miR-144 affects the immune response and activation of inflammatory responses in Cynoglossus semilaevis by regulating the expression of CsMAPK6

MicroRNAs are increasingly recognized for their pivotal role in the immune system, yet the specific regulatory functions of fish-derived microRNAs remain largely unexplored. In this research, we discovered a novel miRNA, Cse-miR-144, in the Chinese tongue sole (Cynoglossus semilaevis), characterized by a 73-base pair precursor and a 21-nucleotide mature sequence. Our findings revealed that the expression of Cse-miR-144 was notably inhibited by various Vibrio species. Utilizing bioinformatics and dual-luciferase assay techniques, we established that the pro-inflammatory cytokine gene CsMAPK6 is a direct target of Cse-miR-144. Subsequent in vitro and in vivo western blotting analyses confirmed that Cse-miR-144 can effectively reduce the protein levels of CsMAPK6 post-transcriptionally. Moreover, CsMAPK6 is known to be involved in the activation of the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB). Additional investigations using qPCR and ELISA demonstrated that suppression of Cse-miR-144 leads to an upsurge in the liver mRNA levels of various immune genes (including MYD88, TRAF6, NF-κB, TRAF2, TRAF3, and TNF), alongside a marked increase in the production and secretion of pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) in the bloodstream of C. semilaevis. These findings collectively underscore the potential of Cse-miR-144 as a key inhibitor of CsMAPK and its crucial role in modulating the immune and inflammatory responses in teleost fish. Compared to the siRNA, miRNA is a better tool in controlling the expression of target gene with a lower cost.

Differentially expressed proteins and microbial communities of the skin regulate disease resistance to Chinese tongue sole (Cynoglossus semilaevis)

Vibriosis, caused by Vibrio, seriously affects the health of fish, shellfish, and shrimps, causing large economic losses. Teleosts are represent the first bony vertebrates with both innate and adaptive immune responses against pathogens. Aquatic animals encounter hydraulic pressure and more pathogens, compared to terrestrial animals. The skin is the first line of defense in fish, constituting the skin-associated lymphoid tissue (SALT), which belongs to the main mucosa-associated lymphoid tissues (MALT). However, little is known about the function of immunity related proteins in fish. Therefore, this study used iTRAQ (isobaric tags for relative and absolute quantitation) to compare the skin proteome between the resistant and susceptible families of Cynoglossus semilaevis. The protein integrin beta-2, the alpha-enolase isoform X1, subunit B of V-type proton ATPase, eukaryotic translation initiation factor 6, and ubiquitin-like protein ISG15, were highly expressed in the resistant family. The 16S sequencing of the skin tissues of the resistant and susceptible families showed significant differences in the microbial communities of the two families. The protein-microbial interaction identified ten proteins associated with skin microbes, including immunoglobulin heavy chain gene (IGH), B-cell lymphoma/leukemia 10 (BCL10) and pre-B-cell leukemia transcription factor 1 isoform X2 (PBX2). This study highlights the interaction between skin proteins and the microbial compositions of C. semilaevis and provides new insights into understanding aquaculture breeding research.

Oral Administration of Antimicrobial Peptide NZ2114 Through the Microalgal Bait Tetraselmis subcordiformis (Wille) Butcher for Improving the Immunity and Gut Health in Turbot (Scophthalmus maximus L.)

Antibiotics are widely used in aquaculture to treat the bacterial diseases. However, the improper use of antibiotics could lead to environmental pollution and development of resistance. As a safe and eco-friendly alternative, antimicrobial peptides (AMPs) are commonly explored as therapeutic agents. In this study, a mutant strain of Tetraselmis subcordiformis containing AMP NZ2114 was developed and used as an oral drug delivery system to reduce the use of antibiotics in turbot (Scophthalmus maximus) aquaculture. The gut, kidney, and liver immune-related genes and their effects on gut digestion and bacterial communities in turbot fed with NZ2114 were evaluated in an 11-day feeding experiment. The results showed that compared with the group fed with wild-type T. subcordiformis, the group fed with T. subcordiformis transformants containing NZ2114 was revealed with decreased levels of both pro-inflammatory factors (TNF-α and IL-1β), inhibitory effect on Staphylococcus aureus, Vibrio parahaemolyticus, and Vibrio splendidus demonstrated by the in vitro simulation experiments, and increased richness and diversity of the gut microbiota of turbot. In conclusion, our study provided a novel, beneficial, and low-cost method for controlling bacteria in turbot culture through the oral drug delivery systems.

Bacterial infection induces pyroptotic signaling-mediated neutrophil extracellular traps (NETs) formation in turbot (Scophthalmus maximus)

Neutrophils can capture and kill pathogens by releasing neutrophils extracellular traps (NETs), which play critical roles in anti-microbial infection in mammals; however, the mechanisms involved in NETs formation and its role in anti-bacterial infection in teleost fish remains largely unknown. In this study, to explore the function of NETs in turbot, we established an in vitro bacterial infection model in head kidney derived neutrophils, and found that the haemolysin over-expressed Edwardsiella piscicida (ethA⁺) could induce a robust phenotype of NETs, compared with that in wild type or ethA mutant (ethA⁺ -ΔethA) strains. Besides, the NETosis was mediated by ethA⁺ -induced pyroptosis, and arms the ability of bacterial killing in neutrophils of turbot. Moreover, we found that neutrophils elastase (NE) might involves in this pyroptotic signaling, rather than inflammatory Smcaspase. Taken together, this study reveals the important role of pyroptosis in NETs formation in turbot neutrophils, suggesting that NETs formation is a critical immune response during bacterial infection in teleost fish.

Characterization and the potential immune role of class A scavenger receptor member 4 (SCARA4) in bacterial infection in turbot (Scophthalmus maximus L.)

The class A scavenger receptors play important roles in innate immunity and are distributed on plasma membrane of macrophages and other cell types. Notably, the class A scavenger receptor 4 (SCARA4) contains a typical C-type (calcium-dependent) lectin domain, which belongs to the collectin family of pattern recognition receptors and is involved in the immune response against infection. Here, one turbot SCARA4 gene was identified with a 2,292 bp open reading frame (ORF) encoding 763 amino acid residues. Multiple sequence analysis and phylogenetic analysis confirmed that SmSCARA4 gene was more close to that of P. olivaceus. Gene structure and syntenic analysis showed conserved exon/intron organization pattern and syntenic pattern across selected vertebrate species. Tissue distribution analysis showed SmSCARA4 was expressed in all the tested healthy tissues with the relative high expression levels in skin, gill and spleen. Following both E. tarda and V. anguillarum challenge in vivo, SmSCARA4 was significantly repressed in gill and intestine. Remarkably, SmSCARA4 showed the strongest binding ability to LPS and strongest upregulation in turbot head kidney macrophages in response to LPS. Knockdown and overexpression of SmSCARA4 revealed its interactions with the two pro-inflammatory cytokines, TNF-α and IL-1β. Finally, repression of SmSCARA4 via combined treatment of LPS and overexpression of SmSCARA4 construct in turbot head kidney macrophages further indicated an inhibitory role of SmSCARA4 in LPS-stimulated inflammation. Taken together, turbot SmSCARA4 plays an important role in turbot immunity, especially in the mucosa-related systems; SmSCARA4 possesses strong binding specificity to LPS, and exerts protective roles in response to LPS infection by reducing the release of pro-inflammatory cytokines. The mechanisms of inhibitory role of SmSCARA4 in LPS-elicited inflammation await further investigation.

Comparative analysis of the miRNA-mRNA regulation networks in turbot (Scophthalmus maximus L.) following Vibrio anguillarum infection

MicroRNAs could not only regulate posttranscriptional silencing of target genes in eukaryotic organisms, but also have positive effect on their target genes as well. These microRNAs have been reported to be involved in mucosal immune responses to pathogen infection in teleost. Therefore, we constructed the immune-related miRNA-mRNA networks in turbot intestine following Vibrio anguillarum infection. In our results, 1550 differentially expressed (DE) genes and 167 DE miRNAs were identified. 113 DE miRNAs targeting 89 DE mRNAs related to immune response were used to construct miRNA-mRNA interaction networks. Functional analysis showed that target genes were associated with synthesis and degradation of ketone bodies, mucin type O-Glycan biosynthesis, homologous recombination, biotin metabolism, and intestinal immune network for IgA production that were equivalent to the function of IgT and IgM in fish intestine. Finally, 10 DE miRNAs and 7 DE mRNAs were selected for validating the accuracy of high-throughput sequencing results by qRT-PCR. The results of this study will provide valuable information for the elucidation of the regulation mechanisms of miRNA-mRNA interactions involved in disease resistance in teleost mucosal immune system.

Characterization of the turbot (Scophthalmus maximus) interleukin-18: Identification of splicing variants, phylogeny, synteny and expression analysis

Interleukin-18 (IL-18) is a pro-inflammatory cytokine that belongs to the interleukin-1 (IL-1) family of cytokines. As occurs with IL-1β, it is synthetized as an inactive precursor peptide that is mainly processed by the cysteine protease caspase-1 in the inflammasome complex. In mammals, and in collaboration with IL-12, it has been described as an important cytokine controlling the Th1-mediated immune responses through the induction of IFN-γ. Although its function in mammals is well stablished, the activity of this cytokine in teleost remains to be elucidated. This could be due, among other things, to the absence of this gene in the fish model species zebrafish, but also to its complex regulation. As it was observed for rainbow trout and human, il18 splicing variants were also found in turbot, which could represent a regulatory mechanism of its bioactivity. In the case of turbot, three splicing variants were observed (SV1-3), and one of them showed an insertion of 10 amino acids in the middle of the potential caspase-1 cleavage position, reflecting that this is probably a form resistant to the processing by the inflammasome. Phylogenetic and three-dimensional analyses of turbot Il18 revealed that it is relatively well-conserved in vertebrates, although only a partial conservation of the gene synteny was observed between fish and mammals. As it was expected, turbot il18 splicing variants were mainly expressed in immune tissues under healthy conditions, and their expression was induced by a bacterial challenge, although certain inhibitions were observed after viral and parasitic infections. In the case of the viral challenge, il18 downregulations did not seem to be due to the effect of type I IFNs.

Immune role of the complement component 6 gene and its associated novel miRNA, miR-727, in half-smooth tongue sole (Cynoglossus semilaevis)

The complement component 6 (C6) gene is a component of the membrane attack complex (MAC), which causes rapid lytic destruction of bacteria. MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene stability, including that of immune genes. However, current research on the function of C6 and its regulation by miRNAs is lacking. In the present study, we identified and characterized C6 and a novel miRNA, miR-727 (designated CsC6 and Cse-miR-727, respectively), of the half-smooth tongue sole (Cynoglossus semilaevis) that responded to infection with Vibrio anguillarum, a Gram-negative pathogen of marine fish. The full-length cDNA of CsC6 contained a 256 bp 5' untranslated region (5'-UTR), a 2820 bp open reading frame (ORF) encoding 939 amino acids, and a 205 bp 3'-UTR. SMART analysis showed that CsC6 contains typical C6 domains, including three TSP1 domains, one LDLa domain, one MACPF domain, two CCP domains and two FIMAC domains. CsC6 and Cse-miR-727 are widely expressed in the 13 tissues of half-smooth tongue sole, and their expression in immune tissues is significantly changed after V. anguillarum infection, generally showing an inverse trend. We confirmed that CsC6 was the target gene of Cse-miR-727 using the dual luciferase reporter assay and that Cse-miR-727 regulated CsC6 at the protein level using quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. The hepatic expression levels of not only the MAC components C7, C8α, C8β, C8γ and C9 but also the MAPKs, NF-κβ, AP-1, IL1β, IL6 and TNFα, which are involved in many signaling pathways, changed significantly in half-smooth tongue sole following stimulation with the Cse-miR-727 agomir and inhibitor. This evidence suggested that CsC6 could be mediated by Cse-miR-727 to affect MAC assembly and immune signaling pathways in half-smooth tongue soles. To our best knowledge, this study is the first to investigate the regulatory mechanism and immune response of complement genes mediated by miRNAs in fish.

The CC and CXC chemokine receptors in turbot (Scophthalmus maximus L.) and their response to Aeromonas salmonicida infection

Chemokines are crucial regulators of cell mobilization for development, homeostasis, and immunity. Chemokines signal through binding to chemokine receptors, a superfamily of seven-transmembrane domain G-coupled receptors. In the present study, eleven CC chemokine receptors (CCRs) and seven CXC chemokine receptors (CXCRs) were identified from turbot genome. Phylogenetic and syntenic analyses were performed to annotate these genes, indicating the closest relationship between the turbot chemokine receptors and their counterparts of Japanese flounders (Paralichthys olivaceus). Evolutionary analyses revealed that the tandem duplications of CCR8 and CXCR3, the whole genome duplications of CCR6, CCR9, CCR12, and CXCR4, and the teleost-specific CCR12 led to the expansion of turbot chemokine receptors. In addition, turbot chemokine receptors were ubiquitously expressed in nine examined healthy tissues, with high expression levels observed in spleen, gill, and head kidney. Moreover, most turbot chemokine receptors were significantly differentially expressed in spleen and gill after Aeromonas salmonicida infection, and exhibited general down-regulations at early time points and then gradually up-regulated. Finally, protein-protein interaction network (PPI) analyses indicated that chemokine receptors interacted with a few immune-related genes such as interleukins, Grk genes, CD genes, etc. These results should be valuable for comparative immunological studies and provide insights for further functional characterization of chemokine receptors in turbots.

Dietary bile acid supplementation reveals beneficial effects on intestinal healthy status of tongue sole (Cynoglossus semiliaevis)

The aim of this study was to investigate the effects of dietary bile acids (BAs) on intestinal healthy status of tongue sole in terms of immunity, antioxidant status, digestive ability, mucosal barrier-related genes expression and microbiota. Three experimental diets were prepared with BA levels at 0 mg/kg (CT), 300 mg/kg (BA1) and 900 mg/kg (BA2) in a commercial basal diet. Each diet was fed to three replicates with 120 fish (10.87 ± 0.32 g) in each tank. After an 8-week feeding trial, growth parameters were significantly enhanced in both BAs supplementary groups (P < 0.05), and compared with CT group, survival rate in BA2 group was significantly improved (P < 0.05). Intestinal lysozyme activity and contents of immunoglobulin M and complement 3 were significantly increased in both BAs supplementary groups (P < 0.05), suggesting an enhancement effect on the non-specific immune response. BAs inclusion also significantly improved intestinal antioxidant capabilities by increasing antioxidase activities and decreasing malondialdehyde levels. In addition, compared with CT group, intestinal digestive ability was substantially enhanced as indicated by the significantly increased lipase activity in BA2 group (P < 0.05) and significantly increased amylase activity in BA1 and BA2 groups (P < 0.05). Coincidentally, BAs inclusion significantly upregulated the relative expression of intestinal mucosal barrier-related genes (P < 0.05). Further, dietary BAs distinctly remodeled intestinal microbiota by decreased the abundance of some potential pathogenic bacteria. In conclusion, dietary BAs supplementation is an effective way to improve the intestinal healthy status of tongue sole.

Identification and functional analysis of the perforin-1 like gene in disease resistance in half smooth tongue sole (Cynoglossus semilaevis)

The pore-forming protein perforin is one of the effectors of cell-mediated killing via the granule exocytosis pathway. In this study, a genome-wide association study was conducted in Vibrio harveyi disease-resistant and disease-susceptible families of half smooth tongue sole (Cynoglossus semilaevis) to determine the genes accounting for host resistance, and a perforin homologue was identified, designated perforin-1 like (CsPRF1l). The full-length cDNA of CsPRF1l is 1835 bp, and encodes 514 amino acids. The CsPRF1l gene consists of 10 exons and 9 introns, spanning approximately 7 kb. The amino acid sequence of CsPRF1l shows 60.35, 54.03, 41.92, and 34.17% identities to Morone saxatilis PRF1l, Oryzias melastigma PRF1l, Danio rerio PRF1.5 and Homo sapiens PRF, respectively. Sequence analysis revealed the presence of membrane attack complex/perforin (MACPF) and C2 domains in CsPRF1l. Quantitative real-time PCR showed that CsPRF1l presented a higher intestinal expression level in disease-resistant families than in susceptible families. Tissue expression pattern analysis showed that CsPRF1l is present in most of the tested tissues and highly expressed in the intestine, brain, stomach and gills. After challenge with V. harveyi, CsPRF1l mRNA was markedly upregulated in the liver, spleen, kidney, intestine, gills and skin. In addition, the recombinant CsPRF1l protein exhibited obvious antimicrobial activity against V. harveyi in vitro and in a zebrafish model. Collectively, these data indicate that CsPRF1l modulates host immune defense against V. harveyi invasion and provide clues about the efficacy of rCsPRF1l in fish that will give rise to useful therapeutic applications for V. harveyi infection in C. semilaevis.

Identification and characterization of a C-type lectin in turbot (Scophthalmus maximus) which functioning as a pattern recognition receptor that binds and agglutinates various bacteria

C-type lectins (CTLs) are important pathogen pattern recognition receptors that recognize carbohydrate structures. In present study, a C-type lectin domain family 4 member E-like gene from turbot, which tentatively named SmCLEC4E-like (SmCLEC4EL), was identified, and the expressional and functional analyses were performed. In our results, SmCLEC4EL showed conserved synteny with CLEC4E-like genes from several fish species in genome, and possessed a typical type II transmembrane CTL architecture: an N-terminal intracellular region, a transmembrane domain and a C-terminal extracellular region which contained a predicted carbohydrate recognition domain (CRD). In addition, SmCLEC4EL exhibited the highest expression level in spleen in healthy fish, and showed significantly induced expression in mucosal tissues, intestine and skin, under bacteria challenge. Finally, the recombinant SmCLEC4EL protein combined with LPS, PGN, LTA and five different kinds of bacteria in a dose-dependent manner, and agglutinated these bacteria strains in the presence of calcium. These findings collectively demonstrated that SmCLEC4EL, a calcium-dependent CTL, could function as a pattern recognition receptor in pathogen recognition and participate in host anti-bacteria immunity.

Genome-wide identification of interleukin-17 (IL-17) / interleukin-17 receptor (IL- 17R) in turbot (Scophthalmus maximus) and expression pattern analysis after Vibrio anguillarum infection

Interleukin-17 (IL-17) is a cytokine secreted by a variety of immune cells that plays an important role in host defense against pathogens. IL-17 usually activates downstream immune signaling pathway by binding to heterodimeric or homodimeric complex formed by IL-17 receptors (IL-17R). Describing the characteristics, tissue distribution of IL-17 and IL-17 receptor family members and their expression after pathogen infection will provide a reference for host defense against disease of turbot. In this study, six IL-17 family members and nine IL-17 receptor family members were identified by analyzing the turbot (Scophthalmus maximus) genome. Different from other vertebrates, most members of the IL-17 receptor family own two copies. Protein structure analysis showed that the six IL-17 family members contained typical "IL-17" domains, and the nine IL-17 receptor family members contained typical "SEFIR domain" or "IL17_R_N domain". Syntenic analysis revealed that all IL-17s and IL-17Rs were chromosomally conserved compared with other fish. The phylogenetic analysis further confirmed the evolutionary conservatism of different copies of IL-17C and IL-17Rs. Tissue distribution results showed that IL-17 and IL-17R genes were highly expressed in immune-related tissues. The expression of IL-17C and its receptor in the mucosal immune tissues after infection with V. anguillarum were analyzed subsequently, which were significantly increased in the skin. The results are consistent with previous studies showing that IL-17 and IL-17 receptor play an important role in promoting innate immune response.

Dual function of a turbot inflammatory caspase in mediating both canonical and non-canonical inflammasome activation

Host protective inflammatory caspase activity must be tightly regulated to prevent pathogens infection, however, the inflammatory caspase-engaged inflammasome activation in teleost fish remains largely unknown. In this study, we reveal a bifurcated evolutionary role of the inflammatory caspase in mediating both non-canonical and canonical inflammasome pathways in teleost fish. Through characterization of a unique inflammatory SmCaspase from the teleost Scophthalmus maximus (turbot), we found it can directly recognize cytosolic lipopolysaccharide (LPS) via its N-terminal CARD domain, resulting in caspase-5-like proteolytic enzyme activity-mediated pyroptosis in Turbot Muscle Fibroblasts. Interestingly, we also found that this inflammatory caspase can be recruited to SmNLRP3-SmASC to form the NLRP3 inflammasome complex, engaging the SmIL-1β release in Head Kidney-derived Macrophages. Consequently, the SmCaspase activation can recognize and cleave the SmGSDMEb to release its N-terminal domain, mediating both pyroptosis and bactericidal activities. Furthermore, the SmCaspase-SmGSDMEb axis-gated pyroptosis governs the bacterial clearance and epithelial desquamation in fish gill filaments in vivo. To our knowledge, this study is the first to identify an inflammatory caspase acting as a central coordinator in NLRP3 inflammasome, as well as a cytosolic LPS receptor; thus uncovering a previously unrecognized function of inflammatory caspase in turbot innate immunity.

Characterization of toll-like receptor 1 (TLR1) in turbot (Scophthalmus maximus L.)

TLRs are the first and best-characterized pattern recognition receptors conserved across all the species. Different from mammals, the TLRs in teleost fishes are very diversified due to various evolutionary mechanisms. Here, we characterized one TLR1 gene in turbot, with a 2,415 bp open reading frame (ORF), that encoding 804 amino acid residues, and have the highest similarity and identity both to Paralichthys olivaceus with 88.9% and 79.9%. In phylogenetic analysis, it was firstly clustered with P. olivaceus, and then clustered with Takifugu rubripes. TLR1 was widely expressed in all the examined healthy tissues with the highest expression level in spleen, followed by head-kidney. In addition, it was significantly regulated in gill, skin and intestine following Edwardsiella tarda and Vibrio anguillarum challenge with different expression patterns. In in vitro stimulation with pathogen-associated molecular patterns, TLR1 showed significantly strong and elevated responses to LPS, but only responded to LTA and Poly(I:C) at the highest evaluated concentration, while no response was detected using PGN stimulation. Moreover, in subcellular localization analysis, TLR1 was distributed in the cytoplasm, membrane and nucleus. Taken together, TLR1 played vital roles for host immune response to bacterial infection, only with strong binding ability to LPS and involved in the production of inflammatory cytokines. However, the specific ligand for TLR1 and its functional association with other TLRs should be further characterized in fish species.

Molecular cloning and immune characterization of CIITA in artificially challenged Chinese tongue sole (Cynoglossus semilaevis) with Vibrio harveyi

In mammals, Class II, major histocompatibility complex (MHC II) transactivator (CIITA) recognizes microbial pathogens and triggers immune responses. In Chinese tongue sole Cynoglossus semilaevis, Cs-CIITA was prevalently expressed in various tissues. Cs-CIITA, Cs-MHC IIA and Cs-MHC IIB were expressed significantly higher in skin in susceptible families infected with Vibrio harveyi, while higher expression of Cs-CIITA and Cs-MHC IIB was examined in liver in resistant families. In addition, the three genes were up-regulated in gill, skin, intestine, liver, spleen and kidney at 48 h or 72 h after V. harveyi infection. Furthermore, the three genes were co-expressed in the epithelial mucous cells of gill, skin, and intestine. Knockdown of Cs-CIITA regulates the expression of other inflammation-related genes, including CD40, IL-1β, IL-8, RelB, NFκB, and Myd88. These results suggest that CIITA functions in the inflammatory responses of C. semilaevis against V. harveyi, via MHC II transcriptional regulation.

Analysis of lncRNA and mRNA expression profiles in peripheral blood leukocytes of the half-smooth tongue sole (Cynoglossus semilaevis) treated with chitosan oligosaccharide

Long noncoding RNAs (lncRNAs) play a multifaceted role in transcriptional regulation and are important regulators of immune function. Scarce information is available regarding lncRNAs in fish. Peripheral blood mononuclear cells participate in the immune response of fish and aid resistance to infection with pathogenic microorganisms. Chitosan oligosaccharide can improve cellular and humoral immunity to enhance disease resistance in fish. In this study, we obtained peripheral blood leukocytes from half-smooth tongue sole and studied the effect of chitosan oligosaccharide on the lncRNA-mRNA expression profile of these cells using high-throughput sequencing and bioinformatics techniques. A total of 609 differentially expressed mRNAs and 50 differentially expressed lncRNAs were identified. The GO term enrichment analysis of the differentially expressed genes was annotated by 220 GO terms, 137 biological processes, 18 cellular components, and 65 molecular functions. Sixteen KEGG pathways, including immune signaling pathways, metabolism, and genetic information processing, were significantly enriched in differentially expressed genes. Thirty-six differentially expressed lncRNAs and 32 differentially expressed mRNAs produced a coexpression network containing 90 relationship pairs. The prediction of lncRNA target genes revealed 244 lncRNAs that potentially cis-regulated 294 differentially expressed mRNAs. qPCR verified that the expression levels of 17 differentially expressed lncRNAs and 15 differentially expressed mRNAs were consistent with the RNA-Seq results. Among them, 6 lncRNAs and 7 mRNAs were differentially expressed genes obtained from the prediction and analysis of lncRNA target genes, and 8 lncRNAs and 4 mRNAs were differentially expressed genes that participated in the construction of the coexpression network. In peripheral blood leukocytes after chitosan oligosaccharide treatment, as well as in peripheral blood and spleen after Vibrio anguillarum stimulation, lncRNAs and mRNAs showed significant differential expression. The results indicated that they may be related to the immune response, providing novel reference information for further research on the role of lncRNAs in immune regulation in half-smooth tongue sole.

Proteomics of mucosal exosomes of Cynoglossus semilaevis altered when infected by Vibrio harveyi

The cargo of exosomes contains proteins with various functions, which might be promising biomarkers for disease diagnosis and prognosis. To explore the impact of the Vibrio harveyi pathogen on Cynoglossus semilaevis from a different perspective and develop promising biomarkers for infection, the exosomes from epidermal mucus of healthy controls（EC）and sick fish（ES）were extracted and identified, coupled with proteomic screening through iTRAQ followed with LC-MS/MS. 1531 credible proteins were obtained relating to structural, metabolic and immunological functions. 359 different expressed proteins (DEPs) (FC > 2 or FC < 0.5) were found, with 161 up-regulated and 198 down-regulated in ES. Based on the database of C. semilaevis on Uniprot, 71 proteins were characterized as concrete names, including 19 up-regulated proteins and 52 down-regulated proteins, and were selected as subjects for further studies. Ferritin, Toll-like receptor 5S protein and Calcium-transporting ATPase were upregulated, while Histone H2B and Eukaryotic translation initiation factor 5A were downregulated, consistent with the expression levels of related mRNAs in skin tissue verified by qRT-PCR. The integrated analysis between miRomics and proteomics also provided possible regulatory relationships mediated by mucous exosomes during infection. The signature proteins in mucosal exosomes could make sense in the explanation of the infection defending mechanism and the development of biomarkers which can differentiate diseased and healthy C. semilaevis individuals.

A teleost bactericidal permeability-increasing protein-derived peptide that possesses a broad antibacterial spectrum and inhibits bacterial infection as well as human colon cancer cells growth

The bactericidal permeability-increasing protein (BPI) is a multifunctional cationic protein produced by neutrophils with antibacterial, antitumor, and LPS-neutralizing properties. In teleost, a number of BPIs have been reported, but their functions are very limited. In this study, an N-terminal peptide, BO18 (with 18 amino acids), derived from rock bream (Oplegnathus fasciatus) BPI, was synthesized and investigated for its antibacterial spectrum, action mechanism, immunoregulatory property as well as the inhibition effects on bacterial invasion and human colon cancer cells growth. The results showed that BO18 was active against Gram-positive bacteria Bscillus subiilis, Micrococcus luteus, and Staphylococcus aureus, as well as Gram-negative bacteria Vibrio alginolyticus, Vibrio litoralis, Vibrio parahaemolyticus and Vibrio vulnificus. BO18 treatment facilitated the bactericidal process of erythromycin and rifampicin by enhancing the permeability of the outer membrane. During its interaction with V. alginolyticus, BO18 exerted its antibacterial activity by destroying cell membrane integrity, penetrating into the cytoplasm and binding to genomic DNA and total RNA. In vitro analysis indicated BO18 could enhance the respiratory burst ability and regulate the expression of immune related genes of macrophages. In vivo detection showed the administration of fish with BO18 before bacterial infection significantly reduced pathogen dissemination and replication in tissues. In addition, BO18 exerted a cytotoxic effect on the growth of human colon cancer cells HT-29. Together, these results add new insights into the function of teleost BPIs, and support that BO18 is a novel and broad-spectrum antibacterial peptide with potential to apply in fighting pathogenic infection in aquaculture.

Characterization of the turbot Scophthalmus maximus (L.) myeloperoxidase. An insight into the evolution of vertebrate peroxidases

We have completed the characterization of the turbot (Scophthalmus maximus) myeloperoxidase (mpx) gene and protein, which we partially described in a previous study. The turbot mpx gene has 15 exons that encode a protein of 767 aa, with a signal peptide, propeptide and light and heavy chains, and also with haem cavities, a Ca⁺²-binding motif and several N- and O-glycosylation sites. The mature protein forms homodimers of about 150 kDa and is very abundant in turbot neutrophils. In addition to the mpx (epx2a) gene, another three peroxidase genes, named epx1, epx2b1 and epx2b2, were identified in the turbot genome. Epx1, Epx2b1 and Epx2b2 proteins also have signal peptides and many structural characteristics of mammalian MPO and eosinophil peroxidase (EPX). Mpx was strongly expressed in head kidney, while epx2b1 and epx2b2 were strongly expressed in the gills, and epx1 was not expressed in any of the tissues or organs analysed. In vitro stimulation of head kidney leucocytes with the parasite Philasterides dicentrarchi caused a decrease in mpx expression and an increase in epx2b1 expression over time. In turbot infected experimentally with P. dicentrarchi a significant increase in mpx expression in the head kidney was observed on day 7 postinfection, while the other genes were not regulated. However, mpx, epx2b1 and epx2b2 were downregulated in the gills of infected fish, and epx1 expression was not affected. These results suggest that the four genes responded differently to the same stimuli. Interestingly, BLAST analysis revealed that Epx1 and Mpx showed greater similarity to mammalian EPX than to MPO. Considering the phylogenetic and synteny data obtained, we concluded that the epx/mpx genes of Gnathostomes can be divided into three main clades: EPX1, which contains turbot epx1, EPX2, which contains turbot mpx (epx2a) and epx2b1 and epx2b2 genes, and a clade containing mammalian EPX and MPO (EPX/MPO). EPX/MPO and EPX2 clades share a common ancestor with the chondrichthyan elephant shark (Callorhinchus milii) and the coelacanth (Latimeria chalumnae) peroxidases. EPX2 was only found in fish and includes two sister groups. One of the groups includes turbot mpx and was only found in teleosts. Finally, the other group contains epx2b1 and epx2b2 genes, and epx2b1-2b2 loci share orthologous genes with other teleosts and also with holosteans, suggesting that these genes appeared earlier on than the mpx gene.

Molecular characterization, expression analysis and immune effect of Galectin-8 from Japanese flounder (Paralichthys olivaceus)

Galectin-8 gene belongs to the agglutinin family, which can specifically recognize β-galactoside bonds and play essential roles in many biological processes. In this study, we researched the sequence characteristics and immune-related function of Galectin-8 gene in Japanese flounder Paralichthys olivaceus, named PoGalectin-8. The results showed that the open reading frame of PoGalectin-8 was 891 bp, which encoding a protein with 296 amino acid residues and containing typical HXNPR and WGXEE motifs in the N-terminal and C-terminal CRD domains. Sequence alignment showed that PoGalectin-8 was conserved in different aquatic animals and exhibited the highest similarity (95.27%) with Seriola dumerili. PoGalectin-8 expressed in all detected tissues and exhibited the highest expression level in spleen, followed by skin and kidney. After infected by Edwardsiella tarda, the expression of PoGalectin-8 was down-regulated in the spleen and skin tissues of P. olivaceus. Further to study its immune-related functions, the recombinant PoGalectin-8 (rPoGalectin-8) was expressed and purified. The rPoGalectin-8 can specifically bind to lipopolysaccharide and peptidoglycan, the main components of cell walls from Gram-negative and Gram-positive bacteria. Bacteria binding and the microbial agglutinating experiments showed that the rPoGalectin-8 could bind and agglutinate all examined Gram-positive and Gram-negative bacteria. This study implied that PoGalectin-8, as a pattern recognition receptor, may play important roles during immune responses against bacterial infection, which laid a foundation for further functional identification of Galectin-8 in aquatic animal immunity.

Extracellular vesicles piwi-interacting RNAs from skin mucus for identification of infected Cynoglossus semilaevis with Vibrio harveyi

Extracellular vesicles play a regulatory role in intracellular and intercellular transmission through a variety of biological information molecules, including mRNA, small RNAs and proteins. piRNAs are one kind of regulatory small RNAs in the vesicles at the post transcriptional level. Hereby, we isolated the extracellular vesicles from skin mucus and screened the piRNA profiles of these vesicles, aiming at developing biomarkers related to bacterial infections in Cynoglossus semilaevis. The different profilings of piRNAs in mucous extracellular vesicles of C. semilaevis were compared through small RNA sequencing, between fish infected with Vibrio harveyi and healthy ones. The number of clean reads on the alignment of exosome sick (ES) group was 105, 345 and that of exosome control (EC) group was 455, 144. GO and KEGG pathway enrichment analysis showed that most of the target genes were involved in cellular process, response to stimulus, biological regulation, immune system process and signal transduction, signal molecular and interaction, transport and catabolism. The 45 final candidate piRNAs related to immunity or infectious diseases included 20 piRNAs with high expression in the ES group and 25 piRNAs with a low expression in the ES group. After verification by qRT-PCR, there was significant difference of five piRNAs expression level between infected fish and healthy fish, in line with the sequencing. The expression level of piR-mmu-16401212, piR-mmu-26829319 and piR-gga-244092 in infected fish were significantly lower than that of control group, while piR-gga-71717 and piR-gga-99034 were higher, which implying that these piRNAs in mucous extracellular vesicles can be used to identify diseased fish from normal ones. This work supplied a novel class of biomarker for infection diagnosis in fish, and it will be benefit for screening disease resistant breeding of C. semilaevis.

Genetic parameters of seven immune factors in turbot (Scophthalmus maximus) infected with Vibrio anguillarum

In this study, 1,800 turbot (Scophthalmus maximus) individuals from 30 full-sib families were experimentally infected with Vibrio anguillarum, and the expression levels of the immune factors lysozyme, hepcidin, heat-shock protein 70 (HSP70), HSP90, immunoglobulin M (IgM), C-type lectin and Lily-type lectin in the liver were measured by real-time PCR. Heritability values of the seven immune factors were 0.289 ± 0.087, 0.092 ± 0.024, 0.282 ± 0.043, 0.244 ± 0.027, 0.343 ± 0.081, 0.092 ± 0.011 and 0.084 ± 0.009, respectively. The ranges of phenotypic, genetic and environmental correlations were -0.889 to 0.759, -0.841 to 0.888 and -0.919 to 0.883, respectively. The heritability values of HSP70, HSP90 and IgM were moderate, and the genetic correlations between HSP70, HSP90 and IgM were moderate to highly positive, which suggests that the immunocompetence of turbot against V. anguillarum can be improved by genetically improving these three immune characters via multi-trait integrated breeding technology or indirect selection.

Characterization and expression analysis of mitochondrial localization molecule: NOD-like receptor X1 (Nlrx1) in mucosal tissues of turbot (Scophthalmus maximus) following bacterial challenge

The NOD-like receptor X1 (NLRX1) is a member of highly conserved nucleotide-binding domain (NBD)- and leucine-rich-repeat (LRR)-containing family (known as NLR), that localizes to the mitochondrial outer membrane and regulate the innate immunity by interacting with mitochondrial antiviral-signaling protein (MAVS). As one of cytoplasmic PRRs, NLRX1 plays key roles for pathogen recognition, autophagy and regulating of subsequent immune signaling pathways. In this study, we identified the nlrx1 in turbot as well as its expression profiles in mucosal surfaces following bacterial infection. In our results, the full-length nlrx1 transcript consists of an open reading frame (ORF) of 4,886 bp encoding the putative peptide of 966 amino acids. The phylogenetic analysis revealed the SmNlrx1 showed the closest relationship to Cynoglossus semilaevis. In addition, the Nlrx1 mRNA expression could be detected in all the examined tissues, with the most abundant expression level in head kidney, and the lowest expression level in liver. Moreover, Nlrx1 showed similar expression patterns following Vibrio anguillarum and Streptococcus iniae infection, that were both significantly up-regulated following challenge, especially post S. iniae challenge. Finally, fluorescence microscopy unveiled that the SmNlrx1 localized to mitochondria in HEK293T by N-terminal mitochondrial targeting sequence. Characterization of Nlrx1 might have an important implication in bioenergetic adaptation during metabolic stress, oncogenic transformation and innate immunity and will probably contribute to the development of novel intervention strategies for farming turbot.

Macrophage colony stimulating factor (MCSF) of Japanese flounder (Paralichthys olivaceus): Immunoregulatory property, anti-infectious function, and interaction with MCSF receptor

Macrophage colony-stimulating factor (MCSF) is an essential growth factor to control the proliferation, differentiation and survival of the macrophage lineage in vertebrates. Sequences of MCSF have been identified in multiple teleost species, however, the functional investigations of MCSF were documented in only a few species. In this study, we examined the biological activity and the immunomodulatory property of a MCSF homologue, PoMCSF, from Japanese flounder (Paralichthys olivaceus). Structural analysis showed that PoMCSF possesses conserved structural characteristics of MCSF proteins, including a signal peptide, a CSF-1 domain, and a transmembrane region closed to the C-terminal. Under normal physiological condition, PoMCSF expression distributes in all the examined tissues, the highest three tissues are blood, muscle, and head kidney. When infected by extracellular and intracellular bacterial pathogens and viral pathogen, the PoMCSF expression patterns vary with different types of microbial pathogens infection and different immune tissues. In vitro experiment showed recombinant PoMCSF promoted the activity of macrophage. In vivo experiment indicated that PoMCSF overexpression boosted the defensive ability of flounder against Edwardsiella piscicida, a severe fish pathogen that infects multiple species of economically important fish, and regulated the expression of multiple immune-related genes. To explore the relationship between PoMCSF and its receptor PoMCSFR, anti-PoMCSFR antibody was prepared and PoMCSFR knockdown was conducted. The neutralization assay showed that when PoMCSFR was neutralized by its antibody, the role of PoMCSF on host defense against E. piscicida was weakened. Knockdown of PoMCSFR impaired the phagocytic capacity of macrophages. Collectively, these findings suggest that PoMCSF plays a crucial role in the immune defense system of Japanese flounder and the effect of PoMCSF is dependent on PoMCSFR. This study provides new insights into the biological activity of MCSF and the relationship between MCSF and MCSFR in teleost.

Tongue sole (Cynoglossus semilaevis) interleukin 10 receptors are involved in the immune response against bacterial infection

Interleukin (IL)-10, an immune-regulatory cytokine, exerts various biological functions through interaction with IL-10 receptors. In teleost, very limited functional studies on IL-10 receptors have been documented. In this study, we reported the expression patterns of IL-10 receptor 1 (CsIL-10R1) and receptor 2 (CsIL-10R2) of tongue sole (Cynoglossus semilaevis) and examined their biological properties. The expression of CsIL-10R1 and CsIL-10R2 occurred in multiple tissues and were regulated by bacterial challenge. In vitro binding studies showed that recombinant extracellular region of CsIL-10R1 (rCsIL-10R1ex) rather than rCsIL-10R2ex could bind with rCsIL-10. Cellular study showed that both CsIL-10R1 and CsIL-10R2 were expressed on peripheral blood leukocytes (PBLs), and blockade of CsIL-10R1 or CsIL-10R2 by antibody could reduce inhibitory effect of CsIL-10 on ROS production of PBLs. When injected in vivo, anti-rCsIL-10R1 or anti-rCsIL-10R2 antibody dramatically promoted the expression of proinflammatory cytokines and suppressed bacterial dissemination in tongue sole tissues. Consistently, the overexpression of CsIL-10R1 or CsIL-10R2 significantly enhanced bacterial dissemination, and the overexpression of CsIL-10R1M bearing STAT3 site mutation reduced bacterial dissemination. Overall, these results demonstrate for the first time teleost IL-10 receptors play a negative role in antibacterial immunity and add insight into the function of CsIL-10 receptors.

Dietary taurine modulates hepatic oxidative status, ER stress and inflammation in juvenile turbot (Scophthalmus maximus L.) fed high carbohydrate diets

This study was conducted to explore the beneficial role of taurine against chronic high carbohydrate diet-induced oxidative stress, endoplasmic reticulum (ER) stress and inflammation, and to understand the underlying molecular mechanisms in turbot. Two 10-week feeding trials were simultaneously conducted. For the one, six experimental diets with graded levels of taurine supplementation (0, 0.4%, 0.8%, 1.2%, 1.6% and, 2.0%, respectively) and 15% of carbohydrate were used. For the other one, three graded levels of dietary taurine supplementation (0.4%, 1.2% and 2.0%, respectively) with 21% of carbohydrate were used. The results showed that higher expression level of inflammation cytokines and ER stress related genes were detected in higher dietary carbohydrate group. In both feeding trials, 1.2% of dietary taurine supplementation improved anti-oxidative status by decreasing the content of malondialdehyde, increasing the catalase activity and total anti-oxidative capacities. In feeding trial 1, appropriate taurine supplementation lowered contents of tumour necrosis factor-a, interleukin-6, aspartate aminotransferase and alkaline phosphatase in plasma, and decreased the expressions of pro-inflammatory cytokines, such as interleukin-8 (il-8) and interferon-γ (ifn-γ). Furthermore, dietary taurine reduced ER stress by decreasing the mRNA levels of activating transcription factor 6, protein kinase R-like endoplasmic reticulum kinase and G protein-coupled receptor 78. The optimal dietary taurine content was estimated as 1.40% based on the analysis of specific growth rate. In feeding trial 2, dietary taurine supplementation attenuated liver inflammation partly referring to significantly down-regulated mRNA levels of nuclear transcription factor-κB p65, ifn-γ, interleukin1β and up-regulate the transcript of ribosomal protein S6 kinase 1. Dietary taurine supplementation in feeding trial 2 significantly increased the Nrf2-related factor 2 protein level and decreased the NFκB p65 protein level only at 21% of dietary carbohydrate level. Taurine can alleviate the oxidative damage and inflammation caused by 21% of dietary carbohydrate to a certain degree. Overall, the present study confirmed that dietary taurine supplementation improved growth performance and anti-oxidative response, and reduced liver inflammatory and ER stress processes induced by high dietary carbohydrate in turbot.

A live attenuated Edwardsiella tarda vaccine induces immunological expression pattern in Japanese flounder (Paralichthys olivaceus) in the early phase of immunization

A previous study showed that an attenuated Edwardsiella tarda strain, TXhfq, as a live vaccine could elicit protective immune effects in fish against E. tarda infection. In the current study, in order to clarify the molecular mechanism of fish immune response at the early stage after TXhfq vaccination, RNA-Seq technology was used to compare the transcriptomes of skin, intestine, and spleen between bath-vaccinated and unvaccinated Japanese flounder (Paralichthys olivaceus). An average of 46.6 million clean reads per library was obtained, ~88.04% of which were successfully mapped to the reference genome, and approximately 24,600 genes were detected in each sample. A total of 565, 878, and 1258 differential expression genes (DEGs) were found in skin, intestine, and spleen, respectively, including 1263 up-regulated genes and 1438 down-regulated genes. The DEGs exhibited different characteristics in each tissue. One hundred and sixteen DEGs belonging to six immune related categories were scrutinized, i.e., inflammatory factors, cytokines, complement and coagulation system, mucins, phagocytosis, and antigen processing and presentation. A protein-protein interaction network was constructed to get the interaction network between immune genes during the early stage of immunization. The top six hub genes highly regulated by TXhfq formed complicated interaction relationship with each other, which were involved in immune processes, notably inflammation and phagocytosis. Our results provide valuable information for the understanding of the immune mechanism underlying the protection of live attenuated vaccines in fish.

Transcriptome analysis reveals temperature-dependent early immune response in flounder (Paralichthys olivaceus) after Hirame novirhabdovirus (HIRRV) infection

Hirame novirhabdovirus (HIRRV), as a highly pathogenic fish virus, is frequently prevalent in a variety of aquaculture fish in recent years, which seriously threatens the healthy development of aquaculture industry. Epidemiological studies show that the outbreak of HIRRV is obviously temperature dependent. Virus proliferation experiments in vitro and in vivo at different temperatures indicate the antiviral response of flounder is a main reason affect the replication of HIRRV. The RNA-Seq was used to analyze the different antiviral response in flounder which infected with HIRRV at different temperatures, the experiment set two temperatures of 10 °C and 20 °C. The flounder infected with HIRRV by artificial injection, and the spleens were collected at 24 h after infection. Meanwhile, the fish injected with EPC supernatant at different temperatures were set as control groups. It can obtain four pairwise comparison groups if determine a single variable, and the differentially expressed genes were further selected. The results showed that after infection with HIRRV at 10 °C and 20 °C, the differentially expressed genes in spleen were significantly enriched in inflammatory and immune-related pathways like Arachidonic acid metabolism, Cytokine-cytokine receptor interaction, Toll-like receptor (TLR) signaling pathway, RIG-I-like receptor (RLRs) signaling pathway, NOD-like receptor (NLR) signaling pathway and Cytosolic DNA-sensing pathway etc. In addition, the expression of phagocytes, lysosomes, endocytosis related genes were significantly upregulated at high temperature whether HIRRV positive or not. But compared to the infected flounder at 10 °C, some genes of RLRs signaling pathway were significantly upregulated at 20 °C, it can be speculated that RLRs pathway may be related to the anti-HIRRV response of flounder. Therefore, key genes of RLRs signaling pathway including mda5, lgp2, mita, mavs, irf3, irf7, ifn I-3 and ifn-γ were selected, and the temporal expression patterns of these genes in infected flounder at different temperatures were further detected by qRT-PCR. The results showed that HIRRV infection can significantly stimulate and activate the RLRs pathway of flounder, and the response level of this pathway was significantly higher at 20 °C than 10 °C. In general, this study provides important data for the further study about the pathogenesis of HIRRV infection in flounder.

Characterization of three connexin32 genes and their role in inflammation-induced ATP release in the Japanese flounder Paralichthys olivaceus

Extracellular ATP (eATP) is a potent singling molecule in activation of fish innate immunity while the molecular determinants for eATP release in fish were not completely understood. Connexin32 (Cx32) is a member of gap junction protein family that plays important immunological functions in mammals. However, the immune relevance of Cx32 and its role in ATP release in fish has not been investigated. Here, we identified, characterized three Cx32 isoform genes (Cx32.2, Cx32.2x and Cx32.7) from the Japanese flounder Paralichthys olivaceus, and investigated their role in inflammation-induced ATP release in fish. Expression analysis revealed that even though all the three Cx32 genes are constitutively expressed in all examined Japanese flounder tissues, Cx32.2 and Cx32.2x are dominantly expressed in liver, and Cx32.7 is highly expressed in intestine and head kidney macrophages. In addition, we showed that gene expression of all the three Cx32 isoforms was modulated by cAMP stimulation and inflammatory challenges. Furthermore, we revealed that Cx32 expression was upregulated in TNF-alpha overexpressed Japanese flounder FG-9307 cells. Moreover, overexpression of the three Cx32 isoforms significantly reduced the gene expression level of LPS-induced pro-inflammatory cytokine IL-8 and TNF-alpha, indicating that Cx32 is involved in modulating inflammatory response in fish. Finally, we showed that inflammation-induced ATP release was significantly increased in Cx32-overexpressed Japanese flounder FG-9307 cells, and this increased ATP release could be attenuated by pre-incubation with gap junction protein blocker carbenoxolone. Taken together, we for the first time reported the involvement of Cx32 in fish immunity. Our findings suggested that in addition to Cx43 and pannexin1 channels, Cx32 also plays a role in inflammation-induced ATP release in fish.

Oral administration of microencapsulated egg yolk immunoglobulin (IgY) in turbot (Scophthalmus maximus) to combat against Edwardsiella tarda 2CDM001 infections

Edwardsiellosis, an extremely harmful disease can be caused by Edwardsiella tarda, severely restricts the development of turbot (Scophthalmus maximus) farming worldwide, especially in China. This study aimed to establish an effective and feasible prophylaxis by feeding chitosan-alginate coated egg yolk immunoglobulin (IgY) against E. tarda 2CDM001 infections in the process of turbot farming. Enzyme-linked immunosorbent assays proved that the obtained specific IgY could specifically target E. tarda 2CDM001 and five other E. tarda isolates (1a5p, Hz-s, 1a1s, fs-a1 and 58p8). In-vitro, the bacteriostatic effects of specific IgY showed dose dependencies at concentrations ranging from 1 to 10 mg/mL. Moreover, E. tarda 2CDM001 incubated with 10 mg/mL specific IgY could induce the destruction of cell wall structures and significantly decrease the bacterial surface hydrophobicity (p < 0.05). In this study, turbots were challenged with 10⁷ CFU E. tarda 2CDM001 after seven days of continuous feeding with basal diets containing microencapsulated IgYs. Survival rates of the 5%, 3% and 1% microencapsulated specific IgY groups were 63.3%, 56.7% and 20% on the tenth day post infection, respectively, while the turbots in the positive control and non-specific IgY groups all died within ten days. Oral administration of basal diets containing 5% microencapsulated specific IgY significantly reduced IL-1β, IL-8, TNF-α and C3 transcript levels in the head kidney and spleen of turbots compared with the positive and non-specific IgY groups at 24 h after E. tarda 2CDM001 challenging (p < 0.05). Pathological increase of leukocytes in the specific IgY group was significantly lower than that in the positive control and non-specific IgY groups (p < 0.05), decreasing slowly after 24 h of infection and showing a recovery trend. Erythrocyte counts and hemoglobin concentrations of turbots in positive and non-specific IgY groups showed a marked decrease compared with the negative and specific groups at 96 h after E. tarda 2CDM001 infection (p < 0.05). These results suggest that passive immunity via feeding microencapsulated specific IgY could be used as a valuable preventative in turbot against E. tarda 2CDM001 infections.

Characterization of a novel live attenuated Edwardsiella piscicida vaccine based on the overexpressed type III secretion system and systematic deletion of the associated effectors

Edwardsiella piscicida causes edwardsiellosis in a variety of fish species and leads to tremendous economic losses in the global aquaculture industries. Thus, effective and safe prevention and control of this bacterium are urgently needed to combat the related infections. Live attenuated vaccines (LAVs) effectively prevent infectious diseases. However, most of the existing E. piscicida LAVs are based on the deletion of genes encoding the translocon components of the type III secretion system (T3SS), the core virulence system, which is the most prominent protective bacterial antigen with the strongest immunogenicity. In this study, we systematically deleted all of the 9 established T3SS effectors in E. piscicida (aka 9Δ) and the rpoS gene encoding the alternative sigma factor, the esrB repressor (10Δ), then we overexpressed esrB and T3SS in E. piscicida to obtain the recombinant strain 10Δ/esrBOE. The modified strains 10Δ and 10Δ/esrBOE exhibited severe attenuation and in vivo colonization defects. Additionally, vaccination by intraperitoneal injection with 10Δ and 10Δ/esrBOE could significantly upregulate the expression of the antigen recognition related gene (TLR5) and the adaptive immune response-related gene (MHC II) in the spleen/kidney of turbot fish, and it also enhanced the hosts' serum bactericidal capacity. Finally, vaccination with 10Δ/esrBOE led to increased immune protection against the challenge of wild type E. piscicida EIB202 in turbot fish. Collectively, these findings demonstrated that 10Δ/esrBOE was a novel LAV strain and therefore a potential novel strategy for the construction of LAVs against bacterial pathogens.

Microalgal extracts induce larval programming and modify growth and the immune response to bioactive treatments and LCDV in Senegalese sole post-larvae

Immunostimulants are key molecules in aquaculture since they heighten defensive responses and protection against pathogens. The present study investigated the treatment of Senegalese sole larvae with a whole-cell crude extract of the microalgae Nannochloropsis gaditana (Nanno) and programming of growth and the immune system. Larvae at hatch were treated with the Nanno extracts for 2 h and thereafter were cultivated for 32 days post-hatch (dph) in parallel with an untreated control group (CN). Dry weight and length at 21 days post-hatch (dph) were higher in post-larvae of the Nanno than CN group. These differences in weight were later confirmed at 32 dph. To evaluate changes in the immune response associated with Nanno-programming treatments, the Nanno and CN post-larvae were supplied with two bioactive compounds yeast β-glucan (Y) and a microalga extract from the diatom Phaeodactylum tricornutum (MAe). The bioactive treatments were administrated to the treatment groups through the live prey (artemia metanauplii, 200 artemia mL^-1) enriched for 30 min with MAe or Y (at 2 mg mL^-1 SW) or untreated prey in the case of the negative control (SW). The effect of the treatments was assessed by monitoring gene expression, enzyme activity and mortality over 48 h. The post-larvae sole supplied with the bioactive compounds Y and MAe had increased mortality at 48 h compared to the SW group. Moreover, mortality was higher in Nanno-programmed than CN post-larvae. Lysozyme and total anti-protease enzymatic activities at 6 and 24 h after the start of the trial were significantly higher in the Nanno and MAe supplied post-larvae compared to their corresponding control (CN and SW, respectively). Immune gene transcripts revealed that il1b, cxc10 and mx mRNAs were significantly different between Nanno and CN post-larvae at 6 and 24 h. Moreover, the expression of il1b, tnfa, cxc10, irf3, irf7 and mx was modified by bioactive treatments but with temporal differences. At 48 h after bioactive treatments, Y and SW post-larvae were challenged with the lymphocystis disease virus (LCDV). No difference existed in viral copy number between programming or bioactive treatment groups at 3, 6 and 24 h after LCDV challenge although the total number of copies reduced with time. Gene expression profiles in the LCDV-challenged group indicated that post-larvae triggered a wide defensive response compared to SWC 24 h after challenge, which was modulated by programming and bioactive compound treatments. Cluster analysis of expressed genes separated the SW and Y groups indicating long-lasting effects of yeast β-glucan treatment in larvae. A noteworthy interaction between Nanno-programming and Y-treatment on the regulation of antiviral genes was observed. Overall, the data demonstrate the capacity of microalgal crude extracts to modify sole larval plasticity with long-term effects on larval growth and the immune responses.

Enhancing immunogenicity of a reporter protein by fusion to glycoprotein and nucleoprotein of viral hemorrhagic septicemia virus (VHSV) particles

The introduction of reverse genetic technology to generate recombinant VHSVs (rVHSVs) has contributed to the uncovering of functional roles of viral genes and to the development of attenuated prophylactic vaccines. In this study, to assess the possible use of rVHSVs as a tool of combined vaccines, we newly rescued rVHSVs that harbor viral envelop-studded eGFP (rVHSV-A-SGT) or nucleoprotein-fused eGFP (rVHSV-A-NLG), and the ability of these rVHSVs to induce adaptive humoral immunity in olive flounder (Paralichthys olivaceus) was compared with that of rVHSV-A-eGFP that expresses eGFP as a soluble form in the cytoplasm of infected cells. The results showed that antibodies against eGFP were efficiently induced by the immunization of olive flounder with rVHSV-A-SGT and rVHSV-A-NLG, while rVHSV-A-eGFP was poor in the ability to induce antibody response against eGFP. These results suggest that the display of heterologous antigens on VHSV envelop is a good way to develop efficient combined vaccines and the fusion of foreign antigen with N protein can also be a way to enhance immunogenicity of a foreign antigen. The present recombinant VHSVs - rVHSV-A-SGT and rVHSV-A-NLG - not only express foreign antigens in host cell cytoplasm but also display antigens in or on the virus particles. Further researches on the availability of recombinant VHSVs as combined vaccines against multiple fish pathogens are needed.

Effect of water temperature on the protective efficacy of single-cycle rVHSV-GΔTM vaccine in olive flounder (Paralichthys olivaceus)

Water temperature is an important factor for immune responses in poikilothermic fish. Especially, it has been known that adaptive immunity is more sensitive to temperature than innate immunity in fish. The optimal temperature for olive flounder (Paralichthys olivaceus) culture is known between 20 and 25 °C, and there are several papers reporting the low or no effectiveness of inactivated vaccines in olive flounder kept at low water temperatures. Previously, we had reported that a vaccine based on single-cycle viral hemorrhagic septicemia virus (VHSV) that was modified to produce the transmembrane and C-terminal cytoplasmic region-deleted G protein in host cells (rVHSV-GΔTM) induced significantly higher survival rates in olive flounder than a vaccine of rVHSV-ΔG that had no G gene in the genome. In the present study, we evaluated the availability of rVHSV-GΔTM as a protective vaccine that can be used in olive flounder at low water temperature periods. Olive flounder fingerlings were divided into 6 groups: group 1 and 2 were kept at 14 °C, group 3 and 4 were kept at 20 °C, and group 5 and 6 were kept at 14 °C for 1 week and then shifted to 20 °C. Fish in groups 1, 3, and 5 were intramuscularly (i.m.) immunized with 8.5 × 10⁴ PFU/fish of rVHSV-GΔTM, and fish in groups of 2, 4, and 6 were i.m. Injected with L-15 alone. In the challenge test, the survival rates of fish immunized with rVHSV-GΔTM were significantly higher than those of control group fish that were injected with L-15 alone. Among three vaccination groups (group 1, 3, and 5), group 1 showed no mortality. The cumulative mortalities of group 3 and group 5 were both 25%. While fish in control groups (group 2, 4, and 6) showed 90-100% mortalities. The qPCR genome copy number of rVHSV-GΔTM in the kidney of fish immunized at 14 °C was clearly higher than that in fish immunized at 20 °C, which suggests that higher amount of secretory viral glycoprotein would be produced in fish vaccinated at 14 °C than at 20 °C. Olive flounder immunized with rVHSV-GΔTM at 14 °C showed the serum neutralization activity as high as fish immunized at 20 °C, suggesting that the humoral immune response of olive flounder was effectively induced at lower water temperature. These results suggest that VHSV vaccines based on single-cycle viruses can be used as prophylactic vaccines even at low water temperature period.

The Assessment of Diet Contaminated with Aflatoxin B1 in Juvenile Turbot (Scophthalmus maximus) and the Evaluation of the Efficacy of Mitigation of a Yeast Cell Wall Extract

This study aimed to investigate the effects of dietary AFB₁ on growth performance, health, intestinal microbiota communities and AFB₁ tissue residues of turbot and evaluate the mitigation efficacy of yeast cell wall extract, Mycosorb^® (YCWE) toward AFB₁ contaminated dietary treatments. Nine experimental diets were formulated: Diet 1 (control): AFB₁ free; Diets 2-5 or Diets 6-9: 20 μg AFB₁/kg diet or 500 μg AFB₁/kg diet + 0%, 0.1%, 0.2%, or 0.4% YCWE, respectively). The results showed that Diet 6 significantly decreased the concentrations of TP, GLB, C3, C4, T-CHO, TG but increased the activities of AST, ALT in serum, decreased the expressions of CAT, SOD, GPx, CYP1A but increased the expressions of CYP3A, GST-ζ₁, p53 in liver. Diet 6 increased the AFB₁ residues in serum and muscle, altered the intestinal microbiota composition, decreased the bacterial community diversity and the abundance of some potential probiotics. However, Diet 8 and Diet 9 restored the immune response, relieved adverse effects in liver, lowered the AFB₁ residues in turbot tissues, promoted intestinal microbiota diversity and lowered the abundance of potentially pathogens. In conclusion, YCWE supplementation decreased the health effects of AFB₁ on turbot, restoring biomarkers closer to the mycotoxin-free control diet.

Cloning, expression profile of the complement component C9 gene and influence of the recombinant C9 protein on peripheral mononuclear leukocytes transcriptome in half-smooth tongue sole (Cynoglossus semilaevis)

The ninth complement component (C9) is a terminal complement component (TCC) that is involved in creating the membrane attack complex (MAC) on the target cell surface. In this study, the CsC9 (C9 of Cynoglossus semilaevis) cDNA sequence was cloned and characterized. The full-length CsC9 cDNA measured 2,150 bp, containing an open reading frame (ORF) of 1,803 bp, a 5'-untranslated region (UTR) of 24 bp and a 3'-UTR of 323 bp. A domain search revealed that the CsC9 protein contains five domains, including two TSP1s, an LDLRA, an EGF, and a MACPF. Quantitative real-time PCR analysis showed that CsC9 at the mRNA level was expressed in all the tested tissues, with the highest expression being observed in the liver. CsC9 expression is significantly upregulated in the tested tissues after challenge with Vibrio anguillarum. To further characterize the role of CsC9, peripheral blood mononuclear cells of C. semilaevis were used for transcriptome analysis after incubation with recombinant CsC9 (rCsC9) protein. A total of 3,775 significant differentially expressed genes (DEGs) were identified between the control and the rCsC9-treated group, including 2,063 upregulated genes and 1,712 downregulated genes. KEGG analyses revealed that the DEGs were enriched in cell adhesion molecules, cytokine-cytokine receptor interactions, T cell receptor signaling pathways, B cell receptor signaling pathways and Toll-like receptor signaling pathways. The results of this study indicate that in addition to participating in MAC formation, CsC9 might play multiple roles in the innate and adaptive immunity of C. semilaevis.

Pol-miR-363-3p plays a significant role in the immune defense of Japanese flounder Paralichthys olivaceus against bacterial and viral infection

In this study, we examined the function of a Japanese flounder (Paralichthys olivaceus) microRNA (miRNA), pol-miR-363-3p. We found that pol-miR-363-3p targets an ubiquitin-specific protease (USP), USP32. USP is a family of deubiquitinating enzymes essential to the functioning of the ubiquitin proteasome system. In mammals, USP32 is known to be associated with cancer and immunity. In fish, the function of USP32 is unknown. We found that flounder USP32 (PoUSP32) expression was detected in the major tissues of flounder, particularly intestine. In vitro and in vivo studies showed that pol-miR-363-3p directly regulated PoUSP32 in a negative manner by interaction with the 3'UTR of PoUSP32. Overexpression of pol-miR-363-3p or interference with PoUSP32 expression in flounder cells significantly blocked Streptococcus iniae infection. Consistently, in vivo knockdown of pol-miR-363-3p or overexpression of PoUSP32 enhanced dissemination of S. iniae in flounder tissues, whereas in vivo knockdown of PoUSP32 inhibited S. iniae dissemination. In addition, pol-miR-363-3p knockdown also significantly promoted the tissue dissemination of the viral pathogen megalocytivirus, which, as well as S. iniae, regulated pol-miR-363-3p expression. Together these results revealed an important role of pol-miR-363-3p in flounder immune defense against bacterial and viral infection.

Differentially expressed proteins in the intestine of Cynoglossus semilaevis Günther following a Shewanella algae challenge

Fish intestine is an important constituent of the mucosal immune system. The gut and gut-associated lymphoid tissue construct a local immune environment. A Shewanella algae strain was previously reported to be a pathogen causing ascitic disease accompanied with intestinal inflammation in Cynoglossus semilaevis. This study aimed to investigate the intestine immune response in C. semilaevis to S. algae infection at the protein level. Two-dimensional electrophoresis coupled with mass spectrometry proteomics was utilized to compare protein expression in the intestines from normal and S. algae-infected C. semilaevis. A total of 70 differentially expressed proteins (DEPs), consisting of 16 upregulated and 54 downregulated proteins, were identified in the intestine tissue of C. Semilaevis. These protein expression changes were further validated using western blot analysis and quantitative real-time PCR. Gene ontology enrichment analysis showed that these 70 DEPs could be assigned across three categories: "cellular components", "molecular function", and "biological process". Forty-one DEPs (six up-regulated and 35 down-regulated proteins) related to metabolic processes were identified. In addition, 20 DEPs (eight up-regulated and 12 down-regulated proteins) related to stress and immune responses were identified. A protein-protein interaction network generated by the STRING (Search Tool for the Retrieval of Interacting Genes/protein) revealed that 30 DEPs interacted with one another to form an integrated network. Among them, 29 DEPs were related to stress, immune, and metabolism processes. In the network, some of the immune related proteins (C9, FGB, KNG1, apolipoprotein A-IV-like, and PDIA3) were up-regulated and most DEPs involved in metabolism processes were down-regulated. These results indicate that the immune defense response of the intestine was activated and the intestinal function associated with metabolism processes was disturbed. This study provides valuable information for further research into the functions of these DEPs in fish.

Mucosal immune responses in Senegalese sole (Solea senegalensis) juveniles after Tenacibaculum maritimum challenge: A comparative study between ocular and blind sides

Most pathogens start the process of infection at the mucosal surfaces and therefore the mucosal immune response plays an essential role in the course of the infection. Due to the Senegalese sole (Solea senegalensis Kaup) condition of flatfish, the present comparative study aimed to analyse several immune-related enzymes as well as the bactericidal activity in the skin mucus from ocular and blind sides. For this purpose, Senegalese sole juveniles were bath challenged with a sub-lethal dose of Tenacibaculum maritimum for 24 h and sampled at 1, 2 and 3 weeks. The haematological profile and immune-related parameters were also measured in plasma in order to evaluate the systemic immune response after T. maritimum challenge. Results from this study showed that most parameters tested increased in skin mucus of bath challenged fish compared to unchallenged ones. In contrast, the sub-lethal dose tested did not influence the haematological profile including peripheral numbers the different leucocyte types. No variations were observed in plasma lysozyme, peroxidase, protease and haemolytic complement activities between unchallenged and bath challenged fish. This study suggests that the studied innate immune-related molecules are constitutively present in both skin mucus sides but at different levels. Interestingly, the levels of most parameters measured were higher on the ocular side than on the blind side, possibly due to the higher exposure to invasion by waterborne microorganisms on this side. Therefore, the present study brings some insights regarding local immune responses after bacterial challenge in skin mucus from the ocular and blind sides in one of the most valuable flatfish species in southern Europe.

Transcriptome analysis reveals seven key immune pathways of Japanese flounder (Paralichthys olivaceus) involved in megalocytivirus infection

Megalocytivirus is a serious viral pathogen to many farmed fish including Japanese flounder (Paralichthys olivaceus). In this study, in order to systematically identify host immune genes induced by megalocytivirus infection, we examined the transcription profiles of flounder infected by megalocytivirus for 2, 6, and 8 days. Compared with uninfected fish, virus-infected fish exhibited 1242 differentially expressed genes (DEGs), with 225, 275, and 877 DEGs occurring at 2, 6, and 8 days post infection, respectively. Of these DEGs, 728 were upregulated and 659 were downregulated. The majority of DEGs were time-specific and formed four distinct expression profiles well correlated with the time of infection. The DEGs were classified into diverse Gene Ontology (GO) functional terms and enriched in 27 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, approximately one third of which were related to immunity. Weighted co-expression network analysis (WGCNA) was used to identify 16 key immune DEGs belonging to seven immune pathways (RIG-I-like receptor signaling pathway, JAK-STAT signaling pathway, TLR signaling pathway, cytokine-cytokine receptor interaction, phagosome, apoptosis, and p53 signaling pathway). These pathways interacted extensively and formed complicated networks. This study provided a global picture of megalocytivirus-induced gene expression profiles of flounder at the transcriptome level and uncovered a set of key immune genes and pathways closely linked to megalocytivirus infection. These results provided a set of targets for future delineation of the key factors implicated in the anti-megalocytivirus immunity of flounder.

Characterization of the Japanese flounder NLRP3 inflammasome in restricting Edwardsiella piscicida colonization in vivo

NLRP3 inflammasome is one of the most well-known inflammasomes in mammals, which plays critical roles in innate immunity. However, knowledge about this inflammasome in non-mammalian species, especially in teleost fish, remains rarely known. Herein, we established an Edwardsiella piscicida-head-kidney macrophages (HKMs) infection model in Japanese flounder, and found a robust caspase-1 activation and IL-1β maturation. To characterize the upstream receptor, we established a bioinformatic screening analysis, and found an NLRP3 homolog (JfNLRP3) from Japanese flounder, which shares an overall conservative structure architecture to human NLRP3. Moreover, the JfNLRP3 can assemble JfASC through PYD-PYD domain interaction and trigger JfCaspase-1 activation and JfIL-1β maturation. Meanwhile, the classical inflammasome activation stimulators, including nigericin, ATP or MSU, can trigger the JfCaspase-1 activation and JfIL-1β maturation in Japanese flounder HKMs. During intraperitoneal infection of E. piscicida in Japanese flounder, we found a dynamic up-regulated transcription of JfNLRP3 and JfCaspase-1 in vivo. Furthermore, knockdown of either JfNLRP3 or JfCaspase-1 reduces the serum JfIL-1β level, and promotes the bacterial colonization in systemic immune organs at 2 day-post infection, while overexpression of JfNLRP3 or JfCaspase-1 hampers the bacterial colonization in these organs of Japanese flounder. Taken together, our results identified the NLRP3 inflammasome paradigm in Japanese flounder, which not only providing new insight into the molecular mechanisms of teleost NLRP3 inflammasome and revealing its role in restricting bacterial infection in vivo, but also shedding light on the evolutionary of NLRP3 inflammasome in teleost.

Characterization and functional study of Galectin3 from Japanese flounder (Paralichthys olivaceus)

Galectins belong to the β-galactoside binding protein family and participate in both innate and acquired immunity. In this study, we described the molecular characteristics of Galectin3 gene from Japanese flounder (Paralichthys olivaceus), designed as PoGalectin3. Its open reading frame was 1128 bp, encoding a protein composed of 375 amino acids. PoGalectin3 belongs to chimeric galactose agglutinin, which contains a C-terminal carbohydrate recognition domain (CRD) (L₂₅₀-P₃₇₂), and its N-terminal is rich in proline (P) and glycine (G). Multiple sequence alignment and phylogenetic tree showed that PoGalectin3 was conservative in different aquatic animals. Tissue distribution confirmed that PoGalectin3 showed significantly highest expression in brain, moderate expression in liver, intestine and muscle. PoGalectin3 was significantly increased post infection with Edwardsiella tarda from intestine tissue of P. olivaceus. In order to investigate the binding ability of PoGalectin3 to pathogen-associated molecular patterns, the recombinant PoGalectin3 protein (rPoGalectin3) was successfully expressed and purified, and an Enzyme linked immunosorbent assay (ELISA) experiment was performed. ELISA refers to the qualitative and quantitative detection method of immune response by combining soluble antigen or antibody with solid-phase carrier. It was confirmed that rPoGalectin3 exhibited high affinity to lipopolysaccharide and peptidoglycan. The rPoGalectin3 also exhibited a concentration dependent binding capacity with Gram-positive bacteria (Bacillus pumilus, Bacillus subtilis, Bacillus cereus) and Gram-negative bacteria (Aeromonas salmonicida, E. tarda, Vibrio vulnificus). In addition, the results of microbial agglutination experiment showed that rPoGalectin3 could agglutinate Gram-positive bacteria (B. pumilus, B. subtilis) and Gram-negative bacteria (A. salmonicida, E. tarda) in the presence of Ca²⁺. In conclusion, this research laid an important foundation for the specific function analysis of PoGalectin3, which provide theoretical basis for the prevention and control of aquatic diseases.

Administration of commensal Shewanella sp. MR-7 ameliorates lipopolysaccharide-induced intestine dysfunction in turbot (Scophthalmus maximus L.)

This study was designed to evaluate whether the administration of commensal Shewanella sp. MR-7 (MR-7) could ameliorate lipopolysaccharide (LPS)-induced intestine dysfunction in turbot. Fish (body weight: 70.00 ± 2.00 g) were randomly divided into three groups including the control group treated with dough, the LPS group treated with dough plus LPS, and the LPS+MR-7 (LMR) group treated with dough plus LPS and MR-7. These three groups with 24 fish each were force-fed with 1 g dough daily for 7 continuous days. The results revealed that MR-7 administration ameliorated LPS-induced intestinal injury, showing higher intestinal villus and microvillus height. Further results showed that MR-7 could inhibit LPS-induced activation of TLR-NF-κB signaling thus maintaining the normal expression levels of cytokines and finally ameliorate the intestinal inflammatory response in turbot. Compared with the LPS group, LMR group had less goblet cells and lower mucin-2 expression level. Moreover, MR-7 restored LPS-induced down-regulation of tight junction protein-related gene expression (zonula occluden-1, occludin, tricellulin and claudin-3). Further investigations indicated that MR-7 partially counteracted LPS-induced changes in gut microbiota composition, enhanced the beneficial bacteria Lactobacillus and reduced the Pseudomonas, thus maintaining the overall microbiota balance. Taken together, the administration of MR-7 could effectively restore LPS-induced intestine function disorder in turbot by ameliorating inflammatory response, mucosal barrier dysfunction and microbiota dysbiosis.

Characterization of a novel lncRNA (SETD3-OT) in turbot (Scophthalmus maximus L.)

LncRNAs have been demonstrated to play pivotal roles in virous biological processes, especially the gene expression regulation, including transcriptional regulation, posttranscriptional control and epigenetic processes. However, most of the current studies of lncRNAs are still limited in mammalian species, the investigations of functional roles of lncRNAs in teleost species are still lacking. In current study, we identified a novel lncRNA (SETD3-OT) in turbot, with 2,504 bp full-length obtained by 5' and 3' RACE, located in turbot chromosome 17, ranged from 20,933,835 to 20,936,302 bp. In addition, 8 neighboring genes of SETD3-OT were identified within 100 kbp in genome location. From the annotation of the neighboring adjacent genes, SETD3-OT might involve in regulation of cell apoptosis and cycle, the immune cell development, and the immune response against infection, and its expression pattern is similar to majority of the neighboring genes following Aeromonas salmonicida challenge. Intriguingly, SETD3-OT showed significant high expression levels in mucosal surfaces (intestine, gill and skin), and was dramatically down-regulated in these mucosal tissues following Vibrio anguillarum challenge, especially in gill and skin. In addition, SETD3-OT was distributed in nucleus, it might regulate the neighboring genes in cis or in trans. Taken together, our results provide insights for lncRNA in fish innate immunity, further studies should be conduct to explore the detailed molecular mechanism of the gene regulation between SETD3-OT and its neighboring genes.

Genome-wide identification, expression signature and immune functional analysis of two cathepsin S (CTSS) genes in turbot (Scophthalmus maximus L.)

Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, play multiple roles at physiological and pathological states. Cathepsin S is a lysosomal cysteine endopeptidase of the papain family, and exerts critical roles in the regulation of MHC class II immune responses. In the present study, we captured two Cathepsin S genes in turbot (SmCTSS1 and SmCTSS2.1), characterized their expression patterns following V. anguillarum and S. iniae infections, and explored their binding ability and agglutination capability. Firstly, the SmCTSS1 contained a 990 bp ORF encoding 329 amino acids, while SmCTSS2.1 contained a 1,014 bp ORF encoding 337 amino acids. The phylogenetic analysis revealed that both genes showed the closest relationship to their counterparts of Japanese flounder (Paralichthys olivaceus). In addition, both genes were ubiquitously expressed in all examined healthy tissues, with the highest expression level observed in spleen and intestine, respectively, while the lowest expression level both observed in liver. Both SmCTSS1 and SmCTSS2.1 were significantly differentially expressed, and exhibited general down-regulations at most time points in skin and intestine after two bacterial infections. Finally, both rSmCTSS1 and rSmCTSS2.1 showed significant binding ability to three examined microbial ligands (LPS, PGN and LTA), and strong agglutination effect to different bacteria (E. tarda, S. agalactiae, S. aureus and V. anguillarum). Collectively, this study provided valuable data for understanding the roles of CTSS in the host defense against bacterial infections in turbot, and indicated the potential vital roles of CTSS in innate immune responses of teleost species.

Effects of the sulfated polysaccharide ulvan from Ulva ohnoi on the modulation of the immune response in Senegalese sole (Solea senegalensis)

Sulfated polysaccharides derived from green seaweeds exhibit many beneficial biological activities and have great potential to be used as nutraceutical in aquaculture. In this work, we evaluated the effects of the sulfated polysaccharide ulvan from Ulva ohnoi on Senegalese sole (Solea senegalensis) juveniles at the transcriptomic level. Cytotoxicity assay performed in liver primary cell cultures from sole determined that the different ulvan concentrations assayed did not impair cell viability. Juveniles were intraperitoneally (IP) injected with ulvan (0.5 mg/fish) followed by a challenge with Photobacterium damselae subsp. piscicida (Phdp) at 7 days. RNASeq analyses at 2 days post injection (dpi) revealed that 402 transcripts were differentially expressed in liver between ulvan IP injected and control groups before the challenge. Genes related to bacterial and antiviral defence, complement system, chemokines, proteasomes and antigen presentation were upregulated in ulvan treated groups. A detailed expression analysis of sixteen genes related to innate and adaptive immune system was performed in two systemic tissues: liver and spleen. Ulvan injection provoked the upregulation of tlr22 and a transient inflammatory response was initiated in both liver and spleen at 2 dpi. As consequence, expression of acute phase proteins, antimicrobial peptides and complement genes was induced. Moreover, expression of mhcI, mhcII, psmb10 and bcl6 was also induced 2 dpi. At 2 dpi with Phdp, inflammatory cytokines and genes related to bacterial and antiviral defense, iron metabolism, complement system and antigen presentation were differentially modulated in survival juveniles previously IP injected with ulvan. Moreover, mortality was retarded in ulvan treated juveniles. These results provide new evidence about the role of ulvan as a bioactive compound with immunomodulatory activity in Senegalese sole as well as its possible use as vaccine adjuvant against Phdp. This is the first published study that evaluates the transcriptomic response of Senegalese sole IP injected with ulvan.

Inclusion of dietary Ulva ohnoi 5% modulates Solea senegalensis immune response during Photobacterium damselae subsp. piscicida infection

Macroalgae represent valuable sources of functional ingredients for fish diets, and the influence of supplemented aquafeeds on growth performance has been studied for some fish and seaweed species. In the present work, the potential immunomodulation exerted by U. ohnoi (5%) as dietary ingredient was investigated in Senegalese sole. After feeding with the experimental diets for 90 d, fish immune response before and after challenge with Photobacterium damselae subsp. piscicida (Phdp) was assessed. In absence of infection, systemic immune response was not modified by 5% U. ohnoi dietary inclusion for 90 d. Thus, no differences in liver and head kidney immune gene transcription or serum lysozyme, peroxidase, antiprotease and complement activities were observed based on the diet received by Senegalese sole specimens. Regarding mucosal immune parameters, no changes in gene transcription were detected in the skin and gills, whilst only tnf, cd4 and cd8 were significantly up-regulated in the intestine of fish fed with U. ohnoi, compared to the values obtained with control diet. On the contrary, when S. senegalensis specimens were challenged with Phdp, modulation of the immune response consisting in increased transcription of genes encoding complement (c1q4, c3, c9), lysozyme g (lysg), tumor necrosis factor alpha (tnfα) as well as those involved in the antioxidant response (gpx, sodmn) and iron metabolism (ferrm, hamp-1) was observed in the liver of fish fed with U. ohnoi. In parallel, decreased inflammatory cytokine and complement encoding gene transcription was displayed by the spleen of fish receiving the algal diet. Though mortality rates due to Phdp challenge were not affected by the diet received, lower pathogen loads were detected in the liver of soles receiving U. ohnoi diet. Further research to investigate the effects of higher inclusion levels of this seaweed in fish diets, feeding during short periods as wells as to assess the response against other pathogens needs to be carried out.

The effect of dietary cecropin AD on intestinal health, immune response and disease resistance of juvenile turbot (Scophthalmus maximus L.)

Cecropin AD (CAD) is a commercial cationic antimicrobial peptide that has been seldom studied in marine fish. This study investigated the effects of dietary CAD on intestinal health, immune response, disease resistance, and growth performance of turbot. A diet using fishmeal and plant protein as the main protein resources was used as the control (crude protein 53%, crude lipid 12%). CAD was supplemented into the control diet at the level of 250, 500, 750, and 1000 mg kg^-1 to formulate four experimental diets, C1, C2, C3, and C4, respectively. No significant difference was observed in fish growth performance, feed utilization efficiency and whole-body composition among all groups. Dietary CAD significantly increased the activity of lysozyme and complement component 3 level in both serum and distal intestine (DI), as well as the immunoglobulin M content in DI. The gene expression of immune cytokines such as IFN-γ, IL-1β, and chemokine SmCCL19, and the goblet cell number in DI were also significantly increased by dietary CAD supplementation. Compared with the control group, the microbiota analysis indicated group C4 showed significantly decreased α-diversity, obvious alternation in dominant bacteria composition at phylum level, different clustering, and significantly decreased relative abundance of Lactobacillus. Besides, the relative abundance of Bacteroides was significantly decreased in groups C1, C3, and C4. In addition, the lowest mortality of turbot challenged with Edwardsiella tarda was observed in fish fed diets C2 and C3. In conclusion, moderate levels of CAD in diet of turbot improved the intestinal immune response without disrupting the intestinal bacterial community, and enhanced the disease resistance. However, dietary CAD at 1000 mg kg^-1 greatly affected the intestinal bacterial composition and showed potentially inhibitory effects towards Lactobacillus.

The efficacy of lactic acid bacteria usage in turbot Scophthalmus maximus on intestinal microbiota and expression of the immune related genes

To understand the efficacy of lactic acid bacteria (LAB) as probiotics on the growth, immune response and intestinal microbiota of turbot Scophthalmus maximus, in this study, the Leuconostoc mesenteroides HY2 strain screened from wide caught fish was bath administrated for juvenile turbot with no bacteria administrated as control. The mRNA levels of toll-like receptors 3 (TLR3), interleukin 8 (IL-8) and interferon induced with helicase C domain 1 (IFIH1) in different organs (i.e. intestine, liver, spleen, kidney, brain and skin) were analyzed using RT-PCR technology. The intestinal microbiota was analyzed by 16S rRNA sequencing, in which principal co-ordinates analysis (PCoA) as well as cluster analysis was performed. The results showed that the specific growth rate of turbot in the LAB treatment was significantly higher than those of the control group (P < 0.05). The expression levels of TLR3, IL-8 and IFIH1 were significantly up-regulated in the organs of LAB treatment, except that IL-8 was slightly down-regulated in kidney. A total of 42 phyla in intestinal microbiota were identified. The composition of intestinal microbiota showed significant differences between LAB treatment and the control group. Shannon index in the LAB treatment was significantly increased while Simpson index significantly declined. The PCoA and cluster analysis exhibited significant differences in the composition and abundance between the two groups. Firmicutes, Proteobacteria, Bacteroidetes and Actinobacteria acted as biomarkers which may have effects to promote absorption and/or trigger the immune function. In conclusion, the administration of HY2 strain was capable of improving growth performance of turbot by enhancing immune response and optimizing structure and diversity of intestinal microbiota.