cDNA cloning and expression analysis of a hepcidin gene from yellow catfish Pelteobagrus fulvidraco (Siluriformes: Bagridae)

Characterization, Expression, and Functional Analysis of the Northern Snakehead (Channa argus) Hepcidin

Hepcidin, an antimicrobial peptide (AMP), is a well-conserved molecule present in various species such as fish, amphibians, birds, reptiles, and mammals. It exhibits broad-spectrum antimicrobial activity and holds a significant role in the innate immune system of host organisms. The northern snakehead (Channa argus) has become a valuable freshwater fish in China and Asia. In this investigation, the cDNA encoding the hepcidin gene of northern snakehead was cloned and named caHep. The amino acid sequences and protein structure of caHep are similar to those of hepcidins from other fish. The eukaryotic expression product of the caHep gene showed broad-spectrum antibacterial activity. Scanning electron microscope analysis indicated that the caHep peptide inhibited bacterial growth by damaging their cell membranes. Lipopolysaccharide (LPS) injection induced significant expression of caHep, implying the involvement of caHep in the innate immune response of northern snakeheads. This investigation showed that the caHep peptide is potentially a robust antibacterial drug against bacterial diseases in aquaculture animals.

Molecular cloning of the hepcidin gene from crescent sweetlips (Plectorhinchus cinctus) and characterization of its encoded antimicrobial peptide

Hepcidin has been identified as an important antimicrobial peptide exerting important innate immunomodulatory activities in many fish species. In the present study, reverse transcription PCR coupled with the rapid amplification of cDNA ends was used to obtain the full-length cDNA of the crescent sweetlips hepcidin gene, which is 829 bp in length and includes an 273 bp ORF encoding a peptide with 90 amino acid residues. Sequence alignment showed a typical RXKR motif and eight conserved cysteine residues in the deduced amino acid sequences. Four disulfide bonds were predicted to form between these eight cysteines, which may stabilize the hairpin structure in hepcidin molecule. Furthermore, phylogenetic analysis showed that the deduced amino acid sequences of crescent sweetlips hepcidin had high sequence homology to hepcidins from fish species of Eupercaria. In addition, the crescent sweetlips hepcidin peptide demonstrated a strong antimicrobial activity in vitro against several types of pathogenic bacteria in fish. In conclusion, the obtained results suggested that crescent sweetlips hepcidin possessed the typical structure similar to other fish hepcidins and had strong antibacterial activity, which showed great potential in the prevention of fish diseases in aquaculture.

Characterization of hepcidin gene and protection of recombinant hepcidin supplemented in feed against Aeromonas hydrophila infection in Yellow River carp (Cyprinus carpio haematopterus)

Hepcidin is a small peptide of defensins with antibacterial activity, and plays an important role in innate immunity against pathogenic microorganisms, which can also participate in the regulation of iron metabolism. The hepcidin gene in Yellow River carp (Cyprinus carpio haematopterus) (CcHep) was cloned and identified. The total length of CcHep cDNA was 480 bp, containing an open reading frame (ORF) that encoded 91 amino acids (aa), which contained a 24-aa signal peptide, a 42-aa propeptide, and a 25-aa mature peptide. The mature peptide had a typical RX (K/R) R motif and eight conserved cysteine residues forming four pairs of disulfide bonds. Homology and phylogenetic tree analysis showed that CcHep had the closest relationship with that of crucian carp. The expression levels of hepcidin mRNA in healthy and Aeromonas hydrophila stimulated fish were measured by real-time fluorescence quantitative PCR. The results showed that CcHep mRNA was expressed in different tissues of healthy fish with the highest relative expression level in liver, followed by kidney and intestine, and the lowest expression level was observed in heart. The hepcidin gene was extremely significantly up-regulated in head kidney, intestine, liver, skin, spleen, and gill at 6 h and 12 h after A. hydrophila infection. Furthermore, the immunoregulation effect of dietary recombinant protein was evaluated. The recombinant hepcidin protein (rCcHep) was successfully expressed by Pichia pastoris X-33 and showed strong antibacterial activity against A. hydrophila, Escherichia coli, Vibrio anguillarum and Bacillus subtilis in vitro. In order to evaluate the preventive effect of rCcHep, fish were fed with basal diet or diet supplemented with different doses of rCcHep, and then challenged with A. hydrophila. The results showed that immune genes were up-regulated to varying degrees, and feed additive groups exhibited a significantly improved up-regulation expressions of Lysozyme, Toll-like receptor 5 (TLR 5), Major histocompatibility complex classⅡ (MHCⅡ), while inhibited up-regulation expressions of Interleukin 1β (IL-1β), Interleukin 8 (IL-8), and Tumor necrosis factor α (TNF-α) in liver and spleen compared to the control. Meanwhile, the relative immune protection rate in 120 mg/kg feed additive group was 28%, and the bacterial clearance rate in tissues of this group was higher than that of the control. Collectively, these results indicated that rCcHep had antibacterial activity and showed an immune protection effect against A. hydrophila, and could be considered as a dietary supplement to apply in aquaculture.

Antimicrobial peptide hepcidin contributes to restoration of the intestinal flora after Aeromonas hydrophila infection in Acrossocheilus fasciatus

Hepcidin is a cysteine-rich antimicrobial peptide that serves an important role in the immunity system of fishes. It exhibits antibacterial, antifungal, antiviral, and antitumor activities. However, the exact role of fish hepcidin in the regulation of the intestinal flora still remains a mystery. In our study, we sequenced and characterized hepcidin from the liver of Acrossocheilus fasciatus. Phylogenetic tree analysis showed that A. fasciatus hepcidin and Gobiocypris rarus hepcidin were the most closely related, and both belonged to the fish HAMP1 cluster. Studies conducted on in vivo tissue distribution showed that the expression of hepcidin was highest in healthy A. fasciatus liver. Aeromonas hydrophila infection was confirmed by the increased expression of pro-inflammatory cytokine genes and bacterial loads in A. fasciatus tissues. After A. hydrophila infection, hepcidin expression significantly increased in the liver, spleen, and head kidney. In vitro antibacterial assays showed that hepcidin exhibits strong broad spectrum antibacterial activity. Furthermore, we examined the regulatory effect of hepcidin on the intestinal flora and found that A. fasciatus hepcidin restored the reduced diversity and compositional changes in intestinal flora caused by A. hydrophila infection. Our results suggest that hepcidin could regulate the intestinal flora in fishes; however, the underlying mechanisms need to be explored in greater detail.

A hepatic antimicrobial peptide, hepcidin from Indian major carp, Catla catla: molecular identification and functional characterization

Background

Increase of antibiotic resistance in pathogenic microbes necessitated novel molecules for curing infection. Antimicrobial peptides (AMPs) are the gene-encoded evolutionarily conserved small molecules with therapeutic value. AMPs are considered as an alternative drug for conventional antibiotics. Hepcidin, the cysteine-rich antimicrobial peptide, is an important component in innate immune response. In this study, we identified and characterized hepcidin gene from the fish, Catla catla (Indian major carp) and termed it as Cc-Hep.

Results

Open reading frame of Cc-Hep consists of 261 base pair that encodes 87 amino acids. Cc-Hep is synthesized as a prepropeptide consisting of 24 amino acid signal peptide, 36 amino acid propeptide, and 26 amino acid mature peptide. Sequence analysis revealed that Cc-Hep shared sequence similarity with hepcidin from Sorsogona tuberculata. Phylogenetic analysis indicated that Cc-Hep was grouped with HAMP2 family. Structure analysis of mature Cc-Hep identified two antiparallel beta sheets stabilized by four disulphide bonds and a random coil. The mature peptide region of Cc-Hep has a charge of + 2, isoelectric value 8.23 and molecular weight 2.73 kDa.

Conclusion

Functional characterization predicted antibacterial, antioxidant, and anticancer potential of Cc-Hep, which can be explored in aquaculture or human health care.

Hepcidin Protects Yellow Catfish (Pelteobagrus fulvidraco) against Aeromonas veronii-Induced Ascites Disease by Regulating Iron Metabolism

Aeromonas veronii (A. veronii) is one of the main pathogens causing bacterial diseases in aquaculture. Although previous studies have shown that hepcidin as an antimicrobial peptide can promote fish resistance to pathogenic bacterial infections, but the mechanisms remain unclear. Here, we expressed and purified recombinant yellow catfish (Pelteobagrus fulvidraco) hepcidin protein (rPfHep). rPfHep can up-regulate the expression of ferritin and enhance the antibacterial activity in primary hepatocytes of yellow catfish. We employed berberine hydrochloride (BBR) and Fursultiamine (FSL) as agonists and antagonists for hepcidin, respectively. The results indicated that agonist BBR can inhibit the proliferation of pathogenic bacteria, and the antagonist FSL shows the opposite effect. After gavage administration, rPfHep and the agonist BBR can enhance the accumulation of iron in liver, which may hinder the iron transport and limit the amount of iron available to pathogenic bacteria. Moreover, rPfHep and the agonist BBR can also reduce the mortality rate, bacterial load and histological lesions in yellow catfish infected with A. veronii. Therefore, hepcidin is an important mediator of iron metabolism, and it can be used as a candidate target for prevent bacterial infections in yellow catfish. Hepcidin and BBR have potential application value in preventing anti-bacterial infection.

Sequence analysis of hepcidin in barbel steed (Hemibarbus labeo): QSHLS motif confers hepcidin iron-regulatory activity but limits its antibacterial activity

Fish hepcidin genes are generally classified into two groups: hamp1-and hamp2-type isoforms. Hamp1-type hepcidin exhibits iron regulatory and antimicrobial activity, while hamp2-type shows a unique role in the immune response against various pathogens. An iron-regulatory motif exists at the N-terminus of hamp1-type hepcidin; however, the functional effect of this motif in fish is not well understood. Here, cDNA of the barbel steed (Hemibarbus labeo) hepcidin gene was cloned and sequenced. The predicted amino acid sequence comprised a signal peptide, a prodomain, and a mature peptide. Phylogenetic tree analysis revealed that barbel steed hepcidin belongs to the fish HAMP1 cluster and is closely related to Chinese rare minnow (Gobiocypris rarus) hepcidin. Barbel steed hepcidin is constitutively expressed in healthy fish tissues, predominantly in the liver. Following iron dextran treatment or Aeromonas hydrophila infection, expression of barbel steed hepcidin increased significantly in tested tissues. In vivo administration of intact hepcidin mature peptide (hep25) significantly and dose-dependently reduced ferroportin 1 expression, while truncated hepcidin mature peptide (hep20) lacking a QSHLS motif had no such effect. In vitro treatment of barbel steed monocytes/macrophages with hep25, but not hep20, increased the labile iron pool levels. Hep25 and hep20 conferred antibacterial activity only against A. hydrophila and Vibrio vulnificus, with greater activity of the latter at low concentrations. Neither hep25 nor hep20 impaired the cell membrane integrity of A. hydrophila, but could hydrolyze its genomic DNA; lack of a QSHLS motif enables hep20 to have a better hydrolytic effect. In summary, we identified an iron-regulatory motif in a fish species and demonstrated that this motif confers hamp1-type hepcidin iron-regulatory activity, but attenuates its antibacterial activity.

Molecular characterization and expression analysis of Tf_TLR4 and Tf_TRIL in yellow catfish Tachysurus fulvidraco responding to Edwardsiella ictaluri challenge

Toll-like receptors play significant roles in defensing against pathogen invasion. In this study, TLR4 and TRIL from Yellow catfish Tachysurus fulvidraco (Tf), were identified and characterized. The open reading frames of the Tf_TLR4 and Tf_TRIL genes were 2466 bp and 1827 bp in length, encoding 821 and 608 amino acids, respectively. The Tf_TLR4 consists of LRRs, a transmembrane domain and a TIR domain, and Tf_TRIL only contains LRRs and TIR domain. Homologous identity revealed that both Tf_TLR4 and Tf_TRIL have high protein sequence similarity with that of channel catfish Ictalurus punctatus. Both the Tf_TLR4 and Tf_TRIL genes were highly expressed in head kidney and brain, respectively. The mRNA expression levels of Tf_TLR4 and Tf_TRIL genes were up-regulated in intestine and immune-related tissues after challenge of Edwardsiella ictaluri. The microscopic observation of the gut showed that the pathological changes in midgut and hindgut are more obvious than that in foregut after challenged with E. ictaluri. These results indicate that these two genes play potential roles in the host defense against E. ictaluri invasion. This study will provide valuable information to better understand the synergistic roles of TLR4 and TRIL in the innate immune system of yellow catfish and other fish.

Identification and characterization of SaRpAMP, a 60S ribosomal protein L27-derived antimicrobial peptide from amur catfish, Silurus asotus

Aquatic freshwater fish like catfish, Silurus asotus, lives in microbe-rich environments, which enable this fish to develop necessary defense mechanisms. Antimicrobial peptides, along with other innate immune factors, are regarded as an important group in this defense. An antimicrobial peptide, which was isolated from the skin of S. asotus, was identified as a C-terminal fragment of 60S ribosomal protein L27 from S. asotus. The peptide was, then, designated Silurus asotus 60S ribosomal protein L27-derived antimicrobial peptide, SaRpAMP. Primary structure analyses and cDNA cloning revealed that SaRpAMP was 4185.36 Da and composed of 33 amino acids (AAs). Its precursor had a total of 136 AAs containing a pro-sequence of 103 AAs encoded by the nucleotide sequence of 512 bp that comprises a 5' untranslated region (UTR) of 32 bp, an open reading frame (ORF) of 411 bp, and a 3' UTR of 69 bp. Secondary structure analyses showed that SaRpAMP had two α-helices with turns and coils and an amphiphilic structure, a finding consistent with the 3D model of the peptide. SaRpAMP exhibited potent antibacterial activity comparable to piscidin 1, a powerful positive control. Its antimicrobial activity against fungus C. albicans was relatively weak. The antimicrobial activity of SaRpAMP was not diminished by heat treatment and changes in pH but was abolished by proteolytic enzyme digestion. Membrane permeability assays suggested that SaRpAMP interacts with both the outer and inner bacterial membranes. This was consistent with the results of lipid titration and quenching of Trp fluorescence that demonstrated SaRpAMP's interaction with acidic liposomes. Collectively, these findings suggest that the identified peptide, SaRpAMP, was the first antimicrobial peptide reported to be derived from the C-terminal region of 60S ribosomal protein L27. The findings also suggest that the action mechanism of SaRpAMP involved the interaction of the peptide with the bacterial membranes.

CCR7, CD80/86 and CD83 in yellow catfish (Pelteobagrus fulvidraco): Molecular characteristics and expression patterns with bacterial infection

Dendritic cells (DCs) have a strong ability to stimulate naive T lymphocyte proliferation, so DCs play an important regulatory role in the initiation of the specific immune response. DCs cannot play the role of antigen presentation without the expression of surface molecules. The chemokine receptor CCR7 and the costimulatory molecules CD80/86 and CD83 are not only markers of DC maturation but also important functional molecules in the immune response of DC-T cells. In this study, partial cDNA sequences of CCR7, CD80/86 and CD83 were obtained by rapid amplification of cDNA ends (RACE) technology from yellow catfish. Bioinformatics analysis of deduced amino acid sequences of these three genes showed that CCR7, CD80/86 and CD83 genes in yellow catfish have similar functional domains to the homologs in other vertebrates, which indicated that the functions of these genes may be somewhat conserved during the evolution process. Afterward, the expression characteristics of these three genes in different tissues were detected by q-PCR. This result indicated that CCR7, CD80/86 and CD83 were expressed in all examined tissues, and the highest expression levels of CCR7 and CD80/86 and CD83 were detected in the trunk kidney, muscle and midgut, respectively. Meanwhile, the expression levels of CCR7 and CD80/86 were lowest in the gill, and the expression of CD83 was lowest in the stomach. Finally, healthy yellow catfish were infected with A.hydrophila (1.0 × 10⁷ CFU/mL) or E.ictaluri (1.0 × 10⁶ CFU/mL), q-PCR results indicated that both pathogenic bacteria can induce significant upregulation of CCR7, CD80/86 and CD83 in immune organs, and the expression levels of these genes in the intestine were higher than those in the skin and gill. Our results in this study provide a molecular basis for exploring the role of CCR7, CD80/86 and CD83 in the immune responses induced by bacteria, and can help us to understand the difference of immune responses induced by extracellular and intracellular bacteria.

Hepcidin-Expressing Fish Eggs as A Novel Food Supplement to Modulate Immunity against Pathogenic Infection in Zebrafish (Danio rerio)

Hepcidin antimicrobial peptides are difficult to produce in prokaryotic expression systems due to their complex structure and antimicrobial activity. Although synthetic hepcidin provides an alternative to solve this issue, its high cost limits its practical application in various industries. The present study used zebrafish eggs as bioreactors to produce convict cichlid (Amatitlania nigrofasciata) hepcidin (AN-hepc) using the oocyte-specific zona pellucida (zp3) promoter. The expression plasmid pT2-ZP3-AN-hepc-ZP3-EGFP, using EGFP as a reporter of AN-hepc expression, was designed to establish the transgenic line Tg(ZP3:AN-hepc:ZP3:EGFP) for the expression of AN-hepc. The AN-hepc peptide was produced successfully in fertilized eggs, as evidenced by RT-PCR and Western blotting. The AN-hepc-expressing eggs exhibited antimicrobial activity against a variety of aquatic pathogens and antibiotic-resistant pathogens, suggesting that the AN-hepc expressed in fish eggs was bioactive. The immunomodulatory effects of AN-hepc-expressing fertilized eggs on zebrafish innate immunity were evaluated by determining the expression of indicator genes after feeding with AN-hepc-expressing fertilized eggs for two months. Zebrafish supplementation with AN-hepc-expressing fertilized eggs significantly increased the expression of innate immunity-related genes, including IL-1β, IL-6, IL-15, TNF-α, NF-κb, complement C3b, lysozyme and TLR-4a. The zebrafish administered AN-hepc-expressing eggs exhibited higher cumulative survival than fish supplemented with wild-type and control eggs after infection with Aeromonas hydrophila and Streptococcus iniae. In conclusion, the present results showed that supplementation with AN-hepc-expressing fish eggs enhanced zebrafish innate immunity against pathogenic infections, suggesting that fertilized eggs containing AN-hepc have the potential to be developed as a food supplement for improving health status in aquaculture.

Antibacterial and immunoregulatory activity of a novel hepcidin homologue in diploid hybrid fish (Carassius auratus cuvieri ♀ × Carassius auratus red var ♂)

Hepcidin, a multifunctional hormone oligopeptide, not only exhibits a regulatory role in iron metabolism, but also participates in the regulation of teleostean immunity. In this study, ORF sequence of WR-hepcidin was 258 bp and encoded 85 amino acid residues. Tissue-specific analysis revealed that the highest expression of WR-hepcidin was observed in liver. Aeromonas hydrophila challenge can sharply increased WR-hepcidin mRNA expression in liver, trunk kidney and spleen. The purified WR-hepcidin fusion peptide can directly bind to A. hydrophila and Streptococcus agalactiae, reduce the relative bacterial activity, limit bacterial growth and attenuate their dissemination to tissues in vivo. In addition, the treatment of WR-hepcidin fusion protein can diminish the production of pro-inflammatory cytokines. These results indicated that WR-hepcidin can play a negative regulatory role in bacteria-stimulated pro-inflammatory cytokines production and MyD88-IRAK4 activation.

Hepcidin cDNA evolution in vertebrates

Hepcidin, belonging to the β-defensin family, was isolated for the first time from plasma and human urine. It is a cationic peptide, rich in cysteine bound with four disulfide bridges, which plays a major role in innate immunity and iron homeostasis. Some vertebrate species have multiple hepcidin homolog genes and each contains only one copy that functions as an iron regulator except hepcidin sequences in the pigeon (Columba livia). The aim of this chapter is to investigate the molecular evolution of several hepcidin gene from searches of the literature and public genomic databases from 17 different species, all among the vertebrates.

Mudskipper (Boleophthalmus pectinirostris) Hepcidin-1 and Hepcidin-2 Present Different Gene Expression Profile and Antibacterial Activity and Possess Distinct Protective Effect against Edwardsiella tarda Infection

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in fish immunity against pathogens. Most fish species have two or more hepcidin homologs that have distinct functions. This study investigated the immune functions of mudskipper (Boleophthalmus pectinirostris) hepcidin-1 (BpHep-1) and hepcidin-2 (BpHep-2) in vitro and in vivo. Upon infection with Edwardsiella tarda, the expression of BpHep-1 and BpHep-2 mRNA in immune tissues was significantly upregulated, but the expression profiles were different. Chemically synthesized BpHep-1 and BpHep-2 mature peptides exhibited selective antibacterial activity against various bacterial species, and BpHep-2 exhibited a stronger antibacterial activity and broader spectrum than BpHep-1. BpHep-1 and BpHep-2 both inhibited the growth of E. tarda in vitro, with the latter being more effective than the former. In addition, both peptides induced hydrolysis of purified bacterial genomic DNA (gDNA) or gDNA in live bacteria. In vivo, an intraperitoneal injection of 1.0 μg/g BpHep-2 significantly improved the survival rate of mudskippers against E. tarda infection compared with 0.1 μg/g BpHep-2 or 0.1 and 1.0 μg/g BpHep-1. Similarly, only BpHep-2 treatment effectively reduced the tissue bacterial load in E. tarda-infected mudskippers. Furthermore, treatment with 1.0 or 10.0 μg/ml BpHep-2 promoted the phagocytic and bactericidal activities of mudskipper monocytes/macrophages (MO/MФ). However, only the highest dose (10.0 μg/ml) of BpHep-1 enhanced phagocytosis, and BpHep-1 exerted no obvious effects on bactericidal activity. In conclusion, BpHep-2 is a stronger bactericide than BpHep-1 in mudskippers, and acts not only by directly killing bacteria but also through an immunomodulatory function on MO/MФ.

Molecular characterization of a hepcidin homologue in starry flounder (Platichthys stellatus) and its synergistic interaction with antibiotics

Hepcidins are small cysteine-rich antimicrobial peptides that play an important role in host immunity against pathogenic organisms. Most fish hepcidins exert bactericidal activities against a wide range of pathogens. In this study, we identified a cDNA sequence encoding a hepcidin homologue (PsHepcidin) in the starry flounder Platichthys stellatus. The predicted amino acid sequence of PsHepcidin comprises a signal peptide and a prodomain, which are followed by the mature peptide. Sequence analysis revealed that PsHepcidin belongs to the fish HAMP2 cluster and that it is closely related to mudskipper hepcidin-2. Expression of PsHepcidin mRNA was detected in all examined immune-related tissues, with the highest transcript levels being found in the liver. In response to lipopolysaccharide treatment, PsHepcidin was significantly up-regulated in the liver, kidney, and spleen in a time-dependent manner. Chemically synthesized mature peptides of PsHepcidin were found to exhibit broad antimicrobial activity in vitro. We also investigated the combined effect of PsHepcidin and conventional antibiotics and found that these combinations showed synergistic effects against most of the examined bacterial strains. Collectively, the results of this study indicate that PsHepcidin exhibits potent antibacterial activity both independently and when used in combination with conventional antibiotics.

Molecular characterization and expression analysis of IL-22 and its two receptors genes in yellow catfish (Pelteobagrus filvidraco) in response to Edwardsiella ictaluri challenge

Interleukin (IL)-22, as a member of the interleukin (IL)-10 family, is an important mediator between the immune cells and epithelial tissues during infection and inflammation. This study reported the characterization and mRNA expression patterns of Pf_IL-22 gene and its cell surface-associated receptors Pf_IL-22RA1 and soluble Pf_IL-22RA2 genes in yellow catfish (Pelteobagrus filvidraco). The open reading frames (ORFs) of the Pf_IL-22, Pf_IL-22RA1 and Pf_IL-22RA2 genes were 546 bp, 1740 bp and 690 bp in length, encoding 181, 579 and 229 amino acids, respectively. Alignments of the deduced amino acid sequences present that the Pf_IL-22 has a conserved IL-10 family signature motif, and the Pf_IL-22RA1 and Pf_IL-22RA2 have two conserved fibronectin type-III domains. Quantitative real-time PCR (qPCR) analyses showed that the Pf_IL-22 and Pf_IL-22RA1 mRNAs were highly expressed in mucosal tissues such as the fin, gill, intestine, skin mucus and stomach, and were weakly expressed in the kidney, liver and head kidney of adult yellow catfish, indicating that the Pf_IL-22 transcripts may be mainly produced by mucosal immune cells/tissues in healthy yellow catfish. The mRNA expression levels of the Pf_IL-22RA2 gene were high in the muscle and liver, and were relatively low in the spleen and kidney. The mRNA expression levels of the Pf_IL-22 and its two receptor genes were significantly up-regulated in both mucosal tissues (gill, hindgut, and skin mucus) and systemic immune tissues (spleen, head kidney and blood) after Edwardsiella ictaluri challenge. These results indicated that the Pf_IL-22 and its two receptors genes might play an important role in the innate immune defense against bacterial invasion.

Pathogen invasion changes the intestinal microbiota composition and induces innate immune responses in the zebrafish intestine

Numerous bacteria are harbored in the animal digestive tract and are impacted by several factors. Intestinal microbiota homeostasis is critical for maintaining the health of an organism. However, how pathogen invasion affects the microbiota composition has not been fully clarified. The mechanisms for preventing invasion by pathogenic microorganisms are yet to be elucidated. Zebrafish is a useful model for developmental biology, and studies in this organism have gradually become focused on intestinal immunity. In this study, we analyzed the microbiota of normal cultivated and infected zebrafish intestines, the aquarium water and feed samples. We found that the predominant bacteria in the zebrafish intestine belonged to Gammaproteobacteria (67%) and that feed and environment merely influenced intestinal microbiota composition only partially. Intestinal microbiota changed after a pathogenic bacterial challenge. At the genus level, the abundance of some pathogenic intestinal bacteria increased, and these genera included Halomonas (50%), Pelagibacterium (3.6%), Aeromonas (2.6%), Nesterenkonia (1%), Chryseobacterium (3.4‰), Mesorhizobium (1.4‰), Vibrio (1‰), Mycoplasma (0.7‰) and Methylobacterium (0.6‰) in IAh group. However, the abundance of some beneficial intestinal bacteria decreased, and these genera included Nitratireductor (0.8‰), Enterococcus (0.8‰), Brevundimonas (0.7‰), Lactococcus (0.7‰) and Lactobacillus (0.4‰). Additionally, we investigated the innate immune responses after infection. ROS levels in intestine increased in the early stages after a challenge and recovered subsequently. The mRNA levels of antimicrobial peptide genes lectin, hepcidin and defensin1, were upregulated in the intestine after pathogen infection. These results suggested that the invasion of pathogen could change the intestinal microbiota composition and induce intestinal innate immune responses in zebrafish.

Deciphering transcriptome profile of the yellow catfish (Pelteobagrus fulvidraco) in response to Edwardsiella ictaluri

Edwardsiella ictaluri is one of the most important pathogens posing a serious threat for yellow catfish (Pelteobagrus fulvidraco), a highly valuable fish species of increasing commercial interest in China. Here, a transcriptomic strategy was undertaken to investigate the yellow catfish gene expression profile against infection by the bacterial pathogen E. ictaluri. Comparison of the transcriptome profiles between the infected and uninfected samples showed that a massive gene expression change occurred in yellow catfish following bacterial exposure. A total of 5527 differentially expressed genes (DEGs) were detected, of which 2265 showed up-regulation and 3262 down-regulation. Gene set enrichment analysis revealed the presence of canonical pathways directly linked to innate and adaptive immune response, such as pattern recognition receptor (PRR) signaling pathways, complement and coagulation cascades, as well as T-cell receptor (TCR) and B-cell receptor (BCR) signaling pathways. Additionally, 47,526 putative EST-liked simple sequence repeats (SSRs) markers were retrieved for use in genetic studies. This study establishes the first molecular clues to understand the potential mechanisms of yellow catfish resistance to E. ictaluri, thus enabling future efforts on disease control programs in this valuable aquaculture species.

Transcriptome analysis of yellow catfish (Pelteobagrus fulvidraco) liver challenged with polyriboinosinic polyribocytidylic acid (poly I:C)

Yellow catfish (Pelteobagrus fulvidraco) is one of the most important economic freshwater species in China. However, infection by bacterial pathogenic diseases has caused high mortality and great economic loss in aquaculture. It is necessary for disease control to know more about the P. fulvidraco immune system and its related genes in response to bacterial or viral infections. In this study, the transcriptomic profiles of liver from P. fulvidraco stimulated by polyriboinosinic polyribocytidylic acid (poly I:C) was analyzed using high-throughput sequencing method. After assembly and annotation, total 67,447 unigenes were acquired, with an average length of 1091 bp. Under the infection of poly I:C, 522 differentially expressed genes (DEGs) were identified, including 307 up-regulated genes and 215 down-regulated genes. To further investigate the immune-related DEGs, Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment were performed. The result of GO enrichment indicated gene response to external stimulus, regulation of response to stimulus, cellular response to stimulus, immune response and immune system progress. Significant KEGG enrichment analysis identified major immune related pathways. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis revealed that 13 immune response genes were identified to be up-regulated after 12 h of poly I:C stimulation compared to controls. Taken together, the results of our study are beneficial for better understanding of the immune system and defense mechanisms of yellow catfish in response to poly I:C infection.

Molecular Characterisation of a Novel Isoform of Hepatic Antimicrobial Peptide, Hepcidin (Le-Hepc), from Leiognathus equulus and Analysis of Its Functional Properties In Silico

Hepcidin represents a family of cysteine-rich antimicrobial peptides that are mainly expressed in the liver of living organisms. In this study, we have identified and characterised a novel isoform of hepcidin from the common pony fish, Leiognathus equulus (Le-Hepc). A 261-bp fragment cDNA coding for 86 amino acids was obtained. Homologous analysis showed that Le-Hepc belongs to the hepcidin super family and shares sequence identity with other known fish pre-propeptide hepcidin sequences. The ORF encodes for a 24-amino acid (aa) signal peptide coupled to a 36-aa prodomain followed by a 26-aa mature peptide. The mature peptide region has a calculated molecular weight of 2.73 kDa, a net positive charge of +2 and a theoretical pI of 8.23. Phylogenetic analysis of Le-Hepc showed a strong relationship with other fish hepcidin sequences and clustered into HAMP2 group hepcidins. Secondary structural analysis indicated that Le-Hepc mature peptide contains two antiparallel β-sheets strengthened by four disulphide bonds formed by eight conserved cysteine residues. The physicochemical properties of the peptide and its structural parameters are in agreement with characteristic features of an antimicrobial peptide. This is the first report of an antimicrobial peptide from the common pony fish, L. equulus.