Shrimp molecular responses to viral pathogens

Immune signaling of Litopenaeus vannamei c-type lysozyme and its role during microsporidian Enterocytozoon hepatopenaei (EHP) infection

The microsporidian Enterocytozoon hepatopenaei (EHP) is a fungi-related, spore-forming parasite. EHP infection causes growth retardation and size variation in shrimp, resulting in severe economic losses. Studies on shrimp immune response have shown that several antimicrobial peptides (AMPs) were upregulated upon EHP infection. Among those highly upregulated AMPs is c-type lysozyme (LvLyz-c). However, the immune signaling pathway responsible for LvLyz-c production in shrimp as well as its function against the EHP infection are still poorly understood. Here, we characterized major shrimp immune signaling pathways and found that Toll and JAK/STAT pathways were up-regulated upon EHP infection. Knocking down of a Domeless (DOME) receptor in the JAK/STAT pathways resulted in a significant reduction of the LvLyz-c and the elevation of EHP copy number. We further elucidated the function of LvLyz-c by heterologously expressing a recombinant LvLyz-c (rLvLyz-c) in an Escherichia coli. rLvLyz-c exhibited antibacterial activity against several bacteria such as Bacillus subtilis and Vibrio parahaemolyticus. Interestingly, we found an antifungal activity of rLvLyz-c against Candida albican, which led us to further investigate the effects of rLvLyz-c on EHP spores. Incubation of the EHP spores with rLvLyz-c followed by a chitin staining showed that the signals were dramatically decreased in a dose-dependent manner, suggesting that rLvLyz-c possibly digest a chitin coat on the EHP spores. Transmission electron microscopy analysis revealed that an endospore layer, which is composed mainly of chitin, was digested by rLvLyz-c. Lastly, we observed that EHP spores that were treated with rLvLyz-c showed a significant reduction of the spore germination rate. We hypothesize that thinning of the endospore of EHP would result in altered permeability, hence affecting spore germination. This work provides insights into shrimp immune signaling pathways responsible for LvLyz-c production and its anti-EHP property. This knowledge will serve as important foundations for developing EHP control strategies.

Effects of PmDOME and PmSTAT knockdown on white spot syndrome virus infection in Penaeus monodon

Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway plays an important role in antiviral immunity. This research reports the full-length DOME receptor gene in Penaeus monodon (PmDOME) and examines the effects of PmDOME and PmSTAT silencing on immune-related gene expressions in shrimp hemocytes during white spot syndrome virus (WSSV) infection. PmDOME and PmSTAT were up-regulated in shrimp hemocytes upon WSSV infection. Suppression of PmDOME and PmSTAT showed significant impacts on the expression levels of ProPO2 (melanization), Vago5 (interferon-like protein) and several antimicrobial peptides, including ALFPm3, Penaeidin3, CrustinPm1 and CrustinPm7. Silencing of PmDOME and PmSTAT reduced WSSV copy numbers and delayed the cumulative mortality caused by WSSV. We postulated that suppression of the JAK/STAT signaling pathway may activate the proPO, IFN-like antiviral cytokine and AMP production, resulting in a delay of WSSV-related mortality.

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

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

Guava (Psidium guajava) leaf extract enhances immunity, growth, and resistance against Vibrio parahaemolyticus in white shrimp Penaeus vannamei

This study investigated the effects of guava leaf extract (GLE) on immune responses, growth performance, and resistance to Vibrio parahaemolyticus in white shrimp (Penaeus vannamei). To examine the effect of GLE on the immune response of white shrimps, they were treated with various concentrations of GLE on hemocyte (in vitro) and were orally administered (in vivo) feed containing various concentrations of 0, 1, 5, and 10 g kg^-1 GLE (control, GLE1, GLE5, and GLE10, respectively) for 28 days. Furthermore, their growth performance was evaluated for 56 days. In a separate experiment, the shrimps were challenged with V. parahaemolyticus injection after 7 days of culture. In vitro experiments indicated that GLE is nontoxic and can activate immune response. In vivo experiments revealed that the GLE5 led to the highest total hemocyte count, phenoloxidase activity, phagocytic activity, and superoxide anion production and the highest upregulation of lipopolysaccharide, β-1,3-glucan-binding protein, peroxinectin, lysozyme, crustin, penaeidin 2, penaeidin 3, clotting protein, superoxide dismutase, and glutathione peroxidase. Moreover, better growth performance was observed in the GLE groups, with GLE5 exhibiting the highest specific growth rate, weight gain, and feed conversion rate. In addition, GLE5 enhanced resistance to V. parahaemolyticus, with a survival rate of 72.27%. In conclusion, GLE was found to be effective in enhancing nonspecific immune response and growth performance and in reducing V. parahaemolyticus infection in white shrimp.

The Molecular Mechanism of Hemocyte Immune Response in Marsupenaeus japonicus Infected With Decapod Iridescent Virus 1

As a new type of shrimp lethal virus, decapod iridescent virus 1 (DIV1) has caused huge economic losses to shrimp farmers in China. Up to now, DIV1 has been detected in a variety of shrimps, but there is no report in Marsupenaeus japonicus. In the current study, we calculated the LC₅₀ to evaluate the toxicity of DIV1 to M. japonicus and determined through nested PCR that M. japonicus can be the host of DIV1. Through enzyme activity study, it was found that DIV1 can inhibit the activities of superoxide dismutase, catalase, lysozyme, and phenoloxidase, which could be a way for DIV1 to achieve immune evasion. In a comprehensive study on the transcriptomic changes of M. japonicus in response to DIV1 infection, a total of 52,287 unigenes were de novo assembled, and 20,342 SSR markers associated with these unigenes were obtained. Through a comparative transcriptomic analysis, 6,900 differentially expressed genes were identified, including 3,882 upregulated genes and 3,018 downregulated genes. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that some GO terms related to virus invasion, replication, and host antiviral infection were promoted under DIV1 infection, such as carbohydrate binding, chitin binding, chitin metabolic process, and DNA replication initiation, and some KEGG pathways related to immune response were significantly influenced by DIV1 infection, including Toll and IMD signaling pathway, JAK-STAT signaling pathway, IL-17 signaling pathway, C-type lectin receptor signaling pathway, complement and coagulation cascades, antigen processing and presentation, necroptosis, apoptosis, NOD-like receptor signaling pathway, apoptosis-multiple species, and TNF signaling pathway. Further analysis showed that STAT, Dorsal, Relish, heat shock protein 70 (HSP70), C-type lectins, and caspase play an important role in DIV1 infection. This is the first detailed study of DIV1 infection in M. japonicus, which initially reveals the molecular mechanism of DIV1 infection in M. japonicus by using the transcriptome analysis of hemocytes combined with enzyme activity study.

Transcriptomic analysis of the black tiger shrimp (Penaeus monodon) reveals insights into immune development in their early life stages

With the rapid growth in the global demand, the shrimp industry needs integrated approaches for sustainable production. A high-quality shrimp larva is one of the crucial key requirements to maximize shrimp production. Survival and growth rates during larval development are often criteria to evaluate larval quality, however many aspects of gene regulation during shrimp larval development have not yet been identified. To further our understanding of biological processes in their early life, transcriptomic analysis of larval developmental stages (nauplius, zoea, mysis, and postlarva) were determined in the black tiger shrimp, Penaeus monodon using next-generation RNA sequencing. Gene clustering and gene enrichment analyses revealed that most of the transcripts were mainly related to metabolic processes, cell and growth development, and immune system. Interestingly, Spätzle and Toll receptors were found in nauplius stage, providing evidence that Toll pathway was a baseline immune system established in early larval stages. Genes encoding pathogen pattern-recognition proteins (LGBP, PL5-2 and c-type lectin), prophenoloxidase system (PPAE2, PPAF2 and serpin), antimicrobial peptides (crustin and antiviral protein), blood clotting system (hemolymph clottable protein) and heat shock protein (HSP70) were expressed as they developed further, suggesting that these immune defense mechanisms were established in later larval stages.

Molecular Characterization of Complement Component 3 (C3) in the Pearl Oyster Pinctada fucata Improves Our Understanding of the Primitive Complement System in Bivalve

As the central component in the complement system, complement component 3 (C3) plays essential roles in both the innate and adaptive immune responses. Here, a C3 gene (designated as pf-C3) was obtained from the pearl oyster Pinctada fucata by RT-PCR and rapid amplification of cDNA ends (RACE). The pf-C3 cDNA consists of 5,634 bp with an open reading frame (ORF) of 5,193 bp encoding a protein of 1,730 amino acids with a 19 residue signal peptide. The deduced pf-C3 protein possessed the characteristic structural features present in its homologs and contained the A2M_N_2, ANATO, A2M, A2M_comp, A2M_recep, and C345C domains, as well as the C3 convertase cleavage site, thioester motif, and conserved Cys, His, and Glu residues. Phylogenetic analysis revealed that pf-C3 is closely related to the C3s from other mollusks. Pf-C3 mRNA was expressed in all examined tissues including gill, digestive gland, adductor muscle, mantle and foot, while the highest expression was found in the digestive gland. Following the challenge with Vibrio alginolyticus, pf-C3 expression was significantly induced in hemocytes. Luciferase reporter assays indicated that pf-C3a could activate the NF-κB signal pathway in HEK293T cells. Further knockdown of pf-C3 by specific siRNA could significantly reduce the phagocytosis of V. alginolyticus by hemocytes in vitro. These results would help increase understanding of the function of C3 in the invertebrate immune system and therefore provide new insights into the roles of the primitive complement system in invertebrates.

Innate immune responses against viral pathogens in Macrobrachium

Some members of genus Macrobrachium are important economically prawns and valuable objects for studying the innate immune defense mechanism of crustaceans. Studies have focused on immune responses against bacterial and fungal infections and have expanded to include antiviral immunity over the past two decades. Similar to all living organisms, prawns are exposed to viruses, including white spot syndrome virus, Macrobrachium rosenbergii nodavirus, and Decapod iridescent virus 1 and develop effective defense mechanisms. Here, we review current understanding of the antiviral host defense in two species of Macrobrachium. The main antiviral defense of Macrobrachium is the activation of intracellular signaling cascades, leading to the activation of cellular responses (apoptosis) and humoral responses (immune-related signaling pathways, antimicrobial and antiviral peptides, lectins, and prophenoloxidase-activating system).

GSK3β Plays a Negative Role During White Spot Syndrome Virus (WSSV) Infection by Regulating NF-κB Activity in Shrimp Litopenaeus vannamei

Glycogen synthase kinase-3 (GSK3), a cytoplasmic serine/threonine-protein kinase involved in a large number of key cellular processes, is a little-known signaling molecule in virus study. In this study, a GSK3 protein which was highly similar to GSK3β homologs from other species in Litopenaeus vannamei (designated as LvGSK3β) was obtained. LvGSK3β was expressed constitutively in the healthy L. vannamei, at the highest level in the intestine and the lowest level in the eyestalk. White spot syndrome virus (WSSV) reduced LvGSK3β expression was in immune tissues including the hemocyte, intestine, gill and hepatopancreas. The inhibition of LvGSK3β resulted in significantly higher survival rates of L. vannamei during WSSV infection than the control group, and significantly lower WSSV viral loads in LvGSK3β-inhibited L. vannamei were observed. Knockdown of LvGSK3β by RNAi resulted in increases in the expression of LvDorsal and several NF-κB driven antimicrobial peptide (AMP) genes (including ALF, PEN and crustin), but a decrease in LvCactus expression. Accordingly, overexpression of LvGSK3β could reduce the promoter activity of LvDorsal and several AMPs, while the promoter activity of LvCactus was increased. Electrophoretic mobility shift assays (EMSA) showed that LvDorsal could bind to the promoter of LvGSK3β. The interaction between LvGSK3β and LvDorsal or LvCactus was confirmed using co-immunoprecipitation (Co-IP) assays. In addition, the expression of LvGSK3β was dramatically reduced by knockdown of LvDorsal. In summary, the results presented in this study indicated that LvGSK3β had a negative effect on L. vannamei by mediating a feedback regulation of the NF-κB pathway when it is infected by WSSV.

Differential transcriptomic analysis of crayfish (Procambarus clarkii) from a rice coculture system challenged by Vibrio parahaemolyticus

Rice-crayfish (Procambarus clarkii) coculture is an effective farming mode and has been promoted in various regions of China. However, infection in crayfish can be a significant economic drain. We found crayfish infected with Vibrio parahemolyticus (VP), and to understand the molecular mechanisms of the immune responses of crayfish to VP infection, Illumina sequencing was employed to identify changes in the mRNA of hepatopancreatic tissue. A total of 47.30 and 43.01million high-quality transcriptome reads were generated from the hepatopancreatic samples of the experimental group (EG) and control group (CG), respectively. We found 5559 genes were significantly differentially expressed, including 2521 up-regulated genes (45.35%) and 3038 down-regulated genes (54.65%). These genes were enriched in 126 GO terms and 76 KEGG pathways (P ≤ 0.05), including the MAPK and PI3K-Akt signaling pathways and cell adhesion molecules, with 23 up-regulated genes and 3 down-regulated genes related to immune responses in the EG relative to the CG. Histopathological analysis revealed that the epithelial cells of the hepatopancreatic tubules in the EG were severely atrophic, necrotic, and exfoliated, resulting in thin and collapsing hepatopancreatic tubules. The expression patterns of 8 differentially expressed genes involved in immune responses were validated by quantitative real-time RT-PCR. These results provide a valuable basis for the immune responses of crayfish to acute hepatopancreatic necrosis disease at transcriptome level.

White spot syndrome virus (WSSV) disturbs the intestinal microbiota of shrimp (Penaeus vannamei) reared in biofloc and clear seawater

White spot syndrome virus (WSSV) is one of the most virulent pathogens afflicting shrimp farming. Understanding its influence on shrimp intestinal microbiota is paramount for the advancement of aquaculture, since gut dysbiosis can negatively impact shrimp development, physiology, and immunological response. Thereupon, the data presented herein assesses the influence of WSSV infection and different rearing systems on the intestinal microbiota of Penaeus vannamei. Our study aimed to describe and correlate the composition of shrimp (Penaeus vannamei) gut microbiota, when reared in biofloc and clear seawater, before and (48 h) after WSSV experimental infection. Shrimp were kept in two different systems (biofloc and clear seawater) and experimentally infected with WSSV. Intestine and water samples were characterized by 16S rRNA gene sequencing, before and after viral infection. We observed (i) WSSV induced higher mortality among shrimp reared in biofloc; (ii) WSSV led to a loss of intestinal microbiota heterogeneity, at the genus level, in shrimp kept in clear seawater; (iii) there was a prevalence of Cetobacterium and Bacillus in the intestine of shrimp from both systems; (iv) WSSV did not cause significant changes in intestinal microbiota diversity or richness; (v) regardless of the type of system and time of infection, intestinal microbiota was dissimilar to that of the surrounding water, despite being influenced by the type of system. Therefore, WSSV infection leads to punctual dysbiotic changes in shrimp microbiota, although the virus is sufficiently virulent to cause high mortalities even in well-managed systems, such as a balanced experimental biofloc system. KEY POINTS: • WSSV infection leads to a perturbed gut microbiota in shrimp. • WSSV infection greater impacts microbiota of shrimp reared in CSW than those in BFT. • WSSV infection caused higher mortality levels in shrimp reared in BFT than in CSW. • Rearing system influences shrimp gut microbiota composition. Graphical abstract.

Oligosaccharides derived from dragon fruit modulate gut microbiota, reduce oxidative stress and stimulate toll-pathway related gene expression in freshwater crustacean Daphnia magna

Dragon fruit oligosaccharide (DFO) is an indigestible prebiotic. In this study, we aimed to investigate the effects of DFO on gut microbiota, oxidative stress and immune-related gene expression in Daphnia magna. The 10-day-old D. magna were treated with 0, 9, and 27 mg l^-1 DFO for 85 h. The gut bacterial communities, superoxide dismutase (SOD) activity, lipid peroxidation and the expressions of genes in Toll signaling pathway were observed. The results showed that D. magna treated with 9 and 27 mg l^-1 DFO altered gut microbiota composition by increasing Limnohabitans and Lactobacillus, and significantly increased SOD activity and reduced lipid peroxidation. Moreover, the expressions of Toll2, Toll3, Toll5, Toll7 and Pelle genes were significantly increased in D. magna treated with 9 and 27 mg l^-1 DFO. Our results suggested that DFO changed the composition of the gut microbiota of D. magna by increasing the beneficial bacteria. DFO also had the ability to stimulate innate immunity in D. magna by increasing SOD activity, reducing lipid peroxidation, and increasing the expression of immune-related genes.

Effect in white shrimp Litopenaeus vannamei of Eleutherine bulbosa (Mill.) Urb. Powder on immune genes expression and resistance against Vibrio parahaemolyticus infection

This study investigated the influence of Eleutherine bulbosa (Mill.) Urb. on the immune responses, bacterial population in the intestines, and resistance of white shrimp, Litopenaeus vannamei, against infection with Vibrio parahaemolyticus. Shrimp were fed with three dosages of powder, at 6.25 g kg-1 (P6.25), 12.5 g kg-1 (P12.5), and 25 g kg-1 (P25). One dosage of the crude extract was provided, 1.25 g kg-1 (E1.25), and the controls without administration of E. bulbosa consisted of a positive control (PC) and a negative control (NC). Feed supplementation was carried out for 30 days; then shrimp from all treatments were challenged by intramuscular injection with V. parahaemolyticus (10⁶ cfu/mL), except for the NC. The results showed that supplementation with the powder and extract of E. bulbosa for 30 days resulted in significantly higher (P < 0.05) immune responses (total hemocyte count (THC), phenoloxidase activity (PO), respiratory bursts (RBs)), gene expression (prophenoloxidase (proPO), lipopolysaccharide- and β-1,3-glucan-binding protein (LGBP)), and total bacterial count (TBC) compared to PC/NC. In post challenge testing, there were significantly higher levels for THC, PO, RBs, proPO, LGBP, and PE (peroxinetin), and the treatments were able to suppress V. parahaemolyticus in the intestines, hepatopancreas, and muscles and to reduce damage to the muscles and hepatopancreas. The survival rate with P12.5 was significantly higher compared to the other treatments. It was concluded that the shrimp receiving supplementation with the powder and extract of E. bulbosa had increased immunity and resistance against V. parahaemolyticus infection, with the best dosage being the P12.5 treatment.

How do abiotic environmental conditions influence shrimp susceptibility to disease? A critical analysis focussed on White Spot Disease

White Spot Syndrome Virus (WSSV) causes White Spot Disease (WSD) and is historically the most devastating disease in the shrimp industry. Global losses from this disease have previously exceeded $3 bn annually, having a major impact on a global industry worth US$19 bn per annum. Shrimp are cultured predominantly in enclosed ponds that are subject to considerable fluctuations in abiotic conditions and WSD outbreaks are increasingly linked to periods of extreme weather, which may cause major fluctuations in pond culture conditions. Combined with the intensity of production in these systems, the resulting suboptimal physicochemical conditions have a major bearing on the susceptibility of shrimp to infection and disease. Current knowledge indicates that pond temperature and salinity are major factors determining outbreak severity. WSSV appears to be most virulent in water temperatures between 25 and 28 °C and salinities far removed from the isoosmotic point of shrimp. Elevated temperatures (>30 °C) may protect against WSD, depending on the stage of infection, however the mechanisms mediating this effect have not been well established. Other factors relating to water quality that may play key roles in determining outbreak severity include dissolved oxygen concentration, nitrogenous compound concentration, partial pressure of carbon dioxide and pH, but data on their impacts on WSSV susceptibility in cultured shrimps is scarce. This illustrates a major research gap in our understanding of the influence of environmental conditions on disease. For example, it is not clear whether temperature manipulations can be used effectively to prevent or mitigate WSD in cultured shrimp. Therefore, developing our understanding of the impact of environmental conditions on shrimp susceptibility to WSSV may provide insight for WSD mitigation when, even after decades of research, there is no effective practical prophylaxis or treatment.

Molecular characterization of troponin C (TnC) in Scylla paramamosain and its role in white spot syndrome virus and Vibrio alginolyticus infection

Troponin C (TnC) is one member of the EF-hand superfamily. In many species, this gene had been identified and related functions had been elucidated. The TnC gene was still blank in the Scylla paramamosain. We obtained the TnC gene for the first time in the S. paramamosain. And we systematically analyzed the possible role of this gene in the innate immunity of S. paramamosain while infected with white spot syndrome virus (WSSV) or Vibrio alginolyticus. The full-length 1427 bp sequence of TnC contains a 453 bp open reading frame (ORF) for encoding a 151 amino acid protein. Detection of tissue specificity of gene expression showed that the TnC was primarily expressed in muscle tissue. The expression of TnC was successfully inhibited by RNA interference technology, and several immune genes were affected. The activity of phenoloxidase and superoxide dismutase increased, and the total hemocytes counts increased after RNAi of TnC. It was found that after infection with V. alginolyticus and WSSV, the expression of TnC in hemocytes decreased. Infected with V. alginolyticus and WSSV, the cumulative mortality and apoptotic rate of hemocytes increased after silencing the TnC gene. Our results indicate that TnC takes participate in the innate immunity of S. paramamosain and may plays a different role in the antiviral and antibacterial immune response.

Evaluation of a new Argovit as an antiviral agent included in feed to protect the shrimp Litopenaeus vannamei against White Spot Syndrome Virus infection

In this study, four experimental assays were conducted to evaluate the use of a new silver nanoparticle formulation named Argovit-4, which was prepared with slight modifications to enhance its biological activity against white spot syndrome virus (WSSV) in shrimp culture. The goals of these assays were to (1) determine the protective effect of Argovit-4 against WSSV, (2) determine whether Argovit-4 supplemented in feed exhibits toxicity towards shrimp, (3) determine whether Argovit-4 as antiviral additive in feed can prevent or delay/reduce WSSV-induced shrimp mortality, and (4) determine whether Argovit-4 supplemented in feed alters the early stages of the shrimp immune response. In bioassay 1, several viral inocula calibrated at 7 SID₅₀(shrimp infectious doses 50% endpoint) were exposed to 40, 100, 200 and 1,000 ng/SID₅₀ of Ag⁺ and then intramuscularly injected into shrimp for 96 h. In bioassay 2, shrimp were fed Argovit-4 supplemented in feed at different concentrations (10, 100 and 1,000 µg per gram of feed) for 192 h. In bioassay 3, shrimp were treated with Argovit-4 supplemented in feed at different concentrations and then challenged against WSSV for 192 h. In bioassay 4, quantitative real-time RT-qPCR was performed to measure the transcriptional responses of five immune-relevant genes in haemocytes of experimental shrimp treated with Argovit-4 supplemented in feed at 0, 6, 12, 24 and 48 h. The intramuscularly injected Argovit-4 showed a dose-dependent effect (p < 0.05) on the cumulative shrimp mortality from 0–96 h post-infection. In the second bioassay, shrimp fed Argovit-4 supplemented in feed did not show signs of toxicity for the assayed doses over the 192-h experiment. The third and fourth bioassays showed that shrimp challenged with WSSV at 1,000 µg/g feed exhibited reduced mortality without altering the expression of some immune system-related genes according to the observed level of transcriptional. This study is the first show that the new Argovit-4 formulation has potential as an antiviral additive in feed against WSSV and demonstrates a practical therapeutic strategy to control WSSV and possibly other invertebrate pathogens in shrimp aquaculture.

Apoptosis of hemocytes is associated with the infection process of white spot syndrome virus in Litopenaeus vannamei

Previous studies have demonstrated that white spot syndrome virus (WSSV) could induce hemocytes apoptosis in shrimps, however the inter-relationship between apoptotic process and the WSSV infection status is still currently underexplored. In the present work, the apoptosis and the viral proliferation in hemocytes of Litopenaeus vannamei were simultaneously investigated post WSSV infection by two-color immunofluorescence flow cytometry and real-time quantitative PCR. The apoptotic hemocytes of WSSV-infected shrimp was significantly increased at 12 h post infection (hpi), whereas underwent a slight decline at 24 hpi subsequently. Since 24 hpi, the apoptotic rate of hemocytes in the WSSV-infected shrimp exhibited a rapid and significant increase, and reached the peak level at 48 hpi with the ratio of 18.1 ± 2.0%. Meanwhile, the percentage of WSSV-infected hemocytes and WSSV copies in hemocytes significantly increased at 24 hpi and maintained at a high level afterwards. With the rapid increase of hemocytes apoptosis, hemocyte density in hemolymph decreased dramatically to less than 20% of the mean value of control. Co-localization assay showed that the apoptotic WSSV-infected hemocytes occupied the dominant proportion of total apoptotic hemocytes, which reached the peak at 48 hpi with 12.6 ± 1.5%. The expression profiles of seven pro-apoptotic genes and two apoptosis-inhibiting genes showed significant differential responses at different stages of WSSV infection, reflecting the interplay between the virus and the host immune response. Our results demonstrated that the apoptotic response of shrimp hemocytes could be significantly influenced by the WSSV infection process, which might provide an insight into deeper relationships between viral infection and apoptosis.

Caspase-3C gene from red swamp crayfish, Procambarus clarki: Characterization and expression in response to pathogenic infection

The caspase is an essential module in the Drosophila immune deficiency (IMD) pathway, which plays a crucial role in countering pathogen infection. In this study, a gene named PcCaspase-3C was found in Procambarus clarkia with a full-length of 4684 bp, including a 1572 bp opening reading frame, which encoded a putative protein of 523 amino acids. PcCaspase-3C contained a CASc domain constituted of 237 amino acids. The PcCaspase-3C gene was primarily expressed in heart, stomach, and intestine, while less in gonad, hepatopancreas, gills, and hemocytes, with the least expression in muscle. Infection with Staphyloccocus aureus, Vibrio parahaemolyticus or white spot syndrome virus (WSSV) induced an up-regulated expression of PcCaspase-3C in intestine or stomach to varying degrees. When PcCaspase-3C was silenced by double-stranded RNA, the expression of some antimicrobial peptides such as ALF2, ALF5, ALF6, Cru3, Cru4, and Lys was significantly inhibited. In addition, silencing of PcCaspase-3C accelerated infection with WSSV in vivo. According to these results, we suggest that PcCaspase-3C might play a crucial role in the immune response of P. clarkia against pathogenic bacterial and viral infections.

Survival and immune response of white shrimp Litopenaeus vannamei following single and concurrent infections with WSSV and Vibrio parahaemolyticus

The survival and immune responses of Litopenaeus vannamei were evaluated during white spot syndrome virus (WSSV) or Vibrio parahaemolyticus single and concurrent infections. The mortality, WSSV load, activities of 4 immune enzymes: acid phosphatase (ACP), alkaline phosphatase (AKP), peroxidase (POD) and superoxide dismutase (SOD), and the transcription of Evolutionarily Conserved Signaling Intermediate in Toll pathways of L.vannamei (LvECSIT) were quantified at 0, 3, 6, 12, 24, 48, 72 and 96 h post-infection (pi). The results showed: (i) the cumulative mortality of the co-infection group (WSSV and V. Parahaemolyticus 83%) was significantly lower than the WSSV infection group (97%) (P < 0.05) at 96 hpi; (ii) copies of WSSV in the co-infection group were significantly lower than that of the single infection group from 24 to 96 hpi (P < 0.05); (iii) ACP, AKP,POD and SOD activity in the gills of the co-infection group was higher than that of the WSSV group at12, 48 and 96 hpi (P < 0.05).The expression of LvECSIT mRNA in the co-infection group was significantly higher than in the WSSV infection group from 12 to 72 hpi (P < 0.05).The results indicate that proliferation of WSSV is inhibited by V.parahaemolyticus infection. In addition, infection with WSSV alone causes a significant reduction in some immune responses of shrimp than co-infection with WSSV and V.parahaemolyticus occurs at 26 °C. Third, LvECSIT, an essential member of TLR signaling pathway might play a crucial role in shrimp defense against WSSV - Vibrio co-infection.

The white spot syndrome virus hijacks the expression of the Penaeus vannamei Toll signaling pathway to evade host immunity and facilitate its replication

The white spot syndrome virus (WSSV), the most lethal pathogen of shrimp, is a dsDNA virus with approximately a 300,000 base pairs and contains approximately 180-500 predicted open reading frames (ORFs), of which only 6% show homology to any known protein from other viruses or organisms. Although most of its ORFs encode enzymes for nucleotide metabolism, DNA replication, and protein modification, the WSSV uses some of its encoded proteins successfully to take control of the metabolism of the host and avoid immune responses. The contribution of the shrimp innate immune response to prevent viral invasions is recognized but yet not fully understood. Thus, the role of several components of Toll pathway of the shrimp Penaeus vannamei against WSSV has been previously described, and the consequential effects occurring through the cascade remain unknown. In the current study the effects of WSSV over various components of the shrimp Toll pathway were studied. The gene expression of Spätzle, Toll, Tube, Cactus and Dorsal was altered after 6-12 h post inoculation. The expression of LvToll3, LvCactus, LvDorsal, decreased ~4.4-, ~3.7- and ~7.3-fold at 48, 24 and 48 hpi, respectively. Furthermore, a remarkable reduction (~18-fold) in the expression of the gene encoding LvCactus in WSSV infected specimens was observed at 6 hpi. This may be a sophisticated strategy exploited by WSSV to evade the Toll-mediated immune action, and to promote its replication, thereby contributing to viral fitness.

Global distribution of white spot syndrome virus genotypes determined using a novel genotyping assay

White spot disease, caused by infection with white spot syndrome virus (WSSV), is a serious panzootic affecting prawn aquaculture. The disease has spread rapidly around the prawn-culturing regions of the world through a number of previously identified mechanisms. The ability to distinguish and trace strains of WSSV is of great benefit to identify, and then limit, the translocation routes of the disease. Here, we describe a novel genotyping method using 34 short tandem repeat regions of the viral genome concurrently. This technique is highly sensitive to strain differences when compared to previous methods. The efficacy of the described method is demonstrated by testing WSSV isolates from around the globe, showing regional genotypic differences. The differences in the genotypes were used to create a global minimum spanning network, and in most cases the observed relationships were substantiated with verification of transboundary movement. This novel panel of STR markers will provide a valuable epidemiological tool for white spot disease. We have applied this to an outbreak of the disease in Queensland, Australia, that occurred in 2016. While the results indicate that the source of this outbreak currently remains cryptic, the analyses have provided valuable insights with which to further study the origins of the strains involved.

The crab Relish plays an important role in white spot syndrome virus and Vibrio alginolyticus infection

Relish is a transcription factor and forms an important part of the immune deficiency signaling pathway. In the current study, a Relish homolog was cloned from the hemolymph of Scylla paramamosain using RT-PCR and RACE. The full length cDNA of Relish consists of 4263 base pairs (bp), including a 3552 bp open reading frame encoding a 1184 amino acid protein. The data showed that Relish was highly expressed in the gonad and digestive organs of S. paramamosain. Furthermore, the expression of Relish was up-regulated by infection with white spot syndrome virus (WSSV) or Vibrio alginolyticus. When Relish was knocked down, immune genes such as Janus Kinase, signal transducer and activator of transcription, crustin antimicrobial peptide, prophenoloxidase, C-type-lectin and myosin-II-essential-light-chain-like-protein were significantly down-regulated (P < 0.01), and Toll-like receptor was significantly up-regulated (P < 0.01) in hemocytes. The mortality of WSSV-infected or V. alginolyticus-infected crabs was enhanced following Relish knockdown. Thus, Relish is very important in the progression of WSSV and V. alginolyticus infection. It was found that Relish knockdown caused the highest level of apoptosis in the disease-free group, and higher levels of apoptosis in the WSSV group and V. alginolyticus group compared with that in the control group. Knockdown of Relish influenced the activity of phenoloxidase (PO) and superoxide dismutase (SOD), and total hemocyte count (THC) following WSSV or V. alginolyticus infection, indicating that Relish plays a regulatory role in the immune response to WSSV or V. alginolyticus infection in crabs. Thus, we conclude that Relish may anticipate host defense mechanisms against pathogen infection by affecting apoptosis, THC, PO activity and SOD activity.

Silver nanoparticles enhance survival of white spot syndrome virus infected Penaeus vannamei shrimps by activation of its immunological system

The global aquaculture has shown an impressive growth in the last decades contributing with a major part of total food fish supply. However, it also helps in the spread of diseases that in turn, causes great economic losses. The White Spot Syndrome Virus (WSSV) is one of the major viral pathogen for the shrimp aquaculture industry. Several attempts to eliminate the virus in the shrimp have been addressed without achieving a long-term effectiveness. In this work, we determine the capacity of the commercial non-toxic PVP-coated silver nanoparticles to promote the response of the immune system of WSSV-infected shrimps with or without an excess of iron ions. Our results showed that a single dose of metallic silver in the nanomolar range (111 nmol/shrimp), which is equivalent to 12 ng/mL of silver nanoparticles, produces 20% survival of treated infected shrimps. The same concentration administered in healthy shrimps do not show histological evidence of damage. The observed survival rate could be associated with the increase of almost 2-fold of LGBP expression levels compared with non-treated infected shrimps. LGBP is a key gene of shrimp immunological response and its up-regulation is most probably induced by the recognition of silver nanoparticles coating by specific pathogen-associated molecular pattern recognition proteins (PAMPs) of shrimp. Increased LGBP expression levels was observed even with a 10-fold lower dose of silver nanoparticles (1.2 ng/shrimp, 0.011 nmol of metallic silver/shrimp). The increase in LGBP expression levels was also observed even in the presence of iron ion excess, a condition that favors virus proliferation. Those results showed that a single dose of a slight amount of silver nanoparticles were capable to enhance the response of shrimp immune system without toxic effects in healthy shrimps. This response could be enhanced by administration of other doses and might represent an important alternative for the treatment of a disease that has still no cure, white spot syndrome virus.

WSSV-host interaction: Host response and immune evasion

As invertebrates, shrimps rely on multiple innate defense reactions, including humoral immunity and cellular immunity to recognize and eliminate various invaders, such as viruses. White spot syndrome virus (WSSV) causes the most prevalent and devastating viral disease in penaeid shrimps, which are the most widely cultured species in the coastal waters worldwide. In the last couple of decades, studies about WSSV implicate a dual role of the immune system in protecting shrimps against the infection; these studies also explore on the pathogenesis of WSSV infection. Herein, we review our current knowledge of the innate immune responses of shrimps to WSSV, as well as the molecular mechanisms used by this virus to evade host immune responses or actively subvert them for its own benefit. Deciphering the interactions between WSSV and the shrimp host is paramount to understanding the mechanisms that regulate the balance between immune-mediated protection and pathogenesis during viral infection and to the development of a safe and effective WSSV defensive strategy.

A transcriptome study on Macrobrachium nipponense hepatopancreas experimentally challenged with white spot syndrome virus (WSSV)

White spot syndrome virus (WSSV) is one of the most devastating pathogens of cultured shrimp, responsible for massive loss of its commercial products worldwide. The oriental river prawn Macrobrachium nipponense is an economically important species that is widely farmed in China and adult prawns can be infected by WSSV. However, the molecular mechanisms of the host pathogen interaction remain unknown. There is an urgent need to learn the host pathogen interaction between M. nipponense and WSSV which will be able to offer a solution in controlling the spread of WSSV. Next Generation Sequencing (NGS) was used in this study to determin the transcriptome differences by the comparison of control and WSSV-challenged moribund samples, control and WSSV-challenged survived samples of hepatopancreas in M. nipponense. A total of 64,049 predicted unigenes were obtained and classified into 63 functional groups. Approximately, 4,311 differential expression genes were identified with 3,308 genes were up-regulated when comparing the survived samples with the control. In the comparison of moribund samples with control, 1,960 differential expression genes were identified with 764 genes were up-regulated. In the contrast of two comparison libraries, 300 mutual DEGs with 95 up-regulated genes and 205 down-regulated genes. All the DEGs were performed GO and KEGG analysis, overall a total of 85 immune-related genes were obtained and these gene were groups into 13 functions and 4 KEGG pathways, such as protease inhibitors, heat shock proteins, oxidative stress, pathogen recognition immune receptors, PI3K/AKT/mTOR pathway, MAPK signaling pathway and Ubiquitin Proteasome Pathway. Ten genes that valuable in immune responses against WSSV were selected from those DEGs to furture discuss the response of host to WSSV. Results from this study contribute to a better understanding of the immune response of M. nipponense to WSSV, provide information for identifying novel genes in the absence of genome of M. nipponense. Furthermore, large number of transcripts obtained from this study could provide a strong basis for future genomic research on M. nipponense.

Molecular characterization of shrimp harbinger transposase derived 1 (HARBI1)-like and its role in white spot syndrome virus and Vibrio alginolyticus infection

The role of the nuclease, HARBI1-like protein (mjHARBI1-like) in the innate immunity of Marsupenaeus japonicus was explored in this study. The 1361 bp cDNA sequence of mjHARBI1-like was cloned from M. japonicus using RACE. RT-qPCR analysis results showed that the gills and hepatopancreas of M. japonicus were the main tissues where mjHARBI1-like is expressed. In addition, it was also found that white spot syndrome virus (WSSV) or Vibrio alginolyticus challenge could stimulate mjHARBI1-like expression. After mjHARBI1-likewas inhibited, expression of immune genes such as toll, p53, myosin, and proPO were significantly downregulated (P < 0.01). However, in shrimp hemocytes, hemocyanin and tumor necrosis factor-α (TNF-α) were up-regulated significantly (P < 0.01). This study demonstrated that mjHARBI1-like plays a key role in the progression of WSSV and V. alginolyticus infection. Specifically, the cumulative mortality of WSSV-infected and V. alginolyticus-infected shrimp was significantly advanced by double-strand RNA interference (dsRNAi) of mjHARBI1-like. Apoptosis studies indicated that mjHARBI1-dsRNA treatment caused a reduction in hemocyte apoptosis in bacterial and viral groups. In addition, phagocytosis experiments illustrated that mjHARBI1-dsRNA treatment led to a lower phagocytosis rate in hemocytes of V. alginolyticus-challenged shrimp. It was also found that knockdown of mjHARBI1-like inhibited shrimp phenoloxidase (PO) activity, superoxide dismutase (SOD) activity, and total hemocyte count (THC) after WSSV or V. alginolyticus infection. These data indicate a regulative role of mjHARBI1-likein the immunity of shrimp in response to pathogen infection. Resultantly, it was concluded that mjHARBI1-like might have a positive effect on the anti-WSSV immune response of shrimp by regulating apoptosis, THC, PO activity, and SOD activity. Additionally, mjHARBI1-like might promote anti-V. alginolyticus infection by participating in regulating phagocytosis, apoptosis, SOD activity, PO activity, and THC.

Novel L-type lectin from fresh water prawn, Macrobrachium rosenbergii participates in antibacterial and antiviral immune responses

L-type lectins (LTLs) play important roles in the secretory pathway of animals, including selective protein trafficking, sorting, and targeting. They have a leguminous lectin domain and can bind to high-mannose-type oligosaccharides. In this study, a novel LTL, designated as MrVIP36, was identified from Macrobrachium rosenbergii. The full-length cDNA of MrVIP36 was 1687 bp with a 972 bp open reading frame encoding a putative protein of 323 deduced amino acids. The deduced MrVIP36 protein contained an LTL-like domain (LTLD) and a transmembrane domain. Phylogenetic tree analysis indicated that MrVIP36 was a member of invertebrate LTLs. It has a closer evolutionary distance with invertebrate LTLs than vertebrate LTLs. Quantitative real time polymerase chain reaction showed that MrVIP36 is expressed widely in all tested tissues, especially in the hepatopancreas and intestine. MrVIP36 was significantly up-regulated in hemocytes of prawns at different time points after Staphylococcus aureus, Vibrio parahaemolyticus, and White spot syndrome virus (WSSV) infections. The recombinant protein MrLTLD (rMrLTLD) could bind and agglutinate all tested bacteria. Sugar binding assay revealed that rMrLTLD could also bind to the glycoconjugates of the bacterial surface, such as lipopolysaccharide and peptidoglycan. Moreover, rMrLTLD could inhibit the growth activities of microorganisms in vitro and accelerate the bacterial clearance in vivo. rMrLTLD could also inhibit WSSV replication in vivo. Survival rate analysis showed that rMrLTLD could protect prawns against WSSV infection. Taken together, our results suggested that MrVIP36 functioned as a pattern recognition receptor involved in the antibacterial and antiviral immune responses of M. rosenbergii.

Transcriptome analysis of 'Huanghai No. 2' Fenneropenaeus chinensis response to WSSV using RNA-seq

White spot syndrome (WSS) is one of the most damaging phenomena in the culturing of shrimp. To characterize the mechanisms of the molecular responses to WSSV infection in 'Huanghai No. 2'' Fenneropenaeus chinensis, we used next-generation sequencing to observe the transcriptome after oral infection. A total of 108.6 million clean reads were obtained and assembled into 64,103 final unigenes with an average length of 845 bp (N50 = 1534 bp). The assembled unigenes contained 14,263 significant unigenes after BLASTX against the Nr database (E-value cut-off of 10^-5). After comparison of digital gene expression data between challenged and control shrimp, a total of 896 DEGs after WSSV infection were identified. Gene pathway analysis indicated that 92, 131 and 142 metabolic pathways were affected at early, peak and late phases respectively. Some pathways were related to the immune response, such as the phagosome, complement and coagulation cascades, the antigen processing and presentation pathway and so on. Many immune-related genes were also identified after pathway analysis. Interestingly, some growth-related genes, such as cathepsin L, myosin regulatory light chain 2 smooth muscle, and alpha-amylase were also differentially expressed after WSSV infection, and the correlation between growth trait and WSSV-resistance trait need further research. The expression patterns of eight DEGs were confirmed by quantitative real-time reverse transcription polymerase chain reaction, and there was good agreement between RNA-seq and qRT-PCR. These data will provide valuable information for characterizing the immune mechanism of the response of shrimp's to WSSV.

Shrimp humoral responses against pathogens: antimicrobial peptides and melanization

Diseases have caused tremendous economic losses and become the major problem threatening the sustainable development of shrimp aquaculture. The knowledge of host defense mechanisms against invading pathogens is essential for the implementation of efficient strategies to prevent disease outbreaks. Like other invertebrates, shrimp rely on the innate immune system to defend themselves against a range of microbes by recognizing and destroying them through cellular and humoral immune responses. Detection of microbial pathogens triggers the signal transduction pathways including the NF-κB signaling, Toll and Imd pathways, resulting in the activation of genes involved in host defense responses. In this review, we update the discovery of components of the Toll and Imd pathways in shrimp and their participation in the regulation of shrimp antimicrobial peptide (AMP) synthesis. We also focus on a recent progress on the two most powerful and the best-studied shrimp humoral responses: AMPs and melanization. Shrimp AMPs are mainly cationic peptides with sequence diversity which endues them the broad range of activities against microorganisms. Melanization, regulated by the prophenoloxidase activating cascade, also plays a crucial role in killing and sequestration of invading pathogens. The progress and emerging research on mechanisms and functional characterization of components of these two indispensable humoral responses in shrimp immunity are summarized and discussed. Interestingly, the pattern recognition protein (PRP) crosstalk is evidenced between the proPO activating cascade and the AMP synthesis pathways in shrimp, which enables the innate immune system to build up efficient immune responses.

Molecular cloning of Kuruma shrimp Marsupenaeus japonicus endonuclease-reverse transcriptase and its positive role in white spot syndrome virus and Vibrio alginolyticus infection

This study investigated the function of endonuclease-reverse transcriptase (mjERT) in Marsupenaeus japonicus. The 1129 bp cDNA sequence of mjERT was cloned from M. japonicus using rapid amplification of cDNA ends (RACE) PCR, and RT-qPCR analysis indicated that mjERT was highly expressed in the gills and hepatopancreas of M. japonicus. We also found that white spot syndrome virus (WSSV) or Vibrio alginolyticus challenge could enhance the expression of mjERT. When mjERT was inhibited, immune genes such as toll, p53, hemocyanin and tumor necrosis factor-α (TNF-α) were significantly down-regulated (P < .01) in the hemocytes of shrimp, while myosin was significantly up-regulated (P < .01). We demonstrated that mjERT is very important for the progression of WSSV infection and that the cumulative mortality of WSSV-infected and V. alginolyticus-infected shrimps was significantly increased following mjERT RNA interfere (RNAi). Apoptosis data provided information to suggest that mjERT-dsRNA challenge caused less apoptosis in hemocytes in both the disease-free and viral group. We also revealed that mjERT-dsRNA treatment resulted in a lower phagocytosis rate in the hemocytes of V. alginolyticus-challenged shrimp. Finally, we found that the absence of mjERT had an significantly negative impact upon shrimp phenoloxidase (PO) activity, superoxide dismutase (SOD) activity and total hemocyte count (THC) following WSSV or V. alginolyticus infection, indicating a regulative role for mjERT in the innate immunity of shrimp in response to pathogenic infection. In summary, we concluded that mjERT might promote the anti-WSSV immune response of shrimp by regulating apoptosis, PO activity, THC and SOD activity, and also exert a positive role in the immune response against V. alginolyticus by regulating phagocytosis, SOD activity, PO activity and THC.

Nonretroviral integrated RNA viruses in arthropod vectors: an occasional event or something more?

With few exceptions, all arthropod-borne viruses (arboviruses) are nonretroviral RNA viruses (NRVs). Despite NRVs do not encode reverse transcriptases and integrases, NRVs-DNA fragments are detected in mosquito cells and mosquitoes at early stages of infection as episomal DNA forms. Additionally, next generation sequencing and bioinformatics analyses have convincingly shown NRVs-vDNA integrated in vector genomes. We hypothesize vDNA role may be linked to host immunity and viral persistence. Key questions remain about nonretroviral integrated RNA virus sequences (NIRVS) in mosquitoes such as what is driving vDNA synthesis from NRVs, how does integration occur and what is their biological function. Here we review current knowledge about NIRVS highlighting connections with host immunity and virus-vector co-evolution and we suggest directions for future research.

Characterization and expression analysis of serpinB3, the first clade B serine protease inhibitor in Pacific white shrimp, Litopenaeus vannamei

Currently, about nine serpin clades (A-I) were preferentially observed in higher animals and clustered on the basis of function. Of these, eight clades contain extracellular proteins, while clade B contains predominantly intracellular proteins. In the present study, the first clade B serpin (named LvserpinB3) was identified from the Pacific white shrimp Litopenaeus vannamei. LvserpinB3 encoded a 412-amino acid protein with a 19-amino acid signal peptide and a serpin domain. Moreover, a transmembrane helix (TMHs) was predicted to be located on the N-terminal of LvserpinB3. Alignment with the cDNA sequence indicated that the genomic LvserpinB3 gene contains 2 exons and 1 intron. The P1-P1' scissile bond of the core feature reactive center loop (RCL) represented for Arginine-Isoleucine (RI), which was in accordance with PmserpinB3, Msserpin-4, -5 and -7. The highest mRNA expression level of LvserpinB3 was detected in hepatopancreas. A significant decrease of LvserpinB3 was detected in hepatopancreas at 6 h post Vibrio anguillarum injection, and later on, the expression of LvserpinB3 was remarkably elevated at 24 h post bacterial challenge. Suppression of LvserpinB3 in vivo by double-stranded RNA (dsRNA) mediated RNA interference (RNAi) led to a significant increase in the transcripts of LvSP1 (Serine protease 1), LvPPAE2 (Prophenoloxidase-activating Enzyme 2) and cumulative mortality. Furthermore, rLvserpinB3 protein was expressed and purified in vitro for the prophenoloxidase inhibition assay. The rLvserpinB3 protein can strongly impede the extent of proPO cascade. All above imply that LvserpinB3 might be an inhibitor for prophenoloxidase-activating system.

Potential of RNAi applications to control viral diseases of farmed shrimp

Viral pathogens pose a primary threat to global shrimp aquaculture. Despite the urgent industry need for them, practical anti-viral control methods are unavailable due, in part, to lack of an adaptive immune response in crustaceans that renders conventional vaccination methods ineffective. One currently studied method of high interest for protecting shrimp against viral infection relies on the post-transcriptional gene silencing mechanism called RNA interference (RNAi) that is induced by gene-specific constructs of double stranded RNA (dsRNA). Although this approach was first described for successful protection of shrimp against white spot disease (WSD) by injecting dsRNA specific to genes of white spot syndrome virus (WSSV) into shrimp in the laboratory in 2005 no practical method for use of dsRNA in shrimp farms has been developed to date. The apparent bottleneck for farm-scale applications of RNAi-mediated viral control in shrimp aquaculture is the lack of simple and cost-effective delivery methods. This review summarizes recent studies on use and delivery of dsRNA to shrimp via injection and oral routes in hatcheries and on farms and it discusses the research directions that might lead to development of practical methods for applications with farmed shrimp. Oral delivery methods tested so far include use of dsRNA-expressing bacteria as a component of dry feed pellets or use of living brine shrimp (Artemia) pre-fed with dsRNA before they are fed to shrimp. Also tested have been dsRNA enclosed in nanocontainers including chitosan, liposomes and viral-like particles (VLP) before direct injection or use as components of feed pellets for hatchery or pond-reared shrimp.

C-type lectin (MrCTL) from the giant freshwater prawn Macrobrachium rosenbergii participates in innate immunity

C-type lectins (CTLs) play important roles in the innate immunity of invertebrates. In this study, a novel CTL with a single carbohydrate recognition domain (CRD) containing an EPN (Glu-Pro-Asn) motif was identified from the giant freshwater prawn Macrobrachium rosenbergii. This CTL was designated as MrCTL. The cDNA of MrCTL is 1788 bp with a 657 bp open reading frame that encodes a protein of 218 amino acids. The cDNA and genome sequences of MrCTL show a polymorphism that leads to MrCTL isoforms. MrCTL was highly expressed in the gills and intestine of normal prawn, and its transcription increased after Vibrio parahaemolyticus or white spot syndrome virus (WSSV) challenge. Recombinant mature MrCTL and its single CRD could agglutinate (Ca²⁺-dependent) and bind both Gram-positive and Gram-negative bacteria. The recombinant proteins could attach to lipopolysaccharide and peptidoglycan in a dose-dependent manner. Recombinant MrCTL could accelerate bacterial clearance. Thus, MrCTL could serve as a pattern recognition receptor involved in the innate immunity of M. rosenbergii.

Dorsal transcription factor is involved in regulating expression of crustin genes during white spot syndrome virus infection

Nuclear factor-kappa B (NF-κB) pathways play important roles in innate immune responses. In this study, we identified a dorsal homolog (MrDorsal) from freshwater prawn Macrobrachium rosenbergii. The full-length cDNA of MrDorsal comprised 2533 bp with an open reading frame of 1986 bp, which encoded a peptide of 661 amino acid residues. Amino acid sequence analysis showed that MrDorsal contains a Rel homolog domain and an IPT/TIG (i.e., Ig-like, plexin, and transcription factors) domain. The signature sequence of dorsal protein FRYMCEG existed in the deduced amino acid sequence. Sequence analysis showed that MrDorsal shared high similarities with Dorsal from invertebrate species. MrDorsal was abundant in the hemocytes and gills of healthy prawns but minute levels were detected in other tissues. The expression of MrDorsal was significantly upregulated 48 h after the white spot syndrome virus (WSSV-) challenge. Knockdown of MrDorsal using double-stranded RNA could suppress the transcription of crustin genes (MrCrustin2 and MrCrustin4) in gills of prawns after 48 h of the WSSV challenge. Results indicated that MrDorsal was involved to regulate the expression of crustin genes and it might play potential important roles during WSSV infection.

The spread of Zika and the potential for global arbovirus syndemics

It is estimated that over a million people die each year from infectious diseases of zoonotic origin and hundreds of millions suffer from these pervasive threats to human well-being. In light of the emergent global concern over the Zika virus, evidence that it has not one but two competent mosquito vector species in the Aedes family, and that both can be co-infected with other pathogens including dengue and chikungunya, this paper examines research suggesting the prospect of significant twenty-first-century outbreaks of arbovirus syndemics. Uniting the concepts 'synergy' with 'epidemic', a syndemics approach recognises that diseases in a population occur neither independent of social and ecological conditions, nor in isolation from other diseases. Assessment of the potential for arbovirus syndemics entails a review of the human role in the global spread of Aedes mosquitoes, the socio-environmental conditions of Aedes diffusion, the increasing likelihood of co-transmission of arbovirus diseases, evidence of co-infection and concern about the adverse health effects of arbovirus syndemic interaction, and the need for an appropriate environment-sensitive framework for effective public health responses. Called Planetary Health, this emergent framework confronts conceptual, knowledge, and governance challenges created by the dramatic shifts in environments, climates, people, vectors, and pathogens in the world.

Minichromosome maintenance protein 7 regulates phagocytosis in kuruma shrimp Marsupenaeus japonicas against white spot syndrome virus

Minichromosome maintenance protein (MCM7) belongs to the MCM protein family and participates in the MCM complex by playing a role in the cell replication cycle and chromosome initiation of eukaryotes. Previously, we found that several genes, including MCM7, were over-expressed in Drosophila melanogaster after white spot syndrome virus (WSSV) infection. In this study, we aimed to further research the MCM7 of kuruma shrimp, Marsupenaeus japonicus (mjMCM7) and determine its role in the innate immune system. To this end, we cloned the entire 2307-bp mjMCM7 sequence, including a 1974-bp open reading frame (ORF) encoding a 658-aa-long protein. Real-time PCR showed that the gene was primarily expressed in the hemolymph and hepatopancreas and over-expressed in shrimp challenged with WSSV. Gene function study was carried out by knocking down the expression of MCM7 using small interference RNA (siRNA). The results revealed that β-actin, hemocyanin, prophenoloxidase (proPO) and tumor necrosis factor-α (TNF-α) were up-regulated while the cytoskeleton proteins such as myosin and Rho were significantly down-regulated at 24 h after treatment. The results indicate a possible relationship between mjMCM7 and the innate immune system, and suggest that mjMCM7 may play a role in phagocytosis. After WSSV challenge, WSSV copies and mortality count were both higher in the MCM7-siRNA-treated groups at 60 h after treatment, and the mortality count approached that of the control groups over time. The phagocytosis rate was significantly lower in the MCM7-siRNA-treated group than in the WSSV group. The findings of this study confirm that mjMCM7 positively regulates phagocytosis and plays an important role against WSSV. These results could help researchers to further understand the function of the MCM7 protein and reveal its potential role in the innate immunity of invertebrates.

Injected phage-displayed-VP28 vaccine reduces shrimp Litopenaeus vannamei mortality by white spot syndrome virus infection

White spot syndrome virus (WSSV) is the most important viral pathogen for the global shrimp industry causing mass mortalities with huge economic losses. Recombinant phages are capable of expressing foreign peptides on viral coat surface and act as antigenic peptide carriers bearing a phage-displayed vaccine. In this study, the full-length VP28 protein of WSSV, widely known as potential vaccine against infection in shrimp, was successfully cloned and expressed on M13 filamentous phage. The functionality and efficacy of this vaccine immunogen was demonstrated through immunoassay and in vivo challenge studies. In ELISA assay phage-displayed VP28 was bind to Litopenaeus vannamei immobilized hemocyte in contrast to wild-type M13 phage. Shrimps were injected with 2 × 10(10) cfu animal(-1) single dose of VP28-M13 and M13 once and 48 h later intramuscularly challenged with WSSV to test the efficacy of the vaccine against the infection. All dead challenged shrimps were PCR WSSV-positive. The accumulative mortality of the vaccinated and challenged shrimp groups was significantly lower (36.67%) than the unvaccinated group (66.67%). Individual phenoloxidase and superoxide dismutase activity was assayed on 8 and 48 h post-vaccination. No significant difference was found in those immunological parameters among groups at any sampled time evaluated. For the first time, phage display technology was used to express a recombinant vaccine for shrimp. The highest percentage of relative survival in vaccinated shrimp (RPS = 44.99%) suggest that the recombinant phage can be used successfully to display and deliver VP28 for farmed marine crustaceans.

Molecular cloning, characterization and expression analysis of Wnt4, Wnt5, Wnt6, Wnt7, Wnt10 and Wnt16 from Litopenaeus vannamei

The Wnt (Wg-type MMTV integration site) signaling represents as the negative regulator of virus-induced innate immune responses. Wnt genes act as ligands to activate the Wnt signaling. To know more about the information of Wnt genes in invertebrates, Litopenaeus vannamei Wnt genes (LvWnts) were identified and characterized. In this study, Six Wnt genes (LvWnt4, LvWnt5, LvWnt6, LvWnt7, LvWnt10 and LvWnt16) were obtained in L. vannamei. The complete cDNAs open reading frames (ORF) of LvWnt4, LvWnt5, LvWnt6, LvWnt7, LvWnt10 and LvWnt16 were 1077 bp, 1107 bp, 1350 bp, 1047 bp, 1509 bp and 1158 bp (GenBank accession no. KU169896, KU169897, KU169898, KU169899, KU169900 and KU169901), encoding 358, 368, 449, 348, 502 and 385 amino acid (aa) residues respectively. All the six members of LvWnts contain a Wnt1 domain, which is considered as an important feature of Wnt gene family. ClustalW analysis with amino acid sequences revealed that the proportion of identity with other species was more than 48% for all the LvWnts except LvWnt10 (36-41%). The phylogenetic relationship analysis illustrated that different subtype of Wnts formed their own separate branches and were placed in branch of invertebrates respectively with strong bootstrap support. The constitutive expressions of LvWnts were confirmed by RT-PCR in all the examined five developmental stages and eleven tissues of L. vannamei with different express patterns. LvWnt4, LvWnt5 and LvWnt10 were expressed highest in nerve while LvWnt6, LvWnt7 and LvWnt16 were expressed highest in intestine, stomach and gill, respectively. In addition, all the LvWnts were regulated by white spot syndrome virus (WSSV) challenges at different levels in hepatopancreas, gill and hemocytes, suggesting that Wnt genes may play a role in the defense against pathogenic virus infection in innate immune of L. vannamei.

Proteomic analysis by iTRAQ in red claw crayfish, Cherax quadricarinatus, hematopoietic tissue cells post white spot syndrome virus infection

To elucidate proteomic changes of Hpt cells from red claw crayfish, Cherax quadricarinatus, we have carried out isobaric tags for relative and absolute quantitation (iTRAQ) of cellular proteins at both early (1 hpi) and late stage (12 hpi) post white spot syndrome virus (WSSV) infection. Protein database search revealed 594 protein hits by Mascot, in which 17 and 30 proteins were present as differentially expressed proteins at early and late viral infection, respectively. Generally, these differentially expressed proteins include: 1) the metabolic process related proteins in glycolysis and glucogenesis, DNA replication, nucleotide/amino acid/fatty acid metabolism and protein biosynthesis; 2) the signal transduction related proteins like small GTPases, G-protein-alpha stimulatory subunit, proteins bearing PDZ- or 14-3-3-domains that help holding together and organize signaling complexes, casein kinase I and proteins of the MAP-kinase signal transduction pathway; 3) the immune defense related proteins such as α-2 macroglobulin, transglutaminase and trans-activation response RNA-binding protein 1. Taken together, these protein information shed new light on the host cellular response against WSSV infection in a crustacean cell culture.

Knockdown of Litopenaeus vannamei HtrA2, an up-regulated gene in response to WSSV infection, leading to delayed shrimp mortality

HtrA2 is an apoptosis-activating gene that enhances the apoptotic process by preventing the formation of the IAP-caspase complex, thereby freeing caspase to trigger the apoptosis pathway. In this study, we presented the full-length cDNA sequence of HtrA2 from Litopenaeus vannamei (LvHtrA2). The full-length LvHtrA2 was 1335 bp, encoding 444 amino acids. This deduced amino acid sequence contained five conserved domains: a mitochondrial targeting signal (MTS), a transmembrane (TM) domain, an IAP-binding motif (IBM), a trimerization motif, a serine protease domain, and a PDZ domain normally found in the HtrA2 proteins of other organisms. A phylogenetic analysis revealed that LvHtrA2 clustered with the HtrA2 from other invertebrates and was closely related to Penaeus monodon HtrA2 (PmHtrA2). RT-PCR with RNA extracts from L. vannamei revealed that LvHtrA2 expression was found in several tissues, including the lymphoid organs, the haemocytes, the hepatopancreas, the gill, and the stomach, with different expression levels. When determining the role of LvHtrA2 in WSSV infection, it was found that LvHtrA2 transcription was early up-regulated in the WSSV-infected shrimp at 8h post-infection (p.i.) and expression still remained high at 48 h p.i.. It also demonstrated that dsRNA specific to LvHtrA2 reduced the cumulative mortality in the WSSV-infected shrimp compared with the control group. Additionally, depletion of the LvHtrA2 transcripts reduced expression levels for caspase-3 (Cap-3) gene in shrimp. This result could suggest that LvHtrA2 may involved in apoptosis mediated mortality rather than providing immune protection during WSSV infection.

Microarray Analysis of Immunity Against WSSV in Response to Injection of Non-specific Long dsRNA in Kuruma Shrimp, Marsupenaeus japonicus

Injection of shrimp with non-specific double-stranded RNA (dsRNA) of diverse lengths, sequences, and base compositions is known to induce non-specific immunity and protect against lethal disease, although the mechanisms are unclear. Previous shrimp studies examined the effects of non-specific RNA on particular pathways, while their global effects have not been examined. To understand the global effects of non-specific RNA in shrimp, we injected kuruma shrimp (Marsupenaeus japonicus) with a dsRNA and a small interfering RNA (siRNA) that is not specific to any gene in the shrimp genome and then examined global gene expression at 24 and 48 h with a microarray. For the non-specific RNA, we chose double-stranded green fluorescent protein (dsGFP) and siGFP because they are commonly used as mock controls and their effects on shrimp have not yet been studied. Injection of PBS was used as a control. The microarray results showed that many genes were up-regulated and some were down-regulated by dsGFP. In addition, dsGFP injection increased survival following WSSV challenge. The changes in expression for several genes were confirmed by quantitative PCR. The up-regulated genes included genes for eight immune-related proteins: c-type lectin 2, hemocyte homeostasis-associated protein, viral responsive protein, fibrinogen-related protein 1, sid-1 like protein, argonaute 2, Dicer 2, and heat shock protein 90. These results show that injection of shrimp with non-specific dsRNA hinders viral accumulation and prevents significant mortalities.

Roles of small RNAs in the immune defense mechanisms of crustaceans

Small RNAs, 21-24 nucleotides in length, are non-coding RNAs found in most multicellular organisms, as well as in some viruses. There are three main types of small RNAs including microRNA (miRNA), small-interfering RNA (siRNA), and piwi-interacting RNA (piRNA). Small RNAs play key roles in the genetic regulation of eukaryotes; at least 50% of all eukaryote genes are the targets of small RNAs. In recent years, studies have shown that some unique small RNAs are involved in the immune response of crustaceans, leading to lower or higher immune responses to infections and diseases. SiRNAs could be used as therapy for virus infection. In this review, we provide an overview of the diverse roles of small RNAs in the immune defense mechanisms of crustaceans.

Future prospects for prophylactic immune stimulation in crustacean aquaculture - the need for improved metadata to address immune system complexity

Future expansion of the crustacean aquaculture industry will be required to ensure global food security. However, this expansion must ensure: (a) that natural resources (including habitat use and fish meal) are sustainably exploited, (b) that the socio-economic development of producing nations is safeguarded, and (c) that the challenge presented by crustacean diseases is adequately met. Conventionally, the problem of disease in crustacean aquaculture has been addressed through prophylactic administration of stimulants, additives or probiotics. However, these approaches have been questioned both experimentally and philosophically. In this review, we argue that real progress in the field of crustacean immune stimulants has now slowed, with only incremental advances now being made. We further contend that an overt focus on the immune effector response has been misguided. In light of the wealth of new data reporting immune system complexity, a more refined approach is necessary - one that must consider the important role played by pattern recognition proteins. In support of this more refined approach, there is now a much greater requirement for the reporting of essential metadata. We propose a broad series of recommendations regarding the 'Minimum Information required to support a Stimulant Assessment experiment' (MISA guidelines) to foster new progression within the field.

Cellular immune responses against viral pathogens in shrimp

Shrimp is one of the most important commercial marine species worldwide; however, viral diseases threaten the healthy development of shrimp aquaculture. In order to develop efficient control strategies against viral diseases, researchers have begun focusing increasing attention to the molecular mechanism of shrimp innate immunity. Although knowledge of shrimp humoral immunity has grown significantly in recent years, very little information is available about the cell-mediated immune responses. Several cellular processes such as phagocytosis, apoptosis, and RNA interference critical in cellular immune response play a significant role in endogenous antiviral activity in shrimp. In this review, we summarize the emerging research and highlight key mediators of cellular immune response to viral pathogens.