Catfish hepcidin gene is expressed in a wide range of tissues and exhibits tissue-specific upregulation after bacterial infection

Detection of the hepcidin prepropeptide and mature peptide in liver of rainbow trout

Hepcidin is a small, cationic peptide which displays antimicrobial activities and iron regulatory function. Originally identified in mammals, this peptide is also present in fish. Hepcidin mRNA is predominantly expressed in liver and is regulated by iron and pathogen infection. In this work, we characterized the expression of trout hepcidin at protein level using rabbit antisera. Results showed that the prepropeptide of hepcidin can be detected by Western Blot in liver tissue from trout injected with iron or lipopolysaccharide. The mature hepcidin peptide was detected at the ionized state 5+(m/z 577.2) by HPLC-ESI-MS in acid extracts from liver tissue. Moreover, hepcidin peptide was located in trout liver imprints by immunofluorescence. These results showed that hepcidin peptide is up-regulated by iron and bacterial components in the trout liver. This up-regulation could be a potential indicator of disease susceptibility, suggesting that hepcidin regulates iron homeostasis in salmonids.

Molecular characterization of hepcidin gene in common carp (Cyprinus carpio L.) and its expression pattern responding to bacterial challenge

Hepcidin is a cysteine-rich cationic antimicrobial peptide (AMP), which plays an important role in host innate immune system and iron regulation. A great many of hepcidin genes have been identified from vertebrates, including various fish species. Here we report the cloning and identification of a hepcidin cDNA from the liver of common carp (Cyprinus carpio L.). The full-length cDNA of the common carp hepcidin was 647 bp, which contained an ORF of 276 bp encoding a prepropeptide of 91 amino acid residues. The predicted preprohepcidin consisted of three domains: a signal peptide of 24 amino acids, a prodomain of 42 amino acids and a mature peptide of 25 amino acids, which containd eight cysteine residues at the identical conserved position. The genomic organization of common carp hepcidin was identified, which contained three exons and two introns, similarly to corresponding genes in mammals and other fish species. Sequence alignment and phylogenetic analysis showed that hepcidins were conserved in different species, and common carp hepcidin was type 1 hepcidin according to the phylogenetic tree, which had the highest identity with mud loach and zebrafish. Real-time PCR assay showed that the hepcidin gene was mostly expressed in liver, and expressed in all the other tested tissues of common carp in different levels. When challenged with pathogenic bacterium, Vibrio anguillarum, the expression level of common carp hepcidin was quickly up-regulated in liver, spleen, head kidney and hindgut, implying that hepcidin may be an important component of the innate immune system of common carp and involved in mucosal immune response against invading pathogens.

Molecular cloning and expression analysis of liver-expressed antimicrobial peptide 1 (LEAP-1) and LEAP-2 genes in the blunt snout bream (Megalobrama amblycephala)

Liver-expressed antimicrobial peptide 1 (LEAP-1) and LEAP-2 are widespread in fish and extremely important components of the host innate immune system. In this study, full-length cDNAs of LEAP-1 and LEAP-2 were cloned and sequenced from blunt snout bream, Megalobrama amblycephala. The open reading frames (ORF) of LEAP-1 and LEAP-2 genes encode putative peptides of 94 and 92 amino acids, which possess eight and four conserved cysteine residues, respectively. The homologous identities of deduced amino acid sequences show that the LEAP-1 and LEAP-2 of blunt snout bream share considerable similarity with those of grass carp. The mRNA expressions of LEAP-1 and LEAP-2 were detectable at different early developmental stages of blunt snout bream and varied with embryonic and larval growth. LEAP-1 and LEAP-2 were expressed in a wide range of adult tissues, with the highest expression levels in the liver and midgut, respectively. Bacterial challenge experiments showed that the levels of LEAP-1 and LEAP-2 mRNA expression were up-regulated in the liver, spleen, gill and brain of juvenile blunt snout bream. These results indicate that the LEAP-1 and LEAP-2 may play important roles in early development of embryos and fry, and may contribute to the defense against the pathogenic bacterial invasion. This study will further our understanding of the function of LEAP-1 and LEAP-2 and the molecular mechanism of innate immunity in teleosts.

Four lysozymes (one c-type and three g-type) in catfish are drastically but differentially induced after bacterial infection

Lysozyme is an important component of the innate immune system. In this study, four lysozyme genes including one c-type lysozyme and three g-type lysozymes were identified from channel catfish (Ictalurus punctatus). The lysozyme genes are highly conserved in their structural features as compared to those from other species. Phylogenetic analyses were conducted allowing annotation of these genes. Additional analyses using conserved syntenies allowed determination of orthologies for the c-type lysozyme. Phylogenetic analysis indicated that the g-type lysozyme may have gone through species-specific gene duplications leading to multiple copies in some teleost species. Channel catfish possessed three copies of the g-type lysozyme genes. Expression analysis revealed that the catfish lysozyme genes were expressed in a broad range of tissues. The highest levels of expression were found in head kidney, liver, spleen, and trunk kidney, compatible with the immune functions of these tissues/organs. The c-type and g-type lysozymes were drastically induced after bacterial infection, but exhibited large differences in the extent of induction and the tissue with the highest level of induction, with the g-type lysozyme being most highly induced in the head kidney whereas the other three lysozymes being most highly induced in the liver, suggesting their cooperative actions in the immune responses but difference in their detailed functions.

Mechanisms of intrinsic resistance to antimicrobial peptides of Edwardsiella ictaluri and its influence on fish gut inflammation and virulence

The genus Edwardsiella comprises a genetically distinct taxon related to other members of the family Enterobacteriaceae. It consists of bacteria differing strongly in their biochemical and physiological features, natural habitats, and pathogenic properties. Intrinsic resistance to cationic antimicrobial peptides (CAMPs) is a specific property of the genus Edwardsiella. In particular, Edwardsiella ictaluri, an important pathogen of the catfish (Ictalurus punctatus) aquaculture and the causative agent of a fatal systemic infection, is highly resistant to CAMPs. E. ictaluri mechanisms of resistance to CAMPs are unknown. We hypothesized that E. ictaluri lipopolysaccharide (LPS) plays a role in both virulence and resistance to CAMPs. The putative genes related to LPS oligo-polysaccharide (O-PS) synthesis were in-frame deleted. Individual deletions of wibT, gne and ugd eliminated synthesis of the O-PS, causing auto-agglutination, rough colonies, biofilm-like formation and motility defects. Deletion of ugd, the gene that encodes the UDP-glucose dehydrogenase enzyme responsible for synthesis of UDP-glucuronic acid, causes sensitivity to CAMPs, indicating that UDP-glucuronic acid and its derivatives are related to CAMP intrinsic resistance. E. ictaluri OP-S mutants showed different levels of attenuation, colonization of lymphoid tissues and immune protection in zebrafish (Danio rerio) and catfish. Orally inoculated catfish with O-PS mutant strains presented different degrees of gut inflammation and colonization of lymphoid tissues. Here we conclude that intrinsic resistance to CAMPs is mediated by Ugd enzyme, which has a pleiotropic effect in E. ictaluri influencing LPS synthesis, motility, agglutination, fish gut inflammation and virulence.

Pathogen recognition receptors in channel catfish: III phylogeny and expression analysis of Toll-like receptors

Toll-like receptors (TLRs) were the earliest characterized and the most extensively studied pathogen recognition receptors (PRRs). The majority of tetrapod TLR orthologs have been found in teleost fish. In addition, a group of "fish-specific" TLRs have been identified. In catfish, a number of TLR-related sequences have been reported, but systematic phylogenetic analyses have not been conducted. In this study, we conducted phylogenetic and comparative analysis of 20 catfish TLR genes against their counterparts from various species. TLR25 and TLR26 are TLRs identified only in channel catfish. Phylogenetic analyses suggested that four catfish TLR genes have duplicated copies in the genome, i.e., TLR4, TLR5, TLR8, and TLR20. Six fish-specific TLRs were identified, and the vast majority of these belong to the TLR11 subfamily. In healthy catfish tissues, most of the tested TLR genes were ubiquitously expressed although expression levels varied among the 11 tested tissues. We tested nine TLRs for their expression in response to Edwardsiella ictaluri infection. They were significantly up-regulated in the spleen and liver, but down-regulated in the head kidney, suggesting their involvement in the immune responses against the intracellular bacterial pathogen in a tissue-specific manner in catfish, perhaps through rapid migration of phagocytes to infection sites.

Iron-metabolic function and potential antibacterial role of Hepcidin and its correlated genes (Ferroportin 1 and Transferrin Receptor) in turbot (Scophthalmus maximus)

Antimicrobial peptide plays an important role in fish immunity. The small molecular antimicrobial peptide Hepcidin in turbot was studied and reported in this paper. The Ferroportin 1 (FPN1) and Transferrin Receptor (TFR) genes, which are related to Hepcidin, were cloned in turbot. The characteristics of Hepcidin and its related genes were studied, including an analysis of the expression patterns and cloning of the Hepcidin promoter, the relationship between Hepcidin and NF-κB and the regulation of iron-metabolism. The results showed that the promoter of SmHepcidin contains the binding sites of NF-κB, and NF-κB may directly or indirectly receive feedback signals from SmHepcidin. In the liver, spleen and kidney, in which there was an increased SmHepcidin expression level, SmFPN1 dramatically decreased and SmTFR was also either decreased or exhibited no obvious change after bacterial/viral infection and an injection of exogenous Hepcidin protein. RNAi experiments in turbot kidney cells confirmed the expression changes of these gene patterns. Furthermore, the administration of exogenous Hepcidin protein, which regulates the level of chelatable iron in cells, further confirmed the function of Hepcidin in iron metabolism. It is speculated that the rapidly increased expression of SmHepcidin may induce changes in the expression of related genes, and that the in vivo chelatable iron concentration which participates in the antibacterial process was also changed when exogenous pathogens are present in turbot. It is suggested that SmHepcidin plays a defensive role against pathogenic infection.

The effect of peptidoglycan enriched diets on antimicrobial peptide gene expression in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of feeding rainbow trout (Oncorhynchus mykiss) peptidoglycan (PG) enriched diets on antimicrobial peptide (AMP) gene expression. Fish were divided into 5 groups and fed diets containing 0, 5, 10, 50 and 100 mg PG/Kg, and sampled 1, 7 and 14 days later. The expression of eight AMP genes (four defensins, two cathelicidins and two liver expressed AMPs) was determined in skin, gill, gut and liver, tissues important for first lines of defence or production of acute phase proteins. Up-regulation of many AMPs was found after feeding the PG enriched diets, with sequential expression seen over the time course studied, where defensins were typically expressed early and cathelicidins and LEAPs later on. A number of clear differences in AMP responsiveness between the tissues examined were also apparent. Of the four PG concentrations used, 5 mg PG/Kg did not always elicit AMP gene induction or to the same degree as seen with the other diets. The three higher dose groups generally showed similar trends although differences in fold change were more pronounced in the 50 and 100 mg PG/Kg groups. Curiously several AMPs were down-regulated after 14 days of feeding in gills, gut and liver. Nevertheless, overall the PG enriched diets had a positive effect on AMP expression. Further investigations now need to be undertaken to confirm whether this higher AMP gene expression correlates with protection against common bacterial diseases and if PG enriched diets have value as a means to temporarily boost the piscine immune system.

The innate immune-related genes in catfish

Catfish is one of the most important aquaculture species in America (as well as in Asia and Africa). In recent years, the production of catfish has suffered massive financial losses due to pathogen spread and breakouts. Innate immunity plays a crucial role in increasing resistance to pathogenic organisms and has generated increasing interest in the past few years. This review summarizes the current understanding of innate immune-related genes in catfish, including pattern recognition receptors, antimicrobial peptides, complements, lectins, cytokines, transferrin and gene expression profiling using microarrays and next generation sequencing technologies. This review will benefit the understanding of innate immune system in catfish and further efforts in studying the innate immune-related genes in fish.

Purification and characterization of YFGAP, a GAPDH-related novel antimicrobial peptide, from the skin of yellowfin tuna, Thunnus albacares

A 3.4 kDa of antimicrobial peptide was purified from an acidified skin extract of the yellowfin tuna, Thunnus albacares, by preparative acid-urea-polyacrylamide gel electrophoresis and C(18) reversed-phase HPLC. A comparison of the N-terminal amino acid sequence of the purified peptide with that of other known polypeptides revealed high homology with the N-terminus of glyceraldehyde-3-phosphate dehydrogenase (GAPDH); thus, this peptide was designated as the yellowfin tuna GAPDH-related antimicrobial peptide (YFGAP). YFGAP showed potent antimicrobial activity against Gram-positive bacteria, such as Bacillus subtilis, Micrococcus luteus, and Streptococcus iniae (minimal effective concentrations [MECs], 1.2-17.0 μg/mL), and Gram-negative bacteria, such as Aeromonas hydrophila, Escherichia coli D31, and Vibrio parahaemolyticus (MECs, 3.1-12.0 μg/mL) without significant hemolytic activity. According to the secondary structural prediction and the homology modeling, this peptide forms an amphipathic structure and consists of three secondary structural motifs including one α-helix and two parallel β-strands. This peptide did not show membrane permeabilization ability and its activity was bacteriostatic rather than bactericidal. This is the first report of the isolation of an antimicrobial peptide from a tuna species and the first description of the antimicrobial function of the N-terminus of GAPDH of an animal species.

Transcriptomic signatures of attachment, NF-κB suppression and IFN stimulation in the catfish gill following columnaris bacterial infection

Outbreaks of columnaris disease (Flavobacterium columnare) are common in wild and cultured freshwater fish worldwide. Disease occurrences, particularly those caused by virulent genomovar II isolates, in aquaculture species such as channel catfish can be devastating. In contrast to other important aquaculture pathogens, little is known about host immune responses to columnaris. Adhesion of F. columnare to gill tissue has been correlated in some previous studies to virulence and host susceptibility. Here, therefore, we conducted the first transcriptomic profiling of host responses to columnaris following an experimental challenge. We utilized Illumina-based RNA-seq expression profiling to examine transcript profiles at three timepoints (4h, 24h, and 48h) in catfish gill after bath immersion infection. Enrichment and pathway analyses of the differentially expressed genes revealed several central signatures following infection. These included the dramatic upregulation of a rhamnose-binding lectin, with putative roles in bacterial attachment and aggregation, suppression of NF-κB signalling via IκBs, BCL-3, TAX1BP1, and olfactomedin 4, and strong induction of IFN-inducible responses including iNOS2b, IFI44, and VHSV genes. Fifteen differentially expressed genes with varying expression profiles by RNA-seq, were validated by QPCR (correlation coefficients 0.85-0.94, p-value <0.001). Our results highlight several putative immune pathways and individual candidate genes deserving of further investigation in the context of development of therapeutic regimens and laying the foundation for selection of resistant catfish lines against columnaris.

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

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

Purification and characterization of an antimicrobial histone H1-like protein and its gene from the testes of olive flounder, Paralichthys olivaceus

An approximately 21 kDa antimicrobial protein was purified from an acidified testis extract of olive flounder, Paralichthys olivaceus, by ion-exchange and C(18) reversed-phase HPLC. A comparison of the N-terminal amino acid sequence with those of other known antimicrobial polypeptides revealed high homology between this antimicrobial protein and other histone H1 molecules; thus, it was designated flounder histone H1-like protein (fH1LP). fH1LP showed potent antimicrobial activity against Gram-positive bacteria, including Bacillus subtilis, Staphylococcus aureus, and Streptococcus iniae (minimal effective concentrations [MECs], 2.8-30.0 μg/ml), Gram-negative bacteria, including Aeromonas hydrophila, Escherichia coli D31, Vibrio parahaemolyticus (MECs, 1.4-12.0 μg/ml), and Candida albicans (MEC, 2.0 μg/ml). cDNA cloning and tissue distribution studies of fH1LP indicated that it is constitutively expressed in testis and ovary. The fH1LP expression level was significantly dependent on developmental stage, and decreased dramatically after hatching. However, lipopolysaccharide stimulation did not induce fH1LP mRNA in other immune organs, including the kidney and spleen. These results suggest that fH1LP plays an important role in innate immunity in fish during reproduction, including mating, fertilization, and hatching.

Pathogen recognition receptors in channel catfish: II. Identification, phylogeny and expression of retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs)

Vertebrates including teleost fish have evolved an array of pathogen recognition receptors (PRRs) for detecting and responding to various pathogen-associated molecular patterns (PAMPs), including Toll-like receptors (TLRs), nucleotide-binding domain, leucine-rich repeat containing receptors (NLRs), and the retinoic acid inducible gene I (RIG-I) like receptors (RLRs). As a part of the series of studies targeted to characterize catfish PRRs, we described 22 NLR receptors in the sister contribution. Here in this study, we focused on cytosolic PRRs recognizing nucleotide pathogen-associated molecular patterns (PAMPs) of invading viruses, the retinoic acid-inducible gene I (RIG-I)-like receptors (RLR receptors). Three RLRs with DExD/H domain containing RNA helicases, retinoic acid inducible gene-I (RIG-I), melanoma differentiation-associated gene 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2), were identified from channel catfish, Ictalurus punctatus. The catfish RIG-I encodes 937 amino acids that contains two CARDs, a DExDc, a HELICc and a RD domains. MDA5 encodes 1005 amino acids with all the domains identified for RIG-I. LGP2 encodes 677 amino acids that contain other domains but not the CARD domain at the N-terminus. Phylogenetic analyses of the three genes of catfish showed close clustering with their counterparts from other teleost fish. All the genes were found to be constitutively expressed in various tissues of catfish with minor variations. Channel catfish ovarian cells when infected with channel catfish virus showed significant increase in the transcript abundance of all the three genes. Further, RLR genes showed significant increases in expression in the liver tissue collected at different time-points after bacterial infection as well. The results indicate that the catfish RLRs may play important roles in antiviral and anti-bacterial immune responses.

BIRC7 gene in channel catfish (Ictalurus punctatus): identification and expression analysis in response to Edwardsiella tarda, Streptococcus iniae and Channel catfish Hemorrhage Reovirus

A family member of inhibitor of apoptosis protein (IAP) termed baculoviral IAP repeat-containing 7 (BIRC7) from channel catfish (Ictalurus punctatus) was identified, the full length cDNA sequence of channel catfish BIRC7 (CcBIRC7) was 1686 bp, containing a 5'UTR of 93 bp, a 3'UTR of 399 bp with a poly (A) tail and an ORF of 1194 bp encoding a putative protein of 398 amino acids. The putative CcBIRC7 protein contains two BIR super-family conservative domains and a C-terminal RING finger motif. Phylogenetic analysis showed that catfish CcBIRC7 was moderately conserved with other BIRC7. Quantitative real-time PCR was conducted to examine the expression profiles of CcBIRC7 in healthy tissues and responding to different pathogens (Edwardsiella tarda, Streptococcus iniae and Channel catfish Hemorrhage Reovirus (CCRV)). CcBIRC7 was widely expressed in healthy tissues of channel catfish and with the highest 37.28-fold expression in blood. E. tarda and S. iniae could induce CcBIRC7 gene expression drastically in head kidney, liver and spleen, which the peak value reached 31.6-fold, 613.9-fold and 34.4-fold increase by E. tarda infection, and 248.3-fold, 1540.3-fold and 120.4-fold increase post S. iniae challenge, respectively. While, CCRV virus could slightly induce CcBIRC7 expression in head kidney and liver but reduce it in spleen. The result suggested BIRC7 may play a potential role in channel catfish innate immune system against bacterial and virus infections, especially as the anti-bacteria immune gene. This is the first report of BIRC7 gene identification and its expression in fish.

Pathogen recognition receptors in channel catfish: I. Identification, phylogeny and expression of NOD-like receptors

Innate immune system plays a significant role in all multicellular organisms. The key feature of the system is its ability to recognize and respond to invading microorganisms. Vertebrates including teleost fish have evolved an array of pathogen recognition receptors (PRRs) for detecting and responding to various pathogen-associated molecular patterns (PAMPs), including Toll-like receptors (TLRs), nucleotide-binding domain, leucine-rich repeat containing receptors (NLRs), and the retinoic acid inducible gene I (RIG-I) like receptors (RLRs). In this study, we identified 22 NLRs including six members of the NLR-A subfamily (NODs), two members of the NLR-B subfamily, 11 members of the NLR-C subfamily, and three genes that do not belong to any of these three subfamilies: Apaf1, CIITA, and NACHT-P1. Phylogenetic analysis indicated that orthologs of the mammalian NOD1, NOD2, NOD3, NOD4, and NOD5 were all identified in catfish. In addition, an additional truncated NOD3-like gene was also identified in catfish. While the identities of subfamily A NLRs could be established, the identities of the NLR-B and NLR-C subfamilies were inconclusive at present. Expression of representative NLR genes was analyzed using RT-PCR and qRT-PCR. In healthy catfish tissues, all the tested NLR genes were found to be ubiquitously expressed in all 11 tested catfish tissues. Analysis of expression of these representative NLR genes after bacterial infection with Edwardsiella ictaluri revealed a significant up-regulation of all tested genes in the spleen and liver, but a significant down-regulation in the intestine and head kidney, suggesting their involvement in the immune responses of catfish against the intracellular bacterial pathogen in a tissue-specific manner. The up-regulation and down-regulation of the tested genes exhibited an amazing similarity of expression profiles after infection, suggesting the co-regulation of these genes.

Miiuy croaker hepcidin gene and comparative analyses reveal evidence for positive selection

Hepcidin antimicrobial peptide (HAMP) is a small cysteine-rich peptide and a key molecule of the innate immune system against bacterial infections. Molecular cloning and genomic characterization of HAMP gene in the miiuy croaker (Miichthys miiuy) were reported in this study. The miiuy croaker HAMP was predicted to encode a prepropeptide of 99 amino acids, a tentative RX(K/R)R cleavage motif and eight characteristic cysteine residues were also identified. The gene organization is also similar to corresponding genes in mammals and fish consisting of three exons and two introns. Sequence polymorphism analysis showed that only two different sequences were identified and encoded two proteins in six individuals. As reported for most other species, the expression level was highest in liver and an up-regulation of transcription was seen in spleen, intestine and kidney examined at 24 h after injection of pathogenic bacteria, Vibrio anguillarum, the expression pattern implied that miiuy croaker HAMP is an important component of the first line defense against invading pathogens. In addition, we report on the underlying mechanism that maintains sequences diversity among fish and mammalian species, respectively. A series of site-model tests implemented in the CODEML program revealed that moderate positive Darwinian selection is likely to cause the molecular evolution in the fish HAMP2 genes and it also showed that the fish HAMP1 genes and HAMP2 genes under different selection pressures.

Expression profiles of seven channel catfish antimicrobial peptides in response to Edwardsiella ictaluri infection

Using quantitative polymerase chain reaction (QPCR), the relative transcriptional levels of seven channel catfish antimicrobial peptide (AMP) genes (NK-lysin type 1, NK-lysin type 2, NK-lysin type 3, bactericidal permeability-increasing protein, cathepsin D, hepcidin and liver-expressed AMP 2) in response to Edwardsiella ictaluri infection were determined. None of the AMP genes tested was significantly upregulated at 2 h post-infection. Hepcidin was the only one that was significantly (P<0.05) upregulated at 4, 6 and 12 h post-infection. At 24 and 48 h post-infection, four AMPs (hepcidin, NK-lysin type 1, NK-lysin type 3 and cathepsin D) were significantly (P<0.05) upregulated. Among all the AMPs that were significantly upregulated at different time points, hepcidin at 4, 6 and 12 h post-infection was upregulated the most. When catfish were injected with different doses of E. ictaluri, all lethal doses were able to induce significant (P <0.05) upregulation of hepcidin in the posterior kidney, whereas sublethal doses failed to induce any significant upregulation of hepcidin. In vitro growth studies revealed that the presence of synthetic hepcidin peptide at a concentration of 16 μm or higher significantly inhibited the cell proliferation of E. ictaluri. Taken together, our results suggest that hepcidin might play an important role in the channel catfish defence against E. ictaluri infection.

The inhibitory effect of environmental ammonia on Danio rerio LPS induced acute phase response

Ammonia is a toxic by-product of amino acid catabolism and a common environmental pollutant that has been associated with increased disease susceptibility in fish although the mechanism is not well understood. We addressed the hypothesis that elevated environmental ammonia acts by impairing the acute phase response (APR). Specifically, we determined the impact of sub-lethal acute (24 h) and chronic (14 d) ammonia exposure on acute phase protein gene expression in zebrafish (Danio rerio) in response to a challenge with bacterial lipopolysaccharide (LPS: i.p. 10 μg/g after 24h). A panel of LPS-responsive genes (SAA, HAMP, LECT2, Hp and IL1β) were identified and evaluated by real-time quantitative PCR. Ammonia was found to impair induction of SAA, HAMP and LECT2 by 50-90%. Both short (15 min, 1h and 24h) and long-term (14 days) exposure to high environmental ammonia concentrations significantly elevated whole-body cortisol levels compared with control fish. Our results reveal for the first time that exposure to high environmental levels of ammonia suppresses the innate immune response in fish. We hypothesize that high environmental ammonia-mediated elevation of cortisol levels in zebrafish may be playing a key role in this immunosuppression, while the mechanisms involved remains to be elucidated.

Alternative complement pathway of channel catfish (Ictalurus punctatus): molecular characterization, mapping and expression analysis of factors Bf/C2 and Df

The complement system is important in both innate and adaptive host defense against microbial infection in vertebrates. It contains three pathways: the classical, alternative, and lectin pathways. Complement component factors B and D are two crucial proteases in the alternative pathway. In this study, the genes of complement factors Bf/C2 and Df from channel catfish, Ictalurus punctatus were identified and characterized. Two complement factor B-related genes, Bf/C2A and Bf/C2B, and factor D gene Df were identified. Phylogenetic analysis suggested that Bf/C2A and Bf/C2B is likely orthologous to factor B and factor C2, respectively. Southern blot results suggested that these three genes are all single-copy genes in the catfish genome. The catfish Bf/C2A, Bf/C2B and Df genes were genetically mapped on linkage group 3, 20 and 29, respectively. Bf/C2A and Bf/C2B are highly expressed in liver and kidney, while Df is highly expressed in gill and spleen. After infection with Edwardsiella ictaluri, the expression of Bf/C2A, Bf/C2B and Df genes were found to be remarkably induced in the gill, liver, spleen and kidney at some sampling times, indicating that these three complement factors play a pivotal role in immune responses after the bacterial infection in catfish.

Transcriptional profiles of multiple genes in the anterior kidney of channel catfish vaccinated with an attenuated Aeromonas hydrophila

A total of 22 uniquely expressed sequence tags (ESTs) were identified from channel catfish anterior kidney subtractive cDNA library at 12 h post vaccination with an attenuated Aeromonas hydrophila (AL09-71 N+R). Of the 22 ESTs, six were confirmed to be significantly (P < 0.05) induced by the vaccination. Of 88 channel catfish genes selected from literature, 14 were found to be significantly (P < 0.05) upregulated by the vaccination. The transcriptional levels of the total 20 genes induced by the vaccination were then compared to that induced by the virulent parent A. hydrophila (AL09-71) at different time points. At 3 h post vaccination (hpv) or infection (hpi), Na(+)/K(+) ATPase α subunit was upregulated the most. At 6 and 12 hpv or hpi, hepcidin and interleukin-1β were induced the highest. At 24 hpv or hpi, hepcidin was upregulated the most, followed by lysozyme c. At 48 hpi, lysozyme c and hepcidin were significantly induced. When vaccinated fish were challenged by AL09-71, relative percent of survival of vaccinated fish were 100% at 14 days post vaccination (dpv). Transcriptional levels of toll-like receptor 5 and hepcidin were significantly upregulated in vaccinated fish at 14 dpv. Taken together, our results suggest that vaccination with attenuated A. hydrophila mimics infection by live bacteria, inducing multiple immune genes in channel catfish.

Genomic organization and tissue-specific expression of hepcidin in the pacific mutton hamlet, Alphestes immaculatus (Breder, 1936)

Hepcidin is a cysteine-rich peptide involved in iron metabolism, inflammatory response and as antimicrobial peptide. Despite the fact that hepcidins have been identified in several fish species, only few have been completely characterized. This study, described the identification and complete molecular characterization of the hepcidin antimicrobial peptide 1 (HAMP1) gene of Alphestes immaculatus. Moreover, its specific expression level at both basal and lipopolysaccharide (LPS)-induced conditions in different tissues was also determined by real-time PCR. Results showed that the HAMP1gene consists of three exons and two introns encoding a preprohepcidin composed of 90 aa (24 aa for signal peptide, 40 aa for prodomain and 26 aa for mature peptide). The promoter region analysis revealed a TATA box sequence and several putative transcription factor binding sites. A comparative analysis showed CEBPα, CEBPβ, NF-kB, HNF3, GATA-1 and c-Rel as the most common found in fishes. The mature peptide possesses a pI of 8.34, which is the average among fish hepcidin. In addition, the structural modeling showed a hairpin structure with four putative disulfide bonds. A phylogenetic analysis revealed that this hepcidin gene is a HAMP1 class, and is clustered into the same group with the Serranid fish Epinephelus moara and the Antarctic fish Lycodichthys dearborni. Finally, the relative expression levels showed high basal values in liver and muscle, whereas in LPS-induced fish the relative expression tendency changed, with the highest values in spleen and head kidney tissues. This study describes the completely characterized HAMP1 gene of A. immaculatus and their patterns of expression level at different conditions and in different tissues, showing by first time muscle hepcidin expression could be relevant in the immune response in fish.

Molecular characterization of hepcidin gene from mud loach (Misgurnus mizolepis; Cypriniformes)

The gene encoding hepcidin, an antimicrobial peptide, was isolated and characterized in the mud loach Misgurnus mizolepis (Cypriniformes). Mud loach hepcidin shows a considerable degree of structural homology to other vertebrate hamp1 orthologues at both the gene and protein levels, particularly with respect to its tripartite genomic organization, typical transcription-factor-binding motifs in its promoter, and conserved cysteine residues in the mature cationic peptide. The mud loach possesses at least two allelic forms of hamp1, which are expected to be translated into the same hepcidin preproprotein. The two alleles are transmitted from parental fish to offspring with a Mendelian inheritance pattern, as demonstrated with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) genotyping. Southern blot hybridization analysis showed a high degree of polymorphisms in the restriction patterns of individuals. Mud loach hamp1 mRNA is predominantly expressed in the liver, although many other tissues showed detectable levels of hamp1 transcripts in RT-PCR assay. Lipopolysaccharide and bacterial challenges induced significant hamp1 expression, whereas hamp1 was not clearly stimulated by polyinosinic:polycytidylic acid [poly(I:C)] injection. Iron overload and Cu exposure also elevated hamp1 transcripts in various tissues. The transcriptional activation of mud loach hamp1 in response to these stimuli varied among tissue types, and the liver appears predominantly involved in hepcidin-mediated iron regulation. However, hepcidin expression in the kidney and spleen was preferentially modulated by inflammation-mediated signals produced by immune challenges. Our results suggest that mud loach hepcidin has two basic functions, in iron regulation and antimicrobial activity, and that its transcription is also modulated by other environmental perturbations, including heavy metal exposure.

Molecular mechanisms of hepcidin regulation in sea bass (Dicentrarchus labrax)

Hepcidin, an antimicrobial peptide described as a key regulator of iron metabolism, is known to respond in mammals to several stimuli, including iron overload, anemia, hypoxia and inflammation, through a number of molecular pathways. In order to understand the molecular pathways involved in the regulation of hepcidin expression in teleost fish, we have isolated for European sea bass (Dicentrarchus labrax) several coding sequences of known molecules involved on these pathways in mammals, namely jak3, stat3, tmprss6, bmp6, bmpr2, hjv, smad4, smad5, tfr1 and tfr2. The transcription levels of the isolated genes were evaluated by real-time PCR on fish subjected to experimental iron modulation (overload/deficiency) or infection with Photobacterium damsela. Results show that genes associated with the major pathway of the inflammatory response (IL6/JAK/STAT pathway) in mammals are also modulated in sea bass, being up-regulated during infection. Similarly, genes of the pathways classically associated with the response to variations in iron status (the HJV/BMP/SMAD and HFE/TfR pathways) are also modulated, mostly through down-regulation in iron deficiency and up-regulation during iron overload. Interestingly, many of these genes are also found to be up-regulated during infection, which may indicate a crosstalk between the known pathways of hepcidin regulation. These observations suggest the evolutionary conservation of the mechanisms of hepcidin regulation in teleost fish.

Two hepcidin-like antimicrobial peptides in Barramundi Lates calcarifer exhibit differing tissue tropism and are induced in response to lipopolysaccharide

Genes encoding two hepcidin-like antimicrobial peptides were discovered in Barramundi, Lates calcarifer (barramundi, Giant sea perch). Analysis of the coding regions indicated that genes for each hepcidin comprised 3 exons and 2 introns. The deduced amino acid sequences for each molecule resulted in a protein comprising a signal sequence of 24 aa in each case, coupled to a prepropeptide of 75 aa for hepcidin 1 and 78 aa for hepcidin 2. A cleavage site was identified in each prepropetide at amino acid 64 with the cleavage motif--QKR/QS--resulting in mature peptides of 25 and 28 amino acids respectively. Each mature peptide contained 8 conserved cysteine residues and 3 dimensional modeling predicted a β-hairpin and β-sheet structure characteristic of human Liver Expressed Antimicrobial Peptide (LEAP). Analysis of the deduced amino acid sequences by BLAST with phylogenetic supported indicated that hepcidin 1 was a HAMP1-type peptide closely related to hepcidins identified in other Perciformes (Micropterus and Pseudosciaena), whilst hepcidin 2 was a HAMP2-type peptide most similar to a hepcidin previously identified in black rock fish (Sebastes schlegeli). Both hepcidin genes were inducible in barramundi following intraperitoneal injection with lipopolysaccharide, with elevated expression detected in liver and head kidney 3 h post IP injection for hepcidin 1 and in liver only for hepcidin 2. The elevated expression was transient with return to normal levels within 24-48 h. No significant expression of either peptide was detected in spleen, skin or gill following IP injection with LPS.

The action of fish peptide Orpotrin analogs on microcirculation

In order to investigate the relationship between the primary structure of Orpotrin, a vasoactive peptide previously isolated from the freshwater stingray Potamotrygon gr. orbignyi, and its microcirculatory effects, three Orpotrin analogs were synthesized. The analogs have a truncated N-terminal with a His residue deletion and two substituted amino acid residues, where one Nle is substituted for one internal Lys residue and the third analog has a substitution of a Pro for an Ala (Orp-desH(1) , Orp-Nle and Orp-Pro/Ala, respectively). Only Orp-desH(1) could induce a lower vasoconstriction effect compared with the natural Orpotrin, indicating that besides the N-terminal, the positive charge of Lys and the Pro residues located at the center of the amino acid chain is crucial for this vasoconstriction effect. Importantly, the suggestions made with bioactive peptides were based on the molecular modeling and dynamics of peptides, the presence of key amino acids and shared activity in microcirculation, characterized by intravital microscopy. Moreover, this study has demonstrated that even subtle changes in the primary structure of Orpotrin alter the biological effects of this native peptide significantly, which could be of interest for biotechnological applications.

Molecular cloning and characterization of two novel hepcidins from orange-spotted grouper, Epinephelus coioides

Orange-spotted grouper, Epinephelus coioides is one of the most important economic species of marine-cultured fish in China and Southeast Asia countries. However, very little information of the innate immune mechanisms against microbial pathogens is available in grouper, Epinephelus sp. Hepcidin, as an antimicrobial peptide (AMP), is a very important component in the innate immune system and widespread in fish. In this study, two novel types of hepcidin gene (designated EC-hepcidin1 and EC-hepcidin2) were cloned from E. coioides. They consist of open reading frames (ORFs) of 267 bp and 263 bp encoding the putative peptides of 88 and 87 amino acids, respectively. The homologous identity of deduced amino acid sequences between EC-hepcidin1 and EC-hepcidin2 is up to 79%, and predicted mature regions of both them have four cysteines residues. Genomic DNAs of both EC-hepcidin1 and EC-hepcidin2 consist of three exons and two introns. RT-PCR results showed that EC-hepcidin1 transcript was most abundant in liver and less in stomach. However, the transcript of EC-hepcidin2 was only detected in liver. The expressions of both EC-hepcidins were up-regulated by microbial and viral challenges, and iron overload, respectively, and EC-hepcidin1 was more responsive. The growth of Gram-negative bacterium of Vibrio vulnificus and Gram-positive bacterium of Staphylococcus aureus was inhibited by synthetic EC-hepcidins, and EC-hepcidin1 displayed stronger antimicrobial activity. The replication of Singapore grouper iridovirus (SGIV) was inhibited in the EC-hepcidin1 and EC-hepcidin2 over-expressed stable transfected fish cell lines (GS/pcDNA-Hep1, GS/pcDNA-Hep2) indicative of the antiviral activity of EC-hepcidins. These data should offer important information on the antimicrobial and antiviral roles of EC-hepcidins, and will be help to the better understanding of molecular mechanisms of grouper innate immunity.

Molecular characterization of hepcidin AS-hepc2 and AS-hepc6 in black porgy (Acanthopagrus schlegelii): expression pattern responded to bacterial challenge and in vitro antimicrobial activity

There are more diversified isoforms of the hepcidin gene that exist in fishes than in mammals, and elucidating the differences between these isoforms should provide insight into the functioning of hepcidin in fishes. In our study, AS-hepc2 and AS-hepc6 hepcidin isoforms from black porgy were characterized for their in vivo expression patterns following bacterial challenge, and their in vitro antimicrobial activities against Gram-positive and Gram-negative bacteria as well as fungi. As a result, two isoforms were observed to be widely distributed in all the tissues tested. AS-hepc2 was a liver-expressed hepcidin peptide which was always highly more expressed in the liver than in the other tissues tested no matter whether this was before or after bacterial challenge. AS-hepc6 was detected mainly in the head kidney and trunk kidney of normal fish, but, in the challenged fish, its expression involved more tissues than just the kidneys. The mature peptides of AS-hepc2 and AS-hepc6 were modeled for 3D structure and then synthesized for antimicrobial assay. AS-hepc6 had a wider antimicrobial spectrum than AS-hepc2 and, in particular, had more potent antifungal activity. Our study indicated that the two hepcidin isoforms had different characteristics in terms of their expression patterns and antimicrobial activity, and they were assumed to play an overlapping role in the innate immune system of black porgy against invading pathogens.

Microarray technology is an effective tool for identifying genes related to the aquacultural improvement of Japanese flounder, Paralichthys olivaceus

Molecular techniques are now essential for discovering new functional genes for the improvement of cultured marine organisms. Such techniques can be used to obtain expressed sequence tags (EST) and, through the use of microarrays, the entire transcriptome. For example, microarrays can be used to reveal biomarkers of health conditions, nutrient changes and immune response in fish and shellfish. EST-based microarray chips were constructed for cultured fish and shellfish species including Japanese flounder (Paralichthys olivaceus). Using the flounder microarray chip, the efficacy of two DNA vaccines derived from pathogenic viruses [hirame rhabdovirus (HRV) and viral hemorrhagic septicemia virus (VHSV)] was evaluated through gene expression profiles. The results suggest that both DNA vaccines were effective in protecting the flounder from HIRRV and VHSV. The flounder microarray was also used to compare gene expression patterns in fish that are susceptible and resistant to Edwardsiella tarda. At 3days post infection, the gene expression patterns between the two groups were dramatically changed. Thus, microarray analysis is a very powerful tool to understand gene expression profiles in fish.

Expression profiles of toll-like receptors in anterior kidney of channel catfish, Ictalurus punctatus (Rafinesque), acutely infected by Edwardsiella ictaluri

Using quantitative PCR (QPCR), the relative transcriptional levels of five toll-like receptors (TLR2, TLR3, TLR5, TLR20a and TLR21) were studied in the channel catfish, Ictalurus punctatus (Rafinesque), under uninfected and acutely infected conditions [1-, 2-, 4-, 6-, 12-, 24-, 36- and 48-h post-injection (hpi)]. Under uninfected conditions, the transcriptional levels of the five TLRs were significantly lower than that of 18S rRNA (P < 0.001). QPCR results also revealed that the transcriptional levels of TLR20a and TLR5 were higher than those of TLR2, TLR3 or TLR21. The transcriptional level of TLR3 was significantly lower than that of the other four TLRs (P < 0.001). However, when channel catfish were acutely infected by Edwardsiella ictaluri through intraperitoneal injection, the transcriptional levels of TLRs increased significantly (P < 0.005) at 6 hpi. Among the five TLRs studied, the transcriptional levels of TLR3, TLR5 and TLR21 were never significantly lower than under uninfected conditions (P = 0.16, 0.27 and 0.19, respectively), suggesting these three TLRs might play important roles in host defence against infection by E. ictaluri. The amount of E. ictaluri in the anterior kidney increased at 12 and 24 hpi but decreased at 36 and 48 hpi. Our results suggest that TLRs are important components in the immune system in the channel catfish, and their rapid transcriptional upregulation (within 6 hpi) in response to acute E. ictaluri infection might be important for survival from enteric septicaemia of catfish.

Development of genomic resources in support of sequencing, assembly, and annotation of the catfish genome

Major progress has been made in catfish genomics including construction of high-density genetic linkage maps, BAC-based physical maps, and integration of genetic linkage and physical maps. Large numbers of ESTs have been generated from both channel catfish and blue catfish. Microarray platforms have been developed for the analysis of genome expression. Genome repeat structures are studied, laying grounds for whole genome sequencing. USDA recently approved funding of the whole genome sequencing project of catfish using the next generation sequencing technologies. Generation of the whole genome sequence is a historical landmark of catfish research as it opens the real first step of the long march toward genetic enhancement. The research community needs to be focused on aquaculture performance and production traits, take advantage of the unprecedented genome information and technology, and make real progress toward genetic improvements of aquaculture brood stocks.

NOD-like subfamily of the nucleotide-binding domain and leucine-rich repeat containing family receptors and their expression in channel catfish

The NLRs (nucleotide-binding domain and leucine-rich repeat containing family receptors) are a recently identified family of pattern recognition receptors in vertebrates. Several subfamilies of NLRs have been characterized in human, mouse, and zebrafish, but studies of NLRs in other species, especially teleost species, have been lacking. Here we report characterization of five NLRs from channel catfish: NOD1, NOD2, NLRC3, NLRC5, and NLRX1. Structural analysis indicated that the genes were organized in a similar fashion as in the mammals and in zebrafish. Phylogenetic analysis suggested that they were orthologous to the NOD-like subfamily of NLRs. All five NOD-like genes exist as a single copy gene in the catfish genome. Hybridization of gene-specific probes allowed mapping of three NLR genes to the catfish physical map, laying a foundation for genome characterization and for establishing orthologies with NLR genes from other species. These genes are widely expressed in various tissues and leukocyte cell lines. While the majority of the NLR genes appeared to be constitutively expressed, NOD1 was induced after infection with a bacterial pathogen, Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC), suggesting its involvement in immunity against the intracellular pathogen.

Molecular cloning and expression analysis of the liver-expressed antimicrobial peptide 2 (LEAP-2) gene in grass carp

Liver-expressed antimicrobial peptide 2 (LEAP-2) is a novel antimicrobial peptide (AMP) recently found in vertebrates, and exhibits distinct amino acid sequence, secondary structure and expression pattern from other peptides. In this study, the LEAP-2 gene and its full-length cDNA were cloned from grass carp. Grass carp LEAP-2 gene consists of two introns and three exons. The translated product contains 92 amino acids, including a 26 amino acids signal peptide and a mature peptide of 41 amino acids. Grass carp LEAP-2 gene was expressed in a wide range of tissues except blood, with the highest level of transcripts found in liver. Upon induction by Aeromonas hydrophila, its expression was significantly up-regulated in liver, gill, skin, muscle, spleen, blood, head kidney, heart and intestine, but down-regulated in trunk kidney and brain. The transcript level was high in embryos at the 16-cell stage but declined gradually afterwards, suggesting that LEAP-2 transcripts in early embryos might be maternal. Mature peptides obtained by in vitro expression displayed selective antimicrobial activities. These results together further our understanding of the physiological function of LEAP-2 in vertebrates.

Isolation and characterization of a hepcidin peptide from the head kidney of large yellow croaker, Pseudosciaena crocea

Large yellow croaker (Pseudosciaena crocea) is one of the most important marine cultured fish in China. Acidic extracts of five tissues of large yellow croaker showed strong anti-Vibrio alginolyticus activity. Acidic extract of head kidney tissue was subjected to heat-treatment in boiling water, and solid-phase extraction on Sep-Pak C(18) cartridge. It was found that the antibacterial substances were heat stable, and 20% acetonitrile effluent exhibited strong antibacterial activity. Active extract was further applied to Sephadex G-25 gel permeation chromatography and StableBond C(18) RP-HPLC. An antibacterial peptide with a single peak was obtained. The results of amino acid sequencing and MALDI-TOF MS suggested that the peptide was RCRFCCRCCPRMRGCGICCRF with an observed molecular mass of 2523.2 Da. BLAST searching suggested that the purified antibacterial peptide was the mature peptide section of the hepcidin preproprotein presumed from cDNA of large yellow croaker, thus designated hepcidin-Pl. Hepcidin-P1 exhibited strong antibacterial activity against four marine vibrios.

Identification of centrarchid hepcidins and evidence that 17beta-estradiol disrupts constitutive expression of hepcidin-1 and inducible expression of hepcidin-2 in largemouth bass (Micropterus salmoides)

Hepcidin is a highly conserved antimicrobial peptide and iron-regulatory hormone. Here, we identify two hepcidin genes (hep-1 and hep-2) in largemouth bass (Micropterus salmoides) and smallmouth bass (Micropterus dolomieu). Hepcidin-1 contains a putative ATCUN metal-binding site in the amino-terminus that is missing in hepcidin-2, suggesting that hepcidin-1 may function as an iron-regulatory hormone. Both hepcidins are predominately expressed in the liver of largemouth bass, similar to other fish and mammals. Experimental exposure of pond-raised largemouth bass to 17beta-estradiol and/or the bacteria Edwardsiella ictaluri led to distinct changes in expression of hep-1 and hep-2. Estradiol reduced the constitutive expression of hep-1 in the liver. Bacterial exposure induced expression of hep-2, suggesting that hepcidin-2 may have an antimicrobial function, and this induction was abolished by estradiol. To our knowledge, this is the first report of the regulation of hepcidin expression by estradiol in either fish or mammals.

Evaluation of candidate reference genes for QPCR during ontogenesis and of immune-relevant tissues of European seabass (Dicentrarchus labrax)

The expression level of mRNA can vary significantly in different experimental conditions, such as stress, infection, developmental stage or tissue. Suitable reference genes are expected to exhibit constant expression levels. However no single gene is constitutively expressed in all cell types and under all experimental conditions. It has become clear that expression stability of the intended reference gene has to be examined before each experiment. For expression studies using quantitative real-time PCR (qPCR) at least two reference genes have to be applied. So far expression studies in the European seabass (Dicentrarchus labrax) as well as in the Gilthead seabream (Sparus aurata) have been performed with only one reference gene (S18, Ef-1 alpha or Gapdh). Though significant variations showed up in other teleost species such as the Atlantic halibut and the zebrafish affirming the need for proper normalization strategies, the present study aims at identifying suitable reference genes among nine candidates [glyceraldehyde-phosphate-dehydrogenase (Gapdh), beta-actin (two regions of beta-actin), 40S ribosomal protein S30 (Fau), ribosomal protein L13 a (L13a), beta2-tubulin (Tubb2) and tyrosine 3 monooxygenase/tryptophan 5-monooxygenase activation protein (Tyr)] for expression analysis of 8 developmental stages and a tissue panel (spleen, liver, kidney and brain) with samples infected with Nodavirus and Vibrio anguillarum in D. labrax. Besides the analysis of raw Ct-values, the gene expression stability was determined using two different software applications BestKeeper and NormFinder. According to both algorithms the best two reference genes for an appropriate normalization approach during D. labrax development are Ef-1 alpha and L13a whereas in the tissue panel Fau and L13a are recommended for qPCR normalization.

Immunological differences in intestine and rectum of Atlantic cod (Gadus morhua L.)

The defence system of the distal gut (hindgut and rectum) of Atlantic cod, (Gadus morhua L.) was studied using (immuno)histochemical, electron microscopical and real-time quantitative PCR techniques. The uptake and transport of macromolecules in the intestinal epithelium was also investigated. In this study we observed that cod has many and large goblet cells in its intestinal epithelium and that IgM(+) cells are present in the lamina propria and their number is considerably higher in the rectum than in the intestine. Myeloperoxidase staining revealed low numbers of granulocytes in and under the epithelium of the distal intestine, whereas high numbers were found clustered in the submucosa of the rectum. Electron microscopy not only confirmed these observations, but also revealed the presence of lymphoid cells and macrophages within the intestinal epithelium. Acid phosphatase staining demonstrated more positive macrophage-like cells in the rectum than in the distal intestine. Antigen uptake studies showed a diffused absorption of horse radish peroxidase (HRP) and LTB-GFP, whereas ferritin uptake could not be detected. Basal gene expression of cytokines (IL-1beta, IL-8 and IL-10) and immune relevant molecules (hepcidin and BPI/LPB) were compared in both the intestine and rectum and revealed approximately 2-9 times higher expression in the rectum, of which IL-1beta expression showed the most prominent difference. The present results clearly indicate that intestinal immunity is very prominent in the rectum of cod.

Expression of iron-related genes in human brain and brain tumors

BACKGROUND

Defective iron homeostasis may be involved in the development of some diseases within the central nervous system. Although the expression of genes involved in normal iron balance has been intensively studied in other tissues, little is known about their expression in the brain. We investigated the mRNA levels of hepcidin (HAMP), HFE, neogenin (NEO1), transferrin receptor 1 (TFRC), transferrin receptor 2 (TFR2), and hemojuvelin (HFE2) in normal human brain, brain tumors, and astrocytoma cell lines. The specimens included 5 normal brain tissue samples, 4 meningiomas, one medulloblastoma, 3 oligodendrocytic gliomas, 2 oligoastrocytic gliomas, 8 astrocytic gliomas, and 3 astrocytoma cell lines.

RESULTS

Except for hemojuvelin, all genes studied had detectable levels of mRNA. In most tumor types, the pattern of gene expression was diverse. Notable findings include high expression of transferrin receptor 1 in the hippocampus and medulla oblongata compared to other brain regions, low expression of HFE in normal brain with elevated HFE expression in meningiomas, and absence of hepcidin mRNA in astrocytoma cell lines despite expression in normal brain and tumor specimens.

CONCLUSION

These results indicate that several iron-related genes are expressed in normal brain, and that their expression may be dysregulated in brain tumors.

Profiling of infection specific mRNA transcripts of the European seabass Dicentrarchus labrax

Background

The European seabass (Dicentrarchus labrax), one of the most extensively cultured species in European aquaculture productions, is, along with the gilthead sea bream (Sparus aurata), a prospective model species for the Perciformes which includes several other commercially important species. Massive mortalities may be caused by bacterial or viral infections in intensive aquaculture production. Revealing transcripts involved in immune response and studying their relative expression enhances the understanding of the immune response mechanism and consequently also the creation of vaccines. The analysis of expressed sequence tags (EST) is an efficient and easy approach for gene discovery, comparative genomics and for examining gene expression in specific tissues in a qualitative and quantitative way.

Results

Here we describe the construction, analysis and comparison of a total of ten cDNA libraries, six from different tissues infected with V. anguillarum (liver, spleen, head kidney, gill, peritoneal exudates and intestine) and four cDNA libraries from different tissues infected with Nodavirus (liver, spleen, head kidney and brain). In total 9605 sequences representing 3075 (32%) unique sequences (set of sequences obtained after clustering) were obtained and analysed. Among the sequences several immune-related proteins were identified for the first time in the order of Perciformes as well as in Teleostei.

Conclusion

The present study provides new information to the Gene Index of seabass. It gives a unigene set that will make a significant contribution to functional genomic studies and to studies of differential gene expression in relation to the immune system. In addition some of the potentially interesting genes identified by in silico analysis and confirmed by real-time PCR are putative biomarkers for bacterial and viral infections in fish.

Cloning and expression of a hepcidin gene from a marine fish (Pseudosciaena crocea) and the antimicrobial activity of its synthetic peptide

Hepcidin gene is widely expressed in various fish, suggesting that this antimicrobial peptide is a very important component in the innate immune system. Large yellow croaker (Pseudosciaena crocea) is one of the important economic species of marine-cultured fish but knowledge of its innate immune mechanism is lacking. In this study, we characterize a P. crocea hepcidin gene named as PC-hepc. It consists of an open reading frame of 258 bases encoding 85 amino acids and has a conserved sequence in common with other known hepcidins. The genomic DNA of PC-hepc contains three exons and two introns, the same organization as other reported hepcidins, indicating that PC-hepc is one member of the hepcidin family in fish. The tissue-specific expression of PC-hepc gene in normal fish and the expression pattern in LPS-challenged fish at the time course of stimulation were investigated. The expression of PC-hepc mRNA was significantly increased in the spleen, heart and stomach but not significantly induced in the liver after LPS challenge. An interesting finding is the demonstration of high amounts of PC-hepc transcripts in the kidney in normal fish and their maintenance through 48h exposure to LPS challenge. The synthetic PC-hepc demonstrated a rather wide spectrum of antimicrobial activity in vitro against bacteria and fungi tested, and particularly showed strong activity against the principal fish pathogens, Aeromonas hydrophila, Vibrio parahaemloyticus, Vibrio alginolyticus and Vibrio harvryi. The study indicates that PC-hepc may play a role with a tissue-specific mode in the innate immunity of P. crocea.

Gene structure and differential modulation of multiple rockbream (Oplegnathus fasciatus) hepcidin isoforms resulting from different biological stimulations

Hepcidin, an antimicrobial and iron-regulating peptide, is a key molecule of the innate immune system of bony fish. In this study, four isoforms of hepcidin genes were characterized from a marine Perciform fish, rockbream (Oplegnathus fasciatus), and the transcriptional modulations of these isoforms in response to different biological stimulations were also examined. All rockbream hepcidin isoform genes exhibited a tripartite structure and their promoter regions displayed typical binding motifs for the transcription factors including C/EBP, HNF, AP, NF-kbeta, GATA, USF and/or STAT. Hepcidin transcripts in juvenile or fingerling tissues were dramatically induced during experimental challenges with various bacterial species, iron overload and rockbream iridovirus infection. The transcription ofhepcidins was regulated in an isoform- and tissue-specific fashion. In addition, we identified for the first time that partially processed hepcidin transcripts were significantly elevated during bacterial infection and iron overload. Results from this study provide a good basis to better understand the isoform-specific role of hepcidin in the fish innate immune system.

Antimicrobial peptides derived from hemoglobin are expressed in epithelium of channel catfish (Ictalurus punctatus, Rafinesque)

The beta-chain of the respiratory protein hemoglobin (Hbbeta), has recently been identified in novel sites, including mammalian macrophages and alveolar epithelium, as well as in gill microsomes of fish. However, the functional significance of extra-erythrocytically expressed hemoglobin has been unclear. Here we show inducible expression and upregulation of antimicrobial peptides (AMPs) homologous to Hbbeta in the gill epithelium of channel catfish (Ictalurus punctatus) in response to parasitic (Ichthyophthirius multifiliis, ich) infection. One peptide (HbbetaP-1), while having activity against some fish bacterial pathogens (e.g., Aeromonas hydrophila), had especially potent antiparasitic activity that was specifically lethal (lytic) to the feeding (trophont) stage of ich and also appeared to accelerate the differentiation of trophonts. However, it had no apparent effect on either the disseminative (theront) or reproductive (tomont) stages, nor was it lytic to channel catfish erythrocytes. Fish experimentally challenged with ich confirmed that the HbbetaP-1 sequence was both transcribed and translated in skin and gill epithelium, the target tissues for ich. The Hb AMP concentration expressed in vivo appeared to be well within the antiparasitic concentrations measured in vitro. Our findings suggest that hemoglobin-derived AMPs might play a significant role in the non-specific immune response.