Coiled-coil scallops (Chlamys farreri) peptide hydrogel with metal ionic and temperature tunable assembly

Self-assembly of peptides is a powerful method of preparing nanostructured materials. Peptides frequently utilize charged groups as a convenient switch for controlling assembly state by pH, ionic strength or temperature. In this study, the molecular properties and gel-forming ability of Chlamys farreri protein hydrolysates were studied. According to self-assembled theory, the presence of isoleucine at position 'a' and leucine at 'd' causes a switch between coiled-coil structures. Compared to P-2-CG, the components of α-helix (23.60 ± 0.56%) were changed into β-sheet (4.83 ± 2.86%) in the secondary structure of the hydrogel induced by ZnCl2. NMR siginals appeared at high field,which indicated hydrogen bonds were formed between P-2-CG and solvent environments at 20 °C. With temperature going up, the hydrogen bonds were broken and nanofibrils were changed into dense aggregates. We expected that P-2-CG could provide a new candidate for preparing metal-induced nanofibers or hydrogels with further applications in food industry.

Unique structural characteristics and biological activities of heparan sulfate isolated from the mantle of the scallop Chlamys farreri

Marine animals are a huge resource of various glycosaminoglycans (GAGs) with specific structures and functions. A large number of byproducts, such as low-edible mantle, are produced during the processing of Chlamys farreri, which is one of the most cultured scallops in China. In this study, a major GAG component was isolated from the mantle of C. farreri, and its structural characteristics and biological activities were determined in detail. Preliminary analysis by agarose electrophoresis combined with specific enzymatic degradation evaluations showed that this component was heparan sulfate and was named CMHS. Further analysis by HPLC and NMR revealed that CMHS has an average molecular weight of 35.9 kDa and contains a high proportion (80%) of 6-O-sulfated N-acetyl-D-glucosamine/N-sulfated-D-glucosamine (6-O-sulfated GlcNAc/GlcNS) residues and rare 3-O-sulfated β-D-glucuronic acid residues. Bioactivity analysis showed that CMHS has much lower anticoagulant activity than heparin and it can interact with various growth factors with high affinity. Moreover, CMHS binds strongly to the morphogen Wnt 3a to inhibit glypican-3-stimulated Wnt 3a signaling. Thus, the identification of CMHS with unique structural and bioactive features will provide a promising candidate for the development of GAG-type pharmaceutical products and promote the high-value utilization of C. farreri mantle.

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.

Effects of Benzo[a]pyrene on Food Metabolism and Reproductive Endocrine and Ovarian Development in Female Scallop Chlamys farreri at Different Reproductive Stages

Benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon (PAH) with the most carcinogenic effects of all the PAHs, has multiple toxic effects on marine bivalves. We investigated the interference mechanism of B[a]P on food metabolism (sugars, proteins, and sugars), and on reproductive endocrine and ovarian development in female scallops (Chlamys farreri). Scallops were exposed to different concentrations of B[a]P concentrations of 0, 0.38, 3.8, and 38 μg/L throughout gonadal development. Total cholesterol and triglyceride contents in the digestive glands were increased, and their synthesis genes were upregulated. The plasma glucose contents decreased with the inhibition of glycogen synthesis genes and the induction of glycolysis genes in the digestive gland. The results showed that B[a]P had endocrine-disrupting effects on scallops, that it negatively affected genes related to ovarian cell proliferation, sex differentiation, and egg development, and that it caused damage to ovarian tissue. Our findings supplement the information on B[a]P disruption in gonadal development of marine bivalves. Environ Toxicol Chem 2024;00:1-14. © 2023 SETAC.

Insights into mechanism of DNA damage and repair-apoptosis in digestive gland of female scallop Chlamys farreri under benzo[a]pyrene exposure during reproductive stage

As one of the most carcinogenic persistent organic pollutants (POPs), benzo[a]pyrene (B [a]P) brings high toxicity to marine bivalves. Digestive gland is the most important metabolism-related organ of aquatic animals. This study conducted the digestive gland transcriptome of Chlamys farreri under B[a]P treatment at reproductive stages. And the reproductive-stage dependence metabolism-DNA repair-apoptosis process of scallops under 0, 0.04, 0.4 and 4 μg/L B[a]P was studied by qRT-PCR. The results demonstrated that the detoxification metabolism was disturbed after ovulation except for CYP3A4. In antioxidant system, antioxidant enzyme CAT and GPX, and GGT1 (one of the non-enzymatic antioxidants synthesis gene) continuously served the function of antioxidant defense. Three types of DNA repair were activated under B[a]P stress, however, DNA strand breaks were still serious. B[a]P exposure weakened death receptor pathway as well as enhanced mitochondrial pathway, surprisingly suppressing apoptosis in scallops. In addition, ten indicators were screened by Spearman correlation analysis. This study will provide sound theoretical basis for bivalve toxicology and contribute to the biomonitoring of marine POPs pollution.

Potential pathway and mechanisms underlining the immunotoxicity of benzo[a]pyrene to Chlamys farreri

The long-distance migration of polycyclic aromatic hydrocarbons (PAHs) promotes their release into the marine environment, posing a serious threat to marine life. Studies have shown that PAHs have significant immunotoxicity effects on bivalves, but the exact mechanism of immunotoxicity remains unclear. This paper aims to investigate the effects of exposure to 0.4, 2, and 10 μg/L of benzo(a)pyrene (B[a]P) on the immunity of Chlamys farreri under environmental conditions, as well as the potential molecular mechanism. Multiple biomarkers, including phagocytosis rate, metabolites, neurotoxicity, oxidative stress, DNA damage, and apoptosis, were adopted to assess these effects. After exposure to 0.4, 2, and 10 μg/L B[a]P, obvious concentration-dependent immunotoxicity was observed, indicated by a decrease in the hemocyte index (total hemocyte count, phagocytosis rate, antibacterial and bacteriolytic activity). Analysis of the detoxification metabolic system in C. farreri revealed that B[a]P produced B[a]P-7,8-diol-9,10-epoxide (BPDE) through metabolism, which led to an increase in the expression of protein tyrosine kinase (PTK). In addition, the increased content of neurotransmitters (including acetylcholine, γ -aminobutyric acid, enkephalin, norepinephrine, dopamine, and serotonin) and related receptors implied that B[a]P might affect immunity through neuroendocrine system. The changes in signal pathway factors involved in immune regulation indicated that B[a]P interfered with Ca2+ and cAMP signal transduction via the BPDE-PTK pathway or neuroendocrine pathway, resulting in immunosuppression. Additionally, B[a]P induced the increase in reactive oxygen species (ROS) content and DNA damage, as well as an upregulation of key genes in the mitochondrial pathway and death receptor pathway, leading to the increase of apoptosis rate. Taken together, this study comprehensively investigated the detoxification metabolic system, neuroendocrine system, and cell apoptosis to explore the toxic mechanism of bivalves under B[a]P stress.

Identification and characterization of gonadotropin-releasing hormone (GnRH) in Zhikong scallop Chlamys farreri during gonadal development

Gonadotropin-releasing hormone (GnRH) controls synthesis of sex steroid hormones through hypothalamic-pituitary-gonadal (HPG) axis in vertebrates. But in mollusks, research on neuroendocrine control of gonadal function, such as the function of GnRH during gonadal development is limited. In this study, we investigated the morphology and structure of the nerve ganglia of Zhikong scallop Chlamys farreri by physiological and histological observations. We also cloned the ORF and studied the expression patterns of GnRH in the scallop. Tissue expression analysis showed that GnRH was highly expressed in parietovisceral ganglion (PVG). The in situ hybridization result further confirmed that GnRH mRNA only distributed in some good-sized neurons in the posterior lobe (PL) and some pint-sized neurons in the lateral lobe (LL). In addition, by examining the expression of GnRH during gonadal development in ganglia, we found GnRH displayed higher expression in the female scallops, and showed significant high expression at the growing stage of female scallops in PVG. This study would contribute to gaining insight into the mechanism underlying reproduction regulation by GnRH in the scallop and help to provide a better understanding of reproductive neuroendocrine in mollusks.

Study of DNA methylation of hsd17β, er and reproductive endocrine disrupting effects in female Chlamys farreri under benzo[a]pyrene stress

Benzo[a]pyrene (B[a]P) is one kind of persistent organic pollutants (POPs) in the marine environment which has multiple toxic effects. However, epigenetic studies correlated with reproductive endocrine disruption in invertebrates have not been explored. In our study, Chlamys farreri in the mature stage were exposed to B[a]P (0, 0.4, 2 and 10 μg/L) for 5 and 10 d to explore the effects on reproductive endocrine and DNA methylation. The results proved that B[a]P stress significantly restrained the growth of mature oocytes, reduced the content of sex hormones, and affected the expression of genes related to ovarian development. Histological observation showed that the ovarian microstructure was damaged. The detection of SAM/SAH, dnmts, GNMT in the ovary showed that the level of global DNA methylation fluctuated. Significant hypermethylation of the hsd17β promoter region in the ovary was associated with a significant downregulation of its gene expression. In summary, our results suggested that exposure to B[a]P might affect DNA methylation to regulate key reproductive genes, interfere with the synthesis of sex hormones, and inhibit ovarian development. These findings provide a basis for a better understanding of how epigenetic mechanisms are involved in the response of marine invertebrates to POPs stress, opening up new avenues for incorporating environmental epigenetic approaches into marine invertebrate management and conservation plans.

A novel TBK1/IKKϵ is involved in immune response and interacts with MyD88 and MAVS in the scallop Chlamys farreri

Inhibitor of κB kinase (IKK) family proteins are key signaling molecules in the animal innate immune system and are considered master regulators of inflammation and innate immunity that act by controlling the activation of transcription factors such as NF-κB. However, few functional studies on IKK in invertebrates have been conducted, especially in marine mollusks. In this study, we cloned the IKK gene in the Zhikong scallop Chlamys farreri and named it CfIKK3. CfIKK3 encodes a 773-amino acid-long protein, and phylogenetic analysis showed that CfIKK3 belongs to the invertebrate TBK1/IKKϵ protein family. Quantitative real-time PCR analysis showed that CfIKK3 mRNA is ubiquitously expressed in all tested scallop tissues. The expression of CfIKK3 transcripts was significantly induced after challenge with lipopolysaccharide, peptidoglycan, or poly(I:C). Co-immunoprecipitation (co-IP) assays confirmed the direct interaction of CfIKK3 with MyD88 (the key adaptor in the TLR pathway) and MAVS (the key adaptor in the RLR pathway), suggesting that this IKK protein plays a crucial role in scallop innate immune signal transduction. In addition, the CfIKK3 protein formed homodimers and bound to CfIKK2, which may be a key step in the activation of its own and downstream transcription factors. Finally, in HEK293T cells, dual-luciferase reporter gene experiments showed that overexpression of CfIKK3 protein activated the NF-κB reporter gene in a dose-dependent manner. In conclusion, our experimental results confirmed that CfIKK3 could respond to PAMPs challenge and participate in scallop TLR and RLR pathway signaling, ultimately activating NF-κB. Therefore, as a key signaling molecule and modulator of immune activity, CfIKK3 plays an important role in the innate immune system of scallops.

CfIRF8-like interacts with the TBK1/IKKε family protein and regulates host antiviral innate immunity

The interferon regulatory factor (IRF) family, a class of transcription factors with key functions, are important in host innate immune defense and stress response. However, further research is required to determine the functions of IRFs in invertebrates. In this study, the coding sequence of an IRF gene was obtained from the Zhikong scallop (Chlamys farreri) and named CfIRF8-like. The open reading frame of CfIRF8-like was 1371 bp long and encoded 456 amino acids. Protein domain prediction revealed a typical IRF domain in the N-terminus of the CfIRF8-like protein and a typical IRF3 domain in the C-terminus. Multiple sequence alignment confirmed the conservation of the amino acid sequences of these two functional protein domains. Phylogenetic analysis showed that CfIRF8-like clustered with mollusk IRF8 proteins and then clustered with vertebrate IRF3, IRF4, and IRF5 subfamily proteins. Quantitative real-time PCR detected CfIRF8-like mRNA in all tested scallop tissues, with the highest expression in the gills. Simultaneously, the expression of CfIRF8-like transcripts in gills was significantly induced by polyinosinic-polycytidylic acid challenge. The results of protein interaction experiments showed that CfIRF8-like could directly bind the TBK1/IKKε family protein of scallop (CfIKK2) via its N-terminal IRF domain, revealing the presence of an ancient functional TBK1/IKKε-IRF signaling axis in scallops. Finally, dual-luciferase reporter assay results showed that the overexpression of CfIRF8-like in human embryonic kidney 293T cells could specifically activate the interferon β promoter of mammals and the interferon-stimulated response element promoter in dose-dependent manners. The findings of this preliminary analysis of the signal transduction and immune functions of scallop CfIRF8-like protein lay a foundation for an in-depth understanding of the innate immune function of invertebrate IRFs and the development of comparative immunology. The experimental results also provide theoretical support for the breeding of scallop disease-resistant strains.

Analyzing toxicological effects of AsIII and AsV to Chlamys farreri by integrating transcriptomic and metabolomic approaches

Inorganic arsenic (iAs) is a widespread contaminant in marine environments, which is present in two different oxidation states (arsenate (AsV) and arsenite (AsIII)) that have complex toxic effects on marine organisms. The scallop Chlamys farreri (C. farreri) accumulates high levels of As and is a suitable bioindicator of As. In this report, we integrated transcriptomics and metabolomics to investigate genetic and metabolite changes and functional physiological disturbances in C. farreri exposured to inorganic arsenic. Physiological indicators antioxidant factors and cell apoptosis analysis macroscopically corroborated the toxic effects of inorganic arsenic revealed by omics results. Toxic effects of inorganic arsenic on C. farreri were signaling-mediated, causing interference with a variety of cell growth and small molecule metabolism. The results provide evidence that inorganic arsenic disrupts the physiological functions of bivalves, highlighting the correlations between different metabolic pathways and providing new insights into the toxic effects of environmental pollutants on marine organisms.

Use of GAL4 factor-based yeast assay to quantify the effects of xenobiotics on RXR homodimer and RXR/PPAR heterodimer in scallop Chlamys farreri

Retinoid X receptor (RXR) and peroxisome proliferators-activated receptors (PPAR) have been shown as important targets of endocrine disrupting effects caused by organotin compounds (OTCs). In vitro methods for non-model species are instrumental in revealing not only mechanism of toxicity but also basic biology. In the present study, we constructed the GAL4 factor-based recombinant yeast systems of RXRα/RXRα (RR), RXRα/PPARα (RPα) and RXRα/PPARγ (RPγ) of the scallop Chlamys farreri to investigate their transcriptional activity under the induction of OTCs (tributyltin chloride, triphenyltin chloride, tripropyltin chloride and bis(tributyltin)oxide), their spiked sediments and five other non‑tin compounds (Wy14643, rosiglitazone, benzyl butyl phthalate, dicyclohexyl phthalate and bis(2-ethylhexyl) phthalate). The results showed that the natural ligand of RXR, 9-cis-retinoic acid (9cRA), induces transcriptional activity in all three systems, while four OTCs induced the transcriptional activity of the RR and RPα systems. None of the five potential non‑tin endocrine disruptors induced effects on the RPα and RPγ systems. The spiked sediment experiment demonstrated the feasibility of the recombinant yeast systems constructed in this study for environmental sample detection. These results suggest that OTCs pose a threat to affect function of RXRα and PPARα of bivalve mollusks. The newly developed GAL4 factor-based yeast two-hybrid system can be used as a valuable tool for identification and quantification of compounds active in disturbing RXR and PPAR of bivalves.

A preliminary report of exploration of the exosomal shuttle protein in marine invertebrate Chlamys farreri

Exosomes are extracellular vesicles secreted by diverse cell under normal or abnormal physiological conditions, which could carry a range of bioactive molecules and play significant roles in biological processes, such as intercellular communication and immune response. In the current study, a preliminary study was performed to investigate the exosomal shuttle protein in Chlamys farreri (designated as CfesPro) and to predict the potential function of exosomes in scallop innate immunity. The serum derived exosomes (designated as CfEVs) were obtained from lipopolysaccharide (LPS)-stimulated C. farreri and untreated ones. After confirmation and characterization by transmission electron microscopy (TEM), nano-HPLC-MS/MS spectrometry was performed on CfEVs using a label-free quantitative method. Totally 2481 exosomal shuttle proteins were identified in CfEVs proteomic data, which included many innate immune related proteins. GO and KOG functional annotation showed that CfesPro participated in cellular processes, metabolism reactions, signaling transductions, immune responses and so on. Moreover, 1421 proteins in CfesPro were enriched to 324 pathways by KEGG analysis, including several immune-related pathways, such as autophagy, apoptosis and lysosome pathway. Meanwhile, eight autophagy-related proteins were initially identified in CfesPro, indicating that CfEVs had a potential role with autophagy. All these findings showed that CfEVs were involved in C. farreri innate immune defenses. This research would enrich the protein database of marine exosomes and provide a basis for the exploration of immune defense systems in marine invertebrates.

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.

Effects of benzo[a]pyrene exposure on oxidative stress and apoptosis of gill cells of Chlamys farreri in vitro

As a common pollutant in marine environment, benzo[a]pyrene (B[a]P) has high toxicity to economic shellfish. In order to explore the mechanism of oxidative stress and apoptosis, the effects of 0, 2, 4, 8 μg/mL B[a]P on gill cells of C. farreri at 12 and 24 h were studied. The results showed that B[a]P decreased the activity of gill cells, increased the content of reactive oxygen species (ROS) and the expression of antioxidant defense genes. Besides, B[a]P could induce oxidative damage to nucleus and mitochondria. The gene expression and enzyme activity of apoptosis pathway related factors were changed. In conclusion, these results showed that B[a]P could cause oxidative stress and oxidative damage in gill cells of C. farreri, and mediate gill cell apoptosis through mitochondrial pathway and death receptor pathway. This article provides a theoretical basis for clarifying the molecular mechanism of PAHs-included oxidative stress and apoptosis in bivalves.

Reproductive toxicity induced by benzo[a]pyrene exposure: first exploration highlighting the multi-stage molecular mechanism in female scallop Chlamys farreri

Reproductive toxicity induced by benzo[a]pyrene (B[a]P) exposure has received great ecotoxicological concerns. However, huge gaps on the molecular mechanism still exist in bivalves. In this study, reproduction-related indicators were investigated in female scallops Chlamys farreri during life cycle of proliferative, growth, mature, and spawn stages, under gradient concentrations of B[a]P at 0, 0.04, 0.4, and 4 μg/L. Meanwhile, a multi-stage ovarian transcriptome analysis under 4 μg/L B[a]P exposure was also conducted to elucidate the potential molecular mechanisms. The results indicated that life-cycle exposure to 0.4 and 4 μg/L B[a]P significantly decreased GSI and sex steroid levels. Even 0.04 μg/L B[a]P could play the adverse role in DNA integrity at the mature and spawn stages. Ovarian histological sections showed that B[a]P inhibited the maturation and release of oocytes. Through the functional enrichment analysis of differentially expressed genes (DEGs) from transcriptome data, 18 genes involved in endocrine disruption effects, DNA damage and repair, and oogenesis were selected and further determined by qRT-PCR. The downregulation of genes involved in steroidogenic and estrogen signaling pathways indicated that B[a]P could cause endocrine disruption through both receptor-dependent and receptor-independent pathways. The variations of gene expressions involved in DNA single-strand break and repair implied the presence of toxic mechanisms similar with vertebrates. Additionally, the changes of gene expressions of cell cycle, apoptosis, and cell adhesion suggested that exposure to B[a]P possibly caused the reproductive toxicity effects by affecting oogenesis. Taken together, this study was a pioneer in combining genome-wide transcriptomic analysis with its corresponding reproductive indicators (GSI, sex steroid levels, DNA single-strand break, and histological sections) to explore the bivalves' toxic mechanisms under B[a]P exposure. Meanwhile, some genes involved in estrogen signaling pathway and DNA damage were firstly analyzed in bivalves, and the expression data might be useful in establishing new hypotheses and discovering new biomarkers for marine biomonitoring.

Immunotoxicity pathway and mechanism of benzo[a]pyrene on hemocytes of Chlamys farreri in vitro

Benzo[a]pyrene (B[a]P), a typical PAHs widely existing in the marine environment, has been extensively studied for its immunotoxicity due to its persistence and high toxicity. Nevertheless, the immunotoxicity mechanism remain incompletely understood. In this study, isolated hemocytes of Chlamys farreri were exposed at three concentrations of B[a]P (5, 10 and 15 μg/mL), and the effects of B[a]P on detoxification metabolism, signal transduction, humoral immune factors, exocytosis and phagocytosis relevant proteins and immune function at 0, 6, 12, 24 h were studied. Results illustrated the AhR, ARNT and CYP1A1 were significantly induced by B[a]P at 12 h. Additionally, the content of B[a]P metabolite BPDE increased in a dose-dependent manner with pollutants. Under B[a]P stimulation, the expressions of PTK (Src, Fyn) and PLC-Ca²⁺-PKC pathway gene increased significantly, while the transcription level of AC-cAMP-PKA pathway gene decreased remarkably. Additionally, the expressions of nuclear transcription factors (CREB, NF-κB), complement system genes and C-type lectin genes up-regulated obviously. The gene expressions of phagocytosis and exocytosis related proteins were also notably affected. 5 μg/mL B[a]P could promote phagocytosis in a transitory time, but with the increase of exposure time and concentration of B[a]P, the phagocytosis, antibacterial and bacteriolytic activities gradually decreased. These results indicated that similar to vertebrates, BPDE, the metabolite of B[a]P, mediated downstream signal transduction via PTK in bivalves. The declined of the immune defense ability of hemocytes might be closely related to the inhibition of AC-cAMP-PKA pathway and the imbalance of intracellular Ca²⁺ pathway. In addition, the results manifested that complement and lectin systems play a significant role in regulating immune response. In this study, the direct relationship between detoxification metabolism and immune signal transduction in bivalves under B[a]P stress was demonstrated for the first time, which provided important information for the potential molecular mechanism of B[a]P-induced immune system disorder in bivalves.

Insights into disruption of lipid metabolism in digestive gland of female scallop Chlamys farreri under B[a]P exposure

Lipids are the main energy support during gametogenesis. Digestive gland is the key organ of aquatic animal metabolism for storing nutrition and supplying energy. It participates in a variety of life activities (such as growth, digestion, immunity, and reproduction). Nutrients stored in digestive glands, especially lipids, provide energy for reproductive behaviors such as gametogenesis and ovulation. A large number of studies have confirmed the accumulation of lipids from digestive gland to gonad during gametogenesis. At present, the research on the interference mechanism of persistent organic pollutants (POPs) on lipid metabolism of aquatic animals and the adaptive response of aquatic animals to POPs stress focus on biochemical levels or a few genes. The potential molecular mechanism of lipid metabolism interference needs to be further studied. In addition, as an important stage of aquatic animals, the reproductive period is a vigorous period of lipid metabolism. However, at present, there is no report on the molecular mechanism of POPs interfering with the lipid metabolism of the digestive gland in the reproductive process of aquatic animals. In this study, female scallop C. farreri was cultured in natural seawater and exposed to 4 μg/L B[a]P in seawater. Transcriptome analysis of digestive glands at multiple stages (proliferative stage, growth stage, mature stage and spawn stage) was performed, and iPath pathway analysis was used to analyze lipid metabolism pathways and differential genes. The interference mechanism of lipid metabolism in bivalves during reproductive period was revealed. This study will provide valuable genomic information on the role of digestive glands in lipid metabolism and reproduction of C. farreri, and will contribute to further functional genomics of bivalves and other closely related species.

Molecular allocation of PC4s provides implications for deciphering thermal response in Zhikong scallop (Chlamys farreri)

The increasing sea temperature caused by global warming has led to serious death of Zhikong scallop (Chlamys farreri) and improving its thermal tolerance has become an active research area in scallop aquaculture industry. Gene transcriptional coactivator p15 (PC4) plays pivotally multi-faced roles in most vertebrates and some invertebrates, but the systematic identification and characterization of PC4 genes have less been reported in scallops. In this study, 15 PC4 genes (CfPC4s) were identified in Zhikong scallop through whole-genome scanning, including two pairs of tandem duplicate genes located in the same scaffold (CF-19495.9 and CF-19495.10, CF-6819.1 and CF-6819.2). Protein structural and phylogenetic analyses were performed to verify identities and evolutionary relationships of these genes. Spatiotemporal expression patterns were determined at different development stages and in healthy adult tissues, as well as expression regulations in selected tissues (mantles, gills, hemocytes and hearts) after high temperatures challenge (27 °C) with different durations (3 h, 6 h, 12 h, 24 h, 3 d, 6 d, 15 d and 30 d). Spatiotemporal expressions of CfPC4s were ubiquitous but exhibited different patterns, suggesting the functional roles of CfPC4s in all stages of growth and development of the scallop. Expression regulations of CfPC4s and their functional related factors (TFIIA, TFIID, TFIIH and RNAPII) in pre-initiation complex (PIC) in various tissues displayed up- and/or down-regulated responses at different time points, showing time- and/or tissue-dependent expression patterns with function allocation upon different thermal durations. Collectively, this study demonstrated that gene allocation of CfPC4s provided implications for deciphering thermal response in Zhikong scallop and potentially helped in developing strategies for long-term healthy sustainable Zhikong scallop culture.

Potencies of organotin compounds in scallop RXRa responsive activity with a GAL4-based reconstituted yeast assay in vitro

Retinoid X receptor (RXR) has been found to be a major target in various processes of endocrine disruption from the exposure to organotin compounds (OTCs), including imposex in gastropod mollusks. It was also reported in bivalves that OTCs caused intersex and skewed sex ratio. In order to evaluate the effect of these ligand-like OTCs, we constructed a reconstituted yeast system (CfRE system) based on GAL4 yeast two-hybrid principle using scallop Chlamys farreri retinoid X receptor (CfRXRa) and retinoid X response element (RXRE) to investigate the ligand-induced transactivation of CfRXRa. Responses of CfRXRa to 9-cis retinoic acid (9cRA) and tested four OTCs showed concentration-dependent response which is comparable with reported RXRa in vitro assay of human and gastropods. The detective limits of the CfRE system were found to be 100 nM for 9cRA and 10-1000 nM for the tested OTCs. While the tested non-Sn endocrine disrupting chemicals, including Benzo[a]pyrene, 2,4-Dichlorophenol, Nonylphenol, and Tetrabromobisphenol A, showed no effect on CfRXRa response. The present assay system may provide a valuable tool for screening assessments of unidentified environmental ligand chemicals on bivalve mollusks. It is also useful for comparison of sensitivity differences among species exposed to EDCs.

Exacerbation of copper pollution toxicity from ocean acidification: A comparative analysis of two bivalve species with distinct sensitivities

In estuarine ecosystems, bivalves experience large pH fluctuations caused by the anthropogenic elevation of atmospheric CO₂ and Cu pollution. This study investigates whether Cu toxicity increases indiscriminately in two bivalve species from different estuarine habitats as a result of elevated Cu bioaccumulation in acidified seawater. This was carried out by evaluating the effects of Cu exposure on two bivalve species (clams and scallops) for 28 d, at a series of gradient pH levels (pH 8.1, 7.8, and 7.6). The results demonstrated an increase in the Cu content in the soft tissues of clams and scallops in acidified seawater. Cu toxicity increased under acidified seawater by affecting the molecular pathways, physiological function, biochemical responses, and health status of clams and scallops. An iTRAQ-based quantitative proteomic analysis showed increased protein turnover, disturbed cytoskeleton and signal transduction pathways, apoptosis, and suppressed energy metabolism pathways in the clams and scallops under joint exposure to ocean acidification and Cu. The integrated biomarker response results suggested that scallops were more sensitive to Cu toxicity and/or ocean acidification than clams. The proteomic results suggested that the increased energy metabolism and suppressed protein turnover rates may contribute to a higher resistivity to ocean acidification in clams than scallops. Overall, this study provides molecular insights into the distinct sensitivities between two bivalve species from different habitats under exposure to ocean acidification and/or Cu. The findings emphasize the aggravating impact of ocean acidification on Cu toxicity in clams and scallops. The results show that ocean acidification and copper pollution may reduce the long-term viability of clams and scallops, and lead to the degradation of estuarine ecosystems.

Screening and Identification of Transcription Factors Potentially Regulating Foxl2 Expression in Chlamys farreri Ovary

Foxl2 is an evolutionarily conserved female sex gene, which is specifically expressed in the ovary and mainly involved in oogenesis and ovarian function maintenance. However, little is known about the mechanism that regulates Foxl2 specific expression during the ovary development. In the present study, we constructed the gonadal yeast one-hybrid (Y1H) library of Chlamysfarreri with ovaries and testes at different developmental stages using the Gateway technology. The library capacity was more than 1.36 × 10⁷ CFU, and the length of the inserted fragment was 0.75 Kb~2 Kb, which fully met the demand of yeast library screening. The highly transcriptional activity promoter sequence of C. farreri Foxl2 (Cf-Foxl2) was determined at -1000~-616 bp by dual-luciferase reporter (DLR) assay and was used as bait to screen possible transcription factors from the Y1H library. Eleven candidate factors, including five unannotated factors, were selected based on Y1H as well as their expressional differences between ovaries and testes and were verified for the first time to be involved in the transcriptional regulation of Cf-Foxl2 by RT-qPCR and DLR. Our findings provided valuable data for further studying the specific regulation mechanism of Foxl2 in the ovary.

The mechanism of apoptosis of Chlamys farreri hemocytes under benzopyrene stress in vitro

Hemocytes are critical to the immune defense system of bivalves, and polycyclic aromatic hydrocarbons (PAHs) can mediate the immunity of bivalves by affecting the apoptosis of hemocytes. However, the underlying mechanism is still unclear. Chlamys farreri, as an important economic bivalve, was selected as the research subject for this experimentation. The hemocytes were exposed to typical PAHs-benzopyrene (B[a]P) in vitro to explore the apoptosis mechanism through detecting oxidative stress and oxidative damage-related indicators, apoptosis pathway factors, and apoptosis rate within 24 h. The results showed that the reactive oxygen species (ROS) and benzo[a]pyrene-7,8-diol-9,10-epoxide (BPDE) content in hemocytes increased significantly under B[a]P exposure, while antioxidant genes, glutathione peroxidase content and total antioxidant capacity all showed a trend of first rising and subsequent falling. B[a]P also caused serious damage to DNA and lysosomal membrane stability. The proapoptotic factors genes in the mitochondrial apoptosis pathway were significantly up-regulated, and the anti-apoptotic gene Bcl-2 was significantly down-regulated. Besides, mitochondrial membrane potential stability was significantly reduced and caspase 9 enzyme activity was significantly improved with the B[a]P stimulation. The factors of death receptor pathway were also significantly up-regulated by B[a]P. Moreover, the expression levels of Mitogen-Activated Protein Kinases were also induced. The gene expression and enzyme activity of the caspase 3 and the apoptosis rate were significantly increased under B[a]P exposure. In conclusion, these results indicated that ROS was induced by B[a]P, and further triggered the oxidative stress and oxidative damage in hemocytes. B[a]P induced hemocyte apoptosis was mediated by both mitochondrial apoptosis pathway and death receptor apoptosis, and the activation of mitochondrial apoptosis pathway was affected by ROS. In addition, BPDE and MAPKs may play important roles in the B[a]P-mediated apoptosis pathway. This study deepens understanding of the apoptosis pathway and the immunotoxicity mechanism in bivalves hemocytes stimulated by persistent organic pollutants.

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.

Identification and Characterization of HSP90 Gene Family Reveals Involvement of HSP90, GRP94 and Not TRAP1 in Heat Stress Response in Chlamys farreri

Heat shock proteins 90 (HSP90s) are a class of ubiquitous, highly conserved, and multi-functional molecular chaperones present in all living organisms. They assist protein folding processes to form functional proteins. In the present study, three HSP90 genes, CfHSP90, CfGRP94 and CfTRAP1, were successfully identified in the genome of Chlamys farreri. The length of CfHSP90, CfGRP94 and CfTRAP1 were 7211 bp, 26,457 bp, and 28,699 bp, each containing an open reading frame (ORF) of 2181 bp, 2397 bp, and 2181 bp, and encoding proteins of 726, 798, and 726 amino acids, respectively. A transcriptomic database demonstrated that CfHSP90 and CfGRP94 were the primary functional executors with high expression during larval development and in adult tissues, while CfTRAP1 expression was low. Furthermore, all of the three CfHSP90s showed higher expression in gonads and ganglia as compared with other tissues, which indicated their probable involvement in gametogenesis and nerve signal transmission in C. farreri. In addition, under heat stress, the expressions of CfHSP90 and CfGRP94 were significantly up-regulated in the mantle, gill, and blood, but not in the heart. Nevertheless, the expression of CfTRAP1 did not change significantly in the four tested tissues. Taken together, in coping with heat stress, CfHSP90 and CfGRP94 could help correct protein folding or salvage damaged proteins for cell homeostasis in C. farreri. Collectively, a comprehensive analysis of CfHSP90s in C. farreri was conducted. The study indicates the functional diversity of CfHSP90s in growth, development, and environmental response, and our findings may have implications for the subsequent in-depth exploration of HSP90s in invertebrates.

Damages to biological macromolecules in gonadal subcellular fractions of scallop Chlamys farreri following benzo[a]pyrene exposure: Contribution to inhibiting gonadal development and reducing fertility

Benzo[a]pyrene (B[a]P), a representative polycyclic aromatic hydrocarbon (PAH) compound in marine ecosystem, has great potential for chronic toxicity to marine animals. It is becoming increasingly apparent that reproductive system is the major target of B[a]P, but the adverse effects of B[a]P on subcellular fractions in bivalve gonads have not been elucidated. Scallops Chlamys farreri are used as the experimental species since they are sensitive to environmental pollutants. This study was conducted to investigate how B[a]P affected the gonadal subcellular fractions, including plasma membrane, nucleus, mitochondria and microsome in scallops, and whether subcellular damages were related to reproductive toxicity. The results showed that mature gametes' counts were significantly decreased in B[a]P-treated scallops. Three biological macromolecules (viz., DNA, lipids and proteins) in gonadal subcellular fractions obtained by differential centrifugation suffered damages, including DNA damage, lipid peroxidation and protein carbonylation in B[a]P treatment groups. Interestingly, mitochondria and microsome were more vulnerable to lipid peroxidation and protein carbonylation than plasma membrane and nucleus, meanwhile males were more susceptible to DNA damage than females under B[a]P exposure. In addition, histological analysis showed that B[a]P delayed gonadal development in C. farreri. To summarize, our results indicated that B[a]P caused damages to biological macromolecules in gonadal subcellular fractions and then induced damages to gonadal tissues of C. farreri, which further inhibited gonadal development and ultimately leaded to reduction in fertility. This study firstly reports the impacts of PAHs on subcellular fractions in bivalves and their relationship with reproductive toxicity. Moreover, exposure of reproductive scallops to B[a]P leads to defects in reproduction, raising concerns on the possible long-term consequences of PAHs for natural populations of bivalves.

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.

Bioaccumulation and biotransformation of inorganic arsenic in zhikong scallop (Chlamys farreri) after waterborne exposure

Arsenic (As) and As speciation in marine bivalves have been widely investigated. However, little is known about the bioaccumulation and biotransformation of inorganic As in different tissues of scallops. Therefore, the tissue-specific accumulation, biotransformation and subcellular partitioning of As were investigated in Chlamys farreri following 12 d inorganic As [arsenite (AsⅢ) and arsenate (AsⅤ)] exposure and 30 d depuration. Total As levels were highest in the kidneys and lowest in the adductor muscle after 12 d exposure for both As (Ⅲ) and As (Ⅴ) treatment groups, and the bioavailability of As (Ⅲ) was significantly higher than that of As (Ⅴ) for C. farreri. After 30 d elimination, total As levels were significantly decreased to the control levels. The subcellular fate of As in five different tissues was similar for different inorganic As treatment groups. The greatest proportion of As was found in the metallothionein-like protein fraction (MTLP) and the second was the cellular debris (CD). A little part of As (Ⅲ) could be oxidized to As (Ⅴ) in the gill and digestive gland for As (Ⅲ) treatment groups, and the reduction of As (Ⅴ) to As (Ⅲ) happened in the gill and kidney under As (Ⅴ) exposure. Although a high methylation activity was found in C. farreri, it varied in different tissues with different inorganic As species exposure. The present results indicated that exposure to As (Ⅲ) and As (Ⅴ) could induce different responses in bioaccumulation and biotransformation in five tissues of C. farreri.

Identification, Characterization, and Expression Analysis Reveal Diverse Regulated Roles of Three MAPK Genes in Chlamys farreri Under Heat Stress

Mitogen-activated protein kinase (MAPK) cascades are fundamental signal transduction modules in all eukaryotic organisms, participating growth and development, as well as stress response. In the present study, three MAPK genes were successfully identified from the genome of Chlamys farreri, respectively, named CfERK1/2, CfJNK, and Cfp38, and only one copy of ERK, JNK, and p38 were detected. Domain analysis indicated that CfMAPKs possessed the typical domains, including S_TKc, Pkinase, and PKc_like domain. Phylogenetic analysis showed that three CfMAPKs of MAPK subfamilies exists in the common ancestor of vertebrates and invertebrates. All CfMAPKs specifically expressed during larval development and in adult tissues, and the expression level of CfERK1/2 and Cfp38 was apparently higher than that of CfJNK. Under heat stress, the expression of CfERK1/2 and Cfp38 were significantly downregulated and then upregulated in four tissues, while the expression of CfJNK increased in all tissues; these different expression patterns suggested a different molecular mechanism of CfMAPKs for bivalves to adapt to temperature changes. The diversity of CfMAPKs and their specific expression patterns provide valuable information for better understanding of the functions of MAPK cascades 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.

Tissue-Biased and Species-Specific Regulation of Glutathione Peroxidase (GPx) Genes in Scallops Exposed to Toxic Dinoflagellates

Marine bivalves could accumulate paralytic shellfish toxins (PSTs) produced by toxic microalgae, which might induce oxidative stress. Glutathione peroxidases (GPxs) are key enzymes functioning in the antioxidant defense, whereas our understanding of their roles in PST challenge in bivalves is limited. Herein, through genome-wide screening, we identified nine (CfGPx) and eight (PyGPx) GPx genes in Zhikong scallop (Chlamys farreri) and Yesso scallop (Patinopecten yessoensis), respectively, and revealed the expansion of GPx3 sub-family in both species. RNA-Seq analysis revealed high expression of scallop GPx3s after D stage larva during early development, and in adult hepatopancreas. However, in scallops exposed to PST-producing dinoflagellates, no GPx was significantly induced in the hepatopancreas. In scallop kidneys where PSTs were transformed to higher toxic analogs, most CfGPxs were up-regulated, with CfGPx3s being acutely and chronically induced by Alexandrium minutum and A. catenella exposure, respectively, but only one PyGPx from GPx3 subfamily was up-regulated by A. catenella exposure. Our results suggest the function of scallop GPxs in protecting kidneys against the oxidative stresses by PST accumulation or transformation. The tissue-, species-, and toxin-dependent expression pattern of scallop GPxs also implied their functional diversity in response to toxin exposure.

Temporal transcriptome analysis in female scallop Chlamys farreri: First molecular insights into the disturbing mechanism on lipid metabolism of reproductive-stage dependence under benzo[a]pyrene exposure

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widespread persistent organic pollutants (POPs) in marine environment. Benzo[a]pyrene (B[a]P), the most toxic carcinogen of PAHs, is widely studied as a representative that interferes with lipid metabolism. However, the underlying molecular mechanisms of lipid metabolism by B[a]P interference towards bivalve, one of the marine-pollution bio-indicators have not been elucidated yet, especially during gonadal development which is closely associated with lipids. In this study, female scallops Chlamys farreri were cultured with natural and 4 μg/L B[a]P exposed seawater, respectively, and a multi-stage (proliferative, growth, mature, and spawn stage) ovarian transcriptome profiling was performed to decipher the reproductive stage-dependence disturbing mechanisms on lipid metabolism caused by B[a]P in bivalves. The results revealed the potential molecular mechanism of B[a]P-induced triglycerides (TGs) accumulation, which probably resulted from the collaboration of promoting synthesis and inhibiting metabolization of TGs, notably, this mechanism also occurred at spawn stage. Correspondingly, B[a]P and TGs contents measured in ovary offered direct biochemical evidences for the interference effects and stage-dependent accumulation patterns of B[a]P. Moreover, the gene expressions of fatty acids synthesis related enzymes were down-regulated cooperatively, illustrating the molecular compensatory mechanism that reduced susceptibility from oxidative damage. And these results further emphasized the important role of prostaglandins (PGs) in immune response mediated by arachidonic acid metabolism. In addition, this study explored the underlying molecular mechanism affected by B[a]P on sterol metabolism, which possibly posed a threat to normal reproductive functions in bivalves. Taken together, our findings filled the gap of the stage-dependent interference molecular mechanisms on lipid metabolism behind bivalves, and provided a new perspective for investigating the adaptive mechanisms of bivalves under POPs stress.

Benzo[a]pyrene exposure disrupts steroidogenesis and impairs spermatogenesis in diverse reproductive stages of male scallop (Chlamys farreri)

Benzo[a]pyrene (BaP), a model compound of polycyclic aromatic hydrocarbon known to impair reproductive functions of vertebrates, while the data is scarce in marine invertebrates. To investigate the toxic effects of BaP on invertebrates reproduction, we exposed male scallop (Chlamys farreri) to BaP (0, 0.38 and 3.8 μg/L) throughout three stages of reproductive cycle (early gametogenesis stage, late gametogenesis stage and ripe stage). The results demonstrated that BaP decreased the gonadosomatic index and mature sperms counts in a dose-dependent manner. Significant changes in sex hormones contents and increased 17β-estradiol/testosterone ratio suggested that BaP produced the estrogenic endocrine effects in male scallops. In support of this view, we confirmed that BaP significantly altered transcripts of genes along the upstream PKA and PKC mediated signaling pathway like fshr, lhcgr, adcy, PKA, PKC, PLC and NR5A2. Subsequently, the expressions of genes encoding downstream steroidogenic enzymes (e.g., 3β-HSD, CYP17 and 17β-HSD) were impacted, which corresponded well with hormonal alterations. In addition, BaP suppressed transcriptions of spermatogenesis-related genes, including ccnd2, SCP3, NRF1 and AQP9. Due to different functional demands, these transcript profiles involved in spermatogenesis exhibited a stage-specific expression pattern. Furthermore, histopathological analysis determined that BaP significantly inhibited testicular development and maturation in male scallops. Overall, the present findings indicated that, playing as an estrogenic-like chemical, BaP could disrupt the steroidogenesis pathway, impair spermatogenesis and caused histological damages, thereby inducing reproductive toxicities with dose- and stage-specific effects in male scallops. And the adverse outcomes might threaten the stability of bivalve populations and destroy the function of marine ecosystems in the long term.

Study on the AhR signaling pathway and phase II detoxification metabolic enzymes isoforms in scallop Chlamys farreri exposed to single and mixtures of PAHs

This study aimed to investigate the detoxification metabolism responses in scallop Chlamys farreri exposed to phenanthrene (PHE), chrysene (CHR), benzo[a]pyrene (B[a]P) and PHE + CHR + B[a]P for 15 days under laboratory conditions. The mRNA expression levels of AhR signaling pathway (AhR, HSP90, XAP2 and ARNT), detoxification system (phase I: CYP1A1 and CYP1B1; phase II: SULTs, UGT and GSTs) and ATP-binding cassette transporters (phase 0: ABCB1 and phase III: ABCC1, ABCG2) in digestive glands of scallops exposed to PHE (0.7, 2.1 μg/L), CHR (0.7, 2.1 μg/L), B[a]P (0.7, 2.1 μg/L), and PHE + CHR + B[a]P (0.7 + 0.7 +0.7, 2.1 + 2.1 + 2.1 μg/L) were detected. In present study, key genes (AhR, HSP90, XAP2 and ARNT) of the AhR signaling pathway can be significantly induced by pollutants, suggesting that the AhR/ARNT signaling pathway plays a role directly or indirectly. AhR, HSP90 and ARNT reached the maximum value on day 6, which can be preliminarily understood as the synchronization of their functions. Besides, the results also indicated that different genes had specific response to different pollution exposure. CYP1B1, GST-2, GST-omega and GST-microsomal could be potional indexes to PHE, ARNT, GST-sigma 2 and GST-3 were sensitive to CHR exposure, HSP90, GST-theta and ABCG2 were considered as potional indexes to BaP while CYP1A1 and UGT were possible to be indexes for monitoring the mix exposure of these three PAHs. These findings in C. farreri suggested that phase II detoxification metabolic enzymes isoforms played an essential role in detoxification mechanisms and mRNA expression levels of specific SULTs, UGTs and GSTs were potentially to be ideal indexes in PAHs pollution research. In summary, this study provides more valuable information for the risk assessments of different rings of PAHs.

Distribution patterns of microplastics in various tissues of the Zhikong scallop (Chlamys farreri) and in the surrounding culture seawater

Microplastics have adverse effects on marine organisms. However, there are limited data on microplastics distribution patterns in various tissues of marine organisms. Microplastics in seawater and nine types of tissues of the Zhikong scallop (Chlamys farreri) from three coastal aquaculture areas were analysed. The results showed that in seawater, microplastics were mainly fibrous. There were no significant differences in microplastics abundance among the three areas. The concentrations of microplastics in the scallop anus, intestinal tract and kidney were substantially higher than those in the other tissues. Microplastics abundance ranged from 8 to 13 particles per scallop. Microplastics colours were mainly black, transparent and blue, and there were no significant tissue distribution patterns. Microplastics size ranged from 5 μm to 1 mm. The microplastics abundance in the haemolymph was significantly correlated with those of the surrounding seawater. Additional study is necessary to determine the toxic effects of microplastics on marine organisms.

Characterizing transcriptome in female scallop Chlamys farreri provides new insights into the molecular mechanisms of reproductive regulation during ovarian development and spawn

Bivalve mollusks are descendants of an early-Cambrian lineage and have successfully evolved unique strategies for reproduction. Nonetheless, the molecular mechanisms underlying reproductive regulation in mollusks remain to be elucidated. In this study, transcriptomes of ovary at four reproductive stages in female Chlamys farreri were characterized by RNA-Seq. Regarding signaling pathways, ECM-receptor interaction pathway, mTOR signaling pathway, Fanconi anemia pathway, FoxO signaling pathway, Wnt signaling pathway and Hedgehog signaling pathway were enriched during ovarian development processes. In addition, pathways related to energy metabolism such as Nitrogen metabolism and Arachidonic acid metabolism were enriched at spawn stage. Interestingly, Neuroactive ligand-receptor interaction was significantly enriched involved in ovarian development and spawn, and indicated the potential functions of nervous system on reproductive regulation in C. farreri. What's more, this study identified and characterized fourteen genes involved in "sex hormones synthesis and regulation", "ovarian development and spawn" and "maternal immunity" during the four reproductive stages in C. farreri. We determined that CYP17 uniquely affected gamete release by influencing the physiological balance among the steroid hormones and showed that receptors of the 5-HT and GABA neurotransmitters were tightly associated with ovarian maturation. Furthermore, to the best of our knowledge, this is the first study to report the maternal effect gene Zar1 in bivalve mollusks, likewise the maternal immunity genes displayed coordinated and cooperative expression during reproductive periods, which strengthened the environmental adaptation mechanisms of bivalves. Taken together, this study provides the first dynamic transcriptomic analysis of C. farreri at four key reproductive stages, which will assist in revealing the molecular mechanisms underlying bivalves on reproductive regulation in ovarian development and spawn.

Benzo[a]pyrene exposure induced reproductive endocrine-disrupting effects via the steroidogenic pathway and estrogen signaling pathway in female scallop Chlamys farreri

Benzo[a]pyrene (B[a]P), as one of the typical polycyclic aromatic hydrocarbons and environmental contaminants, may cause endocrine disrupting effects and reproductive impairments in bivalves. However, the molecular mechanisms are still not fully understood. In this study, three reproductive stages (proliferative stage, growing stage and mature stage) of female scallops Chlamys farreri were exposed to B[a]P at 0, 0.38 and 3.8 μg/L. The present study determined the adverse effects of B[a]P on gonadosomatic index, circulating hormone concentrations, endocrine-associated gene expression and ovarian histology. Significant decrease in sex hormones including progesterone (P), testosterone (T) and 17β-estradiol (E2), was observed in B[a]P-treated C. farreri at growing stage and mature stage. These effects were associated with down-regulated expression of steroidogenic enzymes, including 3β-HSD, CYP17 and 17β-HSD, which were regulated by the upstream adenylate cyclase (Adcy) - protein kinase (PKA) signaling pathway. Ovarian transcript levels of estrogen receptor (ER) and caveolin-1 (cav-1) were decreased in B[a]P-treated C. farreri. Vitellogenin (Vtg), an estrogen-mediated gene involved in ovarian development, was down-regulated by B[a]P. Furthermore, ovarian histology was investigated to clarify the impairment of B[a]P on ovaries at growing stage and mature stage. Overall, the present results elucidated the anti-estrogenic mechanisms along the steroidogenic pathway and estrogen signaling pathway for the stage-dependent endocrine-disrupting effects of B[a]P. This finding provides important information regarding to the underlying molecular mechanisms of B[a]P-induced endocrine disruption in different reproductive stages of bivalves. In addition, the adverse effects should be taken into concertation during protection of bivalves germplasm resources and comprehensive evaluation of ecological risks.

The mechanism of Mitogen-Activated Protein Kinases to mediate apoptosis and immunotoxicity induced by Benzo[a]pyrene on hemocytes of scallop Chlamys farreri in vitro

Benzo [a]pyrene (B [a]P) has received widespread attention for serious pollution in the sea, which may reduce immunity and lead to the outbreak of disease in bivalves. However, the mechanism of immunotoxicity induced by B [a]P in bivalves was still unclear. Previous studies have found that Mitogen-Activated Protein Kinases (MAPKs) including three classic pathways (ERK, p38 and JNK) play an important role in mediating this process. Thus, in order to explore the mechanism of immunotoxicity induced by B [a]P in scallop Chlamys farreri, hemocytes were treated with PD98059 (ERK inhibitor), SB203580 (p38 inhibitor) and SP600125 (JNK inhibitor) for 1 h and then incubation with B [a]P for 24 h at 1 μg/mL. Indexes including oxidative damage, apoptotic rate, and immune indicators were detected in the present study. The results showed that the increase of Reactive Oxygen Species (ROS) and DNA damage induced by B [a]P was inhibited with PD98059 and SB203580. Besides, lysosomal membrane stability (LMS) damage was promoted by PD98059, while it was opposite when treated with SB203580. Moreover, the ascended apoptosis rate induced by B [a]P was increased significantly after treatment with PD98059, but it was remarkably attenuated by SB203580 and SP600125. However, the opposite pattern was showed in phagocytosis compared with apoptosis rate in all of three inhibitors. In addition, antibacterial activity and bacteriolytic activity were enhanced by SB203580 while inhibited by PD98059. Therefore, these results showed that MAPKs directly or indirectly mediate the decrease of oxidative damage, apoptosis and immune defense ability of C. farreri hemocytes, which suggesting ERK/p38/JNK pathways have different functions in the apoptosis and immunity of C. farreri hemocytes after B [a]P exposure. In conclusion, this study intended to enrich the theoretical basis for immunotoxicology of bivalves exposed to pollutants.

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.

[Carbon dioxide fluxes at the water-air interface and the main influencing factors from diffe-rent aquaculture systems of Sebastes schlegelii and Chlamys farreri]

The static chamber-gas chromatography method was applied to observe CO₂ fluxes across the water-air interface from different aquaculture systems, including four groups of mesocosms, i.e., blank control system (CK), monoculture system of Sebastes schlegelii (F), monoculture system of Chlamys farreri (B) and polyculture system of S. schlegelii and C. farreri (FB). Meanwhile, the physical, chemical and biological indices of the water were measured. The results showed that the group CK was a stable CO₂ source, with the mean flux of 12.42 mg·m^-2·h^-1. The group B was a CO₂ source during the early and middle periods of the experiment and a CO₂ sink at the end of the experiment, with the mean flux during the experiment being 10.95 mg·m^-2·h^-1. The change trends of CO₂ flux in the group F and FB were generally consistent, acting as CO₂ sources in the early period and as CO₂ sinks subsequently. The mean fluxes of those two groups during the expe-riment were -3.53 and -10.49 mg·m^-2·h^-1, respectively. Water pH was a good predictor for CO₂ flux across the water-air interface according to the result of regression analysis, with pH value of 8.25 as the critical threshold between efflux and influx. The net primary production of water column was the main factor influencing the CO₂ flux, indicating that phytoplankton might be the main internal force regulating the CO₂ flux across the water-air interface. Our results indicated that C. farreri at present stocking density in the polyculture system could promote phytoplankton biomass as well as primary production and therefore enhance the CO₂ sink function.

Integrative Biomarker Assessment of the Influence of Saxitoxin on Marine Bivalves: A Comparative Study of the Two Bivalve Species Oysters, Crassostrea gigas, and Scallops, Chlamys farreri

Harmful algae blooms have expanded greatly in recent decades, and their secreted toxins pose a severe threat to human health and marine ecosystems. Saxitoxin (STX) is a main paralytic shellfish poison naturally produced by marine microalgae of the genus Alexandrium. Despite numerous studies have assessed the impacts of STX on marine bivalves, comparative in vivo study on the toxicity of STX on bivalves with distinct accumulation ability (such as oysters and scallops) has been seldom investigated. The aim of this study was to identify whether distinct sensitivity exists between oysters, Crassostrea gigas, and scallops, Chlamys farreri under the same amount of STX exposure using multiple biomarker responses. The responses of different biochemical markers including oxidative stress markers (catalase, superoxide dismutase, glutathione S-transferase, and lipid peroxidation) and immunotoxicity biomarkers (hemocyte phagocytosis rate, reactive oxidative species production, and DNA damages) were evaluated in bivalves after 12, 48, and 96 h of exposure to STX. The integrated biomarker responses value combined with two-way ANOVA analysis suggested that STX posed slightly severer stress on scallops than oysters for the extended period of time. This study provided preliminary results on the usefulness of a multi-biomarker approach to assess the toxicity associated with STX exposure in marine bivalves.

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.

Expression characteristics and functional analysis of Krüppel-like factor 4 in adductor muscle and mantle of Zhikong scallop Chlamys farreri

Krüppel-like factor 4 (KLF4) is an important transcription factor involving in formation and maintenance of muscles in mammals. However, no data are available on KLF4 function in shellfish muscles which play vital roles in the movement, stress response, and physiology in shellfish. In the present study, we revealed that the Klf4 mRNA of Zhikong scallop Chlamys farreri was expressed in most tissues, which has high level in adductor muscle, mantle, kidney, and testis. Positive signals of the Klf4 mRNA and protein were visible in all skeletal muscle fibers of adductor muscle, and all the cells of C. farreri mantle. Furthermore, the knockdown of Klf4 mRNA in adductor muscle and mantle by means of in vivo RNA interference led to some different phenotypes, including disordered arrangement of muscle fibers in adductor muscle and mantle, abnormal structures of skeletal muscles, and reduced muscle fibers under endepidermis of mantle. Our findings demonstrated that Klf4 plays important roles in maintenance of muscle functions in C. farreri adductor muscle and mantle, and suggested that its regulatory way in skeletal muscle may be different from the smooth muscle in shellfish.

The various components implied the diversified Toll-like receptor (TLR) signaling pathway in mollusk Chlamys farreri

Toll-like receptor (TLR) signaling pathway, composed of various components, plays pivotal roles in host innate immune defense mechanism. In the present study, twenty-nine TLR signaling pathway components, including receptors, adaptors, transduction molecules and immune effectors, were identified in Zhikong scallop Chlamys farreri via assembling and screening public available transcriptomic data and expression sequence tags (ESTs). These identified TLR signaling pathway components were constitutively expressed and detectable in various tissues, and almost all of them were highly expressed in gill and hepatopancreas. These results indicated the presence of TLR signaling pathways in both MyD88-dependent and MyD88-independent forms in scallop, and implied the diversified TLR signaling pathway in mollusk C. farreri.

Effect of Ball Mill Treatment on the Physicochemical Properties and Digestibility of Protein Extracts Generated from Scallops (Chlamys farreri)

The effects of ball mill treatment (0, 2, 4, 6, 8, and 10 min) on the physicochemical and digestible properties of scallops (Chlamys farreri) protein (CFP) were investigated. The CFP particle size decreased with increasing ball-milling time. The content of free sulfhydryl (SH) of CFP increased from 13.08 ± 0.25 μmol/g protein to 18.85 ± 0.24 μmol/g protein when the ball-milling time increased from 0 min to 10 min. A sharp increase of the surface hydrophobicity index (H₀) from 48.53 ± 0.27 to 239.59 ± 0.37 was found when the ball-milling time increased from 0 min to 4 min. Furthermore, the foaming capacity increased from 46.08 ± 6.12% to 65.11 ± 1.05% with increasing ball-milling time from 0 min to 6 min, after which it reached a plateau. SDS-PAGE results showed that ball mill treatment did not change the primary structure of CFP. Digestible properties of BMCFP simulated gastrointestinal digestion as a function of ball mill treatment were analyzed by Tricine-SDS-PAGE and nitrogen recovery index. After 60 min of simulated human gastro digestion, nitrogen recovery index of CFP had a significant rise from 42.01 ± 0.31% to 58.78 ± 3.37% as the ball-milling time increased from 0 min to 6 min. Peptides from hydrolysates of Chlamys farreri protein (CFP) were identified by ultraperformance liquidchromatographysystem coupled to a Synapt Mass Quadrupole Time-of-Flight Mass Spectrometer (UPLC-Q-TOF-MS). After 2 h and 4 h of simulated human duodenal digestion, the number of peptides with 7–10 amino acids length increased apparently with the ball-milling time increased. This study presents an approach to investigating the effect of the ball-milling process on the physicochemical and digestible properties of CFP, which may provide valuable information on the application of CFP as an ingredient in food products.

Application of activated carbon to accelerate detoxification of paralytic shellfish toxins from mussels Mytilus galloprovincialis and scallops Chlamys farreri

Contamination of economic bivalves with paralytic shellfish toxins (PST) occurs frequently in many parts of the world, which potentially threatens consumer health and the marine aquaculture economy. It is the objective of this study to develop a suitable technology for accelerating detoxification of PST from shellfish using activated carbon (AC). The adsorption efficiency of PST by eight different AC materials and by different particle sizes of wood-based AC (WAC) were tested and compared. Then WAC particles (37-48µm) were fed to mussels Mytilus galloprovincialis and scallops Chlamys farreri previously contaminated with PST through feeding with dinoflagellate Alexandrium tamarense ATHK. Results showed that the maximum adsorption ratio (65%) of PST was obtained by WAC. No significant differences in adsorption ratios were found between different particle sizes of WAC. The toxicity of mussels decreased by 41% and 68% after detoxification with WAC for 1 d and 3 d, respectively. Meanwhile, the detoxification ratio of mussels was approximately 3 times higher than that of scallops. This study suggests that the WAC could be used to accelerate the detoxification of PST by shellfish.

A mitochondrial manganese superoxide dismutase involved in innate immunity is essential for the survival of Chlamys farreri

Superoxide dismutase (SOD) ubiquitously found in both prokaryotes and eukaryotes functions as the first and essential enzyme in the antioxidant system. In the present study, a manganese SOD (designated as CfmtMnSOD) was cloned from Zhikong scallop Chlamys farreri. The complete cDNA sequence of CfmtMnSOD contained a 681 bp open reading frame (ORF), encoding a peptide of 226 amino acids. A SOD_Fe_N domain and a SOD_Fe_C domain were found in the deduced amino acid sequence of CfmtMnSOD. The mRNA transcripts of CfmtMnSOD were constitutively expressed in all the tested tissues, including gill, gonad, hepatopancreas, hemocytes, mantle and muscle, with the highest expression level in hemocytes. After the stimulation of Vibrio splendidus, Staphylococcus aureus and Yarrowia lipolytica, the mRNA transcripts of CfmtMnSOD in hemocytes all significantly increased. The purified rCfmtMnSOD protein exhibited Mn²⁺ dependent specific and low stable enzymatic activities. After Vibrio challenge, the cumulative mortality of CfmtMnSOD-suppressed scallops was significantly higher than those of control groups and the semi-lethal time for CfmtMnSOD-suppressed scallops was rather shorter than those of control groups either. Moreover, the final mortality rate of CfmtMnSOD-suppressed group was significant higher than those of control groups, even without Vibrio challenge. All these results indicated that CfmtMnSOD was efficient antioxidant enzyme involved in the innate immunity, and also essential for the survival of C. farreri.

The first CUB-domain containing serine protease from Chlamys farreri which might be involved in larval development and immune response

Serine proteases (SPs) are one of the most well understood enzyme families, which play an important role in regulating many physiological events. In the present study, one CUB-domain containing serine protease was identified from Chlamys farreri (designated as CfCUBSP). The full-length cDNA of CfCUBSP was of 3181 bp with an open reading frame of 2688 bp encoding a polypeptide of 896 amino acids. CfCUBSP shared closer phylogenetic relationship with those multi-domain SPs which consisted of one SP domain, and different numbers of CUB domain and LDLa domain than other SPs. The mRNA transcripts of CfCUBSP were detected in all developmental stages with the highest expression level in fertilized eggs and the lowest in trochophore larvae. In adult scallop, the CfCUBSP mRNA could be detected in all examined tissues with the highest level in hepatopancreas, and CfCUBSP protein was dominantly located in the gills, hepatopancreas, gonad and kidney. The mRNA expression of CfCUBSP in hemocytes was significantly up-regulated after the stimulation of lipopolysaccharide (LPS), peptidoglycan (PGN) and β-glucan (GLU) (P < 0.05). All the results collectively indicated that CfCUBSP was a primitive member of the invertebrate SPs which might be involved in larval development and immune response against Gram-negative (G-) and Gram-positive (G+) bacteria and fungus in scallop.

Primary culture of Zhikong scallop Chlamys farreri hemocytes as an in vitro model for studying host-pathogen interactions

Primary cultured cells can be a useful tool in studies on physiology, virology, and toxicology. Hemocytes play an important role in animal rapid response to pathogen invasion. In this study, an appropriate medium for primary culture of hemocytes of the bivalve Chlamys farreri was developed by adding 5% fetal bovine serum and 1% C. farreri serum to Leibovitz L-15 medium. These primary cultured hemocytes were maintained for more than 40 d in vitro and were classified into 3 types: (1) granulocytes containing numerous granules in the cytoplasm, (2) hyalinocytes with no or few granules, (3) a small percentage of macrophage-like cells. Furthermore, the primary cultured hemocytes were observed to be sensitive to bacterial and viral challenges. These hemocytes could phagocytose the bacterium Vibrio anguillarum, and presented cytopathic effects on the extracellular products (ECPs) of V. anguillarum; the mRNA level of QM, which plays an important role in immune response, also significantly increased 12 h after infection. When these hemocytes were challenged with ostreid herpesvirus 1 (OsHV-1), virus particles and empty capsids in the cells infected for 48 h were observed by transmission electron microscopy, and the QM mRNA level increased significantly at 12 h and 24 h following OsHV-1 challenge. This primary culture system is available for C. farreri hemocytes which can be used in the future to study host-pathogen interactions.

Piwi1 is essential for gametogenesis in mollusk Chlamys farreri

Piwi (P-element induced wimpy testis) is an important gene involved in stem cell maintenance and gametogenesis in vertebrates. However, in most invertebrates, especially mollusks, the function of Piwi during gametogenesis remains largely unclear. To further understand the function of Piwi during gametogenesis, full-length cDNA of Piwi1 from scallop Chlamys farreri (Cf-Piwi1) was characterized, which consisted of a 2,637 bp open reading frame encoding an 878-amino acid protein. Cf-Piwi1 mRNA was mainly localized in the spermatogonia, spermatocytes, oogonia, oocytes of early development and intra-gonadal somatic cells. Additionally, the knockdown of Cf-Piwi1 by injection of Cf-Piwi1-dsRNA (double-stranded RNA) into scallop adductor led to a loss of germ cells in C. farreri gonads. Apoptosis was observed mainly in spermatocytes and oocytes of early development, as well as in a small number of spermatogonia and oogonia. Our findings indicate that Cf-Piwi1 is essential for gametogenesis in the scallop C. farreri.