Molecular cloning, genomic organization and functional analysis of an anti-lipopolysaccharide factor from Chinese mitten crab Eriocheir sinensis

A circadian clock protein cryptochrome inhibits the expression of inflammatory cytokines in Chinese mitten crab (Eriocheir sinensis)

Cryptochrome (Cry), as important flavoprotein, plays a key role in regulating the innate immune response, such as the release of inflammatory cytokines. In the present study, a cryptochrome homologue (EsCry) was identified from Chinese mitten crab Eriocheir sinensis, which contained a typical DNA photolyase domain, a FAD binding domain. The transcripts of EsCry were highly expressed at 11:00, and lowest at 3:00 within one day, while those of Interleukin enhancer binding factor (EsILF), Lipopolysaccharide-induced TNF-alpha factor (EsLITAF), Tumor necrosis factor (EsTNF) and Interleukin-16 (EsIL-16) showed a rhythm expression pattern contrary to EsCry. After EsCry was knocked down by dsEsCry injection, mRNA transcripts of Timeless (EsTim), Cycle (EsCyc), Circadian locomotor output cycles kaput (EsClock), Period (EsPer), and EsLITAF, EsTNF, EsILF, EsIL-16, as well as phosphorylation level of Dorsal significantly up-regulated. The transcripts of EsLITAF, EsTNF, EsILF, and EsIL-16 in EsCry-RNAi crabs significantly down-regulated after injection of NF-κB inhibitor. The interactions of EsCyc and EsCry, EsCyc and Dorsal were observed in vitro. These results indicated that EsCry negatively regulated the expression of the cytokine TNF and IL-16 via inhibiting their transcription factor LITAF and ILF through NF-κB signaling pathway, which provide evidences to better understand the circadian regulation mechanism of cytokine production in crabs.

Effects of Prometryn Exposure on Hepatopancreas Oxidative Stress and Intestinal Flora in Eriocheir sinensis (Crustacea: Decapoda)

There is growing evidence that long-term exposure to prometryn (a widely used herbicide) can induce toxicity in bony fish and shrimp. Our previous study demonstrated its 96 h acute toxicity on the crab Eriocheir sinensis. However, studies on whether longer exposure to prometryn with a lower dose induces toxicity in E. sinensis are scarce. Therefore, we conducted a 20 d exposure experiment to investigate its effects on the hepatopancreas and intestine of E. sinensi. Prometryn reduce the activities of antioxidant enzymes, increase the level of lipid peroxidation and cause oxidative stress. Moreover, long-term exposure resulted in immune and detoxification fatigue, while short-term exposure to prometryn could upregulate the expression of genes related to immunity, inflammation and detoxification. Prometryn altered the morphological structure of the hepatopancreas (swollen lumen) and intestine (shorter intestinal villi, thinner muscle layer and thicker peritrophic membrane). In addition, prometryn changed the species composition of the intestinal flora. In particular, Bacteroidota and Proteobacteria showed a dose-dependent decrease accompanied by a dose-dependent increase in Firmicutes at the phylum level. At the genus level, all exposure groups significantly increased the abundance of Zoogloea and a Firmicutes bacterium ZOR0006, but decreased Shewanella abundance. Interestingly, Pearson correlation analysis indicated a potential association between differential flora and hepatopancreatic disorder. Phenotypic abundance analysis indicated that changes in the gut flora decreased the intestinal organ's resistance to stress and increased the potential for opportunistic infection. In summary, our research provides new insights into the prevention and defense strategies in response to external adverse environments and contributes to the sustainable development of E. sinensis culture.

Cloning and expression of two anti-lipopolysaccharide factors in Eriocheir hepuensis under Vibrio alginolyticus-induced stress

Anti-lipopolysaccharide factors (ALFs) are small basic proteins that exhibit broad-spectrum antiviral properties and antibacterial activity. In this research, we cloned and studied two Eriocheir hepuensis ALFs, EhALF2 and EhALF3. The results showed that the open reading frame lengths of EhALF2 and EhALF3 were 363 and 372 bp, encoding 120 and 123 amino acids, respectively. Their sequences both contained an Lipopolysaccharide-binding (LPS) domain and were highly similarity to other crab ALFs. qRT-PCR showed that EhALF2 and EhALF3 were detected in nine examined tissues and were expressed the highest in the haemocytes. After challenge with Vibrio alginolyticus, in the hepatopancreas, the expression levels of EhALF2 and EhALF3 reached the highest levels at 48 and 3 h, respectively. In the heart, the expression levels of the two genes were highest at 12 h. These results indicate that EhALF2 and EhALF3 could participate in the resistance of E. hepuensis to V. alginolyticus stress within a short time. They have potential applications in the study of environmental stress markers and disease-resistance factors in E. hepuensis.

MEK homologue is involved in immune response by regulating antimicrobial peptides expression in Chinese mitten crab Eriocheir sinensis

MEK activates the phosphorylation of downstream molecules involved in various immune responses. In this study, an MEK homologue gene in Chinese mitten crab Eriocheir sinensis (designated as EsMEK) was investigated. EsMEK mRNA was constitutively expressed in all tissues with higher expression in hepatopancreas, hemocytes, and gills. EsMEK protein was mainly localized in the cytoplasm. Lipopolysaccharide (LPS) and Aeromonas hydrophila challenge significantly increased the mRNA levels of EsMEK in hemocytes. In addition, the mRNA expression level of some antimicrobial peptides (AMPs), including EsWAP, EsDWD1, and EsALF decreased significantly due to the inhibition of EsMEK by specific dsRNA in LPS-challenged crabs. Downstream pathway analysis revealed that the phosphorylation of EsERK decreased prominently after EsMEK inhibition. These results suggested that EsMEK played an important role in regulating the expression of antimicrobial peptides in E. sinensis through MEK-ERK pathway.

The potential of antimicrobial peptides isolated from freshwater crayfish species in new drug development: A review

The much-publicised increased resistance of pathogenic bacteria to conventional antibiotics has focused research effort on the characterization of new antimicrobial drugs. In this context, antimicrobial peptides (AMPs) extracted from animals are considered a promising alternative to conventional antibiotics. In recent years, freshwater crayfish species have emerged as an important source of bioactive compounds. In fact, these invertebrates rely on an innate immune system based on cellular responses and on the production of important effectors in the haemolymph, such as AMPs, which are produced and stored in granules in haemocytes and released after stimulation. These effectors are active against both Gram-positive and Gram-negative bacteria. In this review, we summarise the recent progress on AMPs isolated from the several species of freshwater crayfish and their prospects for future pharmaceutical applications to combat infectious agents.

The Elevated Expressions of Anti-lipopolysaccharide Factors After Priming Stimulation Confer Lastingly Humoral Protection in Crab Eriocheir sinensis

Evidence of immune memory in invertebrates (immune priming) has accumulated in various organisms, and both cellular and humoral immune reactions are speculated to be involved in immune priming. However, there is a lack of understanding of the molecular mechanisms involved. In the present study, the protective effect of primed haemolymph was further validated by the increased survival rate of naïve crabs receiving a transfusion of primed haemolymph. By proteomic analysis, there were 474 proteins identified from the primed haemolymph, and most of them were functionally annotated in transport and metabolism classes. A total of 70 proteins were found to be differentially expressed in haemolymph at 12 hours and 7 days after priming stimulation with Aeromonas hydrophila, among which anti-lipopolysaccharide factor 1 (EsALF-1) and 3 (EsALF-3) were identified as the most significant (p < 0.05). After being challenged with A. hydrophila, EsALF-1 and EsALF-3 were highly expressed at both mRNA (in haemocytes) and protein (in haemolymph) levels compared with blank crabs, and the mRNA expressions of components in the EsTLR1-EsMyd88-EsPelle-EsALF pathway also increased significantly (p < 0.05). The EsALF-3 and EsMyd88 were even significantly higher expressed in response to the second A. hydrophila challenge, but their expressions all decreased (p < 0.05) when EsTLR1 was knocked down by RNAi. After the naïve crabs received an injection with the recombinant protein of EsALF-1 (rEsALF-1) or EsALF-3 (rEsALF-3), their survival rate increased significantly (p < 0.05) upon A. hydrophila stimulation. In contrast, the survival rate of the primed crabs reduced significantly (p < 0.05) after they received an injection with the antibody of EsALF-1 or EsALF-3. The enhanced expressions of EsALF-1 and EsALF-3 after A. hydrophilap riming stimulation could sustain for four weeks. All the results suggested that the EsTLR1-mediated productions of EsALF-1 and EsALF-3 in haemolymph played an indispensable role in the month-long humoral immune protection induced by A. hydrophila, which provides solid evidence of immune priming in crabs and a valuable reference for further understanding immune memory in invertebrates.

Transcriptome analysis of immune-related genes in Sesarmops sinensis hepatopancreas in reaction to peptidoglycan challenge

Sesarmops sinensis is a dominant omnivorous crab species, which plays an important ecological function in salt marsh ecosystems. To better understand its immune system and immune related genes under pathogen infection, the transcriptome was analyzed by comparing the data of S. sinensis hepatopancreas stimulated by PBS and PGN. A set of assembly and annotation identified 39,039 unigenes with an average length of 1105 bp, obtaining 1300 differentially expressed genes (DEGs) in all, which included 466 remarkably up-regulated unigenes and 834 remarkably down-regulated unigenes. In addition, based on mensurable real time-polymerase chain reaction and high-throughput sequencing, several immune responsive genes were found to be markedly up-regulated under PGN stimulation. In conclusion, in addition to enriching the existing transcriptome data of S. sinensis, this study also clarified the immune response of S. sinensis to PGN stimulation, which will help us to further understand the crustacean's immune system.

Vitellogenin receptor expression in ovaries controls innate immunity in the Chinese mitten crab (Eriocheir sinensis) by regulating vitellogenin accumulation in the hemolymph

The vitellogenin receptor (Vgr), which is specific for vitellogenin (Vtg), recognises and transports Vtg into the ovaries. Accumulating evidence suggests that Vtg also performs an immune defence function and plays critical roles in innate immunity in oviparous animals. However, whether Vgr is involved in innate immunity in the Chinese mitten crab (Eriocheir sinensis) is unknown. In this study, we obtained a 3009 nucleotide partial cDNA of the E. sinensis vitellogenin receptor gene (Es-vgr) encoding an open reading frame of 1003 amino acid residues. Bioinformatics analysis showed that the domains of Es-vgr were conserved during evolution. Quantitative real-time PCR and western blotting revealed that the highest Es-vgr expression levels occurred in the ovary, and expression was specific. Comparison of the expression levels of Es-vgr and the Vtg gene (Es-vtg1) at different ovary developmental stages suggested that there may be some regulatory relationship between them. Bacterial challenge induced high-level expression of antimicrobial peptide genes and reduced Es-vgr expression in ovaries, resulting in massive accumulation of Vtg in the hemolymph. The survival rate of crabs increased significantly after injection with recombinant Es-vtg1 protein following bacterial infection. Collectively, these results demonstrate that Es-vgr plays critical roles in antimicrobial function by regulating the accumulation of Vtg in the hemolymph.

Immunological and antibiofilm property of haemocyanin purified from grooved tiger shrimp (Penaeus semisulcatus): An in vitro and in silico approach

Haemocyanin (Hc) is a non-specific innate immune protein present in the haemolymph of arthropods and molluscs. In the current study, we characterized the structural and immunological properties of Hc from grooved tiger shrimp, Penaeus semisulcatus. Hc was isolated from the haemolymph of P. semisulcatus by gel filtration column chromatography using Sephadex G-100. High-performance liquid chromatography of the purified Hc emerged as a single peak through a retention time of 3.3 min demonstrating the homogeneity nature of the protein. X-ray diffraction analysis revealed a distinct peak at 31.7° indicating the crystalline character of the purified Hc. Circular dichroism spectra of the purified Hc displayed negative ellipticity bands close to 225 nm and 208 nm representing β-sheet secondary structure. The purified Hc agglutinated sheep RBCs, yeast Saccharomyces cerevisiae and fungal Candida albicans. In addition, the purified Hc displayed antibacterial activity against Gram-positive bacteria (Bacillus thuringiensis and Bacillus pumilis) and Gram-negative bacteria (Vibrio parahaemolyticus and Vibrio alginolyticus) with a minimal inhibitory concentration of 50 μg/ml. Antibiofilm activity revealed the potential of purified Hc to inhibit biofilm formation of both Gram-positive and Gram-negative bacterial pathogens. Furthermore, live/dead staining of biofilms demonstrated the reduced viability of bacterial cells after exposure to the purified Hc. In silico molecular modeling was carried out using the sequence of Hc from SwissProt and molecular docking was performed with the cell surface components found in Gram-positive and Gram-negative bacteria. Overall our study demonstrates the involvement of Hc in the native immune reaction of P. semisulcatus by eliciting pathogen recognition. Thus, Hc could enhance disease resistance against pathogenic infection in shrimp aquaculture.

Research progress in innate immunity of freshwater crustaceans

Invertebrates lack adaptive immunity and innate immunity plays important roles in combating foreign invasive pathogens. Freshwater crustaceans, which are invertebrates, depend completely on their innate immune system. In recent years, many immune-related molecules in freshwater crustaceans, as well as their functions, have been identified. Three main immune signaling pathways, namely, Toll, immune deficiency (IMD), and Janus kinase-signal transducer activator of transcription (JAK/STAT) pathways, were found in freshwater crustaceans. A series of pattern recognition receptors (PRRs), including Toll receptors, lectins, lipopolysaccharide and β-1,3-glucan binding protein, scavenger receptors, Down syndrome cell adhesion molecules, and thioester-containing proteins, were reported. Prophenoloxidase activation system and antimicrobial peptide synthesis are two important immune effector systems. These components are involved in the innate immunity of freshwater crustaceans, and they function in the innate immune defense against invading pathogens. This review mainly summarizes innate immune signaling pathways, PRRs, and effector molecules in freshwater crustaceans.

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.

EsGPCR89 regulates cerebral antimicrobial peptides through hemocytes in Eriocheir sinensis

G protein-coupled receptors (GPCRs) are important transmembrane receptors that participate in diverse physiological processes including metabolism, cell growth and immune processes by transmitting extracellular signals to intracellular effectors. In this study, a gene belonging to the GPCR family was cloned from Eriocheir sinensis and named EsGPCR89. The full-length gene includes an open reading frame (ORF) of 465 amino acid residues, and bioinformatic analysis confirmed the high conservation between species. EsGPCR89 was detected in various tissues of E. sinensis, and was up-regulated in brain following Staphylococcus aureus infection. Expression levels of cerebral antimicrobial peptides (AMPs) were also up-regulated following bacterial challenge, reflecting their function in cerebral immunity. Additionally, EsGPCR89 silencing in hemocytes by RNA interference, down-regulated AMPs in brain after S. aureus infection. Moreover, through Immunisation assay and Polyacrylamide gel electrophoresis (SDS-PAGE) experiments, we could infer that bacterially infected hemocytes released effectors under the regulation of EsGPCR89, thereby activating transcription of cerebral AMPs. These results demonstrate that EsGPCR89 plays important roles in cerebral antimicrobial function via hemocytes.

Rab7 controls innate immunity by regulating phagocytosis and antimicrobial peptide expression in Chinese mitten crab

The Rab family is the most significant subfamily of small GTP-binding proteins. These proteins have widespread intracellular localization and play an important role in many biological processes. Rab7 plays a crucial role in the innate immune system of crustaceans. In the present study, we cloned and characterized Rab7 from Chinese mitten crab (Eriocheir sinensis), designated EsRab7. The full-length of the EsRab7 cDNA sequence is 1,257 bp and contains a 618-bp open reading frame encoding a 205-amino acid polypeptide. Bioinformatics analysis showed that the Rab7 protein was highly conserved during evolution. Quantitative real-time PCR showed the highest tissue expression in muscle, followed by hepatopancreas. EsRab7 was significantly upregulated in hemocytes after stimulation by Gram-positive Staphylococcus aureus or Gram-negative Vibrio parahaemolyticus. Further studies showed that EsRab7 knockdown during bacterial stimulation resulted in decreased bacterial phagocytosis. In addition, EsRab7 regulated the expression of antimicrobial peptides via the Toll signaling pathway. Collectively, these results demonstrate that EsRab7 plays critical roles in antimicrobial function in the Chinese mitten crab.

Hydroxymethylation of protein-encoding genes in the testes involved in precocious puberty of Eriocheir sinensis

To investigate the possible effects of epigenetic modification of testis protein-encoding genes on precocious puberty of Eriocheir sinensis, we used MeDIP-seq and hMeDIP-seq techniques to compare the methylation and hydroxymethylation of 263 E. sinensis protein-encoding genes known in the NCBI database in precocious testes with those in normally developing testes. The results showed that total methylation level of those genes was lower than their total hydroxymethylation level. Moreover, their total hydroxymethylation level in precocious testes was significantly lower than that in normal testes. In addition, no methylated genes had significant difference, but there were 37 different hydroxymethylated genes (DhMGs) in the precocious testes compared to the normal ones. Among the DhMGs, 21 were hypo-hydroxymethylated and 16 were hyper-hydroxymethylated. The hypo-hydroxymethylated DhMGs were associated with development, cell structural and cytoskeletal proteins, and response to stress. However, the hyper-hydroxymethylated DhMGs included immune-related genes, free radicals removement-related genes, protein folding-related genes, and so on. In addition, some DhMGs were hyper-hydroxymethylated while their homologous DhMGs were hypo-hydroxymethylated. The results of a qRT-PCR assay showed that the expression levels of 5 DhMGs randomly chosen presented a positive correlation with their hydroxymethylation levels. It can be seen that hydroxymethylation might regulate the expression of genes and be involved in precocious puberty to cause high mortality of crabs. Therefore, the hydroxymethylation level of DhMGs may be used as an evaluation index with economically meaningful growth and breeding traits.

JAK/STAT signalling regulates antimicrobial activities in Eriocheir sinensis

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling pathway plays a significant role in immune responses to pathogens. In invertebrates, three core components (Domeless, Hopscotch and STAT92E) of the JAK/STAT pathway were first identified in Drosophila melanogaster. In the present study, we report the cloning and characterisation of DOME, JAK and STAT from Eriocheir sinensis. EsDOME, EsJAK and EsSTAT are 1299, 1110 and 794 amino acid proteins encoded by 4200, 3333 and 2385 bp open reading frames, respectively. Bioinformatics analysis revealed that all three share specific domains with corresponding functions. Quantitative real-time PCR showed that all three components were highly expressed in various tissues including the gill, hepatopancreas and hemocytes. Moreover, EsDOME, EsJAK and EsSTAT were upregulated significantly in hemocytes after bacterial challenge. In addition, the JAK/STAT signalling pathway positively regulates antimicrobial peptide expression during the antibacterial immune response. Thus, the JAK/STAT pathway plays a critical role in bacterial immune responses in E. sinensis.

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.

NEDD8-conjugated Cullin4 positive regulates antimicrobial peptides expression in Eriocheir sinensis

The ubiquitin-proteasome system is involved in numerous cellular processes, such as signal transduction, autophagy, cell cycle control, embryogenesis, and regulation of immune response. Neural precursor cell expressed developmentally downregulated 8 (NEDD8) is a ubiquitin-like protein that activates Cullin-RING ligases and modifies substrates via neddylation. However, there is limited information on how neddylation regulates innate immunity in crustaceans. In the present study, we identified the evolutionarily conserved NEDD8 with the ubiquitin homologue domain in the Chinese mitten crab (Eriocheir sinensis), named it EsNEDD8. Then, we analyzed the expression patterns and cellular location of its substrate, EsCullin4. qRT-PCR showed that both EsNEDD8 and EsCullin4 were widely expressed in all the selected tissues, and EsCullin4 was significantly upregulated in hemocytes after bacterial stimulation. Moreover, silencing of EsCullin4 significantly suppressed the expression of antimicrobial peptides (AMPs) in the hemocytes after bacterial stimulation, and inhibition of EsCullin4 neddylation by treatment with the NEDD8-activating enzyme inhibitor MLN4924 significantly inhibited the expression of the AMPs. Thus, the results show that EsNEDD8-modified EsCullin4 could control antimicrobial activities via regulation of AMPs expression in the Chinese mitten crab.

Effects of glycinin and β-conglycinin on growth performance and intestinal health in juvenile Chinese mitten crabs (Eriocheir sinensis)

This study investigates the effects of two soybean antigens (glycinin and β-conglycinin) as an antinutritional substance in the diet on the growth, digestive ability, intestinal health and microbiota of juvenile Chinese mitten crabs (Eriocheir sinensis). The isonitrogenous and isolipidic diets contained two soybean antigens at two levels each (70 and 140 g/kg β-conglycinin, 80 and 160 g/kg glycinin) and a control diet without β-conglycinin or glycinin supplementation, and were used respectively to feed juvenile E. sinensis for seven weeks. Dietary inclusion of either glycinin or β-conglycinin significantly reduced crab survival and weight gain. The crabs fed diets containing soybean antigens had higher malondialdehyde concentrations and lower catalase activities in the intestine than those in the control. The activities of trypsin and amylase in the intestine were suppressed by dietary β-conglycinin and glycinin. Dietary glycinin or β-conglycinin impaired the immunity and morphological structure of intestine, especially the peritrophic membrane. The mRNA expression of constitutive and inducible immune responsive genes (lipopolysaccharide-induced TNF-α factor and interleukin-2 enhancer-binding factor 2) increased while the mRNA expression of the main genes related to the structural integrity peritrophic membrane (peritrophin-like gene and peritrophic 2) significantly decreased in the groups with soybean antigen addition. Soybean antigen could also change the intestinal microbial community. The abundance of pathogenic bacteria (Ochrobactrum, Burkholderia and Pseudomonas) increased significantly in both soybean antigen groups. Although pathogenic bacteria Vibrio were up-regulated in the glycinin group, the abundance of Dysgonomonas that degraded lignocellulose and ameliorated the gut environment decreased in the glycinin group. This study indicates that existence of soybean antigens (glycinin or β-conglycinin) could induce gut inflammation, reshape the community of gut microbiota, and cause digestive dysfunction, ultimately leading to impaired growth in crabs.

Transcriptomic analysis of immune-related genes in the lipopolysaccharide-stimulated hepatopancreas of the mudflat crab Helice tientsinensis

The mudflat crab Helice tientsinensis is one of the most economically important aquaculture species in China. Nevertheless, it is susceptible to various diseases caused by viruses, bacteria and rickettsia-like organisms. A better understanding of the immune system and genes related to the responses to bacterial and viral infection is required. Herein, the hepatopancreas transcriptome of H. tientsinensis was analyzed by comparing control and lipopolysaccharide (LPS)-stimulated RNA-Seq data, yielding 91,885,038 bp and 13.78 Gb of clean reads. Following assembly and annotation, 93,207 unigenes with an average length of 883 bp were identified, of which 31,674 and 13,700 were annotated in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. Following LPS, 4845 differentially expressed genes (DEGs) were identified, of which 2491 and 2354 were up- and down-regulated, respectively. To further investigate immune-related DEGs, KEGG enrichment analysis identified immune response pathways, most notably the peroxisome and Toll-like receptor signaling pathways. Quantitative real time-PCR (qRT-PCR) confirmed the up-regulation of a random selection of DEGs. This systematic transcriptomic analysis of the innate immune pathway in H. tientsinensis expands our understanding of the immune system in crabs.

A class B scavenger receptor from Eriocheir sinensis (EsSR-B1) restricts bacteria proliferation by promoting phagocytosis

Scavenger receptors (SRs) are important pattern recognition receptors (PRRs), which play significant roles in host defense against pathogens by identifying pathogen-associated molecular patterns (PAMPs). In this study, we report the cloning and characterization of a SR from Eriocheir sinensis (EsSR-B1) which is a 500 amino acid protein encoded by a gene comprised of 2726 nucleotides with a 1503 bp open reading frame. The domains of EsSR-B1 were found to be evolutionarily conserved. EsSR-B1 was widely detected in different tissues of E. sinensis and significantly up-regulated in hemocytes after stimulation by Staphyloccocus aureus or Vibrio parahaemolyticus. Recombinant EsSR-B1 protein could bind to bacteria and promote phagocytosis upon bacterial stimulation. Moreover, antimicrobial peptide expression was reduced in EsSR-B1-silenced hemocytes after challenge by S. aureus or V. parahaemolyticus. Thus, EsSR-B1 has a critical role in the binding of bacteria and subsequent promotion of hemocyte phagocytosis.

Vitellogenin regulates antimicrobial responses in Chinese mitten crab, Eriocheir sinensis

Vitellogenin (Vtg) is traditionally regarded as a key supplier of nutrients and energy during the early development of embryos and larvae, but accumulating evidence suggests that Vtg is also involved in innate immune defense. Whether Vtg is involved in innate immunity in Eriocheir sinensis, and its functions, remain largely unknown. In this study, a cDNA representing the vitellogenin1 gene from E. sinensis (Es-vtg1) was cloned. The full-length Es-vtg1 cDNA comprised 7939 nucleotides, encoding an open-reading frame of 2567 amino acid residues. Bioinformatic analysis showed that the domains of Es-Vtg1 have been conserved during evolution. Quantitative real-time PCR and western blotting showed that Es-vtg1 was highly expressed in ovary and hepatopancreas. Moreover, bacteria could induce the high-level expression of Es-Vtg1. Es-Vtg1 plays important roles in immunological defense, including binding to bacteria, inhibiting bacterial proliferation, and regulating the expression of antimicrobial peptides. Collectively, these results demonstrate that Es-Vtg1 plays critical roles in antimicrobial function.

Characterization and antimicrobial evaluation of SpPR-AMP1, a proline-rich antimicrobial peptide from the mud crab Scylla paramamosain

Antimicrobial peptide (AMP) is an important molecule in the innate immune system. Here, we report the cloning and functional studies of proline-rich AMPs (PR-AMPs) from the three species of mud crab: Scylla paramamosain, S. serrata, and the swimming crab Portunus pelagicus. The deduced peptides revealed that they contain the putative signal peptides and encode for mature peptides, which contain sequence architecture similar to a 6.5-kDa proline-rich AMP of the shore crab, Carcinus maenas which showed similarity with the bactenecin7. Tissue distribution analysis indicated that the SpPR-AMP1 was expressed in a wide range of adult tissues, with the highest expression levels in the crab hemocyte. Challenge experiments showed that the levels of SpPR-AMP1 mRNA expression were up-regulated in the hemocyte after peptidoglycan stimulation. To evaluate the biological properties of mature SpPR-AMP1, peptides were chemically synthesized and recombinantly expressed. SpPR-AMP1 showed strong antibacterial activity against both Gram-positive bacteria Micrococcus luteus and Gram-negative bacteria Vibrio harveyi. The results indicate that the SpPR-AMP1 plays a role in crab immunity.

Fatty acid binding protein regulate antimicrobial function via Toll signaling in Chinese mitten crab

Fatty acid binding proteins (FABPs) are members of the lipid binding protein superfamily and play crucial role in fatty acid transport and lipid metabolism. In macrophages, Adipocyte-type FABP is an important mediator of inflammation. However, the immune functions of FABPs in invertebrates are not well understood; here, we obtained the gene structure of Eriocheir sinensis FABP 3 and FABP 9 (EsFABP 3 and EsFABP 9), and compared with EsFABP 10. The mRNA expression profiles show that all three FABPs were significantly up-regulated in hemocytes after being challenged with bacteria. Of the three, EsFABP 3 was the most stable and also the most highly up-regulated. Further studies showed that knockdown of EsFABP 3 led to higher bacterial counts in the hemocyte culture medium and a significant decrease in the mRNA expression of some antimicrobial peptides following bacterial stimulation. Moreover, a subcellular study demonstrated that EsFABP 3 can affect nuclear translocation of the dorsal after Gram-positive bacterial stimulation in hemocytes. These findings support the notion that EsFABP 3 could inhibit bacterial proliferation by regulating antimicrobial peptides expression via the Toll signaling pathway.

Antiviral action of the antimicrobial peptide ALFPm3 from Penaeus monodon against white spot syndrome virus

The anti-lipopolysaccharide factor isoform 3 (ALFPm3), the antimicrobial peptide from Penaeus monodon, possesses antibacterial and antiviral activities. Although the mechanism of action of ALFPm3 against bacteria has been revealed but its antiviral mechanism is still unclear. To further study how the ALFPm3 exhibits antiviral activity against the enveloped virus, white spot syndrome virus (WSSV), the ALFPm3-interacting proteins from WSSV were sought and identified five ALFPm3-interacting proteins, WSSV186, WSSV189, WSSV395, WSSV458, and WSSV471. Only the interaction between ALFPm3 and WSSV189, however, has been confirmed to be involved in anti-WSSV activity of ALFPm3. Herein, the interactions between ALFPm3 and rWSSV186, rWSSV395, rWSSV458, or rWSSV471 were further analyzed and confirmed by in vitro pull-down assay. Western blot analysis and immunoelectron microscopy showed that the uncharacterized proteins, WSSV186 and WSSV471, were nucleocapsid and envelope proteins, respectively. The decrease of shrimp survival after injection the shrimp with mixtures of each rWSSV protein, rALFPm3 and WSSV as compared to those injected with rALFPm3-neutralizing WSSV was clearly observed indicating that all rWSSV proteins could interfere with the neutralization effect of rALFPm3 on WSSV similar to that reported previously for WSSV189. Morphological change on WSSV after incubation with rALFPm3 was observed by TEM. The lysed WSSV virions were clearly observed where both viral envelope and nucleocapsid were dismantled. The results lead to the conclusion that the ALFPm3 displays direct effect on the viral structural proteins resulting in destabilization and breaking up of WSSV virions.

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.

Antimicrobial functions of EsLecH, a C-type lectin, via JNK pathway in the Chinese mitten crab, Eriocheir sinensis

C-type lectins (CTLs) are pattern recognition proteins that play significant roles in the innate immune system by identifying and eliminating pathogens. Here, we have reported a CTL (EsLecH) from the Chinese mitten crab that can bind to microorganisms and regulate antimicrobial peptide (AMP) expression via the c-Jun N-terminal kinase (JNK) pathway. EsLecH was found to have an N-terminal signal peptide and a single carbohydrate recognition domain. The EsLecH transcript was detected abundantly in various tissues, and it was significantly upregulated in hemocytes after challenging with lipopolysaccharides and bacteria. Recombinant (r)EsLecH could bind to microorganisms, but at different levels. Ca(2+) significantly increased rEsLecH binding affinity to microorganisms. Furthermore, growth inhibition by rEsLecH increased with increasing rEsLecH levels. Knockdown of EsLecH was accompanied by a significant reduction in AMP expression and JNK phosphorylation; AMP expression was reduced with JNK silencing and can not rescued by rEsLecH when absence of JNK. These results indicate that EsLecH could regulate AMPs via JNK signaling.

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.

Identification, characterization, and functional studies of a Pelle gene in the Chinese mitten crab, Eriocheir sinensis

The toll-like receptor/NF-κB signaling pathways play an important role in the innate immune system. In the present study, one Pelle gene (named EsPelle) was identified for the first time from the Chinese mitten crab Eriocheir sinensis. The full-length cDNA of EsPelle is 3797 bp with a 3156 bp-long open reading frame that encodes a 1051 amino acid protein. EsPelle protein contains a death domain at the N-terminal and a serine/threonine kinase domain at the C-terminal. A neighbor joining phylogenetic tree showed that the EsPelle protein, which is closest to those of Scylla paramamosain Pelle and Litopenaeus vannamei Pelle, was clustered to a group of crustacean Pelle proteins. EsPelle was expressed in all tested tissues of normal crabs, and its expression was regulated in hemocytes and hepatopancreas of crabs challenged with lipopolysaccharide, peptidoglycan, Staphyloccocus aureus, Vibrio parahaemolyticus, and Aeromonas hydrophila. Overexpression of EsPelle in Drosophila Schneider 2 cells could upregulate the expression of Drosophila antimicrobial peptides, namely, metchnikowin (Mtk), attacinA (Atta), drosomycin (Drs), and cecropinA (CecA). Moreover, EsPelle silencing by siRNA reduced the transcription of anti-lipopolysaccharide factor 1 and 2, crustin 2, and lysozyme in crabs challenged with V. parahaemolyticus. From the results, we speculated that EsPelle was involved in innate immune defense against V. parahaemolyticus in E. sinensis.

Identification and molecular characterization of a peritrophin-like gene, involved in the antibacterial response in Chinese mitten crab, Eriocheir sinensis

Peritrophin was first isolated from insect peritrophic membrane (PM) and was thought to protect insects from invasion of microorganisms and to stimulate digestion of food. In this study, a peritrophin-like gene (EsPT) was obtained from Eriocheir sinensis. The full length cDNA of EsPT was 1232 bp, which contained 1005 bp ORF encoding a protein of 334 amino acids, including a 22 amino acid signal peptide, and 3 conserved chitin binding type 2 domains (ChtBD2) characterized by having a 6-cysteine motif. Phylogenetic analysis showed that EsPT was clustered together with 2 insect peritrophin-44-like proteins (MdP44L from Musca domestica and CcP44L from Ceratitis capitata), an insect chitin binding peritrophin-A domain containing protein (CfPT from Coptotermes formosanus) and a crustacean peritrophin (MnPT from Macrobrachium nipponense). Tissue distribution analysis revealed that EsPT was mainly expressed in hepatopancreas, intestine and hemocytes. The expression of EsPT is regulated by lipopolysaccharide, peptidoglycan, Staphylococcus aureus, Vibrio parahaemolyticus and Aeromonas hydrophila challenge. The recombinant EsPT could bind to different microbes, and enhanced the clearance of V. parahaemolyticus in vivo. In crabs, silencing of EsPT by siRNA suppressed the elimination of V. parahaemolyticus and increasing number of bacteria, finally upregulated the expression of anti-lipopolysaccharide factor (ALF) and clip domain serine proteases (cSP). The results might indicate that EsPT was involved in the anti-bacterial innate immunity of crabs.

Macrobrachium rosenbergii mannose binding lectin: synthesis of MrMBL-N20 and MrMBL-C16 peptides and their antimicrobial characterization, bioinformatics and relative gene expression analysis

Mannose-binding lectin (MBL), an antimicrobial protein, is an important component of innate immune system which recognizes repetitive sugar groups on the surface of bacteria and viruses leading to activation of the complement system. In this study, we reported a complete molecular characterization of cDNA encoded for MBL from freshwater prawn Macrobrachium rosenbergii (Mr). Two short peptides (MrMBL-N20: (20)AWNTYDYMKREHSLVKPYQG(39) and MrMBL-C16: (307)GGLFYVKHKEQQRKRF(322)) were synthesized from the MrMBL polypeptide. The purity of the MrMBL-N20 (89%) and MrMBL-C16 (93%) peptides were confirmed by MS analysis (MALDI-ToF). The purified peptides were used for further antimicrobial characterization including minimum inhibitory concentration (MIC) assay, kinetics of bactericidal efficiency and analysis of hemolytic capacity. The peptides exhibited antimicrobial activity towards all the Gram-negative bacteria taken for analysis, whereas they showed the activity towards only a few selected Gram-positive bacteria. MrMBL-C16 peptides produced the highest inhibition towards both the Gram-negative and Gram-positive bacteria compared to the MrMBL-N20. Both peptides do not produce any inhibition against Bacillus sps. The kinetics of bactericidal efficiency showed that the peptides drastically reduced the number of surviving bacterial colonies after 24 h incubation. The results of hemolytic activity showed that both peptides produced strong activity at higher concentration. However, MrMBL-C16 peptide produced the highest activity compared to the MrMBL-N20 peptide. Overall, the results indicated that the peptides can be used as bactericidal agents. The MrMBL protein sequence was characterized using various bioinformatics tools including phylogenetic analysis and structure prediction. We also reported the MrMBL gene expression pattern upon viral and bacterial infection in M. rosenbergii gills. It could be concluded that the prawn MBL may be one of the important molecule which is involved in antimicrobial mechanism. Moreover, MrMBL derived MrMBL-N20 and MrMBL-C16 peptides are important antimicrobial peptides for the recognition and eradication of viral and bacterial pathogens.

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.

Immunotoxic effect of Benzo[α]Pyrene and chrysene in juvenile white shrimp Litopenaeus vannamei

The effects of benzo(a)pyrene (Bap) (0.03, 0.3 and 3 μg L−1) and chrysene (CHR) (0.3, 2.1 and 14.7 μg L−1) on the function of the immune system of juvenile white shrimp Litopenaeus vannamei were determined under laboratory conditions. This included the total hemocyte count (THC) in the hemolymph, phagocytic activityand pro-phenoloxidase (pro-PO) activity of the hemocyte, phenoloxidase (PO) activity, α2-macroglobulin (α2-M) activity, bacteriolytic activity and antibacterial activity in the hemolymph. The results showed that BaP and CHR could inhibit the immune function of L. vannamei significantly under high concentration BaP and CHR exposure. The results of this study indicated that the immunotoxicity of PAHs in a descending order was BaP>CHR. Moreover, the results indicated the THC in hemolymph, pro-PO activity and phagocytic activity of hemocyte, and bacteriolytic activity in hemolymphcould be used as potentially suitable biomarkersfor early warning indication of PAHs toxicity, this could provide useful information for toxic risk assessment of environmental pollutants.

Identification and characterization of a novel phage-type like lysozyme from Manila clam, Ruditapes philippinarum

A novel lysozyme gene (RpLysPh) with high similarity to the bacteriophage lysozymes was identified in Manila clam, Ruditapes philippinarum. The full length cDNA of RpLysPh is 828bp and contains a 462bp open reading frame (ORF) that codes for a 154 amino acid protein. Multiple sequence alignment analysis revealed that the three residues essential for catalytic activity in phage-type lysozyme (Glu(20), Asp(29), and Thr(35)) are conserved in RpLysPh. The comparison of the 3D models of RpLysPh and Coxiella burnetii lysozyme also suggested that the active sites involved in the binding of substrate have similar conformations. Phylogenetic analysis suggested that RpLysPh shares a similar origin with the bacterial phage-type lysozyme group. The highest level of expression of RpLysPh was observed in hemocytes, followed by mantle. Induction of RpLysPh expression was observed in gills in response to lipopolysaccharide (LPS), peptidoglycan (PGN), polyinosinic-polycytidylic acid (Poly(I:C)), and whole glucan particles (WGP) challenge. The recombinant protein of RpLysPh showed antibacterial activity against both Gram-positive and Gram-negative bacteria.

Characterization and function analysis of an anti-lipopolysaccharide factor (ALF) from the Chinese shrimp Fenneropenaeus chinensis

Anti-lipopolysaccharide factor (ALF) is one of the widely-studied antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity and antiviral property. Previous studies show the existence of multiform of ALFs in crustacean which are important for immunity of the animals. In the present study, we characterized one isoform of ALF from the Chinese shrimp Fenneropenaeus chinensis (FcALF2). Tissue distribution analysis revealed that FcALF2 showed the highest expression level in the lymphoid organ (Oka) of the shrimp. The expression level of FcALF2 in shrimp was significantly up-regulated when they were injected with Micrococcus lysodeikticus and Vibrio anguillarum. A peptide corresponding to the LPS-binding domain of FcALF2 (FcALF2-LBD) was synthesized to analyze its antimicrobial activities. Data demonstrated that FcALF2-LBD possessed strong antibacterial activity against Gram-positive bacteria Micrococcus luteus and M.lysodeikticus with MIC ranges of 2-4 μM and 1-2 μM respectively and significant inhibition activity against white spot syndrome virus (WSSV). The antibacterial activities of the sequence modified peptides (FcALF2-LBDb, FcALF2-LBDv) were apparently enhanced and broadened after the amount of basic amino acids was increased in the synthetic LPS-binding domain. These data provide more insights into understanding the function of LPS-binding domain of ALF and the role of ALF in shrimp immunity.

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.

A novel single-domain peptide, anti-LPS factor from prawn: synthesis of peptide, antimicrobial properties and complete molecular characterization

In this study, we reported a complete molecular characterization including bioinformatics features, gene expression, peptide synthesis and its antimicrobial activities of an anti-lipopolysaccharide (LPS) factor (ALF) cDNA identified from the established cDNA library of freshwater prawn Macrobrachium rosenbergii (named as MrALF). The mature protein has an estimated molecular weight of 11.240 kDa with an isoelectric point of 9.46. The bioinformatics analysis showed that the MrALF contains an antimicrobial peptide (AMP) region between T54 and P77 with two conserved cysteine residues (Cys55 and Cys76) which have an anti-parallel β-sheet confirmation. The β-sheet is predicted as cationic with hydrophobic nature containing a net charge of +5. The depicted AMP region is determined to be amphipathic with a predicted hydrophobic face 'FPVFI'. A highest MrALF gene expression was observed in hemocytes and is up-regulated with virus [white spot syndrome baculovirus (WSBV)], bacteria (Aeromonas hydrophila) and Escherichia coli LPS at various time points. The LPS binding region of MrALF peptide was synthesized to study the antimicrobial property, bactericidal efficiency and hemolytic capacity. The peptide showed antimicrobial activity against both the Gram-negative and Gram-positive bacteria. The bactericidal assay showed that the peptide recognized the LPS of bacterial cell walls and binding on its substrate and thereby efficiently distinguishing the pathogens. The hemolytic activity of MrALF peptide is functioning in a concentration dependant manner. In summary, the comprehensive analysis of MrALF showed it to be an effective antimicrobial peptide and thus it plays a crucial role in the defense mechanism of M. rosenbergii.

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.

Transcriptome profiling analysis on whole bodies of microbial challenged Eriocheir sinensis larvae for immune gene identification and SNP development

To study crab immunogenetics of individuals, newly hatched Eriocheir sinensis larvae were stimulated with a mixture of three pathogen strains (Gram-positive bacteria Micrococcus luteus, Gram-negative bacteria Vibrio alginolyticus and fungi Pichia pastoris; 10⁸ cfu·mL^-1). A total of 44,767,566 Illumina clean reads corresponding to 4.52 Gb nucleotides were generated and assembled into 100,252 unigenes (average length: 1,042 bp; range: 201-19,357 bp). 17,097 (26.09%) of 65,535 non-redundant unigenes were annotated in NCBI non-redundant protein (Nr) database. Moreover, 23,188 (35.38%) unigenes were assigned to three Gene Ontology (GO) categories, 15,071 (23.00%) to twenty-six Clusters of orthologous Groups (COG) and 8,574 (13.08%) to six Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, respectively. Numerous genes were further identified to be associated with multiple immune pathways, including Toll, immune deficiency (IMD), janus kinase (JAK)-signal transducers and activators of transcription (STAT) and mitogen-activated protein kinase (MAPK) pathways. Some of them, such as tumor necrosis factor receptor associated factor 6 (TRAF6), fibroblast growth factor (FGF), protein-tyrosine phosphatase (PTP), JNK-interacting protein 1 (JIP1), were first identified in E. sinensis. TRAF6 was even first discovered in crabs. Additionally, 49,555 single nucleotide polymorphisms (SNPs) were developed from over 13,309 unigenes. This is the first transcriptome report of whole bodies of E. sinensis larvae after immune challenge. Data generated here not only provide detail information to identify novel genes in genome reference-free E. sinensis, but also facilitate our understanding on host immunity and defense mechanism of the crab at whole transcriptome level.

Two Rab GTPases, EsRab-1 and EsRab-3, involved in anti-bacterial response of Chinese mitten crab Eriocheir sinensis

Rab GTPase is essential for the control of intracellular membrane trafficking in all eukaryotic cells and further affects the ability of phagocytic cells to scavenge pathogen. In the present study, the cDNAs for two crab Rab proteins (EsRab-1 and EsRab-3) were identified from the Chinese mitten crab Eriocheir sinensis by rapid amplification of cDNA ends (RACE) approaches and expressed sequence tag (EST) analysis. The full-length cDNAs of EsRab-1 and EsRab-3 were of 892 bp and 965 bp with ORFs of 615 bp and 630 bp, respectively. The cDNAs encoded two peptides of 204 and 209 amino acid residues with the conserved GTP/Mg(2+) binding sites, Switch I region and Switch II region in RAB domains. The mRNA transcripts of EsRab-1 and EsRab-3 were both highest expressed in hepatopancreas, and marginally expressed in other tissues including hemocytes, muscle, gonad, gill and heart. After the crabs were challenged by bacteria Vibrio anguillarum, the expression levels of both EsRab-1 and EsRab-3 in hemocytes were significantly up-regulated, and reached the highest level at 1.5 h post-stimulation, which was 7-fold (P < 0.05) and 6-fold (P < 0.01) of blank group for EsRab-1 and EsRab-3, respectively. No significant change of mRNA expression was detected for either EsRab-1 or EsRab-3 in crabs stimulated by Pichia pastoris. These results clearly suggested the involvement of Rab proteins in crab anti-bacterial immunity.

Polymorphisms of anti-lipopolysaccharide factors in the swimming crab Portunus trituberculatus and their association with resistance/susceptibility to Vibrio alginolyticus

Anti-lipopolysaccharide factor (ALF) is an important antimicrobial peptide (AMP) that can bind and neutralize major component of Gram-negative bacteria cell wall, lipopolysaccharide (LPS). Seven isoforms of anti-lipopolysaccharide factors (PtALF1-7) were previously identified from the swimming crab Portunus trituberculatus in our laboratory. Here, polymorphisms of PtALF1-7 were detected and their association with resistance/susceptibility to Vibrio alginolyticus (a main Gram-negative bacteria causing high mortality in P. trituberculatus) were investigated. We identified 127, 96, 103, 53 and 158 single nucleotide polymorphisms (SNPs) in genomic fragments of PtALF1-3, PtALF4, PtALF5, PtALF6 and PtALF7, respectively. Among them, totally sixteen SNPs were significantly associated with resistance/susceptibility to V. alginolyticus (P < 0.05). Of these sixteen SNPs, most were located in introns and noncoding exons, while two synonymous SNPs and one nonsynonymous SNP were in coding exons. Additionally, simple sequence repeats (SSRs) were only identified in introns and noncoding exons of PtALF4, PtALF5 and PtALF7. Although no significant difference of allele frequencies was found, these SSRs had different polymorphic alleles according to the repeat number between susceptible and resistant stocks. After further confirmation, polymorphisms investigated here might be applied as potential molecular markers for future selection of resistant strains to diseases caused by Gram-negative bacteria.

Transcriptome analysis on Chinese shrimp Fenneropenaeus chinensis during WSSV acute infection

Previous studies have discovered a lot of immune-related genes responding to white spot syndrome virus (WSSV) infection in crustacean. However, little information is available in relation to underlying mechanisms of host responses during the WSSV acute infection stage in naturally infected shrimp. In this study, we employed next-generation sequencing and bioinformatic techniques to observe the transcriptome differences of the shrimp between latent infection stage and acute infection stage. A total of 64,188,426 Illumina reads, including 31,685,758 reads from the latent infection group and 32,502,668 reads from the acute infection group, were generated and assembled into 46,676 unigenes (mean length: 676 bp; range: 200-15,094 bp). Approximately 24,000 peptides were predicted and classified based on homology searches, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Among which, 805 differentially expressed genes were identified and categorized into 11 groups based on their possible function. Genes in the Toll and IMD pathways, the Ras-activated endocytosis process, the RNA interference pathway, anti-lipopolysaccharide factors and many other genes, were found to be activated in shrimp from latent infection stage to acute infection stage. The anti-bacterially proPO-activating cascade was firstly uncovered to be probably participated in antiviral process. These genes contain not only members playing function in host defense against WSSV, but also genes utilized by WSSV for its rapid proliferation. In addition, the transcriptome data provides detail information for identifying novel genes in absence of the genome database of shrimp.

Molecular cloning, genomic structure and antimicrobial activity of PtALF7, a unique isoform of anti-lipopolysaccharide factor from the swimming crab Portunus trituberculatus

Anti-lipopolysaccharide factors (ALFs), as the potent antimicrobial peptides, are becoming predominant candidates for potential therapeutic agents of bacterial and viral diseases. In this study, a unique isoform of ALF (PtALF7) was identified from hemocytes cDNA library of the swimming crab Portunus trituberculatus. The PtALF7 cDNA contained an open reading frame (ORF) of 372 bp encoding 123 amino acids. The deduced peptide of PtALF7 shared high similarity with our previously reported PtALF1-3 but low with PtALF4-6. The PtALF7 gene consisted of three exons interrupted by two introns, and was clearly transcribed from different genomic loci compared with other PtALF isoforms. Totally 128 SNPs including 12 in coding region and 116 in noncoding region were detected in PtALF7 gene by direct sequencing of 20 samples. The mRNA expression of PtALF7 transcript was primarily observed in hemocytes followed by gill and eyestalk, but barely detectable in hepatopancreas. After challenge with Vibrio alginolyticus, a main pathogen causing high mortality in P. trituberculatus, the PtALF7 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 PtALF7 protein exhibited 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 a potential involvement for PtALF7 in the innate immune response of P. trituberculatus.

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.