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

Effects of Low-Fish-Meal Diet Supplemented with Coenzyme Q10 on Growth Performance, Antioxidant Capacity, Intestinal Morphology, Immunity and Hypoxic Resistance of Litopenaeus vannamei

The aim of this study was to evaluate the effects of a low-fish-meal diet supplemented with coenzyme Q10 on the growth, antioxidant capacity, immunity, intestinal health and hypoxic resistance of Litopenaeus vannamei. L.vannamei with an initial weight of 0.66 g were fed with the experimental diets for 56 days. Diets D1 (20% FM level) and D2-D7 (15% FM level), supplemented with 0%, 0.002%, 0.004%, 0.006%, 0.008% and 0.01% coenzyme Q10 were formulated. In terms of growth performance, the weight gain and specific growth rate in the D2 diet were significantly lower than those in the D1 diet (p < 0.05). The final body weight, weight gain and specific growth rate in the D2-D7 diets had an upward trend, and the condition factor in the D2-D7 diets was lower than those in the D1 diet (p < 0.05). There were no significant differences in the crude protein and crude lipid levels in the whole body among all diet treatments (p > 0.05). In terms of hepatopancreas antioxidant parameters, the D5 and D6 diets significantly promoted the total antioxidant capacity and total superoxide dismutase activity, and significantly decreased the malondialdehyde content (p < 0.05). The expression levels of cat, mnsod and gpx in shrimp fed with the D5 and D6 diets were significantly higher than those of shrimp fed with the D2 diet (p < 0.05). In addition, the mRNA level of ProPO was increased in the D4 and D5 diets, and LZM expression was increased in the D6 diet compared with the D1 diet (p < 0.05). The villus height of shrimp fed with diets supplemented with coenzyme Q10 was significantly increased (p < 0.05), and the intestinal thickness and submucosal thickness of shrimp fed with the D6 diet were the highest (p < 0.05). After acute hypoxia stress, lethal dose 50 time in the D3-D7 diets was significantly increased compared with the D1 and D2 diets (p < 0.05), and the highest value was found in the D4 diet (p < 0.05). After stress, the expression levels of TLR pathway-related genes (Toll, Myd88, Pelle, TRAF6 and Dorsal) in the D4 and D6 diets were significantly increased compared with the D2 diet. In general, Litopenaeus vannamei fed with the D6 diet achieved the best growth, antioxidant capacity, immunity, and intestinal morphology among all low FM diets and D4-D6 diets improved hypoxic resistance.

Identification and characterization of mitogen-activated protein kinase kinase 4 (MKK4) from the mud crab Scylla paramamosain in response to Vibrio alginolyticus and White Spot Syndrome Virus (WSSV)

Mitogen-activated protein kinase kinase 4 (MKK4), serves as a critical component of the mitogen-activated protein kinase signaling pathway, facilitating the direct phosphorylation and activation of the c-Jun N-terminal kinase (JNK) and p38 families of MAP kinases in response to environmental stresses. In the current research, we identified two MKK4 subtypes, namely SpMKK4-1 and SpMKK4-2, from Scylla paramamosain, followed by the analysis of their molecular characteristics and tissue distributions. The expression of SpMKK4s was induced upon WSSV and Vibrio alginolyticus challenges, and the bacteria clearance capacity and antimicrobial peptide (AMP) genes' expression upon bacterial infection were significantly decreased after knocking down SpMKK4s. Additionally, the overexpression of both SpMKK4s remarkably activated NF-κB reporter plasmid in HEK293T cells, suggesting the activation of the NF-κB signaling pathway. These results indicated the participation of SpMKK4s in the innate immunity of crabs, which shed light on a better understanding of the mechanisms through which MKK4s regulate innate immunity.

Marine Invertebrate Antimicrobial Peptides and Their Potential as Novel Peptide Antibiotics

Marine invertebrates constantly interact with a wide range of microorganisms in their aquatic environment and possess an effective defense system that has enabled their existence for millions of years. Their lack of acquired immunity sets marine invertebrates apart from other marine animals. Invertebrates could rely on their innate immunity, providing the first line of defense, survival, and thriving. The innate immune system of marine invertebrates includes various biologically active compounds, and specifically, antimicrobial peptides. Nowadays, there is a revive of interest in these peptides due to the urgent need to discover novel drugs against antibiotic-resistant bacterial strains, a pressing global concern in modern healthcare. Modern technologies offer extensive possibilities for the development of innovative drugs based on these compounds, which can act against bacteria, fungi, protozoa, and viruses. This review focuses on structural peculiarities, biological functions, gene expression, biosynthesis, mechanisms of antimicrobial action, regulatory activities, and prospects for the therapeutic use of antimicrobial peptides derived from marine invertebrates.

A novel tumor necrosis factor receptor-associated factor 6 (TRAF6) gene from Macrobrachiumrosenbergii involved in antibacterial defense against Aeromonas hydrophila

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an adapter protein that triggers downstream cascades mediated by both TNFR and the interleukin-1 receptor/Toll-like receptor (IL-1R/TLR) superfamily. TRAF6 is involved in various biological processes, including innate and adaptive immunity. In the present study, a homolog of TRAF6 from Macrobrachium rosenbergii (MrTRAF6) was identified and characterized. The full-length cDNA of MrTRAF6 consisted of 2,114 nucleotides with an open reading frame (ORF) of 1,695 nucleotides encoding a 564-amino acid protein that contained a conserved TRAF family motif including two RING-type zinc fingers and a C-terminal meprin and TRAF homology (MATH) domain. The putative amino sequence of MrTRAF6 shared 45.5-97.3% identity with TRAF6s from other crustacean species with the highest identity to Macrobrachium nipponense TRAF6. Phylogenetic analysis revealed that MrTRAF6 was closely related to TRAF6 of invertebrates and clustered with crustaceans. According to gene expression analysis, the MrTRAF6 transcript demonstrated broad expression in all tissues tested, with the highest expression level in gill and the lowest in muscle tissues. Upon immune challenge with Aeromonas hydrophila, significant upregulation of MrTRAF6 expression was found in the gill, hepatopancreas, hemocyte, and muscle. Furthermore, an RNA interference assay showed that silencing MrTRAF6 by dsRNA could reduce the expression of mannose-binding lectin (MBL) and crustin, but no significant change was detected in anti-lipopolysaccharide factor 5 (ALF5) levels. In addition, the cumulative mortality rate of MrTRAF6-silenced M. rosenbergii was significantly increased after A. hydrophila infection. These findings indicated that MrTRAF6 is involved in antibacterial activity and plays a critical role in the innate immune response of M. rosenbergii.

Duox mediated ROS production inhibited WSSV replication in Eriocheir sinensis under short-term nitrite stress

Nitrite stress and white spot syndrome virus (WSSV) infection are major problems threatening the sustainable and healthy development of Eriocheir sinensis. Some studies have found that nitrite stress can lead to the production of reactive oxygen species (ROS), whereas synthetic ROS plays a vital role in the signaling pathway. However, whether nitrite stress influences the infection of crabs by WSSV remains unclear. NADPH oxidases, including NOX1-5 and Duox1-2, are important for ROS production. In the present study, a novel Duox gene (designated as EsDuox) was identified from E. sinensis. The studies found that nitrite stress could increase the expression of EsDuox during WSSV infection and decrease the transcription of the WSSV envelope protein VP28. Moreover, nitrite stress could increase the production of ROS, and the synthesis of ROS relied on EsDuox. These results indicated a potential "nitrite stress-Duox activation-ROS production" pathway that plays a negative role in WSSV infection in E. sinensis. Further studies found that nitrite stress and EsDuox could promote the expression of EsDorsal transcriptional factor and antimicrobial peptides (AMPs) during WSSV infection. Moreover, the synthesis of AMPs was positively regulated by EsDorsal in the process of WSSV infection under nitrite stress. Furthermore, EsDorsal played an inhibitory role in the replication of WSSV under nitrite stress. Our study reveals a new pathway for "nitrite stress-Duox activation-ROS production-Dorsal activation-AMP synthesis" that is involved in the defense against WSSV infection in E. sinensis during short-term nitrite stress.

HSP40 mediated TLR-Dorsal-AMPs pathway in Portunus trituberculatus

Heat shock protein 40 (HSP40) is a kind of molecular chaperone involved in various immune responses. However, the exact roles of HSP40 in immune defense against bacteria remain largely unclear. In this study, the activation function of a type Ⅰ HSP40 from Portunus trituberculatus (PtHSP40-Ⅰ) in the TLR pathway was investigated. The results showed that PtHSP40-Ⅰ can bind to lipopolysaccharide (LPS) and peptidoglycan (PGN). The PtHSP40-Ⅰ also exhibited binding activity toward the extracellular leucine-rich repeat (LRR) domain of Toll-like receptor (TLR). Moreover, the PtHSP40-Ⅰ could promote the transcription factor Dorsal translocated from cytoplasm into the nucleus in hemocytes and participated in regulating the expression of anti-lipopolysaccharide factor (ALF) and crustin. These findings provided insights into the activation mechanisms of TLR pathway mediated by HSP40 and offered basic theory of disease control in P. trituberculatus aquaculture.

White spot syndrome virus impact on the expression of immune genes and gut microbiome of black tiger shrimp Penaeus monodon

The gut microbiome plays an essential role in the immune system of invertebrates and vertebrates. Pre and pro-biotics could enhance the shrimp immune system by increasing the phenoloxidase (PO), prophenoloxidase (ProPO), and superoxide dismutase activities. During viral infection, the host immune system alteration could influence the gut microbiome composition and probably lead to other pathogenic infections. Since the JAK/STAT pathway is involved in white spot syndrome virus (WSSV) infection, we investigated the intestine immune genes of STAT-silenced shrimp. During WSSV infection, expression levels of PmVago1, PmDoral, and PmSpätzle in PmSTAT-silenced shrimp were higher than normal. In addition, the transcription levels of antimicrobial peptides, including crustinPm1, crustinPm7, and PmPEN3, were higher in WSSV-challenged PmSTAT-silenced shrimp than the WSSV-infected normal shrimp. Meanwhile, PmSTAT silencing suppressed PmProPO1, PmProPO2, and PmPPAE1 expressions during WSSV infection. The microbiota from four shrimp tested groups (control group, WSSV-infected, PmSTAT-silenced, and PmSTAT-silenced infected by WSSV) was significantly different, with decreasing richness and diversity due to WSSV infection. The relative abundance of Bacteroidetes, Actinobacteria, and Planctomycetes was reduced in WSSV-challenged shrimp. However, at the species level, P. damselae, a pathogen to human and marine animals, significantly increased in WSSV-challenged shrimp. In constrast, Shewanella algae, a shrimp probiotic, was decreased in WSSV groups. In addition, the microbiota structure between control and PmSTAT-silenced shrimp was significantly different, suggesting the importance of STAT to maintain the homeostasis interaction with the microbiota.

Characterisation of a novel crustin isoform from mud crab, Scylla serrata (Forsskål, 1775) and its functional analysis in silico

A 336-base pair (bp) sized mRNA sequence encoding 111 amino acid size crustin isoform (MC-crustin) was obtained from the gill sample of the green mud crab, Scylla serrata. MC-crustin possessed an N-terminal signal peptide region comprising of 21 amino acid residues, followed by a 90 amino acid mature peptide region having a molecular weight of 10.164 kDa, charge + 4.25 and theoretical pI of 8.27. Sequence alignment and phylogenetic tree analyses revealed the peptide to be a Type I crustin, with four conserved cysteine residues forming the cysteine rich region, followed by WAP domain. MC-crustin was cationic with cysteine/proline rich structure and was predicted with antimicrobial, anti-inflammatory, anti-angiogenic and anti-hypertensive property making it a potential molecule for possible therapeutic applications.

Bovine lactoferricin on non-specific immunity of giant freshwater prawns, Macrobrachium rosenbergii

This study aimed to investigate the effects of dietary Bovine lactoferricin (LFcinB) on the growth performance and non-specific immunity in Macrobrachium rosenbergii. Five experimental diets were 1.0‰ Bovine lactoferricin (LCB1); 1.5‰ Bovine lactoferricin (LCB1.5); 2.0‰ Bovine lactoferricin (LCB2); 2.5‰ Bovine lactoferricin (LCB2.5); the control group, basal diet without Bovine lactoferricin. A total of 600 prawns were randomly assigned to 5 groups in triplicate in 15 tanks for an 8-week feeding trial. The results showed the final weight, weight gain rate, specific growth rate and survival rate of prawns in the treatment groups were significantly improved versus the control (P < 0.05). The feed conversion ratio was reduced significantly in treatment groups compared to the control (P < 0.05). Compared with the control, alkaline phosphatase (AKP), acid phosphatase (ACP), lysozyme (LZM), catalase (CAT), superoxide dismutase (SOD) activities in the hepatopancreas of the treatment groups were significantly enhanced, and malondialdehyde (MDA) content was reduced significantly (P < 0.05). Compared with the control, the relative expression levels of AKP, ACP, LZM, CAT, SOD, Hsp70, peroxiredoxin-5, Toll, dorsal and relish genes were significantly higher among treatment groups, except for the AKP gene in the LCB1 group and the Hsp70 gene in the LCB1.5 group (P < 0.05). Compared with the control, the relative expression levels of TOR, 4E-BP, eIF4E1α and eIF4E2 genes were significantly enhanced in the LCB1.5 group (P < 0.05). When resistance against Vibrio parahaemolyticus in prawn is considered, higher doses of Bovine lactoferricin show better antibacterial ability. The present study indicated that dietary Bovine lactoferricin could significantly improve the growth performance and improve the antioxidative status of M. rosenbergii. The suitable addition level is 1.5 g/kg. LFcinB has great potential as a new feed additive without the threat of drug resistance.

NF-κB-coupled IL17 mediates inflammatory signaling and intestinal inflammation in Artemia sinica

Nuclear factor-κB (NF-κB) plays a role as a rheostatic transcription factor in regulating intestinal inflammation, and its disruption or constitutive activation leads to inflammation and injury. However, the molecular mechanisms of NF-κB regulation remain largely unknown. In this study, the NF-κB-regulated host defenses against pathogen infections and facilitation of IL17 expression during stimulation with different bacteria were investigated. Intestinal inflammation was induced by dextran sulfate sodium, and NF-κB activity was inhibited in an intestinal injury model. Mannose receptor C type, ABF1/2, serpin B13, lysozyme, and β-arrestin were significantly controlled by NF-κB in the inflamed intestinal tissue. High levels of NF-κB activation resulted in less pervasive intestinal damage and the maintenance of intestinal barrier integrity. Intestinal injury robustly increased the expression of IL17. NF-κB activation was enhanced by IL17 deficiency in the intestinal injury model. IL17 inhibition aggravated intestinal inflammation, leading to loss of epithelial architecture and the infiltration of inflammatory cells. These data suggest that NF-κB and IL17 play key mediator roles in the maintenance of gut epithelial integrity and immune homeostasis.

Marine Arthropods as a Source of Antimicrobial Peptides

Peptide therapeutics play a key role in the development of new medical treatments. The traditional focus on endogenous peptides has shifted from first discovering other natural sources of these molecules, to later synthesizing those with unique bioactivities. This review provides concise information concerning antimicrobial peptides derived from marine crustaceans for the development of new therapeutics. Marine arthropods do not have an adaptive immune system, and therefore, they depend on the innate immune system to eliminate pathogens. In this context, antimicrobial peptides (AMPs) with unique characteristics are a pivotal part of the defense systems of these organisms. This review covers topics such as the diversity and distribution of peptides in marine arthropods (crustacea and chelicerata), with a focus on penaeid shrimps. The following aspects are covered: the defense system; classes of AMPs; molecular characteristics of AMPs; AMP synthesis; the role of penaeidins, anti-lipopolysaccharide factors, crustins, and stylicins against microorganisms; and the use of AMPs as therapeutic drugs. This review seeks to provide a useful compilation of the most recent information regarding AMPs from marine crustaceans, and describes the future potential applications of these molecules.

Redclaw crayfish (Cherax quadricarinatus) responds to Vibrio parahaemolyticus infection by activating toll and immune deficiency signaling pathways and transcription of associated immune response genes

In invertebrates, several genes controlled by the Toll and immunodeficiency (IMD) signaling cascade are altered during microbial infection. However, little is known about the expression patterns of innate immune response genes in red-clawed crayfish (Cherax quadricarinatus). In the present study, the transcription of five genes was assessed in C. quadricarinatus challenged with Vibrio parahaemolyticus (V. parahaemolyticus). The expression of Relish, Toll-like receptor (TLR), tumor necrosis factor receptor-related factor 6 (TRAF6), Akirin, and IMD in different tissues and at different time points after infection were assessed. In addition, the Relish gene was amplified, the protein conformation of the Relish gene was predicted, and gene expression changes associated with antimicrobial peptide production in C. quadricarinatus were analyzed using RNA interference (RNAi). During V. parahaemolyticus infection, the transcripts of the above five genes were significantly increased in the hepatopancreas of C. quadricarinatus (P < 0.05). In contrast, TLR was significantly downregulated in muscle tissue at the initial stage of infection (P < 0.05); TRAF6 and IMD were significantly down-regulated throughout infection (P < 0.05); Akirin transcripts had the lowest abundance at 24 h post-infection; Relish, IMD and Akirin genes were significantly up-regulated in gill tissue at the early stage of infection (P < 0.05); only TRAF6 was significantly up-regulated at 6, 24 and 48 h after infection. The Relish gene of C. quadricarinatus is closely related to the Exopalaemon carinicauda. When the Relish gene was knocked down by RNAi, the V. parahaemolyticus challenge showed that the mortality rate of the RANi group was significantly higher than that of the NC group; pathological sections showed that the hepatopancreatic tissue damage was the most severe 12 h after the interference; and the interference significantly inhibited IRF4, NF-κB, ALF, laccase, SOD1, and lectin genes. Therefore, it can be hypothesized that the Toll and IMD pathways are activated in C. quadricarinatus in response to bacterial infection and that genes associated with these pathways are differentially transcribed in different tissues. This study provides insights into the Toll and IMD signaling pathways and the spatiotemporal expression of key genes regulating bacterial infection resistance in C. quadricarinatus.

High-Fat-Diet-Induced Oxidative Stress in Giant Freshwater Prawn (Macrobrachium rosenbergii) via NF-κB/NO Signal Pathway and the Amelioration of Vitamin E

Lipids work as essential energy sources for organisms. However, prawns fed on high-fat diets suffer from oxidative stress, whose potential mechanisms are poorly understood. The present study aimed to explore the regulation mechanism of oxidative stress induced by high fat and the amelioration by vitamin E (VE) of oxidative stress. Macrobrachium rosenbergii were fed with two dietary fat levels (LF 9% and HF 13%) and two VE levels (200 mg/kg and 600 mg/kg) for 8 weeks. The results showed that the HF diet decreased the growth performance, survival rate and antioxidant capacity of M. rosenbergii, as well as inducing hypertrophied lipid droplets, lipophagy and apoptosis. A total of 600 mg/kg of VE in the HF diet alleviated the negative effects induced by HF. In addition, the HF diet suppressed the expression of toll-dorsal and imd-relish signal pathways. After the relish and dorsal pathways were knocked down, the downstream iNOS and NO levels decreased and the MDA level increased. The results indicated that M. rosenbergii fed with a high-fat diet could cause oxidative damage. Its molecular mechanism may be attributed to the fact that high fat suppresses the NF-κB/NO signaling pathway mediating pro-oxidant and antioxidant targets for regulation of oxidative stress. Dietary VE in an HF diet alleviated hepatopancreas oxidative stress and apoptosis.

Effects of dietary tea tree oil on the growth, physiological and non-specific immunity response in the giant freshwater prawn (Macrobrachium rosenbergii) under high ammonia stress

This study aimed to investigate the effects of dietary tea tree oil (TTO) on the performance, intestinal antioxidant capacity, and non-specific immunity after ammonia nitrogen stress in Macrobrachium rosenbergii. Six experimental diets were formulated with 0, 25, 50, 100, 200, 400 mg/kg TTO, respectively. A total of 900 prawns (average initial weight, 0.39 ± 0.01 g) were randomly assigned to 6 groups in triplicate in 18 tanks. After an 8-week feeding trial, 20 prawns from each tank were changed with 20 mg/L ammonia stress for 24 h. The results showed that 100 mg/kg TTO significantly increased prawns performance and survival rate compared with the control group. Moreover, 100 and 200 mg/kg TTO significantly improved intestinal antioxidant capabilities by increasing SOD enzyme activities and decreasing MDA levels. In addition, the prawns fed with 100 mg/kg TTO diet showed the highest survival rate under ammonia stress. After ammonia stress, the group of 100 mg/kg TTO significantly improved antioxidant capacity by increasing hemolymph respiratory burst activity, as well as intestinal anti-superoxide anion activity and SOD. Coincidentally, 100 mg/kg TTO significantly upregulated the intestinal relative expression of antioxidant-related genes (peroxiredoxin-5). Further, it was found that 100 mg/kg TTO activated the toll-dorsal pathway in prawns, which performed the similar function as the classic NF-κB pathway by upregulating the TNF-α and IL-1. Finally, 100 mg/kg TTO increased the levels of iNOS activities and NO contents after ammonia stress and enhanced non-specific immunity. The results indicated that 100 mg/kg TTO could significantly improve the M. rosenbergii performance, antioxidant capacity and ammonia stress resistance. We suggested that the mechanisms may be attributed to that TTO enhanced the antioxidant capacity and non-specific immunity of M. rosenbergii via the NF-κB signal pathway.

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

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

Innate immune responses against viral pathogens in Macrobrachium

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

TRIM9 is involved in facilitating Vibrio parahaemolyticus infection by inhibition of relish pathway in Penaeus monodon

Tripartite motif-containing 9 (TRIM9) has been demonstrated to exert important roles in regulation of innate immune signaling. In this study, a novel TRIM9 homolog was identified from Penaeus monodon (named PmTRIM9). The open reading frame (ORF) of PmTRIM9 was 2064 bp, which encoding a 687-amino-acid polypeptide. Following Vibrio parahaemolyticus challenge, the expression levels of PmTRIM9 mRNA were significantly down-regulated in tested tissues. RNA interference and recombinant protein injection experiments were performed to explore the function of PmTRIM9, and the results showed it could facilitate V. parahaemolyticus replication and lead P. monodon more vulnerable to V. parahaemolyticus challenge. The dual-luciferase reporter assay showed that PmTRIM9 possessed the ability to inhibit the promoter activity in HEK293 T cells. Silencing of PmTRIM9 could increase the expression of the major NF-κB transcription factor, PmRelish. Further studies showed that knockdown of PmRelish promoted the V. parahaemolyticus infection and decreased the expression of specific antimicrobial peptides (AMPs), including PmCRU5, PmCRU7, PmALF6, PmALF3, PmLYZ and PmPEN5. However, knockdown of PmTRIM9 increased expression levels of the same AMPs, but except for PmCRU5, indicating that PmTRIM9 may negatively regulate the PmRelish-mediated expression of AMPs. All these results suggest that PmTRIM9 was involved in facilitating V. parahaemolyticus infection by inhibition of Relish pathway in P. monodon.

Litopenaeus vannamei Notch interacts with COP9 signalosome complex subunit 1 (CNS1) to negatively regulate the NF-κB pathway

Notch signaling pathway is a highly evolutionary conserved signaling pathway, which modulates many biological processes such as cell differentiation, tissue development and immune response. Our previous study revealed that Litopenaeus vannamei Notch (LvNotch) was involved in immune response by regulating reactive oxygen species (ROS) production in hemocytes. However, the immune regulatory networks mediated by LvNotch remain unclear in shrimp. In this study, 21 proteins that potentially interact with LvNotch were identified by GST pull-down and liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses. Among these proteins, COP9 signalosome complex subunit 1 (CSN1) was chosen for further studies due to its putative role in immune response. The interaction between LvNotch and LvCSN1 was confirmed by Far-Western blot and GST pull-down analyses. In vivo knockdown of LvNotch resulted in an increase in LvCSN1 expression in hemocytes, which suggest that the COP9 signalosome complex might be negatively regulated by LvNotch. In addition, in vivo silencing of LvNotch upregulated the expression of LvDorsal, LvTNFSF and LvCrustin2 (NF-κB pathway related-genes), while their expression decreased after LvCSN1 depletion. Collectively, the current results indicate that LvNotch negatively regulates the NF-κB pathway by modulating LvCSN1 in shrimp. SIGNIFICANCE: Although the Notch signaling pathway has been implicated in the regulation of immune response in vertebrates and invertebrates, the functions and immune-related interacting networks of Notch in shrimp immune response remain unknown. In this study, twenty-one proteins including COP9 signalosome complex subunit 1 (CSN1) were identified as potential interacting partners of LvNotch. Further analysis revealed that LvNotch negatively regulates the NF-κB pathway by binding to CSN1 and modulating its expression. These findings for the first time suggest that the Notch signaling pathway has cross-talk with the NF-κB pathway in shrimp as part of the immune response.

Identification of a dorsal transcription factor (MnDorsal) from Macrobrachium nipponense and its role in innate immunity

Rel/nuclear factor (NF)-κB family of transcription factors paly vital roles in innate immunity response to bacterial and viral infection. Here, we cloned and identified a dorsal homologue (named as MnDorsal) from Macrobrachium nipponense. The full-length cDNA of MnDorsal is 2573 bp with a 1986 bp open reading frame that encodes 661 amino acids. Predicted MnDorsal protein contained a RHD (Rel homology domain), an IPT (Iglike, plexins, and transcriptions factors) domain, and two low complexity regions. Phylogenetic analysis showed that MnDorsal has a closer genetic distance with dorsal homologues from invertebrates. MnDorsal was widely expressed in a variety of tissues, including hemocytes, heart, hepatopancreas, gills, stomach, and intestine. Expression patterns analysis showed that the transcriptional level of MnDorsal in the gills was evidently up-regulated after Staphylococcus aureus, Vibrio parahaemolyticus, white spot syndrome virus, or polyinosinic-polycytidylic acid challenge, suggesting that MnDorsal participates in the immune defenses against pathogens and stimulant challenges. Additionally, the dsRNA-mediated RNA interference analysis showed that knockdown of MnDorsal can significantly inhibit the expression of anti-lipopolysaccharide factor (ALF) and crustin. Further studies revealed that the up-regulated expression of ALFs (MnALF2, MnALF3, and MnALF4) and crustins (MnCrustin3 and MnCrustin4) caused by S. aureus infection were obviously decreased after silencing MnDorsal. These findings suggest that MnDorsal positively regulate the expression of antibacterial peptides (AMPs) during S. aureus infection. Our study will promote to better understand the role of Toll-Dorsal-AMPs pathway in innate immunity response to gram-positive bacterial infection in crustacean.

Response of Macrobrachium rosenbergii to Vegetable Oils Replacing Dietary Fish Oil: Insights From Antioxidant Defense

The study was conducted to evaluate the effects of fish oil replacement by vegetable oils on growth performance, histology, and antioxidant capacity of Macrobrachium rosenbergii. Three isonitrogenous and isoenergetic diets were formulated with different lipid sources included. DFO diet contained 6% fish oil, whereas DSO and DRO diets included 6% soybean oil and rapeseed oil (RO) as alternatives for fish oil, respectively. Prawns were fed thrice daily for 8 weeks. The results showed that prawns in DFO group showed significantly lower final weight, weight gain ratio, and specific growth rate (SGR), but higher feed intake and feed coefficient ratio than those in DSO and DRO groups. In hepatocellular ultrastructure, malformed and atrophic nucleus and higher apoptosis ratio were observed in DFO group. In addition, levels of haemolymph proinflammatory cytokines, activities of anti-superoxide anion, inducible-type NO-synthase (iNOS) and content of nitric oxide, and hepatopancreas NF-κB signal pathway gene expression in DFO group increased markedly compared to those of DSO and DRO groups. The results suggested that vegetable oils, such as soybean oil and RO might be the better lipid sources in diets for Macrobrachium rosenbergii than fish oil, it may be attributed to modified oxidative status induced by NF-κB-NO signal pathway.

The Two NF-κB Pathways Regulating Bacterial and WSSV Infection of Shrimp

The outbreak of diseases ordinarily results from the disruption of the balance and harmony between hosts and pathogens. Devoid of adaptive immunity, shrimp rely largely on the innate immune system to protect themselves from pathogenic infection. Two nuclear factor-κB (NF-κB) pathways, the Toll and immune deficiency (IMD) pathways, are generally regarded as the major regulators of the immune response in shrimp, which have been extensively studied over the years. Bacterial infection can be recognized by Toll and IMD pathways, which activate two NF-κB transcription factors, Dorsal and Relish, respectively, to eventually lead to boosting the expression of various antimicrobial peptides (AMPs). In response to white-spot-syndrome-virus (WSSV) infection, these two pathways appear to be subverted and hijacked to favor viral survival. In this review, the recent progress in elucidating microbial recognition, signal transduction, and effector regulation within both shrimp Toll and IMD pathways will be discussed. We will also highlight and discuss the similarities and differences between shrimps and their Drosophila or mammalian counterparts. Understanding the interplay between pathogens and shrimp NF-κB pathways may provide new opportunities for disease-prevention strategies in the future.

Characterization of an immune deficiency (IMD) homolog from the oriental river prawn, Macrobrachium nipponense

The immune deficiency (IMD) signal pathway mediates innate immunity against Gram-negative bacteria in crustaceans. In the present study, an IMD homolog (MnIMD) from the oriental river prawn, Macrobrachium nipponense was identified. The full-length cDNA of MnIMD was 782bp with an open reading frame of 549 bp that encodes a putative protein of 182 amino acids including a death domain at the C-terminus. Multiple alignment analysis showed that IMDs in prawn M. nipponense and other crustaceans shared high similarity. The recombinant protein of MnIMD was expressed and purified for further functional analyses. Western blot analysis indicated that MnIMD was present in many tissues, but with the highest level in the gills, which was consistent with the qRT-PCR results. After Vibrio parahaemolyticus challenge, MnIMD was significantly induced in gills. RNA interference analysis showed that the IMD pathway was involved in regulating the expression of different antimicrobial peptide (AMP) genes, including Cru4 and Cru6. These results are helpful in promoting research on the innate immunity in M. nipponense.

Three newly identified galectin homologues from triangle sail mussel (Hyriopsis cumingii) function as potential pattern-recognition receptors

Galactoside-binding lectins, also known as galectins, play crucial roles in innate immune response in invertebrates. In this study, three cDNA sequences from Hyriopsis cumingii were identified and collectively called HcGalec genes. Each of the three deduced HcGalec proteins contained a galactose-binding lectin domain or a GLECT domain. All the three HcGalec genes are mainly present in the hepatopancreas and gills, and their expression is induced at 24 h after bacterial challenge. Three recombinant HcGalec proteins can bind and agglutinate (Ca²⁺-dependent) various microorganisms, including Gram-positive and Gram-negative bacteria. These proteins can attach to mannan and peptidoglycan. Meanwhile, the expression of the three HcGalec genes in the gills were significantly down-regulated after dsRNA interference (HcGalec1-RNAi, HcGalec2-RNAi, and HcGalec3-RNAi) and Vibrio parahaemolyticus injection. The expression levels of some antimicrobial peptides, including lysozyme 1 and lysozyme 2, were also markedly decreased after dsRNA interference. Overall, these results suggested that these three HcGalec proteins may function as potential receptors participating in the innate immune responses of H. cumingii against bacterial infection.

Host MicroRNA-217 Promotes White Spot Syndrome Virus Infection by Targeting Tube in the Chinese Mitten Crab (Eriocheir sinensis)

MicroRNAs (miRNAs), a group of small molecule non-encoding RNAs, are key post-transcriptional regulators of gene expression that are implicated in many biological processes. In the current study, miR-217 from Eriocheir sinensis was selected for studying its roles during host-virus interaction. Overexpression or silencing of miR-217 led to considerable effects on white spot syndrome virus (WSSV) replication, implying that miR-217 played a positive role in WSSV infection. In insect High Five cells, miR-217 significantly inhibited Tube gene expression by binding to the 3'-untranslated region of the Tube. Overexpression of miR-217 in crab led to downregulation of tube expression. Knockdown of Tube in vivo led to significant enhancement of WSSV infection and inhibited the expression of five antimicrobial peptide (AMP) genes (Anti-lipopolysaccharide factor ALF1, ALF2, ALF3; Crustin Crus1, Crus2) in WSSV-challenged crabs. Overexpression of miR-217 also led to downregulation of these AMP genes in WSSV-challenged crabs. Our results showed that host miRNA played positive roles in virus infection by regulation of host tube gene, which is the key component of Toll signaling pathway.

Characterization of molecular properties and regulatory pathways of CrustinPm1 and CrustinPm7 from the black tiger shrimp Penaeus monodon

CrustinPm1 and crustinPm7 are the two most abundant isoforms of crustins identified from the hemocytes of the black tiger shrimp, Penaeus monodon. CrustinPm1 inhibits only Gram-positive bacteria, while crustinPm7 acts against both Gram-positive and Gram-negative bacteria. This work aims to characterize the molecular properties of recombinant crustinPm1 and crustinPm7, and the regulatory pathways of these two crustins. Circular dichroism spectroscopy revealed that crustinPm1 contained 40.81% alpha-helix and 22.34% beta-sheet, whereas crustinPm7 is made up of 32.86% alpha-helix and 27.53% beta-sheet. CrustinPm1 and crustinPm7 bound to phosphatidic acid (PA) with positive cooperativity of Hill slope (H) > 2, indicating that at least two molecules of crustins bind with one PA molecule. It is worth noting that both crustins bound to PA with significantly higher affinity than to lipoteichoic acid (LTA) and lipopolysaccharide (LPS). We speculate that crustin might also achieve antimicrobial activity by targeting PA, a signaling lipid. Regulatory pathways of crustinPm1 and crustinPm7 were investigated by knockdown of PmRelish and PmMyD88. This study demonstrated that crustinPm1 is mediated through the Toll signaling pathway, while crustinPm7 is regulated via both Toll and Imd pathways.