Full-length sequence and expression analysis of a myeloid differentiation factor 88 (MyD88) in half-smooth tongue soleCynoglossus semilaevis

Molecular characterization and expression analyses of five genes involved in the MyD88-dependent pathway of yellow catfish (Pelteobagrus fulvidraco) responding to challenge of Aeromonas hydrophila

MyD88-dependent pathway mediated by Toll-like receptor is one of the vital ways activating immune responses. In order to identify the role of MyD88-dependent signaling pathway in yellow catfish, the Pf_MyD88, Pf_IRAK4, Pf_IRAK1, Pf_TRAF6 and Pf_NFκB1 (p105) (Pf: abbreviation of Pelteobagrus fulvidraco) were cloned and characterized respectively. The Pf_MyD88, Pf_IRAK4, Pf_IRAK1 and Pf_TRAF6 were all highly conserved among species and showed the highest homology to that of Pangasianodon hypophthalmus. Pf_NFκB1 showed the highest homology to that of Ictalurus punetaus. All of the five genes showed similar expression patterns in various tissues, with the highest expression level in the liver. These genes also showed similar expression levels in different embryonic development stages, except Pf_IRAK4. The higher expression level was detected from fertilized eggs to 1 day post hatching (dph), lower expression from 3 dph to 30 dph. After stimulation of inactivated Aeromonas hydrophila, the mRNA expressions of Pf_MyD88, Pf_IRAK4, Pf_IRAK1, Pf_TRAF6 and Pf_NFκB1 were significantly increased at 24 h in the liver, spleen, head kidney and trunk kidney, suggesting that all the five genes were involved in the innate immune response of yellow catfish. These results showed that MyD88-dependent signaling pathway plays important roles for disease defensing in the innate immune response. Meanwhile, inactivated A. hydrophila can cause strong innate immune response, which provides theoretical bases for the application of inactivated vaccines in defense against bacterial diseases of teleost.

Towards Understanding PRPS1 as a Molecular Player in Immune Response in Yellow Drum (Nibea albiflora)

Phosphoribosyl pyrophosphate synthetases (EC 2.7.6.1) are key enzymes in the biological synthesis of phosphoribosyl pyrophosphate and are involved in diverse developmental processes. In our previous study, the PRPS1 gene was discovered as a key disease-resistance candidate gene in yellow drum, Nibea albiflora, in response to the infection of Vibrio harveyi, through genome-wide association analysis. This study mainly focused on the characteristics and its roles in immune responses of the PRPS1 gene in yellow drum. In the present study, the NaPRPS1 gene was cloned from yellow drum, encoding a protein of 320 amino acids. Bioinformatic analysis showed that NaPRPS1 was highly conserved during evolution. Quantitative RT-PCR demonstrated that NaPRPS1 was highly expressed in the head-kidney and brain, and its transcription and translation were significantly activated by V. harveyi infection examined by RT-qPCR and immunohistochemistry analysis, respectively. Subcellular localization revealed that NaPRPS1 was localized in cytoplasm. In addition, semi-in vivo pull-down assay coupled with mass spectrometry identified myeloid differentiation factor 88 (MyD88) as an NaPRPS1-interacting patterner, and their interaction was further supported by reciprocal pull-down assay and co-immunoprecipitation. The inducible expression of MyD88 by V. harveyi suggested that the linker molecule MyD88 in innate immune response may play together with NaPRPS1 to coordinate the immune signaling in yellow drum in response to the pathogenic infection. We provide new insights into important functions of PRPS1, especially PRPS1 in the innate immunity of teleost fishes, which will benefit the development of marine fish aquaculture.

NOP56 negatively regulates MyD88-mediated NF-κB signaling in miiuy croaker, Miichthys miiuy

MyD88 is a critical adaptor in the TLRs signaling pathway, which can activate NF-κB signaling pathway and promote proinflammatory cytokines production. However, the molecular mechanisms that modulate MyD88 expression, especially in teleost, remain largely unknown. In this study, we showed that NOP56 serve as a negative regulator of the MyD88-mediated NF-κB signaling pathway. NOP56 overexpression inhibited the protein expression of MyD88. Whereas, siRNA knockdown of NOP56 had opposite effect. Furthermore, we found that the NOSIC domain is responsible for the suppressive effect of NOP56 in MyD88 expression at protein level. Therefore, we identified NOP56 as a negative regulator of MyD88-mediated NF-κB signaling by inhibiting MyD88 expression and provided new insight into the regulation mechanism in teleost fish.

Comparison of polymeric immunoglobulin receptor between fish and mammals

Polymeric immunoglobulin receptor (pIgR) functions in transporting polymeric immunoglobulin across epithelial cells into external secretion in animals. During animal evolution, fish was situated at a transition point on the phylogenetic spectrum between species possessing only innate immunity (i.e., invertebrates) and species depending heavily on adaptive immunity (i.e., mammals). Previous studies reported that fish and mammals significantly differ in pIgR. This review summarized the differences in pIgR structure, function, and transcriptional regulation between fish and mammals. A model of the transcriptional regulation of the pIgR gene was suggested. In this model, microbes could activate Toll-like receptor, trigger the cascade reactions in the signaling pathway, and then activate transcription factors that regulate pIgR expression through combining with the pIgR promoter. This review provides some suggestions for further studies on the function and regulatory mechanism of pIgR in fish and other animals.

Transcriptome Analysis of Epithelioma Papulosum Cyprini Cells Infected by Reovirus Isolated from Allogynogenetic Silver Crucian Carp

The present study aimed to identify differentially expressed genes (DEGs) and major signal transduction pathways that were related to the immune response of epithelioma papulosum cyprinid (EPC) cells to reoviruses isolated from allogynogenetic silver crucian carp. The study also lays a theoretical foundation for the pathogenesis and immunity of the reovirus, which is helpful to the breeding of cyprinids fish. Reovirus infected and uninfected EPC cells were analyzed by using a new-generation high-throughput sequencing technology. DEGs were identified, annotated, and classified, and the signal pathways involved in the response to reovirus infection were identified by using bioinformatics tool. The data were assembled into 92,101 contigs with an average length of 835.24 bp and an N50 value of 1432 nt. Differential expression analysis of all the genes identified 3316 DEGs at a false discovery rate (FDR) of <0.01 and a fold-change of ≥3, of which 1691 were upregulated genes, 1625 were downregulated, and about 305 were immune-related genes. Gene Ontology (GO) enrichment analysis resulted in the annotation of 3941 GO terms, including 2719 biological processes (37,810 unigenes), 376 cell components (7943 unigenes), and 846 molecular functions (11,750 unigenes). KEGG metabolic pathway analysis matched the DEGs from pre-and post-infection EPC cells to 193 pathways, of which 35 were immune-related, including the Toll-like receptor, cytokine-cytokine receptor interaction, and the JAK-STAT signaling pathways.

Complement factor I from flatfish half-smooth tongue (Cynoglossus semilaevis) exhibited anti-microbial activities

Complement factor I (Cfi) is a soluble serine protease which plays a crucial role in the modulation of complement cascades. In the presence of substrate modulating cofactors (such as complement factor H, C4bp, CR1, etc), Cfi cleaves and inactivates C3b and C4b, thereby controlling the complement-mediated processes. In this study, we sequenced and characterized Cfi gene from Cynoglossus Semilaevis (designated as CsCfi) for the first time. The full-length cDNA of CsCfi was 2230 bp in length, including a 98 bp 5'-untranslated region (UTR), a 164 bp 3'-UTR and a 1968 bp open reading frame (ORF). It encoded a polypeptide of 656 amino acids, with a molecular mass of 72.28 kDa and an isoelectric point of 7.71. A signal peptide was defined at N-terminus, resulting in a 626-residue mature protein. Multiple sequence alignment revealed that Cfi proteins were well conserved with the typical modular architecture and identical active sites throughout the vertebrates, which suggested the conserved function of Cfi. Phylogenetic analysis indicated that CsCfi and the homologous Cfi sequences from teleosts clustered into a clade, separating from another clade from the cartilaginous fish and other vertebrates. Tissue expression profile analysis by quantitative real-time PCR (qRT-PCR) showed that CsCfi mRNA constitutively expressed in all tested tissues, with the predominant expression in liver and the lowest in stomach. Temporal expression levels of CsCfi after challenging with Vibrio anguillarum showed different expression patterns in intestine, spleen, skin, blood, head kidney and liver. The recombinant CsCfi (rCsCfi) protein showed broad-spectrum antimicrobial activities against the Gram-positive bacteria Staphylococcus aureus and the Gram-negative bacteria Escherichia coli, Pseudomonas aeruginosa and Shewanella putrefaciens. The research revealed that CsCfi plays an important role in C. Semilaevis immunity.

Molecular cloning and expression studies of the adapter molecule myeloid differentiation factor 88 (MyD88) in turbot (Scophthalmus maximus)

Myeloid differentiation factor 88 (MyD88) is an adapter protein involved in the interleukin-1 receptor (IL-1R) and Toll-like receptor (TLR)-mediated activation of nuclear factor-kappaB (NF-κB). In this study, a full length cDNA of MyD88 was cloned from turbot, Scophthalmus maximus. It is 1619 bp in length and contains an 858-bp open reading frame that encodes a peptide of 285 amino acid residues. The putative turbot (Sm)MyD88 protein possesses a N-terminal death domain and a C-terminal Toll/IL-1 receptor (TIR) domain known to be important for the functions of MyD88 in mammals. Phylogenetic analysis grouped SmMyD88 with other fish MyD88s. SmMyD88 mRNA was ubiquitously expressed in all examined tissues of healthy turbots, with higher levels observed in immune-relevant organs. To explore the role of SmMyD88, its gene expression profile in response to stimulation of lipopolysaccharide (LPS), CpG oligodeoxynucleotide (CpG-ODN) or turbot reddish body iridovirus (TRBIV) was studied in the head kidney, spleen, gills and muscle over a 7-day time course. The results showed an up-regulation of SmMyD88 transcript levels by the three immunostimulants in all four examined tissues, with the induction by CpG-ODN strongest and initiated earliest and inducibility in the muscle very weak. Additionally, TRBIV challenge resulted in a quite high level of SmMyD88 expression in the spleen, whereas the two synthetic immunostimulants induced the higher levels in the head kidney. These data provide insights into the roles of SmMyD88 in the TLR/IL-1R signaling pathway of the innate immune system in turbot.

sghC1q, a novel C1q family member from half-smooth tongue sole (Cynoglossus semilaevis): identification, expression and analysis of antibacterial and antiviral activities

The C1q family includes many proteins that contain a globular (gC1q) domain, and this family is widely conserved from bacteria to mammals. The family is divided into three subgroups: C1q, C1q-like and ghC1q. In this study, a novel C1q family member, sghC1q, was cloned and identified from Cynoglossus semilaevis (named CssghC1q). The full-length CssghC1q cDNA spans 905 bp, including an open reading frame (ORF) of 768 bp, a 5'-untranslated region (UTR) of 25 bp and a 3'-UTR of 112 bp. The ORF encodes a putative protein of 255 amino acids (aa) with a deduced molecular weight of 28 kDa. The predicted protein contains a signal peptide (aa 1-19), a coiled-coil region (aa 61-102) and a globular C1q (gC1q) domain (aa 117-255). Protein sequence alignment indicated that the C-terminus of CssghC1q is highly conserved across several species. Phylogenetic analysis indicated that CssghC1q is most closely related to Maylandia zebra C1q-like-2-like. The CssghC1q genomic sequence spanned 1562 bp, with three exons and two introns. CssghC1q is constitutively expressed in all evaluated tissues, with the highest expression in the liver and the weakest in the heart. After a challenge with Vibrio anguillarum, CssghC1q transcript levels exhibited distinct time-dependent response patterns in the blood, head kidney, skin, spleen, intestine and liver. Recombinant CssghC1q protein exhibited antimicrobial activities against Gram-negative bacteria, Gram-positive bacteria and viruses. The minimum inhibitory concentration (MIC) values against Vibrio harveyi, Vibrio anguillarum, Pseudomonas aeruginosa and Staphylococcus aureus were 0.043 mg/mL, 0.087 mg/mL, 0.174 mg/mL and 0.025 mg/mL, respectively. A low concentration (0.06 mg/mL) of CssghC1q showed significant antiviral activity in vitro against nervous necrosis virus (NNV). These results suggest that CssghC1q plays a vital role in immune defense against bacteria and viruses.

Toll-pathway in tiger shrimp (Penaeus monodon) responds to white spot syndrome virus infection: evidence through molecular characterisation and expression profiles of MyD88, TRAF6 and TLR genes

The Toll-pathway plays key roles in regulating the innate immune response in invertebrates. Myeloid differentiation factor 88 (MyD88) and Tumour necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) are key molecules in this signalling pathway. To investigate the role of Toll-pathway in innate immune response of shrimp, Penaeus monodon, MyD88 (PmMyD88) and TRAF6 (PmTRAF6) were identified and characterised. PmMyD88 cDNA is 1716 bp long with an open reading frame (ORF) of 1449 bp encoding a putative protein of 482 amino acids, with a death domain, a TIR domain and C-terminal extension domain. PmTRAF6 cDNA is 2563 bp long with an ORF of 1785 bp (594 amino acids) with an N-terminal RING-type zinc finger domain, two TRAF-type zinc finger domains, a coiled region and a MATH domain. In healthy shrimp, PmMyD88, PmTRAF6 and PmToll were detected in 15 tissues with the highest expression in midgut, eyestalk and lymphoid organ, respectively. Responses of these genes to WSSV in experimentally-infected P. monodon as well as in cultured haemocytes and also effect of poly I:C on the gene expression in vitro was investigated at six time-points in seven tissues. PmToll showed significant up-regulation at all time-points of infection in six tissues and until 24 h post-infection in vitro. However, poly I:C-induced haemocytes showed up-regulation of the gene until 48 h post-exposure. WSSV caused significant up-regulation of PmMyD88 in most of the tissues tested. The virus challenge as well as poly I:C induction in vitro also resulted in significant up-regulation of the gene. Up-regulated expression of PmTRAF6 was detected in haemocytes and lymphoid organ at late stage of infection. In vitro virus challenge showed significant up-regulation of PmTRAF6 at almost all time-points whereas no significant change in the expression was observed on poly I:C induction. The responses of these key genes, observed in the present study, suggest that Toll-pathway as a whole may play a crucial role in the immune response against viruses in shrimp.

Ligand specificities of Toll-like receptors in fish: indications from infection studies

Toll like receptors (TLRs) are present in many different fish families from several different orders, including cyprinid, salmonid, perciform, pleuronectiform and gadiform representatives, with at least some conserved properties among these species. However, low conservation of the leucine-rich repeat ectodomain hinders predictions of ligand specificities of fish TLRs based on sequence information only. We review the presence of a TLR genes, and changes in their gene expression profiles as result of infection, in the context of different fish orders and fish families. The application of RT-qPCR and availability of increasing numbers of fish genomes has led to numerous gene expression studies, including studies on TLR gene expression, providing the most complete dataset to date. Induced changes of gene expression may provide (in)direct evidence for the involvement of a particular TLR in the reaction to a pathogen. Especially when findings are consistent across different studies on the same fish species or consistent across different fish species, up-regulation of TLR gene expression could be a first indication of functional relevance. We discuss TLR1, TLR2, TLR4, TLR5 and TLR9 as presumed sensors of bacterial ligands and discuss as presumed sensors of viral ligands TLR3 and TLR22, TLR7 and TLR8. More functional studies are needed before conclusions on ligands specific to (groups of) fish TLRs can be drawn, certainly true for studies on non-mammalian TLRs. Future studies on the conservation of function of accessory molecules, in conjunction with TLR molecules, may bring new insight into the function of fish TLRs.

The antiviral innate immune response in fish: evolution and conservation of the IFN system

Innate immunity constitutes the first line of the host defense after pathogen invasion. Viruses trigger the expression of interferons (IFNs). These master antiviral cytokines induce in turn a large number of interferon-stimulated genes, which possess diverse effector and regulatory functions. The IFN system is conserved in all tetrapods as well as in fishes, but not in tunicates or in the lancelet, suggesting that it originated in early vertebrates. Viral diseases are an important concern of fish aquaculture, which is why fish viruses and antiviral responses have been studied mostly in species of commercial value, such as salmonids. More recently, there has been an interest in the use of more tractable model fish species, notably the zebrafish. Progress in genomics now makes it possible to get a relatively complete image of the genes involved in innate antiviral responses in fish. In this review, by comparing the IFN system between teleosts and mammals, we will focus on its evolution in vertebrates.

Identification and characterization of a hepcidin from half-smooth tongue sole Cynoglossus semilaevis

Hepcidin, an antimicrobial peptide, has a dual function including innate immunity and iron regulation. Here, based on the sequence of an EST database, we have isolated and characterized a hepcidin gene (referred to as CsHepcidin) from half-smooth tongue sole (Cynoglossus semilaevis). Analysis of the coding regions indicated CsHepcidin gene comprised 3 exons and 2 introns. The putative CsHepcidin showed a great similarity to other hepcidin orthologues, particularly with respect to its 24 aa signal peptide, typical RX(K/R)R motif and eight conserved cysteine residues in the mature cationic peptide. Phylogenic analysis indicated that CsHepcidin was a hepcidin 1-type peptide of acanthopterygians, with highly homologous with Solea senegalensis hepcidin. In C. semilaevis ontogeny, CsHepcidin mRNA was detected at a low level in unfertilized eggs, increased on 6 d after hatching, and decreased remarkably at metamorphic stage. CsHepcidin transcripts showed a constitutive basal expression in most of the tissues, especially in liver. Challenge with formalin-inactivated Vibrio anguillarum led to significantly up-regulations of CsHepcidin gene in liver, head kidney and spleen in time-dependent manners. Biological activity analysis showed that recombinant CsHEP exhibited direct antimicrobial activity against bacterial pathogens in vitro, particularly showed strong activity against the principal fish pathogens, V. anguillarum and Edwardsiella tarda. All these results suggest that CsHepcidin may be involved in the initial response to invasion of microbial pathogens. Further exploration to elucidate the role of CsHepcidin in iron regulation and embryogenesis in C. semilaevis are needed.

Ontogeny of anti-viral hemorrhagic septicemia virus (VHSV) immunity in developing Japanese flounder

We examined the ability of developing Japanese flounder (Paralichthys olivaceus) to acquire protective immunity after exposure to viral hemorrhagic septicemia virus (VHSV). Juveniles measuring 9.8 cm average body length were not susceptible to infection with VHSV at 20 °C, while the smaller fish were susceptible. Mortality was not observed after secondary infection at 15 °C in the 9.8 cm cohort that had previously been exposed to the virus at 20 °C, while the smaller fish were susceptible to secondary infection. The expression of interferon (IFN)-related genes was shown to be better developed in larger fish upon virus infection and basal expression levels of the virus recognition proteins were higher in larger fish. Virus-specific antibody was detected in the larger fish, but not in smaller fish. These data indicate that the largest juvenile (9.8 cm) acquired immunity against VHSV infection at the first virus challenge, but smaller fish did not. The anti-viral immune system in the Japanese flounder matures when juveniles reach approximately 10 cm.

Myeloid differentiation factor 88 gene is involved in antiviral immunity in grass carp Ctenopharyngodon idella

A full-length MyD88 cDNA (CiMyD88) was cloned and characterized from grass carp Ctenopharyngodon idella. CiMyD88 was found to be broadly expressed and was up-regulated by grass carp reovirus (GCRV) and CiMyD88 transcripts in vitro were rapidly elevated in C. idella kidney (CIK) cells after challenge with poly(I:C). These results suggest that CiMyD88 may be involved in the antiviral immune defence in C. idella.