cDNA cloning and characterization of a new member of the tumor necrosis factor receptor family gene from scallop, Chlamys farreri

Effects of the tumor necrosis factor on hemocyte proliferation and bacterial infection in Chinese mitten crab (Eriocheir sinensis)

Tumor necrosis factor (TNF) is an important cytokine that can regulate a variety of cellular responses by binding tumor necrosis factor receptor (TNFR). We studied whether the TNF of Eriocheir sinensis can regulate hemocyte proliferation. The results showed that the EsTNF and EsTNFR were constitutively expressed in all tested tissues, including the heart, hepatopancreas, muscles, gills, stomachs, intestines, and hemocytes. We found that low levels of EsTNF and EsTNFR transcripts were present in hemocytes. The gene expression levels were significantly increased in the hemocytes after being stimulated by Staphylococcus aureus or Vibrio parahaemolyticus. We also found some genes related to cell proliferation were expressed at a higher level in pulsing rTNF-stimulated hemocytes compared with the control group. We also knocked down the EsTNFR gene with RNAi technology. The results showed that the expression level of these genes related to cell proliferation was significantly down-regulated compared with the control group when the TNF does not bind TNFR. We used Edu technology to repeat the above experiments and the results were similar. Compared with the control group, the hemocytes stimulated by rTNF showed more significant proliferation, and the proliferation rate was significantly down-regulated after knocking down the EsTNFR gene. Therefore, we indicate that TNF binding TNFR can affect the proliferation of E. sinensis hemocytes, which might be manifested by affecting the expression of some proliferation-related genes.

Genome-Wide Association Study Reveals PC4 as the Candidate Gene for Thermal Tolerance in Bay Scallop (Argopecten irradians irradians)

The increasing sea temperature caused by global warming has resulted in severe mortalities in maricultural scallops. Therefore, improving thermal tolerance has become an active research area in the scallop farming industry. Bay scallop (Argopecten irradians irradians) was introduced into China in 1982 and has developed into a vast aquaculture industry in northern China. To date, genetic studies on thermal tolerance in bay scallops are limited, and no systematic screening of thermal tolerance-related loci or genes has been conducted in this species. In the present study, we conducted a genome-wide association study (GWAS) for thermal tolerance using the Arrhenius break temperature (ABT) indicators of 435 bay scallops and 38,011 single nucleotide polymorphism (SNP) markers. The GWAS identified 1,906 significant thermal tolerance-associated SNPs located in 16 chromosomes of bay scallop. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed that 638 genes were enriched in 42 GO terms, while 549 annotated genes were enriched in aggregation pathways. Additionally, the SNP (15-5091-20379557-1) with the lowest P value was located in the transcriptional coactivator p15 (PC4) gene, which is involved in regulating DNA damage repair and stabilizing genome functions. Further analysis in another population identified two new thermal tolerance-associated SNPs in the first coding sequence of PC4 in bay scallops (AiPC4). Moreover, AiPC4 expression levels were significantly correlated (r = 0.675-0.962; P < 0.05) with the ABT values of the examined bay scallops. Our data suggest that AiPC4 might be a positive regulator of thermal tolerance and a potential candidate gene for molecular breeding in bay scallop aiming at thermal tolerance improvement.

Identification, characterization and expression analyses of cholinesterases genes in Yesso scallop (Patinopecten yessoensis) reveal molecular function allocation in responses to ocean acidification

Cholinesterases are key enzymes in central and peripheral cholinergic nerve system functioning on nerve impulse transmission in animals. Though cholinesterases have been identified in most vertebrates, the knowledge about the variable numbers and multiple functions of the genes is still quite meagre in invertebrates, especially in scallops. In this study, the complete cholinesterase (ChE) family members have been systematically characterized in Yesso scallop (Patinopecten yessoensis) via whole-genome scanning through in silico analysis. Ten ChE family members in the genome of Yesso scallop (designated PyChEs) were identified and potentially acted to be the largest number of ChE in the reported species to date. Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of these genes. The expression profiles of PyChEs were determined in all developmental stages, in healthy adult tissues, and in mantles under low pH stress (pH 6.5 and 7.5). Spatiotemporal expression suggested the ubiquitous functional roles of PyChEs in all stages of development, as well as general and tissue-specific functions in scallop tissues. Regulation expressions revealed diverse up- and down-regulated expression patterns at most time points, suggesting different functional specialization of gene superfamily members in response to ocean acidification (OA). Evidences in gene number, phylogenetic relationships and expression patterns of PyChEs revealed that functional innovations and differentiations after gene duplication may result in altered functional constraints among PyChEs gene clusters. Collectively, our results provide the potential clues that the selection pressures coming from the environment were the potential inducement leading to function allocation of ChE family members in scallop.

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

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

Molecular cloning, characterization, and expression of two TNFRs from the pearl oyster Pinctada fucata martensii

Proteins in the tumor necrosis factor receptor (TNFR) superfamily play significant roles in many physiological and pathological events, such as inflammation, apoptosis, autoimmunity, and organogenesis. Here, two TNFR gene homologs (PmTNFR1 and PmTNFR5) were identified in the pearl oyster Pinctada fucata martensii. The predicted PmTNFR1 and PmTNFR5 protein sequences were 406 and 533 amino acids long, respectively, and both possessed motifs characteristic of the TNFR family, including a TNFR homology domain (CRD), a transmembrane domain (TM), and death domains. However, the predicted amino acid sequences of PmTNFR1 and PmTNFR5 had low identity (~16-23%) with sequences of vertebrate TNFR family proteins. Furthermore, PmTNFR5 had a death domain at the C-terminal, indicating that this protein may be a novel member of the TNFR superfamily. Constitutive PmTNFR1 and PmTNFR5 mRNA expression was detected in all six pearl oyster tissues tested, with comparatively greater transcript abundance in the hepatopancreas and gill. The gene expression levels of PmTNFR1 and PmTNFR5, as well as those of downstream signaling molecules related to the NF-κB pathway (RIP, TRAF2, TRAF3, IKK, and NF-κB), were quantified in the gill after LPS challenge and in the hemocytes after nucleus insertion surgery using real-time PCR (qRT-PCR). We found that all genes were significantly upregulated at 6 h and 12 h post-injection, as well as at 15 d post-insertion. We used RNAi to inhibit the expression of the PmTNFR1 and PmTNFR5 genes. We then quantified the expression levels of PmTNFR1 and PmTNFR5, as well as downstream genes, using qRT-PCR. We found that RNAi inhibition of PmTNFR1 and PmTNFR5 downregulated the downstream genes (RIP, TRAF2, TRAF3, IKK, and NF-κB). Therefore, our results suggested that PmTNFR1 and PmTNFR5 mediate the NF-κB signaling pathway, and are closely related to immune defense, particularly allograft immunity, in the pearl oyster P. fucata martensii.

Alternative splicing, spatiotemporal expression of TEP family genes in Yesso scallop (Patinopecten yessoensis) and their disparity in responses to ocean acidification

The complement system constitutes a highly sophisticated and powerful body defense machinery acting in the innate immunity of both vertebrates and invertebrates. As central components of the complement system, significant effects of thioester-containing protein (TEP) family members on immunity have been reported in most vertebrates and in some invertebrates, but the spatiotemporal expression and regulatory patterns of TEP family genes under environmental stress have been less widely investigated in scallops. In this study, expression profiling of TEP family members in the Yesso scallop Patinopecten yessoensis (designated PyTEPs) was performed at all developmental stages, in different healthy adult tissues, and in mantles during exposure to different levels of acidification (pH = 6.5 and 7.5) for different time points (3, 6, 12 and 24 h); this profiling was accomplished through in silico analysis of transcriptome and genome databases. Spatiotemporal expression patterns revealed that PyTEPs had specific functional differentiation in all stages of growth and development of the scallop. Expression analysis confirmed the inducible expression patterns of PyTEPs during exposure to acidification. Gene duplication and alternative splicing events simultaneously occurred in PyTEP1. Seven different cDNA variants of PyTEP1 (designated PyTEP1-A-PyTEP1-G) were identified in the scallop mantle transcriptome during acidic stress. These variants were produced by the alternative splicing of seven differentially transcribed exons (exons 18-24), which encode the highly variable central region. The responses to immune stress may have arisen through the gene duplication and alternative splicing of PyTEP1. The sequence diversity of PyTEP1 isoforms and their different expression profiles in response to ocean acidification (OA) suggested a mechanism used by scallops to differentiate and regulate PyTEP1 gene expression. Collectively, these results demonstrate the gene duplication and alternative splicing of TEP family genes and provide valuable resources for elucidating their versatile roles in bivalve innate immune responses to OA challenge.

The GRP94 gene of Yesso scallop (Patinopecten yessoensis): Characterization and expression regulation in response to thermal and bacterial stresses

The 94-kDa glucose-regulated protein (GRP94) belonging to the HSP90 family is an endoplasmic reticulum (ER) chaperone. It plays critical roles in ER quality control, and has been implicated as a specialized immune chaperone to regulate both innate and adaptive immunity. In this study, we identified and characterized a GRP94 gene (PyGRP94) from Yesso scallop (Patinopecten yessoensis). The protein sequence of PyGRP94 is highly conserved with its homologs in vertebrates, with a signal sequence in N-terminal, an ER retrieval signal sequence in C-terminal and a HATPase_c domain. Expression analysis suggests that PyGRP94 transcripts in early embryos are maternally derived and the zygotic expression is started from D-shaped larvae. This gene is also expressed in almost all the adult tissues examined except smooth muscle, with the highest expression level in hemocytes. Besides, PyGRP94 was demonstrated to be induced by heat shock and both Gram-positive (Micrococcus luteus) and Gram-negative (Vibrio anguillarum) bacterial infection, with much more dramatic changes being observed after V. anguillarum challenge. Our results suggest the involvement of PyGRP94 in response to thermal stress, and that it might play an important role in the innate immune defense of scallop.

Identification and characterization of TEP family genes in Yesso scallop (Patinopecten yessoensis) and their diverse expression patterns in response to bacterial infection

Thioester-containing protein (TEP) family members are characterized by their unique intrachain β-cysteinyl-γ-glutamyl thioesters, and they play important roles in innate immune responses. Although significant effects of TEP members on immunity have been reported in most vertebrates, as well as certain invertebrates, the complete TEP family has not been systematically characterized in scallops. In this study, five TEP family genes (PyC3, PyA2M, PyTEP1, PyTEP2 and PyCD109) were identified from Yesso scallop (Patinopecten yessoensis) through whole-genome scanning, including one pair of tandem duplications located on the same scaffold. Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of the five genes (PyTEPs). The vast distribution of PyTEPs in TEP subfamilies confirmed that the Yesso scallop contains relatively comprehensive types of TEP members in evolution. The expression profiles of PyTEPs were determined in hemocytes after bacterial infection with gram-positive (Micrococcus luteus) and gram-negative (Vibrio anguillarum) using quantitative real-time PCR (qRT-PCR). Expression analysis revealed that the PyTEP genes exhibited disparate expression patterns in response to the infection by gram bacteria. A majority of PyTEP genes were overexpressed after bacterial stimulation at most time points, especially the notable elevation displayed by duplicated genes after V. anguillarum challenge. Interestingly, at different infection times, PyTEP1 and PyTEP2 shared analogous expression patterns, as did PyC3 and PyCD109. Taken together, these results help to characterize gene duplication and the evolutionary origin of PyTEPs and supplied valuable resources for elucidating their versatile roles in bivalve innate immune responses to bacterial pathogen challenges.

Genome-wide identification, characterization and expression analyses of TLRs in Yesso scallop (Patinopecten yessoensis) provide insight into the disparity of responses to acidifying exposure in bivalves

Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing specific pathogen-associated molecular patterns, including lipoproteins, lipopeptides, lipopolysaccharide, flagellin, dsRNA, ssRNA and CpG DNA motifs. Although significant effects of TLRs on immunity have been reported in most vertebrates and some invertebrates, the complete TLR superfamily has not been systematically characterized in scallops. In this study, 18 TLR genes were identified from Yesso scallop (Patinopecten yessoensis) using whole-genome scanning. Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of the 18 genes. Extensive expansion of TLR genes from the Yesso scallop genome indicated gene duplication events. In addition, expression profiling of PyTLRs was performed at different acidifying exposure levels (pH = 6.50, 7.50) with different challenge durations (3, 6, 12 and 24 h) via in silico analysis using transcriptome and genome databases. Our results confirmed the inducible expression patterns of PyTLRs under acidifying exposure, and the responses to immune stress may have arisen through adaptive recruitment of tandem duplications of TLR genes. Collectively, this study provides novel insight into PyTLRs as well as the specific role and response of TLR signaling pathways in host immune responses against acidifying exposure in bivalves.

Cloning, characterization and comparative analysis of four death receptorTNFRs from the oyster Crassostrea hongkongensis

Apoptosis plays an important role in homeostasis of the immune systems. The tumor necrosis factor receptors (TNFRs) play critical roles in the extrinsic apoptosis pathways and in determining cell fate. In this study, four death receptors (DR) named ChEDAR, ChTNFR27, ChTNFR5, and ChTNFR16 were identified from the oyster Crassostrea hongkongensis. These ChDRs proteins had 382, 396, 414 and 384 amino acids, respectively, with the typical domains of death receptors, such as the signal peptide (SP), transmembrane helix region (TM) and death domains. Phylogenetic analysis showed that the ChDR proteins clustered into three distinct groups, indicating that these subfamilies had common ancestors. mRNA expression of the ChDRs were detected in all 8 of the selected oyster tissues and at different stages of development. Furthermore, expression of all the genes was increased in the hemocytes of oysters challenged with pathogens or air stress. Fluorescence microscopy revealed that the full-length proteins of the ChDRs were located in the plasma membrane of HEK293T cells. Over-expression of the ChDRs activated the NF-κB-Luc reporter in HEK293T cells in a dose-dependent manner. These results indicate that the ChDRs may play important roles in the extrinsic apoptotic pathways in oysters.

Cloning and mineralization-related functions of the calponin gene in Chlamys farreri

Calponin is a widely distributed protein which is associated with the bio-mineralization process in vertebrates. Recently, a new type of calponin has been found in shellfish; the present study aimed to determine if this gene in shellfish functions in bio-mineralization, one of the most important processes in a mollusk's growth. We chose Chlamys farreri, a seashell species with great economic value, as the object of the study and obtained its full-length cDNA to study the function of calponin by gene expression analysis, shell notching experiment and RNA interference assays. Calponin in C. farreri is a basic protein that is highly conserved among mollusk species. Except for high expression in the adductor muscle and foot, which correlated with its function of regulating muscle contraction, the calponin gene was expressed more in the mantle than in other tissues. The expression of the gene was induced by shell notching and an RNA interference assay showed that inhibition of calponin expression caused the growth of irregular mineral crystals on the shell. Further analysis indicated that calponin might function by regulating the expression of other mineralization-related genes. Calponin is a mineralization-related protein in C. farreri that might influence mineral crystal growth by affecting the expressions of other proteins, such as matrix proteins and mineralization-regulating proteins.

Genome-wide identification, characterization and expression analyses of two TNFRs in Yesso scallop (Patinopecten yessoensis) provide insight into the disparity of responses to bacterial infections and heat stress in bivalves

Tumor necrosis factors receptors (TNFRs) comprise a superfamily of proteins characterized by a unique cysteine-rich domain (CRD) and play important roles in diverse physiological and pathological processes in the innate immune system, including inflammation, apoptosis, autoimmunity and organogenesis. Although significant effects of TNFRs on immunity have been reported in most vertebrates as well as some invertebrates, the complete TNFR superfamily has not been systematically characterized in scallops. In this study, two different types of TNFR-like genes, including PyTNFR1 and PyTNFR2 genes were identified from Yesso scallop (Patinopecten yessoensis, Jay, 1857) through whole-genome scanning. Phylogenetic and protein structural analyses were carried out to determine the identities and evolutionary relationships of the two genes. The expression profiling of PyTNFRs was performed at different development stages, in healthy adult tissues and in hemocytes after bacterial infection and heat stress. Expression analysis revealed that both PyTNFRs were significantly induced during the acute phase (3 h) after infection with Gram-positive (Micrococcus luteus) and Gram-negative (Vibrio anguillarum) bacteria, though much more dramatic chronic-phase (24 h) changes were observed after V. anguillarum challenge. For heat stress, only PyTNFR2 displayed significant elevation at 12 h and 24 h, which suggests a functional difference in the two PyTNFRs. Collectively, this study provides novel insight into the PyTNFRs and the specific role and response of TNFR-involved pathways in host immune responses against different bacterial pathogens and heat stress in bivalves.

Molecular Basis for Adaptation of Oysters to Stressful Marine Intertidal Environments

Oysters that occupy estuarine and intertidal habitats have well-developed stress tolerance mechanisms to tolerate harsh and dynamically changing environments. In this review, we summarize common pathways and genomic features in oyster that are responsive to environmental stressors such as temperature, salinity, hypoxia, air exposure, pathogens, and anthropogenic pollutions. We first introduce the key genes involved in several pathways, which constitute the molecular basis for adaptation to stress. We use genome analysis to highlight the strong cellular homeostasis system, a unique adaptive characteristic of oysters. Next, we provide a global view of features of the oyster genome that contribute to stress adaptation, including oyster-specific gene expansion, highly inducible expression, and functional divergence. Finally, we review the consequences of interactions between oysters and the environment from ecological and evolutionary perspectives by discussing mass mortality and adaptive divergence among populations and related species of the genus Crassostrea. We conclude with prospects for future study.

The immune system and its modulation mechanism in scallop

Scallops are a cosmopolitan family of bivalves, and some of them are highly prized as dominant aquaculture species. In the past decades, there have been increasing studies on the basic biology and immunology of scallops, and this review summarizes the research progresses of immune system and its modulation mechanism in scallop. As invertebrate, scallops lack adaptive immunity and they have evolved an array of sophisticated strategies to recognize and eliminate various invaders by employing a set of molecules and cells. It is evident that basic immune reactions such as immune recognition, signal transduction, and effector synthesis involved in immune response are accomplished in a variety of ways. They rely upon an extensive repertoire of phagocytosis, apoptosis and encapsulation of the circulating hemocytes for eliminating invasive pathogens, as well as the production of immune effectors that are active against a large range of pathogens or sensitive for the environmental stress. Furthermore, the molecular constitutions, metabolic pathways and immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, enkephalinergic system and NO system in scallop are also discussed, which can be taken as an entrance to better understand the origin and evolution of the neuroendocrine-immune regulatory network in lower invertebrates.

An updated molecular basis for mussel immunity

Non-self recognition with the consequent tolerance or immune reaction is a crucial process to succeed as living organisms. At the same time the interactions between host species and their microbiome, including potential pathogens and parasites, significantly contribute to animal life diversity. Marine filter-feeding bivalves, mussels in particular, can survive also in heavily anthropized coastal waters despite being constantly surrounded by microorganisms. Based on the first outline of the Mytilus galloprovincialis immunome dated 2011, the continuously growing transcript data and the recent release of a draft mussel genome, we explored the available sequence data and scientific literature to reinforce our knowledge on the main gene-encoded elements of the mussel immune responses, from the pathogen recognition to its clearance. We carefully investigated molecules specialized in the sensing and targeting of potential aggressors, expected to show greater molecular diversification, and outlined, whenever relevant, the interconnected cascades of the intracellular signal transduction. Aiming to explore the diversity of extracellular, membrane-bound and intracellular pattern recognition receptors in mussel, we updated a highly complex immune system, comprising molecules which are described here in detail for the first time (e.g. NOD-like receptors) or which had only been partially characterized in bivalves (e.g. RIG-like receptors). Overall, our comparative sequence analysis supported the identification of over 70 novel full-length immunity-related transcripts in M. galloprovincialis. Nevertheless, the multiplicity of gene functions relevant to immunity, the involvement of part of them in other vital processes, and also the lack of a refined mussel genome make this work still not-exhaustive and support the development of more specific studies.

Structural and functional characterization of a novel molluskan ortholog of TRAF and TNF receptor-associated protein from disk abalone (Haliotis discus discus)

Immune signaling cascades have an indispensable role in the host defense of almost all the organisms. Tumor necrosis factor (TNF) signaling is considered as a prominent signaling pathway in vertebrate as well as invertebrate species. Within the signaling cascade, TNF receptor-associated factor (TRAF) and TNF receptor-associated protein (TTRAP) has been shown to have a crucial role in the modulation of immune signaling in animals. Here, we attempted to characterize a novel molluskan ortholog of TTRAP (AbTTRAP) from disk abalone (Haliotis discus discus) and analyzed its expression levels under pathogenic stress. The complete coding sequence of AbTTRAP consisted of 1071 nucleotides, coding for a 357 amino acid peptide, with a predicted molecular mass of 40 kDa. According to our in-silico analysis, AbTTRAP resembled the typical TTRAP domain architecture, including a 5'-tyrosyl DNA phosphodiesterase domain. Moreover, phylogenetic analysis revealed its common ancestral invertebrate origin, where AbTTRAP was clustered with molluskan counterparts. Quantitative real time PCR showed universally distributed expression of AbTTRAP in selected tissues of abalone, from which more prominent expression was detected in hemocytes. Upon stimulation with two pathogen-derived mitogens, lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (poly I:C), transcript levels of AbTTRAP in hemocytes and gill tissues were differentially modulated with time. In addition, the recombinant protein of AbTTRAP exhibited prominent endonuclease activity against abalone genomic DNA, which was enhanced by the presence of Mg(2+) in the medium. Collectively, these results reinforce the existence of the TNF signaling cascade in mollusks like disk abalone, further implicating the putative regulatory behavior of TTRAP in invertebrate host pathology.

Identification of a LPS-induced TNF-α factor (LITAF) from mollusk Solen grandis and its expression pattern towards PAMPs stimulation

Lipopolysaccharide-induced TNF-α factor (LITAF) is one of the most important transcription factors mediating TNF-α transcription. In the present study, a LITAF gene (designated as SgLITAF) was identified from razor clams Solen grandis. The full-length cDNA of SgLITAF was of 1476 bp, encoding a polypeptide of 130 amino acids showed high similarity to other known LITAFs. SgLITAF encoded a LITAF domain and the Zn(2+)-binding motifs in the domain were well conserved. The mRNA transcripts of SgLITAF were detected in all tested tissues of healthy razor clams, including mantle, gill, gonad, hemocytes, muscle and hepatopancreas, and with the highest expression level in hepatopancreas. The expression level of SgLITAF in hemocytes was significantly up-regulated (P < 0.01) after razor clams were stimulated by LPS or β-1, 3-glucan, but no obvious fluctuation of SgLITAF mRNA expression was observed after PGN stimulation. All the results indicated that there might be a LITAF-regulated TNF-α signaling pathway existing in S. grandis, which involved in the immune response not only against gram-negative bacteria but also towards fungi.

A TRAF and TNF receptor-associated protein (TTRAP) in mollusk with endonuclease activity

Tumor necrosis factor (TNF) signaling pathway plays crucial roles in the regulation of various immune responses. In the present study, a TNF signaling pathway related regulatory factor, TRAF and TNF receptor-associated protein (TTRAP), was firstly identified from the mollusk Zhikong scallop Chlamys farreri (designated as CfTTRAP). The full-length cDNA of CfTTRAP was of 2326bp, containing an open reading frame (ORF) of 1008 bp encoding a polypeptide of 335 amino acids with the predicted molecular weight of 38.4 kDa. There was an Exo_endo_phos domain in CfTTRAP, and it was well conserved when compared with other TTRAPs, especially the endonuclease activity related motifs. The recombinant protein of CfTTRAP exhibited prominent endonuclease activity to digest the genome DNA from C. farreri in the presence of Mg(2+), but it could not digest genome DNA of Escherichia coli and Bacillus subtilis, indicating CfTTRAP was a new member of Mg(2+)/Mn(2+)-dependent phosphodiesterase enzymes (MDP) superfamily. The mRNA transcripts of CfTTRAP were detected in all tested tissues of scallop, including muscle, mantle, gonad, gill, kidney and hemocytes. The expression level of CfTTRAP mRNA in hemocytes varied greatly after the stimulation of LPS, PGN or β-glucan. LPS induced significant down-regulation (P<0.05) of CfTTRAP mRNA expression, while PGN or β-glucan up-regulated the expression significantly (P<0.01), indicating that this regulatory factor was involved in modulating immune responses towards different stimulus. The present results provided new evidences for the potential roles of such molecule in C. farreri, and further confirmed the existence of TTRAP modulated TNF signaling pathway in mollusk.