Signaling pathways regulating innate immune responses in shrimp

Characterization and function of GSK3β from Litopenaeus vannamei in WSSV infection

GSK3β, a serine/threonine protein kinase, is a crucial regulator in several signaling pathway and plays a vital role in multiple cellular processes including cell proliferation, growth, apoptosis and immune response. In this study, a GSK3β homolog from L. vannamei, designed as LvGSK3β, was characterized. Sequence analysis showed that LvGSK3β possessed a highly similarity with GSK3β from other species, which contained a catalytic domain and serine/threonine phosphorylation sites. To analyze the role of LvGSK3β in the process of white spot syndrome virus (WSSV) infection, real-time quantitative PCR and western blot assays were performed. The results showed that the transcription and expression levels of LvGSK3β were inhibited upon WSSV challenge, accompanied with down-regulated phosphorylation levels. When LvGSK3β was silenced, the transcription of WSSV gene ie1 was inhibited, and the apoptosis of hemocytes induced by WSSV was up-regulated remarkably as well. In addition, inactivation of LvGSK3β could also depress virus infection that further validated the results. Conclusively, LvGSK3β was an important protein for shrimp immunomodulation, and shrimp might promote the apoptosis to restrain WSSV infection by inhibition of LvGSK3β. The study will be helpful for understanding the molecular mechanism of host-virus interaction.

Transfection of crayfish hematopoietic tissue cells

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

Dietary yeast hydrolysate and brewer's yeast supplementation could enhance growth performance, innate immunity capacity and ammonia nitrogen stress resistance ability of Pacific white shrimp (Litopenaeus vannamei)

An 8-week feeding trial was conducted to evaluate the effects of dietary yeast hydrolysate and brewer's yeast supplementation on growth, immune-related genes expression and ammonia nitrogen stress resistance of Pacific white shrimp (Litopenaeus vannamei). Three isonitrogenous and isolipidic practical diets were formulated to contain 0% (control diet), 1% yeast hydrolysate and 1% brewer's yeast, respectively. 360 juvenile L. vannamei with an initial weight (0.88 ± 0.01 g) was randomly divided into 3 treatments in four replicates (30 shrimp per replicate). The results indicated that shrimp fed the diet containing 1% yeast hydrolysate had a significantly higher weight gain (WG), and specific growth rate (SGR) than that fed the control diet, and the lowest feed conversion ratio (FCR) was occurred in the 1% yeast hydrolysate supplementation group. Proximate composition in whole body and muscle among all treatments was not significantly influenced by the dietary yeast hydrolysate or brewer's yeast supplementation. The challenge test with ammonia nitrogen showed that lower cumulative survival was observed in those fed the control diet, and the highest cumulative survival was occurred at shrimp fed the 1% yeast hydrolysate supplementation. Shrimp fed the control diet had higher inflammation-related genes expression levels of tnf-α and il-1β in the intestine than those fed the diets supplemented with 1% yeast hydrolysate or 1% brewer's yeast, however, there was no significant difference in expression level of alp in intestine among all treatments. The relative expression levels of mTOR signal pathway genes (eif4ebp, eif4e1a, eif4e2 and p70s6k) were significantly up-regulated in the shrimp fed the diets supplemented with 1% yeast hydrolysate, and the lowest gene expression levels of eif4ebp, eif4e1a, eif4e2 and p70s6k in the intestine were occurred at the control diet. The highest expression levels of the immune-related genes (dorsal, relish, and proPO) in the intestine were observed at shrimp fed the 1% yeast hydrolysate supplementation, and the lowest expression levels of these genes were occurred at shrimp fed the control diet, however, there was no significant difference in gene expression of lysozyme among all treatments. The expression levels of penaeidin3a, crustin, proPO, and IMD in the hepatopancreas were significantly influenced by the dietary yeast hydrolysate, brewer's yeast or no yeast product supplementation, shrimp fed the 1% yeast hydrolysate supplementation had higher expression levels of these genes than those fed the control diet. The present study indicated that dietary 1% yeast hydrolysate or brewer's yeast supplementation could improve growth performance, enhance innate immunity, and strengthen resistance of ammonia nitrogen stress, and dietary 1% yeast hydrolysate supplementation provides better immunostimulatory effects than brewer's yeast of L. vannamei.

Functional domains of Litopenaeus vannamei transglutaminase and their involvement in immunoregulation in shrimp

Shrimps, which mainly rely on their innate immune system to response to infectious pathogens, have clottable proteins as an important component of this system. While transglutaminases (TGase) are found in Litopenaeus vannamei and constitute part of the coagulation system, the specific immune-related roles played by its functional domains in the immunoregulation of shrimp has not been well understood. In the present study, we report that the Ig-like domain of L. vannamei transglutaminase (TGase-C) is the main immune-related domain among the three functional domains, as it had higher bacterial agglutinative activity against Vibrio parahaemolyticus and Streptococcus iniae. Using Co-immunoprecipitation and LC-MS/MS analysis, TGase-C was shown to interact with 474 proteins, of which 52 proteins were annotated to L. vannamei. More than half of the L. vannamei annotated proteins have immune-related functions, including apoptosis. Further analysis using pull-down assay revealed that TGase-C interacted with CAP-3 (a homologue of caspase 3). In addition, siRNA-mediated knockdown of LvTGase significantly (p < 0.01) increased the expression level of LvCAP-3 coupled with a significant (p < 0.01) increase in caspase 3/7 activity, suggesting that probably LvTGase participates in shrimp immune response by modulating the activity of LvCAP-3. These findings thus suggest the Ig-like functional domain of L. vannamei's transglutaminase is the domain that is involved in immunoregulation in shrimp.

Identification and functional analysis of immune deficiency (IMD) from Scylla paramamosain: The first evidence of IMD signaling pathway involved in immune defense against bacterial infection in crab species

Immune deficiency (IMD) pathway, one of the most essential pattern recognition receptor signaling pathways, plays vital roles in innate immune responses to eliminate pathogen infection in invertebrates. In the present study, an immune deficiency (IMD) gene and two NF-κB family members, Relish and Dorsal, were identified and characterized in mud crab Scylla paramamosain for the first time. The deduced SpIMD, SpRelish and SpDorsal protein contained conserved death domain and classical NF-κB domains, respectively. Phylogenetic analysis suggested that SpIMD was classified into the invertebrate IMD branch, and SpRelish could be classified into the type I NF-κB class while SpDorsal could be grouped into the type II NF-κB class. Tissue distribution results showed these three genes were ubiquitously expressed in all tested tissues. The expression patterns of IMD signaling pathway and NF-κB genes, including SpIMD, SpIKKβ, SpIKKε, SpRelish and SpDorsal, were distinct when crabs were stimulated with Vibro alginolyticus, indicating that they might be involved in responding to bacterial infection. When SpIMD was silenced by in vivo RNA interference assay, the expression levels of IMD pathway and antimicrobial peptides (AMPs) genes, including SpIKKβ, SpRelish, SpALF1-6 and SpCrustin, were significantly down-regulated (p < 0.05). Correspondingly, the bacteria clearance ability of hemolymph was extremely impaired in IMD silenced crabs. Overall, the IMD played vital roles in innate immune response by regulating the expressions of its down-stream signaling genes and AMPs in S. paramamosain. These findings might pave the way for a better understanding of innate immune system and establish a fundamental network for the IMD signaling pathway in crustaceans.

A single C4 Zinc finger-containing protein from Litopenaeus vannamei involved in antibacterial responses

The Zinc finger domains (ZnFs), which contain finger-like protrusions stabilized by zinc ions and function to bind DNA, RNA, protein and lipid substrates, are ubiquitously present in a large number of proteins. In this study, a novel protein containing a single C4 type Znf domain (SZnf) was identified from Pacific white shrimp, Litopenaeus vannamei and its role in immunity was further investigated. The ZnF domain of SZnF but not other regions shared high homology with those of fushi tarazu-factor 1 (FTZ-F1) proteins. The SZnF protein was mainly localized in the cytoplasm and was also present in the nucleus at a small level. SZnF was high expressed in the scape and muscle tissues of healthy shrimp and its expression in gill and heptopancreas was strongly up-regulated during bacterial infection. Silencing of SZnf in vivo could strongly increase the susceptibility of shrimp to infection with Vibrio parahaemolyticus but not white spot syndrome virus (WSSV), suggesting that SZnf could be mainly involved in antibacterial responses. Both dual luciferase reporter assays and real-time PCR analysis demonstrated that SZnf could positively regulate the expression of various antimicrobial peptides in vitro and in vivo, which could be part of the mechanism underlying its antibacterial effects. In summary, the current study could help learn more about the function of ZnF-containing proteins and the regulatory mechanisms of immune responses against pathogen infection in crustaceans.

Oxidized fish oil injury stress in Megalobrama amblycephala: Evaluated by growth, intestinal physiology, and transcriptome-based PI3K-Akt/NF-κB/TCR inflammatory signaling

Lipids are essential nutrients for animal. Oxidized lipid might induce injury stress for fish. Here we conducted a 12-week rearing experiment with diets containing 0, 2, 4, and 6% oxidized fish oil (6F, 4F2OF, 2F4OF, and 6OF) to describe the oxidative impairment mechanism on teleost fish blunt snout bream, Megalobrama amblycephala. Results were evaluated by growth performance, intestinal physiology, and transcriptome-based PI3K-Akt/NF-κB/TCR inflammatory signaling. From the results, 6OF reduced growth performance with increased FCR and reduced FBW, WGR and SGR compare with 6 F. Meanwhile, oxidized fish oil treatments also increased antioxidant enzyme activity, suggesting an impaired physiological condition. The plasmatic antioxidant enzyme activity of T-SOD, GSH-Px, ASAFR, concentration of MDA and cortisol were significantly increased in 6OF, while GSH concentration was decreased. Histological ultrastructure revealed the integrity of mid-intestinal cells and villus were destroyed in 6OF. Moreover, transcriptomic analysis revealed PI3K-Akt/NF-κB/TCR inflammatory signaling were active to oxidized fish oil stress. We verified the expression of twelve key genes related to this signaling by RT-PCR, which revealed TLR2, PI3K, Akt, NF-κB, MHCII-β, TCR-α, TGF-β, TNF-α, IL-6, IL-1β, GPx1 and GSTm were all activated under 6OF stimulation. We found that oxidized fish oil may induce oxidative stress, destroy intestinal integrity, produce free radical, dysregulate lipid metabolism and oxidative balance, reversely affect the physiological adaptation, and eventually lead to growth inhibition. This study revealed the mechanism of PI3K-Akt/NF-κB/TCR inflammatory signaling in M. amblycephala under oxidized fish oil stress, which may help to understand the complex regulation involved in lipid oxidative stress resistance.

Transcriptional Identification of Related Proteins in the Immune System of the Crayfish Procambarus clarkii

The freshwater crayfish Procambarus clarkii is an animal model employed for physiological and immunological studies and is also of great economic importance in aquaculture. Although it is a species of easy husbandry, a high percentage of its production is lost annually as a result of infectious diseases. Currently, genetic information about the immune system of crustaceans is limited. Therefore, we used the abdominal nerve cord from P. clarkii to obtain its transcriptome using Next Generation Sequencing (NGS) to identify proteins that participate in the immune system. The reads were assembled de novo and consensus sequences with more than 3000 nucleotides were selected for analysis. The transcripts of the sequences of RNA were edited for annotation and sent to the GenBank database of the National Center for Biotechnology Information (NCBI). We made a list of accession numbers of the sequences which were organized by the putative role of the immune system pathway in which they participate. In this work, we report on 80 proteins identified from the transcriptome of crayfish related to the immune system, 74 of them being the first reported for P. clarkii. We hope that the knowledge of these sequences will contribute significantly to the development of future studies of the immune system in crustaceans.

Identification of the thioredoxin-related protein of 14 kDa (TRP14) from Litopenaeus vannamei and its role in immunity

The thioredoxin system plays essential roles in maintenance and regulation of the redox state of cysteine residues in cellular proteins. The thioredoxin-related protein of 14 kDa (TRP14) is an important member of the TRX superfamily which acts on various substrate proteins, some of which are not overlapped with those of thioredoxin. The knowledge on the function of TRP14 in invertebrates is limited to date. In this study, a TRP14 gene was identified from Pacific white shrimp Litopenaeus vannamei (LvTRP14) and its role in immune responses was investigated. We demonstrated that the expression level of LvTRP14 was high in hepatopancreas and intestine, low in eyestalk, and medium in other tissues of healthy shrimp. The transcription of LvTRP14 in vivo was significantly down-regulated in Relish-silencing shrimp but up-regulated in STAT-silencing shrimp, indicating a complex regulation of LvTRP14 expression. Although the LvTRP14 expression showed little change after immune stimulation with different type of pathogens, knockdown of LvTRP14 expression using RNAi strategy could significantly facilitate the infection of white spot syndrome virus (WSSV) and Vibrio parahaemolyticus in shrimp. Dual luciferase reporter assays demonstrated that LvTRP14 enhanced the transcription factor activity of Relish but attenuated that of Dorsal. Furthermore, silencing of LvTRP14 in vivo had opposite effects on expression of different type of antimicrobial peptides. These suggested that LvTRP14 could play a complex role in shrimp immunity.

A chitinase from pacific white shrimp Litopenaeus vannamei involved in immune regulation

Chitinases are a group of hydrolytic enzymes that hydrolyze chitin and widely exist in organisms. Studies in mammals have demonstrated that chitinases play important roles in regulation of humoral and cellular immune responses. In arthropods, although it is well known that chitinases are involved in growth, molting and development, the current knowledge on the role of chitinases in immunity, especially in immune regulation, remains largely unknown. In this study, a chitinase (LvChi5) from Litopenaeus vannamei was representatively selected for studying its immune function. The start codon of LvChi5 was corrected by 5'RACE analysis and its protein sequence was reanalyzed. LvChi5 contains a catalytic domain and a chitin binding domain and shows no inhibitory effect on growth of bacteria in vitro. However, in vivo experiments demonstrated that silencing of LvChi5 increased the mortality of shrimp infected with white spot syndrome virus (WSSV) and Vibro parahaemolyticus and significantly upregulated the load of pathogens in tissues. The expression of various immune related genes, including transcription factors, antimicrobial peptides and other functional proteins with antibacterial and antiviral activities, was widely changed in LvChi5 silencing shrimp. Moreover, the recombinant LvChi5 protein could enhance the phagocytic activity of hemocytes against bacteria. These suggested that shrimp chitinase could play a role in regulation of both humoral and cellular immune responses in shrimp.

Epigallocatechin-3-gallate protects Kuruma shrimp Marsupeneaus japonicus from white spot syndrome virus and Vibrio alginolyticus

Epigallocatechin-3-gallate (EGCG) is the most abundant catechin in green tea and exhibits potential antibacterial and anticancer activities. In this study, EGCG was used in pathogen-challenge experiments in shrimp to discover its effect on the innate immune system of an invertebrate. Kuruma shrimp Marsupeneaus japonicus was used as an experimental model and challenged with white spot syndrome virus (WSSV) and the Gram-negative bacterium Vibrio alginolyticus. Pathogen-challenge experiments showed that EGCG pretreatment significantly delayed and reduced mortality upon WSSV and V. alginolyticus infection, with VP-28 copies of WSSV also reduced. Quantitative reverse transcription polymerase chain reaction revealed the positive influence of EGCG on several innate immune-related genes, including IMD, proPO, QM, myosin, Rho, Rab7, p53, TNF-alpha, MAPK, and NOS, and we observed positive influences on three immune parameters, including total hemocyte count and phenoloxidase and superoxide dismutase activities, by EGCG treatment. Additionally, results showed that EGCG treatment significantly reduced apoptosis upon V. alginolyticus challenge. These results indicated the positive role of EGCG in the shrimp innate immune system as an enhancer of immune parameters and an inhibitor of apoptosis, thereby delaying and reducing mortality upon pathogen challenge. Our findings provide insight into potential therapeutic or preventive functions associated with EGCG to enhance shrimp immunity and protect shrimp from pathogen infection.

Identification and functional analysis of inhibitor of NF-κB kinase (IKK) from Scylla paramamosain: The first evidence of three IKKs in crab species and their expression profiles under biotic and abiotic stresses

IKK (inhibitor of NF-κB kinase) is the critical regulator for NF-κB (nuclear factor-κB) pathway against pathogenic invasion in vertebrates or invertebrates. However, the IKK from crab species has not yet been identified. In the present study, three full-length cDNA sequences of IKKs from mud crab Scylla paramamosain, designated as SpIKKβ, SpIKKε1 and SpIKKε2, were firstly cloned through RT-PCR and RACE methods. This is also the first report about the identification of two IKKε genes in mud crab and even in crustaceans. The SpIKKβ cDNA was 2824 bp in length with an open reading frame (ORF) of 2382 bp, which encoded a putative protein of 793 amino acids (aa). The ORF of two SpIKKε isoforms, SpIKKε1 and SpIKKε2, were 2400 bp and 2331 bp in length encoding 799 aa and 776 aa, respectively. The crucial conserved residues and functional domains, including the kinase domains (KDs) and leucine zipper (LZ), were identified in all SpIKKs. Phylogenetic analysis suggested that SpIKKβ was classified into the IKKs class while SpIKKεs could be grouped into the IKK-related kinases class. The qRT-PCR analysis showed that three SpIKKs were constitutively expressed in all tested tissues and the highest expression levels of SpIKKβ and SpIKKεs were all in hemocyte. The gene expression profiles of SpIKKs were distinct when crabs suffered biotic and abiotic stresses including the exposures of Vibrio alginolyticus, poly (I:C), cadmium and air exposure, suggesting that the SpIKKs might play different roles in response to pathogens infections, heavy metal and air exposure. Moreover, IKKs from mud crab can significantly activate mammalian NF-κB pathway, suggesting the function of IKKs might be evolutionally well-conserved. Results of the RNAi experiments suggested that SpIKKs might regulate the immune signaling pathway when hemocytes were challenged with V. parahemolyticus or virus-analog poly (I:C). All of these results indicated that the obtained SpIKKs might be involved in stress responses against biotic or abiotic stresses, and it also highlighted their functional conservation in the innate immune system from crustaceans to mammals.

Transcriptome analysis of Pacific white shrimp (Litopenaeus vannamei) challenged by Vibrio parahaemolyticus reveals unique immune-related genes

Pacific white shrimp (Litopenaeus vannamei) is an important cultural species worldwide. However, Vibrio spp. infections have caused a great economic loss in Pacific white shrimp culture industry. The immune responses of Pacific white shrimp to the Vibrio spp. is not fully characterized. In this study, the transcriptomic profiles of L. vannamei hemocytes were explored by injecting with or without Vibrio parahaemolyticus. Totally, 42,632 high-quality unigenes were obtained from RNAseq data. Comparative genome analysis showed 2258 differentially expressed genes (DEGs) following the Vibrio challenge, including 1017 up-regulated and 1241 down-regulated genes. Eight DEGs were randomly selected for further validation by quantitative real-time RT-PCR (qRT-PCR) and the results showed that are consistent with the RNA-seq data. Due to the lack of predictable adaptive immunity, shrimps rely on an innate immune system to defend themselves against invading microbes by recognizing and clearing them through humoral and cellular immune responses. Here we focused our studies on the humoral immunity, five genes (SR, MNK, CTL3, GILT, and ALFP) were selected from the transcriptomic data, which were significantly up-regulated by V. parahaemolyticus infection. These genes were widely expressed in six different tissues and were up-regulated by both Gram negative bacteria (V. parahaemolyticus) and Gram positive bacteria (Staphylococcus aureus). To further extend our studies, we knock-down those five genes by dsRNA in L. vannamei and analyzed the functions of specific genes against V. parahaemolyticus and S. aureus by bacterial clearance analysis. We found that the ability of L. vannamei was significantly reduced in bacterial clearance when treated with those specific dsRNA. These results indicate that those five genes play essential roles in antibacterial immunity and have its specific functions against different types of pathogens. The obtained data will shed a new light on the immunity of L. vannamei and pave a new way for fighting against the bacterial infection in Pacific white shrimp.

The Rho signalling pathway mediates the pathogenicity of AHPND-causing V. parahaemolyticus in shrimp

An emerging bacterial disease, acute hepatopancreatic necrosis disease (AHPND), is caused by strains of Vibrio parahaemolyticus with an additional AHPND-associated plasmid pVA1 encoding a virulent toxin (Pir^vp ) that damages the shrimp's hepatopancreas. Like other species of Vibrio, these virulent strains initially colonise the shrimp's stomach, but it is not yet understood how the bacteria or toxins are subsequently able to cross the epithelial barrier and reach the hepatopancreas. Here, by using transcriptomics and system biology methods, we investigate AHPND-induced changes in the stomach of AHPND-causing V. parahaemolyticus (5HP)-infected shrimp and identify host molecular mechanisms that might explain how the integrity of the stomach barrier is compromised. We found that the expression of 376 unique genes was differentially regulated by AHPND infection. Gene ontology, protein interaction, and gene-to-gene correlation expression interaction analyses indicated that in addition to the immune system, a number of these genes were involved in cytoskeleton regulation by Rho GTPase. The involvement of Rho pathway regulation during AHPND pathogenesis was further supported by experiments showing that while Rho inhibitor pretreatment delayed the infection, pretreatment with Rho activator enhanced the pathogenicity of 5HP, and both the bacteria and toxin were detected sooner in the hepatopancreas. Further, disruption of the stomach epithelial structure was found in both Rho preactivated shrimp and in 5HP-infected shrimp. Taken together, we interpret our results to mean that Rho signalling helps to mediate AHPND pathogenesis in shrimp.

Shrimp hemocyte homeostasis-associated protein (PmHHAP) interacts with WSSV134 to control apoptosis in white spot syndrome virus infection

Hemocyte homeostasis-associated protein (PmHHAP) was first identified as a viral-responsive gene, due to a high upregulation in transcription following white spot syndrome virus (WSSV) infection. Functional studies using RNA interference have suggested that PmHHAP is involved in hemocyte homeostasis by controlling apoptosis during WSSV infection. In this study, the role of PmHHAP in host-viral interactions was further investigated. Yeast two-hybrid assay and co-immunoprecipitation revealed that PmHHAP binds to an anti-apoptosis protein, WSSV134. The viral protein WSSV134 is a late protein of WSSV, expressed 24 h post infection (hpi). Gene silencing of WSSV134 in WSSV-infected shrimp resulted in a reduction of the expression level of the viral replication marker genes VP28, wsv477, and ie-1, which suggests that WSSV134 is likely involved in viral propagation. However, co-silencing of PmHHAP and WSSV134 counteracted the effects on WSSV infection, which implies the importance of the host-pathogen interaction between PmHHAP and WSSV134 in WSSV infection. In addition, caspase 3/7 activity was noticeably induced in the PmHHAP and WSSV134 co-silenced shrimp upon WSSV infection. Moreover, PmHHAP and WSSV134 inhibited caspase-induced activation of PmCasp in vitro in a non-competitive manner. Taken together, these results suggest that PmHHAP and WSSV134 play a role in the host-pathogen interaction and work concordantly to control apoptosis in WSSV infection.

Effects of dietary inulin and mannan oligosaccharide on immune related genes expression and disease resistance of Pacific white shrimp, Litopenaeus vannamei

The effects of inulin and mannan oligosaccharide (MOS) at different doses (2.5, 4 and 10 mg/g) in singular or combined diet on growth rate, immune related genes expression, and resistance to white spot syndrome virus (WSSV) and Vibrio alginolyticus in Pacific white shrimp (Litopenaeus vannamei) were investigated. At the end of 28-day singular feeding experiment, the highest values of specific growth rate (SGR) and the expression of toll-like receptor1, 2 and 3 (TLR1, 2, 3), signal transducer and activator of transcription (STAT), crustin, anti-lipopolysaccharide factor (ALF) as well as prophenoloxidase (proPO) were observed in shrimp individually fed with 5 mg/g dietary inulin or MOS, respectively. Compared with individual treatments, diet containing combined prebiotics (5 mg/g inulin and MOS) significantly improved the expression of TLRs, STAT, proPO, crustin and ALF in L. vannamei after four-week feeding. Additionally, Pacific white shrimp fed with combined dietary prebiotics showed significantly higher expression of immune related genes and lower cumulative mortality in WSSV and Vibrio alginolyticus challenges, compared to the singular feeding groups and control. These results in the present study demonstrated that the combined supplementation of inulin (5 mg/g) and MOS (5 mg/g) remarkably enhanced innate immune response and pathogen resistance of shrimp, and should be considered as a promising immunostimulatory additive for the culture of Pacific white shrimp.

Enzymatic characterization and functional analysis of EcChi3C from ridgetail white prawn Exopalaemon carinicauda

Chitinase belongs to the glycosyl hydrolases family 18 and plays key role in the development and pathogen resistance of crustaceans. In this study, the enzymatic characterization of chitinase 3C (EcChi3C) of Exopalaemon carinicauda was analyzed. In addition, we analyzed the expression profiles of EcChi3C at different tissues and different molting stages. In the all tested tissues, it was predominantly expressed in hepatopancreas, and then stomach, but poor in other tissues. In all tested molting periods, it was mainly expressed in intermolt and molting stages, but poor in other stages. The results of molting, mortality and the uropod ultrastructure of prawns after being injected with EcChi3C dsRNA were in accordance with those of the control group. In addition, there is no difference for endopodite morphology between the survival and dead individuals in experimental group. After being challenged with bacteria, the expression of EcChi3C was up-regulated significantly at 12 h and followed with a comeback at 96 h. These results suggest that EcChi3C is an important immune related gene but not a necessary gene in the molting process of E. carinicauda.

Mechanisms for type-II vitellogenesis-inhibiting hormone suppression of vitellogenin transcription in shrimp hepatopancreas: Crosstalk of GC/cGMP pathway with different MAPK-dependent cascades

Vitellogenesis is the process of yolk formation via accumulating vitellin (Vn) with nutrients in the oocytes. Expression of vitellogenin (Vg), the precursor of Vn, is one of the indicators for the start of vitellogenesis. In Pacific white shrimp (Litopenaeus vannamei), the type-II vitellogenesis-inhibiting hormone (VIH-2) effectively suppresses hepatopancreatic Vg mRNA expression. In this study, we demonstrate the increasing transcript levels of hepatopancreatic Vg during L. vannamei ovarian development, suggesting that the hepatopancreas-derived Vg/Vn may also contribute to vitellogenesis in this species. Using a combination of in vivo injections and in vitro primary cell cultures, we provide evidences that the inhibition of VIH-2 on hepatopancreatic Vg gene expression is mediated through a functional coupling of the GC/cGMP pathway with different MAPK-dependent cascades in female shrimp. In VIH-2 signaling, the NO-independent GC/cGMP/PKG cascades were upstream of the MAPKs. Activations of the MAPK signal by VIH-2 include the phosphorylation of JNK and the mRNA/protein expression of P³⁸MAPK. Additionally, the cAMP/PKA pathway is another positive intracellular signal for hepatopancreatic Vg mRNA expression but is independent of its VIH-2 regulation. Our findings establish a model for the signal transduction mechanism of Vg regulation by VIH and shed light on the biological functions and signaling of the CHH family in crustaceans.

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.

Wnt5b regulates apoptosis in Litopenaeus vannamei against white spot syndrome virus

The Wnt signaling mediated by Wnt proteins that orchestrate and influence a myriad of cellular processes, such as cell proliferation, differentiation, tumorigenesis, apoptosis, and participation in immune defense during microbe infection. Wnt5b is one of the Wnt signaling molecules that initiate the cascade. In this study, we cloned and characterized a Wnt5b homolog from Litopenaeus vannamei designed as LvWnt5b. The full length of LvWnt5b transcript was 1726 bp with an 1107 bp open reading frame that encoded a 368 aa protein, which contained 24 discontinuous and highly conserved cysteine. Real-time quantitative PCR showed that the transcriptional level of LvWnt5b was down-regulated when infected with white spot syndrome virus (WSSV). Knock-down of LvWnt5b resulted in inhibition of the transcriptional level of WSSV gene ie1, indicating that LvWnt5b mediated signaling pathway may play an important role in defense against WSSV infection. When LvWnt5b was silenced, caspase3/7 activity in hemocytes was increased significantly, and the transcription of viral gene was decreased as well. Moreover, overexpression of LvWnt5b in HEK293T cells led to inhibition of caspase3/7 activity, which further proved the role of LvWnt5b in restraining apoptosis. The study showed that the shrimp may decrease the expression of LvWnt5b initiatively to act as an immune defense mechanism against WSSV infection via promoting apoptosis. It will be helpful for understanding the function of Wnt signaling pathway in virus invasion and host defense.

Identification and analysis of an MKK4 homologue in response to the nucleus grafting operation and antigens in the pearl oyster, Pinctada fucata

The mitogen-activated protein kinase kinase 4 (MKK4) is a key component of the c-Jun N-terminal kinase (JNK) signaling pathway and regulates multiple cellular activities. However, little is known about the roles of this kinase in pearl oyster. In this study, we identified an MKK4 homologue in Pinctada fucata by using a transcriptome database. Sequence analysis and protein structure prediction showed that PfMKK4 is highly conserved to MKK4 from other vertebrate and invertebrate species. Phylogenetic analysis revealed that PfMKK4 has the closest relationship with that from Crassostrea gigas. QPCR was used to investigate expression profiles in different healthy adult tissues and developmental stages of P. fucata. We found that PfMKK4 was ubiquitously expressed in all tissues and developmental stages examined except for in D-shaped larvae. Gene expression analysis suggested that PfMKK4 is involved in the response to the nucleus insertion operation. Lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid [poly(I:C)] stimulation in vivo reduced PfMKK4 mRNA expression at 6 h, 48 h and 48 h, 72 h, respectively. LPS and poly(I:C) induced PfMKK4 phosphorylation in a primary mantle cell culture. These results contribute to better understanding of the potential role played by PfMKK4 in protecting the pearl oyster from injury caused by grafting or disease.

A single WAP domain (SWD)-containing protein with antiviral activity from Pacific white shrimp Litopenaeus vannamei

The single whey acidic protein (WAP) domain (SWD)-containing proteins, also called type III crustins, are a group of antimicrobial peptides (AMPs) in crustaceans. At present, a number of SWDs have been identified in shrimp, which showed essential antibacterial activities. However, the roles of SWDs in antiviral immune responses have not been reported up to now. In this study, a novel SWD (LvSWD3) was identified from Pacific white shrimp, Litopenaeus vannamei, which contained a typical single WAP domain homologous to those of other crustacean SWDs. Although lacking the pro and arg-rich region between the signal peptide and the WAP domain, LvSWD3 was closely clustered with other shrimp SWDs in the phylogenetic tree. Similar to many shrimp SWDs, the highest expression of LvSWD3 was detected in hemocytes. The LvSWD3 expression exhibited only limited changes after challenges with Vibrio parahaemolyticus, Poly (I:C) and lipopolysaccharide, but was significantly up-regulated after white spot syndrome virus (WSSV) infection. Silencing of LvSWDs significantly accelerated the death of the WSSV-infected but not the V. parahaemolyticus-infected shrimp. The recombinant LvSWD3 protein did not show proteinase inhibitory and antibacterial activities but could significantly postpone the death of WSSV-infected shrimp and reduce the viral load in tissues. These suggested that LvSWD3 was a novel SWD with antiviral activity.

Trypsin of Litopenaeus vannamei is required for the generation of hemocyanin-derived peptides

Hemocyanin is a copper containing respiratory glycoprotein in arthropods and mollusks, which also have multiple functions in vivo. Recent studies have shown that hemocyanin could generate several peptides, which play important roles in shrimp innate immunity. However, how these hemocyanin-derived peptides are generated is still largely unknown. In this study, we report for the first time that the generation of hemocyanin-derived peptides was closely correlated with trypsin expression in shrimp hepatopancreas following infection with different bacteria. RNA interference (RNAi) mediated knockdown of trypsin or treatment with the serine protease inhibitor, aprotinin, resulted in significant decrease in the levels of hemocyanin-derived peptides. Moreover, recombinant trypsin (rTrypsin) was able to hydrolyse hemocynin in vitro with the hydrolysate having a high bacterial agglutination activity while the denatured hemocynin untreated with rTrypsin lost its agglutination activity. Taken together, our current results showed that the generation of hemocyanin-derived peptides correlates with an increase trypsin expression.

A molting-inhibiting hormone-like protein from Pacific white shrimp Litopenaeus vannamei is involved in immune responses

The molting-inhibiting hormones (MIHs) from the crustacean hyperglycemic hormone (CHH) family are a group of neuropeptides that are implicated in regulation of molting and reproduction in crustaceans. In this study, a novel protein containing a typical crustacean neuropeptide domain was identified from Litopenaeus vannamei. The protein showed high homology with other shrimp MIHs and was then designated as a MIH-like protein (MIHL). Among the detected tissues, the heart expressed the highest level of MIHL. The expression of MIHL could be significantly up-regulated after infection with white spot syndrome virus (WSSV), gram-negative bacterium Vibro parahaemolyticus and gram-positive bacterium Staphylococcus aureus, indicating that MIHL could be involved in immune responses. The promoter of MIHL was predicted to contain two NF-κB binding sites and could be regulated by the NF-κB family protein Relish but not Dorsal, suggesting that MIHL could be an effector gene of the IMD/Relish pathway. Silencing of MIHL in vivo by RNAi strategy significantly down-regulated the expression of many immune effector genes and increased the mortalities of shrimp infected by V. parahaemolyticus and WSSV and their copy numbers in tissues. These confirmed that MIHL could play a role in antiviral and antibacterial immune responses in shrimp.

The shrimp hormone receptor acts as an anti-apoptosis and anti-inflammatory factor in innate immunity

Previously, we found that the expression of several genes, including HR, varied in Drosophila melanogaster after white spot syndrome virus (WSSV) infection. In this present study, we further investigated the role of HR in Kuruma shrimp, Marsupenaeus japonicus and determined its anti-apoptosis and anti-inflammation role in the innate immune system. We successfully identified a partial sequence (866 bp in length) of the M. japonicus hormone receptor ligand binding domain (mjHR_LBD/mjHR). The 5' end of mjHR was successfully obtained; the open reading frame (ORF) ran from 33 to 701 bp, and encoded a protein containing 222 amino acids. mjHR belonged to the ligand binding domain of hormone receptors, was most likely part of a nuclear hormone receptor, and shared a close evolutionary relationship with other arthropods, such as insects. mjHR was expressed predominantly in immunity tissues such as gills, hemolymph and the hepatopancreas. WSSV infection could cause the down-regulation of mjHR, while infection with Vibrio alginolyticus could cause significant up-regulation of mjHR. The expression of mjHR was knocked down by dsRNA expressed by an engineered LITMUS 38i-HR plasmid. Virus and bacteria challenge experiment showed that the mortality of WSSV-infected shrimps was elevated in the absence of HR while the mortality of shrimps infected with V. alginolyticus was slightly reduced. Phenoloxidase (PO) activity, phagocytosis and apoptosis were promoted, while superoxide dismutase (SOD) activity was impaired, indicating that mjHR functions in an anti-apoptosis and anti-inflammation manner to prevent shrimp death caused by an over-load of immunity responses. Differences between mjHR expression and mortality change after WSSV or V. alginolyticus infection indicated that there was a different strategy for viruses or bacteria when confronted with the innate immune system.

Transcriptome analysis of hepatopancraes of Procambarus clarkii challenged with polyriboinosinic polyribocytidylic acid (poly I:C)

Crustacean hepatopancreas regulates metabolic processes, biogenesis and innate immune processes, and the knowledge on its immune genes are crucial to understand antimicrobial mechanisms. In this study, we reported the transcriptomic profile of Procambarus clarkii hepatopancreas after poly I:C administration using high-throughput sequencing. Following de novo assembly 56,716 unigene sequences with an average length of 810 bp was obtained. The unigene sequences were annotated to three ontologies including cellular components, biological processes and molecular functions, further 56,716 unigene sequences were mapped to 25 COG categories. A total of 2497 differentially expressed genes (DEGs) were identified following the comparative analysis between poly I:C treated and control group, and then KEGG enrichment analysis were performed to detect immune related pathways. Quantitative real time polymerase chain reaction showed that the selected DEGs significantly up-regulated following poly I:C administration in comparison to control group. The transcriptomic sequence information will improve the knowledge of this economically important crustacean, and will shed light on its antiviral immune mechanisms.

Transcriptome profiling of red swamp crayfish (Procambarus clarkii) hepatopancreas in response to lipopolysaccharide (LPS) infection

The RNA-sequencing followed by de novo assembly generated 61,912 unigene sequences of P. clarkii hepatopancreas. Comparison of gene expression between LPS challenged and PBS control samples revealed 2552 differentially expressed genes (DEGs). Of these sequences, 1162 DEGs were differentially up-regulated and 1360 DEGs differentially down-regulated. The DEGs were then annotated against gene ontology (GO) database and Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Some immune-related pathways such as PPAR signaling pathway, lysosome, Chemical carcinogenesis, Peroxisome were predicted by canonical pathways analysis. The reliability of transcriptome data was validated by quantitative real time polymerase chain reaction (qRT-PCR) for the selected genes. The data presented here shed light into antibacterial immune responses of crayfish. In addition, these results suggest that transcriptomic data provides valuable sequence resource for immune-related gene identification and helps to understand P. clarkii immune functions.

Transcriptomic and morphological analyses of Litopenaeus vannamei intestinal barrier in response to Vibrio paraheamolyticus infection reveals immune response signatures and structural disruption

The white shrimp Litopenaeus vannamei has been greatly impacted by Vibrio infection. In this study, we investigated the intestinal barrier response of L vannamei following challenge with Vibrio parahaemolyticus E1, by examining morphological changes and transcriptome expression levels. A total of 16,4420 unigenes were obtained from RNAseq data after quality control and assembly, and 4646 differentially expressed genes (DEGs) were identified following Vibrio challenge, of which 2469 unigenes were significantly up-regulated and 2177 were significantly down-regulated. DEGs were determined to be involved in various physical, chemical and immunological intestinal barrier functions, including peritrophin, cytoskeleton and cell junction, pattern recognition receptors, antimicrobial peptide and immune signaling pathways, serine protease/protease inhibitor and prophenoloxidase system, apoptosis and phagocytosis, and antioxidant systems. Fifteen DEGs were randomly selected for validation by real-time quantitative PCR (RT-qPCR) and showed results consistent with the RNA-seq data. Intestinal epithelial cell morphology was also affected by Vibrio challenge, showing epithelial detachment, nuclear pyknosis, and destruction of cell junctions. These results improve our current understanding of the intestinal barrier function in the shrimp response to bacterial infection.

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.

Identification, characterization, and function analysis of the NF-κB repressing factor (NKRF) gene from Litopenaeus vannamei

The NF-κB family transcription factors regulate a wide spectrum of biological processes, in particular immune responses. The studies in human suggest that the NF-κB repressing factor (NKRF) negatively regulates the activity of NF-κB through a direct protein-protein interaction. However, the function of NKRF has not been studied outside mammals up to now. The current study identified a NKRF gene (LvNKRF) from the Pacific white shrimp, Litopenaeus vannamei, which showed homology with NKRFs from insects, fishes and mammals. LvNKRF was high expressed in intestine, stomach and muscle tissues and was localized in the nucleus. LvNKRF could interact with both Dorsal and Relish, the two members of the shrimp NF-κB family. Interestingly, although sharing a similar protein structure with that of human NKRF, LvNKRF showed no inhibitory but instead enhancing effects on activities of Dorsal and Relish, which was contrary to those of mammalian NKRFs. The expression of LvNKRF could not be induced by Gram-positive and -negative bacteria and immunostimulants lipopolysaccharide (LPS) and poly (I:C) but was significantly up-regulated after white spot syndrome virus (WSSV) infection. Silencing of LvNKRF significantly decreased the mortalities of shrimp caused by WSSV infection and down-regulated the WSSV copies and the expression of WSSV structural gene in tissues. These suggested that LvNKRF could facilitate the infection of shrimp by WSSV, which may be an additional strategy for WSSV to hijack the host NF-κB pathway to favor its own replication. The current study could provide a valuable context for further investigating the evolutionary derivation of NKRFs and facilitate the study of regulatory mechanisms of invertebrate NF-κB pathways.

Characterization and function of a β-catenin homolog from Litopenaeus vannamei in WSSV infection

As a conserved signaling pathway, Wnt/β-catenin signaling pathway participates in many physiological activities, including cell differentiation, apoptosis and so on. β-catenin is the key molecule of Wnt/β-catenin signaling pathway and plays a pivotal role. In this article, a β-catenin homolog from Litopenaeus vannamei (designed as Lv-β-catenin) was cloned and its role in WSSV infection was investigated. Sequence analysis suggested that Lv-β-catenin had characters of β-catenin family. Semi-quantitative RT-PCR showed that Lv-β-catenin transcripted in all detected tissues. In the subsequent WSSV infection experiments, it was found that the transcription levels of Lv-β-catenin were down-regulated, as well as the expression levels. Immunofluorescence assay further confirmed that WSSV could reduce the amount of Lv-β-catenin and promoted Lv-β-catenin to translocate into the nucleus. Moreover, we found that WSSV could influence the amount of Lv-β-catenin by ubiquitination. While Lv-β-catenin was up-regulated by a β-catenin activator GSK-3 Inhibitor IX, the transcription of virus immediate early gene WSSV069 was significantly inhibited. In addition, it was found that Lv-β-catenin could interact with WSSV069. Conclusively, our study provided evidences that β-catenin may participate in the WSSV infection, and Wnt/β-catenin signal pathway may play an important role in immune regulation.

Toll-receptor 9 gene in the black tiger shrimp (Penaeus monodon) induced the activation of the TLR-NF-κB signaling pathway

Toll receptors are important pathogen recognition receptors (PRRs) in shrimps, which play a vital role in defending against virus and bacterial challenge. In this paper, the characterization and functional analysis of a Toll9 receptor gene from Penaeus monodon was performed in HEK293T cells. Data showed that PmToll9 can activate the NF-κB promoter activities of TLR pathway, while ISRE and IFN-β promoter cannot be activated obviously in HEK293T cells using dual-luciferase reporter system. The downstream immune factors of IL-8, IκB-α, and TRAF6 were activated by PmToll9 and IL-8 showed the most significant up-regulation in expression levels, indicating the activities of NF-κB can be mediated by PmToll9. Six LRRs-deletion mutants were constructed and results showed these mutants had obvious declines in luciferase activities, among which the mutant pCMV-DeLRR4 showed the most significant decline. qPCR data indicated LRRs-deletion mutants efficiently impaired the activities of the downstream immune factors IL-8, IκB-α, and TRAF6. It demonstrates that LRRs-deletion mutants could result in the weaken abilities of PmToll9 in signaling transduction. Overexpression of PmToll9-GFP fusion protein in Hela cells revealed the primary cellular localization of PmToll9 is in the cytoplasm.

Activation of Toll Pathway Is Different between Kuruma Shrimp and Drosophila

The Toll pathway is essential for inducing an immune response to defend against bacterial invasion in vertebrates and invertebrates. Although Toll receptors and the transcription factor Dorsal were identified in different shrimp, relatively little is known about how the Toll pathway is activated or the function of the pathway in shrimp antibacterial immunity. In this study, three Tolls (Toll1–3) and the Dorsal were identified in Marsupenaeus japonicus. The Toll pathway can be activated by Gram-positive (G⁺) and Gram-negative (G⁻) bacterial infection. Unlike Toll binding to Spätzle in Drosophila, shrimp Tolls could directly bind to pathogen-associated molecular patterns from G⁺ and G⁻ bacteria, resulting in Dorsal translocation into nucleus to regulate the expression of different antibacterial peptides (AMPs) in the clearance of infected bacteria. These findings suggest that shrimp Tolls are pattern recognition receptors and the Toll pathway in shrimp is different from the Drosophila Toll pathway but identical with the mammalian Toll-like receptor pathway in its activation and antibacterial functions.

Identification and characterization of an interleukin-16-like gene from pacific white shrimp Litopenaeus vannamei

Interleukins are a group of cytokines that play essential roles in immune regulation. Almost all interleukin genes are only found in vertebrates. In this study, an interleukin-16-like gene (LvIL-16L) was identified from Pacific white shrimp, Litopenaeus vannamei. LvIL-16L was predicted to encode a precursor (pro-LvIL-16L) with 1378 amino acids, sharing similarities with predicted pro-IL-16-like proteins from insects. The C-terminus of pro-LvIL-16L protein contained two PDZ domains homologous to the mature IL-16 cytokine of vertebrates. In tissues, LvIL-16L could be processed into a ∼36 kDa mature peptide through a caspase-3 cleavage site, which was verified by in vitro site mutation analysis and in vivo RNA interference (RNAi) experiments. The LvIL-16L mRNA could be detected in all the analyzed tissues and the expression of LvIL-16L was significantly up-regulated after immune stimulation. Using RNAi strategy, the role of LvIL-16L in immune responses was initially investigated. Interestingly, knockdown of LvIL-16L could significantly increase the mortality of the Vibro parahaemolyticus infected shrimps but reduce that of the WSSV infected shrimps, suggesting that LvIL-16L could have opposite effects on the antiviral and antibacterial immune responses in shrimp. To our knowledge, this is the first study of an IL-16-like gene in invertebrates, which could help to elucidate interleukin evolution and regulatory mechanisms of shrimp immune responses.

Effect of feeding frequency on growth, body composition, antioxidant status and mRNA expression of immunodependent genes before or after ammonia-N stress in juvenile oriental river prawn, Macrobrachium nipponense

Feeding frequency is important for the improvement of growth performance and immunity of aquatic animals. In this study, the effect of feeding frequency on growth, body composition, antioxidant status and mRNA expression of immunodependent genes before or after ammonia-N stress was examined in Macrobrachium nipponense. Prawns were randomly assigned to one of five feeding frequencies (1, 2, 3, 4 and 6 times/day) following the same ration size over an 8-week growth trial. After the feeding trial, prawns were challenged by ammonia-N. The weight gain of prawns fed with 3-6 times/day was significantly higher than that of prawns fed with 1 time/day. The best feed conversion ratio was obtained from prawns fed with 3-6 times/day. Body crude lipid with feeding frequency of 3, 4 or 6 times/day was quite lower than that with 1 time/day. High feeding frequency (6 times/day) induced significantly elevated hepatopancreas super oxide dismutase and catalase activities. The malondialdehyde level in prawns fed with 6 times/day was also significantly increased, which was higher than that of prawns fed with other feeding frequency. mRNA expression of toll like receptor 3 and myeloid differentiation primary response protein MyD88 was promoted by feeding frequency from 3 to 4 time/day but inhibited by high or low feeding frequency. Similar mRNA expression variation trends of the two genes were observed in prawns after ammonia-N stress. After ammonia-N challenge, the highest cumulative mortality was observed in prawns fed with 6 times/day, which was significantly higher than that of prawns fed with 2-4 times/day. These findings demonstrate that (1) too high feeding frequency induced oxidative stress and malondialdehyde accumulation, negatively affecting the health status of prawns and reduced its resistance to ammonia-N stress; (2) the optimal feeding frequency to improve growth and immune response of this species at juvenile stage is 3-4 times/day; (3) considering costs of labour, a feeding frequency of 3 times/day is recommended for this prawn.

Molecular cloning, characterization and function of a germinal center kinase MST4 gene from Litopenaeus vannamei in response to Vibrio alginolyticus challenge in TLR-TRAF6 signaling pathway

The serine/threonine protein kinase MST4 plays multiple roles in the regulation of signaling pathways that govern cellular processes including mitosis, migration, homeostasis, polarity, proliferation, differentiation and apoptosis. Here we report the identification and characterization of the full-length sequence of LvMST4 from the shrimp L. vannamei, and investigations into its role in the shrimp's immune response to infection by the pathogenic bacterium Vibrio alginolyticus. Subcellular localization assays demonstrated the enzyme's presence in the shrimp's cytoplasm, and tissue-specific expression analysis revealed that it is expressed ubiquitously but at different levels in different tissues. Infection with V. alginolyticus increased LvMST4 expression and induced a rapid response via the TLR-TRAF6 signaling pathway, causing a decline in the total hemocyte count (THC) and an increase in respiratory burst (RB) activity. In non-infected shrimp, RNAi silencing of LvMST4 with dsRNA had no significant effect on THC but seemed to activate the TRAF6-MKK6-p38 pathway and reduced RB activity. In shrimp challenged with V. alginolyticus, LvMST4 silencing reduced bacterial clearance and increased the initial upregulation of LvTRAF6 while reducing the expression of LvMKK6 and Lvp38. LvMST4 silencing also slightly reduced the THC but caused pronounced increases in RB activity and cumulative mortality. These findings suggest that LvMST4 contributes to antimicrobial responses via the TLR-TRAF6 signal pathway, and helps maintain immunological homeostasis in L. vannamei.

Establishment of lysozyme gene RNA interference systemand its involvement in salinity tolerance in sea cucumber (Apostichopus japonicus)

The lysozyme gene was silenced using RNA interference (RNAi) to analyze the function of lysozyme in sea cucumber under salt stress. The interfering efficiency of four lysozyme RNAi oligos ranged from 0.55 to 0.70. From the four oligos, p-miR-L245 was used for further interfering experiments because it had the best silencing efficiency. Peristomial film injection of p-miR-L245 (10 μg) was used for further interfering experiments. The lowest gene expression, determined by RT-PCR assay, in muscle, coelomic fluid, and parapodium occurred 48 h after p-miR-L245 injection, while that of body wall and tube foot was 96 h and 24 h, respectively. Lysozyme activity in muscle and body wall was significantly lower than the controls. The lowest lysozyme activity in muscle, body wall and parapodium, was found at 48, 72, and 48 h, respectively, which was consistent with the transcription expression of lysozyme. The lowest point of lysozyme activity was at 96 h in coelomic fluid and tube foot, which was laid behind lysozyme expression in transcription level. The expression profile of the lysozyme transcription level and lysozyme activity in the body wall and tube foot increased at 12 h after p-miR-L245 injection before the interference effect appeared. NKA gene expression was expressed at a high level in the positive control (PC) and negative control (NC) groups at 12, 24, and 48 h, while NKA was expressed at low levels in the lysozyme RNAi injection group at 12 and 24 h. The level of NKA gene expression recovered to the level of the PC and NC group at 48, 72, and 96 h after the lysozyme RNAi injection. NKCC1 gene expression was high in the PC and NC groups at 96 h, while the NKCC1 was expressed at a low level 96 h after lysozyme RNAi injection. The results suggest that lysozyme decay involves NKA and NKCC1 gene expression under salinity 18 psμ. The K⁺ and Cl^- concentration after lysozyme RNAi injection was lower than in the PC and NC group.

Characterization of PmSpӓtzle 1 from the black tiger shrimp Peneaus monodon

Spätzle is a signaling ligand in innate immune response that signals pathogenic infection via Toll receptor and Toll pathway into the cells for the synthesis of antimicrobial proteins. Herein, three PmSpӓtzle isoforms were identified in Penaeus monodon, namely PmSpz1, 2 and 3. The PmSpz1 was chosen for detailed study. The PmSpz1 gene was expressed in all nine tissues tested including the hemocytes, stomach, hepatopancreas, gill, lymphoid tissue, eyestalk, muscle, intestine and heart. Its expression was up-regulated upon white spot syndrome virus (WSSV) infection. Western blot analysis of hemolymph showed that the PmSpz1 mostly existed as a cleaved active form awaiting to activate the Toll pathway. Injection of a recombinant PmSpz1 rendered the shrimp less susceptible to the WSSV infection. Injection of a recombinant active form of PmSpz1 into a normal shrimp activated the synthesis of crustinPm1, crustinPm7, ALFPm3, penaeidin3 but not penaeidin5 indicating that the expression of all antimicrobial proteins but not penaeidin5 was under the regulation of Toll pathway.

Shrimp TAB1 interacts with TAK1 and p38 and activates the host innate immune response to bacterial infection

Mammalian TAB1 has been previously identified as transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) binding protein, which functions as the activator of TAK1 and p38. This report, for the first time, identified and characterized the homolog of TAB1 in shrimp, to be specific, the homolog gene from Litopenaeus vannamei, containing a 1560-bp open reading frame (ORF) that encoded a putative protein of 519 amino acids with the conserved PP2Cc (Serine/threonine phosphatases, family 2C, catalytic) domain in N-terminal and a TAK1 binding motif in C-terminus, has been cloned and named LvTAB1. LvTAB1 was most abundant in gills and its expression could respond significantly to a series of stimuli, including LPS, Vibrio parahemolyticus and Staphylococcus aureus. Moreover, Co-immunoprecipitation (Co-IP) experiments showed that LvTAB1 could combine with LvTAK1 as well as Lvp38, two members of IMD-NF-κB/MAPK pathway, which meant LvTAB1 could have a role in regulating the activities of these kinases. Over-expression of LvTAB1 in drosophila S2 cells could improve the transcriptional levels of antimicrobial peptide genes (AMPs) such as Diptericin (Dpt), the hallmark of drosophila NF-κB activated genes, indicating its activation effect on NF-κB pathway. Furthermore, suppression of LvTAB1 expression in vivo by RNA-interference increased the sensibility of shrimps to V. parahaemolyticus infection, implying its protective role against bacterial infection. In conclusion, these results provide some insight into the function of LvTAB1 during bacterial infection.

Comparative genomic analysis of innate immunity reveals novel and conserved components in crustacean food crop species

BACKGROUND

Growing global demands for crustacean food crop species have driven large investments in aquaculture research worldwide. However, large-scale production is susceptible to pathogen-mediated destruction particularly in developing economies. Thus, a thorough understanding of the immune system components of food crop species is imperative for research to combat pathogens.

RESULTS

Through a comparative genomics approach utilising extant data from 55 species, we describe the innate immune system of the class Malacostraca, which includes all food crop species. We identify 7407 malacostracan genes from 39 gene families implicated in different aspects of host defence and demonstrate dynamic evolution of innate immunity components within this group. Malacostracans have achieved flexibility in recognising infectious agents through divergent evolution and expansion of pathogen recognition receptors genes. Antiviral RNAi, Toll and JAK-STAT signal transduction pathways have remained conserved within Malacostraca, although the Imd pathway appears to lack several key components. Immune effectors such as the antimicrobial peptides (AMPs) have unique evolutionary profiles, with many malacostracan AMPs not found in other arthropods. Lastly, we describe four putative novel immune gene families, potentially representing important evolutionary novelties of the malacostracan immune system.

CONCLUSION

Our analyses across the broader Malacostraca have allowed us to not only draw analogies with other arthropods but also to identify evolutionary novelties in immune modulation components and form strong hypotheses as to when key pathways have evolved or diverged. This will serve as a key resource for future immunology research in crustacean food crops.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) participates in peroxinectin gene expression in Fenneropenaeus penicillatus

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an important cytoplasm signal adaptor that mediates signals activated by tumor necrosis factor receptor (TNFR) superfamily and the Interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily. In the study, the full-length cDNA of a TRAF6 homolog (FpTRAF6) was identified from Fenneropenaeus penicillatus. The full-length cDNA of FpTRAF6 is 2033 bp long, with an open reading frame (ORF) encoding a putative protein of 594 amino acids, including a RING type Zinc finger, two TRAF-type Zinc fingers, and a conserved C-terminal meprin and TRAF homology (MATH) domain. The overall amino acid sequence identity between FpTRAF6 and other TRAF6s ranged from 62.7 to 94.1% for crustaceans and from 45.6 to 59.3% for mollusca. Real-time qRT-PCR indicated that FpTRAF6 was constitutively expressed in various tissues of F. penicillatus. The temporal expression patterns of FpTRAF6 mRNA were different in the different tissues after microbial challenge. FpTRAF6 was downregulated in the heart, no obvious changes in the gill, intestine and hemocytes, and upregulated in other tested tissues after WSSV challenge. After V. alginolyticus injection, FpTRAF6 was downregulated in the heart and intestine, upregulated in the gill, lymphoid organ and hematopoietic organ, and no obvious changes in other tested tissues. RNAi assay was carried out to investigate the function of FpTRAF6. The results showed that silencing FpTRAF6 gene could inhibit peroxinectin expression in vivo, and enhance the sensitivity of shrimps to WSSV and V. alginolyticus challenge, suggesting FpTRAF6 could play a positive role against bacterial and viral pathogens. In conclusion, the results of the study provide some insights into the function of FpTRAF6 in activating TLRs signaling pathway and the host defense against invading pathogens.

Tick Humoral Responses: Marching to the Beat of a Different Drummer

Ticks transmit a variety of human pathogens, including Borrelia burgdorferi, the etiological agent of Lyme disease. Multiple pathogens that are transmitted simultaneously, termed “coinfections,” are of increasing importance and can affect disease outcome in a host. Arthropod immunity is central to pathogen acquisition and transmission by the tick. Pattern recognition receptors recognize pathogen-associated molecular patterns and induce humoral responses through the Toll and Immune Deficiency (IMD) pathways. Comparative analyses between insects and ticks reveal that while the Toll pathway is conserved, the IMD network exhibits a high degree of variability. This indicates that major differences in humoral immunity exist between insects and ticks. While many variables can affect immunity, one of the major forces that shape immune outcomes is the microbiota. In light of this, we discuss how the presence of commensal bacteria, symbionts and/or coinfections can lead to altered immune responses in the tick that impact pathogen persistence and subsequent transmission. By investigating non-insect arthropod immunity, we will not only better comprehend tick biology, but also unravel the intricate effects that pathogen coinfections have on vector competence and tick-borne disease transmission.

Characterization and function analysis of interleukin-1 receptor-associated kinase-1 (IRAK-1) from Fenneropenaeus penicillatus

The interleukin-1 receptor-associated kinase-1 (IRAK-1) is an important adapter protein which links downstream of MyD88, and involved in the complex composed of MyD88 and TRAF6 to activate TLRs signaling pathway. In this study, an IRAK-1 homolog (FpIRAK-1) was cloned from the red tail shrimp Fenneropenaeus penicillatus. The ORF of FpIRAK-1 consisted of 2874 bp encoding a protein of 957 amino acids which contains a death domain (DD) and a catalytic domain of serine/threonine kinases (STKc). Homology analysis revealed that the predicted amino acid sequence of FpIRAK-1 shared 71% similarities with IRAK-1 of Litopenaeus vannamei. Real-time RT-PCR indicated that FpIRAK-1 was constitutively expressed in various tissues of F. penicillatus. The expression level of FpIRAK-1 mRNA was significantly up-regulated and then decreased gradually after white spot syndrome virus (WSSV) and Vibrio alginolyticus challenge. Gene knockdown of FpIRAK-1 enhanced the sensitivity of shrimps to WSSV and V. alginolyticus challenge, suggesting FpIRAK-1 could play a positive role against bacterial and viral pathogens. In conclusion, the results of this study provide some insights into the function of FpIRAK-1 in activating Toll signaling pathway and the host defense against invading pathogens.

Gene set based association analyses for the WSSV resistance of Pacific white shrimp Litopenaeus vannamei

White Spot Syndrome Virus (WSSV) is regarded as a virus with the strongest pathogenicity to shrimp. For the threshold trait such as disease resistance, marker assisted selection (MAS) was considered to be a more effective approach. In the present study, association analyses of single nucleotide polymorphisms (SNPs) located in a set of immune related genes were conducted to identify markers associated with WSSV resistance. SNPs were detected by bioinformatics analysis on RNA sequencing data generated by Illimina sequencing platform and Roche 454 sequencing technology. A total of 681 SNPs located in the exons of immune related genes were selected as candidate SNPs. Among these SNPs, 77 loci were genotyped in WSSV susceptible group and resistant group. Association analysis was performed based on logistic regression method under an additive and dominance model in GenABEL package. As a result, five SNPs showed associations with WSSV resistance at a significant level of 0.05. Besides, SNP-SNP interaction analysis was conducted. The combination of SNP loci in TRAF6, Cu/Zn SOD and nLvALF2 exhibited a significant effect on the WSSV resistance of shrimp. Gene expression analysis revealed that these SNPs might influence the expression of these immune-related genes. This study provides a useful method for performing MAS in shrimp.

Fatty acid synthase plays a positive role in shrimp immune responses against Vibrio parahaemolyticus infection

Fatty acid synthase (FAS) is an important enzyme that catalyzes the synthesis of fatty acids. In this study, the role of the FAS gene from pacific white shrimp Litopenaeus vannamei (LvFAS) in immune responses against Vibrio parahaemolyticus infection was studied. The expression of LvFAS could be up-regulated upon infection of V. parahaemolyticus and stimulation of lipopolysaccharide and poly (I:C). The promoter of LvFAS was predicted to harbor a NF-κB binding site and dual-luciferase reporter assays demonstrated that the NF-κB family proteins Relish, sRelish and Dorsal could activate the transcription of LvFAS. After knockdown of LvFAS expression using RNAi strategy, both the mortality of V. parahaemolyticus infected shrimps and the bacterial load in shrimp tissues were significantly increased. Meanwhile, the expression of many immune-responsive genes, such as antimicrobial peptides, C-type lectins (CTLs), lysozyme and hemolin, was down-regulated. These suggested that LvFAS could play a positive role in anti-V. parahaemolyticus responses in shrimp. To our knowledge, this is the first study that investigates the role of FAS in antibacterial immunity in animals, which may indicate the relationship between the anabolism of fatty acids and immune responses in crustaceans.

Identification of 10 transcripts of FREP in penaeid shrimp Litopenaeus vannamei

Fibrinogen-related proteins (FREPs) are widely distributed in vertebrates and invertebrates and known having Fibrinogen-related domains (FReDs) which function in multiple aspects, especially in innate immune response as pattern recognition receptors. However, there is no any report about FREP in penaeid shrimp Litopenaeus vannamei. Here, totally 10 transcripts of FREP were isolated and named LvFREP1.1, 1.2 until 1.10. All of the 10 transcripts have high identity in their 3' ends and encode conserved FReDs. Since the 10 transcripts are highly similar we could not design any primers that can amplify a single transcript. We chose a pair of primers corresponding to part of LvFREP1.1 and LvFREP1.5 to examine their expression. Tissue distribution indicated LvFREP1.1 and LvFREP1.5 mRNA locates in hemocytes, gills, intestine, hearts and slightly in nerve. The expression of LvFREP1.1 and LvFREP1.5 behaves differently post bacteria and virus infection. Besides, recombinant LvFReD could agglutinate bacteria Vibrio harveyi in the presence of Ca²⁺. These initial data presents the diversity of FREPs in penaeid shrimp and also push us to further explore their roles in shrimp immune response.

PcToll3 was involved in anti-Vibrio response by regulating the expression of antimicrobial peptides in red swamp crayfish, Procambarus clarkii

Tolls and Toll-like receptors (TLRs) play an important role in host immune defenses by regulating the expression of antimicrobial peptides (AMPs) and cytokines, but the functional differences of crustacean Tolls from Drosophila Tolls or Mammal TLRs are largely unknown. A novel Toll receptor, named PcToll3, was identified from red swamp crayfish, Procambarus clarkii. It was widely expressed in all detected tissues, and its transcript in hemocytes was up-regulated at 12 h after Vibrio parahemolyticus (Vibrio) injection or at 24 h post white spot syndrome virus (WSSV) challenge. After knockdown of PcToll3, the activity of bacterial clearance was inhibited, and the expression levels of AMPs including Crustin1 (Cru1), Anti-lippopolysaccharide factor 1 (ALF1), and Lysozymes1 (Lys1), which could be up-regulated by Vibrio, were all affected. Meanwhile, PcToll3 silencing influenced the expression of myeloid differentiation factor 88 (PcMyd88), tumor necrosis factor-associated factor 6 (PcTRAF6), and PcDorsal, which were the counterparts of Drosophila Toll signaling pathway. Interestingly, PcToll3 silencing inhibited translocation of PcDorsal from cytoplasm to nucleus. Furthermore, the knockdown of PcDorsal also impaired the expression of AMPs after Vibrio challenge. Hence, we concluded that, besides participating in antiviral immunity, PcToll3 might also regulate the expression of Cru1 and Lys1 to participate in anti-Vibrio immune responses by promoting PcDorsal translocation into nucleus.