Genomic characterization and expression analysis of five novel IL-17 genes in the Pacific oyster, Crassostrea gigas

A trace amine associated receptor mediates antimicrobial immune response in the oyster Crassostrea gigas

Trace amine-associated receptors (TAARs) are a class of G protein-coupled receptors, playing an immunomodulatory function in the neuroinflammatory responses. In the present study, a TAAR homologue with a 7tm_classA_rhodopsin-like domain (designated as CgTAAR1L) was identified in oyster Crassostrea gigas. The abundant CgTAAR1L transcripts were detected in visceral ganglia and haemocytes compared to other tissues, which were 55.35-fold and 32.95-fold (p < 0.01) of those in adductor muscle, respectively. The mRNA expression level of CgTAAR1L in haemocytes significantly increased and reached the peak level at 3 h after LPS or Poly (I:C) stimulation, which was 4.55-fold and 12.35-fold of that in control group, respectively (p < 0.01). After the expression of CgTAAR1L was inhibited by the injection of its targeted siRNA, the mRNA expression levels of interleukin17s (CgIL17-1, CgIL17-5 and CgIL17-6), and defensin (Cgdefh1) significantly decreased at 3 h after LPS stimulation, which was 0.51-fold (p < 0.001), 0.39-fold (p < 0.01), 0.48-fold (p < 0.05) and 0.41-fold (p < 0.05) of that in the control group, respectively. The nuclear translocation of Cgp65 protein was suppressed in the CgTAAR1L-RNAi oysters. Furthermore, the number of Vibrio splendidus in the haemolymph of CgTAAR1L-RNAi oysters significantly increased (4.11-fold, p < 0.001) compared with that in the control group. In contrast, there was no significant difference in phagocytic rate of haemocytes to V. splendidus in the CgTAAR1L-RNAi oysters. These results indicated that CgTAAR1L played an important role in the immune defense against bacterial infection by inducing the expressions of interleukin and defensin.

The expression patterns of exosomal miRNAs in the Pacific oyster after high-temperature stress or Vibrio stimulation

The exosomal miRNA plays a crucial role in the intercellular communication response to environmental stress and pathogenic stimulation. In the present study, the expression of exosomal miRNAs in the Pacific oyster Crassostrea gigas after high-temperature stress or Vibrio splendidus stimulation was investigated through high-throughput sequencing. The exosomes were identified to be teardrop-like vesicles with the average size of 81.7 nm by transmission electron microscopy. There were 66 known miRNAs and 33 novel miRNAs identified, of which 10 miRNAs were differentially expressed after both high-temperature stress and Vibrio stimulation compared to the control group. A total of 1868 genes were predicted as the putative targets of miRNAs, of which threonine aspartase 1-like was targeted by the highest number of related miRNAs. The robustness and reliability of miRNA expression from the sRNA sequencing data were verified by employing eight miRNAs for qPCR. GO and KEGG clustering analyses revealed that apoptosis was significantly enriched by the target genes of differentially expressed exosomal miRNAs after high-temperature stress, and autophagy and cytokine activity were significantly enriched after Vibrio stimulation. Energy metabolism was found to be significantly shared in the target gene enrichments after both high-temperature stress and Vibrio stimulation. These findings would improve our understanding of the regulatory mechanisms of exosomal miRNAs in C. gigas after high-temperature stress or Vibrio stimulation.

CgSHIP2 negatively regulates the mRNA expressions of CgIL-17s in response to Vibrio splendidus stimulation in Crassostrea gigas

SH2 domain containing inositol polyphosphate5-phosphatase-2 (SHIP2) is a member of the 5-phosphatase family, acting as a vital negative regulator of immune response in vertebrates. In the present study, a SHIP2 homologue (designed as CgSHIP2) was identified from Pacific oyster, Crassostrea gigas. There was a SH2 domain, an IPPc domain and a SAM domain in CgSHIP2. The mRNA transcripts of CgSHIP2 were widely expressed in all the tested tissues with the highest expression in haemolymph. The mRNA expressions of CgSHIP2 in haemocytes increased significantly at 6, 12, 48 and 72 h after Vibrio splendidus stimulation. The positive green signals of CgSHIP2 protein were mainly located in cytoplasm of haemocytes. After the expression of CgSHIP2 was inhibited by RNA interference, the mRNA transcripts of interleukin 17s (CgIL-17-1, CgIL-17-2, CgIL-17-3 and CgIL-17-6) in the haemocytes increased significantly at 24 h after V. splendidus stimulation, which were 8.15-fold (p < 0.001), 3.44-fold (p < 0.05), 2.15-fold (p < 0.01) and 4.63-fold (p < 0.05) compared with that in NC-RNAi group, respectively. Obvious branchial swelling and cilium shedding in gills were observed in CgSHIP2-RNAi group at 24 h after V. splendidus stimulation. The results suggested that CgSHIP2 played an important role in controlling inflammatory response induced by bacteria in oysters.

The IL-17 pathway intertwines with neurotrophin and TLR/IL-1R pathways since its domain shuffling origin

The IL-17 pathway displays remarkably diverse functional modes between different subphyla, classes, and even orders, yet its driving factors remains elusive. Here, we demonstrate that the IL-17 pathway originated through domain shuffling between a Toll-like receptor (TLR)/IL-1R pathway and a neurotrophin-RTK (receptor-tyrosine-kinase) pathway (a Trunk-Torso pathway). Unlike other new pathways that evolve independently, the IL-17 pathway remains intertwined with its donor pathways throughout later evolution. This intertwining not only influenced the gains and losses of domains and components in the pathway but also drove the diversification of the pathway's functional modes among animal lineages. For instance, we reveal that the crustacean female sex hormone, a neurotrophin inducing sex differentiation, could interact with IL-17Rs and thus be classified as true IL-17s. Additionally, the insect prothoracicotropic hormone, a neurotrophin initiating ecdysis in Drosophila by binding to Torso, could bind to IL-17Rs in other insects. Furthermore, IL-17R and TLR/IL-1R pathways maintain crosstalk in amphioxus and zebrafish. Moreover, the loss of the Death domain in the pathway adaptor connection to IκB kinase and stress-activated protein kinase (CIKSs) dramatically reduced their abilities to activate nuclear factor-kappaB (NF-κB) and activator protein 1 (AP-1) in amphioxus and zebrafish. Reinstating this Death domain not only enhanced NF-κB/AP-1 activation but also strengthened anti-bacterial immunity in zebrafish larvae. This could explain why the mammalian IL-17 pathway, whose CIKS also lacks Death, is considered a weak signaling activator, relying on synergies with other pathways. Our findings provide insights into the functional diversity of the IL-17 pathway and unveil evolutionary principles that could govern the pathway and be used to redesign and manipulate it.

The Modification of H3K4me3 Enhanced the Expression of CgTLR3 in Hemocytes to Increase CgIL17-1 Production in the Immune Priming of Crassostrea gigas

Increasing evidence confirms that histone modification plays a critical role in preserving long-term immunological memory. Immune priming is a novel form of immunological memory recently verified in invertebrates. Toll-like receptor (TLR) signaling and cytokines have been reported to be involved in the immune priming of the Pacific oyster Crassostrea gigas. In the present study, the expression of Toll-like receptor 3 (CgTLR3), myeloid differentiation factor 88-2 (CgMyd88-2) and interleukin 17-1 (CgIL17-1) was found to be elevated in the hemocytes of C. gigas at 6 h after the secondary stimulation with Vibrio splendidus, which was significantly higher than that at 6 h after the primary stimulation (p < 0.05). A significant increase in histone H3 lysine 4 trimethylation (H3K4me3) enrichment was detected in the promoter region of the CgTLR3 gene at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05). After the treatment with a histone methyltransferase inhibitor (5'-methylthioadenosine, MTA), the level of H3K4me3 at the promoter of the CgTLR3 gene decreased significantly at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was significantly repressed at 6 h after the secondary stimulation with V. splendidus (p < 0.05). Conversely, the treatment with monomethyl fumarate (MEF, an inhibitor of histone demethylases) resulted in a significant increase in H3K4me3 enrichment levels at the CgTLR3 promoter at 7 d after the primary stimulation (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was observed to increase significantly at 6 h after the secondary stimulation (p < 0.05). These results suggested that H3K4me3 regulated MyD88-dependent TLR signaling in the hemocytes of C. gigas, which defined the role of histone modifications in invertebrate immune priming.

Molecular characterization and expression of twenty interleukin-17 transcripts in the common Chinese cuttlefish (Sepiella japonica) in response to Vibrio harveyi infection

The common Chinese cuttlefish (Sepiella japonica) is an essential species for stock enhancement by releasing juveniles in the East China Sea now. S. japonica is susceptible to bacterial diseases during parental breeding. In vertebrates, Interleukin-17 (IL-17) cytokine family plays critical roles in both acute and chronic inflammatory responses. In Cephalopoda, few studies have been reported on IL-17 genes so far. In this study, twenty IL-17 transcripts obtained from S. japonica were divided into eight groups (designated as Sj_IL-17-1 to Sj_IL-17-8). Multiple alignment analysis showed that IL-17s in S. japonica and human both contained four β-folds (β1-β4), except for Sj_IL-17-6 with two β-folds (β1 and β2), and the third and fourth β-folds of Sj_IL-17-5 and Sj_IL-17-8 were longer than those of other Sj_IL-17. Protein structure and conserved motifs analysis demonstrated that Sj_IL-17-5 and Sj_IL-17-6 displayed different protein structure with respect to other six Sj_IL-17 proteins. The homology and phylogenetic analysis of amino acids showed that Sj_IL-17-5, Sj_IL-17-6 and Sj_IL-17-8 had low homology with the other five Sj_IL-17s. Eight Sj_IL-17 mRNAs were ubiquitously expressed in ten examined tissues, with dominant expression in the hemolymph. qRT-PCR data showed that the mRNA expression levels of Sj_IL-17-2, Sj_IL-17-3, Sj_IL-17-6, and Sj_IL-17-8 were significantly up-regulated in infected cuttlefishes, and Sj_IL-17-2, Sj_IL-17-6, Sj_IL-17-7, and Sj_IL-17-8 mRNAs Awere significantly up-regulated after bath infection of Vibrio harveyi, suggesting that certain Sj_IL-17s were involved in the immune response of S. japonica against V. harveyi infection. These results implied that Sj_IL-17s were likely to have distinct functional diversification. This study aims to understand the involvement of Sj_IL-17 genes in immune responses of cuttlefish against bacterial infections.

Identification of a Putative CFSH Receptor Inhibiting IAG Expression in Crabs

The crustacean female sex hormone (CFSH) is a neurohormone peculiar to crustaceans that plays a vital role in sexual differentiation. This includes the preservation and establishment of secondary female sexual traits, as well as the inhibition of insulin-like androgenic gland factor (IAG) expression in the androgenic gland (AG). There have been no reports of CFSH receptors in crustaceans up to this point. In this study, we identified a candidate CFSH receptor from the mud crab Scylla paramamosain (named Sp-SEFIR) via protein interaction experiments and biological function experiments. Results of GST pull-down assays indicated that Sp-SEFIR could combine with Sp-CFSH. Findings of in vitro and in vivo interference investigations exhibited that knockdown of Sp-SEFIR could significantly induce Sp-IAG and Sp-STAT expression in the AG. In brief, Sp-SEFIR is a potential CFSH receptor in S. paramamosain, and Sp-CFSH controls Sp-IAG production through the CFSH-SEFIR-STAT-IAG axis.

A C-type lectin from Crassostrea gigas with novel EFG/FVN motif involved in recognition of various PAMPs and induction of interleukin expression

C-type lectins (CTLs) are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins, which participate in the nonself-recognition and triggering the transduction pathways in the innate immunity. In the present study, a novel CTL (designated as CgCLEC-TM2) with a carbohydrate-recognition domain (CRD) and a transmembrane domain (TM) was identified from the Pacific oyster Crassostrea gigas. Two novel EFG and FVN motifs were found in Ca²⁺-binding site 2 of CgCLEC-TM2. The mRNA transcripts of CgCLEC-TM2 were detected in all tested tissues with the highest expression level in haemocytes, which was 94.41-fold (p < 0.01) of that in adductor muscle. The relative expression level of CgCLEC-TM2 in haemocytes significantly up-regulated at 6 h and 24 h after the stimulation of Vibrio splendidus, which was 4.94- and 12.77-fold of that in control group (p < 0.01), respectively. The recombinant CRD of CgCLEC-TM2 (rCRD) was able to bind lipopolysaccharide (LPS), mannose (MAN), peptidoglycan (PGN), and poly (I: C) in a Ca²⁺-dependent manner. The rCRD exhibited binding activity to V. anguillarum, Bacillus subtilis, V. splendidus, Escherichia coli, Pichia pastoris, Staphylococcus aureus and Micrococcus luteus in a Ca²⁺-dependent manner. The rCRD also exhibited agglutination activity to E. coli, V. splendidus, S. aureus, M. luteus and P. pastoris in a Ca²⁺-dependent manner. The phagocytosis rate of haemocytes towards V. splendidus significantly down-regulated from 27.2% to 20.9% after treatment of anti-CgCLEC-TM2-CRD antibody, while the growth of V. splendidus and E. coli was inhibited compared with the TBS and rTrx groups. After the expression of CgCLEC-TM2 was inhibited by RNAi, the expression level of phospho-extracellular regulated protein kinases (p-CgERK) in haemocytes, and the mRNA expressions of interleukin17s (CgIL17-1 and CgIL17-4) decreased significantly after V. splendidus stimulation, compared with that in EGFP-RNAi oysters, respectively. These results suggested that CgCLEC-TM2 with novel motifs served as a pattern recognition receptor (PRR) involved in the recognition of microorganisms, and induction of CgIL17s expression in the immune response of oysters.

A MASP-like functions as PRR to regulate the mRNA expressions of inflammatory factors in the Pacific oyster Crassostrea gigas

Mannose-binding lectin-associated serine protease (MASP) is a type of central serine protease in the complement lectin pathway. In the present study, a MASP-like was identified from the Pacific oyster Crassostrea gigas, defined as CgMASPL-2. The cDNA sequence of CgMASPL-2 was of 3399 bp with an open reading frame of 2757 bp and encoded a polypeptide of 918 amino acids containing three CUB domains, an EGF domain, two IG domains, and a Tryp_SPC domain. In the phylogenetic tree, CgMASPL-2 was firstly clustered with Mytilus californianus McMASP-2-like, and then assigned into the invertebrate branch. CgMASPL-2 shared similar domains with M. californianus McMASP-2-like and Littorina littorea LlMReM1. CgMASPL-2 mRNA was expressed in all the tested tissues with the highest expression in haemolymph. CgMASPL-2 protein was mainly distributed in the cytoplasm of haemocytes. The mRNA expression of CgMASPL-2 increased significantly in haemocytes after Vibrio splendidus stimulation. The recombinant 3 × CUB-EGF domains of CgMASPL-2 displayed binding activities to diverse polysaccharides (lipopolysaccharide, peptidoglycan and mannose) and microbes (Staphylococcus aureus, Micrococcus luteus, Pichia pastoris, Vibrio anguillarum, V. splendidus and Escherichia coli). In anti-CgMASPL-2 treated oysters, the mRNA expressions of CgIL17-1 and CgIL17-2 in haemocytes decreased significantly after V. splendidus stimulation. The results indicated that CgMASPL-2 could directly sense microbes and regulate the mRNA expressions of inflammatory factors.

Exploring the Role of a Novel Interleukin-17 Homolog from Invertebrate Marine Mussel Mytilus coruscus in Innate Immune Response: Is Negative Regulation by Mc-Novel_miR_145 the Key?

Interleukin-17 (IL-17) represents a class of proinflammatory cytokines involved in chronic inflammatory and degenerative disorders. Prior to this study, it was predicted that an IL-17 homolog could be targeted by Mc-novel_miR_145 to participate in the immune response of Mytilus coruscus. This study employed a variety of molecular and cell biology research methods to explore the association between Mc-novel_miR_145 and IL-17 homolog and their immunomodulatory effects. The bioinformatics prediction confirmed the affiliation of the IL-17 homolog with the mussel IL-17 family, followed by quantitative real-time PCR assays (qPCR) to demonstrate that McIL-17-3 was highly expressed in immune-associated tissues and responded to bacterial challenges. Results from luciferase reporter assays confirmed the potential of McIL-17-3 to activate downstream NF-κb and its targeting by Mc-novel_miR_145 in HEK293 cells. The study also produced McIL-17-3 antiserum and found that Mc-novel_miR_145 negatively regulates McIL-17-3 via western blotting and qPCR assays. Furthermore, flow cytometry analysis indicated that Mc-novel_miR_145 negatively regulated McIL-17-3 to alleviate LPS-induced apoptosis. Collectively, the current results showed that McIL-17-3 played an important role in molluscan immune defense against bacterial attack. Furthermore, McIL-17-3 was negatively regulated by Mc-novel_miR_145 to participate in LPS-induced apoptosis. Our findings provide new insights into noncoding RNA regulation in invertebrate models.

TLR4 involved in immune response against Vibrio Parahaemolyticus by MyD88-dependent pathway in Crassostrea hongkongensis

Vibrio parahaemolyticus (V. parahaemolyticus) is a salt-loving gram-negative bacterium, and is the leading cause of mortality in cultured shellfish in recent years. Toll-like Receptor 4 (TLR4) is a classical pattern recognition receptor (PRRs) that recognizes pathogen-associated molecular patterns (PAMPs) of pathogenic microorganism and activates the immune response. However, the function and signal pathway of TLR4 in oyster are still unknown. In this study, a new TLR4 gene was identified from the Crassostrea hongkongensis (C. hongkongensis). The ChTLR4 contained an open reading frame of 2643 bp, encoding 880 amino acids with seven leucine-rich repeat (LRR) domains and a Toll/IL-1R (TIR) domain. The ChTLR4 shared the highest sequence identity (83.0%) with TLR4 of Crassostrea gigas. Tissue expression analysis revealed that ChTLR4 showed the highest constitutive expression in the gill and hepatopancreas, and was significantly upregulated in immune tissues post V. parahaemolyticus infection, especially in gill and hemocytes. Moreover, TLR4 silencing significantly inhibited the immune-enzyme activities, including SOD, CAT, ACP, AKP in gill and LZM in hemolymph supernatant, and increased MDA content in hemolymph supernatant. Meanwhile, the antimicrobial activities of the hemolymph supernatant were also significantly inhibited by TLR4 silencing. These data demonstrated that the ChTLR4 involved in innate immune response of C. hongkongensis against V. parahaemolyticus challenge. Finally, qRT-PCR analysis showed that ChTLR4 silencing clearly inhibited the expression of genes in TLR4-MyD88 pathway, indicating that MyD88-dependent pathway played a crucial role in ChTLR4-mediated immune response against V. parahaemolyticus.

An Interleukin-17 Isoform from Thick Shell Mussel Mytilus coruscus Serves as a Mediator of Inflammatory Response

The inflammatory cytokine interleukin-17 (IL17) plays an important role in innate immunity by binding to its receptors (IL17Rs) to activate immune defense signals. To date, information on members of the IL17 family is still very limited in molluscan species. Here, a novel member of the IL17 family was identified and characterized from thick shell mussel Mytilus coruscus, and this gene was designated as McIL17-1 by predicting structural domains and phylogenetic analysis. McIL17-1 transcripts existed in all examined tissues with high expression levels in gills, hemocytes and digestive glands. After the stimuli of different pathogen associated molecular patterns (PAMPs) for 72 h, transcriptional expression of McIL17-1 was significantly upregulated, except for poly I:C stimulation. Cytoplasm localization of McIL17-1 was shown in HEK293T cells by fluorescence microscopy. Further, in vivo and in vitro assays were performed to evaluate the potential function of McIL17-1 played in immune response. McIL17-1 was either knocked down or overexpressed in vivo through RNA inference (RNAi) and recombinant protein injection, respectively. With the infection of living Vibrio alginolyticus, a high mortality rate was exhibited in the McIL17-1 overexpressed group compared to the control group, while a lower mortality rate was observed in the McIL17-1 knocked down group than control group. In vitro, the flow cytometric analysis showed that the apoptosis rate of McIL17-1 inhibited hemocytes was significantly lower than that of the control group after lipopolysaccharide stimulation. These results collectively suggested that the newly identified IL17 isoform is involved in the inflammatory response to bacterial infection in M. coruscus.

CgDM9CP-5-Integrin-MAPK Pathway Regulates the Production of CgIL-17s and Cgdefensins in the Pacific Oyster, Crassostrea gigas

DM9 domain containing protein (DM9CP) is a family of newly identified recognition receptors exiting in most organisms except plants and mammals. In the current study, to our knowledge, a novel DM9CP-5 (CgDM9CP-5) with two tandem DM9 repeats and high expression level in gill was identified from the Pacific oyster, Crassostrea gigas. The deduced amino acid sequence of CgDM9CP-5 shared 62.1% identity with CgDM9CP-1 from C. gigas, and 47.8% identity with OeFAMeT from Ostrea edulis. The recombinant CgDM9CP-5 (rCgDM9CP-5) was able to bind d-mannose, LPS, peptidoglycan, and polyinosinic-polycytidylic acid, as well as fungi Pichia pastoris, Gram-negative bacteria Escherichia coli and Vibrio splendidus, and Gram-positive bacteria Staphylococcus aureus. The mRNA transcript of CgDM9CP-5 was highly expressed in gill, and its protein was mainly distributed in gill mucus. After the stimulations with V. splendidus and mannose, mRNA expression of CgDM9CP-5 in oyster gill was significantly upregulated and reached the peak level at 6 and 24 h, which was 13.58-fold (p < 0.05) and 14.01-fold (p < 0.05) of that in the control group, respectively. CgDM9CP-5 was able to bind CgIntegrin both in vivo and in vitro. After CgDM9CP-5 or CgIntegrin was knocked down by RNA interference, the phosphorylation levels of JNK and P38 in the MAPK pathway decreased, and the expression levels of CgIL-17s (CgIL-17-3, -4, -5, and -6), Cg-Defh1, Cg-Defh2, and CgMolluscidin were significantly downregulated. These results suggested that there was a pathway of DM9CP-5-Integrin-MAPK mediated by CgDM9CP-5 to regulate the release of proinflammatory factors and defensins in C. gigas.

β-1,3-Glucan/chitin unmasking in the Saccharomyces cerevisiae mutant, Δmnn9, promotes immune response and resistance of the Pacific oyster (Crassostrea gigas) to Vibrio coralliilyticus infection

Yeast cells can play a crucial role in immune activation in fish and shellfish predominantly due to the cell wall component β-1,3-glucan, providing protection against bacterial or viral infections. However, the immunostimulatory capacity of dietary yeast cells remains poorly studied in bivalves. To understand the role of yeast cell wall components (mannan, β-glucan and chitin) as immune activators, this study characterized the surface carbohydrate exposure of the wild-type baker's yeast Saccharomyces cerevisiae (WT) and its Δmnn9 mutant, which presents a defective mannan structure, and compared these profiles with that of β-glucan particles, using fluorescein isothiocyanate (FITC)-labeled lectin binding analysis. Then, a first trial evaluated the immunological response in Crassostrea gigas juveniles after being fed for 24 h with an algae-based diet (100A) and its 50% substituted version (based on dry weight) with WT (50A50WT) and Δmnn9 (50A50Y), and the posterior resistance of the juveniles against Vibrio coralliilyticus infection (trial 1). The mRNA expression was measured for β-glucan-binding protein (CgβGBP), Toll-like receptor 4 (CgTLR4), C-type lectin receptor 3 (CgCLec-3), myeloid differentiation factor 88 (CgMyD88), nuclear factor-kappa B (CgNFκB), lysozyme (CgLys), interleukin 17-5 (CgIL17-5), and superoxide dismutase (CgSOD), in oysters, before and 24 h after the bacterial inoculation. A second trial tested the effect of incorporating Δmnn9 into the 100A diet for 24 h at different substitution levels: 0, 5, 10, 25, and 50% (100A, 95A5Y, 90A10Y, 75A25Y, and 50A50Y), followed by the bacterial challenge with V. coralliilyticus (trial 2). Our findings showed that the outer cell wall surface of WT is largely composed of mannan, while Δmnn9 presents high exposure of β-glucan and chitin, exhibiting similar FITC-lectin binding profiles (fluorescence intensity) to β-glucan particles. A significantly higher survival after the bacterial challenge was observed in oysters fed on 50A50Y compared to those fed 50A50WT and 100A in trial 1. This better performance of 50A50Y was supported by significantly higher gene expressions of CgLys, CgSOD, CgMyD88, and CgβGBP compared to 100A, and CgSOD and CgNFκB in relation to those fed on 50A50WT, prior to the bacterial inoculation. Furthermore, improved survival was observed in oysters fed 50A50Y compared to those offered lower Δmnn9 levels and 100A in trial 2. The superior performance of Δmnn9-fed oysters is mostly associated with the elevated presence of unmasked β-glucans on Δmnn9 cell wall surface, facilitating their interactions with oyster hemocytes. Further studies are needed to evaluate administration dose and frequency of Δmnn9 to develop strategies for long-term feeding.

A stimulator of interferon gene (CgSTING) involved in antimicrobial immune response of oyster Crassostrea gigas

The stimulator of interferon gene (STING), an intracellular sensor of cyclic dinucleotides, is critical to the innate immune response, especially the induction of type I interferon (IFN) during pathogenic infection. A STING homologue (CgSTING) regulating the expression of IFN-like protein (CgIFNLP) was previously identified in the Pacific oyster Crassostrea gigas, and its involvement in antibacterial immunity was further investigated in the present study. The mRNA transcripts of CgSTING were ubiquitously detected in all the three subpopulations of haemocytes with the highest expression in semi-granulocytes. After the stimulation with Vibrio splendidus, the mRNA expression of CgSTING in haemocytes was significantly up-regulated and peaked at 72 h, which was 12.91-fold of that in control group (p < 0.01). The CgSTING protein was mainly located in the cytoplasm of haemocytes. After the expression of CgSTING was knocked down (0.12-fold of that in control group, p < 0.05) by RNAi, the mRNA expression levels of interleukin17-1 (CgIL17-1), interleukin17-3 (CgIL17-3), interleukin17-4 (CgIL17-4), defensins (Cgdefh1, Cgdefh2), big defensin (CgBigDef1), interferon-like protein (CgIFNLP), tumor necrosis factor (CgTNF) and nuclear factor-κB (CgRel) all decreased significantly at 12 h after V. splendidus stimulation, which was 0.12-fold-0.72-fold (p < 0.05) of that in control group, respectively. The positive signals of CgRel were observed in the haemocyte nucleus after V. splendidus stimulation. The nuclear translocation of CgRel was suppressed in CgSTING-RNAi oysters, and the green signals of CgRel were mainly observed in the haemocyte cytoplasm after V. splendidus stimulation. Furthermore, the number of V. splendidus in the haemolymph of CgSTING-RNAi oysters increased significantly, which was 26.78-fold (p < 0.01) of that in the control group at 12 h after V. splendidus stimulation. These results indicated that CgSTING played important role in the immune defense against bacterial infection by inducing the expressions of cytokines and defensins.

CgHMGB1 functions as a broad-spectrum recognition molecule to induce the expressions of CgIL17-5 and Cgdefh2 via MAPK or NF-κB signaling pathway in Crassostrea gigas

High-mobility group box 1 (HMGB1), a highly conserved nucleoprotein, functions in immune recognition, inflammation and antibacterial immunization in vertebrates. In the present study, the mediation mechanism of CgHMGB1 in activating MAPK and NF-κB/Rel signaling pathways to induce the expressions of immune effectors was investigated. CgHMGB1 mRNA was detected in all tested developmental stages from fertilized egg to D-larvae, with the higher expressions in 4-cell and 8-cell stages. CgHMGB1 proteins were mainly distributed in haemocyte granulocytes. The expressions of CgHMGB1 mRNA in haemocytes increased significantly after Vibrio splendidus stimulation, and CgHMGB1 protein translocated into the haemocyte cytoplasm and release into cell-free haemolymph. The phosphorylation of CgERK and CgP38 were induced, the nuclear translocation of CgRel were promoted, and the mRNA expressions of CgIL17-5 and Cgdefh2 increased significantly after rCgHMGB1 treatment. Obvious branchial swelling and cilium shedding were observed after rCgHMGB1 treatment. rCgHMGB1 exhibited binding activity to different polysaccharides, bacteria, and fungi. rCgHMGB1 also displayed obvious antibacterial activity to V. splendidus and E. coli. These results indicated that CgHMGB1 functioned as an immune recognition molecule to recognize various PAMPs and bacteria to induce the mRNA expressions of CgIL17-5 and Cgdefh2 via the activation of MAPK and NF-κB signaling pathways in oysters.

CgIL17-5 regulates the mRNA expressions of immune effectors through inducing the phosphorylation of CgMAPKs and the nuclear translocation of CgRel and CgAP-1 in the Pacific oyster Crassostrea gigas

Interleukin-17 (IL-17) is a classic pro-inflammatory cytokine that plays an important role in the immune and inflammatory response. In the present study, the sequence feature of CgIL17-5 and its function as a pro-inflammatory factor in inducing the mRNA expressions of downstream immune effectors were investigated in oyster Crassostrea gigas. There were two tightly folded alpha helixes and two pairs of antiparallel beta-pleated sheet in the amino acid sequence of CgIL17-5. The mRNA transcripts of CgIL17-5 were constitutively distributed in all the tested tissues, with the highest level in haemocytes. The mRNA expression level of CgIL17-5 in haemocytes increased significantly at 24 h after Vibrio splendidus stimulation. CgIL17-5 protein was mainly detected in granulocytes which were the main immunocompetent haemocytes in C. gigas. The phosphorylation of mitogen-activated protein kinases (CgJNK, CgERK and CgP38) and nuclear translocation of the transcription factors (CgRel and CgAP-1) in haemocytes were induced after the oysters received an injection of recombinant CgIL17-5 for 2 h. The mRNA expression levels of CgIL-17s, CgTNF-1, Cgdefh1 and Cgdefh2 increased significantly in haemocytes. At the same time, obvious branchial swelling and cilium shedding in gills were observed at 24 h after the oysters received an injection of rCgIL17-5. All the results collectively suggested that CgIL17-5 promoted the activation of CgMAPKs and the nuclear translocation of CgRel and CgAP-1 to promote the mRNA expressions of cytokines and antibacterial peptides.

IL-17/IL-17 Receptor Pathway-Mediated Inflammatory Response in Apostichopus japonicus Supports the Conserved Functions of Cytokines in Invertebrates

Inflammation participates in host defenses against infectious agents and contributes to the pathophysiology of many diseases. IL-17 is a well-known proinflammatory cytokine that contributes to various aspects of inflammation in vertebrates. However, the functional role of invertebrate IL-17 in inflammatory regulation is not well understood. In this study, we first established an inflammatory model in the Vibrio splendidus-challenged sea cucumber Apostichopus japonicus (Echinodermata). Typical inflammatory symptoms, such as increased coelomocyte infiltration, tissue vacuoles, and tissue fractures, were observed in the V. splendidus-infected and diseased tissue of the body wall. Interestingly, A. japonicus IL-17 (AjIL-17) expression in the body wall and coelomocytes was positively correlated with the development of inflammation. The administration of purified recombinant AjIL-17 protein also directly promoted inflammation in A. japonicus Through genome searches and ZDOCK prediction, a novel IL-17R counterpart containing FNIII and hypothetical TIR domains was identified in the sea cucumber genome. Coimmunoprecipitation, far-Western blotting, and laser confocal microscopy confirmed that AjIL-17R could bind AjIL-17. A subsequent cross-linking assay revealed that the AjIL-17 dimer mediates the inflammatory response by the specific binding of dimeric AjIL-17R upon pathogen infection. Moreover, silencing AjIL-17R significantly attenuated the LPS- or exogenous AjIL-17-mediated inflammatory response. Functional analysis revealed that AjIL-17/AjIL-17R modulated inflammatory responses by promoting A. japonicus TRAF6 ubiquitination and p65 nuclear translocation and evenly mediated coelomocyte proliferation and migration. Taken together, our results provide functional evidence that IL-17 is a conserved cytokine in invertebrates and vertebrates associated with inflammatory regulation via the IL-17-IL-17R-TRAF6 axis.

BCL10 regulates the production of proinflammatory cytokines by activating MAPK-NF-κB/Rel signaling pathway in oysters

B cell lymphoma/leukemia 10 (BCL10) is an important member of the caspase recruitment domain-containing (CARD) protein family, which plays crucial roles in mediating the host inflammatory response. In the present study, a BCL10 homologue was identified from Pacific oyster Crassostrea gigas (designed as CgBCL10). The full length cDNA of CgBCL10 was of 897 bp with an open reading frame of 522 bp encoding a polypeptide of 174 amino acids containing a classical CARD domain. The deduced amino acid sequence of CgBCL10 shared low similarity with the previously identified BCL10s from other species. In the phylogenetic tree, CgBCL10 was firstly clustered with CvBCL10 from Crassostrea virginica and then assigned into the branch of invertebrate BCL10s. The mRNA transcripts of CgBCL10 were highly expressed in gonad, gill, adductor muscle, and haemocytes. After Vibrio splendidus stimulation, the mRNA expression level of CgBCL10 in haemocytes increased significantly (p < 0.01) at 24, 72 and 96 h. In CgBCL10-RNAi oysters, the phosphorylation level of mitogen-activated protein kinases (MAPKs), nuclear translocation of NF-κB/Rel and activator protein-1 (AP-1) in haemocytes were inhibited, and the mRNA expressions of inflammatory cytokines including CgIL17-1, CgIL17-2, CgIL17-3, CgIL17-6 and CgTNF all decreased significantly (p < 0.01) at 12 h after V. splendidus stimulation. These results suggested that CgBCL10 regulated the expression of inflammatory cytokines by activating MAPK kinase, and nuclear translocation of NF-κB/Rel and AP-1 to defense pathogen.

The involvement of CgCaspase-8-2 in regulating the expressions of cytokines, antibacterial peptide and autophagy-related genes in oysters

Caspase-8 has been reported to be involved not only in apoptosis, but also in many other important immune response processes, such as inflammation and autophagy. In the present study, the open reading frame of CgCaspase-8-2 was cloned from the Pacific oyster Crassostrea gigas, which was of 2160 bp encoding 737 amino acids. There were two death effector domains (DEDs) and a cysteine aspartase cysteine structural (CASc) domain in the deduced amino acid sequences of CgCaspase-8-2. The mRNA expressions of CgCaspase-8-2 in haemocytes and gills all increased significantly after Vibrio splendidus stimulation at 3 h, 6 h, and 24 h. The cleaved CgCaspase-8-2 protein was observed in haemocytes at 3 h after V. splendidus stimulation and the expression of CgCaspase-8-2 protein was relatively higher in granulocytes, compared with that in agranulocytes. In CgCaspase-8-2-RNAi oysters, the mRNA expressions of CgIL17s (CgIL17-1, -2, -3, -4, -6), CgTNF, CgIFNLP and CgBigDef1 all decreased significantly at 12 h after V. splendidus stimulation. Meanwhile, the mRNA expressions of CgATG5 and CgBeclin1 decreased significantly at 12 h after V. splendidus stimulation, while CgBcl2 increased significantly. These results indicated that CgCaspase-8-2 was involved in not only the regulation of cytokine and antibacterial peptide production, but also autophagy-related gene expressions.

Histopathology, antioxidant responses, transcriptome and gene expression analysis in triangle sail mussel Hyriopsis cumingii after bacterial infection

Bacterial disease outbreaks in filter feeder bivalve Hyriopsis cumingii as water contamination become more frequent in the water ecosystem, especially in intensive aquaculture habitats. To characterize host-pathogen interactions between H. cumingii and bacterial infection, we investigated the effects of Stenotrophomonas maltophilia HOP3 and Aeromonas veronii GL1 on the antioxidant response, tissue invasion and transcriptome expression of H. cumingii by infectivity trials. We showed that bacterial infections resulted in tubular necrosis of the hepatopancreas and induced the acute immune response in H. cumingii. The transcriptomic study identified a total of 5957 differentially expressed genes (DEGs) after A. veronii challenge. These DEGs were implicated in 302 KEGG pathways, notably in Apoptosis, Phagosome and Lysosome. The results showed that the relative expressions of all six immune-related DEGs were effectively stimulated with A. veronii, accompanied by tissue differences. Overall, these findings will contribute to an analysis of the immune response of H. cumingii to bacterial infection at the transcriptomic level and its genomic resource for research.

The DNA cytosine-5-methyltransferase 3 (DNMT3) involved in regulation of CgIL-17 expression in the immune response of oyster Crassostrea gigas

DNA methyltransferase, a key enzyme mediating DNA methylation, is involved in numerous processes including genomic imprinting, X chromosome inactivation, transposable element suppression, and immune defense in vertebrates. In the present study, a DNA cytosine-5-methyltransferase 3 was identified from oyster Crassostrea gigas (designed as CgDNMT3). There were a PWWP domain, a PHD domain and a DNA-methylase domain in the deduced amino acid sequences of CgDNMT3, and the conserved motifs I, IV, VI, Ⅷ, IX and X were identified in its C-terminal catalytic DNA-methylase domain. The mRNA transcripts of CgDNMT3 were detected in haemocytes, mantle, gill, adductor muscle, digestive gland and labial palp, with higher expression level in haemocytes (6.54 folds of those in gill, p < 0.01). The expression level of CgDNMT3 mRNA in haemocytes increased significantly after LPS primed (2.87 folds of that in control group, p < 0.05) in vitro or Vibrio splendidus challenging (1.94 folds of that in control group, p < 0.05) in vivo. Immunocytochemical analysis revealed that CgDNMT3 protein was distributed mainly in cytoplasm and partial in nucleus of oyster haemocytes. After CgDNMT3 was transfected and expressed in HEK293T cells, the DNA 5-methylcytosine (5-mc) level in the transfected group was significantly increased, which was 1.22 folds (p < 0.05) of the pcDNA-3.1 group. The expressions of oyster CgIL17-1, CgIL17-2 and CgIL17-5 in haemocytes increased (13.05 folds, 4.78 folds and 9.41 folds of that in control group, respectively) at 12 h after V. splendidus challenging, but the increase were significantly inhibited when the oysters were pre-treated with DNA methyltransferase inhibitor 5-Azacytidine, which were 9 folds, 1.93 folds and 3.22 folds of that in control group, respectively. These results collectively suggested that CgDNMT3 was a conserved member of DNA methyltransferase 3 family in oyster, and participated in regulating the expression of cytokines during immune response.

A hexokinase from the oyster Crassostrea gigas is involved in immune recognition as a pattern recognition receptor

Hexokinase (HK) is generally recognized as a crucial enzyme participating in glycolysis. In the present study, a HK (named CgHK) was identified as a potential pattern recognition receptor (PRR) from the Pacific oyster Crassostrea gigas. The open reading frame (ORF) of CgHK was of 1395 bp, encoding a peptide of 464 amino acids with one Hexokinase_1 domain and one Hexokinase_2 domain. The predicted amino acid sequence of CgHK shared 17%-29% similarities with that of other known HKs. The mRNA transcripts of CgHK were constitutively detected in all the examined tissues, with relative high expression level in labial palp and haemocytes. CgHK protein was mainly observed in the cytoplasm of oyster haemocytes. The mRNA expression level of CgHK in haemocytes was significantly up-regulated and peaked at 3 h after Vibrio splendidus (7.64-fold, p < 0.001) and lipopolysaccharide (LPS) (11.86-fold, p < 0.001) stimulations. The recombinant CgHK protein (rCgHK) exhibited Mg²⁺-dependent adenosine triphosphate (ATP) binding activity in vitro and activity to bind D-(+)-glucose (GLU) and various pathogen-associated molecular pattern (PAMPs) such as LPS and peptidoglycan (PGN) in the absence of Mg²⁺. It also displayed higher binding activity towards V. splendidus and relatively lower binding activity towards Staphylococcus aureus, Escherichia coli, and Micrococcus luteus. After the mRNA expression of CgHK in haemocytes was knocked down by dsRNA interference, the expression of CgIL17-5 mRNA in haemocytes was considerably down-regulated at 3 h after the stimulation with V. splendidus (0.33-fold, p < 0.001). These results collectively indicated that CgHK was able to recognize various PAMPs and pathogenic bacteria as a PRR apart from being the enzyme to exert ATP binding activity in glycolysis, and activate the anti-bacterial immune response by promoting the expression of pro-inflammatory cytokines CgIL17-5 in oyster haemocytes.

Transcriptome Profiling of the Pacific Oyster Crassostrea gigas Visceral Ganglia over a Reproduction Cycle Identifies Novel Regulatory Peptides

The neuropeptides involved in the regulation of reproduction in the Pacific oyster (Crassostrea gigas) are quite diverse. To investigate this diversity, a transcriptomic survey of the visceral ganglia (VG) was carried out over an annual reproductive cycle. RNA-seq data from 26 samples corresponding to VG at different stages of reproduction were de novo assembled to generate a specific reference transcriptome of the oyster nervous system and used to identify differentially expressed transcripts. Transcriptome mining led to the identification of novel neuropeptide precursors (NPPs) related to the bilaterian Eclosion Hormone (EH), crustacean female sex hormone/Interleukin 17, Nesfatin, neuroparsin/IGFBP, prokineticins, and urotensin I; to the protostome GNQQN, pleurin, prohormones 3 and 4, prothoracotropic hormones (PTTH), and QSamide/PXXXamide; to the lophotrochozoan CCWamide, CLCCY, HFAamide, and LXRX; and to the mollusk-specific NPPs CCCGS, clionin, FYFY, GNamide, GRWRN, GSWN, GWE, IWMPxxGYxx, LXRYamide, RTLFamide, SLRFamide, and WGAGamide. Among the complete repertoire of NPPs, no sex-biased expression was observed. However, 25 NPPs displayed reproduction stage-specific expression, supporting their involvement in the control of gametogenesis or associated metabolisms.

The Evolution and Diversity of Interleukin-17 Highlight an Expansion in Marine Invertebrates and Its Conserved Role in Mucosal Immunity

The interleukin-17 (IL-17) family consists of proinflammatory cytokines conserved during evolution. A comparative genomics approach was applied to examine IL-17 throughout evolution from poriferans to higher vertebrates. Cnidaria was highlighted as the most ancient diverged phylum, and several evolutionary patterns were revealed. Large expansions of the IL-17 repertoire were observed in marine molluscs and echinoderm species. We further studied this expansion in filter-fed Mytilus galloprovincialis, which is a bivalve with a highly effective innate immune system supported by a variable pangenome. We recovered 379 unique IL-17 sequences and 96 receptors from individual genomes that were classified into 23 and 6 isoforms after phylogenetic analyses. Mussel IL-17 isoforms were conserved among individuals and shared between closely related Mytilidae species. Certain isoforms were specifically implicated in the response to a waterborne infection with Vibrio splendidus in mussel gills. The involvement of IL-17 in mucosal immune responses could be conserved in higher vertebrates from these ancestral lineages.

CLec-TM1-ERK-GSK3β Pathway Regulates Vibrio splendidus-Induced IL-17 Production in Oyster

C-type lectins are a family of pattern recognition receptors that recognize microbial components and subsequently activate the signaling cascade to induce the production of proinflammatory cytokines. In the current study, the homologs of ERK (named as CgERK) and GSK3β (named as CgGSK3β) and a novel C-type lectin with a transmembrane domain (named as CgCLec-TM1) were identified from oyster Crassostrea gigas CgCLec-TM1 was able to bind Escherichia coli and Vibrio splendidus through its carbohydrate recognition domain and then activated CgERK by inducing its phosphorylation. The activated CgERK interacted with CgGSK3β to phosphorylate it at Ser⁹, which eventually induced the expressions of CgIL-17-1 and CgIL-17-5. The interaction between CgERK and CgGSK3β, as well as the phosphorylation of CgGSK3β, could be inhibited by ERK inhibitor (PD98059) to reduce the expressions of CgIL-17-1 and CgIL-17-5. CgGSK3β in oyster was proposed as a new substrate of CgERK. The results defined a CLec-TM1-ERK-GSK3β signaling pathway in oyster, which was activated by V. splendidus and then induced CgIL-17 productions.

Characterization and expression analysis of tandemly duplicated nicotinic acetylcholine receptors in pearl oysters after stimulation of pathogen-related molecular patterns

Nicotinic acetylcholine receptors (nAChRs) are a class of ligand-gated ion channels that participate in signal transduction and are reported to play an important role in the immunomodulation of vertebrates and invertebrates. Previous studies have shown that the nAChRs in mollusks have undergone large-scale expansion after tandem repeats and retrotransposition, with the most expansion observed in bivalves. This study characterized the sequence of a tandem repeat nAChR unique to several bivalve mollusks and investigated its functions in Pinctada fucata martensii. Firstly, phylogenetic analysis revealed that the tandem arrays of nAChRs existed before bivalve differentiation and m ost tandem-replicated nAChR genes have a conserved genomic structure and domain combination. In present study, five tandemly duplicated nAChR genes were cloned from P. f. martensii and designated as PmnAChR-1 to PmnAChR-5. qRT-PCR analysis revealed that five PmnAChRs were specifically expressed in adult gills. In addition, after PAMP stimulation, the expression of PmnAChRs in hemocytes of P. f. martensii were strongly induced but exhibited different responses to different stimuli. PmnAChR-1, PmnAChR-4, and PmnAChR-5 exhibited strong and wide responsiveness to lipopolysaccharide (LPS) stimulation but had no response to peptidoglycan (PGN) stimulation. PmnAChR-2 expression was notably upregulated at 6 h after PGN challenge but had no response to LPS stimulation. Polyinosinic-polycytidylic acid challenge upregulated nearly all PmnAChRs, except for PmnAChR-5. Furthermore, Pm-miR-873-3p, Pm-miR-4577, Pm-miR-103a-3p, and Pm-miR-6753-3p were identified as the regulatory miRNA of PmnAChR-1, PmnAChR-3, PmnAChR-4, and PmnAChR-5, respectively. These findings suggested that these tandem arrays of nAChRs are unique to bivalves, and the tandem duplication of nAChR genes may be involved in the immune regulation process after pathogen stimulation.

Identification, expression and pro-inflammatory effect of interleukin-17 N in common carp (Cyprinus carpio L.)

Two interleukin (IL)-17 N genes (CcIL-17Na and b) present on different linkage groups were identified in the common carp (Cyprinus carpio) genome and confirmed by polymerase chain reaction (PCR) and real time (RT)-PCR in this experiment. Synteny analysis revealed that IL-17 N is transcribed by the complement sequence of TOP3B's intron 2. It is flanked by SDF2L and PPM1F in all fish studied to date, except fugu (Takifugu rubripes). The open reading frames of the two CcIL-17Ns are 411 base pairs long and encode 136 amino acids. The amino acid identity/similarity between CcIL-17Na and b is 91.2%/97.1%. The CcIL-17Ns share identity (46.8-90.4%) with their orthologs from other teleosts. Identities/similarities to other members of the IL-17 family in common carp were low at 21.4-30.2%/31.4-51.4%. In the phylogenetic tree, IL-17Ns from spotted gar (Lepisosteus oculatus, the ancestor of teleosts) and coelacanth (Latimeria chalumnae, the ancestor of tetrapods) were grouped within the same branch with a high bootstrap value of 97%, which indicates that IL-17 N is an ancient and conserved gene. Quantitative RT-PCR results showed that CcIL-17Ns were most highly expressed in the brain of healthy individuals. The expression in brain was significantly induced at 6 h post Aeromonas hydrophila infection; at 1 day post infection, expression in liver, muscle, skin, spleen, and head kidney was up-regulated. In addition, the upregulated expression of proinflammatory cytokines IL-1β, IFN-γ, IL-6, chemokine CCL20, NF - κ B and TRAF6 in kidney tissue by ccIL-17 N recombinant protein also indicate that IL-17 N can promote inflammation through NF-κB pathway and induce the expression of chemokines and inflammatory factors.

IMPACT OF LOW SALINITY ON HEMOCYTES MORPHOLOGY AND FUNCTIONAL ASPECTS IN INVASIVE CLAM ANADARA KAGOSHIMENSIS (TOKUNAGA, 1906)

Impact of low salinity on morphology and function of hemocytes in ark clam species Anadara kagoshimensis was investigated using light microscopy and flow cytometry. In control group the water salinity was adjusted to 19.6‰, and experimental group was maintained at 14.8‰ and 8.8‰. Two cell types, amebocytes and erythrocytes, were identified in control group of ark clams. Erythrocytes constituted the main type of the cells, and amounted to 92.3±3.9 %. Hyposalinity changed that proportion: the number of amebocytes decreased 2.7 times and number of erythrocytes increased 7.6 times. Morphometric characteristics of hemocytes didn’t show statistically significant changes. As far as salinity decreased, the number of erythrocyte shades in hemolymph increased (3.5 times at salinity 8.8‰) and, in hemocytes, the reactive oxygen species (ROS) production grew (3.5. times at salinity 8.8‰).

Estrogen receptor regulates immune defense by suppressing NF-κB signaling in the Crassostrea hongkongensis

The crosstalk between the estrogen receptor (ER) and NF-κB signalling pathways has merged in vertebrates and plays a key role in the control of genes involved in inflammation, cell proliferation and apoptosis. However, such crosstalk between the endocrine and immune systems needs to be explored in lower invertebrates. In this study, we identified a 2856-bp homologue of the estrogen receptor from Hong Kong oyster (ChER), containing a 5' untranslated region (UTR) of 234 bp, a 3' UTR of 387 bp, and an open reading frame (ORF) of 2235 bp. We observed that overexpression of ChER suppressed ChRel-dependent NF-kappaB (NF-κB) activation in the HEK293T (human embryonic kidney 293T) cell line, and depletion of ChER in vivo resulted in upregulation of two NF-κB-responsive marker genes, namely, TNF-α and IL-17, which confirmed its potential role in controlling NF-κB signalling. Furthermore, an EMSA (electrophoretic mobility shift assay) showed that ChER could negatively regulate the binding of ChRel to NF-κB probe-responsive elements. Serial domain requirement analysis showed that both region C (DNA-binding domain) and region E (ligand-binding domain) of ChER were essential for mediating the crosstalk underlying ChER-dependent NF-κB suppression. In conclusion, we demonstrate for the first time the negative regulatory role of the ER in NF-κB signalling in oysters, strongly indicating the presence of complex crosstalk between the endocrine and immune systems in lower marine molluscs.

A novel Adiponectin receptor (AdipoR) involved in regulating cytokines production and apoptosis of haemocytes in oyster Crassostrea gigas

Adiponectin receptors (AdipoRs) comprise a seven-transmembrane domain-containing protein family, which specifically recognize adiponectin (APN) and play critical roles in the immunological and physiological processes in vertebrates. In the present study, a novel AdipoR is identified from oyster Crassostrea gigas (designated as CgAdipoR). The full-length cDNA of CgAdipoR is of 1209 bp encoding a polypeptide of 343 amino acids. There is an N-terminal domain, a Hly III domain, and a C-terminal domain in CgAdipoR. After the transfection of CgAdipoR, the level of intracellular Ca²⁺ into HEK293T cells increases significantly (1.36-fold, p < 0.05) after APN incubation. The mRNA transcripts of CgAdipoR are widely distributed in all the tested tissues, with the highest expression level in haemocytes (3.20-fold of that in hepatopancreas, p < 0.05). After lipopolysaccharide (LPS), Vibrio splendidus and polyinosinic-polycytidylic acid (poly (I:C)) stimulations, the mRNA expression of CgAdipoR in haemocytes is significantly up-regulated and reached the highest level at 24 h (15.07-fold, p < 0.01), 6 h (4.39-fold, p < 0.01) and 24 h (5.62-fold, p < 0.01) compared to control group, respectively. After CgAdipoR is interfered by specific CgAdipoR-dsRNA, the expression level of interleukins (CgIL17-1, CgIL17-2, CgIL17-3 and CgIL17-5) in haemocytes decreases significantly (p < 0.01) at 24 h post LPS stimulation, while the expression level of CgTNF-1 increases significantly (1.68-fold, p < 0.01), compared to that in the dsEGFP group. In CgAdipoR dsRNA-injected oysters, the mRNA expressions of anti-apoptotic B-cell lymphoma-2 (Bcl-2) in haemocytes significantly decreases at 24 h after LPS challenge, which is (0.58-fold, p < 0.05) of that in dsEGFP-injected oysters, while the apoptotic rate of haemocytes is significantly up-regulated (1.93-fold of that in dsEGFP group, p < 0.05). These results collectively suggest that CgAdipoR plays an important role in the immune response of oysters by regulating the expressions of inflammatory cytokines and haemocyte apoptosis.

A novel programmed cell death protein 4 negatively regulates CgIL17-5 expression in hemocytes of oyster Pacific oyster (Crassostrea gigas)

The programmed cell death protein 4 (PDCD4) is a newly defined transcriptional and translational inhibitor, which plays a key role in regulating the synthesis of inflammatory cytokines in vertebrates species. In the present study, the full-length cDNA of PDCD4 from oyster Crassostrea gigas (designed as CgPDCD4) was identified to explore its possible involvement in immune response. The open reading frame of pdcd4 gene was of 1344 bp encoding a polypeptide of 447 amino acids with two conserved MA-3 domains. The deduced amino acid sequence of CgPDCD4 shared 60.18% similarity with PDCD4 from Mizuhopecten yessoensis. The mRNA transcripts of CgPDCD4 could be detected in all the tested tissues with a higher expression level in adductor muscle and hemocytes. The mRNA expression of CgPDCD4 in hemocytes was significantly down-regulated at 3 h and 6 h (0.61-fold and 0.42-fold of that in PBS group, p < 0.01, respectively) after LPS stimulation. In hemocytes, CgPDCD4 protein was found to be mainly located in the cytoplasm. After the mRNA expression of CgPDCD4 in hemocytes was knocked down (0.40-fold of that in EGFP-RNAi group) by CgPDCD4 dsRNA (dsCgPDCD4) injection, the CgIL17-5 transcripts were up-regulated (20.11-fold of that in PBS group, p < 0.01) post LPS stimulation, which was significantly higher than that in dsEGFP-injected oysters (7.06-fold of that in PBS group, p < 0.01). Meanwhile, the nuclear translocation of CgRel (homologue of Rel/NF-κB) was significantly enhanced (about 1.36-fold of that in PBS group, p < 0.01), but it was similar as that in EGFP-RNAi group (about 1.52-fold of that in PBS group, p < 0.01) after LPS stimulation. All the results suggested that CgPDCD4 in oysters played the same role as PDCD4 of vertebrates in negatively regulating the production of interleukin in immune response, but the underpinning signal pathway was not conserved during evolution.

AP-1 regulates the expression of IL17-4 and IL17-5 in the pacific oyster Crassostrea gigas

The activator protein-1 (AP-1) plays an important role in inducing the immune effector production in response to cellular stress and bacterial infection. In the present study, an AP-1 was identified from Pacific oyster Crassostrea gigas (designed as CgAP-1) and its function was investigated in response against lipopolysaccharide (LPS) stimulation. CgAP-1 was consisted of 290 amino acids including a Jun domain and a basic region leucine zipper (bZIP) domain. CgAP-1 shared 98.6% similarities with ChAP-1 from oyster C. hongkongensis, and assigned into the branch of invertebrates in the phylogenetic tree. The mRNA transcripts of CgAP-1 gene were detected in all tested tissues with highest expression level in hemocytes, especially in granulocytes. The mRNA expression level of CgAP-1 gene in hemocytes was significantly up-regulated (8.53-fold of that in PBS group, p < 0.01) at 6 h after LPS stimulation. CgAP-1 protein could be translocated into the nucleus of oyster hemocytes after LPS stimulation. The mRNA transcripts of interleukin17s (CgIL17-4 and CgIL17-5) in the hemocytes of CgAP-1-RNAi oysters decreased significantly at 24 h after LPS stimulation, which were 0.37-fold (p < 0.05) and 0.17-fold (p < 0.01) compared with that in EGFP-RNAi oysters, respectively. The results suggested that CgAP-1 played an important role in the immune response of oyster by regulating the expression of CgIL17s.

CgRel involved in antibacterial immunity by regulating the production of CgIL17s and CgBigDef1 in the Pacific oyster Crassostrea gigas

The NF-κB/Rel transcription factors play essential roles in the induction and regulation of innate immune responses. In the present study, the full-length cDNA of CgRel from the Pacific oyster Crassostrea gigas was of 2,647 bp with an RHD and an IPT domain. The mRNA of CgRel was found to be constitutively expressed in all the tested tissues including gills, hepatopancreas, gonad, adductor muscle, labial palps, mantle, hemocytes, and ganglion. After lipopolysaccharide (LPS) stimulation, the expression level of CgRel mRNA in hemocytes was up-regulated to the first peak at 3 h (3.06-fold compared to the control group, p < 0.001) and second peak at 48 h (1.96-fold, p < 0.05). It increased significantly at 3 h (7.68-fold compared to the control group, p < 0.001), 24 h (3.63-fold, p < 0.05) and 48 h (1.99-fold, p < 0.05) post Vibrio splendidus stimulation, respectively. The protein of CgRel was translocated from cytoplasm into nucleus of oyster hemocytes after LPS stimulation. The mRNA expression levels of interleukin17s (CgIL17s) and big defensin (CgBigDef1) in hemocytes were examined after the expression of CgRel was silenced by RNAi. The transcripts of CgIL17-1 (0.25-fold of the control group, p < 0.01), CgIL17-2 (0.12-fold, p < 0.01), CgIL17-4 (0.33-fold, p < 0.01), CgIL17-6 (0.27-fold, p < 0.05) and CgBigDef1 (0.38-fold, p < 0.01) in CgRel-knockdown oysters decreased significantly at 12 h after LPS stimulation. The results indicated that CgRel played important roles in the immune defense against bacteria by regulating the expression of CgIL17 and CgBigDef1.

CgSOCS6 negatively regulates the expression of CgIL17s and CgDefh1 in the pacific oyster Crassostrea gigas

As a family of negatively feedback regulating factors, the suppressor of cytokine signaling (SOCS) can depress cytokine signal transduction, and eventually modulate growth, development, differentiation, and immune response. In the present study, a SOCS homologue (designated as CgSOCS6) was identified from oyster Crassostrea gigas. The open reading frame of CgSOCS6 cDNA was of 1167 bp encoding a peptide of 388 amino acid residues with a central Src homology 2 (SH2) domain, a conserved C-terminal SOCS box, and a nucleus localization sequence (NLS) in its N-terminus. The deduced amino acid sequence of CgSOCS6 shared 37.9-45.5% similarity with other SOCS6/7 family members. In the unrooted phylogenetic tree, CgSOCS6 was clustered with EsSOCS6 from Chinese mitten crab Eriocheir sinensis and assigned into the SOCS6/7 group. The mRNA transcripts of CgSOCS6 were constitutively distributed in all the tested tissues, with the highest level in hemocytes. After lipopolysaccharide (LPS) stimulation, the mRNA expression of CgSOCS6 in hemocytes was significantly up-regulated to the highest level at 6 h (8.48-fold compared to the control group, p < 0.01), and then kept at a relatively higher level from 12 h to 72 h. CgSOCS6 protein could be translocated into the hemocyte nucleus after LPS stimulation. The mRNA expressions of interleukin 17-4 (CgIL17-4), CgIL17-5, and defensin (CgDefh1) in the hemocytes of CgSOCS6-knockdown oysters increased significantly (2.55-fold, 2.68-fold, 4.68-fold of that in EGFP-RNAi oysters, p < 0.05, p < 0.05, p < 0.001, respectively) after LPS stimulation. These findings suggested that CgSOCS6 was involved in the oyster immune response by regulating the expressions of CgIL17-4, CgIL17-5, and CgDefh1.

A SPRY domain-containing SOCS box protein 3 (SPSB3) involved in the regulation of cytokine production in granulocytes of Crassostrea gigas

The sp1A/ryanodine receptor (SPRY) family members have been reported to involve in important biological pathways, including innate immune signaling, cytokine signaling suppression, development, cell growth, and retroviral restriction. In the present study, a SPRY domain-containing SOCS box protein (named as CgSPSB3) was identified and characterized from oyster Crassostrea gigas. The open reading frame of CgSPSB3 gene was of 699 bp, encoding a polypeptide of 232 amino acid residues with a central SPRY domain and a C-terminal SOCS box motif. CgSPSB3 mRNA transcripts could be detected in all the examined tissues with the highest level in hemocytes, which was about 82.72-fold (p < 0.05) of that in gonad. Furthermore, the expression level of CgSPSB3 mRNA in granulocytes was significantly higher than that in semi-granulocytes and agranulocytes, which was about 2.04-fold (p < 0.05) of the average level of hemocytes. Immunofluorescence assay further revealed that CgSPSB3 protein was mainly distributed in the cytoplasm of granulocytes. The mRNA expression of CgSPSB3 in hemocytes was up-regulated after lipopolysaccharide (LPS) and Vibrio splendidus stimulations. The mRNA expression of CgIFNLP, CgIL17-5 and CgTNF-1 decreased significantly (p < 0.05) at 24 h after the CgSPSB3 mRNA was knocked down by RNAi. These results collectively indicated that CgSPSB3 might play an important role in regulating cytokines production in granulocytes of C. gigas.

Immunity in mussels: An overview of molecular components and mechanisms with a focus on the functional defenses

Bivalves' immunity has received much more attention in the last decade, which resulted to a valuable growth in the availability of its molecular components. Such data availability coupled with the economical importance of these organisms aimed to shift the increase in the number of immunological and stress-related studies. Unfortunately, the crowd of generated data deciphering the involved physiological processes, investigators' differential conceptualization and the aimed objectives, has complicated the sensu stricto outlining of immune-related mechanisms. Overall, this review tried to compiles a summary about the molecular components of the mussels' immune response, surveying an overview of the mussels' functional immunity through gathering the most recent-related topics of bivalves' immunity as apoptosis and autophagy which deserves a great attention as stress-related mechanisms, the disseminated neoplasia as outbreak transmissible disease, not only within the same specie but also among different species, the hematopoiesis as topic that still generating interesting debate in the scientific community, the mucosal immunity described as the interface where host-pathogen interactions would occurs and determinate the late immune response, and innate immune memory and transgenerational priming, which described as very recent research topic with extensive applications in shellfish farming industry.

Evolution and function analysis of interleukin-17 gene from Pinctada fucata martensii

Interleukin-17 (IL-17) is a proinflammatory cytokine that plays an important role in immune responses. In this study, we identified 57 IL-17 genes from the genomes of six marine invertebrates, including Pinctada fucata martensii, Crassostrea gigas, Lottia gigantea, Capitella teleta, Mizuhopecten yessoensis, and Mytilus galloprovincialis. Phylogenetic analysis showed that all invertebrate IL-17 genes were clustered into one group, implying that invertebrate IL-17 evolved from one common ancestral gene. From the extron-intron analysis, we found many intronless IL-17 genes in mollusks, which may be caused by retroposition. Tissue and development transcriptomic analysis showed that the expression of PmIL-17 was tissue and developmental stage-specific. Moreover, we cloned the full length of the IL-17-2 gene from P. f. martensii (PmIL-17-2) and explored its function in the immune response. The full-length cDNA of PmIL-17-2 is 719 bp, containing an open reading frame of 564 bp, a 5' -untranslated region (UTR) of 31 bp, and a 3' -UTR of 124 bp with a 30 bp poly (A) tail. PmIL-17-2 had a strong response to lipopolysaccharide (LPS), indicating that the PmIL-17-2 participates in innate immune responses. In situ hybridization of hemocytes showed that PmIL-17-2 was mainly produced by granulosa cells, and the number of the stained granulosa increased after LPS stimulation. These results lay the foundation for the research of IL-17 family in marine invertebrates.

P38 is involved in immune response by regulating inflammatory cytokine expressions in the Pacific oyster Crassostrea gigas

P38 mitogen-activated protein kinases are serine/threonine protein kinases reportedly involved in the innate immunity of vertebrates and invertebrates. In the present study, a P38 homolog (CgP38) was characterized from the Pacific oyster Crassostrea gigas. The full-length cDNA of CgP38 was of 1515 bp containing a 1101 bp open reading frame. A serine/threonine protein kinase (S_TKc) domain with a conserved Thr-Gly-Tyr motif and an ATRW substrate-binding site was found in the deduced amino acid sequence of CgP38. CgP38 shared a close evolutionary relationship with ChP38 from the Hong Kong oyster Crassostrea hongkongensis. The transcript levels of CgP38 in hemocytes increased significantly from 12 h to 48 h after lipopolysaccharide (LPS) stimulation and from 12 h to 24 h after Vibrio splendidus stimulation. The phosphorylation level of CgP38 in oyster hemocytes increased significantly at 2 h after LPS stimulation. CgP38 positively regulated the expression of interleukins, such as CgIL17-1, CgIL17-2, CgIL17-3, CgIL17-4 and CgIL17-6, and tumor necrosis factor CgTNF after LPS or V. splendidus stimulation. These results suggested that CgP38 participated in oyster immune response by regulating the expressions of inflammatory cytokines.

Impacts of the combined exposure to seawater acidification and arsenic on the proteome of Crassostrea angulata and Crassostrea gigas

Proteomic analysis was performed to compare the effects of Arsenic (As), seawater acidification (Low pH) and the combination of both stressors (Low pH + As) on Crassostrea angulata and Crassostrea gigas juveniles in the context of global environmental change. This study aimed to elucidate if two closely related Crassostrea species respond similarly to these environmental stressors, considering both single and combined exposures, to infer if the simultaneous exposure to both stressors induced a differentiated response. Identification of the most important differentially expressed proteins between conditions revealed marked differences in the response of each species towards single and combined exposures, evidencing species-related differences towards each experimental condition. Moreover, protein alterations observed in the combined exposure (Low pH + As) were substantially different from those observed in single exposures. Identified proteins and their putative biological functions revealed an array of modes of action in each condition. Among the most important, those involved in cellular structure (Actin, Atlastin, Severin, Gelsolin, Coronin) and extracellular matrix modulation (Ependymin, Tight junction ZO-1, Neprilysin) were strongly regulated, although in different exposure conditions and species. Data also revealed differences regarding metabolic modulation capacity (ATP β, Enolase, Aconitate hydratase) and oxidative stress response (Aldehyde dehydrogenase, Lactoylglutathione, Retinal dehydrogenase) of each species, which also depended on single or combined exposures, illustrating a different response capacity of both oyster species to the presence of multiple stressors. Interestingly, alterations of piRNA abundance in C. angulata suggested genome reconfiguration in response to multiple stressors, likely an important mode of action related to adaptive evolution mechanisms previously unknown to oyster species, which requires further investigation. The present findings provide a deeper insight into the complexity of C. angulata and C. gigas responses to environmental stress at the proteome level, evidencing different capacities to endure abiotic changes, with relevance regarding the ecophysiological fitness of each species and competitive advantages in a changing environment.

A novel JNK is involved in immune response by regulating IL expression in oyster Crassostrea gigas

The c-Jun N-terminal kinase (JNK) is a member of mitogen-activated protein kinases (MAPK) highly conserved from yeast to mammals and participates in regulating many physiological and pathological processes. In the present study, a novel JNK was identified from oyster Crassostrea gigas (designated as CgJNK) and its biological functions were investigated in response against lipopolysaccharide (LPS) stimulation. The CgJNK consists of 415 amino acids, which includes a serine/threonine protein kinase (S_TKc) domain with a conserved Thr-Pro-Tyr (TPY) motif. Phylogenetic analysis revealed that CgJNK shared high similarity with other members of the JNK subfamily. CgJNK mRNA was detected in all the tested tissues and CgJNK mRNA expression levels in hemocytes were significantly up-regulated from 6 to 72 h after LPS stimulation and reached the highest level (16.1-fold, p < 0.01) at 24 h. The phosphorylation level of CgJNK in C. gigas hemocytes was increased at 2 h after LPS stimulation. The subcellular localization of CgJNK phosphorylation in hemocytes was analyzed after LPS stimulation, and CgJNK phosphorylation could be detected in both cytoplasm and nucleus of oyster hemocytes at 2 h post LPS stimulation. Additionally, the interleukins (CgILs) were detected in hemocytes of CgJNK-knockdown oysters. CgIL17-1, CgIL17-2, CgIL17-4 and CgIL17-6 transcripts were decreased significantly in CgJNK-knockdown oysters at 24 h post LPS stimulation. In summary, these results suggested that CgJNK played an important role in the immune response of oysters by regulating IL expression.

The oyster immunity

Oysters, the common name for a number of different bivalve molluscs, are the worldwide aquaculture species and also play vital roles in the function of ecosystem. As invertebrate, oysters have evolved an integrated, highly complex innate immune system to recognize and eliminate various invaders via an array of orchestrated immune reactions, such as immune recognition, signal transduction, synthesis of antimicrobial peptides, as well as encapsulation and phagocytosis of the circulating haemocytes. The hematopoietic tissue, hematopoiesis, and the circulating haemocytes have been preliminary characterized, and the detailed annotation of the Pacific oyster Crassostrea gigas genome has revealed massive expansion and functional divergence of innate immune genes in this animal. Moreover, immune priming and maternal immune transfer are reported in oysters, suggesting the adaptability of invertebrate immunity. Apoptosis and autophagy are proved to be important immune mechanisms in oysters. This review will summarize the research progresses of immune system and the immunomodulation mechanisms of the primitive catecholaminergic, cholinergic, neuropeptides, GABAergic and nitric oxidase system, which possibly make oysters ideal model for studying the origin and evolution of immune system and the neuroendocrine-immune regulatory network in lower invertebrates.

The first invertebrate NFIL3 transcription factor with role in immune defense identified from the Hong Kong oyster, Crassostrea hongkongensis

NFIL3 (nuclear factor interleukin 3-regulated) is a basic leucine zipper type transcription factor that mediates a variety of immune responses in vertebrates. However, the sequence information and function of NFIL3 homologs in invertebrates, especially mollusks, remains unknown. In the present study, the first NFIL3 homolog was identified in a marine mollusk, Crassostrea hongkongensis (designated as ChNFIL3), followed by its functional characterization. The full-length cDNA of ChNFIL3 is 2221 bp and consists of an open reading frame (ORF) of 1536 bp that encodes a polypeptide of 551 amino acids. Simple Modular Architecture Research Tool (SMART) analysis indicated that ChNFIL3 has two basic leucin zipper domains, similar to the other known NFIL3 family proteins. Tissue distribution analysis of NFIL3 in this mollusk revealed high expression in digestive glands and hemocytes. A significant induction in the mRNA level of ChNFIL3 was observed following bacterial stimulation. ChNFIL3 was found to be localized in the nucleus and over expression of ChNIFL3 led to upregulation of transcriptional activity of an NF-κB reporter gene in HEK 293T cells, indicating its role in innate immunity. Furthermore, addition of exogenous recombinant ChNFIL3 proteins resulted in enhanced mRNA level of hemocyte interleukin 17 in vitro. In conclusion, our findings revealed that NFIL3 in molluscs, plays a conserved role in host defense, similar to its mammalian homolog.

Identification and characterization of an interleukin-16-like gene from pacific white shrimp Litopenaeus vannamei

Interleukins are a group of cytokines that play essential roles in immune regulation. Almost all interleukin genes are only found in vertebrates. In this study, an interleukin-16-like gene (LvIL-16L) was identified from Pacific white shrimp, Litopenaeus vannamei. LvIL-16L was predicted to encode a precursor (pro-LvIL-16L) with 1378 amino acids, sharing similarities with predicted pro-IL-16-like proteins from insects. The C-terminus of pro-LvIL-16L protein contained two PDZ domains homologous to the mature IL-16 cytokine of vertebrates. In tissues, LvIL-16L could be processed into a ∼36 kDa mature peptide through a caspase-3 cleavage site, which was verified by in vitro site mutation analysis and in vivo RNA interference (RNAi) experiments. The LvIL-16L mRNA could be detected in all the analyzed tissues and the expression of LvIL-16L was significantly up-regulated after immune stimulation. Using RNAi strategy, the role of LvIL-16L in immune responses was initially investigated. Interestingly, knockdown of LvIL-16L could significantly increase the mortality of the Vibro parahaemolyticus infected shrimps but reduce that of the WSSV infected shrimps, suggesting that LvIL-16L could have opposite effects on the antiviral and antibacterial immune responses in shrimp. To our knowledge, this is the first study of an IL-16-like gene in invertebrates, which could help to elucidate interleukin evolution and regulatory mechanisms of shrimp immune responses.

Peritoneal bacterial infection repressed the expression of IL17D in Siberia sturgeon a chondrostean fish in the early immune response

IL17s are pro-inflammatory cytokines that play important roles in host fighting against extracellular bacteria and auto-immune and allergic diseases. IL17D is believed to be the most ancient IL17 member and its functions are far from clarity. Although it has been found in invertebrates, jawless fish, teleosts, and tetrapods, it has not been described in chondrostean fish. Moreover, there are discrepancies concerning its expression pattern in these animals. In this study, we cloned and characterized the cDNA of il17d in Siberia sturgeon (Acipenser baerii), a chondrostean fish and commercially important species in aquaculture. The sturgeon il17d cDNA encodes a deduced protein of 210aa. The classical characteristics of IL17, such as IL17 domain, cysteine and serine residues importantly for cystine-knot formation, and signal peptide, were observed in sturgeon IL17D. Phylogenetic analysis and multiple alignment suggest it is a counterpart of mammalian IL17D. However, in vivo studies demonstrated that the expression pattern of sturgeon il17d mRNA is different from that of other teleosts and jawless fish, and in most cases its expression was down-regulated at the early time points and gradually increasing at late time points when sturgeon were challenged with bacteria (Aernomas hydrophila or Staphylococcus aureus). The In vitro study by using primary spleen cells stimulated with polyI:C revealed a similar expression pattern to that in vivo studies, while the stimulation with β-glucan or LPS, which normally induced expression of il17d mRNA in target cells in vitro in other animals, did not show apparent changes in the expression of il17d mRNA. The results of present study indicated sturgeon IL17D may possess some different characteristics from its counterparts of other fish and invertebrates in the immune response, and may contribute to the understanding of IL17D functions in evolution as well as the potential use in sturgeon aquaculture.

The systematic regulation of oyster CgIL17-1 and CgIL17-5 in response to air exposure

As a proinflammatory cytokine, vertebrate interleukin 17 (IL17) plays a vital role in the balance of inflammation and homeostasis, and is involved in a systemic regulation of glucose homeostasis. In the present study, a remarkable increase of glucose concentration was observed in oyster serum after 2 d air exposure, which was followed by a rapid up-regulation of CgIL17-1 and CgIL17-5. After oysters was received an injection of extra glucose, the mRNA expressions of CgIL17-1 and CgIL17-5 were also significantly up-regulated. The histopathological changes of hepatopancreas were observed after the oysters were treated by the recombinant proteins of CgIL17-1 and CgIL17-5 in vivo or subjected to air exposure. A significant decrease of GSK3β (Glycogen synthase kinase-3β) protein was also observed after the injection of CgIL17-1 and CgIL17-5 recombinant proteins in vivo. When the oysters with CgIL17-1 and CgIL17-5 genes knocked down were subjected to air exposure, the decline of GSK3β concentration was slowed down and it could still be obviously detected after 7 d compared with that in the control. Meanwhile, the expression of CgDefensin and CgDFFA was inhibited, while CgIAP was up-regulated when CgIL17-1 and CgIL17-5 genes were knocked down, and the oysters exhibited higher mortality (p < 0.05) at 3 d, whereas lower at the late stage of air exposure compared with that in the controls. The results collectively suggested that once oysters were exposed to air, the synthesis of proinflammatory cytokines CgIL17-1 and CgIL17-5 was induced by the up-regulated glucose concentration in oyster serum, which would be not only a negative feedback to the high glucose concentration through mediating the regulation of GSK3β, but also an inducer on tissue damage and immunocompetence as well as the adaptability to stresses.

The first molluscan TRIM9 is involved in the negative regulation of NF-κB activity in the Hong Kong oyster, Crassostrea hongkongensis

TRIM proteins are a group of highly conserved proteins participating in a variety of biological processes such as regulation of development, apoptosis, and innate immunity. However, the functions of these proteins in the mollusk are still poorly understood. In the present study, a TRIM9 homolog (named ChTRIM9) was first identified from a transcript-ome library in the Hong Kong oyster Crassostrea hongkongensis. The full-length cDNA of ChTRIM9 is 2928 bp and has a predicted Open Reading Frame ORF) encoding 721 amino acids, encoding a putative 80.2 kDa protein. SMART analysis indicated that ChTRIM9 contains the three typical TRIM domains, a RING finger, two B-boxes, and a coiled-coil domain in the N-terminal region, whereas the C-terminal region contains a SPRY domain. qRT-PCR analysis revealed a ubiquitous presence of ChTRIM9, with the highest expression in the gills. Upon bacterial challenge in vivo, the ChTRIM9 transcripts in hemocytes were significantly down-regulated, indicating its involvement in signal transduction in immune response of oysters. Furthermore, ChTRIM9 was found to be localized mainly in the cytoplasm, and its over-expression inhibited the transcriptional activity of the NF-κB gene in HEK293T cells, demonstrating its negative role in regulating NF-κB signaling.