research, impacts and future needs in cyanobacterial studies undertaken in Portugal, the southernmost country of Europe, and with a recent multiplication of cyanotoxicity due to climate change events. Microcystins are still the most prevalent, studied and the only regulated cyanotoxins in Portuguese freshwater systems much like most European countries. With the development of some tools, particularly in molecular studies, the recent discovery of cylindrospermopsins, anatoxins and saxitoxins, both genes and toxins, in North and Center ecosystems of our country highlight current impacts that overall communities are facing with increased risks of exposure and uptake to cyanotoxins. Research needs encompass the expansion of studies at all aspects due to the uprising of these cyanotoxins and reinforces the urgent need of increasing the frequency of surveillance to achieve tangible effects of cyanotoxins in Portugal to ultimately implement regulations on cylindrospermopsins, anatoxins and saxitoxins worldwide.

Differences in proteomic profile between two haemocyte types, granulocytes and hyalinocytes, of the flat oyster Ostrea edulis

Haemocytes play a dominant role in shellfish immunity, being considered the main defence effector cells in molluscs. These cells are known to be responsible for many functions, including chemotaxis, cellular recognition, attachment, aggregation, shell repair and nutrient transport and digestion. There are two basic cell types of bivalve haemocytes morphologically distinguishable, hyalinocytes and granulocytes; however, functional differences and specific abilities are poorly understood: granulocytes are believed to be more efficient in killing microorganisms, while hyalinocytes are thought to be more specialised in clotting and wound healing. A proteomic approach was implemented to find qualitative differences in the protein profile between granulocytes and hyalinocytes of the European flat oyster, Ostrea edulis, as a way to evaluate functional differences. Oyster haemolymph cells were differentially separated by Percoll® density gradient centrifugation. Granulocyte and hyalinocyte proteins were separated by 2D-PAGE and their protein profiles were analysed and compared with PD Quest software; the protein spots exclusive for each haemocyte type were excised from gels and analysed by MALDI-TOF/TOF with a combination of mass spectrometry (MS) and MS/MS for sequencing and protein identification. A total of 34 proteins were identified, 20 unique to granulocytes and 14 to hyalinocytes. The results suggested differences between the haemocyte types in signal transduction, apoptosis, oxidation reduction processes, cytoskeleton, phagocytosis and pathogen recognition. These results contribute to identify differential roles of each haemocyte type and to better understand the oyster immunity mechanisms, which should help to fight oyster diseases.

Population genomic footprints of environmental pollution pressure in natural populations of the Mediterranean mussel

Bivalve molluscs of the genus Mytilus are considered a model organism in ecotoxicology and are known to be well adapted to marine ecosystems affected by multiple anthropogenic factors, including pollution. In order to assess whether pollution interferes with the reproductive success of Mytilus and affects the diversity within and between populations, we sequenced the transcriptomes of 72 individuals from 9 populations of Mytilus galloprovincialis collected along a ca. 130-km north-south transect on the Western coast of the Iberian Peninsula. We found that polluted areas are acting as a barrier to gene flow, potentially because of the detrimental effect of anthropogenic chemicals on larvae carried from more pristine environments. Furthermore, we observed an increase in genetic diversity in populations from polluted site, which could be indicative of higher mutagenicity driven by the environment. We propose that a microevolutionary perspective is essential for a full characterization of human activities on the dispersal of M. galloprovincialis and that it should be incorporated into management, and conservation plans and policies in the context of the effects of pollution on populations.

GST transcriptional changes induced by a toxic Microcystis aeruginosa strain in two bivalve species during exposure and recovery phases

Previous studies have demonstrated the modulation of glutathione transferases (GSTs) induced by microcystin (MC) alone or in combination with other cyanobacterial secondary metabolites in bivalves. However, interspecies information about which and how GST isoforms are affected by these secondary metabolites is still scarce, especially considering the dynamic process involving their uptake and elimination routes. In this context, the role of GSTs gene expression changes in response to a toxic Microcystis aeruginosa extract were examined for Mytilus galloprovincialis and Ruditapes philippinarum during exposure and recovery phases. The expression levels of sigma 1, sigma 2, pi and mu-class GST genes were analyzed in the hepatopancreas of both bivalve species during cyanobacteria extract exposure (24 h) and post-exposure (24 and 72 h). Only a significant induction of sigma 1-class GST expression was observed for R. philippinarum upon 24-hour exposure of both bivalve species to Microcystis extract. During the recovery phase, GST transcriptional changes for M. galloprovincialis were characterized by an early induction (24 h) of sigma 1 and sigma 2 transcripts. On the other hand, GST transcriptional changes for R. philippinarum during post-exposure phase were characterized by an early induction (24 h) of sigma 1 and mu transcripts and a later induction (72 h) of the four analyzed GST transcripts. Such differences reflect variable GST response mechanisms to cope with MC-producing cyanobacterial blooms exposure between these two bivalve species, revealing a higher sensitivity of R. philippinarum to Microcystis-induced stress than M. galloprovincialis. The results also suggest a much higher level of activity of the GST detoxification system during the recovery phase compared to the period of the stress exposure for both bivalve species.

Proteomic profile of Ostrea edulis haemolymph in response to bonamiosis and identification of candidate proteins as resistance markers

European flat oyster Ostrea edulis populations have suffered extensive mortalities caused by bonamiosis. The protozoan parasite Bonamia ostreae is largely responsible for this disease in Europe, while its congener B. exitiosa has been detected more recently in various European countries. Both of these intracellular parasites are able to survive and proliferate within haemocytes, the main cellular effectors of the immune system in molluscs. Two-dimensional electrophoresis was used to compare the haemolymph protein profile between Bonamia spp.-infected and non-infected oysters within 3 different stocks, a Galician stock of oysters selected for resistance against bonamiosis, a non-selected Galician stock and a selected Irish stock. Thirty-four proteins with a presumably relevant role in the oyster-Bonamia spp. interaction were identified; they were involved in major metabolic pathways, such as energy production, respiratory chain, oxidative stress, signal transduction, transcription, translation, protein degradation and cell defence. Furthermore, the haemolymph proteomic profiles of the non-infected oysters of the 2 Galician stocks were compared. As a result, 7 proteins representative of the non-infected Galician oysters selected for resistance against bonamiosis were identified; these 7 proteins could be considered as candidate markers of resistance to bonamiosis, which should be further assessed.

Modulation of hepatic glutathione transferases isoenzymes in three bivalve species exposed to purified microcystin-LR and Microcystis extracts

This study compares the role of hepatic cytosolic glutathione transferases (cGST) isoforms of three different bivalve species to a Microcystis aeruginosa extract and purified MC-LR exposure (both at 150 μg MC-LR L^-1) for 24 h. Characterization and alterations of the cytosolic GST activities in Mytilus galloprovincialis, Ruditapes philippinarum and Corbicula fluminea were measured using four class-specific substrates and changes in individual GST isoforms expression were achieved by a subsequent two-dimensional electrophoresis analysis. Evaluation of cGST activity basal levels using the four class-specific substrates denoted quantitative differences between the three bivalves. Purified MC-LR did not induce any significant response from bivalves. On the other hand, cell extracts caused significant alterations according to bivalves and substrates. Among the three bivalves, only R. philippinarum showed a significant induction of cGST activity using generic 1-chloro-2,4-dinitrobenzene (CDNB) substrate. However, no significant alterations were detected in these clams by cell extracts using the other specific substrates. In contrast, C. fluminea revealed significant induction of cGST activity when using 3,4-dichloronitrobenzene (DCNB) and ethacrynic acid (EA). In M. galloprovincialis, cell extracts promoted a significant decrease of cGST activity when using EA substrate. Altered protein expression was quantitatively detected upon exposure to cell extracts for one spot in R. philippinarum and another for C. fluminea, both upregulated (2.0 and 8.5-fold, respectively) and identified as a sigma1-class GST in the case of the first. The results showed that the three bivalves presented specific adaptive biotransformation responses to MCs and other cyanobacteria compounds supported by the modulation of distinct cGST classes.

Toxicological perturbations of zinc oxide nanoparticles in the Coelatura aegyptiaca mussel

More research is needed to understand the interactions of nanoparticles (NPs) with aquatic organisms and their mechanism of toxic action. Zinc oxide nanoparticles (ZnONPs) are the most used engineered metal oxide NPs in consumer products. The present study was designed to evaluate the cytotoxicity, genotoxicity and digestive gland (DG) as well as gill histopathology of the freshwater molluscan bivalve Coelatura aegyptiaca following exposure to ZnONPs (2, 10 and 50 mg/L) for 6 consecutive days. Exposure to ZnONPs (10 and 50 mg/L) induced a significant increase in malondialdehyde, superoxide dismutase and nitric oxide with a concomitant decrease in reduced glutathione, glutathione-S-transferase and catalase levels in the haemolymph, DG and gills of the treated mussels. Following exposure to ZnONPs (50 mg/L), the DG exhibited gradual changes in glandular activity showing hypertrophy and hyperplasia in the glandular cells and irregularity of lamellae and swelling of filaments in the gills. The present investigation revealed that oxidative stress induction, genotoxicity in the haemocytes and histological alterations in the DG and gills of C. aegyptiaca could be the main mechanisms involved in ZnONPs toxicity in aquatic organisms. Thereby, it is suggested that ZnONPs should be applied with more precautions in relevant industries, and occupational health surveillance should be necessarily considered.

Top-Down Proteomics and Farm Animal and Aquatic Sciences

Proteomics is a field of growing importance in animal and aquatic sciences. Similar to other proteomic approaches, top-down proteomics is slowly making its way within the vast array of proteomic approaches that researchers have access to. This opinion and mini-review article is dedicated to top-down proteomics and how its use can be of importance to animal and aquatic sciences. Herein, we include an overview of the principles of top-down proteomics and how it differs regarding other more commonly used proteomic methods, especially bottom-up proteomics. In addition, we provide relevant sections on how the approach was or can be used as a research tool and conclude with our opinions of future use in animal and aquatic sciences.

Shotgun proteomics to unravel marine mussel (Mytilus edulis) response to long-term exposure to low salinity and propranolol in a Baltic Sea microcosm

Pharmaceuticals, among them the β-adrenoceptor blocker propranolol, are an important group of environmental contaminants reported in European waters. Laboratory exposure to pharmaceuticals on marine species has been performed without considering the input of the ecosystem flow. To unravel the ecosystem response to long-term exposure to propranolol we have performed long-term exposure to propranolol and low salinity in microcosms. We applied shotgun proteomic analysis to gills of Mytilus edulis from those Baltic Sea microcosms and identified 2071 proteins with a proteogenomic strategy. The proteome profiling patterns from the 587 highly reproductive proteins among groups define salinity as a key factor in the mussel's response to propranolol. Exposure at low salinity drives molecular mechanisms of adaptation based on a decrease in the abundance of several cytoskeletal proteins, signalling and intracellular membrane trafficking pathway combined with a response towards the maintenance of transcription and translation. The exposure to propranolol combined with low salinity modulates the expression of structural proteins including cilia functions and decreases the expression of membrane protein transporters. This study reinforces the environment concerns of the impact of low salinity in combination with anthropogenic pollutants and anticipates critical physiological conditions for the survival of the blue mussel in the northern areas.

BIOLOGICAL SIGNIFICANCE

Applying shotgun proteomic analysis to M. edulis gills samples from a long-term microcosm exposure to propranolol and following a proteogenomic identification strategy, we have identified 2071 proteins. The proteomic analysis unrevealed which molecular mechanisms drive the adaptation to low salinity stress and how salinity modulates the effects of exposure to propranolol. These results reinforce the idea of the impact of low salinity in combination with anthropogenic pollutants and anticipate critical physiological condition.

Tissue specific responses to cadmium-based quantum dots in the marine mussel Mytilus galloprovincialis

In recent years, Cd-based quantum dots (QDs) have generated interest from the life sciences community due to their potential applications in nanomedicine, biology and electronics. However, these engineered nanomaterials can be released into the marine environment, where their environmental health hazards remain unclear. This study investigated the tissue-specific responses related to alterations in the antioxidant defense system induced by CdTe QDs, in comparison with its dissolved counterpart, using the marine mussel Mytilus galloprovincialis. Mussels were exposed to CdTe QDs and dissolved Cd for 14 days at 10 μgCd L(-1) and biomarkers of oxidative stress [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (total, Se-independent and Se-dependent GPx) and glutathione-S-transferase (GST) activities] were analyzed along with Cd accumulation in the gills and digestive gland of mussels. Results show that both Cd forms changed mussels' antioxidant responses with distinct modes of action (MoA). There were tissue- and time-dependent differences in the biochemical responses to each Cd form, wherein QDs are more pro-oxidant when compared to dissolved Cd. The gills are the main tissue affected by QDs, with effects related to the increase of SOD, GST and GPx activities, while those of dissolved Cd was associated to the increase of CAT activity, Cd accumulation and exposure time. Digestive gland is a main tissue for accumulation of both Cd forms, but changes in antioxidant enzyme activities are smaller than in gills. A multivariate analysis revealed that the antioxidant patterns are tissue dependent, indicating nano-specific effects possibly associated to oxidative stress and changes in redox homeostasis.

Expression profile of eight glutathione S-transferase genes in Crassostrea ariakensis after exposure to DSP toxins producing dinoflagellate Prorocentrum lima

In this study, changes in eight GSTs mRNA level including GST-α, GST-σ, GST-ω, GST-π, GST-μ, GST-ρ, GST-θ and microsomal GST (mGST) in the oyster Crassostrea ariakensis after exposure to Prorocentrum lima have been evaluated by quantitative real-time PCR. Additionally, the contents of five GST isoforms were detected by ELISA. After exposure to P. lima at density of 2 × 10(5) cells/L, mGST mRNA significantly increased in gill, while GST-σ was induced in digestive gland. After exposure to P. lima at density of 2 × 10(6) cells/L, GST-ω and mGST expressions increased in gill, whereas GST-α and GST-σ were induced in digestive gland. The GST content and activity in oysters exposed to P. lima also showed a different pattern when the different isoforms and organs were compared. After exposure to P. lima (2 × 10(6) cell/L), GST-π increased in gill but decreased in digestive gland. The total GST enzyme activity increased in gill, while remained unchanged in digestive gland. These various regulation of GST gene expressions indicated that the GSTs isoenzymes might play divergent physiological roles in the detoxification of DSP toxins in C. ariakensis.

Proteomic profiling of gill GSTs in Mytilus galloprovincialis from the North of Portugal and Galicia evidences variations at protein isoform level with a possible relation with water quality

Glutathione transferases (GSTs) are key for xenobiotic detoxification at the molecular level across phyla. These enzymes are therefore likely to be part of the defence mechanisms used by marine organisms, such as mussels, that thrive in highly polluted environments. Taking this hypothesis into account, we used proteomics to characterize the profile of GSTs from the gills of marine mussel Mytilus galloprovincialis in order to discriminate natural mussel populations exposed to different levels of pollution. Samples were collected between Cabo Home (Spain) and Matosinhos (Portugal) covering a north-south transect of approximately 122 Km of the Atlantic Ocean along the Western Coast of the Iberian Peninsula. GSTs from mussel gills were extracted and purified by affinity chromatography with glutathione as the binding substrate to the solid medium. We studied the abundance of GST isoforms by two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization-time of flight mass spectrometry and assessed total activity. Eleven putative individual GSTs from classes Mu, Pi and Sigma were identified by proteomics. Few variations were observed in total GST activity of post-mitochondrial samples between sampling sites, with animals from Matosinhos (polluted site) showing highest GST activity and Cabo Home (clean site) showing lowest. This contrasts with the increased number of differences in the individual GST isoforms. Each mussel population showed unique GST proteomic profiles. Based on the results we conclude that proteomics surpasses the conventional GST enzymatic activity method to discriminate natural mussel populations and has potential application in environmental monitoring. It is reasonable to suggest that the GST proteomic profiles observed may reflect differences in contamination levels.

Glutathione Transferases Responses Induced by Microcystin-LR in the Gills and Hepatopancreas of the Clam Venerupis philippinarum

A multi-method approach was employed to compare the responses of Glutatione Transferases (GSTs) in the gills and hepatopancreas of Venerupis philippinarum to microcystins (MCs) toxicity. In this way, using the cytosolic fraction, the enzymatic activity of GSTs, superoxide dismutase (SOD), serine/threonine protein phosphatases (PPP2) along with the gene expression levels of four GST isoforms (pi, mu, sigma1, sigma2) were investigated in both organs of the clams exposed for 24 h to 10, 50 and 100 μg L⁻¹ of MC-LR. Cytosolic GSTs (cGSTs) from both organs of the high dose exposed clams were purified by glutathione-agarose affinity chromatography, characterized kinetically and the changes in the expression of cGSTs of the gills identified using a proteomic approach. MC-LR caused an increase in GST enzyme activity, involved in conjugation reactions, in both gills and hepatopancreas (100 μg L⁻¹ exposure). SOD activity, an indicator of oxidative stress, showed significantly elevated levels in the hepatopancreas only (50 and 100 μg L⁻¹ exposure). No significant changes were found in PPP2 activity, the main target of MCs, for both organs. Transcription responses revealed an up-regulation of sigma2 in the hepatopancreas at the high dose, but no significant changes were detected in the gills. Kinetic analysis evidenced differences between gills of exposed and non-exposed extracts. Using proteomics, qualitative and quantitative differences were found between the basal and inducible cGSTs. Overall, results suggest a distinct role of GST system in counteracting MCs toxicity between the gills and the hepatopancreas of V. philippinarum, revealing different roles between GST isoforms within and among both organs.