Anti-lipopolysaccharide factors from the black tiger shrimp, Penaeus monodon, are encoded by two genomic loci

Host Defense Proteins and Peptides with Lipopolysaccharide-Binding Activity from Marine Invertebrates and Their Therapeutic Potential in Gram-Negative Sepsis

Sepsis is a life-threatening complication of an infectious process that results from the excessive and uncontrolled activation of the host's pro-inflammatory immune response to a pathogen. Lipopolysaccharide (LPS), also known as endotoxin, which is a major component of Gram-negative bacteria's outer membrane, plays a key role in the development of Gram-negative sepsis and septic shock in humans. To date, no specific and effective drug against sepsis has been developed. This review summarizes data on LPS-binding proteins from marine invertebrates (ILBPs) that inhibit LPS toxic effects and are of interest as potential drugs for sepsis treatment. The structure, physicochemical properties, antimicrobial, and LPS-binding/neutralizing activity of these proteins and their synthetic analogs are considered in detail. Problems that arise during clinical trials of potential anti-endotoxic drugs are discussed.

Antimicrobial Spectrum of Activity and Mechanism of Action of Linear Alpha-Helical Peptides Inspired by Shrimp Anti-Lipopolysaccharide Factors

Shrimp antilipopolysaccharide factors (ALFs) form a multifunctional and diverse family of antimicrobial host defense peptides (AMPs) composed of seven members (groups A to G), which differ in terms of their primary structure and biochemical properties. They are amphipathic peptides with two conserved cysteine residues stabilizing a central β-hairpin that is understood to be the core region for their biological activities. In this study, we synthetized three linear (cysteine-free) peptides based on the amino acid sequence of the central β-hairpin of the newly identified shrimp (Litopenaeus vannamei) ALFs from groups E to G. Unlike whole mature ALFs, the ALF-derived peptides exhibited an α-helix secondary structure. In vitro assays revealed that the synthetic peptides display a broad spectrum of activity against both Gram-positive and Gram-negative bacteria and fungi but not against the protozoan parasites Trypanosoma cruzi and Leishmania (L.) infantum. Remarkably, they displayed synergistic effects and showed the ability to permeabilize bacterial membranes, a mechanism of action of classical AMPs. Having shown low cytotoxicity to THP-1 human cells and being active against clinical multiresistant bacterial isolates, these nature-inspired peptides represent an interesting class of bioactive molecules with biotechnological potential for the development of novel therapeutics in medical sciences.

ERK is involved in the regulation of CpG ODN 2395 on the expression levels of anti-lipopolysaccharide factors in Chinese mitten crab, Eriocheir sinensis

CpG oligodeoxynucleotides (ODN), as an effective adjuvant or immunopotentiator, activate the immune system and induce various immune responses. Recently, it has also been reported that high dose of CpG ODN can lead to immunosuppression. However, the underlying mechanism of CpG ODN-mediated immune response remains largely unknown in invertebrates. In the present study, the role of ERK in regulating expression levels of anti-lipopolysaccharide factors (ALFs) induced by different doses of CpG ODN 2395 was analyzed in Chinese mitten crab, Eriocheir sinensis. The mRNA expression levels of EsALFs (EsALF1, EsALF2 and EsALF3) and EsERK in haemocytes were observed to increase from 6 h to 48 h post low doses of CpG ODN 2395 (0.5 μg and 2.5 μg) stimulation, while they were suppressed after high dose of CpG ODN 2395 (12.5 μg) injection. Meanwhile, the phosphorylation levels of ERK in haemocytes were significantly promoted after low doses of CpG ODN 2395 injection, and a reduce level of ERK phosphorylation was observed after high dose of CpG ODN 2395 injection. Further investigation showed that the expression levels of EsALFs induced by CpG ODN 2395 were markedly down-regulated after knocking down the expression of EsERK. Similarly, the EsALFs mRNA expression were also inhibited post different doses of CpG ODN 2395 stimulation in PD98059 (ERK inhibitor) injection crabs. These results collectively suggest that ERK is involved in regulating the expression level of EsALFs induced by different dose of CpG ODN 2395 in Chinese mitten crab, which contribute to the understanding of the regulation of CpG ODN involving in immune response in crustaceans.

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

Expression of Anti-Lipopolysaccharide Factor Isoform 3 in Chlamydomonas reinhardtii Showing High Antimicrobial Activity

Antimicrobial peptides are a class of proteins with antibacterial functions. In this study, the anti-lipopolysaccharide factor isoform 3 gene (ALFPm3), encoding an antimicrobial peptide from Penaeus monodon with a super activity was expressed in Chlamydomonas reinhardtii, which would develop a microalga strain that can be used for the antimicrobial peptide production. To construct the expression cluster, namely pH2A-Pm3, the codon optimized ALFPm3 gene was fused with the ble reporter by 2A peptide and inserted into pH124 vector. The glass-bead method was performed to transform pH2A-Pm3 into C. reinhardtii CC-849. In addition to 8 μg/mL zeocin resistance selection, the C. reinhardtii transformants were further confirmed by genomic PCR and RT-PCR. Western blot analysis showed that the C. reinhardtii-derived ALFPm3 (cALFPm3) was successfully expressed in C. reinhardtii transformants and accounted for 0.35% of the total soluble protein (TSP). Furthermore, the results of antibacterial assay revealed that the cALFPm3 could significantly inhibit the growth of a variety of bacteria, including both Gram-negative bacteria and Gram-positive bacteria at a concentration of 0.77 μM. Especially, the inhibition could last longer than 24 h, which performed better than ampicillin. Hence, this study successfully developed a transgenic C. reinhardtii strain, which can produce the active ALFPm3 driven from P. monodon, providing a potential strategy to use C. reinhardtii as the cell factory to produce antimicrobial peptides.

Association between ALFPm3 single nucleotide polymorphism and white spot syndrome virus resistance in black tiger shrimp Penaeus monodon

Here single nucleotide polymorphisms (SNPs) were associated with white spot syndrome virus (WSSV) resistance in black tiger shrimp Penaeus monodon. SNPs were identified by single-strand conformation polymorphism (SSCP) screening and DNA sequencing of shrimp sampled from 3 families (100 shrimp per family) challenged with WSSV. Shrimp that died over the 14 d challenge trial were designated susceptible, with those remaining alive on Day 14 designated resistant. To compare SNPs, 10 samples from the susceptible and resistant groups, each comprising DNA pooled from 3 shrimp, were amplified by polymerase chain reaction (PCR) using primers to 12 selected genes and screened by SSCP. SNPs were only identified in the anti-lipopolysaccharide factor 3 (ALFPm3) gene product. Analysis of complete ALFPm3 gene sequences confirmed the existence of 3 SNPs (g.934C>G, g.1186A>G, and g.1898C>G) that were polymorphic between the susceptible and resistant groups. Further analyses using specific tetra-primer amplification refractory mutation system PCR primer sets associated these 3 SNPS, and particularly the g.1186A>G SNP, with WSSV resistance. This SNP thus has potential for use as a DNA marker to select for WSSV resistance in P. monodon breeding programs.

Anti-lipopolysaccharide Factor from Crucifix Crab Charybdis feriatus, Cf-ALF2: Molecular Cloning and Functional Characterization of the Recombinant Peptide

Antilipopolysaccharide factors (ALFs) are important effectors of innate immunity in crustaceans with broad spectrum antimicrobial activity. Present study deals with the molecular and functional characterization of a 98-amino acid ALF isoform from, crucifix crab, Charybdis feriatus termed as Cf-ALF2. The ALF isoform Cf-ALF2 exhibits characteristic features of an AMP including a cationic net charge of + 9 and a total hydrophobic ratio of 34%. Recombinant peptide rCf-ALF2 showed remarkable antimicrobial activity against Gram-negative and Gram-positive bacteria especially against Staphylococcus aureus (minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 5 µM) and Escherichia coli (MIC 10 µM and MBC 20 µM). Using scanning electron microscopy, bacterial membrane blebbing, disruption, and cell content leakage were observed in peptide treated E. coli. The recombinant peptide was found to be non-hemolytic and non-cytotoxic in NCI-H460 cell line at the highest tested concentration (20 µM). Thus, this study identified a novel isoform of ALF from C. feriatus and revealed the potent antimicrobial property of the recombinant peptide Cf-ALF2 and the future prospects of using the peptide for therapeutic applications in the future.

Functional characterization of NK-lysin in golden pompano Trachinotus ovatus (Linnaeus 1758)

NK-lysin is an important part of the innate immune defence system and plays an important role in resisting the invasion of pathogenic microorganisms. In this study, NK-lysin from golden pompano (Trachinotus ovatus) was characterized and its expression in response to Photobacterium damselae was investigated. The full-length NK-lysin cDNA was 731 bp, which comprised a 5'-UTR of 63 bp, an ORF of 444 bp, and a 3'-UTR of 224 bp, and encoded 147 amino acids; NK-lysin consisted of a conserved saposin B domain and six conserved cysteines that formed three pairs of disulfide bonds. The genomic organization of NK-lysin was also determined and the gene consisted of four introns and five exons. The predicted promoter region of ToNK-lysin contained several putative transcription factor binding sites. Quantitative real-time (qRT-PCR) analysis indicated that ToNK-lysin was ubiquitously expressed in all examined tissues; the highest mRNA levels were observed in the skin, kidney and intestine, while the lowest expression level was detected in the stomach. After P. damselae stimulation, the expression level of NK-lysin mRNA was significantly upregulated in various tissues of golden pompano. In addition, SDS-PAGE showed that the molecular mass of recombinant NK-lysin expressed in pGEX-6P-1 was approximately 37 kDa. The purified recombinant protein showed antibacterial activity against gram-positive and gram-negative bacteria. The results indicate that golden pompano NK-lysin has potential antimicrobial roles in fish innate immunity.

The Anti-lipopolysaccharide Factors in Crustaceans

Anti-lipopolysaccharide factors (ALFs) are a type of antimicrobial peptide (AMP) which show broad-spectrum antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, fungi and viruses. In this chapter, we review the discovery and classification of this kind of antimicrobial peptide in crustaceans. The structure and function, as well as the mechanism of antibacterial and antiviral activities of ALFs will be summarized and discussed. We will then describe the expression and regulation of various ALF genes in different crustacean species. Finally, the application prospects of ALFs in drug development and disease-resistant genetic breeding will be pointed out and discussed. The review will also discuss several key questions such as the systematic classification and expression regulation of the ALF genes, as well as the future application of ALFs and ALF-derived peptides.

Molecular and antimicrobial characterization of a group G anti-lipopolysaccharide factor (ALF) from Penaeus monodon

Anti-lipopolysaccharide factors (ALFs) are important host-defense molecules of crustaceans. They all contain a lipopolysaccharide-binding domain (LBD) and some ALFs exhibit strong antimicrobial activity. In this research, a Group G ALF from Penaeus monodon (ALFPm11) was studied. It is an anionic peptide specifically having a cationic and highly amphipathic LBD, with five positively charged residues separated by aromatic residues. It was abundantly expressed in the hepatopancreas of P. monodon normally but the expression level in other tissues was relatively low or undetectable. However, in the shrimps challenged by Vibrio, expression of ALFPm11 could be detected in all tissues. Chemically synthesized ALFPm11-LBD displayed high inhibitory activity (minimum inhibition concentration≤ 4 μM) against various bacteria, e.g. Exiguobacterium sp. L33, Bacillus sp. T2, and Acinetobacter sp. L32. It also displayed apparent activity in the agar well diffusion assay. Furthermore, it could efficiently induce agglutination of both Gram-positive and Gram-negative bacteria and cause significant membrane permeabilization of the bacteria. As a comparative study, ALFPm11-LBD showed a better or equal antimicrobial function to ALFPm3-LBD which was reported to possess strong antimicrobial activity against Gram-positive, Gram-negative bacteria and fungi. Thus, this research found a new effective ALF in P. monodon and demonstrated its antimicrobial mechanism, suggesting its potential applications in the future.

Genome organization and definition of the Penaeus monodon viral responsive protein 15 (PmVRP15) promoter

The viral responsive protein 15 from the black tiger shrimp Penaeus monodon (PmVRP15) is a highly responsive gene upon white spot syndrome virus (WSSV) challenge. It is identified from hemocyte and important for WSSV trafficking and assembly. However, the knowledge of PmVRP15 gene regulation is limited. In the present study, the genome organization and 5'upstream promoter sequences of PmVRP15 gene were investigated. The PmVRP15 gene was found to contain 4 exons interrupted by 3 introns and the start codon was located in the exon 2. The transcription start site and TATA box were also determined from the 5' upstream sequence. By using the narrow down experiment, the 5' upstream promoter active region was determined to be at the nucleotide positions -525 to +612. Mutagenesis of the putative transcription factor (TF) binding sites revealed that the binding site of interferon regulatory factor (IRF) (-495/-479) was a repressor-binding site whereas those of the octamer transcription factor 1 (Oct-1) (-275/-268) and the nuclear factor of activated T-cells transcription factor (NFAT) (-228/-223) were activator-binding sites. This is the first report on the transcription factors that might play essential roles in modulating the PmVRP15 gene expression. Nevertheless, the underlying regulation mechanism of PmVRP15 gene expression needs further investigation.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Fish pathogen binding to mucins from Atlantic salmon and Arctic char differs in avidity and specificity and is modulated by fluid velocity

Disease outbreaks are limiting factors for an ethical and economically sustainable aquaculture industry. The first point of contact between a pathogen and a host occurs in the mucus, which covers the epithelial surfaces of the skin, gills and gastrointestinal tract. Increased knowledge on host-pathogen interactions at these primary barriers may contribute to development of disease prevention strategies. The mucus layer is built of highly glycosylated mucins, and mucin glycosylation differs between these epithelial sites. We have previously shown that A. salmonicida binds to Atlantic salmon mucins. Here we demonstrate binding of four additional bacteria, A. hydrophila, V. harveyi, M. viscosa and Y. ruckeri, to mucins from Atlantic salmon and Arctic char. No specific binding could be observed for V. salmonicida to any of the mucin groups. Mucin binding avidity was highest for A. hydrophila and A. salmonicida, followed by V. harveyi, M. viscosa and Y. ruckeri in decreasing order. Four of the pathogens showed highest binding to either gills or intestinal mucins, whereas none of the pathogens had preference for binding to skin mucins. Fluid velocity enhanced binding of intestinal mucins to A. hydrophila and A. salmonicida at 1.5 and 2 cm/s, whereas a velocity of 2 cm/s for skin mucins increased binding of A. salmonicida and decreased binding of A. hydrophila. Binding avidity, specificity and the effect of fluid velocity on binding thus differ between salmonid pathogens and with mucin origin. The results are in line with a model where the short skin mucin glycans contribute to contact with pathogens whereas pathogen binding to mucins with complex glycans aid the removal of pathogens from internal epithelial surfaces.

An MBT domain containing anti-lipopolysaccharide factor (PtALF8) from Portunus trituberculatus is involved in immune response to bacterial challenge

Anti-lipopolysaccharide factors are effective antimicrobial peptides that can bind and neutralize lipopolysaccharide (LPS). In the present study, a new sequence encoding for ALF (designated as PtALF8) was cloned by suppression subtractive hybridization method using ovary of swimming crab Portunus trituberculatus as material. The full-length cDNA of PtALF8 consisted of 531 bp with an ORF of 348 bp encoding a peptide of 115 amino acids containing a putative signal peptide of 19 amino acids. The mature PtALF8 had a predicted molecular weight (MW) of 11.28 kDa and theoretical isoelectricpoint (pI) of 5.11. The PtALF8 contains an MBT domain which was not found in the other 7 isoforms of ALF reported in P. trituberculatus. Unlike most ALFs expressed in hemocytes, PtALF8 transcript was predominantly detected in hepatopancreas. After challenge with Vibrio alginolyticus, the temporal expression level of PtALF8 transcript in hemocytes reached the highest level at 3 h, then decreased to the lowest level at 24 h, and started to increase at 48 h. The recombinant protein showed antimicrobial and bactericidal activity against several bacteria, such as Gram-positive bacteria, Staphylococcus aureus, Micrococcus luteus and Gram-negative bacteria, V. alginolyticus, indicated that the PtALF8 isoform might play protective function against invading bacteria in P. trituberculatus.

Marine actinomycetes as bioremediators in Penaeus monodon rearing system

Actinomycetes (277 Nos) isolated from marine environment and shrimp culture pond sediments were tested for hydrolytic enzyme production and biogranulation property. Potential isolates were screened for their efficacy in bioremediation of shrimp culture system. Based on the BOD reduction efficiency and water quality parameters, five actinomycete isolates viz., Streptomyces coelicoflavus (A6), Streptomyces diastaticus (A44), Nocardiopsis alba (A55), Streptomyces parvus (A56) and Streptomyces champavatii (R32) were subjected for tertiary screening in Penaeus monodon larval rearing system and the animals were challenged with white spot syndrome virus (WSSV). The bioremediating effect of actinomycete treatments were assessed by analysing the expression profile of five antimicrobial peptide (AMP) genes viz., anti-lipopolysaccharide factor (ALF), crustin-2, crustin-3, penaeidin-3 and penaeidin-5 and eight immune genes viz., alpha-2-macroglobulin (α-2-M), astakine, glutathione-S-transferase, haemocyanin, peroxinectin, pmCathepsinC, prophenol oxidase (proPO) and Rab-7. Expression of eight WSSV genes viz., DNA polymerase, endonuclease, protein kinase, immediate early gene, latency related gene, ribonucleotide reductase, thymidine kinase and VP28 were also analyzed to detect the presence and intensity of viral infection in the experimental animals post-challenge. Theapplication of consortia (1 g/5 L water) yields better results in terms of significant reduction in BOD of shrimp rearing system showing the bioremediation potential of the marine actinomycete strains. The application of marine actinomycetes viz., Streptomyces coelicoflavus (A6), Streptomyces diastaticus (A44), Nocardiopsis alba (A55), Streptomyces parvus (A56) and Streptomyces champavatii (R32) in granulated form were found to be potential bioremediators in shrimp rearing system.

Regulation of antilipopolysaccharide factors, ALFPm3 and ALFPm6, in Penaeus monodon

ALFPm6, a member of antimicrobial peptide in the antilipopolysaccharide factor (ALF) family from Penaeus monodon, plays important roles in shrimp immunity against pathogens. However, its antimicrobial activity and underlying mechanism have not been reported. The synthetic cyclic ALFPm6#29–52 peptide (cALFPm6#29–52) corresponding to the ALFPm6 LPS-binding domain can agglutinate and exhibited bacterial killing activity toward a Gram-negative bacterium, Escherichia coli 363 and Gram-positive bacteria, Bacillus megaterium, Aerococcus viridans, and Micrococcus luteus, with MIC values of 25–50 μM. Specifically, ALFPm6 and ALFPm3, the most abundant ALF isoforms, are different in terms of gene expression patterns upon pathogen infections. Herein, the regulation of ALFPm3 and ALFPm6 gene expression was studied. The 5′-upstream and promoter sequences were identified and the putative transcription factor (TF)-binding sites were predicted. The narrow down assay indicated that the ALFPm3 promoter and partial promoter of the ALFPm6 active regions were located at nucleotide positions (−814/+302) and (−282/+85), respectively. Mutagenesis of selected TF-binding sites revealed that Rel/NF-κB (−280/−270) of ALFPm3 and C/EBPβ (−88/−78) and Sp1 (−249/−238) sites of ALFPm6 were the activator-binding sites. Knockdown of the PmMyD88 and PmRelish genes in V. harveyi-infected shrimp suggested that the ALFPm3 gene was regulated by Toll and IMD pathways, while the ALFPm6 gene was regulated by the Toll pathway.

A novel anti-lipopolysaccharide factor SpALF6 in mud crab Scylla paramamosain exhibiting different antimicrobial activity from its single amino acid mutant

In crustaceans, anti-lipopolysaccharide factors (ALFs) are important immune effectors that have sequence diversity and exhibit broad antimicrobial activities. In this study, we characterized a novel ALF homolog SpALF6 from mud crab Scylla paramamosain and its variant SpALF6-V, which was generated by mutations of two amino acids (H46 to R and A110 to P) due to the presence of two single nucleotide polymorphisms (SNPs). SpALF6 was an anionic peptide with isoelectric point (pI) 6.79, whereas SpALF6-V was a cationic protein with pI 7.98. These two proteins shared a common lipopolysaccharide (LPS)-binding domain (LBD) with pI 6.05. SpALF6 was expressed mainly in hemocytes and up-regulated by Vibrio parahaemolyticus or Staphylococcus aureus challenge, indicating that SpALF6 may participate in the antibacterial immune responses. To investigate the likely functional differences between SpALF6 and SpALF6-V and elucidate the underlying mechanisms, a single amino acid mutant SpALF6-M (from H46 to R, outside but very close to LBD), which had the same pI as SpALF6-V, was harvested by a fusion PCR. Then, both SpALF6 and SpALF6-M were overexpressed and purified to test antimicrobial activity and binding activity to microbial cells or polysaccharides. SpALF6-M exhibited more potent antimicrobial and cell-binding activity on Gram-positive bacteria and fungi than SpALF6. Furthermore, SpALF6-M possessed stronger lipoteichoic acid (LTA)-binding activity than SpALF6, demonstrating that this particular positively charged amino acid outside but close to LBD contributed to the increase in SpALF6-M antibacterial activity. In addition, SpALF6 LBD peptide and its biotin-labeled form were synthesized in this study. Results showed that this anionic LBD peptide itself did not exhibit any significant antimicrobial activity against 10 kinds of microorganisms but it possessed strong binding activity to LPS, LTA, and peptidoglycan. These findings suggested that this anionic LBD was still an important active center and required collaboration with some particular positively charged amino acids outside LBD to exhibit antibacterial activity. Thus, SpALF6-M antimicrobial activity was increased by the mutation of H46 to R instead of A110 to P, which did not change the protein charge, suggesting that SpALF6-V may have more potent antimicrobial activity than SpALF6 and play more important roles in antibacterial immunity. This study provided a new insight into the mechanisms of how ALF amino acid sequence diversity resulted in their functional divergence.

Two White Spot Syndrome Virus MicroRNAs Target the Dorsal Gene To Promote Virus Infection in Marsupenaeus japonicus Shrimp

In eukaryotes, microRNAs (miRNAs) serve as regulators of many biological processes, including virus infection. An miRNA can generally target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs has not yet been extensively explored during virus infection. This study found that the Spaztle (Spz)-Toll-Dorsal-antilipopolysaccharide factor (ALF) signaling pathway plays a very important role in antiviral immunity against invasion of white spot syndrome virus (WSSV) in shrimp (Marsupenaeus japonicus). Dorsal, the central gene in the Toll pathway, was targeted by two viral miRNAs (WSSV-miR-N13 and WSSV-miR-N23) during WSSV infection. The regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study contributes novel insights into the viral miRNA-mediated Toll signaling pathway during the virus-host interaction.IMPORTANCE An miRNA can target diverse genes during virus-host interactions. However, the regulation of gene expression by multiple miRNAs during virus infection has not yet been extensively explored. The results of this study indicated that the shrimp Dorsal gene, the central gene in the Toll pathway, was targeted by two viral miRNAs during infection with white spot syndrome virus. Regulation of Dorsal expression by viral miRNAs suppressed the Spz-Toll-Dorsal-ALF signaling pathway in shrimp in vivo, leading to virus infection. Our study provides new insight into the viral miRNA-mediated Toll signaling pathway in virus-host interactions.

Newly identified PcToll4 regulates antimicrobial peptide expression in intestine of red swamp crayfish Procambarus clarkii

Tolls or Toll-like receptors (TLRs) have an essential role in initiating innate immune responses against pathogens. In this study, a novel Toll gene, PcToll4, was first identified from the intestinal transcriptome of the freshwater crayfish, Procambarus clarkii. The PcToll4 cDNA is 4849bp long with a 3036bp open reading frame that encodes a 1011-amino acid protein. PcToll4 contains a signal peptide, 13 LRR domains, 3 LRR TYP domains, 2 LRR CT domains, an LRR NT domain, a transmembrane region, and a TIR domain. Quantitative RT-PCR analysis revealed that PcToll4 mRNA was detected in all tested tissues, and the expression of PcToll4 in the intestine was significantly upregulated after white spot syndrome virus (WSSV) challenge. Overexpression of PcToll4 in Drosophila Schneider 2 (S2) cells activates the antimicrobial peptides (AMPs) of Drosophila, including metchnikowin, drosomycin, attacin A, and shrimp Penaeidin-4. Results of RNA interference by siRNA also showed that PcToll4 regulates the expressions of 5 anti-lipopolysaccharide factors (ALFs) in the intestine of crayfish. Our findings suggest that PcToll4 is important for the innate immune responses of P. clarkii because this gene regulates the expressions of AMPs against WSSV.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) participates in anti-lipopolysaccharide factors (ALFs) gene expression in mud crab

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is a key cytoplasm signal adaptor that mediates signals activated by tumor necrosis factor receptor (TNFR) superfamily and the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. The full-length 2492 bp TRAF6 (Sp-TRAF6) from Scylla paramamosain contains 1800 bp of open reading frame (ORF) encoding 598 amino acids, including an N-terminal RING-type zinc finger, two TRAF-type zinc fingers and a conserved C-terminal meprin and TRAF homology (MATH) domain. Multiple alignment analysis shows that the putative amino acid sequence of Sp-TRAf6 has highest identity of 88% with Pt-TRAF6 from Portunus trituberculatus, while the similarity of Sp-TRAF6 with other crustacean sequences was 54-55%. RT-PCR analysis indicated that Sp-TRAF6 transcripts were predominantly expressed in the hepatopancreas and stomach, whereas it was barely detected in the heart and hemocytes in our study. Moreover, Sp-TRAF6 transcripts were significantly up-regulated after Vibrio parahemolyticus and LPS challenges. RNA interference assay was carried out used by siRNA to investigate the genes expression patterns regulated by Sp-TRAF6. The qRT-PCR results showed that silencing Sp-TRAF6 gene could inhibit SpALF1, SpALF2, SpALF5 and SpALF6 expression in hemocytes, while inhibit SpALF1, SpALF3, SpALF4, SpALF5 and SpALF6 expression in hepatopancreas. Taken together, the acute-phase response to immune challenges and the inhibition of SpALFs gene expression indicate that Sp-TRAF6 plays an important role in host defense against pathogen invasions via regulation of ALF gene expression in S. paramamosain.

Molecular Characterization and Phylogenetic Analysis of Novel Isoform of Anti-lipopolysaccharide Factor from the Mantis Shrimp, Miyakea nepa

Anti-lipopolysaccharide factor (ALF) is a cationic anti-microbial peptide representing humoral defence system exhibiting a diverse spectrum of activity against microbial pathogens, including gram-negative and gram-positive bacteria, fungi, parasites and viruses. In this study, we identified and characterized a novel ALF homologue (MnALF) encoding cDNA sequence from the haemocytes of stomatopod mantis shrimp Miyakea nepa. The deduced peptide of MnALF encoded for a 123-amino acid peptide with a 25-residue signal peptide containing selenocysteine followed by a highly cationic mature peptide comprised of a putative LPS-binding domain flanked by two cysteine residues. BLAST analysis of MnALF showed that it exhibits identity to crustacean and limulid ALFs. The mature peptide of MnALF has a net charge of +7 and predicted molecular weight of 10.998 kDa with a theoretical isoelectric point (pI) of 9.93. Spatial structure of MnALF comprises three α-helices packed against a four-stranded β-sheet of which two were linked by a disulphide bond to form an amphipathic loop similar to the structure of Penaeus monodon, ALF-Pm3. All these features suggest that MnALF could play an imperative role in the innate defence mechanism of M. nepa. To our knowledge, this study accounts for the first report of an anti-microbial peptide from the order stomatopoda.

Transcriptional Profiling of Banana Shrimp Fenneropenaeus merguiensis with Differing Levels of Viral Load

Viral pathogens are of serious concern to the culture of penaeid shrimps worldwide. However, little is known about the molecular response of shrimp to viral infection. Selective breeding has been suggested as an effective long-term strategy to manage viral disease, though more information on gene function is needed to help inform breeding programs. The study of cultured banana shrimp (Fenneropenaeus merguiensis) infected with hepatopancreatic parvo-like virus (HPV) provides a unique opportunity to explore the host response to viral infection independent of challenge testing. To gain insight into the genetic mechanisms underlying resistance to high levels of HPV, we examined hepatopancreas tissue from six full-sib groups of banana shrimp with differing levels of HPV infection for differences in gene expression. A total of 404 differentially expressed genes were identified with 180 being over-expressed and 224 under-expressed among high-HPV full-sib groups. Based on homology analysis, a large proportion of these genes were associated with processes reported to be involved in the immune response of crustaceans, including pattern recognition proteins, antimicrobial peptides, components of the prophenoloxidase system, and antiviral activity. The results indicate shrimp from high-HPV full-sib groups appear to have a lower presence of important immune response elements, yet possess upregulated putative antiviral pathways. Within the differentially expressed genes, over 4000 sequence variants were identified to be exclusive to either the high- or low-HPV full-sib groups. To our knowledge, this is the first report of differential expression analysis using RNA-Seq to explore differences in viral load among high- and low-HPV full-sib groups of cultured shrimp. This research has provided additional insight into our understanding of the mechanisms involved in the response of this shrimp species to a naturally occurring viral pathogen. Sequence variants identified in this study offer an exceptional resource for mining gene-associated markers of HPV resistance.

An intimate link between antimicrobial peptide sequence diversity and binding to essential components of bacterial membranes

Antimicrobial peptides and proteins (AMPs) are widespread in the living kingdom. They are key effectors of defense reactions and mediators of competitions between organisms. They are often cationic and amphiphilic, which favors their interactions with the anionic membranes of microorganisms. Several AMP families do not directly alter membrane integrity but rather target conserved components of the bacterial membranes in a process that provides them with potent and specific antimicrobial activities. Thus, lipopolysaccharides (LPS), lipoteichoic acids (LTA) and the peptidoglycan precursor Lipid II are targeted by a broad series of AMPs. Studying the functional diversity of immune effectors tells us about the essential residues involved in AMP mechanism of action. Marine invertebrates have been found to produce a remarkable diversity of AMPs. Molluscan defensins and crustacean anti-LPS factors (ALF) are diverse in terms of amino acid sequence and show contrasted phenotypes in terms of antimicrobial activity. Their activity is directed essentially against Gram-positive or Gram-negative bacteria due to their specific interactions with Lipid II or Lipid A, respectively. Through those interesting examples, we discuss here how sequence diversity generated throughout evolution informs us on residues required for essential molecular interaction at the bacterial membranes and subsequent antibacterial activity. Through the analysis of molecular variants having lost antibacterial activity or shaped novel functions, we also discuss the molecular bases of functional divergence in AMPs. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Identification of five anti-lipopolysaccharide factors in oriental river prawn, Macrobrachium nipponense

Anti-lipopolysaccharide factors (ALFs) are a group of antimicrobial peptides (AMPs) with broad-spectrum antimicrobial activities and antiviral activities mainly found in crustaceans and horseshoe crabs. In the present study, we identified 5 ALF expression sequence tags (ESTs) through analysis of the established M. nipponense transcriptome, and cloned their full-length cDNA sequences using rapid amplification of cDNA ends (RACE) method. The 5 ALFs were designated as MnALF1-5, and all of them showed high similarity with their Macrobrachium rosenbergii homologs in the phylogenetic analyses, especially in LPS binding domains. In healthy adult prawns, we found the highest expression of MnALF2 and MnALF4 in haemocytes, and the highest expression of MnALF4 and MnALF3 in intestine. Some isoforms of MnALF were down-regulated but the majority was up-regulated in different prawn tissues upon Aeromonas hydrophila challenge. To conform the expected antimicrobial activities harbored in MnALFs' LPS binding domains, we used a synthesized peptide cMnALF24 that corresponds to the LPS binding domain of MnALF2 as a representative molecule for the antibacterial activity test, and found that cMnALF24 possessed strong and broad-spectrum antibacterial activity against Gram positive and Gram negative bacteria, but no inhibition activity against fungi; Meanwhile, in the hemolytic test, cMnALF24 showed weak hemolysis activities (around 10%) to the rabbit red blood cells at concentrations of 0.67-33.50 μM. This study provides insights into understanding the antibacterial function of ALFs in the innate immunity of freshwater prawn, and reports a peptide that can be a potential drug candidate with good efficacy against bacterial infection and low toxicity to host cells.

Sequence diversity and evolution of antimicrobial peptides in invertebrates

Antimicrobial peptides (AMPs) are evolutionarily ancient molecules that act as the key components in the invertebrate innate immunity against invading pathogens. Several AMPs have been identified and characterized in invertebrates, and found to display considerable diversity in their amino acid sequence, structure and biological activity. AMP genes appear to have rapidly evolved, which might have arisen from the co-evolutionary arms race between host and pathogens, and enabled organisms to survive in different microbial environments. Here, the sequence diversity of invertebrate AMPs (defensins, cecropins, crustins and anti-lipopolysaccharide factors) are presented to provide a better understanding of the evolution pattern of these peptides that play a major role in host defense mechanisms.

A new group of anti-lipopolysaccharide factors from Marsupenaeus japonicus functions in antibacterial response

Anti-lipopolysaccharide factors (ALFs) are a group of critical effector molecules with a broad spectrum of antimicrobial activities in crustaceans. Four groups of ALFs (A, B, C, and D) have been identified in peneaid shrimp. In the study, we identified a new group of ALFs (designated as MjALF-E) from Marsupenaeus japonicus. This new group (group E) included MjALF-E1 and E2. MjALF-E1 was highly expressed in hemocytes, heart, and intestine, whereas E2 was highly expressed in gills, stomach, and intestine. Expressions of both MjALF-E1 and E2 were upregulated by bacterial challenge. Synthesized LPS-binding domain peptides of MjALF-E1 and E2 strongly bind to bacterial cell wall components lipopolysaccharide (LPS) and peptidoglycan (PGN). The recombinant rMjALF-E2 showed relatively weak binding activity to LPS and PGN. Both synthesized peptides and rMjALF-E2 exhibited antimicrobial activity against Gram-negative bacteria, whereas rMjALF-E2 could promote the clearance of bacteria in vivo. After knockdown of MjALF-E2 and infection with Vibrio anguillarum, shrimp showed high and rapid mortality compared with GFPi shrimp. These results suggest that MjALF-Es serves a protective function against bacterial infection in shrimp.

Characterization of a novel anti-lipopolysaccharide factor isoform (SpALF5) in mud crab, Scylla paramamosain

Anti-lipopolysaccharide factors (ALFs), the potential antimicrobial peptides that bind and neutralize lipopolysaccharide (LPS), are common effectors of innate immunity in crustaceans. In this study, a novel isoform of ALFs (SpALF5) was isolated from the hemocytes of mud crab Scylla paramamosain. The full-length 975bp SpALF5 contains a 375bp open reading frame (ORF) encoding 125 amino acids. Although SpALF5 exhibits a low degree of nucleotide homology with other reported ALFs, it contains the conserved amino acid sequence with a signal peptide and a LPS-binding domain including two conservative cysteine residues. The genomic organization of SpALF5 consists of four exons and three introns, with each intron containing one or more tandem repeats. Unlike most of ALFs mainly distributed in crab hemocytes, SpALF5 transcript was predominantly observed in the brain, muscle and skin, while barely detected in the hemocytes in our study. In situ hybridization assay also showed that SpALF5 mRNA was localized in brain, muscle and skin tissues of mud crab. Further, SpALF5 transcript was significantly up-regulated after challenge with LPS, polyinosinic polycytidylic acid (PolyI:C) (with the except of that in brain), Vibrio parahemolyticus or white spot syndrome virus (WSSV). The recombinant SpALF5 protein showed a varying degree of binding activity towards bacteria and fungus. Moreover, in vitro, the recombinant SpALF5 revealed a strong antimicrobial activity against Gram-negative bacteria (V. parahemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) and fungus (Sacchromyces cerevisiae), but could only inhibited the growth of some Gram-positive bacteria like Staphylococcus aureus. The results suggest that SpALF5 is a potent immune protector and plays an important role in immune defense against invading pathogens in S. paramamosain.

Role of evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) in the antibacterial immunity of Marsupenaeus japonicus

The Toll/Toll-like receptor (TLR) signaling pathway has an important role in the innate immunity of animals. Evolutionarily conserved signaling intermediate in Toll pathways (ECSIT) is a protein that functions as an adaptor protein for the Toll/TLR and bone morphogenetic protein signaling pathways. ECSIT is also a key component in the macrophage bactericidal activity of mammals. However, the function of ECSIT in crustaceans remains unclear. In this study, we cloned and identified a functional ECSIT homologue, MjECSIT 1, from kuruma shrimp Marsupenaeus japonicus. The complementary DNA of MjEcsit 1 is 1442 base pairs long, with an open reading frame of 1221 base pairs that encodes a 407-residue polypeptide. Transcripts of MjEcsit 1 are detected in hemocytes, gills, hepatopancreas, stomach, heart, intestines, testes, and ovaries. Such transcripts are upregulated by Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Vibrio anguillarum) injections. The knockdown of MjEcsit 1 by double-stranded RNA injection increases the sensitivity of M. japonicus to S. aureus challenge and weakens the bacterial clearance ability of M. japonicus in vivo. In addition, suppressing MjEcsit 1 restrains the upregulation of two anti-lipopolysaccharide factors by S. aureus injection. The results indicate that MjECSIT 1 is important in the antibacterial immunity of M. japonicus.

Functional analysis of Fenneropenaeus chinensis anti-lipopolysaccharide factor promoter regulated by lipopolysaccharide and (1,3)-β-D-glucan

Current knowledge on cis-regulatory elements of immune genes of shrimp is poor. In this study, the genomic sequence of the Fenneropenaeus chinensis anti-lipopolysaccharide factor (ALFFc) gene was obtained by using PCR and genome walking techniques, and the promoter was identified. The ALFFc gene contained three exons interrupted by two introns. Immune-related transcription factor binding sites recognized by nuclear factor-kappa B, octamer binding protein 1, GATA binding factor 1 and specificity protein 1 were identified in the regin from +1 to -702. The activity of ALFFc promoter was analyzed in insect sf9 cell lines. The putative promoter sequence of pALF-702 drive the expression of reporter EGFP gene successfully by adding lipopolysaccharide or (1,3)-β-D-glucan, but the shorter promoter sequence pALF-318 is only by (1,3)-β-D-glucan. The results pointed out that these transcription elements might contribute to the differences in promoter of ALFFc. Our results would provide supports for future studies to identify the functional transcription elements in the ALF promoter and to expand our knowledge on regulation of innate immune genes in Chinese shrimp.

The role of biophysical parameters in the antilipopolysaccharide activities of antimicrobial peptides from marine fish

Numerous antimicrobial peptides (AMPs) from marine fish have been identified, isolated and characterized. These peptides act as host defense molecules that exert antimicrobial effects by targeting the lipopolysaccharide (LPS) of Gram-negative bacteria. The LPS-AMP interactions are driven by the biophysical properties of AMPs. In this review, therefore, we will focus on the physiochemical properties of AMPs; that is, the contributions made by their sequences, net charge, hydrophobicity and amphipathicity to their mechanism of action. Moreover, the interactions between LPS and fish AMPs and the structure of fish AMPs with LPS bound will also be discussed. A better understanding of the biophysical properties will be useful in the design of AMPs effective against septic shock and multidrug-resistant bacterial strains, including those that commonly produce wound infections.

SpALF4: a newly identified anti-lipopolysaccharide factor from the mud crab Scylla paramamosain with broad spectrum antimicrobial activity

Anti-lipopolysaccharide factors (ALFs) are antimicrobial peptides with binding and neutralizing activities to lipopolysaccharide (LPS) in crustaceans. This study identified and characterized a novel ALF homolog (SpALF4) from the mud crab Scylla paramamosain. The complete cDNA of SpALF4 had 756 bp with a 381 bp open reading frame encoding a protein with 126 aa. The deduced protein contained a signal peptide and a LPS-binding domain. SpALF4 shared the highest identity with PtALF5 at amino acid level but exhibited low similarity with most of other crustacean ALFs. Furthermore, different from the previously identified three SpALF homologs and most of other ALFs, SpALF4 had a low isoelectric point (pI) for the mature peptide and the LPS-binding domain with the values of 6.93 and 6.74, respectively. These results indicate that SpALF4 may be a unique ALF homolog with special biological function in the mud crab. Similar to the spatial structure of ALFPm3, SpALF4 contains three α-helices packed against a four-strand β-sheet, and an amphipathic loop formed by a disulphide bond between two conserved cysteine residues in LPS-binding domain. SpALF4, mainly distributed in hemocytes, could be upregulated by Vibrio harveyi, Staphylococcus aureus, or white spot syndrome virus. Recombinant SpALF4 could inhibit the growth of Gram-negative bacteria (V. harveyi, Vibrio anguillarum, Vibrio alginolyticus, Aeromonas hydrophila, Pseudomonas putida), Gram-positive bacteria (S. aureus and Bacillus megaterium), and a fungus Candida albicans to varying degrees. Further study showed that it could also bind to all the aforementioned microorganisms except S. aureus. These results demonstrate that SpALF4 is a unique ALF homolog with potent antimicrobial activity against bacteria and fungi. This characteristic suggests SpALF4 plays an essential function in immune defense against pathogen invasion in mud crab.

Identification and expression analysis of differentially expressed genes from shrimp (Penaeus monodon) in response to low salinity stress

Four suppression subtractive hybridization (SSH) cDNA libraries were constructed to identify differentially expressed salinity stress responsive genes of black tiger shrimp, Penaeus monodon exposed to low (3 ppt) salinity conditions. Forward and reverse SSH cDNA libraries were developed from the gill and gut tissues of shrimp and clones having inserts larger than 300 bp were unidirectionally sequenced. Based on the sequence homology search, the identified genes were categorized for their putative functions related to a wide range of biological roles, such as nucleic acid regulation and replication, immune response, energy and metabolism, cell signaling, cellular process, cytoskeleton and membrane structure, stress and osmoregulation. Gene expression levels in response to low salinity conditions at 2 weeks post salinity stress of thirteen selected differentially expressed genes identified from SSH cDNA libraries (14-3-3 like protein, crust in, lysozyme, arginine kinase, Naþ/Kþ-ATPase a-subunit, intracellular fatty acid binding protein, cathepsin B, anti-lipopolysaccharide factor, ferritin, ubiquitin conjugating enzyme E2, calreticulin, innexin 2 and heat shock protein 21) were analyzed by RT-PCR. The highest gene expression levels were observed for Naþ/Kþ-ATPase a-subunit (34.28-folds) in gill tissues, intracellular fatty acid binding protein (13.30-folds) in gut tissues and innexin 2 (14.43-folds) in muscle tissues respectively. The differential and significant levels of gene expression indicate the functional role of these genes in shrimp salinity stress adaptive mechanisms.

Screening of genes regulated by Relish in Chinese shrimp Fenneropenaeus chinensis

Relish is a key NF-κB transcription factor in the innate immunity. Learning the function of Relish in regulating the related genes of shrimp will be helpful to understand the shrimp immunity. In the present study, RNA interference (RNAi) and suppression subtractive hybridization (SSH) techniques were combined together to identify the genes regulated by Relish. A forward SSH library represents the genes whose transcription was regulated by Relish, and the reverse SSH library represents the genes whose transcription was up-regulated after Relish was silenced in shrimp responsive to Vibrio anguillarium (VA) stimulation. In the forward library, 43 unique genes were identified, and in the reverse library, 57 genes were identified. The expression of ten differentially expressed genes, including early cuticle protein5 (ECP5), Toll-like receptor protein (TLRP), antiviral factor (AV), C-type lectin receptor (CLR), thrombospondin (TSP), S-adenosylmethionine synthetase (SAMS), carcinolectin 5b-5 (CL5b-5), QM protein (QMP), heat shock protein 67B2 (HSP67B2), and Thioredoxin-related protein 14 (TRP14) were further confirmed by real-time PCR. The present data provides us a wide view to understand the function of Relish gene in the innate immunity of shrimp.

Functional divergence in shrimp anti-lipopolysaccharide factors (ALFs): from recognition of cell wall components to antimicrobial activity

Antilipopolysaccharide factors (ALFs) have been described as highly cationic polypeptides with a broad spectrum of potent antimicrobial activities. In addition, ALFs have been shown to recognize LPS, a major component of the Gram-negative bacteria cell wall, through conserved amino acid residues exposed in the four-stranded β-sheet of their three dimensional structure. In penaeid shrimp, ALFs form a diverse family of antimicrobial peptides composed by three main variants, classified as ALF Groups A to C. Here, we identified a novel group of ALFs in shrimp (Group D ALFs), which corresponds to anionic polypeptides in which many residues of the LPS binding site are lacking. Both Group B (cationic) and Group D (anionic) shrimp ALFs were produced in a heterologous expression system. Group D ALFs were found to have impaired LPS-binding activities and only limited antimicrobial activity compared to Group B ALFs. Interestingly, all four ALF groups were shown to be simultaneously expressed in an individual shrimp and to follow different patterns of gene expression in response to a microbial infection. Group B was by far the more expressed of the ALF genes. From our results, nucleotide sequence variations in shrimp ALFs result in functional divergence, with significant differences in LPS-binding and antimicrobial activities. To our knowledge, this is the first functional characterization of the sequence diversity found in the ALF family.

A newly identified anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus with broad spectrum antimicrobial activity

Anti-lipopolysaccharide factors (ALFs), exhibiting binding and neutralizing activities to lipopolysaccharide (LPS), are the potent antimicrobial peptides of innate immunity in crustaceans. In this study, a unique isoform of ALF (PtALF6) was identified from eyestalk cDNA library of the swimming crab Portunus trituberculatus. The full-length cDNA of PtALF6 was 669 bp encoding 115 amino acids, relatively short to other known ALFs. The deduced peptide of PtALF6 was conserved; it contained the signal peptide and LPS-binding domain, especially the two conserved cysteine residues at both ends of the domain. Predicted tertiary structures of PtALF6 containing four β-strands and three α-helices were similar to that described in Limulus polyphemus. The genomic fragment of PtALF6 contained three exons separated by two introns. Unlike most ALFs expressed in hemocytes, PtALF6 transcript was predominantly detected in gill with 14.05-fold higher than that in hemocytes. After challenge with Vibrio alginolyticus, the temporal expression level of PtALF6 transcript in hemocytes showed a clear time-dependent response expression pattern with two significant peaks at 12 h and 32 h post-injection. The recombinant PtALF6 protein revealed antimicrobial activity against the test Gram-negative and Gram-positive bacteria, but did not inhibit the growth of fungus Pichia pastoris. These results together indicate that PtALF6 is a potential antimicrobial protein against Gram-negative and Gram-positive bacteria infection, and may play an important role in innate immune response of P. trituberculatus.

Three different anti-lipopolysaccharide factors identified from giant freshwater prawn, Macrobrachium rosenbergii

Anti-lipopolysaccharide factor (ALF) is a type of basic protein and an important antimicrobial peptide that can bind and neutralize lipopolysaccharides (LPS). This protein shows a broad spectrum of antimicrobial activity. In this study, three forms of ALF designated as MrALF5, MrALF6, and MrALF7 were identified from giant freshwater prawn, Macrobrachium rosenbergii. MrALF5, MrALF6, and MrALF7 genes encode 133, 121, and 120 amino acids of the corresponding proteins, respectively. All these ALF proteins contain LPS-binding domain with two conserved cysteine residues. The genomic sequences of MrALF5 and MrALF7 were amplified. The genomic structures of MrALF5 and MrALF7 comprise three exons interrupted by two introns. Phylogenetic analysis showed that MrALF5, MrALF6, and MrALF7 were clustered into clade II. Evolutionary analysis showed that ALF genes from M. rosenbergii may suffer a rapid evolution. MrALF5 was expressed mainly in the hepatopancreas, gills, and heart. MrALF6 was mainly distributed in the intestine and hepatopancreas. The highest expression level of MrALF7 was detected in the hepatopancreas. MrALF6, as well as MrALF7, was downregulated by Escherichia coli challenge, and all three ALF genes were upregulated by Vibrio or white spot syndrome virus challenge. MrALF6 was also upregulated by Staphylococcus aureus challenge. In summary, the three isoforms of ALF genes may participate in the innate immune response against bacteria and virus infecting the giant fresh water prawn.

Molecular cloning, expression pattern and antimicrobial activity of a new isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

A new isoform of anti-lipopolysaccharide factor (PtALF5) was cloned from eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA of PtALF5 was 1045 bp encoding 120 amino acids. PtALF5 shared lower amino acid similarity with other ALFs, yet it contained the conserved LPS-binding domain and was clearly member of the ALF family. The genomic fragment of PtALF5 contained two exons separated by one intron. Several tandem repeats were found in intron. The mRNA transcript of PtALF5 was predominantly expressed in the hemocytes but barely detectable in muscle. After challenge with Vibrio alginolyticus, a main pathogen causing high mortality in P. trituberculatus, the PtALF5 transcript in hemocytes showed a clear time-dependent response expression pattern with obvious decrease at 6 h and significant increase at 24 h. The recombinant PtALF5 protein revealed antimicrobial activity against Gram-negative bacteria V. alginolyticus and Pseudomonas aeruginosa, but did not inhibit the growth of the tested Gram-positive bacteria and fungus. These results together suggest that PtALF5 is a potent antibacterial protein against Gram-negative bacteria infection, and might function as a promising therapeutic agent in disease control of crab aquaculture.

Characterization of two isoforms of antiliopolysacchride factors (Sp-ALFs) from the mud crab Scylla paramamosain

In the previous study of the mud crab (Scylla paramamosain) hemocyte proteins, which interacted with a bacterium, Vibrio parahaemolyticus, a protein known as antilipopolysaccharide factor (Sp-ALF) was isolated in addition to a serine proteinase homolog (Sp-SPH) protein. In the present study, we further reported the characterization of two isoforms of the mud crab ALF - Sp-ALFs genes (designated as Sp-ALF1 and Sp-ALF2, respectively) based on our previous result. The Sp-ALF1 and Sp-ALF2 cDNA contained 1070 bp and 731 bp, respectively, with 123 deduced amino acid residues. Alignment of deduced amino acid sequences showed that Sp-ALFs possessed high identity with other known ALFs from crustaceans and exhibited an overall similarity of 57.7% to those of ALFs compared. Phylogenetic tree analysis revealed a clear group of each species and also suggested that ALFs from Scylla genus and those from Portunus genus were closely related. Tissue distribution analysis in adult crab implied that both Sp-ALF1 and Sp-ALF2 were mainly expressed in hemocytes. The mRNA transcripts were also found in embryo (I, II, III and V), zoea-I and juvenile crab, but were rarely observed in the megalopa stage. To further identify the biological activity of Sp-ALFs, recombinant proteins (rSp-ALFs: designated as rSp-ALF1 and rSp-ALF2, respectively) were obtained by expression in Pichia pastris, and the synthetic peptide fragments (sSp-ALFs: designated as sSp-ALF1 and sSp-ALF2, respectively) including the putative LPS binding loop were also prepared for antimicrobial test. The results indicated that both rSp-ALFs and sSp-ALFs were highly effective against most of the Gram-positive bacteria and Gram-negative bacteria tested. In contrast to cecropin P1, a membrane integrity assay revealed that Sp-ALFs did not affect the Escherichia coli by disruption of membrane integrity. Additionally, the recombinant Sp-ALFs proteins exhibited strong antiviral activity against an important aquaculture pathogen, white spot syndrome virus, in crustaceans. Taken together, these data suggested that Sp-ALFs might play a key role in immune defense against microbial infection in the mud crab S. paramamosain.

A new anti-lipopolysaccharide factor isoform (PtALF4) from the swimming crab Portunus trituberculatus exhibited structural and functional diversity of ALFs

Anti-lipopolysaccharide factors (ALFs) are the potent antimicrobial peptides that can bind and neutralize lipopolysaccharide (LPS). In this study, a new isoform of the ALF homologs (PtALF4) was cloned from eyestalk cDNA library of swimming crab Portunus trituberculatus. PtALF4 shared lower amino acid similarity with other ALFs, yet it contained the conserved LPS-binding domain and was clearly member of the ALF family. The genomic sequence of PtALF4 consisted of three exons interrupted by two introns. Several tandem repeats were found in both introns. Unlike most ALFs expressed in hemocytes, PtALF4 transcript was predominantly detected in eyestalk. After challenge with Vibrio alginolyticus, the temporal expression level of PtALF4 transcript in hemocytes showed a clear time-dependent response expression pattern with two significant peaks. The recombinant proteins of PtALF1, PtALF3 and PtALF4 revealed different antimicrobial activities against bacteria or fungus. These results together suggest that PtALF isoforms might be potent immune effectors to provide multiple protective functions against invading bacteria or fungus in P. trituberculatus.

Gene silencing reveals a crucial role for anti-lipopolysaccharide factors from Penaeus monodon in the protection against microbial infections

Anti-lipopolysaccharide factors (ALFs) are antimicrobial peptides previously identified in various crustaceans. Out of five isoforms identified in Penaeus monodon, ALFPm3 is the best characterized, exhibits antibacterial and antifungal activities and can protect the shrimp from viral infections. Herein, the most recent identified ALFPm, called ALFPm6, is characterized for its potential role in the shrimp's immunity. RNA interference-mediated gene silencing was used to study the function of ALFPm6 in comparison to ALFPm3. Knockdown of ALFPm3 gene led to rapid death with a cumulative shrimp mortality of 86% within 7 days, accompanied by a 12- and 50-fold higher bacterial count after 2 days in the haemolymph and hepatopancreas, respectively, compared to the control shrimp injected with GFP dsRNA. In contrast, gene silencing of ALFPm6 alone had no effect on the shrimp mortality, but led to a significant increase in the cumulative mortality and a faster mortality rate following Vibrio harveyi and white spot syndrome virus (WSSV) infections, respectively. These results support the roles of ALFPm6 and ALFPm3 in the protection of shrimp against microbial infections.

A review of the major penaeid shrimp EST studies and the construction of a shrimp transcriptome database based on the ESTs from four penaeid shrimp

By economic value, shrimp is currently the most important seafood commodity worldwide, and these animals are often the subject of scientific research in shrimp farming countries. High throughput methods, such as expressed sequence tags (ESTs), were originally developed to study human genomics, but they are now available for studying other important organisms, including shrimp. ESTs are short sequences generated by sequencing randomly selected cDNA clones from a cDNA library. This is currently the most efficient and powerful method for providing transcriptomic data for organisms with an uncharacterized genome. This review will summarize the sixteen major shrimp EST studies that have been conducted to date. In addition, we analyzed the EST data downloaded from NCBI dbEST for the four major penaeid shrimp species and constructed a database to host all of these EST data as well as our own analysis results. This database provides the shrimp aquaculture research community with an outline of the shrimp transcriptome as well as a tool for shrimp gene identification.

Cationic antimicrobial peptides in penaeid shrimp

Penaeid shrimp aquaculture has been consistently affected worldwide by devastating diseases that cause a severe loss in production. To fight a variety of harmful microbes in the surrounding environment, particularly at high densities (of which intensive farming represents an extreme example), shrimps have evolved and use a diverse array of antimicrobial peptides (AMPs) as part of an important first-line response of the host defense system. Cationic AMPs in penaeid shrimps composed of penaeidins, crustins, and anti-lipopolysaccharide factors are comprised of multiple classes or isoforms and possess antibacterial and antifungal activities against different strains of bacteria and fungi. Shrimp AMPs are primarily expressed in circulating hemocytes, which is the main site of the immune response, and hemocytes expressing AMPs probably migrate to infection sites to fight against pathogen invasion. Indeed, most AMPs are produced as early as the nauplii developmental stage to protect shrimp larvae from infections. In this review, we discuss the sequence diversity, expression, gene structure, and antimicrobial activities of cationic AMPs in penaeid shrimps. The information available on antimicrobial activities indicates that these shrimp AMPs have potential therapeutic applications in the control of disease problems in aquaculture.

Uncovering the mechanisms of shrimp innate immune response by RNA interference

Because of the importance of shrimp in world aquaculture, there is much interest in understanding their immune system in order to improve their resistance to pathogenic microorganisms. An effective tool in studying genes involved in the immune response in shrimp is RNA interference (RNAi). RNAi, first recognized as an antiviral response against RNA viruses, is a cellular mechanism that is triggered by double-stranded RNAs and results in the degradation of homologous genes. In this review, we describe the current studies of genes in shrimp that employed RNAi technology to elucidate or confirm their functions. We also review the potential of RNAi to elicit antiviral response in shrimp.

Multiple isoforms of immune-related genes from hemocytes and eyestalk cDNA libraries of swimming crab Portunus trituberculatus

Expressed sequence tags (ESTs) analysis has been shown to be an efficient approach not only for gene discovery, but also for gene expression profiles performance. Two full-length enriched cDNA libraries were constructed from hemocytes and eyestalk of Portunus trituberculatus, respectively, and randomly sequenced to collect genomic information and identify genes involved in immune defense response. A total of 99 unigenes including 64 unigenes (6.00% of 1066 unigenes) in hemocytes library and 35 unigens (6.86% of 510 unigenes) in eyestalk library are identified to be immune genes. These genes are categorized into six classes, viz. antimicrobial peptides, redox proteins, melanization related proteins, chaperone proteins, clottable proteins and other immune factors. The content and category of immune genes in eyestalk library indicate eyestalk might have unrecognized role in crab immunity. Five immune genes containing multiple protein isoforms are identified and characterized, including anti-lipopolysaccharide factor (PtALF1-7), crustin (PtCrustin1-3), thioredoxin (PtTrx1-2), clip domain serine proteinase (PtcSP1-5) and kazal-type proteinase inhibitor (PtKPI1-4). Sequence alignment and phylogenetic analysis reveal PtALF1-7 contain two conserved cysteine residues and might be encoded by multiple genomic loci. PtCrustin1-3 share the consensus cysteine motif and are considered as Type I crustins. PtTrx1 possesses the critical structural cysteine residue C⁷³ of Trx-1, while PtTrx2 has the N-terminal mitochondrial translocation signal of Trx-2. Sequence analysis shows PtcSP1-5 contain one clip domain and one partial SP catalytic triad domain. PtKPI1-4 present one typical Kazal domain consisting of six conserved cysteine residues. Some protein isoforms are tissue-specific, which might suggest they have different origins and perform diverse functions. Except PtALF1-3 and PtCrustin1, the other isoformes in this study are firstly identified from P. trituberculatus. Especially, PtTrx2 are firstly identified from crustaceans. Our research will provide useful genomic information of P. trituberculatus and be helpful in understanding the molecular mechanisms of crab immunity.

Differential gene expression profile from haematopoietic tissue stem cells of red claw crayfish, Cherax quadricarinatus, in response to WSSV infection

White spot syndrome virus (WSSV) is one of the most important viral pathogens in crustaceans. During WSSV infection, multiple cell signaling cascades are activated, leading to the generation of antiviral molecules and initiation of programmed cell death of the virus infected cells. To gain novel insight into cell signaling mechanisms employed in WSSV infection, we have used suppression subtractive hybridization (SSH) to elucidate the cellular response to WSSV challenge at the gene level in red claw crayfish haematopoietic tissue (Hpt) stem cell cultures. Red claw crayfish Hpt cells were infected with WSSV for 1h (L1 library) and 12h (L12 library), respectively, after which the cell RNA was prepared for SSH using uninfected cells as drivers. By screening the L1 and L12 forward libraries, we have isolated the differentially expressed genes of crayfish Hpt cells upon WSSV infection. Among these genes, the level of many key molecules showed clearly up-regulated expression, including the genes involved in immune responses, cytoskeletal system, signal transduction molecules, stress, metabolism and homestasis related genes, and unknown genes in both L1 and L12 libraries. Importantly, of the 2123 clones screened, 176 novel genes were found the first time to be up-regulated in WSSV infection in crustaceans. To further confirm the up-regulation of differentially expressed genes, the semi-quantitative RT-PCR were performed to test twenty randomly selected genes, in which eight of the selected genes exhibited clear up-regulation upon WSSV infection in red claw crayfish Hpt cells, including DNA helicase B-like, multiprotein bridging factor 1, apoptosis-linked gene 2 and an unknown gene-L1635 from L1 library; coatomer gamma subunit, gabarap protein gene, tripartite motif-containing 32 and an unknown gene-L12-254 from L2 library, respectively. Taken together, as well as in immune and stress responses are regulated during WSSV infection of crayfish Hpt cells, our results also light the significance of cytoskeletal system, signal transduction and other unknown genes in the regulation of antiviral signals during WSSV infection.

Three isoforms of anti-lipopolysaccharide factor identified from eyestalk cDNA library of swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, can bind and neutralize lipopolysaccharide (LPS) and exhibit broad spectrum antimicrobial activities. In this study, three isoforms of the ALF homologues (PtesALF1-3) were identified from eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA sequences of PtesALF1, 2 and 3 were 1138, 1052 and 1057 bp encoding 92, 108 and 123 amino acids, respectively. PtesALF1-3 contained two conserved cysteine residues and shared high similarity with other reported ALFs. Predicted tertiary structures of PtesALF2 and 3 containing four β-strands and three α-helix were similar to that described in Limulus polyphemus, while PtesALF1 had only one α-helix in its spatial structure. Sequence analysis revealed PtesALF1-3 were encoded by the same genomic locus and generated by alternative splicing of the pre-mRNA. Totally 89 SNPs including 18 in coding region and 71 in noncoding region were detected by direct sequencing of 30 genomic samples. The mRNA expression of PtesALF1 and PtesALF1-3 transcripts was mainly detected in haemocytes but showed different expression pattern in other tissues including hepatopancreas, gill, eyestalk and muscle. After challenge with Vibrio alginolyticus, the temporal expression level of PtesALF1-3 transcripts in haemocytes showed a clear time-dependent response expression pattern with two peaks within the experimental period of 32 h, while PtesALF1 was up-regulated only once with obvious decrease at 6 h and significant increase at 24 h. These results suggest that the PtesALF isoforms have different tissue specificity and might provide multiple protective functions against invading bacteria in P. trituberculatus.