Calcium-mediated regulation of recombinant hybrids of full-length Physarum myosin heavy chain with Physarum/scallop myosin light chains

Physarum myosin is a Ca(2+)-binding protein and its activity is inhibited by Ca(2+) In the present study, to clarify the light chains (LCs) from the different species (Physarum and scallop) and to determine the specific Ca(2+)-regulated effects, we constructed hybrid myosins with a Physarum myosin heavy chain (Ph·HC) and Physarum and/or scallop myosin LCs, and examined Ca(2+)-mediated regulation of ATPases and motor activities. In these experiments, it was found that Ca(2+) inhibited motilities and ATPase activities of Physarum hybrid myosin with scallop regulatory light chain (ScRLC) and Physarum essential light chain (PhELC) but could not inhibit those of the Physarum hybrid myosin mutant Ph·HC/ScRLC/PhELC-3A which lacks Ca(2+)-binding ability, indicating that PhELC plays a critical role in Ca(2+)-mediated regulation of Physarum myosin. Furthermore, the effects of Ca(2+) on ATPase activities of Physarum myosin constructs are in the following order: Ph·HC/PhRLC/PhELC > Ph·HC/ScRLC/PhELC > Ph·HC/PhRLC/ScELC > Ph·HC/ScRLC/ScELC, suggesting that the presence of PhRLC and PhELC leads to the greatest Ca(2+) sensitivity of Physarum myosin. Although we did not observe the motilities of Physarum hybrid myosin Ph·HC/PhRLC/ScELC and Ph·HC/ScRLC/ScELC, our results suggest that Ca(2+)-binding to the PhELC may alter the flexibility of the regulatory domain and induce a 'closed' state, which may consequently prevent full activity and force generation.

Toxic effects upon exposure to polycyclic aromatic hydrocarbon (chrysene) in scallop Chlamys farreri during the reproduction period

This study aims to investigate potential toxic effects of chrysene (CHR) on mature scallop Chlamys farreri during the reproduction period, using indicators of antioxidant defences and oxidative stress. Scallops were exposed to 0.2, 0.8 and 3.2μg/L waterborne CHR for 21 days, at day 10 scallops were induced to spawn. At days 1, 3, 6, 10, 11, 15 and 21, aryl hydrocarbon hydroxylase (AHH), 7-ethoxyresorufin-O-deethylase (EROD), glutathione-s-transferase (GST), glutathione (GSH), superoxide dismutase (SOD), lipid peroxidation (LPO), protein carbonyl (PC) and DNA strand breaks in digestive glands were examined by separately analysing male and female scallops. During the pre-spawn period, Levels of enzymatic activities and oxidative stress were all induced by the exposure to CHR for females and males. GST activity presented a good time- and dose-dependent relationship only in males, and GSH content showed a dose-dependent manner in both sexes. During the post-spawn period, different trends were observed, while PC contents maintained growth in time- and dose-dependent manner. Overall, males were more sensitive than females to CHR exposure in enzyme activities, and correspondingly, females suffered from more serious oxidative damages. Both GSH and PC contents seemed to be potential biomarkers for PAH exposure. These results will offer the information on toxicity of CHR in this species, and ensure the influence of gender and reproductive status on PAH detoxification metabolism.

Molecular characterization of an inhibitor of NF-κB in the scallop Argopecten purpuratus: First insights into its role on antimicrobial peptide regulation in a mollusk

Inhibitors of nuclear factor kappa B (IκBs) are major control components of the Rel/NF-κB signaling pathway, a key regulator in the modulation of the expression of immune-related genes in vertebrates and invertebrates. The activation of the Rel/NF-κB signaling pathway depends largely in the degradation of IκB proteins and thus, IκBs are a main target for the identification of genes whose expression is controlled by Rel/NF-κB pathway. In order to identify such regulation in bivalve mollusks, the cDNA sequence encoding an IκB protein was characterized in the scallop Argopecten purpuratus, ApIκB. The cDNA sequence of ApIκB is comprised of 1480 nucleotides with a 1086 bp open reading frame encoding for 362 amino acids. Bioinformatics analysis showed that ApIκB displays the conserved features of IκB proteins. The deduced amino acid sequence consists of a 39.7 kDa protein, which has an N-terminal degradation motif, six ankyrin repeats and a C-terminal phosphorylation site motif. Phylogenetic analysis revealed a high degree of identity between ApIκB and other IκBs from mollusks, but also to arthropod cactus proteins and vertebrate IκBs. Tissue expression analysis indicated that ApIκB is expressed in all examined tissues and it is upregulated in circulating hemocytes from scallops challenged with the pathogenic Gram-negative bacterium Vibrio splendidus. After inhibiting ApIκB gene expression using the RNA interference technology, the gene expression of the antimicrobial peptide big defensin was upregulated in hemocytes from non-challenged scallops. Results suggest that ApIκB may control the expression of antimicrobial effectors such as big defensin via a putative Rel/NF-κB signaling pathway. This first evidence will help to deepen the knowledge of the Rel/NF-κB conserved pathway in scallops.

Short-Term and Long-Term Biological Effects of Chronic Chemical Contamination on Natural Populations of a Marine Bivalve

Understanding the effects of chronic chemical contamination on natural populations of marine organisms is complex due to the combined effects of different types of pollutants and environmental parameters that can modulate the physiological responses to stress. Here, we present the effects of a chronic contamination in a marine bivalve by combining multiple approaches that provide information on individual and population health. We sampled variegated scallops (Mimachlamys varia) at sites characterized by different contaminants and contamination levels to study the short and long-term (intergenerational) responses of this species to physiological stress. We used biomarkers (SOD, MDA, GST, laccase, citrate synthase and phosphatases) as indicators of oxidative stress, immune system alteration, mitochondrial respiration and general metabolism, and measured population genetic diversity at each site. In parallel, concentration of 14 trace metals and 45 organic contaminants (PAHs, PCBs, pesticides) in tissues were measured. Scallops were collected outside and during their reproductive season to investigate temporal variability in contaminant and biomarker levels. Our analyses revealed that the levels of two biomarkers (Laccase-type phenoloxidase and malondialdehyde) were significantly correlated with Cd concentration. Additionally, we observed significant seasonal differences for four of the five biomarkers, which is likely due to the scallop reproductive status at time of sampling. As a source of concern, a location that was identified as a reference site on the basis of inorganic contaminant levels presented the same level of some persistent organic pollutants (DDT and its metabolites) than more impacted sites. Finally, potential long-term effects of heavy metal contamination were observed for variegated scallops as genetic diversity was depressed in the most polluted sites.

Differential immune response of vitellogenin gene to Vibrio anguillarum in noble scallop Chlamys nobilis and its correlation with total carotenoid content

Vitellogenin (Vg), an egg yolk precursor protein, not only functions as a source of nutrients and a nonpolar molecular carrier that combine and transfer lipids, proteins, vitamin and carotenoids to oocytes during the oogenesis. but also links with the immune defense in many oviparous animals. To investigate whether Vg plays a immune defensive role in noble scallop Chlamys nobilis, an acute Vibrio anguillarum infection experiment was conducted in orange and brown scallops with different carotenoids content. qRT-PCR result showed that Vg transcripts were significantly up-regulated after challenge with V. anguillarum in orange and brown shell scallops compared to the control group and Vg expression reached the highest spot at 6 h, indicated that Vg possessed an immune function in the noble scallop. Interestingly, a significantly positive correlation between Vg transcript levels and total carotenoids content in the ovary was observed, indicating that Vg gene expression was up regulated by carotenoids. The results suggest that Vg is a potent immune protector and carotenoid may linked with Vg plays an important role in host immune system against pathogens in noble scallop C. nobilis.

In vitro study of the effect of metabolism enzymes on benzo(a)pyrene-induced DNA damage in the scallop Chlamys farreri

Acute toxicity effect of benzo(a)pyrene (BaP) on isolated scallop (Chlamys farreri) digestive gland cells was studied and a dose-dependent increase in toxicity was observed. The 8 μg/L of BaP had a significant toxic effect on isolated cells (p<0.05). In order to study the mechanism of CYP450, GST, SOD and MXR transporters involved in the production of DNA strand breakage such as DNA adduct formation and oxidative DNA damage by BaP were investigated in isolated digestive gland cells. Isolated cells were exposed in vitro to 0.8 μg/L of BaP for 24h in the dark at 25 °C in the absence or presence of cytochrome P450 inhibitor, GST inhibitor, Pgp inhibitor and antioxidant enzyme inhibitor. DNA adduct and 8-OHdG content were measured using the Enzyme-linked Immunosorbent Assay. The result indicated that DNA strand breakage was increased to 2 times compared with the control in the 0.8 μg/L of BaP treatment groups. The BaP-induced DNA adduct and 8-OHdG content increased significantly by inhibiting GST, while only 8-OHdG increased significantly when SOD was inhibited. The content of DNA adduct and 8-OHdG had no significant change when CYP450 was inhibited, while it decreased significantly when MXR transporters were inhibited. The result proved that GST play a key role in eliminating the BaP-induced DNA adduct and 8-OHdG, and SOD also had an important function in reducing the production of BaP-induced 8-OHdG.

Genome-wide identification and characterization of TRAF genes in the Yesso scallop (Patinopecten yessoensis) and their distinct expression patterns in response to bacterial challenge

The tumor necrosis factor (TNF) receptor associated factors (TRAFs) are the major signal transducers for the TNF receptor superfamily and the interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) superfamily, which regulate a variety of cellular activities and innate immune responses. TRAF genes have been extensively studied in various species, including vertebrates and invertebrates. However, as one of the key component of NF-κB pathway, TRAF genes have not been systematically characterized in marine invertebrates. In this study, we identified and characterized five TRAF genes, PyTRAF2, PyTRAF3, PyTRAF4, PyTRAF6 and PyTRAF7, in the Yesso scallop (Patinopecten yessoensis). Phylogenetic and protein structural analyses were conducted to determine their identities and evolutionary relationships. In comparison with the TRAF genes from vertebrate species, the structural features were all relatively conserved in the PyTRAF genes. To gain insights into the roles of TRAF genes during scallop innate immune responses, quantitative real-time PCR was used to investigate the expression profiles in the different stages of scallop development, in the healthy adult tissues, and in the hemocytes after bacterial infection with Micrococcus luteus and Vibrio anguillarum. Based on the qRT-PCR analysis, the expression of most of the PyTRAFs was significantly induced in the acute phases (3-6 h) after infection with Gram-positive (M. luteus) and Gram-negative (V. anguillarum) bacteria, and many more dramatic changes in PyTRAFs expression were observed after V. anguillarum challenge. Notably, the strong response in the up-regulation of PyTRAF6 post-bacterial challenge was distinct from that previously reported in scallops and crabs but was similar to that of other shellfish, Echinodermata and even teleost fish. The high level expressions of PyTRAFs in the hemocytes and the gill, and their specific expression patterns after challenges provide insights into the versatile roles and responses of TRAFs in the innate immune system against Gram-negative bacterial pathogens in bivalves.

The immunomodulation of nicotinic acetylcholine receptor subunits in Zhikong scallop Chlamys farreri

Nicotinic acetylcholine receptor (nAChR), the best-studied ionotropic neuron receptor protein, is a key player in neuronal communication, and it has been reported to play an important role in immunomodulation of vertebrates. Although nAChRs have also been identified in most invertebrates, the knowledge about their immunomodulation is still limited. In the present study, two scallop nAChR genes were identified from Chlamys farreri (designed as CfnAChR1 and CfnAChR2), which encoded 384 and 443 amino acids, respectively. The conserved disulfide-linked cystines, ion selectivity residues and the hydrophobic gating residues (L251, V255 and V259) were identified in CfnAChR1 and CfnAChR2. The immunoreactivities of CfnAChR1 and CfnAChR2 were observed in all the tested scallop tissues, including adductor muscle, mantle, gill, hepatopancreas, kidney and gonad. After LPS (0.5 mg mL(-1)) stimulation, the expression of CfnAChR1 mRNA in haemocytes increased significantly by 9.83-fold (P < 0.05) and 12.93-fold (P < 0.05) at 3 h and 24 h, respectively. While the expression level of CfnAChR2 mRNA increased 43.94% at 12 h after LPS stimulation (P < 0.05). After TNF-α (50 ng mL(-1)) stimulation, the expression levels of CfnAChR1 and CfnAChR2 both increased significantly at 1 h, which were 21.33-fold (P < 0.05) and 2.44-fold (P < 0.05) of that in the PBS group, respectively. The results collectively indicated that the cholinergic nervous system in scallops could be activated by immune stimulations through CfnAChR1 and CfnAChR2, which function as the links between the cholinergic nervous system and immune system.

Mantle Branch-Specific RNA Sequences of Moon Scallop Amusium pleuronectes to Identify Shell Color-Associated Genes

Amusium pleuronectes (Linnaeus) that secretes red- and white-colored valves in two branches of mantle tissues is an excellent model for shell color research. High-throughput transcriptome sequencing and profiling were applied in this project to reveal the detailed molecular mechanism of this phenotype differentiation. In this study, 50,796,780 and 54,361,178 clean reads were generated from the left branch (secreting red valve, RS) and right branch (secreting white valve, WS) using the Illumina Hiseq 2000 platform. De novo assembly generated 149,375 and 176,652 unigenes with an average length of 764 bp and 698 bp in RS and WS, respectively. Kyoto encyclopedia of genes and genomes (KEGG) metabolic pathway analysis indicated that the differentially expressed genes were involved in 228 signaling pathways, and 43 genes were significantly enriched (P<0.01). Nineteen of 20 differentially expressed vitellogenin genes showed significantly high expression in RS, which suggested that they probably played a crucial role in organic pigment assembly and transportation of the shell. Moreover, 687 crystal formation-related (or biomineralization-related) genes were detected in A. pleuronectes, among which 144 genes exhibited significant difference between the two branches. Those genes could be classified into shell matrix framework participants, crystal nucleation and growth-related elements, upstream regulation factors, Ca level regulators, and other classifications. We also identified putative SNP and SSR markers from these samples which provided the markers for genetic diversity analysis, genetic linkage, QTL analysis. These results provide insight into the complexity of shell color differentiation in A. pleuronectes so as valuable resources for further research.

The transcriptomic response to copper exposure in the digestive gland of Japanese scallops (Mizuhopecten yessoensis)

The present study was conducted to elucidate the effects of copper exposure on the immune system and lipid metabolism of the Japanese scallop, Mizuhopecten yessoensis. Transcriptional levels of differentially expressed genes (DEGs)in M. yessoensis digestive gland tissue were analyzed using the deep-sequencing platform Illumina HiSeq™ 2000. In total, 841 and 877 genes were identified as significantly up- or down-regulated, respectively. In addition, significant enrichment analysis identified 3 gene ontology terms and 15 pathways involved in the response to copper exposure. Analysis of transcripts related to the immune response revealed a complex pattern of innate recognition receptors, including toll-like receptors, NOD-like receptors and downstream pathway effectors, including those involved in apoptosis. Furthermore, genomic analysis revealed that genes involved in extracellular matrix (ECM)-receptor interactions were enriched in Cu-exposed scallop glands. These results will provide a resource for subsequent gene expression studies regarding heavy metal exposure and the identification of copper-sensitive biomarkers for the aquaculture of M. yessoensis.

Delineation of ¹³⁴Cs uptake pathways (seawater and food) in the variegated scallop Mimachlamys varia

Among bivalves, scallops have been shown to be good bioindicator species for radionuclide monitoring. The present paper looked at the Cs bioaccumulation capacities of the variegated scallop Mimachlamys varia exposed separately via seawater and food under laboratory conditions. Results were compared with data previously obtained for the king scallop Pecten maximus, the only Pectinid species for which Cs accumulation has been studied in laboratory. Results indicated that M. varia has higher uptake capacity (CF: 1.86 ± 0.08) but lower absorption efficiency (A0l: 33 ± 5%) than P. maximus when exposed to waterborne Cs (CF of P. maximus: 0.94 ± 0.05 and A0l: 45 ± 3%). When scallops were fed radiolabeled phytoplankton, the assimilation efficiency of Cs was similar for the two species (AE: 24 ± 3% for M. varia and 28 ± 4% for P. maximus). Interspecific differences in terms of accumulation and retention, can be explained by physiological factors (including size of individuals) and/or difference in storage mechanisms. Indeed, organotropism differed between the two scallop species, suggesting the occurrence of specific redistribution mechanisms towards the tissues involved in Cs storage, excretion and detoxification. Finally, the present study examined the relative contribution of the different exposure pathways (seawater and food) to global (134)Cs bioaccumulation for M. varia. Results showed that food constitutes the main accumulation pathway, contributing for 77% of the global (134)Cs bioaccumulation.

Genome-wide identification and characterization of five MyD88 duplication genes in Yesso scallop (Patinopecten yessoensis) and expression changes in response to bacterial challenge

Myeloid differentiation factor 88 (MyD88) is a pivotal adaptor in the TLR/IL-1R signaling pathway, which plays an important role in activating the innate immune system. Although MyD88 genes have been identified in a variety of species, they have not been systematically characterized in scallops. In this study, five MyD88 genes were identified in Yesso scallop (Patinopecten yessoensis), PyMyD88-1, PyMyD88-2a, PyMyD88-2b, PyMyD88-3 and PyMyD88-4, which consisted of two pairs of tandem duplications located on the same chromosome. To our knowledge, this is the largest number of MyD88 genes found in an invertebrate. Phylogenetic and protein structural analyses were carried out to determine the identities and evolutionary relationships of these genes. PyMyD88s have highly conserved structures compared to MyD88 genes from other invertebrate species, except for PyMyD88-4, which contains only a DD domain, suggesting the evolutionarily conserved form of this particular gene member. We investigated the expression profiles of PyMyD88 genes at different developmental stages and in healthy adult tissues and hemocytes after Micrococcus luteus and Vibrio anguillarum infection using quantitative real-time PCR (qRT-PCR). The expression of most PyMyD88s was significantly induced in the acute phase (3-6 h) after infection with both gram-positive (M. luteus) and gram-negative (V. anguillarum) bacteria, with much more dramatic changes in PyMyD88 expression being observed after V. anguillarum challenge. Collectively, the abundance of MyD88s and their specific expression patterns provide insight into their versatile roles in the response of the bivalve innate immune system to gram-negative bacterial pathogens.

Integration of Transcriptomic and Proteomic Approaches Provides a Core Set of Genes for Understanding of Scallop Attachment

Attachment is an essential physiological process in life histories of many marine organisms. Using a combination of transcriptomic and proteomic approach, scallop byssal proteins (Sbps) and their associated regulatory network genes were investigated for the first time. We built the first scallop foot transcriptome library, and 75 foot-specific genes were identified. Through integration of transcriptomic-proteomic approach, seven unique Sbps were identified. Of them, three showed significant amino acid sequence homology to known proteins. In contrast, the rest did not show significant protein matches, indicating they are possibly novel proteins. Our transcriptomic and proteomic analyses also suggest that post-translational modification may be one of the significant features for Sbps as well. Taken together, our study provides the first multidimensional collection of a core set of genes that may be potentially involved in scallop byssal attachment.

A novel multi-domain C1qDC protein from Zhikong scallop Chlamys farreri provides new insights into the function of invertebrate C1qDC proteins

The C1q domain containing (C1qDC) proteins are a family of proteins possessing globular C1q (gC1q) domains, and they rely on this domain to recognize various ligands such as PAMPs, immunoglobulins, ligands on apoptotic cell. In the present study, a novel multi-domain C1qDC protein (CfC1qDC-2) was identified from scallop Chlamys farreri, and its full length cDNA was composed of 1648 bp, encoding a signal peptide and three typical gC1q domains. BLAST analysis revealed significant sequence similarity between CfC1qDC-2 and C1qDC proteins from mollusks. Three gC1q domains were predicted in its tertiary structure to form a tightly packed bell-shaped trimer, and each one adopted a typical 10-stranded sandwich fold with a jelly-roll topology and contained six aromatic amino acids forming the hydrophobic core. The mRNA transcripts of CfC1qDC-2 were mainly detected in the tissues of hepatopancreas and gonad of adult scallops, and the expression level was up-regulated in hemocytes after stimulated by LPS, PGN and β-glucan. During the embryonic development of scallop, the mRNA transcripts of CfC1qDC-2 were presented in all the detected stages, and the expression level was up-regulated from D-hinged larvae and reached the highest at eye-spot larvae. The recombinant protein of MBP-CfC1qDC-2 (rCfC1qDC-2) could bind various PAMPs including LPS, PGN, LTA, β-glucan, mannan as well as polyI:C, and different microorganisms including three Gram-negative bacteria, three Gram-positive bacteria and two yeasts, as well as scallop apoptotic cells. Meanwhile, rCfC1qDC-2 could interact with human heat-aggregated IgG and IgM, and inhibit the C1q-dependent hemolysis of rabbit serum. All these results indicated that CfC1qDC-2 could recognize not only PAMPs as a PRR, but also the apoptotic cells. Moreover, the similar structures and functions shared by CfC1qDC-2 and complement C1q provided a new insight into the evolution of C1qDC proteins in complement system.

Characterization of GnRH-like peptides from the nerve ganglia of Yesso scallop, Patinopecten yessoensis

There is yet no firm experimental evidence that the evolutionary ancient gonadotropin-releasing hormone GnRH (i.e., GnRH1) also acts in invertebrate gametogenesis. The objective of this paper is to characterize candidate invGnRH peptides of Yesso scallop Patinopecten yessoensis (i.e., peptide identification, immunohistochemical localization, and immunoquantification) in order to reveal their bioactive form in bivalves. Using mass spectrometry (MS), we identified two invGnRH (py-GnRH) peptides from the scallop nerve ganglia: a precursor form of py-GnRH peptide (a non-amidated dodecapeptide; py-GnRH12aa-OH) and a mature py-GnRH peptide (an amidated undecapeptide; py-GnRH11aa-NH2). Immunohistochemical staining allowed the localization of both py-GnRH peptides in the neuronal cell bodies and fibers of the cerebral and pedal ganglia (CPG) and the visceral ganglion (VG). We found that the peptides showed a dimorphic distribution pattern. Notably, the broad distribution of mature py-GnRH in neuronal fibers elongating to peripheral organs suggests that it is multi-functional. Time-resolved fluorescent immunoassays (TR-FIA) enabled the quantification of each py-GnRH form in the single CPG or VG tissue obtained from one individual. In addition, we observed greater abundance of mature py-GnRH in VG compared with its level in CPG, suggesting that VG is the main producing organ of mature py-GnRH peptide and that py-GnRH may play a central regulatory role in neurons of scallops. Our study provides evidence, for the first time, for the presence of precursor and mature forms of invGnRH peptides in the nerve ganglia of an invertebrate.

Exposure of Chlamys farreri to tetrabromobisphenol A: accumulation and multibiomarker responses

Tetrabromobisphenol A (TBBPA) is currently the most widely used brominated flame retardant (BFR). To date, the toxic effects of TBBPA remains poorly understood in aquatic organisms, especially in bivalves. The objective of this experiment was to examine bioaccumulation and multibiomarker responses in the scallop Chlamys farreri exposed to TBBPA under laboratory conditions. The results showed that TBBPA was rapidly accumulated in and then eliminated from the gill and digestive gland of the scallops. TBBPA exposure invoked alterations in the detoxification system and induced oxidant stress and biomacromolecule damages in the gill and digestive gland of C. farreri. Additionally, glutathione-S-transferase (GST) activity, lipid peroxidation (LPO) level, cytochrome b5 (Cyt b5) content, and DNA strand break had good correlations with TBBPA accumulation levels in the gill and digestive gland of C. farreri. Summarizing, these results enabled us to hypothesize several toxic mechanisms of TBBPA and select potential biomarkers for TBBPA pollution monitoring.

The genome-wide identification of mitogen-activated protein kinase kinase (MKK) genes in Yesso scallop Patinopecten yessoensis and their expression responses to bacteria challenges

Mitogen-activated protein kinase kinases (MKK) are the essential components of the evolutionarily conserved MAPK signaling cascade, which regulates a variety of cellular activities and innate immune responses. Although MKK genes have been extensively studied in various vertebrate and invertebrate species, they have not been systematically characterized in bivalves. In this study, we identified and characterized five MKK genes (PyMKK1/2, PyMKK4, PyMKK5, PyMKK3/6 and PyMKK7) in the Yesso scallop (Patinopecten yessoensis). Phylogenetic and protein structural analyses were conducted to determine their identities and evolutionary relationships. To gain insights into the possible roles of MKK genes during scallop innate immune responses, quantitative real-time PCR (qRT-PCR) was used to investigate their expression profiles during different developmental stages in samples taken from healthy adult tissues and hemocytes after Micrococcus luteus and Vibrio anguillarum bacterial infections. The Yesso scallop MKKs (PyMKKs) were found to have highly conserved structural features compared to the MKK genes from other invertebrate species. Using qRT-PCR analysis, three distinct expression patterns were detected among the PyMKKs over the course of ten different developmental stages. In adult scallops, the majority of the PyMKKs were highly expressed in mantle, gill, muscle and hemocytes. The differential expression patterns of the five PyMKKs after M. luteus (Gram-positive) and V. anguillarum (Gram-negative) bacterial infections suggested their possible involvement in the innate immune response and provide the foundation and resource for the further study on innate immune response of MAPK signal pathway in mollusk.

Identification and functional characterization of two Bcl-2 family protein genes in Zhikong scallop Chlamys farreri

Apoptosis plays significant roles in maintenance of homeostasis, immune defense and development. The Bcl-2 family proteins are important regulators of the intrinsic apoptosis. In the study, we have characterized a Bcl-2-like gene (named CfBcl-2) and a Bax-like gene (named CfBax) from the Zhikong scallop Chlamys farreri. The full-length of the CfBcl-2 cDNA is 944 nucleotides (nt) encoding a putative protein of 225 amino acid residues (aa) that contains four Bcl-2 homology (BH) domains, and the CfBax cDNA is 505 nt encoding a putative protein of 115 aa that contains three Bcl-2 BH domains. Sequence and phylogenetic analysis demonstrate that CfBcl-2 and CfBax present typical domain organization of the corresponding Bcl-2 related proteins and are more similar and clustered with their homologues of other molluscs. The two genes are ubiquitously expressed in six tissues of C. farreri, with the highest expression level of CfBcl-2 in adductor muscle and highest expression level of CfBax in gill. The expressions of CfBcl-2 and CfBax in hemocytes were both significantly up-regulated after an in vivo exposure of scallops to air, injection with lipopolysaccharide and infection with acute viral necrobiotic disease virus, and the expression patterns of the two genes after the three treatments vary in different change magnitude and up-regulation timespan. Yeast two-hybrid assay reveals a direct interaction between the CfBcl-2 and CfBax proteins. These results indicate that the CfBcl-2 and CfBax may participate in the apoptosis-based stress and immune responses against noxious stimulation.

Gender differences in detoxification metabolism of polycyclic aromatic hydrocarbon (chrysene) in scallop Chlamys farreri during the reproduction period

This study aims to investigate the effects of chrysene (CHR) on biotransformation and detoxification responses of mature scallop Chlamys farreri during the reproduction period. Scallops were exposed to 0.2, 0.8 and 3.2 μg/L CHR for 21 days; at day 10 scallops were induced to spawn. At days 1, 3, 6, 10, 11, 15 and 21, enzymatic activities of 7-ethoxyresorufin O-deethylase (EROD) and glutathione-s-transferase (GST), related mRNA expression levels of CYP1A1, GST-pi and P-glycoprotein (P-gp) in digestive glands and CHR bioaccumulation in tissues were examined by separately analyzing male and female scallops. During the pre-spawn period, CHR concentrations of the treated groups in tissues except the hemolymph increased rapidly. Levels of enzymatic activities and related gene expressions were all induced by the exposure to CHR for females and males. GST activity and GST-pi mRNA expression showed a good time- and dose-dependent relationship only in males, and P-gp mRNA expression exhibited a dose-dependent manner in both sexes. During the post-spawn period, spawning caused significant reductions of bioaccumulation in tissues but the gill and hemolymph. Enzymatic activities and related gene expressions were for females significantly depressed at day 21 at 0.8 or 3.2 μg/L CHR. Overall, females accumulated more CHR than males, while males were more sensitive than females to CHR exposure in gene expressions and enzyme activities. P-gp mRNA expression seemed to be a potential biomarker for PAH exposure. These results will offer the information on CHR biotransformation in this species, and ensure the influence of gender and reproductive status on PAH detoxification metabolism.

Environmentally relevant concentrations of benzo[a]pyrene affect steroid levels and affect gonad of male scallop Chlamys farreri

Sexually mature male Chlamys farreri were exposed to benzo[a]pyrene for 10 days at four concentrations at 0, 0.025, 0.5 and 10 μg/L. Fluctuations in sex steroids during the exposure period were observed, which indicated that sex steroids have a role in gamete development. Exposure to B[a]P altered levels of 17β-estradiol, testosterone, and progesterone. Furthermore, B[a]P treatments induced oxidative stress in a dose-dependent manner on spermary of scallop and led to delayed development and damaged spermatid in germinal epithelium of spermary. Overall, B[a]P affected the steroid levels and induced gonadal toxicity at environmentally relevant concentrations.

An EPD/WSD motifs containing C-type lectin from Argopectens irradians recognizes and binds microbes with broad spectrum

C-type lectins are a superfamily of Ca(2+)-dependent carbohydrate-recognition proteins consisting of at least one carbohydrate-recognition domain (CRD), which play significant roles in nonself-recognition and clearance of invaders. The immune function of a C-type lectin (AiCTL-7) with EPD/WSD motifs from Argopectens irradians was investigated in the present study. The recombinant protein of AiCTL-7 (rAiCTL-7) could bind LPS, PGN, mannan, yeast glucan and poly I:C in vitro, and displayed a broader microbes binding spectrum towards Gram-positive bacteria Staphylococcus aureus, Gram-negative bacteria Escherichia coli, Vibrio anguillarum, as well as fungi Pichia pastoris and Yarrowia lipolytica. Moreover, it could also inhibit the growth of E. coli and significantly (P < 0.01) mediate the cell-cell adhesion in vitro. The results clearly suggested that EPD/WSD motifs containing lectin AiCTL-7 could serve as PRR with wider recognition spectrum, and function both as collectin and selectin participating in the immunity against invaders in scallops. It could be inferred that the diversity and complexity of motifs in Ca(2+) binding site 2 in CRDs endowed C-type lectins with comprehensive recognition spectrum and multiple immune functions against complex living environment.

The polymorphisms in the promoter of HSP90 gene and their association with heat tolerance of bay scallop

The heat shock protein 90 (HSP90) is a highly abundant and ubiquitous molecular chaperone which plays essential roles in many cellular processes. In the present study, the messenger RNA (mRNA) expressions of HSP90 after acute heat stress were investigated in two bay scallop populations (Argopecten irradians irradians and Argopecten irradians concentricus). The heat-resistant scallop A. i. concentricus, which is distributed in Zhanjiang, China, exhibited significantly higher induction of HSP90 compared with that of the heat-sensitive scallop A. i. irradians, which is distributed in Qinhuangdao, China. The promoter sequence of HSP90 gene from bay scallop (AiHSP90) was cloned, and the polymorphisms within this region were investigated by sequencing to analyze their association with heat tolerance. A total of six single nucleotide polymorphisms (SNPs), including -1167 T-C, -1023 A-C, -799 C-T, -774 A-G, -686 C-T, and -682 A-C, were identified in the amplified promoter region, and most of them affected the putative transcription factor binding sites except for locus -1167. All the six SNP sites were found to be associated with heat tolerance after Hardy-Weinberg equilibrium (HWE) and association analysis. Moreover, haplotypes CACACC and TCTATC were also found to be associated with heat tolerance based on the result of linkage disequilibrium and association analysis. The results provided insights into the molecular mechanisms underlying the thermal adaptation of different congener endemic bay scallops, which suggested that the increased heat tolerance of A. i. concentricus (compared with A. i. irradians) was associated with the higher expression of AiHSP90. Meanwhile, the six genotypes (-1167 TT, -1023 CC, -799 TT, -774 GG, -686 CC, and -682 AA) and two haplotypes (CACACC and TCTATC) could be used as potential markers for scallop selection breeding with higher heat tolerance.

Tissue-specific Cd and Pb accumulation in Peruvian scallop (Argopecten purpuratus) transplanted to a suspended and bottom culture at Sechura Bay, Peru

In order to understand the effect of different culture systems on Cd and Pb accumulation, suspended long-line and bottom cultures of Argopecten purpuratus were conducted during January until April 2010 (120 days). The Cd tissue levels were the highest at the middle of the experiment (30-d till 70-d) for suspended-cultured individuals, while bottom-cultured individuals showed an increasing trend. Gonad Pb levels were also higher during the same period for all cultures, while adductor muscle exhibited no considerable variations. Cd and Pb tissue concentrations were mainly greater in deeper cultures. There were no significant differences in Cd and Pb accumulation between individual sizes. The Cd and Pb levels in edible tissue (gonad+adductor muscle) did not exceed the EU and FDA maximum levels. Based on the target hazard quotient (THQ) and the provisional tolerance weekly intake (PTWI), no risk (THQ<1 and %PTWI<30) was found for human consumption.

Transcriptome sequencing and characterization of Japanese scallop Patinopecten yessoensis from different shell color lines

Shell color is an important trait that is used in breeding the Japanese scallop Patinopecten yessoensis, the most economically important scallop species in China. We constructed four transcriptome libraries from different shell color lines of P. yessoensis: the left and right shell mantles of ordinary strains of P. yessoensis and the left shell mantles of the ‘Ivory’ and ‘Maple’ strains. These four libraries were paired-end sequenced using the Illumina HiSeq 2000 platform and contained 54,802,692 sequences, 40,798,962 sequences, 74,019,262 sequences, and 44,466,166 sequences, respectively. A total of 214,087,082 expressed sequence tags were assembled into 73,522 unigenes with an average size of 1,163 bp. When the data were compared against the public Nr and Swiss-Prot databases using BlastX, nearly 30.55% (22,458) of the unigenes were significantly matched to known unique proteins. Gene Ontology annotation and pathway mapping analysis using the Kyoto Encyclopedia of Genes and Genomes categorized unigenes according to their diverse biological functions and processes and identified candidate genes that were potentially involved in growth, pigmentation, metal transcription, and immunity. Expression profile analysis was performed on all four libraries and many differentially expressed genes were identified. In addition, 5,772 simple sequence repeats were obtained from the P. yessoensis transcriptomes, and 464,197, 395,646, and 310,649 single nucleotide polymorphisms were revealed in the ordinary strains, the ‘Ivory’ strain, and the ‘Maple’ strain, respectively. These results provide valuable information for future genomic studies on P. yessoensis and improve our understanding of the molecular mechanisms involved in the growth, immunity, shell coloring, and shell biomineralization of this species. These resources also may be used in a variety of applications, such as trait mapping, marker-assisted breeding, studies of population genetics and genomics, and work on functional genomics.

Dietary accumulation of tetrabromobisphenol A and its effects on the scallop Chlamys farreri

Tetrabromobisphenol A (TBBPA) is currently the most widely-used brominated flame retardant (BFR) and has been proven to have a very high toxicity to aquatic organisms including bivalves. In this study, a laboratory experiment was conducted to obtain a better understanding of the role of algae food on the bioaccumulation of TBBPA and its effects on the suspension-feeding bivalve, the scallop, Chlamys farreri. Scallops were exposed to TBBPA via algae food alone or food+water for 10 days. Results showed that TBBPA was accumulated rapidly by scallops, reaching an approximate steady state in soft tissues within 3 days. The primary route of TBBPA accumulation was via the water, while dietary uptake was relatively minor. TBBPA exposure led to significant inhibition on microsomal cytochrome P450 and cytochrome b5 levels in gills and digestive gland, whereas GST activity and GSH level increased significantly, which indicated that TBBPA could be a suitable substrate to directly participate in phase II metabolism. TBBPA clearly induced the activity of SOD, suggesting the oxidant stress induced by TBBPA. This study suggests that dietary uptake was not the predominant uptake route for TBBPA in bivalves and also provides a preliminary basis for studying the detoxification and antioxidant responses of marine bivalves upon exposure to TBBPA.