Potential roles of hydroxybenzoate paralytic shellfish toxins in modulating toxin biokinetics in scallops

Paralytic shellfish toxins (PSTs) produced by some marine dinoflagellates can cause severe human intoxication via vectors like bivalves. Toxic dinoflagellate Gymnodinium catenatum produce a novel group of hydroxybenzoate PSTs named GC toxins, but their biokinetics in bivalves haven't been well examined. In this experiment, we analyzed PSTs in bay scallops Argopecten irradians exposed to G. catenatum (strain MEL11) to determine their accumulation, elimination, anatomical distribution, and biotransformation. To our surprise, up to 30% of the PSTs were accumulated in the adductor muscle of scallops at the end of the experiment, and the toxicity of adductor muscle exceeded the regulatory limit of 800 μg STXeq/kg in only 6 days. High concentration of toxins in the adductor muscle are likely linked to the rapid transfer of GC toxins from viscera to other tissues. Moreover, most GC toxins in scallops were found rapidly transformed to decarbamoyl toxins through enzyme-mediated hydrolysis, which was further supported by the in vitro incubation experiments. Our study demonstrates that GC toxins actively participate in toxin distribution and transformation in scallops, which may increase the risks of food poisoning associated with the consumption of scallop adductor muscle. ENVIRONMENTAL IMPLICATION: The negative impacts of harmful algal blooms (HABs) have become a global environmental concern under the joint effects of cultural eutrophication and climate change. Our study, targeted on the biokinetics of paralytic shellfish toxins in scallops exposed to Gymnodinium catenatum producing unique GC toxins, aims to elucidate potential risks of seafood poisoning associated with GC toxins. The findings of this study will help us to understand the roles of GC toxins in seafood poisoning, and to develop effective management strategies against toxic algal blooms and phycotoxins.

Somatostatin Receptor Gene Functions in Growth Regulation in Bivalve Scallop and Clam

Bivalves hold an important role in marine aquaculture and the identification of growth-related genes in bivalves could contribute to a better understanding of the mechanism governing their growth, which may benefit high-yielding bivalve breeding. Somatostatin receptor (SSTR) is a conserved negative regulator of growth in vertebrates. Although SSTR genes have been identified in invertebrates, their involvement in growth regulation remains unclear. Here, we identified seven SSTRs (PySSTRs) in the Yesso scallop, Patinopecten yessoensis, which is an economically important bivalve cultured in East Asia. Among the three PySSTRs (PySSTR-1, -2, and -3) expressed in adult tissues, PySSTR-1 showed significantly lower expression in fast-growing scallops than in slow-growing scallops. Then, the function of this gene in growth regulation was evaluated in dwarf surf clams (Mulinia lateralis), a potential model bivalve cultured in the lab, via RNA interference (RNAi) through feeding the clams Escherichia coli containing plasmids expressing double-stranded RNAs (dsRNAs) targeting MlSSTR-1. Suppressing the expression of MlSSTR-1, the homolog of PySSTR-1 in M. lateralis, resulted in a significant increase in shell length, shell width, shell height, soft tissue weight, and muscle weight by 20%, 22%, 20%, 79%, and 92%, respectively. A transcriptome analysis indicated that the up-regulated genes after MlSSTR-1 expression inhibition were significantly enriched in the fat digestion and absorption pathway and the insulin pathway. In summary, we systemically identified the SSTR genes in P. yessoensis and revealed the growth-inhibitory role of SSTR-1 in bivalves. This study indicates the conserved function of somatostatin signaling in growth regulation, and ingesting dsRNA-expressing bacteria is a useful way to verify gene function in bivalves. SSTR-1 is a candidate target for gene editing in bivalves to promote growth and could be used in the breeding of fast-growing bivalves.

The Glucose-Succinate Pathway: A Crucial Anaerobic Metabolic Pathway in the Scallop Chlamys farreri Experiencing Heat Stress

Recently, the increase in marine temperatures has become an important global marine environmental issue. The ability of energy supply in marine animals plays a crucial role in avoiding the stress of elevated temperatures. The investigation into anaerobic metabolism, an essential mechanism for regulating energy provision under heat stress, is limited in mollusks. In this study, key enzymes of four anaerobic metabolic pathways were identified in the genome of scallop Chlamys farreri, respectively including five opine dehydrogenases (CfOpDHs), two aspartate aminotransferases (CfASTs) divided into cytoplasmic (CfAST1) and mitochondrial subtype (CfAST2), and two phosphoenolpyruvate carboxykinases (CfPEPCKs) divided into a primitive type (CfPEPCK2) and a cytoplasmic subtype (CfPEPCK1). It was surprising that lactate dehydrogenase (LDH), a key enzyme in the anaerobic metabolism of the glucose-lactate pathway in vertebrates, was absent in the genome of scallops. Phylogenetic analysis verified that CfOpDHs clustered according to the phylogenetic relationships of the organisms rather than substrate specificity. Furthermore, CfOpDHs, CfASTs, and CfPEPCKs displayed distinct expression patterns throughout the developmental process and showed a prominent expression in muscle, foot, kidney, male gonad, and ganglia tissues. Notably, CfASTs displayed the highest level of expression among these genes during the developmental process and in adult tissues. Under heat stress, the expression of CfASTs exhibited a general downregulation trend in the six tissues examined. The expression of CfOpDHs also displayed a downregulation trend in most tissues, except CfOpDH1/3 in striated muscle showing significant up-regulation at some time points. Remarkably, CfPEPCK1 was significantly upregulated in all six tested tissues at almost all time points. Therefore, we speculated that the glucose-succinate pathway, catalyzed by CfPEPCK1, serves as the primary anaerobic metabolic pathway in mollusks experiencing heat stress, with CfOpDH3 catalyzing the glucose-opine pathway in striated muscle as supplementary. Additionally, the high and stable expression level of CfASTs is crucial for the maintenance of the essential functions of aspartate aminotransferase (AST). This study provides a comprehensive and systematic analysis of the key enzymes involved in anaerobic metabolism pathways, which holds significant importance in understanding the mechanism of energy supply in mollusks.

Effect of acute cadmium exposure on oxidative stress and antioxidant system of the scallop Aequipecten tehuelchus

This study aimed to assess the impact of acute exposure (96 h) to Cd in gills, digestive gland and muscle of the Tehuelche scallop Aequipecten tehuelchus from San José gulf in Patagonia, Argentina. Scallops were exposed to Cd concentrations of 0, 25, 50, 100, 150, 204, 275, 371, and 500 μg/L, and mortality rates were recorded after 96 h of exposure. Surviving organisms were analyzed for the biochemical response through reactive oxygen and nitrogen species (RONS), activities of catalase (CAT) and glutathione-S-transferase (GST), metallothioneins (MT), lipid peroxidation (LPO) and liposoluble antioxidants α-tocopherol (α-T) and β-carotene (β-C). The mean lethal concentration (LC50) was 155.8 μg Cd/L, a lower value than other scallops' species, showing that A. tehuelchus has a particular sensitivity to Cd. In the three tissues, at all exposure concentrations, there was no significant response in RONS levels, GST activity or LPO. Nevertheless, CAT activity and α-T levels decreased in the gills but increased in the digestive gland, with no significant response in the muscle. Two-way ANOVA revealed a significant interaction between Cd concentration and tissue on MT, which increased significantly in gills, decreased in digestive gland with 100 compared to 50 μg Cd/L; whereas in muscle a significant increase was observed with 25 μg Cd/L compared to control. The results show a significant effect of Cd in scallop's gills on CAT activity and α-T levels, highlighting this tissue as the primary target against relevant concentrations of metal in seawater. The effect on digestive gland and muscle was minimal. The overall results suggest that Cd toxicity is tissue-specific. This study will help reduce the existence knowledge gap regarding potential impacts of acute exposure to Cd in a bivalve species with high ecological and commercial importance, as well as identifying the most responsive biomarkers associated with Cd stress for monitoring assessment.

Interactive effects of multiple antibiotic residues and ocean acidification on physiology and metabolome of the bay scallops Argopecten irradians irradians

Coastal areas are confronted with compounding threats arising from both climatic and non-climatic stressors. Antibiotic pollution and ocean acidification are two prevalently concurrent environmental stressors. Yet their interactive effects on marine biota have not been investigated adequately and the compound hazard remain obscure. In this study, bay scallops Argopecten irradians irradians were exposed to multiple antibiotics (sulfamethoxazole, tetracycline, oxytetracycline, norfloxacin, and erythromycin, each at a concentration of 1 μg/L) combined with/without acidic seawater (pH 7.6) for 35 days. The single and interactive effects of the two stressors on A. irradians irradians were determined from multidimensional bio-responses, including energetic physiological traits as well as the molecular underpinning (metabolome and expressions of key genes). Results showed that multiple antibiotics predominantly enhanced the process of DNA repair and replication via disturbing the purine metabolism pathway. This alternation is perhaps to cope with the DNA damage induced by oxidative stress. Ocean acidification mainly disrupted energy metabolism and ammonia metabolism of the scallops, as evidenced by the increased ammonia excretion rate, the decreased O:N ratio, and perturbations in amino acid metabolism pathways. Moreover, the antagonistic effects of multiple antibiotics and ocean acidification caused alternations in the relative abundance of neurotransmitter and gene expression of neurotransmitter receptors, which may lead to neurological disorders in scallops. Overall, the revealed alternations in physiological traits, metabolites and gene expressions provide insightful information for the health status of bivalves in a natural environmental condition under the climate change scenarios.

Biochemical response and tissue-specific accumulation of scallop Aequipecten tehuelchus from Patagonia, Argentina after exposure to inorganic arsenic

This study investigates the effects of different inorganic arsenic (As III) concentrations (0, 125, 500 and 1000 μg As/L) following two exposure times (7 and 14 days) on gills, digestive gland and muscle of scallop Aequipecten tehuelchus from Patagonia, Argentina. A biochemical approach was used to investigate oxidative stress-related parameters after different As concentrations and exposure times. Although the accumulation of As was of the same order of magnitude in all tissues, the results showed distinct tissue-specific oxidative responses to this metalloid. Furthermore, the variation in exposure time had no significant effect on As accumulation in any of the three tissues. In gills, despite no reactive oxygen and nitrogen species (RONS) were detected, there was an increase in catalase (CAT) activity and metallothionein (MT) levels. Conversely, digestive gland showed RONS production without a rise in CAT and glutathione S-transferases (GST) activities, but with an increase in MT levels. In muscle, RONS production and CAT activity kept constant or decreased, while MT levels remained unchanged. In addition, exposure time demonstrated its critical role in gills by influencing the response of CAT, GST and MT, particularly at high As concentrations, while exposure time did not affect the biochemical stress parameters in the digestive gland and muscle. Interestingly, neither concentration of As produced lipid damage, showing the effectiveness of the antioxidant mechanisms to avoid it. These results emphasize that A. tehuelchus exhibited no time-dependent effects in response to As exposure, while showing tissue-specific responses characterized by significant concentration-dependent effects of As. This study provides a comprehensive insight by considering the combined effects of time and concentration of a contaminant and distinguishing its effects on specific tissues, a dimension often overlooked in the existing literature. Subsequent studies should prioritize the analysis of additional contaminants in species with increased sensitivity.

Genome-wide investigation of the TGF-β superfamily in scallops

BACKGROUND

Transforming growth factor β (TGF-β) superfamily genes can regulate various processes, especially in embryogenesis, adult development, and homeostasis. To understand the evolution and divergence patterns of the TGF-β superfamily in scallops, genome-wide data from the Bay scallop (Argopecten irradians), the Zhikong scallop (Chlamys farreri) and the Yesso scallop (Mizuhopecten yessoensis) were systematically analysed using bioinformatics methods.

RESULTS

Twelve members of the TGF-β superfamily were identified for each scallop. The phylogenetic tree showed that these genes were grouped into 11 clusters, including BMPs, ADMP, NODAL, GDF, activin/inhibin and AMH. The number of exons and the conserved motif showed some differences between different clusters, while genes in the same cluster exhibited high similarity. Selective pressure analysis revealed that the TGF-β superfamily in scallops was evolutionarily conserved. The spatiotemporal expression profiles suggested that different TGF-β members have distinct functions. Several BMP-like and NODAL-like genes were highly expressed in early developmental stages, patterning the embryonic body plan. GDF8/11-like genes showed high expression in striated muscle and smooth muscle, suggesting that these genes may play a critical role in regulating muscle growth. Further analysis revealed a possible duplication of AMH, which played a key role in gonadal growth/maturation in scallops. In addition, this study found that several genes were involved in heat and hypoxia stress in scallops, providing new insights into the function of the TGF-β superfamily.

CONCLUSION

Characteristics of the TGF-β superfamily in scallops were identified, including sequence structure, phylogenetic relationships, and selection pressure. The expression profiles of these genes in different tissues, at different developmental stages and under different stresses were investigated. Generally, the current study lays a foundation for further study of their pleiotropic biological functions in scallops.

The immunotoxicity mechanism of hemocytes in Chlamys farreri incubated with noradrenaline and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide alone or in combination

Benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) is the active intermediate metabolite of benzo[a]pyrene (B[a]P) and is considered the ultimate immunotoxicant. The neuroendocrine immunoregulatory network of bivalves is affected under pollutant stress. Besides, bivalves are frequently affected by pollutants in marine environments, yet the combined effects of neuroendocrine factors and detoxification metabolites on bivalves under pollutant stress and the signal pathways that mediate this immunoregulation are not well understood. Therefore, we incubated the hemocytes of Chlamys farreri with the neuroendocrine factor noradrenaline (NA) and the B[a]P detoxification metabolite BPDE, alone or in combination, to examine the immunotoxic effects of NA and BPDE on the hemocytes in C. farreri. Furthermore, the effects of NA and BPDE on the hemocyte signal transduction pathway were investigated by assessing potential downstream targets. The results revealed that NA and BPDE, alone or in combination, resulted in a significant decrease in phagocytic activity, bacteriolytic activity and the total hemocyte count. In addition, the immunotoxicity induced by BPDE was further exacerbated by co-treatment with NA, and the two showed synergistic effects. Analysis of signaling pathway factors showed that NA activated G proteins by binding to α-AR, which transmitted information to the Ca2+-NF-κB signaling pathway to regulate the expression of phagocytosis-associated proteins and regulated cytokinesis through the cAMP signaling pathway. BPDE could activate PTK and affect phagocytosis and cytotoxicity proteins through Ca2+-NF-κB signal pathway, also affect the regulation of phagocytosis and cytotoxicity by inhibiting the AC-cAMP-PKA pathway to down-regulate the expression of NF-κB and CREB. In addition, BPDE and NA may affect the immunity of hemocytes by down-regulating phagocytosis-related proteins through inhibition of the lectin pathway, while regulating the expression of cytotoxicity-related proteins through the C-type lectin. In summary, immune parameters were suppressed through Ca2+ and cAMP dependent pathways exposed to BPDE and the immunosuppressive effects were enhanced by the neuroendocrine factor NA.

Comparative study of domoic acid accumulation, isomer content and associated digestive subcellular processes in five marine invertebrate species

Despite the deleterious effects of the phycotoxin domoic acid (DA) on human health, and the permanent threat of blooms of the toxic Pseudo-nitzschia sp. over commercially important fishery-resources, knowledge regarding the physiological mechanisms behind the profound differences in accumulation and depuration of this toxin in contaminated invertebrates remain very scarce. In this work, a comparative analysis of accumulation, isomer content, and subcellular localization of DA in different invertebrate species was performed. Samples of scallops Pecten maximus and Aequipecten opercularis, clams Donax trunculus, slippersnails Crepidula fornicata, and seasquirts Asterocarpa sp. were collected after blooms of the same concentration of toxic Pseudo-nitzschia australis. Differences (P < 0.05) in DA accumulation were found, wherein P. maximus showed up to 20-fold more DA in the digestive gland than the other species. Similar profiles of DA isomers were found between P. maximus and A. opercularis, whereas C. fornicata was the species with the highest biotransformation rate (∼10 %) and D. trunculus the lowest (∼4 %). DA localization by immunohistochemical analysis revealed differences (P < 0.05) between species: in P. maximus, DA was detected mainly within autophagosome-like vesicles in the cytoplasm of digestive cells, while in A. opercularis and C. fornicata significant DA immunoreactivity was found in post-autophagy residual bodies. A slight DA staining was found free within the cytoplasm of the digestive cells of D. trunculus and Asterocarpa sp. The Principal Component Analysis revealed similarities between pectinids, and a clear distinction of the rest of the species based on their capabilities to accumulate, biotransform, and distribute the toxin within their tissues. These findings contribute to improve the understanding of the inter-specific differences concerning the contamination-decontamination kinetics and the fate of DA in invertebrate species.

Intrinsic and extrinsic pathways of apoptosis induced by multiple antibiotics residues and ocean acidification in hemocytes of scallop Argopecten irradians irradians: An interactionist perspective

The increasing prevalence of antibiotics in seawater across global coastal areas, coupled with the ocean acidification induced by climate change, present a multifaceted challenge to marine ecosystems, particularly impacting the key physiological processes of marine organisms. Apoptosis is a critical adaptive response essential for maintaining cellular homeostasis and defending against environmental threats. In this study, bay scallops Argopecten irradians irradians were exposed to multiple antibiotics (sulfamethoxazole, tetracycline, oxytetracycline, norfloxacin, and erythromycin, each at a concentration of 1 μg/L) combined with/without acidic seawater (pH 7.6) for 35 days. The single and interactive effects of the two stressors on apoptosis and the underlying mechanisms in hemocytes of A. irradians irradians were determined through flow cytometry analysis, comet assay, oxidative stress biomarkers analysis, and transcriptome analysis. Results showed that apoptosis could be triggered by either AM exposure or OA exposure, but through different pathways. Exposure to AM leads to mitochondrial dysfunction and oxidative damage, which in turn triggers apoptosis via a series of cellular events in both intrinsic and extrinsic pathways. Conversely, while OA exposure similarly induced apoptosis, its effects are comparatively subdued and are predominantly mediated through the intrinsic pathway. Additionally, the synergistic effects of AM and OA exposure induced pronounced mitochondrial dysfunction and oxidative damages in the hemocytes of A. irradians irradians. Despite the evident cellular distress and the potential initiation of apoptotic pathways, the actual execution of apoptosis appears to be restrained, which might be attributed to an energy deficit within the hemocytes. Our findings underscore the constrained tolerance capacity of A. irradians irradians when faced with multiple environmental stressors, and shed light on the ecotoxicity of antibiotic pollution in the ocean under prospective climate change scenarios.

Whole-Genome Re-sequencing and Transcriptome Reveal Candidate Genes and Pathways Associated with Hybrid Sterility in Hermaphroditic Argopecten Scallops

The interspecific hybrid scallops generated from the hermaphroditic bay scallops (Argopecten irradians) and Peruvian scallops (Argopecten purpuratus) showed significant heterosis in growth. However, its sterility limits large-scale hybridization and hinders the development of the scallop breeding industry. Hybrid sterility is regulated by plenty of genes and involves a range of biochemical and physiological transformations. In this study, whole-genome re-sequencing and transcriptomic analysis were performed in sterile and fertile hybrid scallops. The potential genetic variations and abnormally expressed genes were detected to explore the mechanism underlying hybrid sterility in hermaphroditic Argopecten scallops. Compared with fertile hybrids, 24 differentially expressed genes (DEGs) with 246 variations were identified to be related to fertility regulation, which were mainly enriched in germarium-derived egg chamber formation, spermatogenesis, spermatid development, mismatch repair, mitotic and meiotic cell cycles, Wnt signaling pathway, MAPK signaling pathway, calcium modulating pathway, and notch signaling pathway. Specifically, variation and abnormal expression of these genes might inhibit the progress of mitosis and meiosis, promote cell apoptosis, and impede the genesis and maturation of gametes in sterile hybrid scallops. Eleven DEGs (XIAP, KAZN, CDC42, MEIS1, SETD1B, NOTCH2, TRPV5, M- EXO1, GGT1, SBDS, and TBCEL) were confirmed by qRT-PCR validation. Our findings may enrich the determination mechanism of hybrid sterility and provide new insights into the use of interspecific hybrids for extensive breeding.

The involvement of AMP-activated protein kinase α in regulating glycolysis in Yesso scallop Patinopecten yessoensis under high temperature stress

AMP-activated protein kinase α subunit (AMPKα), the central regulatory molecule of energy metabolism, plays an important role in maintaining energy homeostasis and helping cells to resist the influence of various adverse factors. In the present study, an AMPKα was identified from Yesso scallop Patinopecten yessoensis (PyAMPKα). The open reading frame (ORF) of PyAMPKα was of 1599 bp encoding a putative polypeptide of 533 amino acid residues with a typical KD domain, a α-AID domain and a α-CTD domain. The deduced amino acid sequence of PyAMPKα shared 59.89-74.78% identities with AMPKαs from other species. The mRNA transcripts of PyAMPKα were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in adductor muscle. PyAMPKα was mainly located in cytoplasm of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyAMPKα, the phosphorylation level of PyAMPKα at Thr170 and the lactic acid (LD) content in adductor muscle all increased significantly, while the glycogen content decreased significantly. The activity of pyruvate kinase (PyPK) and the relative mRNA expression level of phosphofructokinase (PyPFK) were significantly up-regulated at 3 h after high temperature stress treatment (25 °C). Furthermore, the PyAMPKα activator AICAR could effectively upregulate the phosphorylation level of PyAMPKα, and increase activities of PyPFK and pyruvate kinase (PyPK). Meanwhile the glycogen content also declined under AICAR treatment. These results collectively suggested that PyAMPKα was involved in the high temperature stress response of scallops by enhancing glycolysis pathway of glycogen. These results would be helpful for understanding the functions of PyAMPKα in maintaining energy homeostasis under high temperature stress in scallops.

Mitochondria of Live Mizuhopecten yessoensis Scallops Can Sensitively Respond to Quality Changes during Dry/Reimmersed Storage as Determined by TMT-Labeled Proteomic Analysis

Dry/reimmersed storage is often used in the transportation of live scallops. In this study, tandem mass tag (TMT)-labeled protein omics were used to quantitatively analyze the protein changes in scallops during dry/reimmersed stress. The results showed that during dry storage, scallops maintained cellular redox homeostasis through the upregulation of SCO1-like protein and thioredoxin domain-containing protein and reduced organic acids from the ATP synthetic process by the downregulation of NADH dehydrogenase, thereby reducing the damage caused during dry storage. During reimmersed storage, mitochondrial proteins underwent very sensitive changes. By upregulating aerobic respiration-related proteins (including proteins involved in glucose phosphate metabolism, glyceraldehyde 3-phosphate metabolism, etc.), the ATP synthesis ability was improved. However, the damage to the mitochondrial structure by dry storage could not be completely recovered, even by reimmersion. This included some apoptosis-related proteins that were obviously upregulated. In summary, compared with ATP-related indexes, mitochondria can respond more sensitively to dry storage stress.

Sources, bioaccumulation, and toxicity mechanisms of cadmium in Chlamys farreri

The Potentially toxic elements (PTEs) cadmium (Cd) is one of the most serious stressors polluting the marine environment. Marine bivalves have specific high enrichment capacity for Cd. Previous studies have investigated the tissue distribution changes and toxic effects of Cd in bivalves, but the sources of Cd enrichment, migration regulation during growth, and toxicity mechanisms in bivalves have not been fully explained. Here, we used stable-isotope labeling to investigate the contributions of Cd from different sources to scallop tissues. We sampled the entire growth cycle of Chlamys farreri, which is widely cultured in northern China, from juveniles to adult scallops. We found tissue variability in the bioconcentration-metabolism pattern of Cd in different bound states, with Cd in the aqueous accounting for a significant contribution. The accumulation pattern of Cd in all tissues during growth was more significant in the viscera and gills. Additionally, we combined a multi-omics approach to reveal a network of oxidative stress-induced toxicity mechanisms of Cd in scallops, identifying differentially expressed genes and proteins involved in metal ion binding, oxidative stress, energy metabolism, and apoptosis. Our findings have important implications for both ecotoxicology and aquaculture. They also provide new insights into marine environmental assessment and mariculture development.

A sulphated glycosaminoglycan extract from Placopecten magellanicus inhibits the Alzheimer's disease β-site amyloid precursor protein cleaving enzyme 1 (BACE-1)

The clinically important anticoagulant heparin, a member of the glycosaminoglycan family of carbohydrates that is extracted predominantly from porcine and bovine tissue sources, has previously been shown to inhibit the β-site amyloid precursor protein cleaving enzyme 1 (BACE-1), a key drug target in Alzheimer's Disease. In addition, heparin has been shown to exert favourable bioactivities through a number of pathophysiological pathways involved in the disease processes of Alzheimer's Disease including inflammation, oxidative stress, tau phosphorylation and amyloid peptide generation. Despite the multi-target potential of heparin as a therapeutic option for Alzheimer's disease, the repurposing of this medically important biomolecule has to-date been precluded by its high anticoagulant potential. An alternative source to mammalian-derived glycosaminoglycans are those extracted from marine environments and these have been shown to display an expanded repertoire of sequence-space and heterogeneity compared to their mammalian counterparts. Furthermore, many marine-derived glycosaminoglycans appear to retain favourable bioactivities, whilst lacking the high anticoagulant potential of their mammalian counterparts. Here we describe a sulphated, marine-derived glycosaminoglycan extract from the Atlantic Sea Scallop, Placopecten magellanicus that displays high inhibitory potential against BACE-1 (IC₅₀ = 4.8 μg.mL^-1) combined with low anticoagulant activity; 25-fold less than that of heparin. This extract possesses a more favourable therapeutic profile compared to pharmaceutical heparin of mammalian provenance and is composed of a mixture of heparan sulphate (HS), with a high content of 6-sulphated N-acetyl glucosamine (64%), and chondroitin sulphate.

First quantitative biomonitoring study of two ports (marina, commerce) in French littoral area: Evaluation of metals released into the marine environment and resulting from galvanic anodes

Coastal areas are important interface environments between marine and terrestrial ecosystems and are also areas of high economic activity related, among others, to trade, fishing and tourism. The port areas of La Rochelle (France) are part of these areas with strong anthropic activities and are therefore subject to potential contamination, particularly with trace metals. Among the various sources of discharges, galvanic (or sacrificial) cathodic protection can be questioned. Indeed, few studies have been carried out on the potential impact of the degradation of sacrificial anodes in ports on the health of bivalves. A study was therefore carried out on the black scallop Mimachlamys varia in the commercial port and the marina of La Rochelle using the caging method. Several biomarkers of the health status of individuals were observed in the laboratory (SOD, GST, MDA, AChE, and LAC). Among the different results obtained over two exposure periods, it appears that the potential effects of sacrificial anodes, whether new or present on site for several years, are masked by meteorological conditions, as well as by harbor activities.

Bioaccumulation, Detoxification, and Biological Macromolecular Damage of Benzo[a]pyrene in Exposure in Tissues and Subcellular Fractions of Scallop Chlamys farreri

Because of the persistence and high toxicity of benzo[a]pyrene (B[a]P), the bioaccumulation and detoxification mechanisms of B[a]P have been studied extensively at the tissue level; but the data at the subcellular level in bivalves have not been reported. The present study was conducted to investigate the effects of B[a]P exposure on bioaccumulation, detoxification, and biomacromolecular damage in gills, digestive glands, and their subcellular fractions of the scallop Chlamys farreri. The subcellular fraction contains cytoplasm, mitochondria, microsome, nucleus, cell membrane, and overall organelle. The results demonstrated that B[a]P accumulation showed a clear time-dose effect. Based on the time-dependent accumulation of B[a]P in subcellular fractions, we speculated that the intracellular migration order of B[a]P was cell membrane, organelle, and nucleus in turn. Considering the difference of B[a]P accumulation may be related to B[a]P metabolism, we have further confirmed that the activities of B[a]P metabolizing enzymes in scallop tissues and subcellular fractions were significantly tempted by B[a]P (p < 0.05), including 7-ethoxyresorufin O-deethylase (increased), glutathione-S-transferase (GST; decreased), and superoxide dismutase (increased). First, GST was detected in bivalve cytoplasm and microsome. Second, B[a]P exposure also caused biomacromolecules damage. The results demonstrated that mitochondria and microsome were more vulnerable to lipid peroxidation than cell membrane and nucleus. Taken together, the present study fills some of the gaps in our knowledge of the bioaccumulation and detoxification mechanisms of C. farreri exposed to B[a]P in subcellular fractions and deeply explores the transportation and the main metabolic and damage sites of polycyclic aromatic hydrocarbons (PAHs) in cells, which helped us to comprehensively understand the toxic mechanism of PAHs on bivalves. Environ Toxicol Chem 2022;41:2353-2364. © 2022 SETAC.

Intraspecific hybridization as a mitigation strategy of ocean acidification in marine bivalve noble scallop Chlamys nobilis

The driving factors of climate change, especially ocean acidification (OA), have many detrimental impacts on marine bivalves. Hybridization is one of the important methods to improve environmental tolerance of animals and plants. In this study, we explored the feasibility of intraspecific hybridization as an OA mitigation strategy in noble scallop Chlamys nobilis (ecologically and economically important bivalve species). The results of this study revealed that exposure of C. nobilis to OA condition significantly reduced the hatching rate, survival rate, growth rate (shell height, shell length, shell width and shell weight), and total carotenoid content (TCC), as well as increased the deformity rate of C. nobilis larvae. Interestingly, under both ambient water and OA condition, the intraspecific hybridization of C. nobilis exhibited heterosis in terms of hatching rate, survival rate and growth rate (excepted for growth in shell length under OA). Transcriptome sequencing of C. nobilis (inbreed and hybrid under ambient and OA conditions) identified four main differentially expressed genes involved in signal transduction, biological process maintenances, nucleic acid binding and post-translational modification. In addition, the expression of these four genes in hybrid C. nobilis was significantly higher than that in inbreed C. nobilis. In conclusion, hybrid C. nobilis showed heterosis in growth rate and survival rate under both ambient water and acidified seawater condition, which may be the result of enhanced expression of genes related to signal transduction, DNA replication and post-translational modification.

Transcriptome Analysis Reveals MAPK/AMPK as a Key Regulator of the Inflammatory Response in PST Detoxification in Mytilus galloprovincialis and Argopecten irradians

Paralytic shellfish toxins (PSTs) are an increasingly important source of pollution. Bivalves, as the main transmission medium, accumulate and metabolize PSTs while protecting themselves from damage. At present, the resistance mechanism of bivalves to PSTs is unclear. In this study, Mytilus galloprovincialis and Argopecten irradians were used as experimental shellfish species for in situ monitoring. We compared the inflammatory-related gene responses of the two shellfish during PSTs exposure by using transcriptomes. The results showed that the accumulation and metabolism rate of PSTs in M. galloprovincialis was five-fold higher than that in A. irradians. The inflammatory balance mechanism of M. galloprovincialis involved the co-regulation of the MAPK-based and AMPK-based anti-inflammatory pathways. A. irradians bore a higher risk of death because it did not have the balance system, and the regulation of apoptosis-related pathways such as the PI3K-AKT signaling pathway were upregulated. Taken together, the regulation of the inflammatory balance coincides with the ability of bivalves to cope with PSTs. Inflammation is an important factor that affects the metabolic pattern of PSTs in bivalves. This study provides new evidence to support the studies on the resistance mechanism of bivalves to PSTs.

MicroRNA expression signature in the striated and smooth adductor muscles of Yesso scallop Patinopecten yessoensis

Increasing evidences point to the potential role of microRNAs (miRNAs) in muscle growth and development in animals. However, knowledge on the identity of miRNAs and their targets in molluscs remains largely unknown. Scallops have one large adductor muscle, composed of fast (striated) and slow (smooth) muscle types, which display great differences in muscle fibers, meat quality, cell types and molecular components. In the present study, we performed a comprehensive investigation of miRNA transcriptomes in fast and slow adductor muscles of Yesso scallop Patinopecten yessoensis. As a result, 47 differentially expressed miRNAs representing ten miRNA families were identified between the striated and smooth adductor muscles. The KEGG enrichment analysis of their target genes were mainly associated with amino acid metabolism, energy metabolism and glycan biosynthesis. The target genes of miR-133 and miR-71 were validated by the dual-luciferase reporter assays and miRNA antagomir treatment in vivo. The identification and functional validation of these different miRNAs in scallops will greatly help our understanding of miRNA regulatory mechanism that achieves the unique muscle phenotypes in scallops. The present findings provide the direct evidences for muscle-specific miRNAs involved in muscle growth and differentiation in molluscs.

Tissue-Specific and Time-Dependent Expressions of PC4s in Bay Scallop (Argopecten irradians irradians) Reveal Function Allocation in Thermal Response

Transcriptional coactivator p15 (PC4) encodes a structurally conserved but functionally diverse protein that plays crucial roles in RNAP-II-mediated transcription, DNA replication and damage repair. Although structures and functions of PC4 have been reported in most vertebrates and some invertebrates, the PC4 genes were less systematically identified and characterized in the bay scallop Argopecten irradians irradians. In this study, five PC4 genes (AiPC4s) were successfully identified in bay scallops via whole-genome scanning through in silico analysis. Protein structure and phylogenetic analyses of AiPC4s were conducted to determine the identities and evolutionary relationships of these genes. Expression levels of AiPC4s were assessed in embryos/larvae at all developmental stages, in healthy adult tissues and in different tissues (mantles, gills, hemocytes and hearts) being processed under 32 °C stress with different time durations (0 h, 6 h, 12 h, 24 h, 3 d, 6 d and 10 d). Spatiotemporal expression profiles of AiPC4s suggested the functional roles of the genes in embryos/larvae at all developmental stages and in healthy adult tissues in bay scallop. Expression regulations (up- and down-) of AiPC4s under high-temperature stress displayed both tissue-specific and time-dependent patterns with function allocations, revealing that AiPC4s performed differentiated functions in response to thermal stress. This work provides clues of molecular function allocation of PC4 in scallops in response to thermal stress and helps in illustrating how marine bivalves resist elevated seawater temperature.

Physiological and comparative proteomic analyzes reveal immune defense response of the king scallop Pecten maximus in presence of paralytic shellfish toxin (PST) from Alexandrium minutum

The king scallop, Pecten maximus is a highly valuable seafood in Europe. Over the last few years, its culture has been threatened by toxic microalgae during harmful algal blooms, inducing public health concerns. Indeed, phycotoxins accumulated in bivalves can be harmful for human, especially paralytic shellfish toxins (PST) synthesized by the microalgae Alexandrium minutum. Deleterious effects of these toxic algae on bivalves have also been reported. However, its impact on bivalves such as king scallop is far from being completely understood. This study combined ecophysiological and proteomic analyzes to investigate the early response of juvenile king scallops to a short term exposure to PST producing A. minutum. Our data showed that all along the 2-days exposure to A. minutum, king scallops exhibited transient lower filtration and respiration rates and accumulated PST. Significant inter-individual variability of toxin accumulation potential was observed among individuals. Furthermore, we found that ingestion of toxic algae, correlated to toxin accumulation was driven by two factors: 1/ the time it takes king scallop to recover from filtration inhibition and starts to filtrate again, 2/ the filtration level to which king scallop starts again to filtrate after inhibition. Furthermore, at the end of the 2-day exposure to A. minutum, proteomic analyzes revealed an increase of the killer cell lectin-like receptor B1, involved in adaptative immune response. Proteins involved in detoxification and in metabolism were found in lower amount in A. minutum exposed king scallops. Proteomic data also showed differential accumulation in several structure proteins such as β-actin, paramyosin and filamin A, suggesting a remodeling of the mantle tissue when king scallops are subjected to an A. minutum exposure.

Glyphosate exposure modulates lipid composition, histo-architecture and oxidative stress status and induces neurotoxicity in the smooth scallop Flexopecten glaber

Glyphosate is the most sprayed pesticide across the globe. Its toxicity to non-target marine organisms has recently piqued the scientific community's interest. Therefore, the purpose of this study is to investigate the potentially toxic effects of glyphosate on scallops, an ecologically and economically important bivalve group. To do that, specimens of the smooth scallop Flexopecten glaber were exposed to different concentrations (10, 100, and 1000 μg L-1) of the technical-grade glyphosate acid (GLY) for 96 h. The detrimental effects of this pollutant were assayed at cellular and tissular levels. The obtained results showed that the GLY was able to induce oxidative stress in the gills and the digestive gland of F. glaber as revealed by the enhanced hydrogen peroxide (H2O2), protein carbonyls (PCO), malondialdehyde (MDA), and lipid peroxides (LOOH) levels and the altered antioxidant defense system (the glutathione GSH content and the superoxide dismutase (SOD) activity). Additionally, GLY was found to alter the fatty acid profile, to exert a neurotoxic effect through the inhibition of the acetylcholinesterase (AChE) activity, and to provoke several histopathological damages in the two organs studied. The obtained results revealed that the pure form of GLY may exert toxic effects on F. glaber even at relatively low concentrations.

A Systematical Survey on the TRP Channels Provides New Insight into Its Functional Diversity in Zhikong Scallop (Chlamys farreri)

Transient receptor potential (TRP) channel plays a significant role in mediating various sensory physiological functions. It is widely present in the vertebrate and invertebrate genomes and can be activated by multiple compounds, messenger molecules, temperature, and mechanical stimulation. Mollusks are the second largest phylum of the animal kingdom and are sensitive to environmental factors. However, the molecular underpinnings through which mollusks sense and respond to environmental stimulus are unknown. In this study, we systematically identified and characterized 17 TRP channels (C.FA TRPs, seven subfamilies) in the genome of the Zhikong scallop (Chlamys farreri). All C.FA TRPs had six transmembrane structures (TM1–TM6). The sequences and structural features of C.FA TRPs are highly conserved with TRP channels of other species. Spatiotemporal expression profiling suggested that some C.FA TRPs participated in the early embryonic development of scallops and the sensory process of adult tissues. Notably, the expression of C.FA TRPM3 continuously increased during developmental stages and was highest among all C.FA TRPs. C.FA TRPC-α was specifically expressed in eyes, which may be involved in light transmission of scallop eyes. Under high temperature stress, C.FA TRPA1 and C.FA TRPA1-homolog upregulated significantly, which indicated that the TRPA subfamily is the thermoTRPs channel of scallops. Our results provided the first systematic study of TRP channels in scallops, and the findings will provide a valuable resource for a better understanding of TRP evolution and function in mollusks.

Metabolomics comparison of metabolites and functional pathways in the gills of Chlamys farreri under cadmium exposure

The biological processes of Chlamys farreri (C. farreri), an economically important shellfish, are affected when exposed to Cd²⁺. In this study, changes to biological processes and metabolite levels in C. farreri were examined when exposed to Cd²⁺. Ultra-performance liquid chromatography-tandem TOF mass spectrometry (UPLC-TOF/MS)-based untargeted metabolomics was used to examine changes in the metabolism of C. farreri gill tissue exposed to 0.050 mg/L Cd²⁺ for 96 h in a natural environment. Sixty-eight metabolites with significant differences were screened by multivariate statistical analysis. Eleven enriched functional pathways displayed significant changes in inactivity. Differential metabolites, mainly C00157 and C00350, have a significant impact on functional pathways and can be used as potential major biomarkers. Lipid phosphorylation, disruption of signal transduction, and autophagy activation were observed to change in C. farreri when exposed to Cd. The metabolome information supplements research on C. farreri exposure to heavy metals and provides a platform for further multi-omics analysis.

Gonadal somatic cell-specific transforming growth factor-β superfamily member in the Yesso scallop reveals gonadal somatic cell distribution during the reproductive phase

The objective of this study was to identify the gonadal somatic cells in the Yesso scallop using a novel molecular marker. This study is the first to identify the bone morphogenetic protein 2a (Bmp2a) gene as a gonadal somatic cell-specific gene in this bivalve. We performed a transcriptomic survey to identify the transforming growth factor-β (TGFβ) superfamily members that act in Yesso scallop gonad development. BLAST survey, phylogenetic tree, and RT-PCR analyses screened BMP molecules (i.e., bmp2a and bmp10a), which are members of the TGFβ superfamily that show gonad-specific expression. Among the BMPs from the Yesso scallop, in situ hybridization accompanied by RNAscope assay identified that bmp2a mRNA was specifically expressed in the gonadal somatic cells localized in the interspace between germ cells. Real-time quantitative PCR (qPCR) analysis revealed that bmp2a mRNA expression increased during the reproductive phase. The relative expression of bmp2a mRNA was lowest at the beginning of the growing stage and peaked at the mature stage in both sexes. These observations indicate that bmp2a-positive gonadal somatic cells support germ cell growth and differentiation during the reproductive phase for both sexes. This study provides new insights into gonadal somatic cell biology in marine invertebrates and we propose that TGFβ signaling is necessary for gonad development in bivalves.

Identification and Antihypertension Study of Novel Angiotensin I-Converting Enzyme Inhibitory Peptides from the Skirt of Chlamys farreri Fermented with Bacillus natto

The aim of this study was to isolate the angiotensin I-converting enzyme (ACE) inhibitory peptides from the skirt of Chlamys farreri fermented with Bacillus natto and to explore the antihypertension effect through in vivo studies. ACE inhibitory peptides were purified from the fermentation mixture by ultrafiltration, gel filtration chromatography, and reversed-phase high-performance liquid chromatography sequentially. The amino acids' sequence of the five novel ACE inhibitory peptides were identified by liquid chromatography-tandem mass spectrometry. Animal experiments demonstrated that the novel ACE inhibitory peptides significantly reduced the blood pressure in spontaneously hypertensive rats after a single or long-time treatment. Potential mechanisms were explored, and the results indicated that the novel peptides could regulate the renal renin-angiotensin system, improve vascular remodeling, inhibit myocardial fibrosis, and rebalance the gut microbial dysbiosis. Our results suggest that the fermentation products of the Chlamys farreri skirt by B. natto are potential sources of active peptides processing antihypertension activities.

Toxin- and species-dependent regulation of ATP-binding cassette (ABC) transporters in scallops after exposure to paralytic shellfish toxin-producing dinoflagellates

ATP-binding cassette (ABC) transporters are membrane-bound proteins involved in exporting various xenobiotic compounds from living cells. Bivalve mollusks can accumulate large amounts of paralytic shellfish toxins (PSTs) from marine dinoflagellates. For aquatic invertebrates, the importance of ABC proteins in multi-xenobiotic resistance has been demonstrated, however, the systematic identification of ABC transporters is very limited. In this study, 64 and 67 ABC genes containing all eight described subfamilies (A to H) were identified in Yesso scallop (Patinopecten yessoensis) and Zhikong scallop (Chlamys farreri), respectively, with massive gene expansion being observed in the ABCC and ABCG subfamilies. The kidney harbored more specifically expressed ABC genes than other organs/tissues, most of which belonged to ABCB, ABCC, and ABCG subfamilies. After feeding the scallops with PST-producing dinoflagellates, the expression of scallop ABC genes in the kidney was regulated in toxin- and species-dependent manners. In total, 20 and 24 ABC genes in Zhikong scallop (CfABCs) were induced after exposure to Alexandrium minutum and A. catenella, with the up-regulated members from both ABCC and ABCG subfamilies mainly showing acute and chronic induction by A. minutum and A. catenella, respectively, while the up-regulated CfABCBs mainly showing chronic induction by both dinoflagellates. In Yesso scallop, only eight ABC genes (PyABCs) were regulated after A. catenella exposure, and all the five up-regulated PyABCs were acutely induced. Our findings imply the functional diversity of scallop ABC genes in coping with PST accumulation, which may contribute to the lineage-specific adaptation of scallops for dealing with algal toxins challenge.

Biokinetics and biotransformation of paralytic shellfish toxins in different tissues of Yesso scallops, Patinopecten yessoensis

Paralytic shellfish toxins (PSTs) are a group of natural toxic substances often found in marine bivalves. Accumulation, anatomical distribution, biotransformation and depuration of PSTs in different tissues of bivalves, however, are still not very well understood. In this study, we investigated biokinetics and biotransformation of PSTs in six different tissues, namely gill, mantle, gonad, adductor muscle, kidney, and digestive gland, in Yesso scallops Patinopecten yessoensis exposed to a toxic strain of dinoflagellate Alexandrium pacificum. High daily accumulation rate (DAR) was recorded at the beginning stage of the experiment. Most of the PSTs in toxic algae ingested by scallops were retained and the toxicity level of PSTs in scallops exceeded the regulatory limit within 5 days. At the late stage of the experiment, however, DAR decreased obviously due to the removal of PSTs. Fitting results of the biokinetics model indicated that the amount of PSTs transferred from digestive gland to mantle, adductor muscle, gonad, kidney, and gill in a decreasing order, and adductor muscle, kidney, and gonad had higher removal rate than gill and mantle. Toxin profile in digestive gland was dominated by N-sulfocarbamoyl toxins 1/2 (C1/2), closely resembled that of the toxic algae. In contrast, toxin components in kidney were dominated by high-potency neosaxitoxin (NEO) and saxitoxin (STX), suggesting that the kidney be a major organ for transformation of PSTs.

Potential GnRH and steroidogenesis pathways in the scallop Patinopecten yessoensis

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on GnRH and steroidogenesis pathways is still limited. In this study, we first identified two gonadotropin receptor like genes (LGR and LGR5L) and four steroidogenesis-related genes (CYP17A, HSD17B12, HSD3B1 and HSD3B2) in the scallop Patinopecten yessoensis. By examining the expression of 11 genes in the ganglia and/or gonad as well as the concentration of progesterone, testosterone and estradiol in the gonad, we postulate that a potential GnRH signaling pathway (GnRH-GnRHR-GPB5-LGR/LGR5L) in the cerebral and pedal ganglia (CPG) and steroidogenesis pathway (CYP17A, HSD17B12 and HSD3B1) in the gonad are involved in regulating sex steroid hormones. E₂/T index that indicates aromatase activity is higher in the ovary than testis and is positively correlated with the expression of FOXL2 in the gonad, implying the presence of aromatase in the scallop. In addition, we confirmed that expression of most of the downstream genes in the two pathways was significantly elevated after injection of mature py-GnRH peptide. This study would contribute to a new understanding of the molecular basis underlying reproduction regulation by GnRH in mollusks.

Exposure of bay scallop Argopecten irradians to micro-polystyrene: Bioaccumulation and toxicity

Marine microplastic pollution poses a threat to aquatic organisms, including bivalves. In this study, we investigated the accumulation of microplastics and their elicited antioxidant stress response in the bay scallop Argopecten irradians. Scallops were exposed to 1 μm diameter micro-polystyrene (MP) beads at 10, 100, and 1000 beads/mL concentrations for a 7 day period. Bead presence in the digestive diverticula and defense responses in the digestive diverticula and hemolymph were measured at 1, 3, 5, and 7 days. The activity and expression of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) and H₂O₂ in the digestive diverticula and/or hemolymph of scallops increased with microplastic concentration and exposure duration. These results suggest that microplastics can accumulate in the digestive diverticula of A. irradians, and that exposure to microplastics induces oxidative stress in bivalves. It is likely that exposure to high concentrations of micro- or nano-sized plastic particles could potentially have adverse effects in bivalves.

Multiple-Biomarker Approach in a Commercial Marine Scallop from San Jose gulf (Patagonia, Argentina) for Health Status Assessment

The health status of the commercial Tehuelche scallop Aequipecten tehuelchus from San Román and El Riacho in San José gulf (Patagonia, Argentina) was evaluated through biomarkers widely used in ecotoxicological applications. Natural levels of arsenic (As) and cadmium (Cd) were measured to determine their potential relationships with fluctuations of several oxidative stress biomarkers in the scallop. Oxidative biomarkers, such as catalase (CAT), glutathione S-transferase (GST), superoxide dismutase (SOD), metallothioneins (MT), reactive oxygen species (ROS), α-tocopherol (α-T), and lipid peroxidation (LPO) through thiobarbituric acid reactive substances (TBARS) and lipid radical (LR^∙), were measured in gills, digestive gland, and muscle of Tehuelche scallop in winter (August 2015) and summer (January 2016). Levels of As and Cd and of most of the biomarkers (SOD, ROS, TBARS, and LR^∙) showed strong seasonal variability in the three tissues. In general, the highest values were recorded in digestive gland. The Integrated Biomarker Response index indicated that the most stressed condition of A. tehuelchus was in summer in San Román. Additionally, the Integrated Biomarker Response index showed a strong relationship among tissues and As and Cd accumulation. This kind of approach could be used as an integrated tool to identify the health status of scallop A. tehuelchus from San José gulf.

Depuration of cadmium from Chlamys farreri by ZnSO4, EDTA-Na2 and sodium citrate in short time

In view of high content of cadmium (Cd) in Chlamys farreri, a commercial edible shellfish species, depurating Cd from Chlamys farreri is an important topic nowadays, especially in short time. Therefore, three kinds of additives were introduced into seawater respectively, i.e. ZnSO₄, EDTA-Na₂, sodium citrate, to depurate Cd from Chlamys farreri. The alteration of Cd content in separate organs was investigated under several treatments with high depuration efficiency. The results showed that Cd was depurated exceeding 20% within 12 h by the combination of 0.15 g/L sodium citrate, 0.28 g/L ZnSO₄, and 0.42 g/L EDTA-Na₂. No obvious increase of Cd was observed in the adductor muscles, while Cd decreased in the other part, so the reduction of Cd in the whole organism of Chlamys farreri may occur. Cd reduction was found in the following organs: the digestive gland, kidney, gill, and mantle. Furthermore, Cd migration to gonad from other tissues was noticed.

Genome-wide identification, characterization of RLR genes in Yesso scallop (Patinopecten yessoensis) and functional regulations in responses to ocean acidification

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), are crucial sensors with a conserved structure in cytoplasm, inducing the production of cytokines, chemokines and host restriction factors which mediate a variety of intracellular activities to interfere with distinct PAMPs (pathogen-associated molecular patterns) for eliminating pathogens in innate immune system. Although RLR genes have been investigated in most vertebrates and some invertebrates, the systematic identification and characterization of RLR genes have not been reported in scallops. In this study, four RLR genes (PY-10413.4, PY-10413.5, PY-443.7 and PY-443.8, designated PyRLRs) were identified in Yesso scallop (Patinopecten yessoensis) through whole-genome scanning through in silico analysis, including two pairs of tandem duplicate genes located on the same scaffold (PY-10413.4 and PY-10413.5, PY-443.7 and PY-443.8, respectively). Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of these genes. The expression profiles of PyRLRs were determined in all developmental stages, in healthy adult tissues, and in mantles that simulated ocean acidification (OA) exposure (pH = 6.5 and 7.5) at different time points (3, 6, 12 and 24 h). Spatiotemporal expression patterns suggested the functional roles of PyRLRs in all stages of development and growth of the scallop. Regulation expressions revealed PY-10413.4 and PY-10413.5 with one or two CARD(s) (caspase activation and recruitment domain) were up-regulated expressed at most time points, whereas PY-443.8 and PY-10413.4 without CARD were significantly down-regulated at each time points, suggesting functional differentiations in the two pairs of PyRLRs based on the structural differences in response to OA. Collectively, this study demonstrated gene duplication of RLR family genes and provide primary analysis for versatile roles in the response of the bivalve innate immune system to OA challenge.

Effects of thermal stress on mortality and HSP90 expression levels in the noble scallops Chlamys nobilis with different total carotenoid content

The noble scallop Chlamys nobilis is an economically important marine bivalve cultivated in the southern sea of China since the 1980s. Unfortunately, mass mortality of this scallop species often occurs in summer. The present study was conducted to investigate whether the expression of heat shock protein 90 (HSP90) and level of carotenoids could enhance high-temperature stress resistance in scallop. First, the HSP90 homolog of C. nobilis (designated CnHSP90) was identified and cloned. The complete cDNA sequence of CnHSP90 was 2631 bp, including a 2181-bp open reading frame (ORF) encoding a 726 amino acid polypeptide with five HSP90 family signatures, and sharing high homology with members of the HSP90 family. CnHSP90 was ubiquitously expressed in all examined tissues including the intestine, kidney, adductor, mantle, gill, and gonad, with the highest in the gonad. Golden and brown scallops, which contain significantly different total carotenoid content (TCC), were subjected to acute thermal challenge, and the LTE50 (semi-lethal temperature at 36 h heat shock) and LTI50 (semi-lethal time after heat shock) as well as the correlation between CnHSP90 gene expression and TCC were determined. The LTE50 of golden scallop (32.14 °C) was higher than that of brown scallops (31.19 °C), with longer LTI50 at all tested temperatures, indicating that golden scallops were more resistant to thermal stress than brown scallops. Similarly, the mRNA expression levels of CnHSP90 in gill of golden scallops were significantly higher (P < 0.05) than that of brown scallops at 6, 12, 24, and 36 h, with a strong positive correlation between CnHSP90 expression level and TCC. This suggests that both carotenoids and HSP90 levels could improve thermal resistance in the noble scallops.

Peruvian scallop Argopecten purpuratus: From a key aquaculture species to a promising biondicator species

The present study analyzed the Peruvian scallop Argopecten purpuratus and its food sources for metal and fatty acid concentrations in order to determine spatial and temporal differences. Metals such as copper (Cu), manganese (Mn), and zinc (Zn) in gills and iron (Fe) and Zn in sediments were the most significant explaining factors for spatial differentiations (degree of contamination), while for fatty acids, it was C14:0, C15:0, C16:0 and C18:0 in A. purpuratus' muscle and in its food sources, which explained more temporal differences (El Niño-Southern Oscillation (ENSO) effect). Gills, digestive gland and intestine were the tissues where metal accumulation was the highest in A. purpuratus. Cd in digestive gland was always high, up to ∼250-fold higher than in other tissues, as previously reported in other bioindicator species for metal pollution. Fatty acids were good biomarkers when annual comparisons were performed, while metals when locations were compared. ENSO 2017 played an important role to disentangle A. purpuratus' biological conditions and food sources. A. purpuratus from Paracas locations mostly showed higher metal concentrations in gills and digestive glands, and lower fatty acid concentrations in muscle than those from Sechura and Illescas Reserved Zone.

Effect of the Algicide Thiazolidinedione 49 on Immune Responses of Bay Scallop Argopecten Irradians

The thiazolidinedione 49 (TD₄₉) is an effective algaecide against harmful algae; however, its potential effects on the immune function of the edible bay scallop are unclear. Therefore, the present work studied the effects of TD₄₉ on the immune response in bay scallop by evaluating activities of acid phosphatase (ACP), alkaline phosphatase (ALP), and superoxide dismutase (SOD), as well as nitric oxide (NO) levels, total protein content, and expression of immune genes (CTL-6, PGRP, PrxV, MT, and Cu/Zn-SOD) at 3–48 h post-exposure (hpe) to TD₄₉. The activities of ACP and ALP significantly increased in TD₄₉-treated groups at 3–24 hpe, whereas NO levels decreased significantly in 0.58 and 0.68 μM of TD₄₉ at 6–24 hpe, after which the level was similar to that in the untreated control. Moreover, SOD activity significantly increased in all three concentration groups at 3–6 hpe, while it decreased at 12 hpe in the 0.68 μM TD₄₉ treatment group. Notably, total protein content increased with TD₄₉ treatment at each time interval. The results revealed that variable effects on the expression of immune-related genes were observed after treatment with TD₄₉. The findings demonstrate that exposure of scallops to TD₄₉ changes immune responses and expression of immune-related genes. We hypothesize that TD₄₉ may disrupt immune system in bay scallop. The current investigation highlights the potential negative effects of using TD₄₉ as an algaecide on marine economic bivalves to control harmful algal blooms in marine environments.

Functional characterization of an invertebrate gonadotropin-releasing hormone receptor in the Yesso scallop Mizuhopecten yessoensis

The neuropeptide control of bivalve reproduction with particular reference to gonadotropin-releasing hormone (invGnRH) is a frontier yet to be investigated. Bivalves are unique because they have two forms of the invGnRH peptide; however, there has been no functional characterization of the peptide-receptor pair. Therefore, the identification of a cognate receptor is a preliminary step toward exploring the biological roles of invGnRHs in bivalves. In this study, we functionally characterize an invGnRH receptor (invGnRHR) of a bivalve, the Yesso scallop Mizuhopecten yessoensis. In the receptor assay, HEK293 cells were transfected to transiently express the M. yessoensis invGnRHR (my-invGnRHR), which was found to be localized on the plasma membrane, confirming that my-invGnRHR, similar to other G-protein-coupled receptors, functions as a membrane receptor. Using both forms of invGnRH as ligands in a function-receptor assay, my-invGnRH11aa-NH₂ stimulated intracellular Ca²⁺ mobilization but not cyclic AMP production, whereas my-invGnRH12aa-OH did not induce increase in Ca²⁺ levels. Therefore, we concluded that my-invGnRHR is an endogenous receptor specific to my-invGnRH11aa-NH₂ which is hypothesized to be the mature peptide. To the best of our knowledge, this is the first study reporting the functional characterization of a bivalve invGnRHR.

Histological and Expression Differences Among Different Mantle Regions of the Yesso Scallop (Patinopecten yessoensis) Provide Insights into the Molecular Mechanisms of Biomineralization and Pigmentation

The molecular mechanisms of shell formation and pigmentation are issues of great interest in molluscan studies due to the unique physical and biological properties of shells. The Yesso scallop, Patinopecten yessoensis, is one of the most important maricultural bivalves in Asian countries, and its shell color shows polymorphism. To gain more information about the underlying mechanisms of shell formation and pigmentation, this study presents the first analyses of histological and transcriptional differences between different mantle regions of the Yesso scallop, which are thought to be responsible for the formation of different shell layers. The results showed major microstructural differences between the edge and central mantles, which were closely associated with their functions. Different biomineralization-related GO functions, which might participate in the formation of different shell layers, were significantly enriched in the different mantle regions, indicating the different molecular functions of the two mantle regions in shell formation. The melanogenesis pathway, which controls melanin biosynthesis, was the most significantly enriched pathway in the DEGs between the two mantle regions, indicating its important role in shell pigmentation. Tyr, the key and rate-limiting gene in melanogenesis, was expressed at a remarkably high level in the central mantle, while the upstream regulatory genes included in melanogenesis were mainly upregulated in the edge mantle, suggesting the different molecular functions of the two mantle regions in shell pigmentation.

Copper effect on the biomarker state of the Mizuhopecten yessoensis tissues in the prespawning period

The aim of this study was to investigate the sensitivity of the marine scallop Mizuhopecten yessoensis to different copper concentrations (10 and 30 μgl-1) in the prespawning period. Reaction of the scallop to this effect was evaluated by a set of biomarkers, including general metabolism enzymes (acid and alkaline phosphatase activities - AcPase, ALP), and oxidative stress parameters (catalase antioxidant enzyme activity - CAT and levels of damage for DNA, lipids and proteins). Experiment results show that when copper is accumulated in tissues, enzyme activity changes are similar and have phasic character. The dynamics of these changes depends on the copper accumulation levels in tissues. Unlike enzyme reaction to copper accumulation, oxidative damage of biologic molecules changes in tissues in different ways. Copper enters into a scallop's organism, mainly through the gills, where there is a more expressed reaction of biomarkers compared to the digestive gland.

Identification of two ferritin genes and their expression profiles in response to bacterial challenge in noble scallop Chlamys nobilis with different carotenoids content

As a major intracellular iron storage protein, ferritin plays important roles in iron homeostasis and innate immunity. In this study, two novel ferritin subunits from noble scallop Chlamys nobilis (CnFer1 and CnFer2) were identified and analyzed. The open reading frame of CnFer1 and CnFer2 was 522 and 519bp long, encoding 173 and 172 amino acids, respectively. Both ferritins contained a putative iron-binding region signature (IBRS). Analysis of putative conserved domains showed the two CnFer genes contained three key domains of ferritin subunits, a ferroxidase diiron center (E25, Y32, E59, E60, H63, E105, and Q139), an iron ion channel (H116, D129, E132) and a ferrihydrite nucleation center (D58, E59, and E62) that present in M type subunits. A putative iron response element (IRE) was observed at both CnFer genes in the 5' UTR. Phylogenetic analysis result suggested that the two genes are cytoplasmic ferritins and have the closest evolution relationship with ferritins from Mizuhopecten yessoensis. The two ferritin genes were wildly expressed in examined tissues and the highest level was found in gill. After V. parahaemolyticus challenged, both CnFer genes were significantly up-regulated suggesting that they are important proteins involved in host immune defense. Moreover, under bacterial challenge, the expression levels of both two genes in Golden scallops (rich in carotenoids) were significantly higher than that in Brown scallops (less in carotenoids) which suggesting that carotenoids enhance the immunity in scallops to defense against the bacterial stress.

Application of a series of biomarkers in Scallop Chlamys farreri to assess the toxic effects after exposure to a priority hazardous and noxious substance (HNS)-Acrylonitrile

The antioxidant enzymes and detoxification parameters responses of the scallop Chlamys farreri to different degree of acrylonitrile (AN) were investigated. Accordingly, the median lethal concentration (LC₅₀) at 96 h was 98.5 mg/L AN. Results from chronic toxicity test demonstrated that superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were stimulated in the highest two doses of AN (2.0 and 5.0 mg/L), but significantly inhibited in the highest concentration (5.0 mg/L) at the end of the exposure. The levels of DNA strand breaks, lipid peroxidation (LPO) and protein carbonyl (PC) contents showed damage effects exposed AN at the highest two doses. Additionally, AN significantly induced the enzymatic activity of glutathione-s-transferase (GST), related mRNA expression levels of P-glycoprotein (P-gp) and GST-pi; and no significant changes were found on CYP1A1 mRNA expression and ethoxyresorufin O-deethylase (EROD) activity. Our results indicated that P-gp and GST-pi mRNA expression in digestive glands of the scallop C. farreri may potentially be used in ecological risk assessment of hazardous and noxious substances (HNS) contamination of marine.

What is the relationship between the bioaccumulation of chemical contaminants in the variegated scallop Mimachlamys varia and its health status? A study carried out on the French Atlantic coast using the Path ComDim model

Increasing activity along the French Atlantic coast has led to chronic pollution with, in particular, mixtures of contaminants such as hydrocarbons, phytosanitary products, PCBs and heavy metals. Based on previous research, pollution biomarkers were used in this study as they can indicate health status when monitoring the impact of pollutants on coastal species such as the marine bivalve Mimachlamys varia. Mollusc bivalves were sampled in March 2016, in open and semi-open areas (a harbour zone), from thirteen sites which differed in terms of their level of pollution, and were located along the Atlantic coast from Brittany down to the Nouvelle-Aquitaine region. First, analyses of heavy metals and organic contaminants (e.g. pesticides, polycyclic aromatic hydrocarbons, polychlorobiphenyl) in the digestive gland of bivalves were performed. Second, biochemical assays were used to study defence biomarkers: oxidative stress with Superoxide Dismutase (SOD), detoxification of organic compounds with Glutathione-S Transferase (GST), lipid peroxidation with Malondialdehyde (MDA), and immune processes with Laccase. In addition to the biochemical assays, a genetic approach was used to measure genetic diversity (haplotype and nucleotide diversity) at each site. Biomarker assays and genetic diversity were correlated with the chemical contaminants in bivalves using the Path-ComDim statistical model. Our results showed specific correlations between biochemical assays in the digestive glands with heavy metal contaminants, and between genetic diversity and organic pollution. Blocks of responses were analysed for correlations in order to develop standardized tools and guidelines that could improve our understanding of the short-term and long-term impact of contaminants on physiological parameters.

Light control of G protein signaling pathways by a novel photopigment

Channelopsins and photo-regulated ion channels make it possible to use light to control electrical activity of cells. This powerful approach has lead to a veritable explosion of applications, though it is limited to changing membrane voltage of the target cells. An enormous potential could be tapped if similar opto-genetic techniques could be extended to the control of chemical signaling pathways. Photopigments from invertebrate photoreceptors are an obvious choice—as they do not bleach upon illumination -however, their functional expression has been problematic. We exploited an unusual opsin, pScop2, recently identified in ciliary photoreceptors of scallop. Phylogenetically, it is closer to vertebrate opsins, and offers the advantage of being a bi-stable photopigment. We inserted its coding sequence and a fluorescent protein reporter into plasmid vectors and demonstrated heterologous expression in various mammalian cell lines. HEK 293 cells were selected as a heterologous system for functional analysis, because wild type cells displayed the largest currents in response to the G-protein activator, GTP-γ-S. A line of HEK cells stably transfected with pScop2 was generated; after reconstitution of the photopigment with retinal, light responses were obtained in some cells, albeit of modest amplitude. In native photoreceptors pScop2 couples to G_o; HEK cells express poorly this G-protein, but have a prominent Gq/PLC pathway linked to internal Ca mobilization. To enhance pScop2 competence to tap into this pathway, we swapped its third intracellular loop—important to confer specificity of interaction between 7TMDRs and G-proteins—with that of a G_q-linked opsin which we cloned from microvillar photoreceptors present in the same retina. The chimeric construct was evaluated by a Ca fluorescence assay, and was shown to mediate a robust mobilization of internal calcium in response to illumination. The results project pScop2 as a potentially powerful optogenetic tool to control signaling pathways.

Transcriptome analysis of the Yesso scallop, Patinopecten yessoensis gills in response to water temperature fluctuations

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

Change of Arsenic Speciation in Shellfish after Cooking and Gastrointestinal Digestion

Shellfish is a common part of indigenous cuisines throughout the world and one of the major sources of human exposure to arsenic (As). We evaluated As speciation in shellfish after cooking and gastrointestinal digestion in this study. Results showed that washing and cooking (boiling and steaming) can reduce As exposures from shellfish. The use of spices during cooking processes also helped to reduce the bioaccessibility of total As. Through mass balance calculations, we verified the transformation of methylated As compounds into inorganic As in shellfish takes place during cooking and that As demethylation can occur during simulated gastrointestinal digestion. In vivo demethylation of As after gastrointestinal digestion was also demonstrated in laboratory mice. This increase in inorganic As during digestion suggests that risks of As toxicity from shellfish consumption are being underestimated. Further studies on the mechanisms of As speciation transformation in food are necessary for more thorough risk assessments.

Dynamics of paralytic shellfish toxins and their metabolites during timecourse exposure of scallops Chlamys farreri and mussels Mytilus galloprovincialis to Alexandrium pacificum

New C-11 hydroxyl metabolites of paralytic shellfish toxins (PSTs) have been reported in shellfish. To gain further information on these metabolites, as well as the potential for formation of phase-II metabolites and acyl esters of PSTs, bivalves were fed with the PSTs-producing dinoflagellate Alexandrium pacificum (strain ATHK). Through independent experiments, scallops (Chlamys farreri) were fed for 9 days and mussels (Mytilus galloprovincialis) for 5 days plus an additional 5 days of depuration, with representative samples taken throughout. Several common PSTs (C1-4, GTX1-6 and NEO) and metabolites including M1, M3, M5, M7, M9, M2 and M8 were detected in the hepatopancreas of scallops during toxin accumulation and in the hepatopancreas of mussels during both toxin accumulation and elimination periods. The relative molar ratio of metabolites to precursor molecules was used to estimate relative metabolic conversion rates. Conversion rates of C1/2 and GTX2/3 were higher than those of C3/4 and GTX1/4, in scallops and mussels. The first metabolites observed in both bivalve species investigated were M1/3, which are formed from C1/2. However, the conversion of GTX2/3 to M2 was more complete than other biotransformation reactions in both mussels and scallops. In general, metabolic conversion of PSTs was observed after a shorter time and to a greater extent in mussels than in scallops in the exposure period. No acyl esters or conjugation products of PSTs with glucuronic acid, glutathione, cysteine and taurine were detected by liquid chromatography with high resolution tandem mass spectrometry in the samples investigated. Additionally, only GTX1/4 and GTX2/3 were detected in the kidney of scallops, which demonstrates that PSTs are mainly metabolized through the hepatic metabolism pathway in bivalves. This work improves the understanding of PST metabolism during toxin accumulation and depuration in commercially harvested shellfish.

Assessment of the biological quality of port areas: A case study on the three harbours of La Rochelle: The marina, the fishing harbour and the seaport

This work was designed to investigate biological impacts at 3 dates (day 0, day 7 and day 21) on black scallops (Mimachlamys varia) in the three ports areas of La Rochelle town in winter 2017. In order to assess the biological effects on the wild population of black scallops, bivalves were place in four different locations: in the three ports (semi-closed areas), and in a marshland uncontaminated site (closed area). Biomarkers of effects (heavy metals) and exposure (oxidative stress and immunological effects) were assessed in the digestive glands of specimens in order to compare two techniques of sampling: “pool” technique and “inter-subject” technique. Our findings reported in the both techniques show significant modulation of GST (detoxification), SOD (antioxidant response) and MDA (lipid peroxidation) in bivalves exposed to a specific contamination in each port. Laccase-type enzyme also highlighted an important aspect in terms of biomarker response of the immune function at the 7^th day of exposition. Overall, our study demonstrated that the “pool” technique using the same quality indicator M. varia could be used to obtain reliable results at lower costs. In contrast, in fundamental context, the “inter-subject” technique could bring more precise results to light. However, it requires burdensome and costly handling.

Time- and depth-wise trophic niche shifts in Antarctic benthos

Climate change is expected to affect resource-consumer interactions underlying stability in polar food webs. Polar benthic organisms have adapted to the marked seasonality characterising their habitats by concentrating foraging and reproductive activity in summer months, when inputs from sympagic and pelagic producers increase. While this enables the persistence of biodiverse food webs, the mechanisms underlying changes in resource use and nutrient transfer are poorly understood. Thus, our understanding of how temporal and spatial variations in the supply of resources may affect food web structure and functioning is limited. By means of C and N isotopic analyses of two key Antarctic benthic consumers (Adamussium colbecki, Bivalvia, and Sterechinus neumayeri, Echinoidea) and Bayesian mixing models, we describe changes in trophic niche and nutrient transfer across trophic levels associated with the long- and short-term diet and body size of specimens sampled in midsummer in both shallow and deep waters. Samplings occurred soon after the sea-ice broke up at Tethys Bay, an area characterised by extreme seasonality in sea-ice coverage and productivity in the Ross Sea. In the long term, the trophic niche was broader and variation between specimens was greater, with intermediate-size specimens generally consuming a higher number of resources than small and large specimens. The coupling of energy channels in the food web was consequently more direct than in the short term. Sediment and benthic algae were more frequently consumed in the long term, before the sea-ice broke up, while consumers specialised on sympagic algae and plankton in the short term. Regardless of the time scale, sympagic algae were more frequently consumed in shallow waters, while plankton was more frequently consumed in deep waters. Our results suggest a strong temporal relationship between resource availability and the trophic niche of benthic consumers in Antarctica. Potential climate-driven changes in the timing and quality of nutrient inputs may have profound implications for the structure of polar food webs and the persistence of their constituent species, which have adapted their trophic niches to a highly predictable schedule of resource inputs.

De novo assembly, gene annotation, and marker development using Illumina paired-end transcriptome sequencing in the Crassadoma gigantea

Crassadoma gigantea is an important commercial marine bivalve species in Baja California and Mexico. In this study, we have applied RNA-Seq technology to profile the transcriptome of the C. gigantea for the first time. A total of 80,832,518 raw reads were produced from a Illumina HiSeq4000 platform, and 77,306,198 (95.64%) clean reads were generated after trimming the adaptor sequences. The transcriptome assembled into 158,855 transcripts with an N50 size of 1995 bp and an average size of 1008 bp. A number of DNA repair related genes, such as MSH3, EGF, TGF, IGF, FGF, encoding different groups of growth factors were found in the transcriptome data of C. gigantean. In addition, immune related genes Toll-like receptor (TLR) including TLR1, TLR2, TLR3, TLR4, TLR5, TLR6, TLR7, TLR8, and TLR9 was also observed in C. gigantean. A set of 12 polymorphic microsatellite loci were firstly developed and characterized in C. gigantea. The results show that the number of alleles and expected heterozygosity ranged from 3 to 9 and from 0.254 to 0.820, respectively. The average polymorphic information content was 0.790. These microsatellite loci will facilitate future studies of population structure and conservation genetics in this species.