A novel acute phase reactant, serum amyloid A-like 1, from Oplegnathus fasciatus: genomic and molecular characterization and transcriptional expression analysis

Characterization and in vitro antibacterial activity of grass carp (Ctenopharyngodon idella) serum amyloid A

Serum amyloid A (SAA) predominantly synthesized by hepatocytes is a classical acute phase protein and has been extensively studied in mammals. However, the studies on the structure and properties of fish SAA are limited although SAA genes have been cloned and identified from various fishes. In the present study, a cDNA of grass carp (Ctenopharyngodon idella) SAA (gcSAA) was cloned and characterized, displaying a high homology with its counterparts in vertebrates. gcSAA mRNA was expressed with highest abundance in the liver and its levels were increased by a 24-hour infection of Aeromonas hydrophila (A. hydrophila) for more than 5 folds in the intestine, 15 folds in the spleen, 75 folds in the head kidney and 100 folds in the liver, implying that it is an acute phase protein in grass carp. Subsequently, recombinant gcSAA protein (rgcSAA) was prepared from a prokaryotic expression system after codon optimization of its coding sequence. The direct antibacterial activity assay and the plate count assay disclosed that gcSAA inhibited the growth and survival of A. hydrophila but not Edwardsiella piscicida (E. piscicida) which both are common bacterial pathogens in aquaculture. The propidium iodide (PI) uptake assay confirmed the bactericidal property of gcSAA, showing that it is able to enhance the uptake of PI in A. hydrophila but not E. piscicida. These findings revealed the molecular features of gcSAA and its roles in host defense against bacterial infection.

RNA-Seq-based discovery of genetic variants and allele-specific expression of two layer lines and broiler chicken

Recent advances in the selective breeding of broilers and layers have made poultry production one of the fastest-growing industries. In this study, a transcriptome variant calling approach from RNA-seq data was used to determine population diversity between broilers and layers. In total, 200 individuals were analyzed from three different chicken populations (Lohmann Brown (LB), n = 90), Lohmann Selected Leghorn (LSL, n = 89), and Broiler (BR, n = 21). The raw RNA-sequencing reads were pre-processed, quality control checked, mapped to the reference genome, and made compatible with Genome Analysis ToolKit for variant detection. Subsequently, pairwise fixation index (F ST) analysis was performed between broilers and layers. Numerous candidate genes were identified, that were associated with growth, development, metabolism, immunity, and other economically significant traits. Finally, allele-specific expression (ASE) analysis was performed in the gut mucosa of LB and LSL strains at 10, 16, 24, 30, and 60 weeks of age. At different ages, the two-layer strains showed significantly different allele-specific expressions in the gut mucosa, and changes in allelic imbalance were observed across the entire lifespan. Most ASE genes are involved in energy metabolism, including sirtuin signaling pathways, oxidative phosphorylation, and mitochondrial dysfunction. A high number of ASE genes were found during the peak of laying, which were particularly enriched in cholesterol biosynthesis. These findings indicate that genetic architecture as well as biological processes driving particular demands relate to metabolic and nutritional requirements during the laying period shape allelic heterogeneity. These processes are considerably affected by breeding and management, whereby elucidating allele-specific gene regulation is an essential step towards deciphering the genotype to phenotype map or functional diversity between the chicken populations. Additionally, we observed that several genes showing significant allelic imbalance also colocalized with the top 1% of genes identified by the FST approach, suggesting a fixation of genes in cis-regulatory elements.

SAAL1, a novel oncogene, is associated with prognosis and immunotherapy in multiple types of cancer

Serum amyloid A-like 1 (SAAL1) was recently identified as a novel oncogene in hepatocellular carcinoma (HCC). To explore the potential role of SAAL1 in other cancers, we conducted a pan-cancer analysis of SAAL1 expression and its association with tumor microenvironment (TME) immunological profiles, sensitivity to chemotherapy agents, response to immunotherapy, and patient prognosis. SAAL1 was overexpressed in most malignant tumors in association with poor prognosis. Moreover, its expression was positively correlated with TME-relevant immune and mismatch signatures, immunostimulatory infiltrating cells (CD4⁺ memory T cells, activated NK cells, M1 macrophages, and cytotoxic CD8⁺ T cells), microsatellite instability (MSI), tumor mutational burden (TMB), neoantigen load, and immune checkpoint markers (PD-L1, LAG-3 and CTLA-4) in multiple cancers. SAAL1 overexpression was also associated with immunotherapy response and overall survival (OS) in bladder cancer (BLCA) patients who had received anti-PD-L1 treatment. Gene set enrichment analysis (GSEA) further showed significant enrichment of SAAL1 in immune cell signaling, cell cycle, and cell adhesion pathways. Moreover, we detected tumor-specific correlations between SAAL1 expression and either chemoresistance or sensitivity to common chemotherapeutics. Lastly, we showed that SAAL1 silencing suppresses both malignant phenotype and expression of PD-L1 in lung cancer A549 cells in vitro. These findings suggest that SAAL1 contributes to tumorigenesis and antitumor immunity mechanisms in different cancer types, and may thus serve as both a prognostic biomarker and potential target for cancer immunotherapy.

Antimicrobial and Immunoregulatory Activities of TS40, a Derived Peptide of a TFPI-2 Homologue from Black Rockfish (Sebastes schlegelii)

Tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine protease inhibitor. Previous reports have shown that TFPI-2 plays an important role in innate immunity, and the C-terminal region of TFPI-2 proved to be active against a broad-spectrum of microorganisms. In this study, the TFPI-2 homologue (SsTFPI-2) of black rockfish (Sebastods schegelii) was analyzed and characterized, and the biological functions of its C-terminal derived peptide TS40 (FVSRQSCMDVCAKGAKQHTSRGNVRRARRNRKNRITYLQA, corresponding to the amino acid sequence of 187-226) was investigated. The qRT-PCR (quantitative real-time reverse transcription-PCR) analysis showed that the expression of SsTFPI-2 was higher in the spleen and liver. The expression of SsTFPI-2 increased significantly under the stimulation of Listonella anguillarum. TS40 had a strong bactericidal effect on L. anguillarum and Staphylococcus aureus. Further studies found that TS40 can destroy the cell structure and enter the cytoplasm to interact with nucleic acids to exert its antibacterial activity. The in vivo study showed that TS40 treatment could significantly reduce the transmission of L. anguillarum and the viral evasion in fish. Finally, TS40 enhanced the respiratory burst ability, reactive oxygen species production and the expression of immune-related genes in macrophages, as well as promoted the proliferation of peripheral blood leukocytes. These results provide new insights into the role of teleost TFPI-2.

Serum amyloid A is a positive acute phase protein in Russian sturgeon challenged with Aeromonas hydrophila

The immune system of sturgeons, one of the most ancient and economically valuable fish worldwide, is poorly understood. The lack of molecular tools and data about infection biomarkers hinders the possibility to monitor sturgeon health during farming and detect infection outbreaks. To tackle this issue, we mined publicly available transcriptomic datasets and identified putative positive acute-phase proteins (APPs) of Russian sturgeons that could be induced by a bacterial infection and monitored using non-invasive methods. Teleost literature compelled us to focus on five promising candidates: hepcidin, a warm acclimation associated hemopexin, intelectin, serum amyloid A protein (SAA) and serotransferrin. Among them, SAA was the most upregulated protein at the mRNA level in the liver of sturgeons challenged with heat-inactivated or live Aeromonas hydrophila. To assess whether this upregulation yielded increasing SAA levels in circulation, we developed an in-house ELISA to quantify SAA levels in sturgeon serum. Circulating SAA rose upon bacterial challenge and positively correlated with hepatic saa expression. This is the first time serum SAA has been quantified in an Actinopterygii fish. Since APPs vary across different fish species, our work sheds light on sturgeon acute-phase response, revealing that SAA is a positive APP with potential value as infection biomarker.

Identification of the Novel Oncogenic Role of SAAL1 and Its Therapeutic Potential in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer deaths worldwide, affecting over 700,000 people per year. The treatment effect in advanced HCC is still disappointing and prognosis of advanced HCC remains poor. Hence, to find more effective therapeutic targets to improve the treatment outcome of HCC is of urgent need. In this study, we reported the novel oncogenic function of SAAL1 (serum amyloid A-like 1) in HCC, which previously is considered as an inflammation-related gene. We found that SAAL1 was significantly upregulated in HCC tumor tissues when compared to the adjacent normal tissues and high expression of SAAL1 correlated with shorter overall survival in The Cancer Genome Atlas (TCGA) HCC database. Functionally, we showed that the depletion of SAAL1 significantly reduced cell proliferation, 3D colony formation, and migration/invasion abilities of HCC cancer cells. Furthermore, suppression of SAAL1 impaired the HGF/Met-driven Akt/mTOR phosphorylation cascade and increased the chemosensitivity of HCC cells to sorafenib and foretinib treatment. Our data indicated that SAAL1 plays an important role in HCC via mediating oncogenic HGF/Met-driven Akt/mTOR signaling and could serve as an independent prognostic marker, as well as a promising therapeutic target for HCC patients.

Serum Amyloid A1 (SAA1) Revisited: Restricted Leukocyte-Activating Properties of Homogeneous SAA1

Infection, sterile injury, and chronic inflammation trigger the acute phase response in order to re-establish homeostasis. This response includes production of positive acute phase proteins in the liver, such as members of the serum amyloid A (SAA) family. In humans the major acute phase SAAs comprise a group of closely related variants of SAA1 and SAA2. SAA1 was proven to be chemotactic for several leukocyte subtypes through activation of the G protein-coupled receptor FPRL1/FPR2. Several other biological activities of SAA1, such as cytokine induction, reported to be mediated via TLRs, have been debated recently. Especially commercial SAA1, recombinantly produced in Escherichia coli, was found to be contaminated with bacterial products confounding biological assays performed with this rSAA1. We purified rSAA1 by RP-HPLC to homogeneity, removing contaminants such as lipopolysaccharides, lipoproteins and formylated peptides, and re-assessed several biological activities attributed to SAA1 (chemotaxis, cytokine induction, MMP-9 release, ROS generation, and macrophage differentiation). The homogeneous rSAA1 (hrSAA1) lacked most cell-activating properties, but its leukocyte-recruiting capacity in vivo and it’s in vitro synergy with other leukocyte attractants remained preserved. Furthermore, hrSAA1 maintained the ability to promote monocyte survival. This indicates that pure hrSAA1 retains its potential to activate FPR2, whereas TLR-mediated effects seem to be related to traces of bacterial TLR ligands in the E. coli-produced human rSAA1.

Sockeye salmon demonstrate robust yet distinct transcriptomic kidney responses to rhabdovirus (IHNV) exposure and infection

Aquatic rhabdoviruses are globally significant pathogens associated with disease in both wild and cultured fish. Infectious hematopoietic necrosis virus (IHNV) is a rhabdovirus that causes the internationally regulated disease infectious hematopoietic necrosis (IHN) in most species of salmon. Yet not all naïve salmon exposed to IHNV become diseased, and the mechanisms by which some individuals evade or rapidly clear infection following exposure are poorly understood. Here we used RNA-sequencing to evaluate transcriptomic changes in sockeye salmon, a keystone species in the North Pacific and natural host for IHNV, to evaluate the consequences of IHNV exposure and/or infection on host cell transcriptional pathways. Immersion challenge of sockeye salmon smolts with IHNV resulted in approximately 33% infection prevalence, where both prevalence and viral kidney load peaked at 7 days post challenge (dpc). De novo assembly of kidney transcriptomes at 7 dpc revealed that both infected and exposed but noninfected individuals experienced substantial transcriptomic modification; however, stark variation in gene expression patterns were observed between exposed but noninfected, infected, and unexposed populations. GO and KEGG pathway enrichment in concert with differential expression analysis identified that kidney responses in exposed but noninfected fish emphasised a global pattern of transcriptional down-regulation, particularly for pathways involved in DNA transcription, protein biosynthesis and macromolecule metabolism. In contrast, transcriptomes of infected fish demonstrated a global emphasis of transcriptional up-regulation highlighting pathways involved in antiviral response, inflammation, apoptosis, and RNA processing. Quantitative PCR was subsequently used to highlight differential and time-specific regulation of acute phase, antiviral, inflammatory, cell boundary, and metabolic responsive transcripts in both infected and exposed but noninfected groups. This data demonstrates that waterborne exposure with IHNV has a dramatic effect on the sockeye salmon kidney transcriptome that is discrete between resistant and acutely susceptible individuals. We identify that metabolic, acute phase and cell boundary pathways are transcriptionally affected by IHNV and kidney responses to local infection are highly divergent from those generated as part of a disseminated response. These data suggest that primary resistance of naïve fish to IHNV may involve global responses that encourage reduced cellular signaling rather than promoting classical innate antiviral responses.

A novel calreticulin-related molecule that interacts with bacteria and enhances host resistance against bacterial infection in black rockfish, Sebastes schlegeli

Calreticulin (CRT) is a highly conserved and multi-functional protein with diverse localizations. CRT has lectin-like properties and possesses important immunological activities in mammalian. In teleost, very limited studies on CRT immunologic function have been documented. In the present study, a CRT homologue (SsCRT) was cloned, identified and characterized from black rockfish, Sebastes schlegeli, an important aquaculture species in East Asia. The full length of SsCRT cDNA is 2180 bp and encoded a polypeptide of 425 amino acids. SsCRT contains a signal peptide, three distinct structural and functional domains (N-, P- and C-domains), and an endoplasmic reticulum (ER) retrieval signal sequence (KDEL). The deduced amino acid sequence of SsCRT shares 89-92% overall sequence identities with the CRT proteins of several fish species. SsCRT was distributed ubiquitously in all the detected tissues and was highly expressed in the spleen, muscle and liver. After the infection of fish extracellular bacterial pathogen Vibrio anguillarum and intracellular bacterial pathogen Edwardsiella tarda, the mRNA transcripts of SsCRT in spleen, liver, and head kidney were significantly up-regulated. The expression patterns were time-dependent and tissue-dependent. Recombinant SsCRT (rSsCRT) exhibited apparent binding activities against different bacteria and PAMPs. In vivo studies showed that the expressions of multiple immune-related genes such as TNF13B, IL-1β, IL-8, SAA, Hsp70, and ISG15 in head kidney were significantly enhanced when black rockfish were treated with rSsCRT. Furthermore, rSsCRT reduced pathogen dissemination and replication in fish kidney and spleen. These results indicated that SsCRT served as an immune receptor to recognize and eliminate the invading pathogens, which played a vital role in the immune response of Sebastes schlegeli. These findings provide new insights into understanding the roles of CRT proteins in immune response and pathogen infection in teleost.

High mobility group box 2 of black rockfish Sebastes schlegelii: Gene cloning, immunoregulatory properties and antibacterial effect

High-mobility group box 2 (HMGB2) is a non-histone chromosomal protein that involved diverse functions such as transcriptional regulation and innate immune responses in mammalian. In teleost, very limited studies on HMGB2 proteins have been documented. Black rockfish (Sebastes schlegelii) is an economic fish species and cultured worldwide. However, the study of black rockfish about immunology is very scarce. In the present study, a HMGB2 homologue gene (SsHMGB2) was identified and characterized in black rockfish. The open reading frame of SsHMGB2 is 648 bp, and the deduced amino acid sequence of SsHMGB2 shares 74.4%-91.2% overall sequence identities with the HMGB2 proteins of several fish species. In silico analysis identified several conserved features, including two basic HMG boxes and an acidic C-terminal tail composed of 24 Asp/Glu residues. Expression of SsHMGB2 occurred in multiple tissues and was upregulated during pathogens infection. Recombinant SsHMGB2 (rSsHMGB2) exhibited apparent binding activities against DNA. In vivo studies showed that the expressions of multiple immune-related genes in head kidney were significantly enhanced when black rockfish were treated with rSsHMGB2. Furthermore, rSsHMGB2 reduced pathogen dissemination and replication in fish kidney and spleen. Taken together, these results suggest that SsHMGB2 possesses apparent immunoregulatory properties and played a role in fighting bacterial infection.

Extended fasting does not affect the liver innate immune response in rainbow trout

Activation of immune response pathway is energy demanding. We tested the hypothesis that negative energy balance will curtail the liver's capacity to evoke an immune response in rainbow trout (Oncorhynchus mykiss). Fish were either fed or fasted for 118 d and challenged with lipopolysaccharide (LPS) to determine the liver capacity to elicit an immune response. Fasting led to negative specific growth rate, reduced tissue metabolite levels, and higher transcript abundance of SOCS-2. LPS treatment increased the liver transcript abundances of IL-1β and IL-8 and serum amyloid protein A, while SOCS-2 was reduced. LPS lowered plasma cortisol level only in the fasted fish, but did not affect liver glucocorticoid or mineralocorticoid receptor protein expressions. Extended fasting did not suppress the liver capacity to evoke an immune response. Upregulation of liver SOCS-2 may be playing a key role in the energy repartitioning, thereby facilitating immune response activation despite extended fasting in trout.

Molecular, structural, and functional comparison of N lobe and C lobe of the transferrin from rock bream, Oplegnathus fasciatus, with respect to its immune response

The iron-withholding strategy of innate immunity is an effective antimicrobial defense mechanism that combats microbial infection by depriving microorganisms of Fe³⁺, which is important for their growth and propagation. Transferrins (Tfs) are a group of iron-binding proteins that exert their antimicrobial function through Fe³⁺ sequestration. The current study describes both structural and functional characteristics of a transferrin ortholog from rock bream Oplegnathus fasciatus (RbTf). The RbTf cDNA possesses an open reading frame (ORF) of 2079 bp encoding 693 amino acids. It has a molecular mass of approximately 74 kDa and an isoelectric point of 5.4. In silico analysis revealed that RbTf has two conserved domains: N-terminal domain and C-terminal domain. Pairwise homology analysis and phylogenetic analysis revealed that RbTf shared the highest identity (82.6%) with Dicentrarchus labrax Tf. According to the genomic analysis, RbTf possesses 17 exons and 16 introns, similar to the other orthologs. Here, we cloned the N terminal and C terminal domains of RbTf to evaluate their distinct functional features. Results obtained through the CAS (chrome azurol S) assay confirmed the iron-binding ability of the RbTf, and it was further determined that the iron-binding ability of rRbTfN was higher than that of rRbTfC. The antimicrobial functions of the rRbTfN and the rRbTfC were confirmed via the iron-dependent bacterial growth inhibition assay. Tissue distribution profiling revealed a ubiquitous expression with intense expression in the liver. Temporal assessment revealed that RbTf increased after stimulation of LPS, Edwardsiella tarda, and Streptococcus iniae post injection (p.i.). These findings demonstrated that RbTf is an important antimicrobial protein that can combat bacterial pathogens.

The proteomic profile of the acquired enamel pellicle according to its location in the dental arches

OBJECTIVE

This study evaluated the variation in the protein profile of the acquired enamel pellicle (AEP) formed in vivo according to its location in the dental arches.

DESIGN

The AEP was formed for 120min in 9 volunteers. Pellicle formed at upper+lower anterior facial (ULAFa; teeth 13-23 and 33-43), upper anterior palatal (UAPa; teeth 13-23), lower anterior lingual (LALi; teeth 33-43), upper+lower posterior facial (ULPFa; teeth 14-17 24-27, 34-37 and 44-47), upper posterior palatal (UPPa; teeth 14-17 and 24-27) and lower posterior lingual (LPLi; teeth 34-37 and 44-47) regions were collected separately and processed for analysis by label-free LC-ESI-MS/MS.

RESULTS

Three-hundred sixty three proteins were identified in total, twenty-five being common to all the locations, such as Protein S100-A8, Lysozyme C, Lactoferrin, Statherin, Ig alpha-2, ALB protein, Myeloperoxidase and SMR3B. Many proteins were found exclusively in the AEP collected from one of the regions (46-UAPa, 33-LALi, 59-ULAFa, 31-ULPFa, 44-LPLi and 39-UPPa).

CONCLUSIONS

The protein composition of the AEP varied according to its location in the dental arches. These results provide important insights for understanding the differential protective roles of the AEP as a function of its location in the dental arches.

Cloning, expression analysis, and antibacterial propertiesof three serum amyloid A in common carp (Cyprinus carpio)

Three serum amyloid A (SAA) genes were identified from the common carp (Cyprinus carpio) by PCR and RT-PCR. Considering both direction and sequence similarity with mammal's orthologs, they were named CcSAA3a, CcSAA3b and CcSAA1. CcSAA3b and CcSAA1 are adjacent on contig LHQP01017858, suggesting that the prototype of or the simplest SAA multigene family have occurred in common carp. A phylogenetic analysis of the SAAs indicated that the fish SAAs were closer to those of invertebrates and Ornithorhynchus anatinus, a primitive mammal, than to mammalian SAAs. Quantitative real-time RT-PCR results displayed different expression profiles of three CcSAAs. The CcSAA3a was detected in all tested tissues, and was most abundant in the muscle; CcSAA3b was predominately expressed in the intestine and liver, and CcSAA1 in the skin. The expression level of CcSAA3a was higher than that of CcSAA3b and CcSAA1 in most tissues. Stimulation with Aeromonas hydrophila dramatically induced the expression of the three CcSAAs in all examined tissues, especially in the liver. Like Epinephelus coioides SAA, all of three rCcSAA fusion proteins could bind to both Gram-negative bacteria (A. hydrophila and E. coli) and Gram-positive bacterium (S. aureus), playing a role in the identification of bacteria. However, only rCcSAA3a showed significantly anti-A. hydrophila and anti-E. coli in vitro antibacterial activity assays. These results suggested that the three CcSAAs were in functional differentiation and play significant roles in the innate immunity of common carp.

Complement factor D homolog involved in the alternative complement pathway of rock bream (Oplegnathus fasciatus): Molecular and functional characterization and immune responsive mRNA expression analysis

The complement system serves conventional role in the innate defense against common invading pathogens. Complement factor D (CfD) is vital to alternative complement pathway activation in cleaving complement factor B. This catalytic reaction forms the alternative C3 convertase that is crucial for complement-mediated pathogenesis. In this study, rock bream (Oplegnathus fasciatus) CfD (OfCfD) was characterized and OfCfD mRNA expression was investigated. OfCfD encodes 277 amino acids (aa) for a 30-kDa polypeptide. A domain analysis of the deduced OfCfD aa sequence showed a single serine protease trypsin superfamily domain, a serine active region, three active sites, and three substrate-binding sites. Pairwise sequence comparisons indicated that OfCfD has the highest identity (84.5%) with Oreochromis niloticus CfD. The phylogenetic tree revealed a common ancestral origin of CfD members, with fish CfD distinct from other vertebrate orthologs. The structural arrangement of the OfCfD gene (2451 bp) contained five exons interrupted by four introns. A spatial transcriptional analysis indicated that OfCfD transcripts constitutively expressed in all of the examined rock bream tissues, and that they were highest in the spleen and liver. In addition, OfCfD transcripts were immunologically upregulated by lipopolysaccharide (LPS) (12 h p.i.), Streptococcus iniae (12 h p.i.), rock bream iridovirus (RBIV) (6-12 h p.i.), and poly I:C (6 h p.i.) in spleen tissue. OfCfD is a trypsin protease and its recombinant protein showed strong protease activity similar to that of trypsin, indicating its catalytic function in the alternative pathway. Together, our findings suggest that OfCfD might be involved in immune responses in rock bream.

Molecular and functional characterization of goldfish (Carassius auratus L.) Serum Amyloid A

Quantitative expression analysis of goldfish SAA revealed the highest mRNA levels in the kidney, spleen and intestine with lower mRNA levels in muscle and liver. Goldfish SAA was differentially expressed in goldfish immune cells with highest mRNA levels observed in neutrophils. To functionally assess goldfish SAA, recombinant protein (rgSAA) was generated by prokaryotic expression and functionally characterized. Monocytes and macrophages treated with rgSAA exhibited differential gene expression of pro-inflammatory and anti-inflammatory cytokines. rgSAA induced gene expression of both pro-inflammatory (TNFα1, TNFα2) and anti-inflammatory cytokines (IL-10, TGFβ) in monocytes. rgSAA induced IL-1β1 and SAA gene expression in macrophages. rgSAA was chemotactic to macrophages and neutrophils, but not monocytes. rgSAA did not affect respiratory burst induced by heat-killed Aeromonas salmonicida. rgSAA treatment of macrophages down-regulated their production of nitric oxide. rgSAA exhibited antibacterial properties against Escherichia coli in a concentration dependent manner.

Characterization of rock bream (Oplegnathus fasciatus) complement components C1r and C1s in terms of molecular aspects, genomic modulation, and immune responsive transcriptional profiles following bacterial and viral pathogen exposure

The complement components C1r and C1s play a crucial role in innate immunity via activation of the classical complement cascade system. As initiators of the pathogen-induced signaling cascade, C1r and C1s modulate innate immunity. In order to understand the immune responses of teleost C1r and C1s, Oplegnathus fasciatus C1r and C1s genes (OfC1r and OfC1s) were identified and characterized. The genomic sequence of OfC1r was enclosed with thirteen exons that represented a putative peptide with 704 amino acids (aa), whereas eleven exons of OfC1s represented a 691 aa polypeptide. In addition, genomic analysis revealed that both OfC1r and OfC1s were located on a single chromosome. These putative polypeptides were composed of two CUB domains, an EGF domain, two CCP domains, and a catalytically active serine protease domain. Phylogenetic analysis of C1r and C1s showed that OfC1r and OfC1s were evolutionary close to the orthologs of Pundamilia nyererei (identity = 73.4%) and Oryzias latipes (identity = 58.0%), respectively. Based on the results of quantitative real-time qPCR analysis, OfC1r and OfC1s transcripts were detected in all the eleven different tissues, with higher levels of OfC1r in blood and OfC1s in liver. The putative roles of OfC1r and OfC1s in response to pathogenic bacteria (Edwardsiella tarda and Streptococcus iniae) and virus (rock bream iridovirus, RBIV) were investigated in liver and head kidney tissues. The transcription of OfC1r and OfC1s was found to be significantly upregulated in response to pathogenic bacterial and viral infections. Overall findings of the present study demonstrate the potential immune responses of OfC1r and OfC1s against invading microbial pathogens and the activation of classical signaling cascade in rock bream.

A potential antioxidant enzyme belonging to the atypical 2-Cys peroxiredoxin subfamily characterized from rock bream, Oplegnathus fasciatus

Peroxiredoxins (Prxs), a diverse family of antioxidant enzymes, exert their antioxidant function through which different peroxide species are detoxified. This study describes both structural and functional characterization of a mitochondrial Prx identified in rock bream, Oplegnathus fasciatus (RbPrx5). The ORF (573 bp) of RbPrx5 encoded a protein of 190 amino acids (20 kDa) containing a putative mitochondrial targeting sequence (residues 1-20) and a thioredoxin-2 motif (residues 31-190) and three conserved Cys residues. Homology assessment and phylogenetic analysis clearly disclosed relatively higher amino acid sequence similarities and a closer evolutionary position of RbPrx5 with those of other teleost homologs. The ORF of RbPrx5 was distributed among six exons as found in other vertebrates, but it possessed an additional exon in its 5'-UTR. In silico examination of RbPrx5 gene's putative promoter region revealed the presence of several cis-elements which may be important in its transcriptional regulation. Constitutive expression of RbPrx5 was detected in eleven tissues with the highest level in the heart. Modulation of RbPrx5 transcription was evidenced from varying mRNA levels in head kidney post in vivo LPS-, poly I:C-, Edwardsiella tarda bacterial- and rock bream iridoviral-challenges. The antioxidant function of RbPrx5 was investigated using recombinant RbPrx5 protein. Results of an in vitro mixed-function oxidase assay demonstrated a dose-dependent inhibition of DNA damage by rRbPrx5. A H2O2 tolerance assay showed that in vivo overexpression of rRbPrx5 increased the bacterial survival under H2O2-mediated oxidative stress condition. These findings provide an overall insight into the structural, expressional and functional aspects of RbPrx5.

Functional characterization of the evolutionarily preserved mitochondrial antiviral signaling protein (MAVS) from rock bream, Oplegnathus fasciatus

Antimicrobial immune defense is evolutionarily preserved in all organisms. Mammals have developed robust, protein-based antiviral defenses, which are under constant investigation. Studies have provided evidences for the various fish immune factors sharing similarity with those of mammals. In this study, we have identified an ortholog of mitochondrial antiviral signaling protein from rock bream, Oplegnathus fasciatus. RbMAVS cDNA possesses an open reading frame (ORF) of 1758 bp coding for a protein of 586 amino acids with molecular mass of approximately 62 kDa and isoelectric point of 4.6. In silico analysis of RbMAVS protein revealed a caspase recruitment domain (CARD), a proline rich domain and a transmembrane domain. RbMAVS protein also contains a putative TRAF2 binding motif, (319)PVQDT(323). Primary sequence comparison of RbMAVS with other orthologues revealed heterogeneity towards the C-terminus after the CARD region. RbMAVS transcripts were evident in all the examined tissues. RbMAVS expression was induced in vivo after poly I:C challenge in peripheral blood cells, liver, head kidney and spleen tissues. Over-expression of RbMAVS potently inhibited marine birnavirus (MABV) infection in rock bream heart cells and induced various cytokines and signaling molecules in vitro. Thus, RbMAVS is an antiviral protein and potentially involved in the recognition and signaling of antiviral defense mechanism in rock bream.

The first molluscan acute phase serum amyloid A (A-SAA) identified from oyster Crassostrea hongkongensis: molecular cloning and functional characterization

Serum amyloid A (SAA), a major evolutionarily conserved acute-phase protein, participates in many biological processes in eukaryotic cells, including innate immunity. However, little information regarding the relationship between SAA and innate immunity in mollusks is currently available. In this report, the first bivalve SAA (referred to as ChSAA) gene was identified and characterized from the Hong Kong oyster Crassostrea hongkongensis. Its full-length cDNA is 623 bp, including a 5'-UTR of 147 bp, a 3'-UTR of 56 bp containing a poly(A) tail and an open reading frame (ORF) of 420 bp that encodes a polypeptide of 139 amino acids. The predicted amino acid sequence of ChSAA comprises characteristic motifs of the SAA family, including a typical signal peptide and a conserved SAA domain. Comparison and phylogenetic analyses suggested that ChSAA shares a high identity to known acute-phase SAA proteins (A-SAAs). In addition, quantitative real-time PCR analysis revealed that ChSAA is constitutively expressed in all tissues examined, with the highest expression level in the mantle, and that its expression was acutely and significantly up-regulated in hemocytes following challenge by Vibrio alginolyticus (G(-)), Staphylococcus haemolyticus (G(+)) or Saccharomyces cerevisiae (fungus). Furthermore, over-expression of ChSAA via transfection with a ChSAA expression vector led to significantly increased NF-κB activity in HEK293T cells. These results suggest that ChSAA is likely to constitute a member of the A-SAA family involved in anti-pathogen responses in C. hongkongensis.

Tissue-specific molecular immune response to lipopolysaccharide challenge in emaciated anadromous Arctic charr

Anadromous Arctic charr (Salvelinus alpinus) undergo voluntary winter fasting for months in the Arctic. We tested the hypothesis that extended fasting will compromise the ability of this species to evoke an immune response. Charr were either fed or fasted for 85 days and challenged with lipopolysaccharide (LPS), and the molecular immune response in the liver and spleen assessed at 8 and 96 h post-injection. LPS increased IL-1β, IL-8, and serum amyloid protein A (SAA) mRNA levels in both groups, but the liver IL-1β and IL-8, and spleen IL-8 responses were reduced in the fasted group. Fasting upregulated SOCS-1 and SOCS-2 mRNA abundance, while LPS stimulated SOCS-3 mRNA abundance and this response was higher in the fasted liver. Collectively, extended fasting and emaciation does not curtail the capacity of charr to evoke an immune response, whereas upregulation of SOCS may be a key adaptation to conserve energy by restricting the inflammatory response.

Molecular characterization and expressional affirmation of the beta proteasome subunit cluster in rock bream immune defense

Immunoproteasomes are primarily induced upon infection and formed by replacing constitutive beta subunits with inducible beta subunits which possess specific cleavage properties that aid in the release of peptides necessary for MHC class I antigen presentation. In this study, we report the molecular characterization and expression analysis of the inducible immunosubunits PSMB8, PSMB9, PSMB9-L, and PSMB10 from rock bream, Oplegnathus fasciatus. The three subunits shared common active site residues and were placed in close proximity to fish homologues in the reconstructed phylogenetic tree, in which the mammalian homologues formed separate clades, indicating a common ancestral origin. The rock bream immunosubunits possessed higher identity and similarity with the fish homologues. RbPSMB8, RbPSMB9, RbPSMB9-L, and RbPSMB10 were multi-exonic genes with 6, 6, 7 and 8 exons, respectively. These four genes were constitutively expressed in all the examined tissues. Immunostimulants such as lipopolysaccharide and poly I:C induced RbPSMB8, RbPSMB9, RbPSMB9-L, and RbPSMB10 in liver and head kidney, suggesting their possible involvement in immune defense in rock bream.

Molecular cloning and characterization of two types of IκBα orthologues in orange-spotted grouper, Epinephelus coioides

Inhibitors of kappa B (IκBs) are the members of primary regulators of NF-κB, which can inhibit NF-κB activity by blocking the NF-κB in an inactive state in the cytoplasm. In this study, two types of IκBα orthologues (EcIκBαA and EcIκBαB) from orange-spotted grouper, Epinephelus coioides, were cloned and characterized. EcIκBαA and EcIκBαB encoded putative proteins containing 308 and 318 amino acids, which shared 59% and 53% identity to IκBαA and IκBαB of Danio rerio, respectively. Amino acid sequence alignment showed that both EcIκBαA and EcIκBαB contained a conserved degradation motif DSGLDS in the N-terminal region and a PEST sequence in the C-terminal region. In addition, EcIκBαA and EcIκBαB contained 5 and 6 ankyrin repeats, respectively. The genomic DNA of EcIκBαA and EcIκBαB consisted of 6 exons and 5 introns. Both of their transcripts were widely distributed in different tissues, and the expression levels were different in response to various stimuli, including lipopolysaccharide (LPS), Vibrio alginolyticus and Singapore grouper iridovirus (SGIV). Dual-luciferase reporter assay suggested that both EcIκBαA and EcIκBαB were able to inhibit Ecc-Rel and Ecp65 induced NF-κB promoter activity in grouper spleen (GS) cells. Subcellular localization analysis showed that EcIκBαB was present predominantly in the cytoplasm, while EcIκBαA was distributed throughout both the nucleus and the cytoplasm. Furthermore, overexpression of EcIκBαA and EcIκBαB in GS cells inhibited the viral gene transcriptions of MCP, ORF019 and ORF162 of SGIV. Taken together, our findings suggested that both EcIκBαA and EcIκBαB were involved in grouper innate immunity against virus.

Genomic characterization, expression analysis, and antimicrobial function of a glyrichin homologue from rock bream, Oplegnathus fasciatus

Antimicrobial peptides are important innate effector molecules, playing a vital role in antimicrobial immunity in all species. Glyrichin is a transmembrane protein and an antibacterial peptide, exerting its functions against a wide range of pathogenic bacteria. In this study, cDNA and a BAC clone harboring the glyrichin gene were identified from rock bream and characterized. Genomic characterization showed that the OfGlyrichin gene exhibited a 3 exon-2 intron structure. OfGlyrichin is a 79-amino-acid protein with a transmembrane domain at (22)GFMMGFAVGMAAGAMFGTFSCLR(44). Pairwise and multiple sequence alignments showed high identity and conservation with mammalian orthologues. Phylogenetic analysis showed a close relationship with fish species. Higher levels of OfGlyrichin transcripts were detected in the liver from healthy rock bream which were induced by immunogens like lipopolysaccharide, poly I:C, rock bream irido virus, Edwardsiella tarda and Streptococcus iniae. The synthetic peptide (pOf19) showed antibacterial activity against Escherichia coli, E. tarda, and S. iniae. Analysis of the bacterial morphological features after pOf19 peptide treatment showed breakage of the cell membrane, affirming that antibacterial function is accomplished through membrane lysis. The pOf19 peptide also showed antiviral activity against RBIV infection. The high conservation of the genomic structure and protein, together with the antimicrobial roles of OfGlyrichin, provide evidence for the evolutionary existence of this protein playing a vital role in innate immune defense in rock bream.

Genomic structural characterization and transcriptional expression analysis of proteasome activator PA28α and PA28β subunits from Oplegnathus fasciatus

Proteasomes are multicatalytic subunit complexes involved in the degradation of cytosolic proteins and antigen presentation. In this study, we have characterized the alpha and beta subunits of proteasome activator complex from rock bream at the molecular level. RbPA28α and RbPA28β possessed the characteristic features of the subunits identified from mammals and teleosts. The RbPA28α and RbPA28β proteasome subunits contained a proline-rich motif (Region A), subunit-specific insert in the region corresponding to the KEKE motif of the known PA28α (Region B), conserved activation loop (Region C), a potential protein kinase C recognition site (Region D) and a highly homologous C-terminal region (Region E) among all three PA28 subunits. Multiple sequence alignment and pairwise alignment revealed that RbPA28α and RbPA28β proteins shared high homology with the teleosts and mammals. RbPA28α and RbPA28β genome possessed 11 exons interrupted by 10 introns. In silico promoter analysis of RbPA28α and RbPA28β revealed various transcription factor-binding sites displaying their regulation under various stress conditions. Tissue distribution profiling showed a higher expression in blood and gills. Transcriptional expression analysis of RbPA28α and RbPA28β showed up-regulation in the immune tissues following LPS and poly I:C challenges, providing further evidence for the immunological role of RbPA28α and RbPA28β.

Akirin2 homologues from rock bream, Oplegnathus fasciatus: Genomic and molecular characterization and transcriptional expression analysis

Akirins are conserved nuclear resident NF-κB signaling pathway molecules. Isoforms of akirins found in various organisms are known to play diverse roles. In this study, we have characterized two akirin2 homologues from rock bream, OfAk2(1) and OfAk2(2). The proteins derived from OfAk2(1) and OfAk2(2) revealed the presence of nuclear localization signal. Multiple sequence alignment and pairwise alignment of OfAk2(1) and OfAk2(2) with the akirin homologues, revealed high conservation and identity. Phylogenetic tree analysis revealed that the distinct position of OfAk2(1) and OfAk2(2) was close to the fish homologues and separated from the mammals and invertebrates. Genomic structure characterization revealed two distinct structures. OfAk2(1) possessed 6 exons interrupted by 5 introns whereas OfAk2(2) possessed 5 exons interrupted by 4 introns. The promoter analysis revealed the presence of significant transcription factors, which suggests its regulation by diverse stimuli. In addition, transcript expression analysis using real time quantitative reverse-transcriptase polymerase chain reaction post immune challenges with lipopolysaccharide, Edwardsiella tarda and poly I:C revealed upregulation of both OfAk2(1) and OfAk2(2) in liver, spleen and head kidney.

Molecular characterization and expression analysis of IκB from Haliotis discus discus

Innate immune system relies on the recognition of pathogen associated molecular patterns present in the microbes by the pattern recognition receptors leading to the activation of signaling cascade and subsequent synthesis of cytokines. NF-κB is a major stimulus activated transcription factor, which regulates the expression of a diverse array of genes. IκB is an inhibitor of NF-κB, retaining NF-κB in an inactive state in the cytoplasm. In this study, we have reported the characterization of first abalone IκB (HdIκB). The cDNA possessed an ORF of 1200 bp coding for a protein of 400 amino acids with molecular mass of 45 kDa and isoelectric point of 4.7. HdIκB protein possessed a conserved phosphorylation site (58)DSGIFS(63) in the N-terminal region, six ankyrin repeats, and a PEST sequence in the C-terminal region. A casein kinase II phosphorylation site could also be observed in the PEST sequence. Constitutive expression of HdIκB revealed its physiological significance since NF-κB is known to be activated by various stimuli. Elevated expression of HdIκB transcripts could be observed in abalones challenged with various mitogens and live microbes. This novel characterization of abalone IκB would further be a positive approach in the affirmation of evolutionary conservation and significance of this protein as a repressor/inhibitor of a pleiotropic transcription factor like NF-κB.