WSSV-infected Shrimp Research Articles

The Mechanism of Synchronous Precise Regulation of Two Shrimp White Spot Syndrome Virus Targets by a Viral MicroRNA.

MicroRNAs (miRNAs), important factors in animal innate immunity, suppress the expressions of their target genes by binding to target mRNA’s 3′ untranslated regions (3′UTRs). However, the mechanism of synchronous regulation of multiple targets by a single miRNA remains unclear. In this study, the interaction between a white spot syndrome virus (WSSV) miRNA (WSSV-miR-N32) and its two viral targets (wsv459 and wsv322) was characterized in WSSV-infected shrimp. The outcomes indicated that WSSV-encoded miRNA (WSSV-miR-N32) significantly inhibited virus infection by simultaneously targeting wsv459 and wsv322. The silencing of wsv459 or wsv322 by siRNA led to significant decrease of WSSV copies in shrimp, showing that the two viral genes were required for WSSV infection. WSSV-miR-N32 could mediate 5′–3′ exonucleolytic digestion of its target mRNAs, which stopped at the sites of target mRNA 3′UTRs close to the sequence complementary to the miRNA seed sequence. The complementary bases (to the target mRNA sequence) of a miRNA 9th–18th non-seed sequence were essential for the miRNA targeting. Therefore, our findings presented novel insights into the mechanism of miRNA-mediated suppression of target gene expressions, which would be helpful for understanding the roles of miRNAs in innate immunity of invertebrate.

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.

A Novel Vascular Endothelial Growth Factor Receptor Participates in White Spot Syndrome Virus Infection in Litopenaeus vannamei.

Vascular endothelial growth factor (VEGF) signaling pathway is known to play key roles in endothelial cell proliferation, migration, angiogenesis, vascular permeability, inhibition of apoptosis, and virus infection. In the present study, a novel VEGFR gene (LvVEGFR2) was identified and characterized from Litopenaeus vannamei. The deduced amino acid sequence of LvVEGFR2 possessed typical features of VEGFRs reported in other species, including six IG-like domains, a transmembrane motif, a protein kinase (PK) domain, and one tyrosine-PK active site. The transcripts of LvVEGFR2 were mainly detected in hemocytes and lymphoid organ (Oka). Subcellular localization analysis showed that LvVEGFR2 was a membrane protein. Its expression level was obviously upregulated in hemocytes and Oka of the shrimp after white spot syndrome virus (WSSV) infection. Knockdown of LvVEGFR2 gene expression by double-strand RNA mediated interference could lead to a decrease of virus copy number in WSSV-infected shrimp. The interaction between LvVEGFR2 and different LvVEGFs (LvVEGF1, LvVEGF2, and LvVEGF3) in shrimp was analyzed at the transcription level and protein level, respectively. Knockdown of LvVEGF2 or LvVEGF3 could downregulate the expression level of LvVEGFR2, and injection of the recombinant LvVEGF2 or LvVEGF3 could upregulate the expression level of LvVEGFR2. Yeast two-hybrid analysis showed that LvVEGFR2 could interact with LvVEGF2 and LvVEGF3 directly. The study improved our understanding on the VEGF signaling pathway of shrimp and its role during WSSV infection.

WSSV-responsive gene expression under the influence of PmVRP15 suppression

The viral responsive protein 15 from black tiger shrimp Penaeus monodon (PmVRP15), is highly up-regulated and produced in the hemocytes of shrimp with white spot syndrome virus (WSSV) infection. To investigate the differential expression of genes from P. monodon hemocytes that are involved in WSSV infection under the influence of PmVRP15 expression, suppression subtractive hybridization (SSH) of PmVRP15-silenced shrimp infected with WSSV was performed. The 189 cDNA clones of the forward library were generated by subtracting the cDNAs from WSSV-infected and PmVRP15 knockdown shrimp with cDNAs from WSSV-infected and GFP knockdown shrimp. For the opposite subtraction, the 176 cDNA clones in the reverse library was an alternative set of genes in WSSV-infected shrimp hemocytes in the presence of PmVRP15 expression. The abundant genes in forward SSH library had a defense/homeostasis of 26%, energy/metabolism of 23% and in the reverse SSH library a hypothetical protein with unknown function was found (30%). The differential expressed immune-related genes from each library were selected for expression analysis using qRT-PCR. All selected genes from the forward library showed high up-regulation in the WSSV-challenged PmVRP15 knockdown group as expected. Interestingly, PmHHAP, a hemocyte homeostasis associated protein, and granulin-like protein, a conserved growth factor, are extremely up-regulated in the absence of PmVRP15 expression in WSSV-infected shrimp. Only transcript level of transglutaminase II, that functions in regulating hematopoietic tissue differentiation and inhibits mature hemocyte production in shrimp, was obviously down-regulated as observed from SSH results. Taken together, our results suggest that PmVRP15 might have a function relevant to hemocyte homeostasis during WSSV infection.

Functional characterization of a reactive oxygen species modulator 1 gene in Litopenaeus vannamei

Reactive oxygen species (ROS) imparts a dual effect on multicellular organisms, wherein high levels are usually harmful, and low levels could facilitate in combating pathogenic microorganisms; therefore, the regulation of ROS production is critical. Previous studies have suggested that ROS contributes to resistance to the white spot syndrome virus (WSSV) or Vibrio alginolyticus in Litopenaeus vannamei. However, the regulation of ROS metabolism in L. vannamei remains elusive. In the present study, we proved that the overexpression of L. vannamei reactive oxygen species modulator 1 (LvROMO1) increases ROS production in Drosophila Schneider 2 (S2) cells. Real-time RT-PCR analysis indicated that LvROMO1 is induced by WSSV or V. alginolyticus infection and β-glucan or microcystin (MC-LR) injection. Further investigation showed that LvROMO1 responding to MC-LR, thereby inducing hemocytes to undergo apoptosis, and ultimately resulting in hepatopancreatic damage. And LvROMO1 downregulation induced an increase in the cumulative mortality of WSSV-infected shrimp by reducing ROS production and suppressing the expression of antimicrobial peptides genes. The findings of present study suggest that LvROMO1 plays an important role in ROS production in L. vannamei and is involved in innate immunity.

Effect of immune gene silencing in WSSV infected tiger shrimp Penaeus monodon

White spot syndrome virus, continues to cause huge economic loss to aquaculture industry. In the absence of effective therapeutics to control WSSV, it is important to understand the host pathogen interaction at the molecular level. Suppression subtractive hybridization (SSH) cDNA library was constructed which led to identification of several differentially expressed genes in response to WSSV infection in Penaeus monodon. The genes expressed in SSH cDNA library of shrimp gill and gut tissues belonged to a wide range of biological functions. The three differentially expressed genes, Single von Willebrand factor type C domain protein (pmSVC), P53 protein gene (pmP53) and ADP ribosylation factor (pmArf) were up-regulated against WSSV infection and were further characterized by gene silencing to study the role of these shrimp immune genes on WSSV multiplication. The sequence-specific knock down of pmSVC, pmP53 and pmArf using the dsRNA revealed that in pmSVC-dsRNA inoculated shrimps WSSV replication was more with increased viral copy numbers when compared with pmP53-dsRNA and pmArf -dsRNA inoculated shrimps. The varied response of immune genes to WSSV infection, indicated that host genes may either inhibit virus replication to some extent or might act as a target to facilitate viral pathogenesis.

Litopenaeus vannamei activating transcription factor 6 alpha gene involvement in ER-stress response and white spot symptom virus infection

A previous study found that inositol-requiring enzyme-1-X-box binding protein 1 (IRE1-XBP1) pathway and the protein kinase RNA (PKR)-like ER kinase-eIF2α (PERK-eIF2α) pathway of shrimp play roles in the unfolded protein response (UPR). And they also be proved that was involved in white spot symptom virus (WSSV) infection. Yet the functions of the third branch in shrimp UPR are still unclear. In this study, we showed that upon UPR activation, activating transcription factor 6 alpha (LvATF6α) of Litopenaeus vannamei was cleaved and transferred from the cytoplasm to the nucleus in 293T cells, indicating that the ATF6 pathway in shrimp is also a branch of UPR. Furthermore, LvATF6α could reduce the apoptosis rate of Drosophila Schneider 2 (S2) cells treated with actinomycin, and knock-down expression of LvATF6α increased the apoptosis rate of shrimp hemocytes. In vivo testing revealed that the short from LvATF6α (LvATF6α-s) was obviously increased after UPR activation or WSSV infection, indicating that the ATF6 pathway was activated in L. vannamei gills under such circumstances. Moreover, knock-down expression of LvATF6α could reduce the cumulative mortality and WSSV copy number in WSSV-infected shrimp. Further study revealed that WSSV may profit from shrimp ATF6 pathway activation in two aspects. First, LvATF6α-s significantly upregulated the expression of the WSSV genes (wsv023, wsv045, wsv083, wsv129, wsv222, wsv249, and wsv343). Second, LvATF6α-s inhibited apoptosis by negatively regulating the apoptosis signal-regulating kinase 1 - (c-Jun N-terminal kinase) pathway. All of these evidences suggested that the ATF6 pathway is a member of the L. vannamei UPR, and it is also engaged in WSSV infection.

Increased nucleoside diphosphate kinase activity induces white spot syndrome virus infection in Litopenaeus vannamei.

Nucleoside diphosphate kinase (NDK), which has the same sequence as oncoprotein (OP) in humans, can induce nucleoside triphosphates in DNA replication by maintenance of the deoxynucleotide triphosphate (dNTP’s) and is known to be regulated by viral infection in the shrimp Litopenaeus vannamei. This paper describes the relationship between NDK and white spot syndrome virus (WSSV) infection. The recombinant NDK was produced by a prokaryotic expression system. WSSV copy numbers and mRNA levels of IE1 and VP28 were significantly increased in shrimp injected with recombinant NDK at 72 h after WSSV infection. After synthesizing dsRNA-NDK and confirming the efficacy of NDK silencing, we recorded the cumulative mortality of WSSV-infected shrimp injected with NDK and dsRNA-NDK. A comparison between the results demonstrated that silencing NDK delayed the death of shrimps. These findings indicate that NDK has an important role influencing the replication of WSSV replication in shrimp. Furthermore, NDK may have potential target as a new therapeutic strategy against WSSV infection in shrimp.

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.

Anti-melanization mechanism of the white spot syndrome viral protein, WSSV453, via interaction with shrimp proPO-activating enzyme, PmproPPAE2.

Inhibition of the host melanization reaction, activated by the prophenoloxidase activating (proPO) system, is one of the crucial evasion strategies of pathogens. Recently, the shrimp pathogen, white spot syndrome virus (WSSV), was found to inhibit melanization in the shrimp Penaeus monodon. The viral protein WSSV453 was previously shown to interact with PO-activating enzyme 2 (PmPPAE2) and reported to be involved in suppressing the shrimp melanization response after WSSV infection. Here, we characterized how WSSV453 inhibits melanization. WSSV453 is a non-structural viral protein, which was first detected in shrimp haemocytes at 6 hours post-infection (hpi) by WSSV and in shrimp plasma at 24 hpi. We produced recombinant proteins for three components of the P. monodon proPO system: PmproPPAE2, PmproPO1 and PmproPO2. Functional assays showed that active PmPPAE2 processed PmproPO1 and 2 to produce functional PO. Incubation of WSSV453 with PmproPPAE2 dose-dependently reduced PmPPAE2 activity toward PmPO1 or PmPO2. In contrast, WSSV453 had no effect on activated PmPPAE2. The addition of active PmPPAE2 to WSSV-infected shrimp plasma at day 2 post-infection also rescued PO activity. Taken together, these results indicate that the anti-melanization activity of WSSV is due to WSSV453, which interacts with PmproPPAE2 and interferes with its activation to active PmPPAE2.

Wsv023 interacted with Litopenaeus vannamei γ-tubulin complex associated proteins 2, and decreased the formation of microtubules.

A previous study found the key transcription factor of Litopenaeus vannamei PERK-eIF2α pathway cyclic AMP-dependent transcription factor 4 (LvATF4) was involved in the transcriptional regulation of white spot syndrome virus (WSSV) gene wsv023. Knocked-down expression of LvATF4 reduced the viral copy number and the cumulative mortality of WSSV-infected shrimp. These results suggested that wsv023 may be critical to WSSV infection but the precise function of wsv023 was still unknown. By using co-immunoprecipitation and pull-down assays, we show that wsv023 interacts with L. vannamei gamma complex-associated protein 2 (LvGCP2), which is the core protein of the γ-tubulin small complex. Knocked-down, the wsv023 gene significantly reduced the copy number of WSSV in L. vannamei muscle, as well as the cumulative mortality of infected shrimp. And PERK-eIF2α pathway inhibition also showed reduced virus copy number and abrogated shrimp mortality. Furthermore, overexpression of wsv023 inhibited the formation of microtubules in 293T cells. Flow cytometry revealed that WSSV infection similarly decreased the formation of microtubules in L. vannamei haemocytes. These findings suggested that wsv023 plays a role in microtubule organization in host cells, which in turn may be beneficial to WSSV.

Role of Litopenaeus vannamei Yin Yang 1 in the Regulation of the White Spot Syndrome Virus Immediate Early Gene ie1.

Yin Yang 1 (YY1) is a multifunctional zinc finger transcription factor that regulates many key cellular processes. In this study, we report the cloning of YY1 from Litopenaeus vannamei shrimp (LvYY1). This study shows that LvYY1 is ubiquitously expressed in shrimp tissues, and knockdown of LvYY1 expression by double-stranded RNA (dsRNA) injection in white spot syndrome virus (WSSV)-infected shrimp reduced both mRNA levels of the WSSV immediate early gene ie1 as well as overall copy numbers of the WSSV genome. The cumulative mortality rate of infected shrimp also declined with LvYY1 dsRNA injection. Using an insect cell model, we observed that LvYY1 activates ie1 expression, and a mutation introduced into the ie1 promoter subsequently repressed this capability. Moreover, reporter assay results suggested that LvYY1 is involved in basal transcriptional regulation via an interaction with L. vannamei TATA-binding protein (LvTBP). Electrophoretic mobility shift assay (EMSA) results further indicated that LvYY1 binds to a YY1-binding site in the region between positions -119 and -126 in the ie1 promoter. Chromatin immunoprecipitation analysis also confirmed that LvYY1 binds to the ie1 promoter in WSSV-infected shrimp. Taken together, these results indicate that WSSV uses host LvYY1 to enhance ie1 expression via a YY1-binding site and the TATA box in the ie1 promoter, thereby facilitating lytic activation and viral replication.IMPORTANCE WSSV has long been a scourge of the shrimp industry and remains a serious global threat. Thus, there is a pressing need to understand how the interactions between WSSV and its host drive infection, lytic development, pathogenesis, and mortality. Our successful cloning of L. vannamei YY1 (LvYY1) led to the elucidation of a critical virus-host interaction between LvYY1 and the WSSV immediate early gene ie1 We observed that LvYY1 regulates ie1 expression via a consensus YY1-binding site and TATA box. LvYY1 was also found to interact with L. vannamei TATA-binding protein (LvTBP), which may have an effect on basal transcription. Knockdown of LvYY1 expression inhibited ie1 transcription and subsequently reduced viral DNA replication and decreased cumulative mortality rates of WSSV-infected shrimp. These findings are expected to contribute to future studies involving WSSV-host interactions.

MicroRNA-100 is involved in shrimp immune response to white spot syndrome virus (WSSV) and Vibrio alginolyticus infection

In this study, we discovered that shrimp miR-100 was up-regulated at 24 h after WSSV or Vibrio alginolyticus infection, confirming its participation in the innate immune system of shrimp. The anti-miRNA oligonucleotide (AMO-miR-100) was applied to inhibit the expression of miR-100. After AMO-miR-100 treatment, the shrimp was challenged with WSSV or V. alginolyticus. The knockdown of miR-100 expression decreased the mortality of WSSV-infected shrimp from 24 h to 72 h post-infection and enhanced the mortality of V. alginolyticus-infected shrimp significantly. The knockdown of miR-100 affected phenoloxidase (PO) activity, superoxide dismutase (SOD) activity and total hemocyte count (THC) after the infection with WSSV or V. alginolyticus, indicating a regulative role of miR-100 in the immune potential of shrimp in the response to WSSV or V. alginolyticus infection. The knockdown of miR-100 induced the apoptosis of shrimp hemocytes, and V. alginolyticus + AMO-miR-100 treatment caused more hemocyte apoptosis than V. alginolyticus treatment. The miR-100 influenced also the morphology of shrimp hemocytes and regulated the phagocytosis of WSSV or V. alginolyticus. Thus, we concluded that miR-100 may promote the anti-Vibrio immune response of shrimp through regulating apoptosis, phagocytosis and PO activity and affects the progression of WSSV infection at a certain level.

High sensitivity immunochromatographic strip test (ICP11 strip test) for white spot syndrome virus detection using monoclonal antibodies specific to ICP11 non-structural protein

Two monoclonal antibodies (MAbs) specific to different epitopes on ICP11, a non-structural protein of white spot syndrome virus (WSSV), were employed to develop a highly sensitive immunochromatographic strip test (ICP11 strip test). One MAb (WI-11) was conjugated to colloidal gold to bind to ICP11 and another MAb (WI-16) was used to capture colloidal gold MAb-protein complexes at the test line (T) on the nitrocellulose strip. A downstream control line (C) of goat anti-mouse immunoglobulin G (GAM) antibody was used to capture the free colloidal gold conjugated MAb to validate the test performance. Homogenate of shrimp sample in application buffer could be applied directly to the application well and the test result was obtained within 15min. The sensitivity of the kit is 40 times more sensitive than the detection limit of previously reported strip test using MAbs specific to VP28, and approximately 400 times more sensitive than that of Shrimple®, but approximately 50 times less sensitive than that of one-step PCR. For experimentally WSSV-infected shrimps, the ICP11 strip could detect WSSV as early as 12–18h post infection. Due to its high specificity, simplicity and no requirement on sophisticated equipment or specialized skills, the strip test could be adopted to surveillance of early WSSV infection at the pond site.

Effect of silver nanoparticles on the metabolic rate, hematological response, and survival of juvenile white shrimp Litopenaeus vannamei

White spot syndrome virus (WSSV) is highly lethal and contagious in shrimps; its outbreaks causes an economic crisis for aquaculture. Several attempts have been made to treat this disease; however, to date, there is no effective cure. Because of their antimicrobial activities, silver nanoparticles (AgNPs) are the most studied nanomaterial. Although the antiviral properties of AgNPs have been studied, their antiviral effect against viral infection in aquaculture has not been reported. The AgNPs tested herein are coated with polyvinylpyrrolidone (PVP) and possess multiple international certifications for their use in veterinary and human applications.The aim of this work was to evaluate the survival rate of juvenile white shrimps (Litopenaeus vannamei) after the intramuscular administration of AgNPs. For this, different concentrations of metallic AgNPs and PVP alone were injected into the organisms. After 96 h of administration, shrimp survival was more than 90% for all treatments. The oxygen consumption routine rate and total hemocyte count remained unaltered after AgNP injection, reflecting no stress caused. We evaluated whether AgNPs had an antiviral effect in shrimps infected with WSSV. The results revealed that the survival rate of WSSV-infected shrimps after AgNP administration was 80%, whereas the survival rate of untreated organisms was only 10% 96 h after infection. These results open up the possibility to explore the potential use of AgNPs as antiviral agents for the treatment of diseases in aquaculture organisms, particularly the WSSV in shrimp culture.

Effect of mixed-Bacillus spp isolated from pustulose ark Anadara tuberculosa on growth, survival, viral prevalence and immune-related gene expression in shrimp Litopenaeus vannamei

The widespread overuse of antibiotics in aquaculture has led to the emergence of antibiotic-resistance shrimp pathogens, the negative impact on shrimp gut microbiota, and the presence of antimicrobial residues in aquaculture products, with negative consequences on human health. Alternatively, probiotics have positive effects on immunological responses and productive performance of aquatic animals. In this study, three probiotic bacteria, (Bacillus licheniformis MAt32, B. subtilis MAt43 and B. subtilis subsp. subtilis GAtB1), isolated from the Anadara tuberculosa were included in diets for juvenile shrimp, Litopenaeus vannamei, to evaluate their effects on growth, survival, disease prevalence, and immune-related gene expression. Shrimp naturally infected with WSSV and IHHNV were fed with the basal diet (control, T1) and diets supplemented with four levels of bacilli probiotic mix (1:1:1) at final concentration of (T2) 1 × 106, (T3) 2 × 106, (T4) 4 × 106, and (T5) 6 × 106 CFU g−1 of feed. The specific growth rate of shrimp was significantly higher in T2 than in T1 (control) treatment, and the final growth as well as the survival were similar among treated groups. The prevalence of WSSV and IHHNV infected shrimp was reduced in T2 and T4 treatments, respectively, compared with control. The mRNA expression of proPO gene was higher in treatment T4 than control. The LvToll1 gene was significantly up-regulated in treatments T4 and T5 compared to control. The SOD gene was up-regulated in treatment T5 compared to control. In contrast, the mRNA expression of the Hsp70 gene was down-regulated in treatments T4 and T5 respect to control, and the TGase gene remained unaffected by the level of bacillus probiotic mix. As conclusion, the bacilli probiotic mix (Bacillus spp.) enhanced immune-related gene expression in WSSV and IHHNV naturally infected shrimp. This is the first report of probiotic potential of bacteria isolated from A. tuberculosa on the immune response and viral prevalence in shrimp Litopenaeus vannamei.

The Dorsal/miR-1959/Cactus feedback loop facilitates the infection of WSSV in Litopenaeus vannamei.

miR-1959, a novel microRNA identified from Litopenaeus vannamei, mediates a positive feedback loop between Dorsal and Cactus that can continuously maintain the activation of the NF-κB pathway. It has been known that miR-1959 is involved in antibacterial immunity in shrimp, but its function in antiviral responses is still unknown. In this study, we focused on the role of miR-1959 in infection of white spot syndrome virus (WSSV), the major viral pathogen in shrimp worldwide. The expression of miR-1959 in shrimp hemocytes, gill, and hepatopancreas was significantly up-regulated upon WSSV infection. Dual-luciferase reporter assays demonstrated that miR-1959 could enhance the activity of the promoter of WSSV immediate early gene ie1. Invivo experiments also showed that inhibition of miR-1959 led to decrease of the mortality of WSSV-infected shrimp and the genome copies of WSSV in tissues, meanwhile the expression of WSSV ie1 and VP28 genes was down-regulated. In contrast, increase of the miR-1959 level in shrimp by injection of miR-1959 mimics produced opposite results. These suggested that the Dorsal/miR-1959/Cactus feedback loop could favor the infection of WSSV in shrimp. Thus, our study helps further reveal the interaction between WSSV and shrimp immune system.

Six Hours after Infection, the Metabolic Changes Induced by WSSV Neutralize the Host's Oxidative Stress Defenses.

Levels of intracellular ROS (reactive oxygen species) were significantly increased in hemocytes collected from WSSV-infected shrimp within the first 30–120 min after infection. Measurement of the NADPH/NADP+ and GSH/GSSG ratios revealed that after a significant imbalance toward the oxidized forms at 2 hpi, redox equilibrium was subsequently restored. Meanwhile, high levels of lactic acid production, elevated NADH/NAD+ ratios, and metabolic changes in the glycolysis pathway show that the Warburg effect was triggered by the virus. The timing of these changes suggests that WSSV uses this metabolic shift into aerobic glycolysis to counteract the high levels of ROS produced in response to viral infection. We further show that if the Warburg effect is inhibited by chemical inhibition of the PI3K-Akt-mTOR signaling pathway, or if the pentose phosphate pathway is chemically inhibited, then in both cases, the production of intracellular ROS is sustained. We conclude that WSSV uses the PI3K-Akt-mTOR-regulated Warburg effect to restore host redox balance and to counter the ROS produced by the host in response to WSSV infection. We also found that pyruvate kinase activity was inhibited by WSSV. This inhibition is likely to increase the availability of the raw materials essential for WSSV gene expression and replication.

Virus-derived small RNAs in the penaeid shrimp Fenneropenaeus chinensis during acute infection of the DNA virus WSSV.

Small interfering RNAs (siRNAs) and microRNAs (miRNAs) are two classes of small RNAs (sRNAs) that are critical for virus-host interplay via the RNA interference (RNAi) pathway. One virus-derived siRNA and numerous miRNAs has been reported for the double-stranded DNA virus white spot syndrome virus (WSSV), however, the expression profiles of these different types of sRNAs have not been assessed. Here, by sequencing the sRNAs and mRNAs of WSSV-infected Chinese shrimp (Fenneropenaeus chinensis), we found that the viral transcripts were universally targeted by WSSV-derived siRNAs, supporting a pivotal role for RNAi in the anti-viral immunity of shrimp. The genesis of WSSV-derived siRNAs was associated with long RNA structures. Moreover, by separating miRNAs from siRNAs, 12 WSSV miRNAs were identified. Investigation of conserved viral miRNA targets in different host species indicated the involvement of viral miRNAs in host immune responses. Collectively, our data provide new insights into the role of the RNAi pathway in the interplay between DNA viruses and crustaceans.

Identification and functional characterization of a glucose regulated protein 94 gene in Litopenaeus vannamei and its responsiveness in WSSV infection.

In the current study, a cDNA of glucose regulated protein 94 (LvGRP94) was cloned from Litopenaeus vannamei. Subcellular localization assay revealed that LvGRP94 expressed in endoplasmic reticulum (ER). And results of reported gene assays demonstrated that the promoter of LvGRP94 was activated by L. vannamei leucine zipper domain transcription factor X-box binding protein 1 (LvXBP1) or heat shock treatment. Furthermore, LvGRP94 was found to highly express in hemocytes as well as in epidermis by real-time RT-PCR. In addition, it was shown that LvGRP94 inhibited by LvXBP1 knocked-down in the hemocytes, was induced by white spot syndrome virus (WSSV) infection, or unfolded protein response (UPR) pathway activation. Importantly, decreasing LvGRP94 reduced the cumulative mortality of WSSV-infected shrimps and WSSV copies in shrimp muscle. These results suggested that LvGRP94 might involve in shrimp UPR pathway as well as WSSV infection.