Characterization of a shrimp serine protease homolog, a binding protein of yellow head virus

The first report of a C-type lectin contains a CLIP domain involved in antibacterial defense in Macrobrachium nipponense

We identified a novel C-type lectin (CTL) from Macrobrachium nipponense, designated as Mn-clip-Lec. It consists of 1315 bp with an open reading frame of 1098 bp, encoding a polypeptide of 365 amino acids. Mn-clip-Lec contains 6 exons and 5 introns. Mn-clip-Lec possessed a CLIP domain at the N-terminal and two carbohydrate recognition domains at the C-terminal. Interaction between Mn-clip-Lec and MnLec was found by Yeast two-hybrid analysis. The expressions of Mn-clip-Lec, MnLec, prophenoloxidase (proPO)-activating system-associated genes (MnPPAF, MnPPAE, and MnPO), and antimicrobial peptides (AMPs) (MnALF and MnCRU) were up-regulated after the challenge with Staphylococcus aureus. RNA interference (RNAi)-mediated suppression of the Mn-clip-Lec and MnLec genes in S. aureus-challenged prawns reduced the transcripts of MnPPAF, MnPPAE, MnPO, MnALF and MnCRU. Knockdown of Mn-clip-Lec and MnLec resulted in decrease in PO activity in M. nipponense infected with S. aureus. The recombinant Mn-clip-Lec (rMn-clip-Lec) protein bound all tested bacteria and agglutinated S. aureus. A sugar-binding assay revealed that rMn-clip-Lec could bind to LPS or PGN. rMn-clip-Lec accelerated the clearance of S. aureus in vivo. Our findings suggest that Mn-clip-Lec and its interacting MnLec play important roles in the induction of the proPO system and AMPs expression in M. nipponense during bacterial infection.

Effects of the interaction between a clip domain serine protease and a white spot syndrome virus protein on phenoloxidase activity

Clip domain serine proteinases participate in invertebrate innate immunity by acting as crucial enzymes in the signaling cascade involved in shrimp immunity. To functionally characterize its role in Fenneropenaeus merguiensis, FmclipSP cDNA was cloned and characterized. The FmclipSP gene comprised 1353 bp with an open reading frame of 1110 bp and encoded 369 amino acids. The protein contained clip and serine protease domains. FmClipSP mRNA is highly expressed in hemocytes, and its expression was significantly upregulated by bacterial or viral pathogen challenge. Furthermore, FmClipSP recombinant protein (rFmClipSP) was produced and possessed protease activity, stimulating prophenoloxidase activity. Additionally, rFmClipSP exhibited antibacterial activity against pathogens and nonpathogens. ELISA results demonstrated the binding ability of rFmClipSP to a recombinant protein of VP28 (rVP28). Interestingly, the binding significantly inhibited prophenoloxidase activity. Altogether, we partially characterized the function of FmclipSP and demonstrated its association with VP28. This study indicates the importance of clipSP as a component of F. merguiensis innate immunity. However, the role of clipSP in crustaceans remains unclear and requires further investigation.

Viral Shrimp Diseases Listed by the OIE: A Review

Shrimp is one of the most valuable aquaculture species globally, and the most internationally traded seafood product. Consequently, shrimp aquaculture practices have received increasing attention due to their high value and levels of demand, and this has contributed to economic growth in many developing countries. The global production of shrimp reached approximately 6.5 million t in 2019 and the shrimp aquaculture industry has consequently become a large-scale operation. However, the expansion of shrimp aquaculture has also been accompanied by various disease outbreaks, leading to large losses in shrimp production. Among the diseases, there are various viral diseases which can cause serious damage when compared to bacterial and fungi-based illness. In addition, new viral diseases occur rapidly, and existing diseases can evolve into new types. To address this, the review presented here will provide information on the DNA and RNA of shrimp viral diseases that have been designated by the World Organization for Animal Health and identify the latest shrimp disease trends.

Characterization and functional analysis of a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) from Macrobrachium nipponense

Clip domain serine protease (cSPs) play an important role in the innate immune defense of crustaceans. In this study, a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) were identified from Macrobrachium nipponense. The full-length cDNA sequences of MncSP and MncSP-isoform were 2447 and 2351 bp with open reading frames comprising 1497 and 1401 bp nucleotides and encoding 498 and 466 amino acids, respectively. The genome of MncSP had 10 exons and 9 introns. MncSP contained all 10 exons, whereas MncSP-isoform lacked the second exon. MncSP and MncSP-isoform contained a signal peptide, a clip domain, and a Tryp_SPc domain. Phylogenetic tree analysis showed that MncSP and MncSP-isoform clustered with cSPs from Palaemonidae. MncSP and MncSP-isoform were widely distributed in hemocytes, heart, hepatopancreas, gills, stomach, and intestine. The expression profiles of MncSP and MncSP-isoform in the hemocytes of M. nipponense changed after simulation by Vibrio parahaemolyticus or Staphylococcus aureus. The RNAi of MncSP could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. Phenoloxidase activity was also down-regulated in MncSP-silenced prawns. This study indicated that MncSP participated in the synthesis of AMPs and the activation of prophenoloxidase.

Differential white spot syndrome virus-binding proteins in two hemocyte subpopulations of Chinese shrimp (Fenneropenaeus chinensis)

A number of white spot syndrome virus (WSSV)-binding proteins have been identified previously in the hemocytes of Fenneropenaeus chinensis. In order to further investigate the differential WSSV-binding proteins in hemocyte subpopulations, granular hemocytes and hyalinocytes were sorted from WSSV-infected shrimp by immunomagnetic bead (IMB) method. The results of ELISA and immuno-dot blot assay showed that the WSSV-binding activity of granular hemocytes proteins was much stronger than that of hyalinocytes proteins. And the percentage of WSSV-positive granular hemocytes was significantly higher than that of hyalinocytes post WSSV infection, indicating that granular hemocytes were more susceptible to WSSV infection. Moreover, a total of 9 WSSV-binding proteins were successfully identified in granular hemocytes and hyalinocytes by two-dimensional virus overlay protein binding assay (2D-VOPBA) and MALDI-TOF MS analysis, of which 3 binding proteins (arginine kinase, protease 1 and transglutaminase) existing in both hyalinocytes and granular hemocytes and 6 proteins (F₁ATP synthase β-chain, hnRNPs, GAPDH, RACK1, β-actin and cellular retinoic acid) detected only in granular hemocytes. Among these identified WSSV-binding proteins, the transglutaminase (TG) was further recombinantly expressed, and the recombinant TG could be bound with WSSV. Subsequently, quantitative real-time PCR analysis showed that differential expression levels of WSSV-binding proteins were observed in granular hemocytes and hyalinocytes. The results of this study revealed that the WSSV-binding proteins were differentially expressed in granular hemocytes and hyalinocytes, which provided a deeper insight into the interaction between WSSV and hemocyte subpopulations.

Dietary reduced glutathione supplementation can improve growth, antioxidant capacity, and immunity on Chinese mitten crab, Eriocheir sinensis

Eriocheir sinensis is an important aquaculture species in China, and its yield and quality are threatened by oxidative stress caused by deteriorating water conditions. Reduced glutathione (GSH) is an endogenous antioxidant, but whether dietary GSH can increase the resistance of E. sinensis to environmental stress remains unclear. Therefore, in this study, crabs were fed with dietary GSH (0, 300, 600, 900, and 1200 mg/kg diet weight) for up to 10 weeks to determine the effects of different dietary GSH concentrations on growth, antioxidant capacity, and immunity of E. sinensis. The results showed that the weight gain rate and survival rate increased significantly as dietary GSH levels increased from 0 to 900 mg/kg, but decreased at 1200 mg/kg. Compared with the control group, the diet supplemented with 900 mg/kg GSH not only increased the concentration of GSH in the haemolymph and hepatopancreas, but also enhanced the activity of glutathione peroxidase (GSH-Px) (p < 0.05). Diets supplemented with 600 or 900 mg/kg GSH significantly increased the enzymes activities of superoxide dismutase (SOD), lysozyme (LZM), alkaline phosphatase, and acid phosphatase, and significantly decreased the content of malondialdehyde. To understand the changes in the activity of these enzymes further, the expression of related genes was detected. Diets supplemented with 600 or 900 mg/kg GSH significantly upregulated the genes expressions of cytosolic manganese SOD, mitochondrial manganese SOD, copper, zinc-SOD, GSH-Px, LZM, and prophenoloxidase activating factor, and significantly down regulated the expression of Toll-like receptor 1, Toll-like receptor 2, Dorsal, and the myeloid differentiation factor 88. However, a diet supplemented with 1200 mg/kg GSH decreased those positive indicators. Overall, our results demonstrated that an appropriate diet supplemented with 600 or 900 mg/kg GSH enhances antioxidant capacity and immunity, which will enhance the general health of E. sinensis.

A Pacifastacus leniusculus serine protease interacts with WSSV

Serine proteases are involved in many critical physiological processes including virus spread and replication. In the present study, we identified a new clip-domain serine protease (PlcSP) in the crayfish Pacifastacus leniusculus hemocytes, which can interact with the White Spot Syndrome Virus (WSSV) envelope protein VP28. It was characterized by a classic clip domain with six strictly conserved Cys residues, and contained the conserved His-Asp-Ser (H-D-S) motif in the catalytic domain. Furthermore, signal peptide prediction revealed that it has a 16-residue secretion signal peptide. Tissue distribution showed that it was mainly located in P. leniusculus hemocytes, and its expression was increased in hemocytes upon WSSV challenge. In vitro knock down of PlcSP decreased both the expression of VP28 and the WSSV copy number in hematopoietic stem (HPT) cells. Accordingly, these data suggest that the new serine protease may be of importance for WSSV infection into hematopoietic cells.

Identification of a novel clip domain serine proteinase (Sp-cSP) and its roles in innate immune system of mud crab Scylla paramamosain

Clip domain serine proteinases and their homologs are involved in the innate immunity of invertebrates. To identify the frontline defense molecules against pathogenic infection, we isolated a novel clip domain serine proteinase (Sp-cSP) from the hemocytes of mud crab Scylla paramamosain. The full-length 1362 bp Sp-cSP contains a 1155 bp open reading frame (ORF) encoding 384 amino acids. Multiple alignment analysis showed that the putative amino acid sequence of Sp-cSP has about 52% and 51% identity with Pt-cSP2 (AFA42360) and Pt-cSP3 (AFA42361) from Portunus trituberculatus, respectively, while the similarity with other cSP sequences was lower than 30%. However, all cSP sequences possess a conserved clip domain at the N-terminal and a Tryp-SPc domain at the C-terminal. The genomic organization of Sp-cSP consists of nine exons and eight introns, with some introns containing one or more tandem repeats. RT-PCR results indicated that Sp-cSP transcripts were predominantly expressed in the subcuticular epidermis, muscle and mid-intestine, but barely detectable in the brain and heart. Further, Sp-cSP transcripts were significantly up-regulated after challenge with lipopolysaccharides (LPS), Vibrio parahaemolyticus, polyinosinic polycytidylic acid (PolyI:C) or white spot syndrome virus (WSSV). Moreover, in vitro, the recombinant Sp-cSP revealed a strong antimicrobial activity against a Gram-positive (Staphylococcus aureus) and four Gram-negative (V. parahaemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) bacteria in a dose-dependent manner. Taken together, the acute-phase response to immune challenges and the antimicrobial activity assay indicate that Sp-cSP is a potent immune protector and plays an important role in host defense against pathogen invasion in S. paramamosain.

Shrimp serine proteinase homologues PmMasSPH-1 and -2 play a role in the activation of the prophenoloxidase system

Melanization mediated by the prophenoloxidase (proPO) activating system is a rapid immune response used by invertebrates against intruding pathogens. Several masquerade-like and serine proteinase homologues (SPHs) have been demonstrated to play an essential role in proPO activation in insects and crustaceans. In a previous study, we characterized the masquerade-like SPH, PmMasSPH1, in the black tiger shrimp Penaeus monodon as a multifunctional immune protein based on its recognition and antimicrobial activity against the Gram-negative bacteria Vibrio harveyi. In the present study, we identify a novel SPH, known as PmMasSPH2, composed of an N-terminal clip domain and a C-terminal SP-like domain that share high similarity to those of other insect and crustacean SPHs. We demonstrate that gene silencing of PmMasSPH1 and PmMasSPH2 significantly reduces PO activity, resulting in a high number of V. harveyi in the hemolymph. Interestingly, knockdown of PmMasSPH1 suppressed not only its gene transcript but also other immune-related genes in the proPO system (e.g., PmPPAE2) and antimicrobial peptides (e.g., PenmonPEN3, PenmonPEN5, crustinPm1 and Crus-likePm). The PmMasSPH1 and PmMasSPH2 also show binding activity to peptidoglycan (PGN) of Gram-positive bacteria. Using a yeast two-hybrid analysis and co-immunoprecipitation, we demonstrate that PmMasSPH1 specifically interacted with the final proteinase of the proPO cascade, PmPPAE2. Furthermore, the presence of both PmMasSPH1 and PmPPAE2 enhances PGN-induced PO activity in vitro. Taken together, these results suggest the importance of PmMasSPHs in the activation of the shrimp proPO system.

A clip-domain serine proteinase homolog (SPH) in oriental river prawn, Macrobrachium nipponense provides insights into its role in innate immune response

In this study, a clip-domain serine proteinase homolog designated as MnSPH was cloned and characterized from a freshwater prawn Macrobrachium nipponense. The full-length cDNA of MnSPH was 1897 bp and contained a 1701 bp open reading frame (ORF) encoding a protein of 566 amino acids, a 103 bp 5'-untranslated region, and a 93 bp 3'-untranslated region. Sequence comparison showed that the deduced amino acids of MnSPH shared 30-59% identity with sequences reported in other animals. Tissue distribution analysis indicated that the MnSPH transcripts were present in all detected tissues with highest in the hepatopancreas and ovary. The MnSPH mRNA levels in the developing ovary were stable at the initial three developmental stages, then increased gradually from stage IV (later vitellogenesis), and reached a maximum at stage VI (paracmasis). Furthermore, the expression of MnSPH mRNA in hemocytes was significantly up-regulated at 1.5 h, 6 h, 12 h and 48 h post Aeromonas hydrophila injection. The increased phenoloxidase activity also demonstrated a clear time-dependent pattern after A. hydrophila challenge. These results suggest that MnSPH participates in resisting to pathogenic microorganisms and plays a pivotal role in host defense against microbe invasion in M. nipponense.

PmPPAF is a pro-phenoloxidase activating factor involved in innate immunity response of the shrimp Penaeus monodon

One of the major steps in the innate immune response of shrimp includes the activation of serine proteinases of the pro-phenoloxidase pathway by the prophenoloxidase activation enzyme (PPAF). In this study, the cDNA encoding a serine proteinase homologue (SPH) with prophenoloxidase activating activity of Penaeus monodon (PmPPAF) was cloned and characterized. PmPPAF cDNA consists of 1444 nucleotides encoding a protein with 394 amino acid residues. The estimated molecular weight of PmPPAF is 43.5 kDa with an isoelectric point of 5.19. PmPPAF consists of a signal peptide, a CLIP domain and a carboxyl-terminal trypsin-like serine protease domain. It is highly similar to the masquerade-like protein 2A (61% similarity) of the crayfish Pacifastacus leniusculus, other serine proteases (42.9-67% identity) of P. monodon, and the PPAF of the crab (61% similarity). Unlike other SPH of P. monodon, which express mainly in the hemocytes, PmPPAF transcripts were detected in the hemocytes, eyestalk, hypodermis, gill, swimming leg and brain. Similar to the crab PPAF, PmPPAF transcript level is high in shrimp at the premolt stages and PmPPAF expression is up-regulated in shrimp infected with white spot syndrome virus (WSSV). Gene silencing of PmPPAF decreased expression of a prophenoloxidase-like gene and injection of Anti-PmPPAF antibody causes a decrease in PO activity. Taken together, these results provided evidence that PmPPAF is a serine proteinase homologue, and is involved in the pro-PO activation pathway of the shrimp innate immune system.

Comparative proteomic analysis of midgut proteins from male and female Bombyx mori (Lepidoptera: Bombycidae)

Many biological phenotypes of male and female silkworms (Bombyx mori) are quite different, and one of the major differences is the growth rate at various larval stages. Nutrient utilization by midgut varies with sexes. However, the molecular basis of this variation is not clear. To understand the molecular mechanism, comparative proteomic approach was employed to investigate the variation of midgut proteomes between male and female silkworms. Totally, 32 proteins that were grouped into four categories were differentially expressed and subsequently identified by mass spectrometry. Gene ontology analysis revealed that these proteins were attributed with biological functions such as binding, catalytic, and transporter, and these proteins were involved in biological process such as cellular process, localization, and metabolic process. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed that these proteins were involved in pathways such as glycolysis, gluconeogenesis, oxidative phosphorylation, and purine metabolism. At transcription level, the expressional variation was confirmed for six identified proteins including muscle glycogen phosphorylase, uridine 5'-monophosphate synthase, cone cGMP-specific 3',5'-cyclic phosphodiesterase subunit alpha, ATP synthase, thiol peroxiredoxin, and serpin-2. This study provides useful information for understanding the mechanisms of nutrient absorption and the protein-protein interaction in the silkworm.

Cloning and characterization of a clip domain serine protease and its homolog (masquerade) from Eriocheir sinensis

Serine proteinases (SPs) or SP homologs (SPHs) including clip domain SPs (cSPs) or SPHs (cSPHs) play critical roles in digestion, embryonic development, hemolymph coagulation, and melanization. In this study, one cSP (EscSP) and one SPH, similar to Drosophila masquerade (EsMas), were identified from hepatopancreas of the Chinese mittern crab Eriocheir sinensis. They both possess the clip domains at the N-terminal, EscSP has only one clip domain, but EsMas has seven clip domains. One SP or SP-like domain was at the C-terminal of EscSP and EsMas respectively. In contrast to EscSP, absence of a catalytic residue of Ser resulted in the loss of SP activity of EsMas. Tissue distribution analysis showed that EscSP mRNA was mainly expressed in hepatopancreas, nerve and eyestalk tissue; whereas the EsMas transcript was mainly distributed in eyestalk, muscle, nerve and hemocytes. EscSP in hemocytes showed significant increase after a lipopolysaccharide (LPS) or peptidoglycan (PGN) challenge. However, down-regulation of EsMas was observed in hemocytes challenged by LPS from 2 to 24 h, by contrast EsMas could be induced by PGN challenge at 2 and 24 h. All these findings indicated that EscSP and EsMas might be involved in the innate immune defenses in E. sinensis.

Characterization and functional analysis of serine proteinase and serine proteinase homologue from the swimming crab Portunus trituberculatus

Serine proteases (SPs), with their homologues (SPHs), a family of multifunctional proteins, play a crucial role in innate immune system. In our present study, we made an appropriate correction: serine protease homologue PtcSPH (Li et al., [1]) obtained from the swimming crab Portunus trituberculatus was actually a serine protease and re-designated as PtcSP. Sequence analysis revealed PtcSP and PtSP (Li et al., [2]) might be encoded by the same genomic locus and generated by alternative splicing of the pre-mRNA. Eight exons were identified in genomic DNA sequence of PtcSP. A comprehensive phylogenetic analysis was made combined with our previous reports (Cui et al., [3]; Li et al., [1,2]). The result showed SPs and SPHs of P. trituberculatus had different origins in gene evolution. To further characterize the function(s) of proteins, the recombinant serine proteases or homologues were assayed for various biological functions: proteinase activity, antimicrobial activity and microorganisms binding activity. The recombinant protein PtcSP exhibited trypsin-like protease activity and antibacterial activity. PtSPH1 (Li et al., [2]) lacked proteolytic activity but displayed binding activity to yeast and the crab pathogenic bacterium, Vibrio alginolyticus. Further, the N-terminal clip domain of PtcSP had antibacterial activity and the C-terminal SP-like domain had trypsin-like protease activity.

Prophenoloxidase system and its role in shrimp immune responses against major pathogens

The global shrimp industry still faces various serious disease-related problems that are mainly caused by pathogenic bacteria and viruses. Understanding the host defense mechanisms is likely to be beneficial in designing and implementing effective strategies to solve the current and future pathogen-related problems. Melanization, which is performed by phenoloxidase (PO) and controlled by the prophenoloxidase (proPO) activation cascade, plays an important role in the invertebrate immune system in allowing a rapid response to pathogen infection. The activation of the proPO system, by the specific recognition of microorganisms by pattern-recognition proteins (PRPs), triggers a serine proteinase cascade, eventually leading to the cleavage of the inactive proPO to the active PO that functions to produce the melanin and toxic reactive intermediates against invading pathogens. This review highlights the recent discoveries of the critical roles of the proPO system in the shrimp immune responses against major pathogens, and emphasizes the functional characterizations of four major groups of genes and proteins in the proPO cascade in penaeid shrimp, that is the PRPs, serine proteinases, proPO and inhibitors.

Discovery of immune molecules and their crucial functions in shrimp immunity

Several immune-related molecules in penaeid shrimps have been discovered, most of these via the analysis of expressed sequence tag libraries, microarray studies and proteomic approaches. These immune molecules include antimicrobial peptides, serine proteinases and inhibitors, phenoloxidases, oxidative enzymes, clottable protein, pattern recognition proteins, lectins, Toll receptors, and other humoral factors that might participate in the innate immune system of shrimps. These molecules have mainly been found in the hemolymph and hemocytes, which are the main sites where immune reactions take place, while some are found in other immune organs/tissues, such as the lymphoid organs, gills and intestines. Although the participation of some of these immune molecules in the shrimp innate immune defense against invading pathogens has been demonstrated, the functions of many molecules remain unclear. This review summarizes the current status of our knowledge concerning the discovery and functional characterization of the immune molecules in penaeid shrimps.

Reprint of: Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

Host and virus protein interaction studies in understanding shrimp virus gene function

Protein-protein interaction studies have been widely used in several fields to characterize an unknown protein. This in turn helps to find out several pathways to understand a complex mechanism or discover a drug for treatment. Among the methods, yeast two-hybrid has widely been used in human, animal and plant research studies. This aspect of research has also been found useful in understanding the shrimp virus gene function. With respect to White spot syndrome virus, interaction studies have been applied to elucidate virus structure, understand the mode of entry of the virus, mechanism of virus replication and also to discover some of the host anti-viral proteins. Interaction studies on other shrimp viruses are scanty and only few reports available on Yellow head virus and Taura syndrome virus. All these findings are still in preliminary stage and lot more studies are necessary to have the clear picture. Protein interaction research on other shrimp viruses are still lacking. Considering all these, it appears that this field of research has a wide scope to understand the virulence mechanism of shrimp viruses where very little information is available till date.

Comparative proteomic analysis reveals that caspase-1 and serine protease may be involved in silkworm resistance to Bombyx mori nuclear polyhedrosis virus

The silkworm Bombyx mori is of great economic value. The B. mori nuclear polyhedrosis virus (BmNPV) is one of the most common and severe pathogens for silkworm. Although certain immune mechanisms exist in silkworms, most silkworms are still susceptible to BmNPV infection. Interestingly, BmNPV infection resistance in some silkworm strains is varied and naturally existing. We have previously established a silkworm strain NB by genetic cross, which is highly resistant to BmNPV invasion. To investigate the molecular mechanism of silkworm resistance to BmNPV infection, we employed proteomic approach and genetic cross to globally identify proteins differentially expressed in parental silkworms NB and 306, a BmNPV-susceptible strain, and their F(1) hybrids. In all, 53 different proteins were found in direct cross group (NB♀, 306♂, F(1) hybrid) and 21 in reciprocal cross group (306♀, NB♂, F(1) hybrid). Gene ontology and KEGG pathway analyses showed that most of these different proteins are located in cytoplasm and are involved in many important metabolisms. Caspase-1 and serine protease expressed only in BmNPV-resistant silkworms, but not in BmNPV-susceptible silkworms, which was further confirmed by Western blot. Taken together, our data suggests that both caspase-1 and serine protease play a critical role in silkworm resistance against BmNPV infection.

Three clip domain serine proteases (cSPs) and one clip domain serine protease homologue (cSPH) identified from haemocytes and eyestalk cDNA libraries of swimming crab Portunus trituberculatus

Four genes including three clip domain serine proteases (PtcSP1, PtcSP2 and PtcSP3) and one clip domain serine protease homologue (PtcSPH) of the swimming crab Portunus trituberculatus (Decapoda: Brachyura: Portunidae) were characterized based on analysis of expressed sequence tags from haemocytes and eyestalk cDNA libraries. The relative four peptidases, which share high structural similarity to the clip-SPs of other arthropod species, appeared to possess a clip domain at the N-terminus and an enzymatically active serine protease domain at the C-terminus except PtcSPH for its second catalytic residue Asp. (D) replaced by Ala (A). Alignment among the four full-sequences showed that PtcSP2 and PtcSP3 had the highest identical score (58%) while the similarity of other sequences was lower than 24%. The mRNA transcripts of PtcSPs and PtcSPH could be detected widely in all the examined tissues with remarkable different expression levels. The temporal expressions of PtcSPs and PtcSPH demonstrated different time-dependent expression pattern post Vibrio alginolyticus, Micrococcus luteus, and Pichia pastoris challenge. Especially, the expression of PtcSPH transcripts showed greater change against V. alginolyticus compared with the other two microorganisms. These findings suggest that PtcSPs and PtcSPH play different roles in the antibacterial defence mechanism of P. trituberculatus crab.

Feminizing Wolbachia: a transcriptomics approach with insights on the immune response genes in Armadillidium vulgare

BACKGROUND

Wolbachia are vertically transmitted bacteria known to be the most widespread endosymbiont in arthropods. They induce various alterations of the reproduction of their host, including feminization of genetic males in isopod crustaceans. In the pill bug Armadillidium vulgare, the presence of Wolbachia is also associated with detrimental effects on host fertility and lifespan. Deleterious effects have been demonstrated on hemocyte density, phenoloxidase activity, and natural hemolymph septicemia, suggesting that infected individuals could have defective immune capacities. Since nothing is known about the molecular mechanisms involved in Wolbachia-A. vulgare interactions and its secondary immunocompetence modulation, we developed a transcriptomics strategy and compared A. vulgare gene expression between Wolbachia-infected animals (i.e., "symbiotic" animals) and uninfected ones (i.e., "asymbiotic" animals) as well as between animals challenged or not challenged by a pathogenic bacteria.

RESULTS

Since very little genetic data is available on A. vulgare, we produced several EST libraries and generated a total of 28 606 ESTs. Analyses of these ESTs revealed that immune processes were over-represented in most experimental conditions (responses to a symbiont and to a pathogen). Considering canonical crustacean immune pathways, these genes encode antimicrobial peptides or are involved in pathogen recognition, detoxification, and autophagy. By RT-qPCR, we demonstrated a general trend towards gene under-expression in symbiotic whole animals and ovaries whereas the same gene set tends to be over-expressed in symbiotic immune tissues.

CONCLUSION

This study allowed us to generate the first reference transcriptome ever obtained in the Isopoda group and to identify genes involved in the major known crustacean immune pathways encompassing cellular and humoral responses. Expression of immune-related genes revealed a modulation of host immunity when females are infected by Wolbachia, including in ovaries, the crucial tissue for the Wolbachia route of transmission.

Co-interactive DNA-binding between a novel, immunophilin-like shrimp protein and VP15 nucleocapsid protein of white spot syndrome virus

White spot syndrome virus (WSSV) is one of the most serious pathogens of penaeid shrimp. Although its genome has been completely characterized, the functions of most of its putative proteins are not yet known. It has been suggested that the major nucleocapsid protein VP15 is involved in packaging of the WSSV genome during virion formation. However, little is known in its relationship with shrimp host cells. Using the yeast two-hybrid approach to screen a shrimp lymphoid organ (LO) cDNA library for proteins that might interact with VP15, a protein named PmFKBP46 was identified. It had high sequence similarity to a 46 kDa-immunophilin called FKBP46 from the lepidopteran Spodoptera frugiperda (the fall armyworm). The full length PmFKBP46 consisted of a 1,257-nucleotide open reading frame with a deduced amino acid sequence of 418 residues containing a putative FKBP-PPIase domain in the C-terminal region. Results from a GST pull-down assay and histological co-localization revealed that VP15 physically interacted with PmFKBP46 and that both proteins shared the same subcellular location in the nucleus. An electrophoretic mobility shift assay indicated that PmFKBP46 possessed DNA-binding activity and functionally co-interacted with VP15 in DNA binding. The overall results suggested that host PmFKBP46 might be involved in genome packaging by viral VP15 during virion assembly.

Identification of three different types of serine proteases (one SP and two SPHs) in Chinese white shrimp

Serine proteases (SPs) and serine protease homologs (SPHs) participate in digestion, embryonic development, blood coagulation, and immune defense responses. In this paper, we identify one SP and two SPHs, including a masquerade SPH (FcMas), a CUB domain containing SP (FcCUBSP), and a single domain containing SPH (FcSPH2) in Chinese white shrimp, Fenneropenaeus chinensis. FcMas has a Gly-rich region formed by three repeats of LGGQGGG, a clip domain and a C-terminal SP-like domain. Absence of Ser catalytic residue results in the loss of serine protease activity of FcMas, which then functions as an SPH. FcCUBSP has a signal peptide, followed by a CUB domain and an SP domain. FcSPH2 has a signal peptide and an SP-like domain. Loss of one catalytic residue (H) makes FcSPH2 catalytically inactive, which is considered an SPH. Phylogenetic analysis shows that FcMas and other SPHs from shrimp or insect are classified into one group. FcSPH2 is grouped in the chymotrypsin family. RT-PCR results show that FcMas mRNA is mainly distributed in hemocytes and gills. FcCUBSP is only detected in gills, whereas FcSPH2 is found in hepatopancreas only. QRT-PCR is used to analyze changes of FcMas, FcCUBSP and FcSPH2 in some tissues challenged with white spot syndrome virus (WSSV) or Vibrio. FcMas in hemocytes is down-regulated by WSSV or Vibrio challenge, and down-regulated by WSSV in gills. However, it is up-regulated upon Vibrio challenge in gills. FcCUBSP in gills and FcSPH2 in hepatopancreas are up-regulated upon WSSV or Vibrio challenge. Results suggest the roles of FcMas, FcCUBSP and FcSPH2 in shrimp's innate immunity.

Peptidoglycan activation of the proPO-system without a peptidoglycan receptor protein (PGRP)?

Recognition of microbial polysaccharide by pattern recognition receptors triggers the prophenoloxidase (proPO) cascade, resulting in melanin synthesis and its deposition on the surface of invading pathogens. Several masquerade-like proteins and serine proteinase homologues have been shown to be involved in the proPO activation in insects. In this study, a novel serine proteinase homologue, Pl-SPH2, was found and isolated as a 30kDa protein from hemocytes of the freshwater crayfish, Pacifastacus leniusculus, by its binding property to a partially lysozyme digested or TCA-treated insoluble Lysine (Lys)-type peptidoglycan (PGN) and soluble polymeric Lys-type PGN. Two other proteins, the Pl-SPH1 and lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP) were also found in the several different PGN-binding assays. However no PGRP homologue was detected. Neither was any putative PGRP found after searching available crustacean sequence databases. If RNA interference of Pl-SPH2, Pl-SPH1 or LGBP in the crayfish hematopoietic tissue cell culture was performed, it resulted in lower PO activity following activation of the proPO-system by soluble Lys-type PGN. Taken together, we report for the first time that Lys-type PGN is a trigger of proPO-system activation in a crustacean and that two Pl-SPHs are involved in this activation possibly by forming a complex with LGBP and without a PGRP.

Proteomic analysis of differentially expressed proteins in Penaeus monodon hemocytes after Vibrio harveyi infection

Background

Viral and bacterial diseases can cause mass mortalities in commercial shrimp aquaculture. In contrast to studies on the antiviral response, the responses of shrimps to bacterial infections by high throughput techniques have been reported only at the transcriptional level and not at the translational level. In this study, a proteomic analysis of shrimp hemocytes to identify differentially expressed proteins in response to a luminous bacterium Vibrio harveyi was evaluated for its feasibility and is reported for the first time.

Results

The two-dimensional gel electrophoresis (2-DE) patterns of the hemocyte proteins from the unchallenged and V. harveyi challenged shrimp, Penaeus monodon, at 24 and 48 h post infection were compared. From this, 27 differentially expressed protein spots, and a further 12 weakly to non-differentially regulated control spots, were selected for further analyses by the LC-ESI-MS/MS. The 21 differentially expressed proteins that could be identified by homologous annotation were comprised of proteins that are directly involved in the host defense responses, such as hemocyanin, prophenoloxidase, serine proteinase-like protein, heat shock protein 90 and alpha-2-macroglobulin, and those involved in signal transduction, such as the14-3-3 protein epsilon and calmodulin. Western blot analysis confirmed the up-regulation of hemocyanin expression upon bacterial infection. The expression of the selected proteins which were the representatives of the down-regulated proteins (the 14-3-3 protein epsilon and alpha-2-macroglobulin) and of the up-regulated proteins (hemocyanin) was further assessed at the transcription level using real-time RT-PCR.

Conclusions

This work suggests the usefulness of a proteomic approach to the study of shrimp immunity and revealed hemocyte proteins whose expression were up regulated upon V. harveyi infection such as hemocyanin, arginine kinase and down regulated such as alpha-2-macroglobulin, calmodulin and 14-3-3 protein epsilon. The information is useful for understanding the immune system of shrimp against pathogenic bacteria.

Isolation, gene cloning and expression profile of a pathogen recognition protein: a serine proteinase homolog (Sp-SPH) involved in the antibacterial response in the crab Scylla paramamosain

To identify the frontline defense molecules against microbial infection in the crab Scylla paramamosain, a live crab pathogenic microbe, Vibrio parahaemolyticus, was recruited as an affinity matrix to isolate innate immune factors from crab hemocytes lysate. Interestingly, a serine proteinase homolog (Sp-SPH) was obtained together with an antimicrobial peptide-antilipopolysaccharide factor (Sp-ALF). We then determined the full-length cDNA sequence of Sp-SPH, which contained 1298bp with an open reading frame of 1107bp encoding 369 amino acid residues. Multiple alignment analysis showed that the deduced amino acid sequences of Sp-SPH shared overall identity (83.8%) with those of SPH-containing proteins from other crab species. Tissue distribution analysis indicated that the Sp-SPH transcripts were present in various tissues including eye stalk, subcuticular epidermis, gill, hemocyte, stomach, thorax ganglion, brain and muscle of S. paramamosain. The Sp-SPH was highly expressed in selected different development stages including embryo (I, II, III and V), zoea (I), megalopa, and juvenile. Importantly, the prophenoloxidase was also present in the embryos, zoea, juvenile and adult crabs, but relatively lower in megalopa compared to those of other stages. Furthermore, the Sp-SPH mRNA expression showed a statistically significant increase (P<0.05) in both hemocyte and subcuticular epidermis at 24h, and in gill at 96h after challenge of V. parahaemolyticus determined by quantitative real-time PCR. Taken together, the live-bacterial-binding activity and the acute-phase response against bacterial infection of Sp-SPH suggested that it might function as an innate immune recognition molecule and play a key role in host defense against microbe invasion in the crab S. paramamosain.

A clip domain serine proteinase plays a role in antibacterial defense but is not required for prophenoloxidase activation in shrimp

The clip domain serine proteinases (clip-SPs) play critical roles in the signaling processes during embryonic development and in the innate immunity of invertebrates. In the present study, we identified a homolog of the clip-SP, designated as PmClipSP1, by searching the Penaeus monodon EST database (http://pmonodon.biotec.or.th), and using RACE-PCR to obtain the complete gene which contained a 1101bp open reading frame encoding 366 amino acids with a 25 amino acid signal peptide. The deduced PmClipSP1 protein sequence, which shares a predicted structural similarity to the clip-SPs of other arthropod species, appears to possess a clip domain at the N-terminus and an enzymatically active serine proteinase domain at the C-terminus. Tissue distribution analyses revealed that, at the transcript level, PmClipSP1 is mainly expressed in shrimp hemocytes, whilst temporal gene expression analyses showed that the hemocyte PmClipSP1 transcript levels were upregulated at 3h and downregulated at 6-48h following systemic Vibrio harveyi infection. RNAi-mediated silencing of the PmClipSP1 gene, by injection of double-stranded RNA (dsRNA) corresponding to the PmClipSP1 gene into shrimp, significantly reduced PmClipSP1 transcript levels, but neither significantly altered the other clip-SP and clip-SPH transcript levels nor reduced the total phenoloxidase (PO) enzyme activity in shrimp hemocytes, compared to the levels seen in the GFP dsRNA control, suggesting that PmClipSP1 is not involved in the proPO system. However, suppression of the PmClipSP1 gene led to a significant increase in the number of viable bacteria in the hemolymph (approximately 2.4-fold) and in the mortality rate (59%) of shrimp systemically infected with V. harveyi. These findings suggest that PmClipSP1 plays a role in the antibacterial defense mechanism of P. monodon shrimp.

Characterization of a serine proteinase homologous (SPH) in Chinese mitten crab Eriocheir sinensis

The serine protease homologous (SPH) is an important cofactor of prophenoloxidase-activating enzyme (PPAE). The gene of SPH of Chinese mitten crab Eriocheir sinensis (EsSPH) in hemocytes was cloned and characterized using reverse transcript polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The SPH cDNA consisted of 1386 bp with an open reading frame (ORF) encoded a protein of 378 amino acids, 154 bp 5'-untranslated region, and 95 bp 3'-untranslated region. Sequence comparisons against the GenBank database showed that EsSPH deduced amino acids had an overall identity to the gene of serine protease family from 41% to 70% of 15 invertebrate species. The protein had the structural characteristics of SPH, including the conserved six cysteine residues in the N-terminal clip domain and the functional activity (His157, Asp209, Gly311) in the C-terminal serine proteinase-like domain. To analyze the role of EsSPH in an acute infection, the temporal expression of the EsSPH gene after the Aeromonas hydrophila challenge was measured by real-time RT-PCR. The EsSPH transcripts in hemocytes significantly increased at 6 h, 12 h and 48 h over time after the A. hydrophila injection. This expression pattern shows that EsSPH has the potential to defend against invading microorganisms. The mRNA transcripts of EsSPH were detected in all tissues with the highest in the hepatopancreas. Interestingly, the mRNA transcripts of EsSPH and proPO were found in ova and expressed in oosperms, suggesting that the maternal transfer of EsSPH and proPO may exit in crab, but this warrants confirmation in further research.

A clip domain serine protease (cSP) from the Chinese mitten crab Eriocheir sinensis: cDNA characterization and mRNA expression

Clip domain serine protease (cSP), characterized by conserved clip domains, is a new serine protease family identified mainly in arthropod, and plays important roles in development and immunity. In the present study, the full-length cDNA of a cSP (designated EscSP) was cloned from Chinese mitten crab Eriocheir sinensis by expressed sequence tags (ESTs) and PCR techniques. The 1380 bp EscSP cDNA contained a 1152 bp open reading frame (ORF) encoding a putative cSP of 383 amino acids, a 5'-untranslated region (UTR) of 54 bp, and a 3'-UTR of 174 bp. Multiple sequence alignment presented twelve conserved cysteine residues and a canonical catalytic triad (His(185), Asp(235) and Ser(332)) critical for the fundamental structure and function of EscSP. Two types of cSP domains, the clip domain and tryp_spc domain, were identified in the deduced amino acids sequence of EscSP. The conservation characteristics and similarities with previously known cSPs indicated that EscSP was a member of the large cSP family. The mRNA expression of EscSP in different tissues and the temporal expression in haemocytes challenged by Listonella anguillarum were measured by real-time RT-PCR. EscSP mRNA transcripts could be detected in all examined tissues, and were higher expressed in muscle than that in hepatopancreas, gill, gonad, haemocytes and heart. The EscSP mRNA expression in haemocytes was up-regulated after L. anguillarum challenge and peaked at 2 h (4.96 fold, P < 0.05) and 12 h (9.90 fold, P < 0.05). Its expression pattern was similar to prophenoloxidase (EsproPO), one of the components of crab proPO system found in our previous report. These results implied that EscSP was involved in the processes of host-pathogen interaction probably as one of the proPO system members.

Gene silencing of a prophenoloxidase activating enzyme in the shrimp, Penaeus monodon, increases susceptibility to Vibrio harveyi infection

The prophenoloxidase (proPO) activating system is an important innate immune response against microbial infections in invertebrates. The major enzyme, phenoloxidase (PO), is synthesized as an inactive precursor and its activation to an active enzyme is mediated by a cascade of clip domain serine proteinases (clip-SPs). In this study, a cDNA encoding a proPO activating enzyme (PPAE) from the black tiger shrimp, Penaeus monodon, designated as PmPPAE1, was cloned and characterized. The full-length cDNA contains an open reading frame (ORF) of 1392bp encoding a predicted protein of 463 amino acids including an 18 amino acid signal peptide. The PmPPAE1 protein exhibits a characteristic sequence structure of clip-SPs consisting of the clip domain at the N-terminus and a SP domain at the C-terminus. Sequence analysis showed that PmPPAE1 exhibited the highest amino acid sequence similarity (70%) to a PPAE of the crayfish, Pacifastacus leniusculus. PmPPAE1 mRNA is abundantly expressed in hemocytes, and this is regulated after systemic Vibrio harveyi infection supporting that it is an immune-responsive gene. RNA interference-mediated suppression of PmPPAE1, performed by injection of double-stranded RNA (dsRNA) corresponding to the PmPPAE1 gene into shrimp, resulted in a significant reduction of PmPPAE1 but not other clip-SP and related gene transcript levels of P. monodon, suggesting gene-specific knockdown. RNAi-mediated silencing of PmPPAE1 gene significantly decreased the total PO activity (36.7%) in shrimp and additionally increased the mortality of V. harveyi infected shrimp, the latter of which correlated with an increase in the number of viable bacteria in the hemolymph. These results indicate that PmPPAE1 functions in the proPO system and is an important component in the shrimp immune system.

Clip domain serine protease and its homolog respond to Vibrio challenge in Chinese white shrimp, Fenneropenaeus chinensis

Clip domain serine proteases and their homologs are involved in invertebrate innate immunity, including hemolymph coagulation, antimicrobial peptide synthesis, cell adhesion, and melanization. Recognition of pathogens by pattern recognition receptors can trigger activation of a serine protease cascade. We report here the cDNA cloning of a serine protease (FcSP) and a serine protease homolog (FcSPH) from Chinese white shrimp, Fenneropenaeus chinensis. Both FcSP and FcSPH possess a clip domain at the N-terminal and an SP or SP-like domain at the C-terminal. In contrast to FcSP, FcSPH lacks a catalytic residue and is catalytically inactive. Tissue distribution and time course qRT-PCR analysis indicates that FcSP and FcSPH can respond to Vibrio anguillarum challenge in hemocytes, hepatopancreas and intestine. In situ hybridization analysis shows that FcSP is distributed in hemocytes and gills, and originated mainly from the hemocytes. FcSPH protein is expressed in gills and stomach of non-challenged shrimp. Its expression in gill mainly originates from the hemocytes in it. Two immunoreactive bands of FcSP can be detected in gills and stomach of non-challenged shrimp. FcSP protein is partially cleaved in non-challenged shrimp, while FcSPH protein is unprocessed in unchallenged shrimp and is partially cleaved after V. anguillarum challenge. Our results suggest that this Clip domain serine protease and its homolog may be involved in the serine protease cascade and play an important role in innate immunity of the shrimp.

RNA viruses in the sea

Viruses are ubiquitous in the sea and appear to outnumber all other forms of marine life by at least an order of magnitude. Through selective infection, viruses influence nutrient cycling, community structure, and evolution in the ocean. Over the past 20 years we have learned a great deal about the diversity and ecology of the viruses that constitute the marine virioplankton, but until recently the emphasis has been on DNA viruses. Along with expanding knowledge about RNA viruses that infect important marine animals, recent isolations of RNA viruses that infect single-celled eukaryotes and molecular analyses of the RNA virioplankton have revealed that marine RNA viruses are novel, widespread, and genetically diverse. Discoveries in marine RNA virology are broadening our understanding of the biology, ecology, and evolution of viruses, and the epidemiology of viral diseases, but there is still much that we need to learn about the ecology and diversity of RNA viruses before we can fully appreciate their contributions to the dynamics of marine ecosystems. As a step toward making sense of how RNA viruses contribute to the extraordinary viral diversity in the sea, we summarize in this review what is currently known about RNA viruses that infect marine organisms.

Expression of four trypsin-like serine proteases from the Chinese shrimp, Fenneropenaeus chinensis, as regulated by pathogenic infection

Four trypsin-like serine proteases, designated as Fctry1, Fctry2, Fctry3, and Fctry4, were obtained from the hepatopancreas of the Chinese shrimp, Fenneropenaeus chinensis. Three trypsin-like serine proteases, specifically Fctry1, 2, and 3 were observed to have the conserved catalytic triad (H, D, and S). Regarding Fctry4, the catalytic triad S was substituted by F, and the mature peptide was found to be inactive. Further analysis for similarities indicated that Fctry1, 2 and 4 were 89-92% identical to trypsins from Pacific white shrimp (Litopenaeus vannamei); while Fctry3 was only 42% identical to trypsins from salmon louse (Lepeophtheirus salmonis). The genomic organizations of Fctry1, 2 and 4 are also quite different from Fctry3. So, Fctry3 may be a new member of the trypsin-like serine protease family. Moreover, a semi-quantitative reverse transcription polymerase chain reaction (PCR) and quantitative real-time PCR was carried out to analyze the distribution profiles and expression patterns after they were subjected to a bacterial and viral challenge. The results showed that the four trypsin-like serine proteases were upregulated in the hepatopancreas of shrimp infected with the white spot syndrome virus (WSSV), and Fctry3 increased after a bacteria challenge. Therefore, these trypsin-like serine proteases might be involved in the innate defense reactions against different pathogens in Chinese shrimp.