An LDLa domain-containing C-type lectin is involved in the innate immunity of Eriocheir sinensis

The role of pattern recognition receptors in the innate immune system of Chinese mitten crab (Eriocheir sinensis)

Eriocheir sinensis (Chinese mitten crab) is one of the main economic species in China, which has evolved an extremely sophisticated innate immune system to fend off disease invasions. However, bacterial and viral infections have caused significant financial losses for the E. sinensis aquaculture in recent years. Making well-informed judgments for the control microbial infections would require a thorough understanding and clarification of the intricate innate immune system of E. sinensis. Innate immunity is essential for the host's defense against invasive pathogens. Pattern recognition receptors (PRRs) initially recognize pathogen-associated molecular patterns (PAMPs) and trigger an innate immune response, causing the generation of inflammatory cytokine and promoting the clearance and control of pathogens. In E. sinensis, Toll/Toll-like receptors, lipopolysaccharide and β-1,3-glucan binding proteins, C-type lectins, galactoside-binding lectins, L-type lectins, scavenger receptors, and down syndrome cell adhesion molecules have been identified to be PRRs that are involved in the recognition of bacteria, fungi, and viruses. In this review, we give a comprehensive overview of the literature regarding PRRs' roles in the immunological defenses of E. sinensis, with the aim of providing clues to the mechanisms of innate immunity.

PvMR1, a novel C-type lectin plays a crucial role in the antibacterial immune response of Pacific white shrimp, Penaeus vannamei

C-type lectins (CTLs) are important immune molecules in innate immune, which participate in non-self recognition and clearance of pathogens. Here, a new CTL with two distinct C-type lectin domains (CTLDs) from Pacific white shrimp Penaeus vannamei, designated as PvMR1 was identified. The obtained PvMR1 coding sequence (CDS) was 1044 bp long encoding a protein with 347 amino acids. PvMR1 had two CTLD, a conserved mannose-specific EPN motif and a galactose-specific QPD motif, clustering into the same branch as the crustacean CTLs. PvMR1 was widely distributed in shrimp tissues with the highest transcription level in the hepatopancreas, with significantly induced mRNA expression on the hepatopancreas and intestines after immune challenge with Vibrio anguillarum. In vitro assays with recombinant PvMR1 (rPvMR1) protein revealed that it exhibited a wide range of antimicrobial activity, bacterial binding ability, and bacterial agglutination activity in a Ca2+-independent manner. Moreover, PvMR1 promoted bacterial phagocytosis in hemocytes. Furthermore, rPvMR1 treatment could significantly enhance the bacterial clearance in hemolymph and greatly improved the survival of shrimp under V. anguillarum infection in vivo. These results collectively suggest that PvMR1 plays an important role in antibacterial immune response of P. vannamei.

LDLa containing C-type lectin mediates phagocytosis of V.anguillarum and regulates immune effector genes in shrimp

C-type lectins (CTLs) function as pattern recognition receptors (PRRs) by recognizing invading microorganisms, thereby triggering downstream immune events against infected pathogens. In this study, a novel CTL containing a low-density lipoprotein receptor class A (LDLa) domain was obtained from Litopenaeus vannamei, designed as LvLDLalec. Stimulation by the bacterial pathogen Vibrio anguillarum (V. anguillarum) resulted in remarkable up-regulation of LvLDLalec, as well as release of LvLDLalec into hemolymph. The rLvLDLalec protein possessed broad-spectrum bacterial binding and agglutinating activities, as well as hemocyte attachment ability. Importantly, LvLDLalec facilitated the bacterial clearance in shrimp hemolymph and protected shrimp from bacterial infection. Further studies revealed that LvLDLalec promoted hemocytes phagocytosis against V. anguillarum and lysosomes were involved in the process. Meanwhile, LvLDLalec participated in humoral immunity through activating and inducing nuclear translocation of Dorsal to regulate phagocytosis-related genes and antimicrobial peptides (AMPs) genes, thereby accelerated the removal of invading pathogens in vivo and improved the survival rate of L. vannamei. These results unveil that LvLDLalec serves as a PRR participate in cellular and humoral immunity exerting opsonin activity to play vital roles in the immune regulatory system of L. vannamei.

A New C-Type Lectin Homolog SpCTL6 Exerting Immunoprotective Effect and Regulatory Role in Mud Crab Scylla paramamosain

C-type lectin (CTL), a well-known immune-related molecule, has received more and more attention due to its diverse functions, especially its important role in development and host defense of vertebrate and invertebrate. Since the research on crab CTLs is still lack, we screened a new CTL homolog, named SpCTL6 from mud crab Scylla paramamosain. The full-length cDNA sequence of SpCTL6 was 738 bp with a 486 bp of ORF, and the deduced amino acids were 161 aa. SpCTL6 was predicted to have a 17 aa signal peptide and its mature peptide was 144 aa (MW 16.7 kDa) with pI value of 5.22. It had typical CTL structural characteristics, such as a single C-type lectin-like domain, 4 conserved cysteines, similar tertiary structure to that of vertebrate CTLs and a mutated Ca²⁺ binding motif Gln-Pro-Thr (QPT), clustering into the same branch as the crustacean CTLs. SpCTL6 was highly expressed in the entire zoeal larval stages and widely distributed in adult crab tissues with the highest transcription level in testis. During the molting process of juvenile crabs, the expression level of SpCTL6 was remarkably increased after molting. SpCTL6 could be significantly upregulated in two larval stages (Z1 and megalopa) and adult crab testis under immune challenges. Recombinant SpCTL6 (rSpCTL6) was successfully obtained from eukaryotic expression system. rSpCTL6 exhibited binding activity with PAMPs (LPS, lipoteichoic acid, peptidoglycan, and glucan) and had a broad spectrum bacterial agglutination activity in a Ca²⁺-dependent manner. In addition, rSpCTL6 could enhance the encapsulation activity of hemocytes and has no cytotoxic effect on hemocytes. Although rSpCTL6 had no bactericidal activity on Vibrio alginolyticus, rSpCTL6 treatment could significantly reduce the bacterial endotoxin level in vitro and greatly improved the survival of S. paramamosain under V. alginolyticus infection in vivo. The immunoprotective effect of rSpCTL6 might be due to the regulatory role of rSpCTL6 in immune-related genes and immunological parameters. Our study provides new information for understanding the immune defense of mud crabs and would facilitate the development of effective strategies for mud crab aquaculture disease control.

Purification and partial characterization of carbohydrate-recognition protein C-type lectin from Hemifusus pugilinus

A mannose binding lectin (C-type lectin) was detected in a molluscan snail Hemifusus pugilinus, this lectin molecule was isolated and purified from the plasma using mannose-fixed sepharose CL-4B column affinity chromatography. The purified protein corresponds to the molecular weight of 118 kDa on an SDS-PAGE gel. The divalent cation-dependent nature of the H. pugilinus lectin (Hp-Lec) evidenced through pH and thermal stability analysis using Circular Dichroism (CD) and Surface Plasmon Resonance (SPR) respectively. Functional investigations of the Hp-Lec reveal a broad spectrum of bacterial agglutination activity against wide range of Gram-positive and Gram-negative bacterial strains. Furthermore, Hp-Lec displayed the haemo agglutination activity against vertebrate red blood cells (RBCs) and its titers were recorded. Excitingly, microbial virulent pathogens such as fungal strains tested against the purified Hp-Lec (25 and 50 μg/ml), which exhibits the effective antifungal activity against tested fungal pathogens such as Aspergillus niger and A. flavus.

Characterization and Functional Analysis of Two Transmembrane C-Type Lectins in Obscure Puffer (Takifugu obscurus)

C-type lectins (CTLs) have received widespread attention in animal immune responses. In the present study, two CTLs (ToCTL1 and ToCTL2) were identified from obscure puffer Takifugu obscurus. The open reading frames of ToCTL1 and ToCTL2 were 687 and 1,380 bp, respectively. The predicted ToCTL1 and ToCTL2 proteins contained a single transmembrane region and one typical carbohydrate recognition domain (CRD). Quantitative real-time polymerase chain reaction detected ToCTL1 and ToCTL2 transcripts in all examined tissues, with high levels in the intestine and kidney, and their expression levels were remarkably altered upon Vibrio harveyi and Aeromonas hydrophila infection. The recombinant proteins ToCTL1-CRD and ToCTL2-CRD agglutinated the Gram-negative and Gram-positive bacteria in a Ca²⁺-dependent manner. rToCTL1-CRD and rToCTL2-CRD exhibited evident binding activities against seven kinds of bacteria and polysaccharides (lipopolysaccharide and peptidoglycan) in a Ca²⁺-independent manner. Moreover, rToCTL1-CRD and rToCTL2-CRD could inhibit the growth of four types of bacteria in vitro. These findings collectively demonstrated that ToCTL1 and ToCTL2 could be involved in host defense against bacterial infection in T. obscurus.

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.

Two C-type lectins (ReCTL-1, ReCTL-2) from Rimicaris exoculata display broad nonself recognition spectrum with novel carbohydrate binding specificity

C-type lectins are Ca²⁺-dependent carbohydrate-binding proteins containing one or more carbohydrate-recognition domains (CRDs). C-type lectins play crucial roles in innate immunity, including nonself-recognition and pathogen elimination. In the present study, two C-type lectins (designated ReCTL-1 and ReCTL-2) were identified from the shrimp Rimicaris exoculata which dwells in deep-sea hydrothermal vents. The open reading frames of ReCTL-1 and ReCTL-2 encoded polypeptides of 171 and 166 amino acids respectively, which were both composed of a signal peptide and a single CRD. The key motifs determining the carbohydrate binding specificity of ReCTL-1 and ReCTL-2 were respectively Glu-Pro-Ala (EPA) and Gln-Pro-Asn (QPN), which were firstly discovered in R. exoculata. ReCTL-1 and ReCTL-2 displayed similar pathogen-associated molecular pattern (PAMP) binding features and they bound three PAMPs-β-glucan, lipopolysaccharide and peptidoglycan-with relatively high affinity. In addition, both could efficiently recognize and bind Gram-positive bacteria, Gram-negative bacteria and fungi. However, ReCTL-1 and ReCTL-2 exhibited different microbial agglutination activities: ReCTL-1 agglutinated Staphylococcus aureus and Saccharomyces cerevisiae, while ReCTL-2 agglutinated Micrococcus luteus, Vibrio parahaemolyticus and V. fluvialis. Both ReCTL-1 and ReCTL-2 inhibited the growth of V. fluvialis. All these results illustrated that ReCTL-1 and ReCTL-2 could function as important pattern-recognition receptors with broad nonself-recognition spectra and be involved in immune defense against invaders, but their specificities are not the same. In addition, the two ReCTLs possessed different carbohydrate binding specificities from each other and from the classical pattern: ReCTL-1 with an EPA motif bound d-galactose and l-mannose, while ReCTL-2 with a QPN motif bound d-fucose and N-acetylglucosamine.

Involvement of gamma interferon inducible lysosomal thiol reductase in the innate immune responses of red swamp crayfish, Procambarus clarkii

The Gamma interferon inducible lysosomal thiol reductase (GILT) plays a key biological role in the immune responses and involves in the processing of class II MHC-restricted antigen by stimulating disulfide bond reduction in mammals. To determine the biological function of GILT in the innate immune system of crustaceans, we sequenced and cloned GILT gene from red swamp crayfish, Procambarus clarkii (Pc-GILT). The deduced amino acid sequence of Pc-GILT contained the putative conserved structures of the GILT family proteins: the GILT signature (CQHGX2ECX2NX4C) sequence and the active site (CXXS) motif. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis suggested that a recombinant Pc-GILT protein was successfully expressed in Escherichia coli (E. coli). Quantitative real-time PCR analysis showed that Pc-GILT transcript level was highest in the hepatopancreas followed by the gut, heart and muscles. Additionally, we analyzed the transcription level of Pc-GILT gene in hepatopancreas of red swamp crayfish under biotic stress conditions. The expression of Pc-GILT gene upregulated after viral (poly I:C) and bacterial (peptidoglycan, lipopolysaccharide) infection. The suppression of Pc-GILT by double stranded RNA influenced the transcript levels of various immune-related genes. These observations indicate that the Pc-GILT probably plays a key biological role in the innate immune responses of red swamp crayfish, since it modulates the expression of genes associated with immune pathways.

Identification and characterization of a symbiotic agglutination-related C-type lectin from the hydrothermal vent shrimp Rimicaris exoculata

Rimicaris exoculata (Decapoda: Bresiliidae) is one of the dominant species of hydrothermal vent communities, which inside its gill chamber harbors ectosymbioses with taxonomic invariability while compositional flexibility. Several studies have revealed that the establishment of symbiosis can be initiated and selected by innate immunity-related pattern recognition receptors (PRRs), such as C-type lectins (CTLs). In this research, a CTL was identified in R. exoculata (termed RCTL), which showed high expression at both mRNA and protein levels in the scaphognathite, an organ where the ectosymbionts are attached outside its setae. Linear correlationships were observed between the relative quantities of two major symbionts and the expression of RCTL based on analyzing different shrimp individuals. The recombinant protein of RCTL could recognize and agglutinate the cultivable γ-proteobacterium of Escherichia coli in a Ca²⁺-dependent manner, obeying a dose-dependent and time-cumulative pattern. Unlike conventional crustacean CTLs, the involvement of RCTL could not affect the bacterial growth, which is a key issue for the successful establishment of symbiosis. These results implied that RCTL might play a critical role in symbiotic recognition and attachment to R. exoculata. It also provides insights to understand how R. exoculata adapted to such a chemosynthesis-based environment.

Curcumin relieves paraquat‑induced lung injury through inhibiting the thioredoxin interacting protein/NLR pyrin domain containing 3‑mediated inflammatory pathway

When paraquat (PQ) enters the human body, it increases oxidative stress and inflammation, ultimately resulting in acute lung injury (ALI). Curcumin, a naturally occurring compound, has been reported to ameliorate PQ-induced ALI; however, the underlying molecular mechanisms remain unclear. In the present study, normal lung fibroblasts (WI-38VA13) were treated with 10 µmol/l PQ for 48 h, followed by a further 48 h incubation with 300 µmol/l curcumin. Cells were then harvested to determine their viability. Flow cytometry was performed to analyze the levels of reactive oxygen species (ROS) and the rate of apoptosis. The levels of apoptotic proteins and activation of the thioredoxin interacting protein/NLR pyrin domain containing 3 (TXNIP/NLRP3) axis were measured via reverse transcription-quantitative polymerase chain reaction and western blot analyses. Proinflammatory cytokine levels were examined using enzyme-linked immunosorbent assays. Finally, the expression levels of Notch1, extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylated-ERK1/2 were evaluated via western blotting. Following treatment with curcumin, PQ-induced increases in ROS levels and apoptosis were significantly attenuated, and Bcl-2 expression levels were upregulated, whereas those of Bax were downregulated. It was also observed that curcumin treatment downregulated the expression levels of TXNIP, NLRP3, interleukin (IL)-1β and IL-18, and downstream caspase-1 compared with PQ treatment alone. Curcumin significantly attenuated the upregulation of Notch1 without affecting ERK1/2 phosphorylation. The present findings suggested that the inhibitory effects of curcumin on TXINP1 may inhibit activation of the NLRP3 inflammasome, subsequently suppressing the upregulation of proinflammatory cytokines and ultimately improving PQ-induced ALI.

2-Transmembrane C-type lectin from oriental river prawn Macrobrachium nipponense participates in antibacterial immune response

As a type of pattern-recognition proteins (PRRs), C-type lectins (CTLs) perform important functions in non-self recognition and clearance of pathogens in innate immunity. In this study, a unique 2-transmembrane CTL (designated as Mn-2TM-cLec) with a single carbohydrate recognition domain (CRD) was isolated from Macrobrachium nipponense. The full-length cDNA of Mn-2TM-cLec consisted of 3265 bp with an 837 bp open reading frame encoding a protein with 278 amino acids. Mn-2TM-cLec was ubiquitously distributed in various tissues of normal prawn, particularly in the hemocytes, hepatopancreas, and gills. The expression of Mn-2TM-cLec was significantly up-regulated in the gills and hepatopancreas after the prawns were challenged with Staphylococcus aureus and Vibrio parahaemolyticus. RNA interference knock-down of Mn-2TM-cLec gene decreased the transcription levels of three antimicrobial peptides (anti-lipopolysaccharide factor (ALF) 1, ALF2, and Crustin (Crus) 1) after V. parahaemolyticus infection. The recombinant CRD of Mn-2TM-cLec could bind lipopolysaccharide, peptidoglycans, and diverse bacterial strains and agglutinate S. aureus and V. parahaemolyticus in a Ca²⁺-dependent manner. In addition, the rCRD enhanced the clearance of V. parahaemolyticus injected in prawns. In summary, Mn-2TM-cLec might act as a PRR to participate in the prawn immune defense against pathogens through its antimicrobial activity.

Molecular Characterization of Two Toll Receptors in Hyriopsis cumingii and Their Potential Roles in Antibacterial Response

Tolls/Toll-like receptors (TLRs) play a key role in innate immunity by detecting the invading microbes and subsequently activating downstream signaling cascades. In this study, two new molluscan Toll members (designed as HcToll6 and HcToll7) were identified from triangle-shell pearl mussel (Hyriopsis cumingii). The obtained HcToll6 full-length cDNA was 3207 bp consisting of a 2223 bp open reading frame (ORF) that encoded a peptide of 740 amino acids. HcToll7 cDNA is a 3216 bp molecule that contains an ORF of 2139 bp encoding a protein of 712 amino acids. The deduced HcToll6 and HcToll7 proteins share two common structures: extracellular leucine-rich repeat (LRR) domains and intracellular Toll/interleukin-1 receptor (TIR) domain. Quantitative real-time PCR results showed that HcToll6 and HcToll7 were mainly expressed in the hepatopancreas and the gills, and they responded rapidly to bacterial stimulation. RNA interference by dsRNA results revealed that HcToll6 and HcToll7 RNAi strongly decreased the expression of lysozyme (HcLyso) and defensin (HcDef) in the gills of RNAi-treated mussels with Vibrio parahaemolyticus challenge. As a pattern recognition receptor, the prokaryotic expressed the recombinant LRR domains of HcToll6 and HcToll7 (rHcToll6-LRR and rHcToll7-LRR) could bind to Gram-positive and Gram-negative bacteria and had a strong tendency to recognize lipopolysaccharide (LPS) and peptidoglycan (PNG). rHcToll6-LRR and rHcToll7-LRR exhibited a significant in vitro bactericidal activity against V. parahaemolyticus and Staphylococcus aureus. These findings provide useful information to characterize Tolls in mussels.

C-type lectin response to bacterial infection and ammonia nitrogen stress in tiger shrimp (Penaeus monodon)

C-type lectins (CTLs) are pattern recognition receptors (PRRs) that are important in invertebrate innate immunity for the recognition and elimination of pathogens. Although they were reported in many shrimp, C-type lectins subfamily contain a large number of members with different functions that need to research in deep. In this present study, a new type of CTL, PmCL1 with 861 bp long full-length cDNA, that encodes a protein with 164-amino acid from a 495-bp open reading frame, was isolated and characterized from tiger shrimp (Penaeus monodon). The mRNA transcript of PmCL1 showed the highest expression in the hepatopancreas, whereas it was barely detected in the ovary. After the shrimp were stimulated by Vibrio harveyi and Vibrio anguillarum, PmCL1 expression in the hepatopancreas and gill was significantly upregulated. A carbohydrate-binding assay revealed the specificity of PmCL1 for pathogen-associated molecular patterns (PAMPs) that included peptidoglycan (PGN) and lipopolysaccharide (LPS), and saccharides that included d-glucose, galactosamine, α-lactose, treholose, and d-mannose. Recombinant PmCL1 agglutinated gram-positive (Staphylococcus aureus) and gram-negative bacteria (V. harveyi, V. anguillarum, Vibrio alginolyticus, Vibrio parahemolyticus, Vibrio vulnificus, and Aeromonas hydrophila) in the presence of calcium ions and enhanced the efficiency of clearing the invading bacteria. Collectively, our results suggested that PmCL1 might play an important role as a pattern recognition receptor (PRR) in the immune response towards pathogen infections, as well as the response towards ammonia nitrogen stress.

Amyloid β precursor protein silencing attenuates epithelial‑mesenchymal transition of nasopharyngeal carcinoma cells via inhibition of the MAPK pathway

Advances in the treatment of nasopharyngeal carcinoma (NPC) have significantly improved the local control rate; however, distant metastasis remains a principal cause of mortality. Previous studies have demonstrated that the expression levels of amyloid β precursor protein (APP) are increased in NPC. The present study aimed to investigate the association between APP and the development of NPC. In order to knockdown APP expression, an APP-small interfering RNA vector was synthesized and transfected into SUNE-1 cells. Cell Counting Kit-8 assay was performed to assess cell viability. The migratory and invasive abilities of SUNE-1 cells were examined by wound healing and Transwell assays, respectively. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to measure the mRNA and protein expression levels of APP, and additional factors involved in epithelial-mesenchymal transition (EMT) and in the mitogen-activated protein kinase (MAPK) signaling pathway. APP silencing significantly suppressed cell viability, migration and invasion. In addition, APP interference downregulated the expression levels of metastasis-associated 1, matrix metalloproteinase (MMP)-2 and MMP-9; however, knockdown of APP led to upregulation of tissue inhibitor of metalloproteinases 2 and inhibited EMT. The phosphorylation levels of p38, extracellular signal-regulated kinases 1/2 and c-Jun N-terminal kinases 1/2 were decreased following downregulation of APP. The present results suggested that APP knockdown may significantly inhibit the development of NPC by suppressing cell viability, migration and invasion, and by inhibiting the EMT process via downregulation of the MAPK signaling pathway. Therefore, APP may facilitate the development of a novel gene therapy for the treatment of NPC.

HcCUB-Lec, a newly identified C-type lectin that contains a distinct CUB domain and participates in the immune defense of the triangle sail mussel Hyriopsis cumingii

As pattern recognition receptors (PRRs), C-type lectins (CTLs) play crucial roles in recognizing and eliminating pathogens in innate immunity. In this study, a novel CTL (HcCUB-Lec) was identified from the triangle sail mussel Hyriopsis cumingii. The full-length of HcCUB-Lec cDNA was 1558 bp with an open reading frame of 1281 bp that encodes a putative protein of 426 amino acid residues, including an N-terminal signal peptide, a complement Uegf Bmp1 (CUB) domain, a single carbohydrate recognition domain (CRD), and a transmembrane domain. Quantitative real-time PCR analysis revealed that HcCUB-Lec transcript was distributed in all examined tissues with the highest levels in hepatopancreas and was significantly upregulated in gills and hepatopancreas after immune challenge with Staphyloccocus aureus and Vibrio parahaemolyticus. When HcCUB-Lec was silenced by RNAi, the expression levels of three antimicrobial peptides, including whey acidic protein (HcWAP), defensin (HcDef), and lysozyme (HcLyso), were dramatically decreased in gills. The recombinant HcCUB-Lec and its individual CUB and CRD domains can bind with Gram-positive bacteria (S. aureus and Bacillus subtilis), Gram-negative bacteria (V. parahaemolyticus and Aeromonas hydrophila), and polysaccharides (lipopolysaccharide and peptidoglycan). Moreover, rHcCUB-Lec and its domains could also agglutinate S. aureus and V. parahaemolyticus in the presence of Ca²⁺ and can clear V. parahaemolyticus in H. cumingii. Results of this study suggest that HcCUB-Lec acts as an antimicrobial PRR that participates in the innate immune responses of H. cumingii.

Molecular cloning and functional characterization of a short peptidoglycan recognition protein from triangle-shell pearl mussel (Hyriopsis cumingii)

Peptidoglycan (PGN) is an important target of recognition in invertebrate innate immunity. PGN recognition proteins (PGRPs) are responsible for PGN recognition. In this study, we cloned and functionally analyzed a short PGRP (HcPGRP2) from the triangle-shell pearl mussel Hyriopsis cumingii. The full-length cDNA sequence of HcPGRP2 gene was 1185 bp containing an open reading frame of 882 bp encoding a 293 amino acid protein. HcPGRP2 was predicted to have two SH3b domains and a conserved C-terminal PGRP domain. Quantitative real-time RT-PCR showed that HcPGRP2 was expressed in all examined tissues and its expression was induced most significantly by Staphylococcus aureus and Vibrio parahaemolyticus in the hepatopancreas and gills. RNA interference by siRNA results revealed that HcPGRP2 was involved in the regulation of whey acidic protein, theromacin, and defensin expression. As a pattern-recognition receptor, recombinant HcPGRP2 (rHcPGRP2) protein can bind and agglutinate (Ca²⁺ dependent) all tested bacteria. rHcPGRP2 exhibited specific binding to PGN but not to lipopolysaccharide. Moreover, rHcPGRP2 inhibited the growth activities of S. aureus and V. parahaemolyticus in vitro and accelerated the clearance of V. parahaemolyticus in vivo. Overall, our results indicated that HcPGRP2 may play an important role in the antibacterial immune mechanisms of H. cumingii.

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.

Identification of immune-related genes in gills of Chinese mitten crabs (Eriocheir sinensis) during adaptation to air exposure stress

The Chinese mitten crab, Eriocheir sinensis, is the most important crab in China. Air exposure is regarded as one of the crucial restriction factors in the crab cultivation and transportation process. Numerous studies have shown that air exposure stress can cause many negative effects on aquatic farming animals. However, the molecular mechanisms of drying on Chinese mitten crabs are still poorly studied. In this study, gill reference transcriptome was assembled and differentially expressed gene (DGE) analysis was conducted between air exposure 16 h and normal dissolved oxygen of Chinese mitten crab. A total of 76075 transcripts were generated and 50800 unigenes with a mean length of 1090 bp and N50 length of 1584 bp were observed. Transcriptomic comparison revealed 352 DEGs between air exposure 16 h group and control group, including 122 up-regulated genes and 230 down-regulated genes. Gene ontology (GO) analysis revealed that these DEGs involved in 16 biological process subcategories, 8 cellular component subcategories and 6 molecular function subcategories. Further Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis annotated 352 DEGs to 85 pathways, and some pathways were regarded as related with immune system and diseases, such as phagosome, systemic lupus erythematosus, and alcoholism. Eight genes involved in multiple KEGG signaling pathways were validated by qRT-PCR. This study demonstrates the first gill transcriptomic analysis challenged with air exposure stress in Chinese mitten crab and provides valuable gene resources for understanding the crab gill immunity, which can provides insight into the immune response of crab against air exposure stress.

FmLC6: An ultimate dual-CRD C-type lectin from Fenneropenaeus merguiensis mediated its roles in shrimp defense immunity towards bacteria and virus

C-type lectins are a member of pattern recognition receptors (PRRs) that can interact with pathogen-associated molecular patterns of invading microorganisms by using their conserved motifs in carbohydrate recognition domain (CRD). The binding can trigger various immune responses in both direct and indirect mechanisms. Hereby, an ultimate C-type lectin with dual CRDs each of which containing a different motif was identified from hepatopancreas of Fenneropenaeus merguiensis (mentioned as FmLC6). The full-length cDNA of FmLC6 consisted of 1148 bp comprising one 1005 bp open reading frame (ORF) encoding a signal peptide and a mature protein of 317 residues. FmLC6 was composed of two CRDs with a highly conserved QPD (Gln-Pro-Asp) motif and one variant EPQ (Glu-Pro-Gln) motif for illustrating the carbohydrate binding affinity. The transcription of FmLC6 was detected only in hepatopancreas of normal shrimp. After injection with pathogens or immunostimulants, the expression of FmLC6 was significantly up-regulated and reached the highest level at 12 h post-injection except with lipoteichoic acid challenge. The FmLC6 expression was severely suppressed by knockdown based-silencing. This gene silencing with co-injection by Vibrio parahaemolyticus caused increasing in cumulative mortality and reduction of the median lethal time. Purified recombinant proteins of an entire ORF and two individual CRDs of FmLC6 produced in Escherichia coli could induce a broad spectrum of microbial agglutination with calcium dependence. The agglutination induced by rFmLC6, rCRD1 and rCRD2 was suppressed by galactose plus mannose, galactose and mannose, respectively which this event was confirmed by the inhibition of hemagglutination. All three recombinant proteins possessed ability to inhibit the bacterial growth with a dose-response. Purified rFmLC6 could bind directly to white spot syndrome virus particles and also its recombinant proteins including VP15, VP39A and VP28 with different affinity. Altogether, these results indicate that FmLC6 acts as a PRR to recognize invading microorganisms and leads to mediating the immune response to cooperation in pathogenic elimination via the binding, agglutination and antimicrobial activity.

A novel C-type lectin from the sea cucumber Apostichopus japonicus (AjCTL-2) with preferential binding of d-galactose

C-type lectins (CTLs) are Ca²⁺ dependent carbohydrate-binding proteins that share structural homology in their carbohydrate-recognition domains (CRDs). In the present study, a novel CTL was identified from sea cucumber Apostichopus japonicus (named as AjCTL-2). The deduced amino acid sequence of AjCTL-2 was homologous to CTLs from other animals with the identities ranging from 33% to 40%. It contained a canonical signal peptide at the N-terminus, a low density lipoprotein receptor class A (LDLa), a C1r/C1s/Uegf/bone morphogenetic protein 1 (CUB), and a CRD with two motifs Glu-Pro-Asn (EPN) and Trp-Asn-Asp (WND) in Ca²⁺ binding site 2. The mRNA transcripts of AjCTL-2 were extensively expressed in all the tested tissues including respiratory tree, muscle, gut, coelomocyte, tube-foot, body wall and gonad, and the highest expression level of AjCTL-2 in coelomocyte was about 4.2-fold (p < 0.05) of that in body wall. The mRNA expression level of AjCTL-2 in coelomocyte increased significantly after Vibrio splendidus stimulation, and dramatically peaked at 12 h, which was 206.4-fold (p < 0.05) of that in control group. AjCTL-2 protein was mainly detected in cytoplasm of coelomocyte by immunofluorescence. The recombinant AjCTL-2 (rAjCTL-2) displayed binding activity to d-galactose independent of Ca²⁺, while the binding activity to other tested pathogen-associated molecular patterns (PAMPs) including lipopolysaccharide (LPS), peptidoglycan (PGN), and mannose (Man) could not be detected. Surface plasmon resonance (SPR) analysis further revealed the high binding specificity and moderate binding affinity of rAjCTL-2 to d-galactose (KD = 4.093 × 10^-6 M). After rAjCTL-2 was blocked by its polyclonal antibody, the binding activity to d-galactose could not be detected by using a blocking ELISA (B-ELISA). Moreover, rAjCTL-2 could bind various microorganisms including V. splendidus, V. anguillarum, Staphylococcus aureus, Bifidobacterium breve and Yarrowia lipolytica with the strongest binding activity to B. breve. These results collectively suggested that AjCTL-2 was a member of CTL superfamily (CTLs) with preferential binding of d-galactose and participated in the immune response of sea cucumber.

Cloning and Characterization of Two Toll Receptors (PcToll5 and PcToll6) in Response to White Spot Syndrome Virus in the Red Swamp Crayfish Procambarus clarkii

Toll/Toll-like receptors are key components in the innate immune responses of invertebrates. In this study, we identified two novel Toll receptors (PcToll5 and PcToll6) from the red swamp crayfish Procambarus clarkii. The complete cDNA sequence of PcToll5 is 4247 bp, encoding a 1293 amino acid polypeptide. The full-length 4688 bp PcToll6 encodes a putative protein of 1195 amino acids. Quantitative RT-PCR analysis indicated that PcToll5 and PcToll6 were constitutively expressed in all tissues studied. The highest expression levels of PcToll5 and PcToll6 were found in the intestine and gills, respectively, and were significantly upregulated from 24 to 48 h during white spot syndrome virus (WSSV) challenge. siRNA-mediated RNA interference results showed that PcToll5 and PcToll6 might regulate the expression of anti-lipopolysaccharide factors (PcALF2 and PcALF3) in vivo. Overexpression of PcToll5 and PcToll6 in Drosophila Schneider 2 (S2) cells activated the transcription of Drosophila antimicrobial peptides, including drosomycin (Drs), metchnikowin (Mtk), and attacin A (AttA), and shrimp Penaeidin-4 (Pen4). These findings provide significant information that PcToll5 and PcToll6 may contribute to host immune defense against WSSV in P. clarkii.

Identification and characterization of two novel C-type lectins from the larvae of housefly, Musca domestica L

Lectins and antimicrobial peptides (AMPs) are widely distributed in various insects and play crucial roles in primary host defense against pathogenic microorganisms. Two AMPs (cecropin and attacin) have been identified and characterized in the larvae of housefly. In this study, two novel C-type lectins (CTLs) were obtained from Musca domestica, while their agglutinating and antiviral properties were evaluated. Real-time PCR analysis showed that the mRNA levels of four immune genes (MdCTL1, MdCTL2, Cecropin, and Attacin) from M. domestica were significantly upregulated after injection with killed Gram-negative Escherichia coli. Moreover, purified MdCTL1-2 proteins can agglutinate E. coli and Staphylococcus aureus in the presence of calcium ions, suggesting their immune function is Ca²⁺ dependent. Sequence analysis indicated that typical WND and QPD motifs were found in the Ca²⁺ -binding site 2 of carbohydrate recognition domain from MdCTL1-2, which was consistent with their agglutinating activities. Subsequently, antiviral experiments indicated that MdCTL1-2 proteins could significantly reduce the infection rate of Spodoptera frugiperda 9 cells by the baculovirus Autographa californica multicapsid nucleopolyhedrovirus, indicating they might play important roles in insect innate immunity against microbial pathogens. In addition, MdCTL1-2 proteins could effectively inhibit the replication of influenza H₁ N₁ virus, which was similar to the effect of ribavirin. These results suggested that two novel CTLs could be considered a promising drug candidate for the treatment of influenza. Moreover, it is believed that the discovery of the CTLs with antiviral effects in M. domestica will improve our understanding of the molecular mechanism of insect immune response against viruses.

C-type lectin B (SpCTL-B) regulates the expression of antimicrobial peptides and promotes phagocytosis in mud crab Scylla paramamosain

As pattern recognition receptors, C-type lectins (CTLs) play important roles in immune system of crustaceans through identifying and binding to the conservative pathogen-associated molecular patterns (PAMPs) on pathogen surfaces. In this study, a new CTL, SpCTL-B, was identified from the hemocytes of mud crab Scylla paramamosain. The full-length of SpCTL-B cDNA was 1278 bp with an open reading frame (ORF) of 348 bp. The predicted SpCTL-B protein contains a single carbohydrate-recognition domain (CRD). SpCTL-B transcripts were distributed in all examined tissues with the highest levels in hepatopancreas. After challenged with Vibrio parahaemolyticus, LPS, polyI:C and white spot syndrome virus (WSSV), the mRNA levels of SpCTL-B in hemocytes and hepatopancreas were up-regulated. The recombinant SpCTL-B (rSpCTL-B) purified by Ni-affinity chromatography showed stronger binding activities with Staphylococcus aureus, β-hemolytic Streptococcus, Escherichia coli, Aeromonas hydrophila, Vibrio alginolyticus than those with V. parahaemolyticus and Saccharomyces cerevisiae. rSpCTL-B exhibited a broad spectrum of microorganism-agglutination activities against Gram-positive bacteria (S. aureus, β-hemolytic Streptococcus) and Gram-negative bacteria (E. coli, V. parahaemolyticus, A. hydrophila, V. alginolyticus) in a Ca²⁺-dependent manner. The agglutination activities of rSpCTL-B could be inhibited by D-mannose and LPS, but not by d-fructose and galactose. The antimicrobial assay showed that rSpCTL-B exhibited the growth inhibition against all examined gram-positive bacteria and gram-negative bacteria. When SpCTL-B was silenced by RNAi, the bacterial clearance ability in mud crab was decreased and the transcript levels of five antimicrobial peptides (AMPs) (SpCrustin, SpHistin, SpALF4 (anti-lipopolysaccharide factor), SpALF5 and SpALF6) were significantly decreased in hemocytes. In our study, knockdown of SpCTL-B could down-regulate the expression of SpSTAT at mRNA transcriptional level and protein translational level in mud crab. Meantime, the phagocytosis rate and the expression of three phagocytosis related genes were declined after RNAi of SpCTL-B in hemocytes in mud crab. Collectively, our results suggest that SpCTL-B might play its roles as a pattern recognition receptor (PRR) in immune response towards pathogens infection through influencing the expression of AMPs and the phagocytosis of hemocytes in mud crab S. paramamosain.

iTRAQ-based quantitative proteomic analysis of Procambarus clakii hemocytes during Spiroplasma eriocheiris infection

As a new-found aquaculture pathogen, Spiroplasma eriocheiris, has resulted in inconceivable economic losses in aquaculture. In the infection of S. eriocheiris, the Procambarus clakii hemocytes have indicated to be major target cells. What was designed to examine in our study is the hemocytes' immune response at the protein levels. Before the pathogen was injected and after 192 h of post-injection, the differential proteomes of the crayfish hemocytes were analyzed immediately by isobaric tags for relative and absolute quantization (iTRAQ) labeling, followed by liquid chromatogramphytandem mass spectrometry (LC-MS/MS). This research had identified a total of 285 differentially expressed proteins. Eighty-three and 202 proteins were up-regulated and down-regulated, respectively, caused by the S. eriocheiris infection. Up-regulated proteins included alpha-2-macroglobulin (α2M), vitellogenin, ferritin, etc. Down-regulated proteins, involved with serine protease, peroxiredoxin 6, 14-3-3-like protein, C-type lectin, cdc42 homolog precursor, etc. The prophenoloxidase-activating system, antimicrobial action involved in the immune responses of P. clarkii is considered to be damaged due to S. eriocheiris infection. The present work could lay the foundation for future research on the proteins related to the susceptibility/resistance of P. clarkii to S. eriocheiris. In addition, it is helpful for our understanding molecular mechanism of disease processes in crayfishes.

An alternative function of C-type lectin comprising low-density lipoprotein receptor domain from Fenneropenaeus merguiensis to act as a binding receptor for viral protein and vitellogenin

A diversity of C-type lectins (CTLs) was coming reported and they are known to participate in invertebrate innate immunity by act as pattern recognition receptor (PRR). In the present study, a unique CTL containing low-density lipoprotein receptor (LDLR) domain from Fenneropenaeus merguiensis (designated as FmLdlr) was cloned. Its sequence contained a single LDLR domain and one carbohydrate recognition domain (CRD) with a QAP motif putative for galactose-specific binding. The expression of FmLdlr was detected only in hemocytes of healthy shrimp. Its expression was significantly up-regulated by Vibrio parahaemolyticus or white spot syndrome virus (WSSV) challenge. The knockdown by FmLdlr dsRNA resulted in severe gene down-regulation. The gene silencing with pathogenic co-inoculation led to reduction of the median lethal time and increasing in the cumulative mortality including the remained WSSV in WSSV co-challenge group. Recombinant proteins of FmLdlr and two domains could agglutinate various bacterial strains which LDLR domain revealed the lowest activity. Only FmLdlr and CRD could enhance phagocytosis and encapsulation by hemocytes. Both FmLdlr and CRD except LDLR domain exhibited the antibacterial activity by inhibiting the growth of pathogenic V. parahaemolyticus in cultured medium and disk diffusion assay. Only FmLdlr and CRD could bind to WSSV proteins, envelope VP28, tegument VP39A and also capsid VP15, which FmLdlr had the higher binding affinity than that of CRD. Altogether, we concluded that FmLdlr contributed in shrimp immune defense through the main action of CRD in capable of bacterial agglutination, enhancing the phagocytosis and encapsulation, antimicrobial activity and binding to viral proteins. Interestingly, ELISA approach revealed that LDLR domain displayed the highest binding affinity to vitellogenin than whole molecule and CRD. We signified a new function of FmLdlr that it might presumably act as a receptor for vitellogenin transportation in hemolymph during vitellogenesis of shrimp.

Identification and molecular profiling of DC-SIGN-like from big belly seahorse (Hippocampus abdominalis) inferring its potential relevancy in host immunity

Dendritic-cell-specific ICAM-3-grabbing non-integrin (DC-SIGN) is a C-type lectin that functions as a pattern recognition receptor by recognizing pathogen-associated molecular patterns (PAMPs). It is also involved in various events of the dendritic cell (DC) life cycle, such as DC migration, antigen capture and presentation, and T cell priming. In this study, a DC-SIGN-like gene from the big belly seahorse Hippocampus abdominalis (designated as ShDCS-like) was identified and molecularly characterized. The putative, complete ORF was found to be 1368 bp in length, encoding a protein of 462 amino acids with a molecular mass of 52.6 kDa and a theoretical isoelectric point of 8.26. The deduced amino acid sequence contains a single carbohydrate recognition domain (CRD), in which six conserved cysteine residues and two Ca²⁺-binding site motifs (QPN, WND) were identified. Based on pairwise sequence analysis, ShDCS-like exhibits the highest amino acid identity (94.6%) and similarity (97.4%) with DC-SIGN-like counterpart from tiger tail seahorse Hippocampus comes. Quantitative real-time PCR revealed that ShDCS-like mRNA is transcribed universally in all tissues examined, but with abundance in kidney and gill tissues. The basal mRNA expression of ShDCS-like was modulated in blood cell, kidney, gill and liver tissues in response to the stimulation of healthy fish with lipopolysaccharides (LPS), Edwardsiella tarda, or Streptococcus iniae. Moreover, recombinant ShDCS-like-CRD domain exhibited detectable agglutination activity against different bacteria. Collectively, these results suggest that ShDCS-like may potentially involve in immune function in big belly seahorses.

A C1qDC Protein (HcC1qDC6) with Three Tandem C1q Domains Is Involved in Immune Response of Triangle-Shell Pearl Mussel (Hyriopsis cumingii)

C1q-domain-containing (C1qDC) proteins are a family of proteins with a globular C1q (gC1q) domain and participate in several immune responses. In this study, a C1qDC gene was identified from the triangle-shell pearl mussel Hyriopsis cumingii (designated as HcC1qDC6). This gene has a full-length cDNA of 1782 bp and an open reading frame of 1,335 bp that encodes a 444-amino acid polypeptide containing three gC1q domains. HcC1qDC6 contains at least five exons and four introns. The mRNA transcripts of HcC1qDC6 were found to have the highest expression levels in the mantle tissue. The expression levels in the mantle and hepatopancreas were significantly upregulated by Staphylococcus aureus and Vibrio parahaemolyticus challenges. Moreover, knockdown of HcC1qDC6 inhibits the expression of two immune-related genes (tumor necrosis factor and whey acidic protein). The recombinant proteins of C1q1, C1q2, and C1q3 all exhibit a binding activity against seven bacterial species and directly bind to peptidoglycan and lipopolysaccharide. The results indicate that HcC1qDC6 is involved in the innate immunity of H. cumingii.

Identification and function of a novel C1q domain-containing (C1qDC) protein in triangle-shell pearl mussel (Hyriopsis cumingii)

C1q is the target recognition sequence of the classical complement pathway and a major link that connects innate and acquired immunity. In this study, a C1qDC homolog, HcC1qDC5, from the triangle-shell pearl mussel (Hyriopsis cumingii) was identified. The complete nucleotide sequence of HcC1qDC5 cDNA consists of a 5'-untranslated terminal region (UTR) of 123 bp, a 3'-UTR of 105 bp with a poly(A) tail, and an open reading frame (ORF) of 1344 bp, which encodes a polypeptide of 447 amino acids. HcC1qDC5 contains a signal peptide and three typical C1q domains. The HcC1qDC5 gene was expressed in all tested tissues, with the highest expression in the mantle. Staphylococcus aureus or Vibrio parahaemolyticus infection increased the mRNA transcript levels of HcC1qDC5 in the hepatopancreas and mantle. The recombinant HcC1qDC5 protein could bind to Gram-negative and Gram-positive bacteria as well as to different PAMPs (LPS and PGN). RNAi results showed that HcC1qDC5 was involved in V. parahaemolyticus-induced HcTNF and HcWAP expression. The combined results demonstrated that HcC1qDC5 participates in the innate immunity of H. cumingii.

Toll receptor response to white spot syndrome virus challenge in giant freshwater prawns (Macrobrachium rosenbergii)

Toll receptors are evolutionary ancient families of pattern recognition receptors with crucial roles in invertebrate innate immune response. In this study, we identified a Toll receptor (MrToll) from giant freshwater prawns (Macrobrachium rosenbergii). The full-length cDNA of MrToll is 4257 bp, which encodes a putative protein of 1367 amino acids. MrToll contains 17 LRR domains, a transmembrane domain, and a TIR domain. Phylogenetic analysis showed that MrToll was grouped with Drosophila Toll7 and other arthropod Tolls. The transcripts of MrToll are mainly distributed in the heart, hepatopancreas, gills, stomach, and intestine. A low level of MrToll expression can be detected in hemocytes and the lymphoid organ. MrToll expression in gills was gradually upregulated to the highest level from 24 h to 48 h during the white spot syndrome virus (WSSV) challenge. The expression levels of the crustin (Cru) genes Cru3 and Cru7 in gills were relatively lower than those of Cru2 and Cru4. The expression levels of Cru3 and Cru7 were inhibited after the RNA interference of MrToll in gills during the WSSV challenge. The anti-lipopolysaccharide factor (ALF) genes ALF2, ALF3, ALF4, and ALF5 were also regulated by MrToll in gills during the virus challenge. These findings suggest that MrToll may contribute to the innate immune defense of M. rosenbergii against WSSV.

A single CRD C-type lectin from Eriocheir sinensis (EsLecB) with microbial-binding, antibacterial prophenoloxidase activation and hem-encapsulation activities

C-type lectins (CTLs) exist widely in crustaceans. To date, thirteen CTLs have been reported in crustaceans, and play significant roles in pathogen recognition, encapsulation of hemocytes and antimicrobial activity in the innate immune response. Based on the initial expressed sequence tags (EST) of a hepatopancreatic cDNA library, a novel CTL, designated as EsLecB, with a 470 bp open reading frame encodes a polypeptide of 156 amino acids, including a signal peptide of 19 amino acid residues and one carbohydrate-recognition domain of 131 aa residues, was cloned from the crustacean Eriocheir sinensis. By qRT-PCR analysis, EsLecB was detected in all tested tissues, and showed highest expression in hemocytes, hepatopancreas and heart. The expression of EsLecB was up-regulated following injections of PAMPs or bacteria. The recombinant protein (rEsLecB) expressed in Escherichia coli had a calcium-independent but carbohydrate-dependent microbial-binding and microbial-agglutinating, microorganism growth inhibitory and hem-encapsulation activities. Moreover, the rEsLecB could stimulate the activation of prophenoloxidase in vitro. These results indicated that EsLecB, as an antibacterial pattern recognition receptor is involved in innate immunity, and may act as an upstream detector of the prophenoloxidase activating system, which can detect pathogen invasion in E. sinensis.

A novel C-type lectin is involved in the innate immunity of Macrobrachium nipponense

C-type lectins (CTLs) play important roles in invertebrate innate immunity by recognizing and eliminating pathogens. In the present study, a low-density lipoprotein receptor class A (LDLa) domain-containing CTL was identified from the oriental river prawn Macrobrachium nipponense, designated as MnCTLDcp1. The full-length cDNA of MnCTLDcp1 was composed of 1462 bp, with a 999-bp ORF encoding a 332-aa protein. An LDLa and a single C-type lectin-like domain (CTLD) were found. The mRNA transcripts of MnCTLDcp1 was expressed the highest in heart. After the prawns were challenged by Aeromonas hydrophila and Staphylococcus aureus, the expression level of MnCTLDcp1 in heart and hemocytes were all significantly up-regulated. Sugar binding assay revealed that the MnCTLDcp1 could bind to the glycoconjugates of bacteria surface, such as LPS, PGN and they can compete with bacterial as competitors. The recombinant MnCTLDcp1 agglutinates Gram-positive (S. aureus and Bacillus subtilis) and Gram-negative bacteria (A. hydrophila, Vibrio parahaemolyticus, Escherichia coli and Pseudomonas aeruginosa) in the presence of calcium and also could bind to these bacteria. These results clearly suggested that MnCTLDcp1 functions as a pattern-recognition receptor involved in the innate immunity of M. nipponense.

iTRAQ-based quantitative proteomic analysis of Macrobrachium rosenbergii hemocytes during Spiroplasma eriocheiris infection

Spiroplasma eriocheiris, as a novel aquaculture pathogen, has led into catastrophic economic losses in aquaculture. The Macrobrachium rosenbergii hemocytes were major target cells in S. eriocheiris infection. Our study was designed to examine the hemocytes' immune response at the protein levels. The differential proteomes of the prawn hemocytes were analyzed immediately prior to injection with the pathogen, and at 192h post-injection by isobaric tags for relative and absolute quantization (iTRAQ) labeling, followed by liquid chromatogramphytandem mass spectrometry (LC-MS/MS). A total of 69 differentially expressed proteins were identified. Forty-nine proteins were up-regulated and 20 proteins were down-regulated resulting from a S. eriocheiris infection. Up-regulated proteins included vertebrate gliacolin-like protein, vitellogenin, Gram-negative binding protein 1, alpha2 macroglobulin isoform 2 (a2M), etc. Down-regulated proteins, involved with beta-1,3-glucan-binding protein (BGBP), immunoglobulin like, Rab7, lipopolysaccharide and β-1,3-glucan (LGBP), actin-related protein, etc. Selected bioactive factors (tachylectin, α2M and vitellogenin, BGBP, C-type lectin, LGBP and Rab7) were verified by their immune roles in the S. eriocheiris infection using real-time PCR. The present work could serve as a basis for future studies on the proteins implicated in the susceptibility/resistance of M. rosenbergii to S. eriocheiris, as well as contribute to our understanding of disease processes in prawns.

BIOLOGICAL SIGNIFICANCE

This is the first time using an iTRAQ approach to analyze proteomes of M. rosenbergii mobilized against S. eriocheiris infection and substantiated the hemocytes' proteomic changes in M. rosenbergii using an infection model. The results reported here can provide a significant step forward toward a more complete elucidation of the immune relationship between M. rosenbergii and the pathogen S. eriocheiris.

A novel integrin function in innate immunity from Chinese mitten crab (Eriocheir sinensis)

Integrins belong to a superfamily of conserved α β heterodimeric cell surface receptors that have critical function in cell migration, differentiation, and survival. In this study, an integrin called EsIntegrin was identified from Chinese mitten crab Eriocheir sinensis. EsIntegrin cDNA is 4415 bp long with a 2457 bp open reading frame that encodes an 818 amino acid protein. EsIntegrin contains a signal peptide, an integrin beta subunit (N-terminal portion of extracellular region) INB domain, an epidermal growth factor (hEGF) domain, an integrin B tail domain, a transmembrane region, and an integrin b cyt domain. EsIntegrin was mainly expressed in hemocytes and the heart, with a relatively lower expression level in gills, nerves, intestine, hepatopancreas, muscles, and eyestalk. When healthy crabs were challenged with LPS, PGN, Staphyloccocus aureus, or Vibrio parahaemolyticus, EsIntegrin expression level was upregulated significantly. Recombinant EsIntegrin has agglutination activity to Gram-positive (e.g., S. aureus and Bacillus subtilis) and Gram-negative bacteria (e.g., V. parahaemolyticus and Aeromonas hydrophila) in the presence of calcium. Furthermore, rEsIntegrin could not only bind to various bacteria such as S. aureus, Micrococcus luteus, B. subtilis, Bacillus megaterium, Bacillus thuringiensis, V. parahaemolyticus, Vibrio anguillarum, A. hydrophila, Vibrio natriegens, and Escherichia coli, but this compound also helped crabs in clearing virulent Gram-negative bacterium, V. parahaemolyticus, in vivo. These data suggested that EsIntegrin might function as cellular receptor that is involved in anti-bacterial immunity from E. sinensis.

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.

Function of a novel C-type lectin with two CRD domains from Macrobrachium rosenbergii in innate immunity

C-type lectins play crucial roles in innate immunity. In the present study, a novel C-type lectin gene, designated as MrCTL, was identified from Macrobrachium rosenbergii. MrCTL contains 2 carbohydrate-recognition domains (CRDs), namely MrCRD1 and MrCRD2. The MrCRD1 contains a QEP motif and MrCRD2 contains a motif of EPD. MrCTL was mainly expressed in the hepatopancreas. The expression level of MrCTL in hepatopancreas was significantly upregulated after a challenge with Vibrio parahaemolyticus or White spot syndrome virus (WSSV). The recombinant MrCTL, MrCRD1 and MrCRD2 have an ability to agglutinate both Gram-negative (V. parahaemolyticus) and Gram-positive bacteria (Staphylococcus aureus) in a calcium dependent manner. The recombinant MrCTL, MrCRD1 and MrCRD2 bind directly to all tested microorganisms. All these results suggested that MrCTL may have important roles in immune defense against invading pathogens in prawns.

Identification and function of 11 Rab GTPases in giant freshwater prawn Macrobrachium rosenbergii

Rab GTPases, members of the Ras-like GTPase superfamily, are central elements in endocytic membrane trafficking. However, little is known of the Rab genes in the giant freshwater prawn Macrobrachium rosenbergii. In this study, 11 Rab genes were identified from M. rosenbergii. All MrRabs have a RAB domain. Phylogenetic analysis showed that these 11 MrRabs were divided into different groups. The MrRab genes were ubiquitously expressed in heart, hemocytes, hepatopancreas, gills, stomach, and intestines. Real-time polymerase chain reaction revealed that the MrRab genes were significantly upregulated by white spot syndrome virus (WSSV) in the prawns, indicating that MrRabs might play an important role in innate immune response against WSSV. Moreover, after challenge with Vibrio parahaemolyticus, the expression levels of all MrRabs in the hepatopancreas were also upregulated, which might indicated the involvement of MrRabs in prawns antibacterial immunity. In all, these preliminary results showed that MrRabs were involved in innate immunity of M. rosenbergii.

Novel myeloid differentiation factor 88, EsMyD88, exhibits EsTube-binding activity in Chinese mitten crab Eriocheir sinensis

Myeloid differentiation factor 88 (MyD88) is a universal and essential adapter protein that participates in the activation of the Toll-like receptor/interleukin-1 receptor-mediated signaling pathway. In the present study, a new MyD88 gene (named EsMyD88) was identified in the Chinese mitten crab Eriocheir sinensis. The cDNA of EsMyD88 was 2210 bp long with a 1416 bp open reading frame that encoded a protein with 472 amino acids. Predicted EsMyD88 protein had a death domain at the N-terminal and a TIR domain at the C-terminal. BLASTP and phylogenetic analysis results showed that EsMyD88 was clustered in one group together with other crustaceans MyD88 (SpMyD88, FcMyD88, LvMyD88, and LvMyD88-1). EsMyD88 was detected in all the examined tissues of healthy crabs, and was mainly expressed in the hemocytes and nerves. When normal crabs were challenged with lipopolysaccharide, peptidoglycan, Staphylococcus aureus, Vibrio parahaemolyticus, or Aeromonas hydrophila, the expression levels of EsMyD88 significantly increased either in the hepatopancreas or hemocytes. Results of the pull-down assay showed that EsMyD88 could bind to downstream cytosolic adaptor EsTube. Overexpression of EsMyD88 protein in Drosophila Schneider 2 cells led to the activation of antimicrobial peptide genes. RNA interference assay showed that EsMyD88 is involved in regulating the transcription of ALF1 and ALF2, Cru1 and Cru2, and Lys in crab challenged with V. parahaemolyticus. All the results mentioned earlier indicated that EsMyD88 gene has a key function in antibacterial innate immune defense.

Cloning and characterization of two different L-type lectin genes from the Chinese mitten crab Eriocheir sinensis

L-type lectins contain a leguminous lectin domain and bind to high-mannose type oligosaccharides. In the secretory pathway, L-type lectins play crucial functions in the trafficking, sorting, and targeting of maturing glycoproteins. This study identified two novel L-type lectins, designated as EsERGIC-53 and EsVIP36, from the Chinese mitten crab Eriocheir sinensis. The complete nucleotide sequence of ERGIC-53 cDNA was 1955 bp, containing a 1506 bp open reading frame (ORF) encoding a putative protein of 501 deduced amino acids. The full-length cDNA of VIP36 was 3474 bp with a 984 bp ORF encoding a 327-amino acid peptide. The deduced ERGIC-53 and VIP36 proteins contained a putative signal peptide and an L-type lectin-like domain. Phylogenetic analysis showed that ERGIC-53 and VIP36 belonged to different clades of L-type lectin family. Reverse transcription PCR showed that ERGIC-53 and VIP36 were expressed in all tested tissues. Quantitative real-time RT-PCR analysis revealed that ERGIC-53 and VIP36 transcripts in hepatopancreas were significantly induced at various time points after infection with lipopolysaccharide (LPS), peptidoglycan (PGN), Staphylococcus aureus, Vibrio parahaemolyticus, and Aeromonas hydrophila. A bacterium-binding experiment showed that both ERGIC-53 and VIP36 could bind to different microbes. Sugar binding assay revealed that these lectins could also bind to the glycoconjugates of bacteria surface, such as LPS, PGN, d-Mannose, and N-Acetyl-d-mannosamine. Moreover, these two L-type lectins agglutinated bacteria in a calcium-dependent manner, and both exerted the ability of facilitating the clearance of injected bacteria V. parahaemolyticus in the crab. Our results suggested that ERGIC-53 and VIP36 functioned as pattern recognition receptors in the immune system of E. sinensis.

iTRAQ-based proteomic study of the effects of Spiroplasma eriocheiris on Chinese mitten crab Eriocheir sinensis hemocytes

Spiroplasma eriocheiris is as a novel pathogen of Chinese mitten crab Eriocheir sinensis tremor disease. The hemocytes have been shown to be major target cells in S. eriocheiris infection. The aim of this study was to examine the hemocytes' immune response at the protein levels. The differential proteomes of the crab hemocytes were analyzed immediately prior to injection with the pathogen, and at 10 d post-injection by isobaric tags for relative and absolute quantization (iTRAQ) labeling, followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1075 proteins were identified by LC-MS/MS and de novo sequencing data. Using a 1.2-fold change in expression as a physiologically significant benchmark, 76 differentially expressed proteins (7.07%) were reliably quantified by iTRAQ analysis. Thirty-five (3.26%) proteins were up-regulated and 41 (3.81%) proteins were down-regulated resulting from a S. eriocheiris infection. Approximately 20 differential proteins in hemocytes were involved in the stress and immune responses. Up-regulated proteins included alpha-2-macroglobulin (α2M), prostaglandin D synthase (GST), ferritin, and heat shock protein 60. Down-regulated proteins included two lectins (mannose-binding protein and hemocytin), three kinds of serine proteinase inhibitors (two serpins and pacifastin), three different kinds of serine proteases, mitogen-activated protein kinase kinase (MAPKK), and two thioredoxins (Trx), crustin, etc. Selected bioactive factors (α2M, GST, ferritin, tubulin, crustin, thioredoxin, clip domain serine protease and serpin) are verified by their immune roles in the S. eriocheiris infection using Real-time PCR. The variation trend of immune gene's mRNA expression is similar with the result of iTRAQ, except the tubulin. The prophenoloxidase-activating system, antimicrobial action and antioxidant system involved in the immune responses of E. sinensis is believed to be a resistance to S. eriocheiris infection. This is the first report of the proteome response of crab hemocytes against S. eriocheiris infection. These findings contribute to our understanding of tremor disease processes in crabs, and provide the first evidence to promote a search for potential biomarkers of the disease.