Molecular cloning and expression of IRAK-4, IL-17 and I-κB genes in Haliotis rufescens challenged with Vibrio anguillarum

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.

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.

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.

The receptor CgIL-17R1 expressed in granulocytes mediates the CgIL-17 induced haemocytes proliferation in Crassostrea gigas

Inflammatory cytokine interleukin-17 (IL-17) binds its receptors (IL-17Rs) to activate the downstream immune signals and plays an important role in host defense. In the present study, an IL-17 receptor (designated as CgIL-17R1) was identified from oyster Crassostrea gigas with an open reading frame of 3141 bp encoding 1047 amino acids. The amino acid sequence of CgIL-17R1 with two conserved FN3 domains shared higher similarity with other known IL-17Rs from mollusc species. The recombinant CgIL-17R1 protein (rCgIL-17R1) displayed high binding affinity to the recombinant CgIL-17 protein (rCgIL-17) in vitro. The mRNA transcripts of CgIL-17R1 were significantly higher expressed in haemocytes, especially in granunolyctes, compared with that in other tissues. After the stimulation with Vibrio splendidus or rCgIL17-1 in vivo, the expressions of CgIL-17R1 and cell proliferation related genes (CgRunx-1, CgCDC-6, CgCDC-45, and CgCDK-2) were significantly up-regulated in haemocytes (p < 0.01). When the CgIL-17R1 expression was interfered by specific CgIL-17R1-dsRNA, the expressions of these cell proliferation related genes reduced significantly, and the proliferation rate of haemocytes declined dramatically at 6 h post V. splendidus stimulation (p < 0.01), compared to that of blank group. These results collectively indicated that CgIL-17R1 expressed in granulocytes mediated the CgIL-17 induced haemocytes proliferation during immune response in oyster C. gigas, which provided novel information about the regulation of haemocyte proliferation in invertebrates.

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.

Functional Variation of IL-1R-Associated Kinases in the Conserved MyD88-TRAF6 Pathway during Evolution

IL-1R-associated kinases (IRAK) are important regulators in the TLR/IL-1R pathways, but their function appears inconsistent between Drosophila, bony fishes, and vertebrates. This causes a difficulty to understand the IRAK functions. As a step to reveal the evolution of IRAKs, in this study, we performed comparative and functional analysis of IRAKs by exploiting the amphioxus, a pivotal taxon connecting invertebrates and vertebrates. Sequence and phylogenetic analysis indicated three major IRAK lineages: IRAK1/2/3 is a vertebrate-specific lineage, IRAK4 is an ancient lineage conserved between invertebrate and vertebrates, and Pelle is another ancient lineage that is preserved in protostomes and invertebrate deuterostomes but lost in vertebrate deuterostomes. Pelle is closer neither to IRAK4 nor to IRAK1/2/3, hence suggesting no clear functional analogs to IRAK1/2/3 in nonvertebrates. Functional analysis showed that both amphioxus IRAK4 and Pelle could suppress NF-κB activation induced by MyD88 and TRAF6, which are unlike mammalian and Drosophila IRAKs, but, surprisingly, similar to bony fish IRAK4. Also unlike Drosophila IRAKs, no interaction was detected between amphioxus IRAK4 and Pelle, although both of them were shown capable of binding MyD88. These findings, together with previous reports, show that unlike other signal transducers in the TLR/IL-1R pathways, such as MyD88 and TRAF6, the functions of IRAKs are highly variable during evolution and very specialized in different major animal taxa. Indeed, we suggest that the functional variability of IRAKs might confer plasticity to the signal transduction of the TLR/IL-1R pathways, which in return helps the species to evolve against the pathogens.

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.

Integrative transcriptome analysis and discovery of genes involving in immune response of hypoxia/thermal challenges in the small abalone Haliotis diversicolor

In recent years, the abalone aquaculture industry has been threatened by the deteriorating environmental conditions, such as hypoxia and thermal stress in the hot summers. It is necessary to investigate the molecular mechanism in response to these environmental challenges, and subsequently understand the immune defense system. In this study, the transcriptome profiles by RNA-seq of hemocytes from the small abalone Haliotis diversicolor after exposure to hypoxia, thermal stress, and hypoxia plus thermal stress were established. A total of 103,703,074 clean reads were obtained and 99,774 unigenes were assembled. Of the 99,774 unigenes, 47,154 and 20,455 had homologous sequences in the Nr and Swiss-Prot protein databases, while 16,944 and 10,840 unigenes could be classified by COG or KEGG databases, respectively. RNAseq analysis revealed that the differentially expressed genes (DEGs) after challenges of hypoxia, thermal stress, or hypoxia plus thermal stress were 24,189, 29,165 and 23,665, among which more than 3000 genes involved in at least 230 pathways, including several classical immune-related pathways. The genes and pathways that were involved in immune response to hypoxia/thermal challenges were identified by transcriptome analysis and further validated by quantitative real-time PCR and RNAi technology. The findings in this study can provide information on H. diversicolor innate immunity to improve the abalone aquaculture industry, and the analysis of the potential immune-related genes in innate immunity signaling pathways and the obtained transcriptome data can provide an invaluable genetic resource for the study of the genome and functional genes.

Nucleus-translocated matrix metalloprotease 1 regulates innate immune response in Pacific abalone (Haliotis discus hannai)

As an important economical shellfish in coastal area of China, abalone is susceptible to bacterial infection, especially Vibiro parahemolyticus (V. parahemolyticus). Matrix metalloproteinases (MMPs) have been extensively investigated in the immune response of mammals. However, little is known about the involvement of MMP in abalone innate immune system against pathogen infection. In this study, the role of MMP-1 in the immune response of Pacific abalone (Haliotis discus hannai) was explored. The results showed that V. parahemolyticus infection induced significantly elevated expression of MMP-1 as well as immune related genes including allograft inflammatory factor 1 (AIF-1), macrophage expressed gene 1 (MPEG-1) and TPA-inducible sequence 11 family protein (Tis11FP). Notably, silencing of MMP-1 reduced the expression of these genes, suggesting that MMP-1 was an upstream regulatory factor in V. parahemolyticus infection. Further analysis showed that MMP-1 was engaged in the regulation of cellular (phagocytosis, apoptosis) and humoral [superoxide dismutase (SOD), alkaline phosphatase (ALP), acid phosphatase (ACP)] immunity. Interestingly, the extracellularly distributed MMP-1 could be translocated to the nuclei of hemocytes, thereby functioning as a transcriptional regulator or by selectively activating or inactivating other components through proteolysis. Hence, our study established an important role of MMP-1 in abalone innate immunity against V. parahemolyticus infection and it represented the first report on the investigation of MMP in abalone.

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.

Identification and expression analysis of IκB and NF-κB genes from Cyclina sinensis

With the increasing economic importance of Cyclina sinensis aquaculture, interest in its defense mechanisms against pathogenic infection has grown in recent years. Inhibitor of nuclear factor-kappaB (IκB) and nuclear factor-kappaB (NF-κB) are proteins with central roles in many important physiological and pathological processes, such as innate immune responses. In this study, we identified CsIκB and CsNF-κB genes from a C. sinensis transcriptome library. In healthy adult clams, CsIκB and CsNF-κB genes were widely expressed in various tissues and highly expressed in hemocytes. Further, the expression levels of these genes were significantly increased in hemocytes challenged by Vibrio anguillarum, Micrococcus luteus and poly I:C. Inhibition of CsMyD88 expression by RNAi technology significantly altered the mRNA expression patterns of CsIκB and CsNF-κB as measured using quantitative real-time PCR. These results collectively indicated that the NF-κB signaling pathway, including CsIκB and CsNF-κB genes, might be involved in early innate immune responses and may be regulated by a MyD88-dependent signaling pathway in C. sinensis.

Ability of Lactobacillus plantarum lipoteichoic acid to inhibit Vibrio anguillarum-induced inflammation and apoptosis in silvery pomfret (Pampus argenteus) intestinal epithelial cells

Lipoteichoic acid (LTA) is a major constituent of the cell wall of Gram-positive bacteria. The structure and immunomodulation of LTA vary greatly between different species. LTA from Lactobacillus plantarum has been shown to exert anti-pathogenic effects. Vibrio anguillarum is a major causative agent of vibriosis, one of the most prevalent fish diseases. The purpose of this study was to examine the effects of L. plantarum LTA on V. anguillarum growth, adhesion, and induced inflammation and apoptosis in intestinal epithelial cells of silvery pomfret (Pampus argenteus). Our results showed that L. plantarum LTA was unable to inhibit V. anguillarum growth; however, it significantly inhibited adhesion of V. anguillarum. It also showed significant inhibitory effects on EHEC-induced inflammation and apoptosis by modulating the expression of NF-κB (nuclear factor kappa B), IκB (inhibitor of NF-κB), Bcl2 (B-cell leukemia/lymphoma-2), BAX (Bcl-2-associated X protein), IL-8 (interleukin 8) and TNF-α (tumor necrosis factor-α), and via inhibition of caspase-9 and caspase-3 activation. These data extend our understanding of the beneficial effects of L. plantarum LTA, which is related to the inhibition of V. anguillarum, and suggest that L. plantarum LTA has potential as a new therapeutic agent against V. anguillarum-caused vibriosis in fish.

The categorization and mutual modulation of expanded MyD88s in Crassostrea gigas

MyD88 serves as a critical cytosolic adaptor mediating activation of NF-κB in innate immunity. It has been found that there is a considerable expansion of MyD88 in Crassostrea gigas. In the present study, four typical MyD88 genes in Crassostrea gigas (CgMyD88-A to CgMyD88-D) were successfully cloned and their potential functions were investigated together with another two known ones (CgMyD88-T1 and CgMyD88-T2). Multiple alignments revealed that CgMyD88-B and CgMyD88-C remained the conserved DD and TIR domains, while there was a significant variation of E51Q in the DD of CgMyD88-A, and some variations in both DD and TIR domains of CgMyD88-D, respectively. Both truncated CgMyD88-T1 and CgMyD88-T2 lacked Box II in their only TIR domains. Expression pattern analysis showed that CgMyD88-B and CgMyD88-C genes possessed higher expression in normal tissues, compared with the other four. When oysters were under bacteria challenge, CgMyD88-B, CgMyD88-C, CgMyD88-T1 and CgMyD88-T2 were firstly induced, while CgMyD88-A and CgMyD88-D were suppressed. Dual luciferase reporter assays showed that CgMyD88-B and CgMyD88-C could promote the activation of NF-κB signaling pathway, while the other four CgMyD88 genes failed or even suppressed the activities of CgMyD88-B and CgMyD88-C on the activation of NF-κB signaling. It was deduced that after oysters were challenged by bacteria, CgMyD88-B and CgMyD88-C could rapidly and efficiently activate NF-κB signaling pathway to elicit anti-pathogen responses before suppressor CgMyD88 genes (CgMyD88-T1 and CgMyD88-T2) exceeding their expression level. These results suggested that there was mutual modulation of expanded CgMyD88 genes on activating NF-κB signaling pathway in oyster C. gigas.

Characterization of Lamprey IL-17 Family Members and Their Receptors

IL-17 is an ancient cytokine implicated in a variety of immune defense reactions. We identified five members of the sea lamprey IL-17 family (IL-17D.1, IL-17D.2, IL-17E, IL-17B, and IL-17C) and six IL-17R genes (IL-17RA.1, IL-17RA.2, IL-17RA.3, IL-17RF, IL-17RE/RC, and IL-17RD), determined their relationship with mammalian orthologs, and examined their expression patterns and potential interactions to explore their roles in innate and adaptive immunity. The most highly expressed IL-17 family member is IL-17D.1 (mammalian IL-17D like), which was found to be preferentially expressed by epithelial cells of skin, intestine, and gills and by the two types of lamprey T-like cells. IL-17D.1 binding to rIL-17RA.1 and to the surface of IL-17RA.1-expressing B-like cells and monocytes of lamprey larvae was demonstrated, and treatment of lamprey blood cells with rIL-17D.1 protein enhanced transcription of genes expressed by the B-like cells. These findings suggest a potential role for IL-17 in coordinating the interactions between T-like cells and other cells of the adaptive and innate immune systems in jawless vertebrates.

IL-17 signaling components in bivalves: Comparative sequence analysis and involvement in the immune responses

The recent discovery of soluble immune-regulatory molecules in invertebrates takes advantage of the rapid growth of next generation sequencing datasets. Following protein domain searches in the transcriptomes of 31 bivalve spp. and in few available mollusk genomes, we retrieved 59 domains uniquely identifying interleukin 17 (IL-17) and 96 SEFIR domains typical of IL-17 receptors and CIKS/ACT1 proteins acting downstream in the IL-17 signaling pathway. Compared to the Chordata IL-17 family members, we confirm a separate clustering of the bivalve domain sequences and a consistent conservation pattern of amino acid residues. Analysis performed at transcript and genome level allowed us to propose an updated view of the components outlining the IL-17 signaling pathway in Mytilus galloprovincialis and Crassostrea gigas (in both species, homology modeling reduced the variety of IL-17 domains to only two 3D structures). Digital expression analysis indicated more heterogeneous expression levels for the mussel and oyster IL-17 ligands than for IL-17 receptors and CIKS/CIKSL proteins. Besides, new qPCR analyses confirmed such gene expression trends in hemocytes and gills of mussels challenged with heat-killed bacteria. These results uphold the involvement of an ancient IL-17 signaling pathway in the bivalve immune responses and, likewise in humans, suggest the possibility of distinctive modulatory roles of individual IL-17s/IL-17 receptors. Overall, the common evidence of pro-inflammatory cytokines and inter-related intracellular signaling pathways in bivalves definitely adds complexity to the invertebrate immunity.

Molecular characterization of collagen IV evidences early transcription expression related to the immune response against bacterial infection in the red abalone (Haliotis rufescens)

Collagen IV has been described as a structural protein of the basement membrane, which as a whole forms a specialized extracellular matrix. Recent studies have indicated a possible relationship between collagen IV and the innate immune response of invertebrate organisms. The present study characterized the alpha-1 chain of collagen IV in the red abalone Haliotis rufescens (Hr-ColIV) and evaluated its association with the innate immune response against Vibrio anguillarum. To further evidence the immune response, the matrix metalloproteinase-1 (Hr-MMP-1) and C-type lectin (Hr-CLEC) genes were also assessed. The complete sequence of Hr-ColIV was composed of 6658 bp, with a 5'UTR of 154 bp, a 3'UTR of 1177 bp, and an ORF of 5327 bp that coded for 1776 amino acids. The innate immune response generated against V. anguillarum resulted in a significant increase in the transcript levels of Hr-ColIV between 3 and 6 hpi, whereas Hr-MMP-1 and Hr-CLEC had the highest transcript activity 6 and 12 hpi, respectively. The results obtained in this study propose a putative biological function for collagen IV involved in the early innate immune response of the red abalone H. rufescens.

Identification and expression analysis of immune-related genes linked to Rel/NF-κB signaling pathway under stresses and bacterial challenge from the small abalone Haliotis diversicolor

Inhibitor of NF-κB (IκB), nuclear factor-κB (NF-κB), and Akirin2 are all important members of Rel/NF-κB signaling pathway, which plays a pivotal role in regulating the innate immune response of vertebrates and invertebrates. In this study, the IκB (SaIκB) and Akirin2 (SaAkirin2) cDNAs of small abalone Haliotis diversicolor were cloned and characterized. The full length cDNA of SaIκB and SaAkirin2 were 1748 bp and 1452 bp respectively, encoding a protein of 401 aa and 187 aa respectively. A conserved degradation motif (DS56GIYS60) and six ankyrin repeats were identified in the SaIκB by SMART analysis. Meanwhile, a typical nuclear localization signal (NLS) was found at the N-terminal region of the SaAkirin2 protein. Also, the mRNA expression level of SaIκB, SaAkirin2, and AbNF-κB were detected by quantitative real-time PCR. The results revealed that all these three genes were ubiquitously expressed in 7 selected tissues. The expression level of SaIκB in gills was higher than that in other tissues (P < 0.05) while the expression level of AbNF-κB was significantly higher in hepatopancreas and haemocytes. The highest expression level of SaAkirin2 was detected in hepatopancreas, followed by mantle. The mRNA expression levels in either gills or haemocytes of SaIκB, SaAkirin2, and AbNF-κB were significantly up-regulated (P < 0.05) post thermal stress, hypoxia exposure, thermal plus hypoxia stress and the injection of Vibrio parahaemolyticus. These results indicated that these three NF-κB signaling pathway-related genes are involved in response to bacterial infection and play essential roles in response to thermal and hypoxia stress.