Beta-integrin mediates WSSV infection

RNAi-Based Therapy: Combating Shrimp Viral Diseases

Shrimp aquaculture has become a vital industry, meeting the growing global demand for seafood. Shrimp viral diseases have posed significant challenges to the aquaculture industry, causing major economic losses worldwide. Conventional treatment methods have proven to be ineffective in controlling these diseases. However, recent advances in RNA interference (RNAi) technology have opened new possibilities for combating shrimp viral diseases. This cutting-edge technology uses cellular machinery to silence specific viral genes, preventing viral replication and spread. Numerous studies have shown the effectiveness of RNAi-based therapies in various model organisms, paving the way for their use in shrimp health. By precisely targeting viral pathogens, RNAi has the potential to provide a sustainable and environmentally friendly solution to combat viral diseases in shrimp aquaculture. This review paper provides an overview of RNAi-based therapy and its potential as a game-changer for shrimp viral diseases. We discuss the principles of RNAi, its application in combating viral infections, and the current progress made in RNAi-based therapy for shrimp viral diseases. We also address the challenges and prospects of this innovative approach.

Prohibitin mediates the cellular invasion of spring viremia of the carp virus

Spring viremia of carp virus (SVCV) is strongly contagious and pathogenic to common carp and cyprinoid species. However, knowledge of how SVCV enters host cells is still inadequate. In this study, mass spectrometry (MS) was incorporated with tandem affinity purification (TAP) to identify host proteins that interact with SVCV glycoprotein, the main attachment protein of SVCV. Specifically, prohibitin (PHB) received the utmost attention from all the candidate proteins, and its interaction with the SVCV-G protein was confirmed by immunoprecipitation and immunofluorescence assays. Treatment with PHB-specific inhibitors or knockdown of the expression of PHB by siRNAs resulted in a marked reduction in binding and entry of SVCV on host cells, while overexpression of PHB increased SVCV attachment and invasion. Furthermore, binding of SVCV to ZF4 and FHM cells was inhibited by pre-incubating the virus with recombinant PHB protein (rPHB) or blocking the cell surface PHB with its polyclonal antibodies. In addition, overexpression of PHB on SVCV-nonpermissive Grouper spleen cells (GSs) conferred susceptibility to SVCV infection. In vivo, treatment of rPHB could significantly inhibit SVCV propagation within zebrafish and benefit the survival rate of SVCV-infected zebrafish. These results demonstrate that PHB plays a crucial role in both the attachment and entry stages of SVCV infection.

Transcriptome-based insights into the regulatory role of immune-responsive circular RNAs in Litopanaeus vannamei upon WSSV infection

Circular RNAs (circRNAs) are non-coding RNAs (ncRNAs) originating from a post-transcriptional modification process called back-splicing. Despite circRNAs being traditionally considered by-products rather than independently functional, circRNAs play many vital roles, such as in host immunity during viral infection. However, in shrimp, these remain largely unexplored. Therefore, this study aims to identify circRNAs in Litopenaeus vannamei in the context of WSSV infection, one of the most eradicative pathogens threatening shrimp populations worldwide. We identified 290 differentially expressed circRNAs (DECs) in L. vannamei upon WSSV infection. Eight DECs were expressed from their parental genes, including alpha-1-inhibitor-3, calpain-B, integrin-V, hemicentin-2, hemocytin, mucin-17, proPO2, and rab11-FIP4. These were examined quantitatively by qRT-PCR, which revealed the relevant expression profiles to those obtained from circRNA-Seq. Furthermore, the structural and chemical validation of the DECs conformed to the characteristics of circRNAs. One of the functional properties of circRNAs as a miRNA sponge was examined via the interaction network between DECs and WSSV-responsive miRNAs, which highlighted the targets of miRNA sponges. Our discovery could provide insight into the participation of these ncRNAs in shrimp antiviral responses.

Functional Peroral Infectivity Complex of White Spot Syndrome Virus of Shrimp

White spot syndrome virus (WSSV) is a major cause of disease in shrimp cultures worldwide. The infection process of this large circular double-stranded DNA virus has been well studied, but its entry mechanism remains controversial. The major virion envelope protein VP28 has been implicated in oral and systemic viral infection in shrimp. However, genetic analysis of viral DNA has shown the presence of a few genes related to proteins of per os infectivity factor (PIF) complex in baculoviruses. This complex is essential for the entry of baculoviruses, large terrestrial circular DNA viruses, into the midgut epithelial cells of insect larvae. In this study, we aimed to determine whether a PIF complex exists in WSSV, the components of this complex, whether it functions as an oral infectivity complex in shrimp, and the biochemical properties that contribute to its function in a marine environment. The results revealed a WSSV PIF complex (~720 kDa) comprising at least eight proteins, four of which were not identified as PIF homologs: WSV134, VP124 (WSV216), WSSV021, and WSV136. WSV134 is suggested to be a PIF4 homolog due to predicted structural similarity and amino acid sequence identity. The WSSV PIF complex is resistant to alkali, proteolysis, and high salt, properties that are important for maintaining infectivity in aquatic environments. Oral infection can be neutralized by PIF-specific antibodies but not by VP28-specific antibodies. These results indicate that the WSSV PIF complex is critical for WSSV entry into shrimp; the complex's evolutionary significance is also discussed. IMPORTANCE White spot disease, caused by the white spot syndrome virus (WSSV), is a major scourge in cultured shrimp production facilities worldwide. This disease is only effectively controlled by sanitation. Intervention strategies are urgently needed but are limited by a lack of appropriate targets. Our identification of a per os infectivity factor (PIF) complex, which is pivotal for the entry of WSSV into shrimp, could provide new targets for antibody- or dsRNA-based intervention strategies. In addition, the presence of a PIF complex with at least eight components in WSSV, which is ancestrally related to the PIF complex of invertebrate baculoviruses, suggests that this complex is structurally and functionally conserved in disparate virus taxa.

Gain of function studies on predicted host receptors for white spot virus

Three decades after its first outbreak, the shrimp white spot virus (WSV) is still a global cause of concern due to considerable losses and lack of effective control measures. Several candidate host receptor proteins have been identified, but the pathogenesis is not clearly understood, although the key role of the WSV envelope protein VP28 in virus internalization is established. Here, protein-protein docking is applied to evaluate the interaction of VP28 trimeric extracellular region with four host (Penaeus monodon) receptors reported earlier, Rab7 GTPase (PmRab7), glucose transporter 1 (PmGLUT1), C-type lectin (PmCTL) and calreticulin (PmCRT). The stability of predicted complexes evaluated in terms of binding energy per unit buried surface area ranged from -8.46 to -11.82 cal mol^-1/Ų, which is not sufficient for functional interaction. Nevertheless, each of these host proteins was tested by a gain-of-function approach by observing their ability to make a fish cell line permissive to the shrimp WSV. Full-length expression constructs of the four receptors were transfected into SSN1 snakehead fish cells that are non-permissive to WSV. Transfected SSN1 cells and WSV permissive insect Sf9 cells were challenged with purified WSV. After 24 h, the presence of receptor transcripts was confirmed in the treated SSN1 cells, and not in the non-transfected SSN1 cells. Further, vp28 transcript was detected in Sf9 cells, but not in any of the treated SSN1 cells, indicating that none of the receptors were singly sufficient to make SSN1 cells permissive to WSV, even though PmRab7 was a strong candidate that alone showed >85% protection in virus neutralization experiments. For the other 3 candidates, previous reports predicted the involvement of co-receptors, which is confirmed here by their inability to act singly.

Comparative transcriptomics reveals the immune dynamics during the molting cycle of swimming crab Portunus trituberculatus

Molting is one of the most important biological processes of crustacean species, and a number of molecular mechanisms facilitate this complex procedure. However, the understanding of the immune mechanisms underlying crustacean molting cycle remains very limited. This study performed transcriptome sequencing in hemolymph and hepatopancreas of the swimming crab (Portunus trituberculatus) during the four molting stages: post-molt (AB), inter-molt (C), pre-molt (D), and ecdysis (E). The results showed that there were 78,572 unigenes that were obtained in the hemolymph and hepatopancreas of P. trituberculatus. Further analysis showed that 98 DEGs were involved in immunity response of hemolymph and hepatopancreas, and most of the DEGs participated in the process of signal transduction, pattern recognition proteins/receptors, and antioxidative enzymes system. Specifically, the key genes and pathway involved in signal transduction including the GPCR126, beta-integrin, integrin, three genes in mitogen-activated protein kinase (MAPK) signaling cascade (MAPKKK10, MAPKK4, and p38 MAPK), and four genes in Toll pathway (Toll-like receptor, cactus, pelle-like kinase, and NFIL3). For the pattern recognition proteins/receptors, the lowest expression level of 11 genes was found in the E stage, including C-type lectin receptor, C-type lectin domain family 6 member A and SRB3/C in the hemolymph, and hepatopancreatic lectin 4, C-type lectin, SRB, Down syndrome cell adhesion molecule homolog, Down syndrome cell adhesion molecule isoform, and A2M. Moreover, the expression level of copper/zinc superoxide dismutase isoform 4, glutathione peroxidase, glutathione S-transferase, peroxiredoxin, peroxiredoxin 6, and dual oxidase 2 in stage C or stage D significantly higher than that of stage E or stage AB. These results fill in the gap of the continuous transcriptional changes that are evident during the molting cycle of crab and further provided valuable information for elucidating the molecular mechanisms of immune regulation during the molting cycle of crab.

White spot syndrome virus directly activates mTORC1 signaling to facilitate its replication via polymeric immunoglobulin receptor-mediated infection in shrimp

Previous studies have shown that the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway has antiviral functions or is beneficial for viral replication, however, the detail mechanisms by which mTORC1 enhances viral infection remain unclear. Here, we found that proliferation of white spot syndrome virus (WSSV) was decreased after knockdown of mTor (mechanistic target of rapamycin) or injection inhibitor of mTORC1, rapamycin, in Marsupenaeus japonicus, which suggests that mTORC1 is utilized by WSSV for its replication in shrimp. Mechanistically, WSSV infects shrimp by binding to its receptor, polymeric immunoglobulin receptor (pIgR), and induces the interaction of its intracellular domain with Calmodulin. Calmodulin then promotes the activation of protein kinase B (AKT) by interaction with the pleckstrin homology (PH) domain of AKT. Activated AKT phosphorylates mTOR and results in the activation of the mTORC1 signaling pathway to promote its downstream effectors, ribosomal protein S6 kinase (S6Ks), for viral protein translation. Moreover, mTORC1 also phosphorylates eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), which will result in the separation of 4EBP1 from eukaryotic translation initiation factor 4E (eIF4E) for the translation of viral proteins in shrimp. Our data revealed a novel pathway for WSSV proliferation in shrimp and indicated that mTORC1 may represent a potential clinical target for WSSV control in shrimp aquaculture.

White spot syndrome virus (WSSV) is the causative pathogen of white spot disease (WSD) and represents the most destructive viral disease of shrimp. The virus has evolved various strategies to escape from host defenses or exploit host biological pathways for its reproduction. Studies on viral immune-escape mechanisms can provide new strategies for disease prevention and control in shrimp aquaculture. Mechanistic target of rapamycin (mTOR) plays a central role in the regulation of cell growth and metabolism, which nucleates two distinct protein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) with diverse functions at different levels of the signaling pathway. mTORC1 is reported to be exploited by viruses in their reproduction. However, the detail mechanism remains unclear. In this study, we identified a new mechanism of mTOR being hijacked by WSSV in shrimp (Marsupenaeus japonicus). WSSV infects shrimp by its receptor, pIgR and induces the interaction of the intracellular domain of pIgR with Calmodulin. Calmodulin subsequently promotes the activation of AKT by interaction with the pleckstrin homology domain of the kinase. Activated AKT phosphorylates mTOR and results in the activation of the mTORC1 signaling pathway to promote its downstream effectors, S6Ks, for viral protein synthesis. Moreover, mTORC1 also phosphorylates 4EBP1, which results in the separation of 4EBP1 from eIF4E for the translation of viral proteins in shrimp. Our study reveals a novel strategy for WSSV proliferation in shrimp and indicates that the components of mTORC1 may represent potential clinical targets for WSSV control in shrimp aquaculture.

Role of Cellular Receptors in the Innate Immune System of Crustaceans in Response to White Spot Syndrome Virus

Innate immunity is the only defense system for resistance against infections in crustaceans. In crustaceans, white spot diseases caused by white spot syndrome virus (WSSV) are a serious viral disease with high accumulative mortality after infection. Attachment and entry into cells have been known to be two initial and important steps in viral infection. However, systematic information about the mechanisms related to WSSV infection in crustaceans is still limited. Previous studies have reported that cellular receptors are important in the innate immune system and are responsible for the recognition of foreign microorganisms and in the stimulation of the immune responses during infections. In this review, we summarize the current understanding of the functions of cellular receptors, including Toll, C-type lectin, scavenger receptor, β-integrin, polymeric immunoglobulin receptor, laminin receptor, globular C1q receptor, lipopolysaccharide-and β-1,3-glucan-binding protein, chitin-binding protein, Ras-associated binding, and Down syndrome cell adhesion molecule in the innate immune defense of crustaceans, especially shrimp and crabs, in response to WSSV infection. The results of this study provide information on the interaction between viruses and hosts during infections, which is important in the development of preventative strategies and antiviral targets in cultured aquatic animals.

An integrin alpha 4 (ChIntα 4) from oyster Crassostrea hongkongensis mediates the hemocytes phagocytosis towards Vibrio alginolyticus

Integrins, a family of cell adhesion transmembrane receptors, mediate cell adhesion, migration, proliferation, apoptosis, and phagocytosis. In the present study, an integrin ChIntα 4 from Crassostrea hongkongensis was characterized to investigate its role in defensing against pathogenic bacterium Vibrio alginolyticus. The full-length cDNA sequence of ChIntα 4 was 3572 bp with an open reading frame (ORF) of 3168 bp, which encoded a polypeptide with 1055 amino acids. The mRNA expression of ChIntα 4 in the hemocytes was significantly up-regulated at 6 h and 24 h post V. alginolyticus stimulation (p < 0.01). The recombinant ChIntα 4 protein could agglutinate the rabbit red blood cells and Gram-negative bacteria V. alginolyticus and Escherichia coli. Moreover, the phagocytic activity of the hemocytes was significantly down-regulated from 46.9% to 32.7% when blocked with anti-ChIntα 4 antibody, and it was significantly up-regulated from 42.7% to 59.5% post transfection with pCI-neo-ChIntα 4 plasmid (p < 0.05). In conclusion, these findings demonstrated that ChIntα 4 might be involved in resisting V. alginolyticus infection and regulating phagocytosis as a cell adhesion receptor in C. hongkongensis.

A Dicer2 from Scylla paramamosain activates JAK/STAT signaling pathway to restrain mud crab reovirus

A Dicer2 gene from Scylla paramamosain, named SpDicer2, was cloned and characterized. The full length of SpDicer2 mRNA contains a 121 bp 5'untranslated region (UTR), an open reading frame (ORF) of 4518 bp and a 3' UTR of 850 bp. The SpDicer2 protein contains seven characteristic Dicer domains and showed 34%-65% identity and 54%-79% similarity to other Dicer protein domains, respectively. The mRNA of SpDicer2 was high expressed in hemocytes, intestine and gill and low expressed in the eyestalk and muscle. Moreover, expression of SpDicer2 was significantly responsive to challenges by mud crab reovirus (MCRV), Poly(I:C), LPS, Staphylococcus aureus and Vibrio parahaemolyticus. SpDicer2 was dispersedly presented in the cytoplasm except for a small amount in the nucleus. SpDicer2 could activate SpSTAT to translocate from the cytoplasm to the nucleus, and significantly increase the transcription activity of the wsv069 promoter, suggesting that SpDicer2 activated the JAK/STAT pathway. Furthermore, silencing of SpDicer2 in vivo increased the mortality of MCRV infected mud crab and the viral load in tissues and down-regulated the expression of multiple components of Toll, IMD and JAK-STAT pathways and almost all the examined immune effector genes. These results suggested that SpDicer2 could play an important role in defense against MCRV via activating the JAK/STAT signaling pathways in mud crab.

Litopenaeus vannamei peroxiredoxin 2-like is involved in WSSV infection by interaction with wsv089 and VP26

White spot syndrome virus (WSSV) is one of the most dangerous pathogen in shrimp aquaculture, which can cause extremely high mortality of shrimp. A full understanding of virus-host interactions is important to prevent viral infection. In the present study, wsv089-interacting molecule Litopenaeus vannamei peroxiredoxins2-like (LvPrx2-L) was selected by the yeast two-hybrid (Y2H) method. The interaction between wsv089 and LvPrx2-L was confirmed by far-western blotting assay. Interestingly, a further study indicated that LvPrx2-L interacted with VP26, and the molecular docking analysis supported the interaction between LvPrx2-L and VP26. Tissues distribution assay showed that LvPrx2-L was detected in all sampled tissues. The highest expression of LvPrx2-L was appeared in hemocytes. Following WSSV challenge, LvPrx2-L mRNA transcripts were significantly increased in the hemocytes and gill. In addition, the relative expression of IE1 and VP28 were remarkably up-regulated in the hepatopancreas and intestines of LvPrx2-L-knockdown shrimp. Moreover, the cumulative survival rate was significantly lower in the LvPrx2-L- silenced group compared with the control and blank groups. Furthermore, LvPrx2-L could regulate the expression of proPO, crustin, ALF3, and CAT at the mRNA level. These findings would further deepen our understanding of WSSV-host interaction and shrimp antiviral response. All these data might useful for assessing the function of LvPrx2-L in the immune response of crustacean.

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.

Feasibility Study on the Use of Fly Maggots (Musca domestica) as Carriers to Inhibit Shrimp White Spot Syndrome

The shrimp aquaculture industry has encountered many diseases that have caused significant losses, with the most serious being white spot syndrome (WSS). Until now, no cures, vaccines, or drugs have been found to counteract the WSS virus (WSSV). The purpose of this study was to develop an oral delivery system to transport recombinant proteinaceous antigens into shrimp. To evaluate the feasibility of the oral delivery system, we used white shrimp as the test species and maggots as protein carriers. The results indicated that the target protein was successfully preserved in the maggot, and the protein was detected in the gastrointestinal tract of the shrimp, showing that this oral delivery system could deliver the target protein to the shrimp intestine, where it was absorbed. In addition, the maggots were found to increase the total haemocyte count and phenoloxidase activity of the shrimp, and feeding shrimp rVP24-fed maggots significantly induced the expression of penaeidins 2. In the WSSV challenge, the survival rate of rVP24-fed maggots was approximately 43%. This study showed that maggots can be used as effective oral delivery systems for aquatic products and may provide a new method for aquatic vaccine delivery systems.

Penaeidins restrict white spot syndrome virus infection by antagonizing the envelope proteins to block viral entry

Emerging studies have indicated that some penaeidins restrict virus infection; however, the mechanism(s) involved are poorly understood. In the present study, we uncovered that penaeidins are a novel family of antiviral effectors against white spot syndrome virus (WSSV), which antagonize the envelope proteins to block viral entry. We found that the expression levels of four identified penaeidins from Litopenaeus vannamei, including BigPEN, PEN2, PEN3, and PEN4, were significantly induced in hemocytes during the early stage of WSSV infection. Knockdown of each penaeidin in vivo via RNA interference resulted in elevated viral loads and rendered shrimp more susceptible to WSSV, while the survival rate was rescued via the injection of recombinant penaeidins. All penaeidins, except PEN4, were shown to interact with several envelope proteins of WSSV, and all four penaeidins were observed to be located on the outer surface of the WSSV virion. Co-incubation of each recombinant penaeidin with WSSV inhibited virion internalization into hemocytes. More importantly, we found that PEN2 competitively bound to the envelope protein VP24 to release it from polymeric immunoglobulin receptor (pIgR), the cellular receptor required for WSSV infection. Moreover, we also demonstrated that BigPEN was able to bind to VP28 of WSSV, which disrupted the interaction between VP28 and Rab7 – the Rab GTPase that contributes to viral entry by binding with VP28. Taken together, our results demonstrated that penaeidins interact with the envelope proteins of WSSV to block multiple viral infection processes, thereby protecting the host against WSSV.

Roles of extracellular matrix components in Tiger frog virus attachment to fathead minnow (Pimephales promelas) cells

Tiger frog virus (TFV) belongs to the genus Ranavirus (family Iridoviridae) and causes significant harm in cultured frogs, resulting in substantial losses in ecological and economic field in Southern China. Attachment is the first step in viral life cycle, which is dependent on the interactions of virions with extracellular matrix (ECM) components. Studying this process will help in understanding virus infection and controlling viral diseases. In this study, the roles of primary ECM components in TFV attachment were investigated. The results on the kinetics of virus attachment showed TFV successful attachment to the cell surface as a relatively rapid process after TFV was used to inoculate cells for 10 min at 4 °C. Western blot and quantitative PCR analyses results showed that soluble fibronectin, collagen IV, laminin, or hyaluronic acid treatment with TFV caused no significant effect on virus attachment. Soluble heparin, heparan sulfate and chondroitin sulfate A/B could inhibit TFV attachment in a dose-dependent manner. Enzymic digestion by cell surface heparin/heparan sulfate using heparinase I, II, and III could significantly prevent TFV attachment, suggesting that heparan sulfate plays an important role in TFV attachment. Furthermore, the binding assays of heparin-agarose beads and virion showed that TFV virions specifically bound with heparin in a dose-dependent manner. Given that heparin is a structural analogue of heparan sulfate, the above results suggest that heparan sulfate might serve as an attachment factor of TFV infection. Our work would be beneficial to understand the mechanisms of TFV attachment and the interactions of TFV with cellular receptor(s).

Cyst viability and stress tolerance upon heat shock protein 70 knockdown in the brine shrimp Artemia franciscana

Females of the brine shrimp Artemia franciscana produce either free-swimming nauplii via ovoviviparous pathway of reproduction or encysted embryos, known as cysts, via oviparous pathway, in which biological processes are arrested. While previous study has shown a crucial role of ATP-dependent molecular chaperone, heat shock protein 70 (Hsp70) in protecting A. franciscana nauplii against various abiotic and abiotic stressors, the function of this protein in diapausing embryos and cyst development, however, remains unknown. RNA interference (RNAi) was applied in this study to examine the role of Hsp70 in cyst development and stress tolerance, with the latter performed by desiccation and freezing, a common method used for diapause termination in Artemia cysts. Hsp70 knockdown was apparent in cysts released from females that were injected with Hsp70 dsRNA. The loss of Hsp70 affected neither the development nor morphology of the cysts. The time between fertilization and cyst release from Artemia females injected with Hsp70 dsRNA was delayed slightly, but the differences were not significant when compared to the controls. However, the hatching percentage of cysts which lacks Hsp70 were reduced following desiccation and freezing. Taken together, these results indicated that Hsp70 possibly plays a role in the stress tolerance but not in the development of diapause-destined embryos of Artemia. This research makes fundamental contributions to our understanding of the role molecular chaperone Hsp70 plays in Artemia, an excellent model organism for diapause studies of the crustaceans.

Identification of the Immediate-Early Genes of Cyprinid Herpesvirus 2

Cyprinid herpesvirus 2 (CyHV-2), which infects goldfish and crucian carp causing high mortality, is an emerging viral pathogen worldwide. The genome of CyHV-2 is large and comprises double-stranded DNA, including several genes similar to cyprinid herpesvirus 1, ictalurid herpesvirus-1, cyprinid herpesvirus 3, and ranid herpesvirus-1. Genes of DNA viruses are expressed in three temporal phases: immediate-early (IE), early (E), and late (L) genes. Viral IE genes initiate transcription as soon as the virus enters the host, without viral DNA replication. IE gene products enable the efficient expression of E and L genes or regulate the host to initiate virus replication. In the present study, five IE genes of CyHV-2 were identified, including open reading frame (ORF)54, ORF121, ORF141, ORF147, and ORF155. Time course analysis and reverse transcription polymerase chain reaction confirmed five IE genes, thirty-four E genes, and thirty-nine L genes. In addition, all 150 ORFs identified in the CyHV-2 genome are transcribed, and are expressed in chronological order, similar to other herpesviruses. This study is the first to identify the IE genes of CyHV-2, which will provide more information for viral molecular characterization.

Transcriptome analysis reveals the potential mechanism of dietary carotenoids improving antioxidative capability and immunity of juvenile Chinese mitten crabs Eriocheir sinensis

Carotenoids are known to be involved in the regulation of the antioxidative capability, immune response and stress resistance in crustacean species; however, very limited information is available on their underlying molecular mechanisms. This study performed transcriptome sequencing of hemolymph and hepatopancreas of juvenile Chinese mitten crabs (Eriocheir sinensis) that fed with three diets, i.e. diet A containing 90 mg kg^-1 dry weight of astaxanthin, diet B containing 200 mg kg^-1 dry weight of β-carotene and control diet without supplementation of dietary carotenoids. The results showed that there were 2955 and 497 differentially expressed genes (DEGs) in the hemolymph between the astaxanthin treatment and control groups, and between the β-carotene treatment and control groups, respectively. Moreover, compared with the control group, 833 and 1886 DEGs were obtained in the hepatopancreas of the astaxanthin treatment and the β-carotene treatment groups, respectively. The DEGs in the three groups were enriched in 255 specific KEGG metabolic pathways according to KEGG enrichment analysis. Through this study, a series of key genes involved in Nrf2 signalling, ROS production, intracellular antioxidant enzymes and chaperones were significantly affected by dietary carotenoids. Dietary carotenoids also significantly altered the expression levels of immune-related molecules associated with signal transduction, prophenoloxidase cascade, apoptosis, pattern recognition proteins/receptors and antimicrobial peptides. In conclusion, this transcriptomic study provides valuable information for understanding the molecular mechanism and potential pathway of dietary carotenoids improved the antioxidative capability and immunity of juvenile E. sinensis.

The Members of the Highly Diverse Crassostrea gigas Integrin Family Cooperate for the Generation of Various Immune Responses

Studies on invertebrate immune receptors can provide insights into characteristics specific to innate immune system. Here, eight α and three β integrins are identified from an invertebrate, the Pacific oyster Crassostrea gigas, and their possible immune functions are studied. Oyster α/β integrins exhibit a higher degree of sequence and structural variability than the members from Homo sapiens and Drosophila melanogaster. The analysis reveals that oyster RGD- and laminin-binding receptor homologs are present in the phylogenetic tree of α integrins, but the other six oyster α integrins mainly form a species-specific branch; meanwhile, oyster β integrins are clustered with insect β integrins but distinct from a member from the mollusk Biomphalaria glabrata. Although phylogenetically lacking the important α integrin branches of LDV-binding, PS3-type, and αI-containing integrins, oyster integrins can bind to most ECM ligands, including RGDCP, LDVCP, GFOGERCP, and laminin protein in a distinct binding pattern. Besides, oyster integrins are distributed in different hemocyte subpopulations, while only specific integrins are selectively involved in hemocyte phagocytosis, migration, and encapsulation, and some of them participate in more than one immune response in a sophisticated pattern. Especially, oyster β integrins are arranged in the core to mediate complex immune responses, unlike the counterparts in humans that mainly depend on αI-containing integrins to incite immune reactions. This study represents the first comprehensive attempt to reveal the structural and evolutionary features of the integrin family and their involvement in cellular immune responses in the non-model invertebrate C. gigas and sheds light on the characteristics specific to the innate immune system in the integrin family.

A novel cuticle protein involved in WSSV infection to the Pacific white shrimp Litopenaeus vannamei

As the most productive crustacean species in aquaculture, Litopenaeus vannamei is seriously threatened by white spot syndrome virus (WSSV), which has caused huge economic damage in the past decades. Shrimp cuticle proteins are the important components in the frontier target tissues, including cuticle and the chitinous lining of the digestive tract. In present study, a novel cuticle protein gene, named LvCPAP1, was isolated and demonstrated to play an important role in WSSV infection. The deduced amino acid sequence of LvCPAP1 contained a signal peptide and a conserved chitin-binding domain type 2 (ChBD2). Tissue distribution analysis revealed that LvCPAP1 was predominantly expressed in epidermis and stomach. The transcription levels of LvCPAP1 in epidermis and stomach were significantly regulated upon WSSV challenge. DsRNA silencing of LvCPAP1 decreased the in vivo WSSV copy numbers and the death rate of shrimp after WSSV infection, indicating that LvCPAP1 might facilitate WSSV invasion. In addition, the interaction between LvCPAP1 and the major envelop protein VP24 of WSSV was revealed by yeast two-hybrid system and further confirmed by dot blot and pull-down assays. The present study implied that cuticle protein LvCPAP1 might favor the entry process of WSSV, which provided new clues for understanding the role of cuticle proteins during virus infection.

Cellular entry of white spot syndrome virus and antiviral immunity mediated by cellular receptors in crustaceans

Enveloped virus usually utilizes the receptor-mediated multiple endocytic routes to enter permissive host cells for successful infection. Cellular receptors are cell surface molecules, either by helping viral attachment to cell surface followed by internalization or by triggering antiviral immunity, participate in the viral-host interaction. White spot syndrome virus (WSSV), the most lethally viral pathogen with envelope and double strand DNA genome in crustacean farming, including shrimp and crayfish, has been recently found to recruit various endocytic routes for cellular entry into host cells. Meanwhile, other than the typical pattern recognition receptors for recognition of WSSV, more and more putative cellular receptors have lately been characterized to facilitate or inhibit WSSV entry. In this review, recent findings on the endocytosis-dependent WSSV entry, viral entry mediated by putative cellular receptors, the molecular interplay between WSSV and cellular receptors, and the following anti-WSSV immunity are summarized and discussed, which may provide us a better understanding of the WSSV pathogenesis and further possible antiviral control of white spot disease in crustacean farming.

Hemolymph C1qDC promotes the phagocytosis of oyster Crassostrea gigas hemocytes by interacting with the membrane receptor β-integrin

Phagocytosis constitutes a conserved cellular process for multicellular animals to ingest or engulf other cells or particles, which is facilitated by the use of opsonins to bind foreign particles and interact with cell surface receptors. The invertebrate secreted C1q domain-containing proteins (C1qDCs) have been reported to exhibit opsonic activity, while the detailed mechanisms of opsonization still remain unclear. In the present study, a C1qDC (designated as CgC1qDC-5) with opsonic activity was identified from the hemolymph of oyster Crassostrea gigas. CgC1qDC-5 exhibited the ability to bind pathogen-associated molecular patterns (PAMPs) of lipopolysaccharides (LPS) and Lipid A. It could also bind and agglutinate Gram-negative bacteria Escherichia coli, Vibrio splendidus and Vibrio anguillarum, whereas the agglutinating activity could be inhibited by LPS. In addition, CgC1qDC-5 could enhance the phagocytosis of hemocytes toward E. coli, V. splendidus, and V. anguillarum. GST pull-down and surface plasmon resonance assays in vitro revealed that CgC1qDC-5 could interact with β-integrin (CgIntegrin). In vivo, CgC1qDC-5 was observed to bind hemocytes and co-localized with CgIntegrin on the cell membrane of hemocytes. Antibody-mediated blockage of CgIntegrin hindered the CgC1qDC-5-enhanced hemocytic phagocytosis. CgIntegrin also exhibited the ability to bind the Gram-negative bacteria E. coli, V. splendidus, V. anguillarum and Vibrio parahaemolyticus, and PAMP of LPS, but not Lipid A. A phagocytosis assay demonstrated that CgIntegrin could directly mediate phagocytosis toward bacteria as a phagocytic receptor. These results collectively suggested that CgC1qDC-5 could serve as an opsonin to recognize and bind bacteria, and subsequently interact with CgIntegrin on the hemocyte surface to enhance the CgIntegrin-mediated phagocytosis in oyster.

Cell surface transglutaminase required for nodavirus entry into freshwater prawn hemocytes

To identify molecules involved in Macrobrachium rosenbergii nodavirus (MrNV) entry into hemocytes of the giant freshwater prawn M. rosenbergii, biotinylated prawn hemocyte membrane proteins were prepared, purified and separated by SDS-PAGE. The proteins were blotted on the nitrocellulose membrane before incubation with the MrNV capsid protein (MrNV-CP) by a VOPBA technique. Subsequent mass spectrometry and analysis of immune-reactive bands represent putative binding partners including transglutaminase (TG), actin, α2-macroglobulin, α1-tubulin, F₁-ATP synthase β-subunit and a currently uncharacterized protein. The sequence of TG has been characterized and found 5 amino acids differences to a previously reported MrTG (ADX99580), mainly at its N-terminal part and thus, we named it MrTGII (KM008611). Recombinant MrTGII was prepared to produce a polyclonal antibody against it, which was successfully revealed the presence of MrTGII (100 kDa) in prawn hemocyte lysates. Using the pentylamine-biotin incorporation assay, an acyl transfer reaction was observed when hemocyte lysates were added to solutions containing MrNV-CP, suggesting that hemocyte MrTG could use MrNV-CP as the substrate. The expression levels of MrTGII were changed during the course of MrNV infection. By using immunostaining technique, location of MrTGII on the hemocyte surface was confirmed. Specific interaction between MrTGII with MrNV-CP in a dose-dependent manner was confirmed by in vitro ELISA assay. The highest binding activity of MrNV-CP was found with the N-terminal portion of the protein. In vitro neutralization using anti-MrTGII antibody resulted in inhibition of MrNV attachment to the hemocyte surface, accompanied by a dramatic reduction in viral replication. This is the first time that crustacean TG has been shown to be involved in viral entry, in addition to its roles in blood clotting and haematopoiesis.

The activated β-integrin (CgβV) enhances RGD-binding and phagocytic capabilities of hemocytes in Crassostrea gigas

Integrins are an important family of cell receptors that can bind foreign particles and promote cell phagocytosis after they are activated. In the present study, a novel β integrin was identified from pacific oyster Crassostrea gigas with an extracellular domain, a single transmembrane segment, and a short cytoplasmic domain. It was phylogenetically clustered with phagocytosis-related insecta βV, and designated as CgβV. CgβV shared a conserved NPX[Y/F] motif related to integrin activation with other phagocytosis-related β integrins. The mRNA transcripts of CgβV were widely detected in oyster tissues including hemocytes, gonad, adductor muscle, mantle, gill, and hepatopancreas, and the expression level in hemocytes was significantly up-regulated at 12 h after lipopolysaccharide (LPS) stimulation (p < 0.05), which was 2.29-fold higher than that in the control group. CgβV proteins were mainly observed on the hemocytes surface. The oyster hemocytes were found to bind fluorescein isothiocyanate (FITC)-labeled Arg-Gly-Asp-containing peptides (RGDCPs), and the binding capability was significantly up-regulated with the peak percentage of 37.6% at 12 h post LPS stimulation, which was higher than that in the control group (8.8%, p < 0.05), suggesting the activation of RGD-binding integrins on oyster hemocytes surface. The label-free RGDCPs and anti-CgβV antibody inhibited the binding capability of hemocytes towards FITC-labeled RGDCPs, which were significant lower in RGD blocking group (7.4%, p < 0.05) and anti-CgβV blocking group (22.1%, p < 0.05) than that in the control group (37.6%), indicating that CgβV could be a RGD-binding integrin. Phagocytosis assay demonstrated that LPS could enhance the phagocytosis of hemocytes towards Escherichia coli and fluorescent beads with the phagocytic rate (PR) of 18.3% and 17.4%, and phagocytic index (PI) of 5.29 and 37.71, respectively, which were significant higher than that in the control group (11.0% and 3.65 for E. coli, 9.8% and 29.26 for fluorescent beads, respectively, p < 0.05). In addition, both the label-free RGDCPs and anti-CgβV antibody significantly hindered the phagocytosis of hemocytes towards E. coli and fluorescent beads. After the E. coli and fluorescent beads were opsonized by oyster serum, the label-free RGDCPs still inhibited the phagocytosis of hemocytes towards them, while the anti-CgβV antibody could only inhibit the phagocytosis of hemocytes towards E. coli, suggesting that only the activated CgβV was involved in the enhancing phagocytosis for bacteria in oyster. Moreover, the key components of conserved integrin-mediated phagocytosis pathway including GTPases, talin proteins, Ca²⁺ and cAMP were all induced by LPS in hemocytes of oyster. All these results suggested that the activated CgβV enhanced RGD-binding and phagocytic capabilities of hemocytes, shedding lights on the mechanisms of integrin-mediated phagocytosis in mollusks.

Global profiling of megalocytivirus-induced proteins in tongue sole (Cynoglossus semilaevis) spleen identifies cellular processes essential to viral infection

Megalocytivirus is a DNA virus with a broad host range among farmed fish including tongue sole (Cynoglossus semilaevis). In this study, label-free proteomics was performed to examine protein expression in tongue sole spleen induced by megalocytivirus at 8 and 12 days post infection (dpi). Compared to uninfected control fish, virus-infected fish displayed 315 up-regulated proteins and 111 down-regulated proteins at 8 dpi, and 48 up-regulated proteins and 43 down-regulated proteins at 12 dpi. The expressions of five differentially expressed proteins were confirmed by Western blot. The differentially expressed proteins were enriched in the pathways and processes associated with innate immune response and viral infection. Interference with the expression of two up-regulated proteins of the ubiquitin proteasome system (UPS), i.e. proteasome assembly chaperone 2 and proteasome maturation protein, significantly reduced viral propagation in fish, whereas overexpression of these two proteins significantly enhanced viral propagation. Consistently, inhibition of the functioning of proteasome significantly impaired viral replication in vivo. This study provided the first global protein profile responsive to megalocytivirus in tongue sole, and revealed an essential role of UPS in viral infection.

The polymeric immunoglobulin receptor-like protein from Marsupenaeus japonicus is a receptor for white spot syndrome virus infection

Viral entry into the host cell is the first step towards successful infection. Viral entry starts with virion attachment, and binding to receptors. Receptor binding viruses either directly release their genome into the cell, or enter cells through endocytosis. For DNA viruses and a few RNA viruses, the endocytosed viruses will transport from cytoplasm into the nucleus followed by gene expression. Receptors on the cell membrane play a crucial role in viral infection. Although several attachment factors, or candidate receptors, for the infection of white spot syndrome virus (WSSV) were identified in shrimp, the authentic entry receptors for WSSV infection and the intracellular signaling triggering by interaction of WSSV with receptors remain unclear. In the present study, a receptor for WSSV infection in kuruma shrimp, Marsupenaeus japonicus, was identified. It is a member of the immunoglobulin superfamily (IgSF) with a transmembrane region, and is similar to the vertebrate polymeric immunoglobulin receptor (pIgR); therefore, it was designated as a pIgR-like protein (MjpIgR for short). MjpIgR was detected in all tissues tested, and its expression was significantly induced by WSSV infection at the mRNA and protein levels. Knockdown of MjpIgR, and blocking MjpIgR with its antibody inhibited WSSV infection in shrimp and overexpression of MjpIgR facilitated the invasion of WSSV. Further analyses indicated that MjpIgR could independently render non-permissive cells susceptible to WSSV infection. The extracellular domain of MjpIgR interacts with envelope protein VP24 of WSSV and the intracellular domain interacts with calmodulin (MjCaM). MjpIgR was oligomerized and internalized following WSSV infection and the internalization was associated with endocytosis of WSSV. The viral internalization facilitating ability of MjpIgR could be blocked using chlorpromazine, an inhibitor of clathrin dependent endocytosis. Knockdown of Mjclathrin and its adaptor protein AP-2 also inhibited WSSV internalization. All the results indicated that MjpIgR-mediated WSSV endocytosis was clathrin dependent. The results suggested that MjpIgR is a WSSV receptor, and that WSSV enters shrimp cells via the pIgR-CaM-Clathrin endocytosis pathway.

White Spot Syndrome Virus (WSSV) is one of the most virulent pathogens in shrimp farming. Several viral candidate receptors, or attachment factors were reported in previous studies, however, most of them are not authentic transmembrane proteins. In particular, the protein receptor(s) required the intracellular signaling triggering by interaction of WSSV with receptors remain unclear. In the present study, a polymeric immunoglobulin receptor (pIgR) like protein, a bona fide transmembrane receptor, was identified in kuruma shrimp, Marsupenaeus japonicus (MjpIgR for short). Knockdown of MjpIgR by RNA interference, and blocking it by its antibody prevented WSSV infection in shrimp and overexpression of MjpIgR facilitated the invasion of WSSV. Further study found that MjpIgR could independently render non-permissive cells susceptible to WSSV infection. The extracellular cellular domain of MjpIgR interacts with envelope protein VP24 of WSSV and the intracellular domain interacts with calmodulin (MjCaM). MjpIgR was oligomerized and internalized following WSSV infection and the internalization was associated with endocytosis of WSSV. The viral internalization facilitating ability of MjpIgR could be blocked using chlorpromazine, an inhibitor of clathrin dependent endocytosis, indicating that MjpIgR-mediated WSSV endocytosis was clathrin dependent. The results suggested that MjpIgR is a WSSV receptor, and that WSSV enters shrimp cells via the pIgR-CaM-Clathrin endocytosis pathway. This study provides a new target for WSSV control in shrimp aquaculture.

Plasmolipin, PmPLP1, from Penaeus monodon is a potential receptor for yellow head virus infection

Plasmolipin has been characterized as a cell entry receptor for mouse endogenous retrovirus. In black tiger shrimp, two isoforms of plasmolipin genes, PmPLP1 and PmPLP2, have been identified from the Penaeus monodon EST database. The PmPLP1 is highly up-regulated in yellow head virus (YHV)-infected shrimp. Herein, the function of PmPLP1 is shown to be involved in YHV infection. The immunoblotting and immunolocalization showed that the PmPLP1 protein was highly expressed and located at the plasma membrane of gills from YHV-infected shrimp. Moreover, the PmPLP1 expressed in the Sf9 insect cells resided at the cell membrane rendering the cells more susceptible to YHV infection. Using the ELISA binding and mortality assays, the synthetic external loop of PmPLP1 was shown to bind the purified YHV and neutralize the virus resulting in the decrease in YHV infection. Our results suggested that the PmPLP1 was likely a receptor of YHV in shrimp.

Transfection of crayfish hematopoietic tissue cells

Transfection is a powerful tool useful for studying gene function. Establishing transfection methods that enable highly efficient DNA uptake has become increasingly important. The crayfish hematopoietic tissue (Hpt) cell cultures have been proven to be suitable for studies on immunity and cell differentiation in crustaceans including shrimps, but no efficient gene transfer and expression method is available for these cells. Here we report a novel and highly efficient DNA transfection system based on electroporation. This method depends on a recombinant plasmid with the promoter from white spot syndrome virus immediate-early gene wsv249. This plasmid could be introduced into primary cells and efficiently express foreign genes by electroporation. By optimizing different electroporation parameters, more than 30% transfection efficiency could be achieved with the relative viability of cells around 50%. This is the first report of gene introduction to crayfish Hpt cells and will be useful for the expanding our research on crustacean immunity.

A cuticle protein from the Pacific white shrimp Litopenaeus vannamei involved in WSSV infection

White spot syndrome virus (WSSV) is a major viral pathogen in global shrimp farming, causing huge economic damage. Through penetrating the outer surface of the target tissues, WSSV enters into the cells of the target tissue to complete the replication process in the host. In the present study, a cuticle protein gene from Litopenaeus vannamei, designated as LvAMP13.4, was identified and proved to be involved in WSSV invasion. The deduced amino acid sequence of LvAMP13.4 contained a signal peptide and a conserved chitin-binding domain type 4 (ChBD4). This cuticle protein gene was mainly expressed in stomach, gill and epidermis. The expression level of LvAMP13.4 was significantly changed during WSSV infection. Silencing of LvAMP13.4 by dsRNA interference apparently reduced the mortality rate and the WSSV copy number in shrimp upon WSSV infection. Furthermore, yeast two-hybrid system and Co-IP assay were performed to confirm that LvAMP13.4 could interact with the major envelop protein VP24 of WSSV. These data indicated that LvAMP13.4 was involved in the invasion process of WSSV through interaction with VP24. The present results could provide new insights for us in understanding the role of host cuticle proteins during virus invasion.

Transcriptome analysis of Kuruma shrimp (Marsupenaeus japonicus) hepatopancreas in response to white spot syndrome virus (WSSV) under experimental infection

Kuruma shrimp (Marsupenaeus japonicus) is one of the most valuable crustacean species in capture fisheries and mariculture in the Indo-West Pacific. White spot syndrome virus (WSSV) is a highly virulent pathogen which has seriously threatened Kuruma shrimp aquaculture sector. However, little information is available in relation to underlying mechanisms of host-virus interaction in Kuruma shrimp. In this study, we performed a transcriptome analysis from the hepatopancreas of Kuruma shrimp challenged by WSSV, using Illumina-based RNA-Seq. A total of 39,084,942 pair end (PE) reads, including 19,566,190 reads from WSSV-infected group and 19,518,752 reads from non-infected (control) group, were obtained and assembled into 33,215 unigenes with an average length of 503.7 bp and N50 of 601 bp. Approximately 17,000 unigenes were predicted and classified based on homology search, gene ontology, clusters of orthologous groups of proteins, and biological pathway mapping. Differentially expressed genes (DEGs), including 2150 up-regulated and 1931 down-regulated, were found. Among those, 805 DEGs were identified and categorized into 14 groups based on their possible functions. Many genes associated with JAK-STAT signaling pathways, Integrin-mediated signal transduction, Ras signaling pathways, apoptosis and phagocytosis were positively modified after WSSV challenge. The proteolytic cascades including Complement-like activation and Hemolymph coagulations likely participated in antiviral immune response. The transcriptome data from hepatopancreas of Kuruma shrimp under WSSV challenge provided comprehensive information for identifying novel immune related genes in this valuable crustacean species despite the absence of the genome database of crustaceans.

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.

Characterization of a novel non-receptor tyrosine kinase Src from Litopenaeus vannamei and its response to white spot syndrome virus infection

Src family kinases (SFKs), a class of non-receptor tyrosine kinases, mediate a wide aspect of cellular signaling pathways that regulate cell proliferation, differentiation, motility and survival. In this study, we identified and characterized for the first time a novel SFK homologue from Litopenaeus vannamei (designated as LvSrc). Sequence analysis showed that LvSrc had a high homology with the identified SFKs, especially those from invertebrates. LvSrc contained the conserved SH3, SH2 and tyrosine kinase domains, as well as the potential phosphorylation and lipid modification sites. Immunofluorescence analysis demonstrated that LvSrc was mostly localized at the plasma membrane and partly resided in the perinuclear vesicle and nucleus or whole cell. Infection with white spot syndrome virus (WSSV) could up-regulate the transcription and expression levels of LvSrc and further induced its phosphorylation, suggesting that LvSrc was implicated in WSSV infection. Furthermore, our co-immunoprecipitation result confirmed the interaction between Src and focal adhesion kinase (FAK) in shrimp, while the phosphorylation of FAK was markedly enhanced by co-expression with LvSrc. In sum, our studies suggested that LvSrc might act in the FAK-regulated signaling pathway during WSSV infection, which would give us a better insight in understanding the role of SKFs in host-virus interactions in crustaceans.

An update on mechanism of entry of white spot syndrome virus into shrimps

Host-parasite relationships can be best understood at the level of protein-protein interaction between host and pathogen. Such interactions are instrumental in understanding the important stages of life cycle of pathogen such as adsorption of the pathogen on host surface followed by effective entry of pathogen into the host body, movement of the pathogen across the host cytoplasm to reach the host nucleus and replication of the pathogen within the host. White Spot Disease (WSD) is a havoc for shrimps and till date no effective treatment is available against the disease. Moreover information regarding the mechanism of entry of White Spot Syndrome Virus (WSSV) into shrimps, as well as knowledge about the protein interactions occurring between WSSV and shrimp during viral entry are still at very meagre stage. A cumulative and critically assessed information on various viral-shrimp interactions occurring during viral entry can help to understand the exact pathway of entry of WSSV into the shrimp which in turn can be used to device drugs that can stop the entry of virus into the host. In this context, we highlight various WSSV and shrimp proteins that play role in the entry mechanism along with the description of the interaction between host and pathogen proteins.

The Roles of β-Integrin of Chinese Shrimp (Fenneropenaeus chinensis) in WSSV Infection

Our previous study demonstrated that an integrin β subunit of Chinese shrimp (Fenneropenaeus chinensis) (FcβInt) plays an important role in white spot syndrome virus (WSSV) infection. In the present work, in order to further elucidate the potential role of FcβInt in WSSV infection, the recombinant extracellular domain of β integringene of F. Chinensis (rFcβInt-ER) was expressed in Escherichia coli BL21 (DE3), and the eukaryotic expression plasmid PcDNA3.1-FcβInt-ER (PFcβInt-ER) was also constructed. Far-western blotting was performed to determine the binding specificity of rFcβInt-ER to WSSV envelope proteins, and results showed that rFcβInt-ER was able to specifically interact with rVP31, rVP37, rVP110 and rVP187. Moreover, the blocking effects of mouse anti-rFcβint-ER antibodies were both detected in vivo and in vitro. The ELISA and Dot-blotting in vitro assays both showed that mouse anti-rFcβInt-ER antibodies could partially block the binding of WSSV to the hemocyte membrane of F. chinensis. In the in vivo assays, the mortality of shrimp injected with WSSV mixed with anti-rFcβInt-ER antibodies was delayed, and was lower than in the control group. While the shrimp were intramuscularly injected with PFcβInt-ER, transcripts of PFcβInt-ER could be detected in different shrimp tissues within 7 days, and the mortality of shrimp injected with PFcβInt-ER was also delayed and lower compared with the control group post WSSV challenge. Furthermore, gene silencing technology was also used to verify the effect of FcβInt in WSSV infection, and results showed that the expression levels of the WSSV immediate early gene iel, early gene wsv477, and late gene VP28 and the mortality of F. Chinensis were all significantly decreased in the FcβInt knock-down hemocyctes compared to the control group. Taken together, these results suggest that FcβInt plays important roles in WSSV infection.

WSSV envelope protein VP51B links structural protein complexes and may mediate virus infection

White spot syndrome virus (WSSV), an enveloped double-stranded DNA virus, is the causative agent of a disease that has led to severe mortalities of cultured shrimps in Taiwan and many other countries. In the previous study, Penaeus monodon chitin-binding protein (CBP) and glucose transporter 1 (Glut1), two cell membrane proteins, were found to at least interact with other 10 WSSV envelope proteins including VP51B. These envelope proteins might form a protein complex. According to the known information, VP51B was used to identify its role in the protein complex. Western blotting of the intact viral particles and fractionation of the viral components confirmed that VP51B is one of WSSV envelope proteins. In this study, the protein-protein interaction between VP51B and other WSSV envelope proteins was identified by far-western blot experiment and VP51B was found to interact with VP24, VP31, VP32, VP39B and VP41A. Furthermore, the in vivo neutralization experiment using recombinant VP51B plus with VP39B showed the best inhibition. These data indicate that VP51B participates in the WSSV protein complex and plays an important role in WSSV infection.

RNA sequencing analysis to capture the transcriptome landscape during skin ulceration syndrome progression in sea cucumber Apostichopus japonicus

Background

Sea cucumber Apostichopus japonicus is an important economic species in China, which is affected by various diseases; skin ulceration syndrome (SUS) is the most serious. In this study, we characterized the transcriptomes in A. japonicus challenged with Vibrio splendidus to elucidate the changes in gene expression throughout the three stages of SUS progression.

Results

RNA sequencing of 21 cDNA libraries from various tissues and developmental stages of SUS-affected A. japonicus yielded 553 million raw reads, of which 542 million high-quality reads were generated by deep-sequencing using the Illumina HiSeq™ 2000 platform. The reference transcriptome comprised a combination of the Illumina reads, 454 sequencing data and Sanger sequences obtained from the public database to generate 93,163 unigenes (average length, 1,052 bp; N50 = 1,575 bp); 33,860 were annotated. Transcriptome comparisons between healthy and SUS-affected A. japonicus revealed greater differences in gene expression profiles in the body walls (BW) than in the intestines (Int), respiratory trees (RT) and coelomocytes (C). Clustering of expression models revealed stable up-regulation as the main pattern occurring in the BW throughout the three stages of SUS progression. Significantly affected pathways were associated with signal transduction, immune system, cellular processes, development and metabolism. Ninety-two differentially expressed genes (DEGs) were divided into four functional categories: attachment/pathogen recognition (17), inflammatory reactions (38), oxidative stress response (7) and apoptosis (30). Using quantitative real-time PCR, twenty representative DEGs were selected to validate the sequencing results. The Pearson’s correlation coefficient (R) of the 20 DEGs ranged from 0.811 to 0.999, which confirmed the consistency and accuracy between these two approaches.

Conclusions

Dynamic changes in global gene expression occur during SUS progression in A. japonicus. Elucidation of these changes is important in clarifying the molecular mechanisms associated with the development of SUS in sea cucumber.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2810-3) contains supplementary material, which is available to authorized users.

Laminin Receptor in Shrimp Is a Cellular Attachment Receptor for White Spot Syndrome Virus

White spot syndrome virus (WSSV, genus Whispovirus, family Nimaviridae) is causing huge economic losses in global shrimp farming, but there is no effective control. Shrimp cell laminin receptor (Lamr) may have a role in WSSV infection. The objective was to characterize interactions between Penaeus monodon Lamr (PmLamr) and WSSV structural proteins. In this study, PmLamr interacted with nine WSSV structural proteins (based on yeast two-hybrid screening), of which one (VP31) was characterized. Protein pull-down assay confirmed the interaction between PmLamr and VP31; the latter was an envelope protein exposed outside the WSSV virion (based on membrane topology assays). Furthermore, similar to mammalian Lamr, there were two major protein bands in shrimp cells. Cellular localization assay demonstrated VP31 co-localized with PmLamr on transfected cells. Enzyme-link immunosorbent assay (ELISA) and competitive ELISA demonstrated binding of VP31 on PmLamr was dose-dependent; however, addition of WSSV virion competed for binding affinity. Furthermore, based on an in vivo neutralization assay, both VP31 and PmLamr delayed mortality in shrimp challenged with WSSV. We concluded Lamr was an important receptor for WSSV infection and the viral envelope protein VP31 may have a role in host cell recognition and binding. These data contributed to elucidating pathogenesis of WSSV infection and may help in controlling this disease.

SUMO and SUMO-Conjugating Enzyme E2 UBC9 Are Involved in White Spot Syndrome Virus Infection in Fenneropenaeus chinensis

In previous work, small ubiquitin-like modifier (SUMO) in hemocytes of Chinese shrimp Fenneropenaeus chinensis was found to be up-regulated post-white spot syndrome virus (WSSV) infection using proteomic approach. However, the role of SUMO in viral infection is still unclear. In the present work, full length cDNAs of SUMO (FcSUMO) and SUMO-conjugating enzyme E2 UBC9 (FcUBC9) were cloned from F. chinensis using rapid amplification of cDNA ends approach. The open reading frame (ORF) of FcSUMO encoded a 93 amino acids peptide with the predicted molecular weight (M.W) of 10.55 kDa, and the UBC9 ORF encoded a 160 amino acids peptide with the predicted M.W of 18.35 kDa. By quantitative real-time RT-PCR, higher mRNA transcription levels of FcSUMO and FcUBC9 were detected in hemocytes and ovary of F. chinensis, and the two genes were significantly up-regulated post WSSV infection. Subsequently, the recombinant proteins of FcSUMO and FcUBC9 were expressed in Escherichia coli BL21 (DE3), and employed as immunogens for the production of polyclonal antibody (PAb). Indirect immunofluorescence assay revealed that the FcSUMO and UBC9 proteins were mainly located in the hemocytes nuclei. By western blotting, a 13.5 kDa protein and a 18.7 kDa protein in hemocytes were recognized by the PAb against SUMO or UBC9 respectively. Furthermore, gene silencing of FcSUMO and FcUBC9 were performed using RNA interference, and the results showed that the number of WSSV copies and the viral gene expressions were inhibited by knockdown of either SUMO or UBC9, and the mortalities of shrimp were also reduced. These results indicated that FcSUMO and FcUBC9 played important roles in WSSV infection.

Overexpression of CD61 promotes hUC-MSC differentiation into male germ-like cells

OBJECTIVES

Previous studies have shown that germ-like cells can be induced from human umbilical cord mesenchymal stem cell (hUC-MSCs) in vitro. However, induction efficiency was low and a stable system had not been built. CD61, also called integrin-β3, plays a significant role in cell differentiation, in that CD61-positive-cell-derived pluripotent stem cells easily differentiate into primordial germ-like cells (PGC). Here, we have explored whether overexpression of CD61 would promote hUC-MSC differentiation into PGC and male germ-like cells.

MATERIALS AND METHODS

hUC-MSCs were cultured and transduced using pCD61-CAGG-TRIP-pur (oCD61) and pTRIP-CAGG plasmid (Control), and hUC-MSCs overexpressed CD61 were induced by bone morphogenetic protein 4 (BMP4, 12.5 ng/ml), to differentiate into PGC and male germ cells. Quantitative real-time PCR (RT-qPCR), western blotting and immunofluorescence staining were used to examine PGC- and germ cell-specific markers.

RESULTS

High expression levels of PGC-specific markers were detected in oCD61 hUC-MSCs compared to controls. After BMP4 induction, expression levels of male germ cell markers such as Acrosin (ACR), Prm1 and meiotic markers including Stra8, Scp3 in oCD61 were significantly higher than those of the Control group.

CONCLUSIONS

Under induction of BMP4, CD61-overexpressing hUC-MSCs, which had turned into PGC-like cells, could be further differentiated into male germ-like cells. Thus, a simple and efficient approach to study male germ cell development by using hUC-MSCs has been established.

Molecular Mechanisms of White Spot Syndrome Virus Infection and Perspectives on Treatments

Since its emergence in the 1990s, White Spot Disease (WSD) has had major economic and societal impact in the crustacean aquaculture sector. Over the years shrimp farming alone has experienced billion dollar losses through WSD. The disease is caused by the White Spot Syndrome Virus (WSSV), a large dsDNA virus and the only member of the Nimaviridae family. Susceptibility to WSSV in a wide range of crustacean hosts makes it a major risk factor in the translocation of live animals and in commodity products. Currently there are no effective treatments for this disease. Understanding the molecular basis of disease processes has contributed significantly to the treatment of many human and animal pathogens, and with a similar aim considerable efforts have been directed towards understanding host-pathogen molecular interactions for WSD. Work on the molecular mechanisms of pathogenesis in aquatic crustaceans has been restricted by a lack of sequenced and annotated genomes for host species. Nevertheless, some of the key host-pathogen interactions have been established: between viral envelope proteins and host cell receptors at initiation of infection, involvement of various immune system pathways in response to WSSV, and the roles of various host and virus miRNAs in mitigation or progression of disease. Despite these advances, many fundamental knowledge gaps remain; for example, the roles of the majority of WSSV proteins are still unknown. In this review we assess current knowledge of how WSSV infects and replicates in its host, and critique strategies for WSD treatment.

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.

Analysis on the expression and function of syndecan in the Pacific white shrimp Litopenaeus vannamei

Syndecan is considered to be a multifunctional protein which functions as a cell surface receptor involved in cell adhesion, migration, cytoskeleton organization and differentiation. Previous bioinformatic analysis has revealed that syndecan in shrimp might interact with white spot syndrome virus (WSSV). In the present study, we experimentally studied the function of syndecan in shrimp immunity. The syndecan from Litopenaeus vannamei (LvSDC) was cloned and analyzed. The full-length cDNA of LvSDC was 1005 bp, consisting of 59 bp 5'-UTR, 253 bp 3'-UTR, and 693 bp open reading frame encoding 230 amino acids. LvSDC consisted of an extracellular domain (ED), a transmembrane domain (TM) and a cytoplasmic domain (CD). TM and CD shared high similarities with those of syndecan proteins from other species. LvSDC was ubiquitously expressed in all tested tissues, with the highest level in Oka. After WSSV challenge, the transcription level of LvSDC in Oka was apparently up-regulated. Recombinant LvSDC protein and its rabbit polyclonal antibody were prepared for detecting the location of LvSDC in hemocytes using immunocytochemistry approach. Data showed that LvSDC mainly located at the cell membrane and the cytoplasm of hemocytes. After silencing of LvSDC with siRNA, the WSSV copy numbers and mortality of shrimp after WSSV infection were both significantly decreased. These data provide useful information for understanding the immune mechanism of shrimp to WSSV infection.

Recent insights into host-pathogen interaction in white spot syndrome virus infected penaeid shrimp

Viral disease outbreaks are a major concern impeding the development of the shrimp aquaculture industry. The viral disease due to white spot syndrome virus (WSSV) observed in early 1990s still continues unabated affecting the shrimp farms and cause huge economic loss to the shrimp aquaculture industry. In the absence of effective therapeutics to control WSSV, it is important to understand viral pathogenesis and shrimp response to WSSV at the molecular level. Identification and molecular characterization of WSSV proteins and receptors may facilitate in designing and development of novel therapeutics and antiviral drugs that may inhibit viral replication. Investigations into host-pathogen interactions might give new insights to viral infectivity, tissue tropism and defence mechanism elicited in response to WSSV infection. However, due to the limited information on WSSV gene function and host immune response, the signalling pathways which are associated in shrimp pathogen interaction have also not been elucidated completely. In the present review, the focus is on those shrimp proteins and receptors that are potentially involved in virus infection or in the defence mechanism against WSSV. In addition, the major signalling pathways involved in the innate immune response and the role of apoptosis in host-pathogen interaction is discussed.

ATP synthesis is active on the cell surface of the shrimp Litopenaeus vannamei and is suppressed by WSSV infection

BACKGROUND

Over the past a few years, evidences indicate that adenosine triphosphate (ATP) is an energy source for the binding, maturation, assembly, and budding process of many enveloped viruses. Our previous studies suggest that the F1-ATP synthase beta subunit (ATPsyn β, BP53) of the shrimp Litopenaeus vannamei (L. vannamei) might serve as a potential receptor for white spot syndrome virus (WSSV)'s infection.

METHODS

BP53 was localized on the surface of shrimp hemocytes and gill epithelial cells by immunofluorescence assay and immunogold labeling technique. Cell surface ATP synthesis was demonstrated by an in vitro bioluminescent luciferase assay. Furthermore, the expression of bp53 after WSSV infection was investigated by RT-PCR test. In addition, RNAi was developed to knock down endogenous bp53.

RESULTS

BP53 is present on shrimp cell surface of hemocytes and gill epithelia. The synthesized ATP was detectable in the extracellular supernatant by using a bioluminescence assay, and the production declined post WSSV binding and infection. Knocking down endogenous bp53 resulted in a 50% mortality of L. vannamei.

CONCLUSION

These results suggested that BP53, presenting on cell surface, likely served as one of the receptors for WSSV infection in shrimp. Correspondingly, WSSV appears to disturb the host energy metabolism through interacting with host ATPsyn β during infection. This work firstly showed that host ATP production is required and consumed by the WSSV for binding and proceeds with infection process.

GHSC70 is involved in the cellular entry of nervous necrosis virus

Nervous necrosis virus (NNV) is a devastating pathogen of cultured marine fish and has affected more than 40 fish species. NNV belongs to the betanodaviruses of Nodaviridae and is a nonenveloped icosahedral particle with 2 single-stranded positive-sense RNAs. To date, knowledge regarding NNV entry into the host cell remains limited, and no NNV-specific receptor protein has been published. Using grouper fin cell line GF-1 and purified NNV capsid protein in a virus overlay protein binding assay (VOPBA), grouper heat shock cognate protein 70 (GHSC70) and grouper voltage-dependent anion selective channel protein 2 (GVDAC2) were investigated as NNV receptor protein candidates. We cloned and sequenced the genes for GHSC70 and GVDAC2 and expressed them in Escherichia coli for antiserum preparation. Knockdown of the expression of GHSC70 and GVDAC2 genes with specific short interfering RNAs (siRNAs) significantly downregulated viral RNA expression in NNV-infected GF-1 cells. By performing an immunoprecipitation assay, we confirmed that GHSC70 interacted with NNV capsid protein, while VDAC2 did not. Immunofluorescence staining and flow cytometry analysis revealed the presence of the GHSC70 protein on the cell surface. After a blocking assay, we detected the NNV RNA2 levels after 1 h of adsorption to GF-1 cells; the level was significantly lower in the cells pretreated with the GHSC70 antiserum than in nontreated cells. Therefore, we suggest that GHSC70 participates in the NNV entry of GF-1 cells, likely functioning as an NNV receptor or coreceptor protein.

IMPORTANCE

Fish nodavirus has caused mass mortality of more than 40 fish species worldwide and resulted in huge economic losses in the past 20 years. Among the four genotypes of fish nodaviruses, the red-spotted grouper nervous necrosis virus (RGNNV) genotype exhibits the widest host range. In our previous study, we developed monoclonal antibodies with high neutralizing efficiency against grouper NNV in GF-1 cells, indicating that NNV-specific receptor(s) may exist on the GF-1 cell membrane. However, no NNV receptor protein has been published. In this study, we found GHSC70 to be an NNV receptor (or coreceptor) candidate through VOBPA and provided several lines of evidence demonstrating that GHSC70 protein has a role in the NNV entry step of GF-1 cells. To the best of our knowledge, this is the first report identifying grouper HSC70 and its role in NNV entry into GF-1 cells.

Granulocytes of the red claw crayfish Cherax quadricarinatus can endocytose beads, E. coli and WSSV, but in different ways

The hemocytes of the red claw crayfish Cherax quadricarinatus are classified by morphologic observation into the following types: hyalinocytes (H), semi-granulocytes (SG) and granulocytes (G). Density gradient centrifugation with Percoll was developed to separate these three subpopulations of hemocytes. Beads, Escherichia coli, and FITC labeling WSSV were used to investigate the characteristics of granulocytes by using scanning electron microscope, transmission electron microscope, and laser scan confocal microscope. Results showed that granulocytes could phagocytose beads and E. coli by endocytic pathways. WSSV could rely on caveolae-mediated endocytosis to mainly enter into granulocytes. These results could elucidate the mechanism of the innate immunity function of granulocytes, and it also showed the mechanism by which WSSV invaded granulocytes in the red claw crayfish.

A newly identified protein complex that mediates white spot syndrome virus infection via chitin-binding protein

White spot syndrome virus (WSSV) is a large enveloped virus which has caused severe mortality and huge economic losses in the shrimp farming industry. The enveloped virus must be combined with the receptors of the host cell membrane by the virus envelope proteins. In the case of WSSV, binding of envelope proteins with receptors of the host cell membrane was discovered in a number of previous studies, such as VP53A and 10 other proteins with chitin-binding protein (CBP), VP28 with Penaeus monodon Rab7, VP187 with β-integrin, and so on. WSSV envelope proteins were also considered capable of forming a protein complex dubbed an ‘infectome’. In this study, the research was focused on the role of CBP in the WSSV infection process, and the relationship between CBP and the envelope proteins VP24, VP28, VP31, VP32 VP39B, VP53A and VP56. The results of the reverse transcription-PCR analyses showed that CBP existed in a variety of shrimp. The speed of WSSV infection could be slowed down by inhibiting CBP gene expression. Far-Western blot analysis and His pull-down assays were conducted, and a protein complex was found that appeared to be composed of a ‘linker’ protein consisting of VP31, VP32 and VP39B together with four envelope proteins, including VP24, VP28, VP53A and VP56. This protein complex was possibly another part of the infectome and the possible binding region with CBP. The findings of this study may have identified certain points for further WSSV research.

Antiviral defense in shrimp: from innate immunity to viral infection

The culture of penaeid shrimp is rapidly developing as a major business endeavor worldwide. However, viral diseases have caused huge economic loss in penaeid shrimp culture industries. Knowledge of shrimp innate immunity and antiviral responses has made important progress in recent years, allowing the design of better strategies for the prevention and control of shrimp diseases. In this study, we have updated information on shrimp antiviral immunity and interactions between shrimp hosts and viral pathogens. Current knowledge and recent progress in immune signaling pathways (e.g., Toll/IMD-NF-κB and JAK-STAT signaling pathways), RNAi, phagocytosis, and apoptosis in shrimp antiviral immunity are discussed. The mechanism of viral infection in shrimp hosts and the interactions between viruses and shrimp innate immune systems are also analyzed.

Bioinformatic prediction of WSSV-host protein-protein interaction

WSSV is one of the most dangerous pathogens in shrimp aquaculture. However, the molecular mechanism of how WSSV interacts with shrimp is still not very clear. In the present study, bioinformatic approaches were used to predict interactions between proteins from WSSV and shrimp. The genome data of WSSV (NC_003225.1) and the constructed transcriptome data of F. chinensis were used to screen potentially interacting proteins by searching in protein interaction databases, including STRING, Reactome, and DIP. Forty-four pairs of proteins were suggested to have interactions between WSSV and the shrimp. Gene ontology analysis revealed that 6 pairs of these interacting proteins were classified into “extracellular region” or “receptor complex” GO-terms. KEGG pathway analysis showed that they were involved in the “ECM-receptor interaction pathway.” In the 6 pairs of interacting proteins, an envelope protein called “collagen-like protein” (WSSV-CLP) encoded by an early virus gene “wsv001” in WSSV interacted with 6 deduced proteins from the shrimp, including three integrin alpha (ITGA), two integrin beta (ITGB), and one syndecan (SDC). Sequence analysis on WSSV-CLP, ITGA, ITGB, and SDC revealed that they possessed the sequence features for protein-protein interactions. This study might provide new insights into the interaction mechanisms between WSSV and shrimp.