Characterization of a ras-related nuclear protein (Ran protein) up-regulated in shrimp antiviral immunity

Unveiling the biofloc culture potential: Harnessing immune functions for resilience of shrimp and resistance against AHPND -causing Vibrio parahaemolyticus infection

In shrimp aquaculture, disease mitigation may be accomplished by reducing the virulence of the pathogen or by boosting the shrimp's immunity. Biofloc technology is an innovative system that improves the health and resistance of shrimp to microbial infections while providing a viable option for maintaining the quality of culture water through efficient nutrient recycling. This review aimed at demonstrating the efficacy of the biofloc system in boosting the immune responses and protective processes of shrimp against Vibrio parahaemolyticus infection, which is known to cause Acute Hepatopancreatic Necrosis Disease (AHPND). Numerous studies have revealed that the biofloc system promotes the immunological capability of shrimp by raising multiple immune -related genes e.g. prophenoloxidase, serine proteinase gene, ras-related nuclear gene and penaeidinexpression and cellular and humoral responses such as hyperaemia, prophenoloxidase activity, superoxide dismutase activity, phagocytic activity; the protection and survival of shrimp when faced with a challenge from the V. parahaemolyticus strain have been enhanced. Furthermore, the use of the biofloc system improves water quality parameters and potentially bolstering their immune and overall health to effectively resist diseases; hence, promotes the growth of shrimp. The present review suggests that biofloc can serve as an effective therapy for both preventing and supporting the management of probable AHPND infection in shrimp culture. This approach exhibits potential for the progress of sustainable shrimp farming, higher productivity, and improved shrimp health.

A first annotated genome sequence for Haliotis midae with genomic insights into abalone evolution and traits of economic importance

Haliotis midae or "perlemoen" is one of five abalone species endemic to South Africa, and being palatable, the only commercially important abalone species with a high international demand. The higher demand for this abalone species has resulted in the decrease of natural stocks due to overexploitation by capture fisheries and poaching. Facilitating aquaculture production of H. midae should assist in minimising the pressure on the wild populations. Here, the draft genome of H. midae has been sequenced, assembled, and annotated. The draft assembly resulted in a total length of 1.5 Gb, contig N50 of 0.238 Mb, scaffold N50 of 0. 238 Mb and GC level of 40%. Gene annotation, combining ab initio and evidence-based pipelines identified 52,280 genes with protein coding potential. The genes identified were used to predict orthologous genes shared among the four other abalone species (H. laevigata, H. rubra, H. discus hannai and H. rufescens) and 4702 orthologous genes were shared across the five species. Among the orthologous genes in abalones, single copy genes were further analysed for signatures of selection and several molecular regulatory proteins involved in developmental functions were found to be under positive selection in specific abalone lineages. Furthermore, whole genome SNP-based phylogenomic assessment was performed to confirm the evolutionary relationship among the considered abalone species with draft genomes, reaffirming that H. midae is closely related to the Australian Greenlip (H. laevigata) and Blacklip (H. rubra). The study assists in the understanding of genes related to various biological systems underscoring the evolution and development of abalones, with potential applications for genetic improvement of commercial stocks.

The Innate Immune Response to Infection by Polyascus gregaria in the Male Chinese Mitten Crab (Eriocheir sinensis), Revealed by Proteomic Analysis

The Chinese mitten crab (Eriocheir sinensis) is a representative catadromous invertebrate of the Yangtze River and a commercial species widely cultivated in China. Both cultivated and wild crabs suffer from a variety of parasites and pathogens, which can result in catastrophic economic losses in aquaculture revenue. Polyascus gregaria, a parasitic barnacle with a highly derived morphology, is specialized in invading these crabs. This study examines the immunological mechanism in E. sinensis infected with P. gregaria. Tandem mass tags (TMT), a specialized method of mass-spectrometry, was used to analyze the infection by P. gregaria resistance at the protein level. In the hepatopancreas of infected crabs, 598 proteins differentially expressed relating to physiological change, of which, 352 were upregulated and 246 were downregulated. Based on this differential protein expression, 104 GO terms and 13 KEGG pathways were significantly enriched. Differentially expressed proteins, such as ATG, cathepsin, serpin, iron-related protein, Rab family, integrin, and lectin, are associated with the lysosome GO term and the autophagy-animal KEGG pathways, both of which likely relate to the immune response to the parasitic P. gregaria infection. These results show the benefit of taking a detailed, protein-level approach to understanding the innate immune response of aquatic invertebrates to macroparasite infection.

RNAi-based antiviral immunity of shrimp

As a kind of important economic marine crustaceans in aquaculture, shrimp can be infected by more than 20 viruses. To fight against the virus invasion, shrimp have developed the innate immunity, including RNA interference (RNAi). RNAi, mediated by short interfering RNAs (siRNAs) or microRNAs (miRNAs), plays important roles in virus-host interactions. At present, RNAi is considered to be an efficient antiviral response of shrimp. The siRNA-based RNAi, first recognized as an antiviral response of animals to resist RNA viruses, has emerged in animals as an efficient antiviral strategy against the invasion of DNA viruses and RNA viruses. In shrimp, as well as in other animals, siRNA contains a seed region (2nd-7th nt) and a supplementary region (12th-17th nt). Based on the findings in shrimp and other animals, miRNAs are essential regulators of virus-host interactions, such as virus infection/latency, and host apoptosis, autophagy and phagocytosis. Except for the seed sequence (2nd-7th), the complementary bases (to the target mRNA sequence) of a miRNA 9th-18th non-seed sequence are essential for the miRNA targeting. So far, rapidly growing evidences have supported the existence of functional RNAi machinery in shrimp. In this review, we summarize the progress of RNAi in the antiviral immune response of shrimp. The potential applications of RNAi to control shrimp diseases were also summarized.

The Arabidopsis small G-protein AtRAN1 is a positive regulator in chitin-induced stomatal closure and disease resistance

Chitin, a fungal microbial-associated molecular pattern, triggers various defence responses in several plant systems. Although it induces stomatal closure, the molecular mechanisms of its interactions with guard cell signalling pathways are unclear. Based on screening of public microarray data obtained from the ATH1 Affymetrix and Arabidopsis eFP browser, we isolated a cDNA encoding a Ras-related nuclear protein 1 AtRAN1. AtRAN1 expression was enriched in guard cells in a manner consistent with involvement in the control of the stomatal movement. AtRAN1 mutation impaired chitin-induced stomatal closure and accumulation of reactive oxygen species and nitric oxide in guard cells. In addition, Atran1 mutant plants exhibited compromised chitin-enhanced plant resistance to both bacterial and fungal pathogens due to changes in defence-related genes. Furthermore, Atran1 mutant plants were hypersensitive to drought stress compared to Col-0 plants, and had lower levels of stress-responsive genes. These data demonstrate a previously uncharacterized signalling role for AtRAN1, mediating chitin-induced signalling.

White spot syndrome virus infection activates Caspase 1-mediated cell death in crustacean

In vertebrates, pyroptosis is an intense inflammatory form of programmed cell death. This death pathway is critical for controlling pathogenic infection. In invertebrates, however, due to the lack of adaptive immune response, it is still elusive whether Caspase 1-dependent cell death pathway exists. In this study, our data showed that Caspase 1-mediated cell death was activated by white spot syndrome virus to counteract virus infection. Caspase 1 had a higher expression in hemocytes and lymphoid-like organ in shrimp and WSSV infection was promoted upon the inhibition of Caspase 1 enzymatic activity. IL-1β-like protein was identified as the substrate of Caspase 1 and its interaction with Caspase 1 was validated ectopically and endogenously. Moreover, IL-1β like protein was released into extracellular contents under WSSV infection and Prophenoloxidase system was activated, resulting in the reduction of WSSV. Our data unraveled a previously unidentified mechanism through which Caspase 1-dependent cell death controlled virus infection in shrimp.

Carbon: Nitrogen (C:N) ratio level variation influences microbial community of the system and growth as well as immunity of shrimp (Litopenaeus vannamei) in biofloc based culture system

Biofloc technology (BFT) is a novel modern aquaculture farming technique used to reduce toxic nitrogen concentration, act as in situ food source and eradicate pollutants using carbon and therefore to control C:N ratio in an aquaculture system. In this study, effect of different C:N ratios of a biofloc based system on water quality such as the level of Total ammonia nitrogen (TAN) nitrite-nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N) were explored. Further, the growth and immunity status of shrimp L. vannamei under the influence of different C:N ratios were evaluated. Two of the C:N ratios (15 and 20) could significantly (P < 0.05) reduce TAN, NO₂-N and NO₃-N levels (0.456 ± 0.01, 0.145 ± 0.09, and 0.102 ± 0.02 ppm) compared to control (1.45 ± 0.1, 0.749 ± 0.14 and 0.675 ± 0.16 ppm). Large variations in the frequency distribution of operational taxonomic units (OTUs) for the bacterial community in water with different C:N ration (BFT) and control were observed. Vibrios often considered as opportunistic pathogens, where the most dominant bacterial flora of water in control (79%) and C:N5 (37%) group. In C:N10, Thauera (62%) was most represented genus. Similarly, Attheyaceae (56%), followed by Peridiniaceae (30%) were the most dominant groups in C:N15 treatment. The diversity of bacterial flora was more spread in C:N20 treatments with Psychrobacter (26%), Proteobacteria (25%) and Peridiniaceae (20%) as the major groups. The trend of Vibrio dominance decreased with the increase in C:N ratios and thus confirming the dominance of heterotrophic bacteria in high C:N ratio groups. Upon challenge with pathogens, shrimps from C:N10, C:N15 and C:N20 groups showed significantly higher survival (P < 0.05) compared to the C:N5 and control group. Similarly, better growth rate was also observed in BFT tanks compared to control both during the culture and at harvest. Comparatively higher expression of four immune-related genes (ras-related nuclear gene (RAN), serine proteinase gene (SP), prophenoloxidase activating enzyme (PPAE), and crustin were observed in different C:N ratio ponds than control and these were in increasing trend with the C:N ratio. Gene expression analysis showed that the transcripts of those immune genes were significantly increased among all C:N treatments than that of control. Overall, these findings demonstrated that with optimum C:N ratio, BFT can be used to optimize the bacterial community composition for both optimal water quality and optimal shrimp health. This study thus indicates the possibility of obtaining better performance of L. vannamei culture with proper adjustment of C:N ratio in a biofloc based system.

Comparative proteomic analysis between two haemocyte subpopulations in shrimp Fenneropenaeus chinensis

In our previous work, granulocytes and hyalinocytes were successfully separated by immunomagnetic bead (IMB) method using monoclonal antibodies (mAbs) against granulocytes of shrimp (Fenneropenaeus chinensis). In order to elucidate the proteomic differentiation between granulocytes and hyalinocytes, in this paper, the differentially expressed proteins were analyzed between non-fixed/un-permeabilized (NFP) haemocytes and fixed/permeabilized (FP) haemocytes using two-dimensional gel electrophoresis (2-DE) combined with mass spectrometry (MS). Then the FP haemocytes were separated into two haemocyte subpopulations using IMB method, and the comparative proteome between granulocytes and hyalinocytes was investigated. The results showed that 10 differentially expressed protein spots were detected and identified as 4 proteins in the NFP haemocytes. Twenty one differentially expressed proteins were successfully identified between granulocytes and hyalinocytes, which include 4 unique expressed proteins in granulocytes, 4 significantly highly expressed proteins in granulocytes, and 13 significantly high expressed proteins in hyalinocytes. According to Gene Ontology annotation, the identified proteins between granulocytes and hyalinocytes were classified into six categories, including binding proteins, proteins involved in catalytic activity, enzyme regulator activity, structural molecule activity, translation regulator activity, and ungrouped proteins. Furthermore, quantitative PCR confirmed that the trend of transcription levels of three selected genes were consistent with the proteomic data from 2-DE. The results may lead to better understanding of the functions of haemocyte subpopulations.

Identification and function analysis of ras-related nuclear protein from Macrobrachium rosenbergii involved in Spiroplasma eriocheiris infection

A ras-related nuclear protein (Ran) protein was obtained from Macrobrachium rosenbergii, named MrRan. Phylogenetic analysis results showed that MrRan was clustered in one group together with other crustaceans. Tissue distribution analysis revealed that MrRan was expressed mainly in gill, intestine and stomach, and expressed weakly in muscle. The MrRan expression levels in gill and hemocyte of prawns were significantly up-regulated after challenged by Spiroplasma eriocheiris. The copy number of S. eriocheiris in MrRan dsRNA injection group was significantly less than control groups during infection. Meanwhile, silencing MrRan obviously increased the survival rate of prawns. The subcellular localization experiment suggested that recombinant MrRan was mainly located in the nucleus, and relatively weak in the cytoplasm. Finally, over-expression in Drosophila S2 cell indicated that MrRan could increase copies of S. eriocheiris and decrease of cell viability. The present study suggested that MrRan participated in regulating the phagocytosis of S. eriocheiris in M. rosenbergii.

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.

The identification of microRNAs involved in the response of Chinese shrimp Fenneropenaeus chinensis to white spot syndrome virus infection

MicroRNA (miRNA) is a class of small noncoding RNA, which is involved in the post-transcriptional regulation in all metazoan eukaryotes. MiRNAs might play an important role in the host response to virus infection. However, miRNAs in the aquatic crustacean species were not extensively investigated. To obtain a better understanding of the response of Chinese shrimp Fenneropenaeus chinensis to white spot syndrome virus (WSSV) infection, the sequence and expression profile of miRNAs in the hepatopancreas of WSSV-infected F. chinensis were obtained by the high-throughput Illumina HiSeq 2500 deep sequencing technique. A total number of 129 known miRNAs and 44 putative novel miRNAs were identified from the deep sequencing data. The peak size of miRNAs was 22 nt (37.0%). 25 miRNAs were significantly (P < 0.05) differentially expressed post WSSV infection. Six of the differentially expressed miRNAs were randomly selected for further verification by the real-time RT-PCR technique. The results showed that there was a consistency between the deep sequencing and real-time RT-PCR assay. The target genes of differentially expressed miRNAs were predicted. Each miRNA had 4 target genes on average. The results suggested that some specific miRNAs might be involved in the response of F. chinensis to WSSV infection, and further provided basic information for the investigation of specific miRNAs in F. chinensis.

Characterization of a Ran gene from Puccinia striiformis f. sp. tritici involved in fungal growth and anti-cell death

Ran, an important family of small GTP-binding proteins, has been shown to regulate a variety of important cellular processes in many eukaryotes. However, little is known about Ran function in pathogenic fungi. In this study, we report the identification and functional analysis of a Ran gene (designated PsRan) from Puccinia striiformis f. sp. tritici (Pst), an important fungal pathogen affecting wheat production worldwide. The PsRan protein contains all conserved domains of Ran GTPases and shares more than 70% identity with Ran proteins from other organisms, indicating that Ran proteins are conserved in different organisms. PsRan shows a low level of intra-species polymorphism and is localized to the nucleus. qRT-PCR analysis showed that transcript level of PsRan was induced in planta during Pst infection. Silencing of PsRan did not alter Pst virulence phenotype but impeded fungal growth of Pst. In addition, heterologous overexpression of PsRan in plant failed to induce cell death but suppressed cell death triggered by a mouse BAX gene or a Pst Ras gene. Our results suggest that PsRan is involved in the regulation of fungal growth and anti-cell death, which provides significant insight into Ran function in pathogenic fungi.

The Role of Cytokine PF4 in the Antiviral Immune Response of Shrimp

During viral infection in vertebrates, cytokines play important roles in the host defense against the virus. However, the function of cytokines in invertebrates has not been well characterized. In this study, shrimp cytokines involved in viral infection were screened using a cytokine antibody microarray. The results showed that three cytokines, the Fas receptor (Fas), platelet factor 4 (PF4) and interleukin-22 (IL-22), were significantly upregulated in the white spot syndrome virus (WSSV)-challenged shrimp, suggesting that these cytokines played positive regulatory roles in the immune response of shrimp against the virus. Further experiments revealed that PF4 had positive effects on the antiviral immunity of shrimp by enhancing the shrimp phagocytic activity and inhibiting the apoptotic activity of virus-infected hemocytes. Therefore, our study presented a novel mechanism of cytokines in the innate immunity of invertebrates.

Three members of Ras GTPase superfamily are response to white spot syndrome virus challenge in Marsupenaeus japonicus

Members of the Ras-like GTPase superfamily are key regulators of diverse cellular and developmental events, including differentiation, cell division, vesicle transport, nuclear assembly, and cytoskeleton control. In this study, three Ras family members (MjRap, MjRas, and MjRal) were cloned from Marsupenaeus japonicus. The full lengths of MjRap, MjRas, and MjRal are 788, 1330, and 2074 bp, which encode the proteins of 186, 202, and 198 amino acids respectively. Phylogenetic analysis showed that Rap, Ras, and Ral from different species gather together. The MjRap, MjRas, and MjRal genes were ubiquitously expressed in the hemocytes, hepatopancreas, gills, stomach, and muscle. Results from the quantitative real-time polymerase chain reaction (qRT-PCR) showed that MjRal in the gills was upregulated 48 and 72 h post-White spot syndrome virus (WSSV) challenge. No change in the MjRap or MjRas transcript was observed in the gills under the WSSV challenge. The RNAi of MjRal could enhance the WSSV replication. Injection of rMjRal protein could inhibit WSSV replication, but had no effect on VP28 expression. So, it could be concluded that MjRal was involved in shrimp anti-viral innate immune defense by inhibiting the WSSV replication.

Ran Involved in the Development and Reproduction Is a Potential Target for RNA-Interference-Based Pest Management in Nilaparvata lugens

Ran (RanGTPase) in insects participates in the 20-hydroxyecdysone signal transduction pathway in which downstream genes, FTZ-F1, Krüppel-homolog 1 (Kr-h1) and vitellogenin, are involved. A putative Ran gene (NlRan) was cloned from Nilaparvata lugens, a destructive phloem-feeding pest of rice. NlRan has the typical Ran primary structure features that are conserved in insects. NlRan showed higher mRNA abundance immediately after molting and peaked in newly emerged female adults. Among the examined tissues ovary had the highest transcript level, followed by fat body, midgut and integument, and legs. Three days after dsNlRan injection the NlRan mRNA abundance in the third-, fourth-, and fifth-instar nymphs was decreased by 94.3%, 98.4% and 97.0%, respectively. NlFTZ-F1 expression levels in treated third- and fourth-instar nymphs were reduced by 89.3% and 23.8%, respectively. In contrast, NlKr-h1 mRNA levels were up-regulated by 67.5 and 1.5 folds, respectively. NlRan knockdown significantly decreased the body weights, delayed development, and killed >85% of the nymphs at day seven. Two apparent phenotypic defects were observed: (1) Extended body form, and failed to molt; (2) The cuticle at the notum was split open but cannot completely shed off. The newly emerged female adults from dsNlRan injected fifth-instar nymphs showed lower levels of NlRan and vitellogenin, lower weight gain and honeydew excretion comparing with the blank control, and no offspring. Those results suggest that NlRan encodes a functional protein that was involved in development and reproduction. The study established proof of concept that NlRan could serve as a target for dsRNA-based pesticides for N. lugens control.

Growth performance and immunological and antioxidant status of Chinese shrimp, Fennerpenaeus chinensis reared in bio-floc culture system using probiotics

Chinese shrimp Fennerpenaeus chinensis (mean length 1.86 ± 0.15 cm, and weight 137.4 ± 12.7 mg) were reared in the different concentrations of bio-floc (control, 60, 80, 100, 120, and 140%) for 90 days. The growth rate was significantly increased over 100% bio-floc concentrations. In the immunological parameters, the gene expression of proPO and lysozyme was considerably increased over 120% bio-floc concentrations. The gene expression of SP was notably elevated at 140% bio-floc concentration. In the antioxidant enzymes, the activity of SOD was considerably decreased over 80% bio-floc concentrations. A notable decline in the activity of CAT was observed over 120% bio-floc concentrations. The results indicate that rearing of Chinese shrimp in bio-floc system can induce the increase of growth performance, enhancement of immune responses, and reduction of oxidative stress.

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.

Comparison of immune response of Pacific white shrimp, Litopenaeus vannamei, after multiple and single infections with WSSV and Vibrio anguillarum

Our previous study demonstrated that Pacific white shrimp (Litopenaeus vannamei) infected by multiple pathogens showed higher mortality and death occurred more quickly than those infected by a single pathogen (Jang et al., 2014). For better understanding the defense mechanism against white spot syndrome virus (WSSV) and Vibrio anguillarum, immune responses of shrimp were evaluated in this study. The mRNA expression levels of five immune-related genes were analyzed by quantitative reverse real-time PCR, which included proPO-activating enzyme 1 (PPAE1), PPAE2, proPO activating factor (PPAF), masquerade-like serine proteinase (Mas) and ras-related nuclear gene (Ran). Results demonstrated that the transcription was suppressed more intensively in the multiple infection group than those in single infection groups. The transcriptional suppression was directly related to the higher mortality. The hypoimmunity could benefit pathogen invasion, replication and release of toxin in vivo. Results in this study will help to understand immune defense mechanism after shrimp were infected by multiple pathogens in aquaculture.

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.

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.

Involvement of Ran in the regulation of phagocytosis against virus infection in S2 cells

Phagocytosis plays important roles in innate and adaptive immunity in animals. Some small G proteins are found to be related to phagocytosis. However, the Ran GTPase has not been intensively characterized in immunity. In this paper, the sequence analysis showed that the Ran was highly conserved in animals, suggesting that its function was preserved during animal evolution. The results showed that Ran was upregulated in S2 cells in response to DCV infection. It was further revealed that the antiviral phagocytosis could be mediated by Ran in S2 cells. By comparison with the early marker and late marker of phagosomes, the results showed that the Ran protein played an essential role at the early stage of phagocytosis or throughout the entire phagocytic process. Therefore our findings enlarged our limited knowledge about the phagocytosis regulation by small G proteins concerning to the nucleus.

RNA-Seq analysis reveals genes associated with resistance to Taura syndrome virus (TSV) in the Pacific white shrimp Litopenaeus vannamei

Outbreak of Taura syndrome virus (TSV) is one of the major pathogens of the Pacific white shrimp Litopenaeus vannamei. Although selective breeding for improvement of TSV resistance in L. vannamei has been successfully developed and has led to a great benefit to the shrimp farming industry worldwide. The molecular mechanisms underlying the viral resistance in shrimp remain largely unknown. In the present study, we conducted the first transcriptomic profiling of host responses in hemolymph and hemocytes in order to identify the differentially expressed genes associated with resistance to TSV in L. vannamei. High-throughput RNA-Seq was employed, obtaining 193.6 and 171.2 million high-quality Illumina reads from TSV-resistant and susceptible L. vannamei lines respectively. A total of 61,937 contigs were generated with an average length of 546.26 bp. BLASTX-based gene annotation (E-value < 10(-5)) allowed the identification of 12,398 unique proteins against the NCBI non-redundant NR database. In addition, comparison of digital gene expression between resistant and susceptible strains revealed 1374 significantly differentially expressed contigs (representing 697 unigenes). Gene pathway analysis of the differentially expressed gene set highlighted several putative genes involved in the immune response activity including (1) pathogen/antigen recognition including immune regulator, adhesive protein and signal transducer; (2) coagulation; (3) proPO pathway cascade; (4) antioxidation; and (5) protease. The expression patterns of 22 differentially expressed genes involving immune response were validated by quantitative real-time RT-PCR (average correlation coefficients 0.94, p-value < 0.001). Our results provide valuable information on gene functions associated with resistance to TSV in L. vannamei.

Probiotics as antiviral agents in shrimp aquaculture

Shrimp farming is an aquaculture business for the cultivation of marine shrimps or prawns for human consumption and is now considered as a major economic and food production sector as it is an increasingly important source of protein available for human consumption. Intensification of shrimp farming had led to the development of a number of diseases, which resulted in the excessive use of antimicrobial agents, which is finally responsible for many adverse effects. Currently, probiotics are chosen as the best alternatives to these antimicrobial agents and they act as natural immune enhancers, which provoke the disease resistance in shrimp farm. Viral diseases stand as the major constraint causing an enormous loss in the production in shrimp farms. Probiotics besides being beneficial bacteria also possess antiviral activity. Exploitation of these probiotics in treatment and prevention of viral diseases in shrimp aquaculture is a novel and efficient method. This review discusses the benefits of probiotics and their criteria for selection in shrimp aquaculture and their role in immune power enhancement towards viral diseases.

Recent advances in researches on the innate immunity of shrimp in China

The annual production of shrimp culture in mainland of China has been over one million tons for several years. The major cultivated penaeidae species are Litopenaeus vannamei, Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Due to the importance of shrimp aquaculture in China, researchers have paid more attention to the molecular mechanism of shrimp disease occurrence and tried to develop an efficient control strategy for disease. This paper summarizes the research progress related to innate immunity of penaeid shrimp made in the last decade in Mainland China. Several pattern recognition receptors, such as lectin, toll, lipopolysaccharide and β-1,3-glucan binding protein (LGBP) and tetraspanin were identified. The major signal transduction pathways, including Toll pathway, IMD pathway, which might be involved in the immune response of shrimp, were focused on and most of the components in Toll pathway were identified. Also, cellular immune responses such as phagocytosis and apoptosis were regarded playing very important roles in anti-WSSV infection to shrimp. The molecules involved in the maintenance of the immune homeostasis of shrimp and the progress on molecular structure and pathogenic mechanism of WSSV were summarized. Therefore, the brief outline about the immune system of shrimp is drawn based on the recent data which will help us to understand the immune responses of shrimp to different pathogens.

Characterization of myosin light chain gene up-regulated in the large yellow croaker immunity by interaction with RanGTPase

RanGTPases are highly conserved in eukaryotes from yeast to human and have been implicated in many aspects of nuclear structure and function. In our previous study, it was revealed that the RanGTPase was up-regulated in large yellow croaker challenged by pathogen. However, the mechanism of RanGTPase in immunity remains unclear. In this investigation, on the basis of protein interaction, it was found that RanGTPase interacted with myosin light chain (designated as LycMLC), a crucial protein in the process of phagocytosis. Furthermore, it was found and characterized in this marine fish for the first time. The full-length cDNA of LycMLC was 771bp, including a 5'-terminal untranslated region (UTR) of 36bp, 3'-terminal UTR of 279bp and an open reading frame (ORF) of 456bp encoding a polypeptide of 151 amino acids. RT-PCR analysis indicated that LycMLC gene was constitutively expressed in the 9 tissues examined, including kidney, liver, gill, muscle, spleen, skin, heart, intestine and blood. The result of quantitative real-time PCR analysis revealed the highest expression in muscle and the weakest expression in skin. Time course analysis showed that LycMLC expression was obviously up-regulated in blood after immunization with either poly I:C or formalin-inactive Gram-negative bacteria Vibrio parahaemolyticus. It indicated that the highest expression was 4.5 times (at 24h) as much as that in the control (P<0.05) challenged by poly I:C and 5.0 times (at 24h) challenged by bacteria. These results suggested that LycMLC might play an important role in large yellow croaker defense against the pathogen infection. Therefore our study revealed a novel pathway concerning immunity of RanGTPase by the direct interaction with the cytoskeleton protein, which would help to better understand the molecular events in immune response against pathogen infection in fish.

Molecular characterization of a Ran isoform gene up-regulated in shrimp immunity

Diseases caused by viruses are the greatest challenge to worldwide shrimp aquaculture. Ran gene was an important antiviral gene identified from shrimp and its mRNA level was up-regulated in response to viral infection. In this investigation, a Ran isoform gene (named Ran-iso) cDNA was cloned from shrimp, Marsupenaeus japonicus. The full-length cDNA of Ran-iso was 1286 bp, including a 5'-terminal untranslated region (UTR) of 272 bp, 3'-terminal UTR of 366 bp and an open reading frame (ORF) of 648 bp encoding a polypeptide of 215 amino acids. The deduced protein was highly homologous, it shared 90.64%, 84.19%, 81.48% and 67.58% identities with Ran protein of shrimp, honey bee, human and tobacco respectively. Ran-iso gene was constitutively expressed in 6 tissues examined, including gill, hepatopancreas, hemolymph, heart, intestine and muscle. However, Ran-iso was highest expressed in hepatopancreas (p<0.01), whereas the expressions of other five tissues were equal and relatively low. Time course analysis showed that the expression level of Ran-iso was obviously up-regulated 2.8 times (at 6h) as much as that in the control in the hepatopancreas challenged by WSSV. This investigation might provide a clue to elucidate the shrimp innate immunity and would be helpful to shrimp disease control.

Cloning and characterization of Rap GTPase from the Chinese white shrimp Fenneropenaeus chinensis

Ras-related protein Rap GTPase has been implicated in cell adhesion, cell proliferation, and cell junction formation. The first shrimp Rap cDNA (FcRap) was recently identified from the Chinese white shrimp Fenneropenaeus chinensis. The full length of FcRap is 1013 bp, with a 561 bp open reading frame that encodes a 186 amino acid protein. FcRap has a calculated molecular mass of 20.90 kDa and pI of 6.37. Phylogenetic analysis shows that FcRap and other Rap proteins are clustered into one group. Results from the quantitative real-time polymerase chain reaction show that FcRap could be detected mainly in the hemocytes, hepatopancreas, stomach, and gills, whereas a relatively lower expression level could be detected in the heart and intestines. FcRap in the hemocytes was upregulated 2h post Vibrio challenge, and it was upregulated 2h post white spot syndrome virus (WSSV) challenge, and peaked at 6h before it declined at 12h. No variation in the FcRap transcript was observed in the gills under the Vibrio challenge, but it was initially downregulated 2h post WSSV challenge, and then it was upregulated and peaked at 6h before it was eventually went down at 12h. The rFcRap protein was successfully expressed in Escherichia coli BL21DE3. The pull-down analysis showed that rFcRap protein could interact with VP28, an envelope protein of WSSV. The probable roles of Rap GTPase in shrimp innate immunity are presented for the first time.

Effects of immunostimulants targeting Ran GTPase on phagocytosis against virus infection in shrimp

The global shrimp aquaculture has been consistently beset by diseases that cause severe losses in production. To fight various harmful pathogens, the enhanced shrimp immunity by immunostimulants would play key roles against the invading pathogens. In aquaculture, however, the target proteins/genes which can be used for the screening of immunostimulants are very limited. Based on our previous study, in the present study, the shrimp Ran protein, which was required in shrimp antiviral phagocytosis, was used as the target protein to screen for immunostimulants. The GTPase activity assays showed that the IL-4 and lysophosphatidylcholine molecules could enhance the activity of Ran protein, suggesting that the two molecules might function in phagocytosis. When the IL-4 and lysophosphatidylcholine were respectively injected into shrimp, the results indicated that the two molecules enhanced the hemocytic phagocytosis against white spot syndrome virus (WSSV), suggesting that they improved the activity of phagocytosis through the activation of the Ran protein. It was evidenced that the enhancement of phagocytosis activity effectively inhibited the WSSV infection in shrimp, which further led to the decrease of mortalities of WSSV-infected shrimp. Therefore, our study presented a novel strategy for the screening of immunostimulants by using the key proteins in immune responses of aquatic organisms as the target proteins, which would be very helpful for the development of efficient approaches to prevent the aquatic organisms from pathogen infections.

Shrimp molecular responses to viral pathogens

From almost negligible amounts in 1970, the quantity of cultivated shrimp (~3 million metric tons in 2007) has risen to approach that of the capture fishery and it constitutes a vital source of export income for many countries. Despite this success, viral diseases along the way have caused billions of dollars of losses for shrimp farmers. Desire to reduce the losses to white spot syndrome virus in particular, has stimulated much research since 2000 on the shrimp response to viral pathogens at the molecular level. The objective of the work is to develop novel, practical methods for improved disease control. This review covers the background and limitations of the current work, baseline studies and studies on humoral responses, on binding between shrimp and viral structural proteins and on intracellular responses. It also includes discussion of several important phenomena (i.e., the quasi immune response, viral co-infections, viral sequences in the shrimp genome and persistent viral infections) for which little or no molecular information is currently available, but is much needed.

Molecular analysis of a ras-like nuclear (Ran) gene from Penaeus monodon and its expression at the different ovarian stages of development

In the present study, a ras-like nuclear (Ran) gene was obtained from the ovary and neurosecretory organ in eyestalk cDNA library of black tiger prawn (Penaeus monodon). The full-length black tiger prawn Ran (PmRan) cDNA consisted of 1140 nucleotides including an open reading frame (ORF) 648 bp, a 5' untranslated region (5'UTR) of 117 bp and a 3'UTR of 375 bp with a polyadenylation signal sequence "aataaa" and a poly (A) tail. The ORF encoded a peptide of 215 amino acids with molecular mass 24.6 kDa and a theoretical isoelectric point of 7.39. ScanProsite analysis indicated that PmRan protein sequence contained a small GTPase Ran family motif. Homology analysis of the deduced amino acid sequence of the PmRan with other known Ran sequences by MatGAT software revealed that the PmRan show very high homology with the sequences of other animals (92.1-98.6% similarity, 85.6-98.1% identity). Analysis of the tissue expression pattern of the PmRan gene showed that the PmRan mRNA was expressed in all tested tissues, including hepatopancreas, ovary, muscle, intestine, neurosecretory organ in eyestalk, neurosecretory organ in brain, stomach, and heart, with the highest levels in ovary. Furthermore, the PmRan expression was found to be high level in the six ovarian stages of development. The results indicated PmRan might play an important role in ovarian development.

Identification and expression localization of a Ran homologue in mollusc abalone, Haliotis diversicolor supertexta

Ran protein is a central molecular in several key nuclear functions, including nucleocytoplasmic transport, cell-cycle progression and nuclear envelope assembly. In this study, we have isolated and characterized a Ran homologue from a gastropod abalone which we named ab-Ran. The full-length cDNA consists of 1239 bp with an ORF encoding a 220 amino acid protein. The deduced amino acid sequence of ab-Ran shows highly similar to that of other Ran members (84-88%). Moreover, the ab-Ran contains five conserved regions and four carboxy-terminal residues CAAX-box. RT-PCR analysis showed that the ab-Ran was ubiquitously expressed in abalone tissues. The intracellular localization examined by immunofluorescence and immunohistochemistry staining displayed that ab-Ran was largely concentrated in the nuclei and partially in the cytoplasm. To the best of our knowledge, this is the first identification and characterization of a Ran homologue in mollusk.

Characterization of a RacGTPase up-regulated in the large yellow croaker Pseudosciaena crocea immunity

The Rac proteins are members of the Rho family of small G proteins and are implicated in the regulation of several pathways, including those leading to cytoskeleton reorganization, gene expression, cell proliferation, cell adhesion and cell migration and survival. In this investigation, a Rac gene (named as LycRac gene) was obtained from the large yellow croaker and it was expressed in Escherichia coli and purified. Subsequently the specific antibody was raised using the purified fusion protein (GST-LycRac). Moreover, the GTP-binding assay showed that the LycRac protein had GTP-binding activity. The LycRac gene was ubiquitously transcribed and expressed in 9 tissues. Quantitative real-time RT-PCR and Western blot analysis revealed the highest expression in gill and the weakest expression in spleen. Time-course analysis revealed that LycRac expression was obviously up-regulated in blood, spleen and liver after immunization with polyinosinic polycytidynic acid (poly I:C), formalin-inactive Gram-negative bacterium Vibrio parahemolyticus and bacterial lipopolysaccharides (LPS). These results suggested that LycRac protein might play an important role in the immune response against microorganisms in large yellow croaker.

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

Background

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

Results

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

Conclusions

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

Protection of blue shrimp (Litopenaeus stylirostris) against the White Spot Syndrome Virus (WSSV) when injected with shrimp lysozyme

In this study we found that a blue shrimp (Litopenaeus stylirostris) lysozyme gene (Lslzm) was up-regulated in WSSV-infected shrimp, suggesting that lysozyme is involved in the innate response of shrimp to this virus. Shrimp were intramuscularly injected with Lslzm protein to identify how this recombinant protein protects L. stylirostris from WSSV infection and to determine how this protein influences nonspecific cellular and humoral defense mechanisms. Higher survival rates and a lower viral load (compared with controls) were reported for shrimps that were first injected with the Lslzm protein and then infected with WSSV. In addition, the Lslzm expression level and the immunological parameters (including THC, phagocytic activity, respiratory burst activity, phenoloxidase activity and lysozyme activity) were all significantly higher in the WSSV-infected shrimp treated with the Lslzm protein, compared with the controls. These results indicate that lysozyme is effective at blocking WSSV infection in L. stylirostris and that lysozyme modulates the cellular and humoral defense mechanisms after they are suppressed by the WSSV virus.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.

Antiviral immunity in crustaceans

Viral diseases of shrimp have caused negative effects on the economy in several countries in Asia, South America and America, where they have numerous shrimp culture industries. The studies on the immunity of shrimp and other crustaceans have mainly focused on general aspects of immunity and as a consequence little is known about the antiviral responses in crustaceans. The aim of this review is to update recent knowledge of innate immunity against viral infections in crustaceans. Several antiviral molecules have been isolated and characterized recently from decapods. Characterization and identification of these molecules might provide a promising strategy for protection and treatment of these viral diseases. In addition dsRNA-induced antiviral immunity is also included.

Ran GTPase regulates hemocytic phagocytosis of shrimp by interaction with myosin

Ran GTPases, one family of small G protein superfamily, have been widely demonstrated to be involved in the transport system between cytoplasm and the nucleus. However, the function of Ran GTPase in immunity remains unclear. In our study, it was found that the Ran GTPase (designated as PjRan) was up-regulated in virus-resistant shrimp, indicating that the PjRan might be implicated in the innate immune system against virus infection. On the basis of protein interactions, it was found that the PjRan interacted with myosin, a crucial protein in the process of phagocytosis to form a protein complex. The RNAi and mRNA assays showed that the PjRan could regulate shrimp hemocytic phagocytosis. Further data evidenced that the depletion of PjRan by RNAi caused a significant increase of virus copies, and the overexpression of PjRan resulted in a significant decrease of virus copies, suggesting that the PjRan participated in the antiviral immunity by regulating phagocytosis. Therefore, our study revealed a completely novel aspect of Ran GTPase in phagocytosis by the direct interaction with the cytoskeleton protein and presented a novel pathway concerning to antiviral immunity, which will help to better understand the molecular events in immune response against virus infection in invertebrates.

Molecular cloning and analysis of function of nucleoside diphosphate kinase (NDPK) from the scallop Chlamys farreri

Nucleoside diphosphate kinase (NDPK) is a key metabolic enzyme that catalyzes the synthesis of non-adenine nucleoside triphosphate (NTP) by transferring the terminal phosphate between nucleoside diphosphate (NDP) and NTP. NDPK regulates a variety of eukaryotic cellular activities including cell proliferation, development, and differentiation. The ndpk cDNA was cloned from the hemocytes of the scallop Chlamys farreri and designated Cf-ndpk. The full-length sequence of Cf-ndpk consists of 715 bp encoding a polypeptide of 153 amino acids with a calculated molecular mass of 16927.52 daltons and pI of 7.64. The mRNA expression and distribution of Cf-ndpk in both bacterially challenged and unchallenged scallops were studied by Northern blotting and in situ hybridization. The results showed that Cf-ndpk transcripts were present in hemocytes, gill, adductor muscle, mantle, digestive gland, foot, and gonad, and the expression level increased in hemocytes after bacterial challenge. Recombinant Cf-NDPK expressed in Escherichia coli could transfer the terminal phosphate between UDP and ATP. The Cf-NDPK protein was present in all tested tissues including foot, adductor muscle, digestive gland, gonad, mantle, gill, and hemolymph. It was up-regulated in hemolymph after bacterial challenge. Taken together, these results suggest that NDPK may play roles in the innate immune response of scallop.