Immune gene discovery by expressed sequence tag analysis of hemocytes and hepatopancreas in the Pacific White Shrimp, Litopenaeus vannamei, and the Atlantic White Shrimp, L. setiferus

Integration of transcriptome, gut microbiota, and physiology reveals toxic responses of the red claw crayfish (Cherax quadricarinatus) to imidacloprid

Imidacloprid enters the water environment through rainfall and causes harm to aquatic crustaceans. However, the potential chronic toxicity mechanism of imidacloprid in crayfish has not been comprehensively studied. In this study, red claw crayfish (Cherax quadricarinatus) were exposed to 11.76, 35.27, or 88.17 μg/L imidacloprid for 30 days, and changes in the physiology and biochemistry, gut microbiota, and transcriptome of C. quadricarinatus and the interaction between imidacloprid, gut microbiota, and genes were studied. Imidacloprid induced oxidative stress and decreased growth performance in crayfish. Imidacloprid exposure caused hepatopancreas damage and decreased serum immune enzyme activity. Hepatopancreatic and plasma acetylcholine decreased significantly in the 88.17 μg/L group. Imidacloprid reduced the diversity of the intestinal flora, increased the abundance of harmful flora, and disrupted the microbiota function. Transcriptomic analysis showed that the number of up-and-down-regulated differentially expressed genes (DEGs) increased significantly with increasing concentrations of imidacloprid. DEG enrichment analyses indicated that imidacloprid inhibits neurotransmitter transduction and immune responses and disrupts energy metabolic processes. Crayfish could alleviate imidacloprid stress by regulating antioxidant and detoxification-related genes. A high correlation was revealed between GST, HSPA1s, and HSP90 and the composition of gut microorganisms in crayfish under imidacloprid stress. This study highlights the negative effects and provides detailed sequencing data from transcriptome and gut microbiota to enhance our understanding of the molecular toxicity of imidacloprid in crustaceans.

Characterization and function analysis of cathepsin C in Marsupenaeusjaponicus

Cathepsin C is a cysteine protease widely found in invertebrates and vertebrates, and has the important physiological role participating in proteolysis in vivo and activating various functional proteases in immune/inflammatory cells in the animals. In order to study the role of cathepsin C in the disease resistance of shrimp, we cloned cathepsin C gene (MjcathC) from Marsupenaeus japonicus, analyzed its expression patterns in various tissues, performed MjcathC-knockdown, and finally challenged experimental shrimps with Vibrio alginolyticus and WSSV. The results have shown the full length of MjcathC is 1782 bp, containing an open reading frame of 1350 bp encoding 449 amino acids. Homology analysis revealed that the predicted amino acid sequence of MjcathC shared respectively 88.42 %, 87.36 % and 87.58 % similarity with Penaeus monodon, Fenneropenaeus penicillatus and Litopenaeus vannamei. The expression levels of MjcathC in various tissues of healthy M. japonicus are the highest in the liver, followed by the gills and heart, and the lowest in the stomach. The expression levels of MjcathC were significantly up-regulated in all examined tissues of shrimp challenged with WSSV or V. alginolyticus. After knockdown-MjcathC using RNAi technology in M. japonicus, the expression levels of lectin and heat shock protein 70 in MjcathC-knockdown shrimp were significantly down-regulated, and the mortality of MjcathC-knockdown shrimp challenged by WSSV and V. alginolyticus significantly increased. Knockdown of the MjcathC reduced the resistance of M. japonicus to WSSV and V. alginolyticus. The above results have indicated that cathepsin C may play an important role in the antibacterial and antiviral innate immunity of M. japonicus.

PvMR1, a novel C-type lectin plays a crucial role in the antibacterial immune response of Pacific white shrimp, Penaeus vannamei

C-type lectins (CTLs) are important immune molecules in innate immune, which participate in non-self recognition and clearance of pathogens. Here, a new CTL with two distinct C-type lectin domains (CTLDs) from Pacific white shrimp Penaeus vannamei, designated as PvMR1 was identified. The obtained PvMR1 coding sequence (CDS) was 1044 bp long encoding a protein with 347 amino acids. PvMR1 had two CTLD, a conserved mannose-specific EPN motif and a galactose-specific QPD motif, clustering into the same branch as the crustacean CTLs. PvMR1 was widely distributed in shrimp tissues with the highest transcription level in the hepatopancreas, with significantly induced mRNA expression on the hepatopancreas and intestines after immune challenge with Vibrio anguillarum. In vitro assays with recombinant PvMR1 (rPvMR1) protein revealed that it exhibited a wide range of antimicrobial activity, bacterial binding ability, and bacterial agglutination activity in a Ca2+-independent manner. Moreover, PvMR1 promoted bacterial phagocytosis in hemocytes. Furthermore, rPvMR1 treatment could significantly enhance the bacterial clearance in hemolymph and greatly improved the survival of shrimp under V. anguillarum infection in vivo. These results collectively suggest that PvMR1 plays an important role in antibacterial immune response of P. vannamei.

Hemolymph exosomes inhibit Spiroplasma eriocheiris infection by promoting Tetraspanin-mediated hemocyte phagocytosis in crab

Exosomes released from infected cells are thought to play an important role in the dissemination of pathogens, as well as in host-derived immune molecules during infection. As an intracellular pathogen, Spiroplasma eriocheiris is harmful to multiple crustaceans. However, the immune mechanism of exosomes during Spiroplasma infection has not been investigated. Here, we found exosomes derived from S. eriocheiris-infected crabs could facilitate phagocytosis and apoptosis of hemocytes, resulting in increased crab survival and suppression of Spiroplasma intracellular replication. Proteomic analysis revealed the altered abundance of EsTetraspanin may confer resistance to S. eriocheiris, possibly by mediating hemocyte phagocytosis in Eriocheir sinensis. Specifically, knockdown of EsTetraspanin in E. sinensis increased susceptibility to S. eriocheiris infection and displayed compromised phagocytic ability, whereas overexpression of EsTetraspanin in Drosophila S2 cells inhibited S. eriocheiris infection. Further, it was confirmed that intramuscular injection of recombinant LEL domain of EsTetraspanin reduced the mortality of S. eriocheiris-infected crabs. Blockade with anti-EsTetraspanin serum could exacerbate S. eriocheiris invasion of hemocytes and impair hemocyte phagocytic activity. Taken together, our findings prove for the first time that exosomes modulate phagocytosis to resist pathogenic infection in invertebrates, which is proposed to be mediated by exosomal Tetraspanin, supporting the development of preventative strategies against Spiroplasma infection.

FOXO is involved in antimicrobial peptides expression during WSSV infection in Exopalaemon carinicauda

The forkhead box transcription factor O family protein (FOXO) acts as a transcription factor that regulates biological processes regarding DNA repair, immunity, cell cycle regulation, and other biological processes. In this study, EcFOXO was identified from the ridgetail white prawn, Exopalaemon carinicauda. EcFOXO protein contains multiple low-complexity regions and a forkhead (FH) domain. Phylogenetic tree showed that EcFOXO is clustered with crustacean FOXOs. The amino acid sequences of its FH domain are highly similar to the FH domain of FOXOs from other crustaceans. The expression of EcFOXO is altered after white spot syndrome virus (WSSV) stimulation in hepatopancreas and gills. The relationship between EcFOXO and EcRelish was explored by RNA interference (RNAi). Results showed that EcFOXO and EcRelish could positively regulate each other's expression. The expression levels of various antimicrobial peptides (AMPs) significantly reduced after interfering with EcFOXO or EcRelish. These results suggest a positive regulatory loop between EcFOXO and EcRelish, which participates in the innate immunity of ridgetail white prawn by regulating the expression of AMPs during WSSV infection. This study enriches the knowledge about the regulatory mechanism of FOXO in the innate immunity of crustaceans.

Effect of supersaturated dissolved oxygen on growth-, survival-, and immune-related gene expression of Pacific white shrimp (Litopenaeus vannamei)

Background and Aim

Oxygen concentration is an essential water quality parameter for aquaculture systems. Recently, supersaturated dissolved oxygen (DO) has been widely used in aquaculture systems to prevent oxygen depletion; however, the long-term effects of supersaturated DO exposure on aquatic animals have not been studied. In this study, we examined the effects of supersaturated DO on the growth, survival, and gene expression of Pacific white shrimp (Litopenaeus vannamei).

Materials and Methods

Specific pathogen-free shrimp with a body weight of 8.22 ± 0.03 g were randomly assigned to two groups with four replicates at a density of 15 shrimps per tank. Shrimp were cultivated in recirculating tanks containing 50 L of 15 ppt seawater in each replicate. Oxygen was supplied at 5 mg/L to the control tanks using an air microbubble generator and at 15 mg/L to the treatment tanks using a pure oxygen microbubble generator. Shrimp were fed commercial feed pellets containing 39% protein at 4% of their body weight per day for 30 days. Average daily growth (ADG) and feed conversion ratio (FCR) were determined on days 15 and 30. Shrimp molting was measured every day. Individual hemolymph samples were obtained and analyzed for total hemocyte count, differential hemocyte count, and expression of growth- and immune-related genes at the end of the experiment.

Results

Long-term exposure to supersaturated DO significantly affected shrimp growth. After 30 days of supersaturated DO treatment, the final weight and ADG were 14.73 ± 0.16 g and 0.22 ± 0.04, respectively. Shrimp treated with normal aeration showed significantly lower weight (12.13 ± 0.13 g) and ADG (0.13 ± 0.00) compared with the control group. FCR was 1.55 ± 0.04 in the treatment group and 2.51 ± 0.09 in the control group. Notably, the shrimp molting count was 1.55-fold higher in the supersaturated DO treatment than in the supersaturated DO treatment. The expression of growth-related genes, such as alpha-amylase, cathepsin L, and chitotriosidase, was 1.40-, 1.48-, and 1.35-fold higher, respectively, after supersaturated DO treatment. Moreover, the treatment increased the expression of anti-lipopolysaccharide factor, crustin, penaeidin3, and heat shock protein 70 genes by 1.23-, 2.07-, 4.20-, and 679.04-fold, respectively, compared to the controls.

Conclusion

Supersaturated DO increased growth and ADG production and decreased FCR. Furthermore, enhanced immune-related gene expression by supersaturated DO may improve shrimp health and reduce disease risk during cultivation.

Multi-omics analysis of oxidative stress and apoptosis in hepatopancreas cells induced by Polyascus gregaria parasitizing the Eriocheir sinensis

Polyascus gregaria, a parasitic barnacle, poses a significant threat to Eriocheir sinensis farms by inhibiting crab growth. However, the molecular and pathological mechanisms behind P. gregaria infection in the hepatopancreas of E. sinensis remain unclear. In this study, we investigated the impact and underlying mechanisms of P. gregaria infection on E. sinensis through analyzing the infected hepatopancreatic tissues by tandem mass tag technology and RNA-Seq high-throughput sequencing. Among the identified 10,693 differentially expressed genes, 294 genes were significantly altered following P. gregaria infection, including 92 upregulated and 202 downregulated genes. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses further revealed the involvement of these genes in oxidative decomposition, lipid metabolism, inflammation, and hepatopancreas metabolism. Meanwhile, the identified 253 differentially expressed proteins, including 143 upregulated and 110 downregulated proteins, are mainly related to cellular and metabolic processes, catalytic activity, and cell components. The pathway analysis indicated their enrichment in glycolysis/gluconeogenesis, oxidative phosphorylation, endoplasmic reticulum protein processing, and actin cytoskeleton regulation. The involvement of these differentially expressed genes and proteins in the peroxisome proliferator-activated receptors pathway during host immune responses against P. gregaria infection has been highlighted. Furthermore, pathological examinations and biochemical indicators jointly demonstrated the hepatopancreatic damage and increased oxidative stress and apoptosis in the infected E. sinensis. Collectively, our study provides crucial insights into the mechanisms underlying the E. sinensis-P. gregaria interactions, and may contribute to the development of novel strategies for parasite control and reducing economic losses in aquaculture.

Three STAT isoforms formed by selective splicing are involved in the regulation of anti-lipopolysaccharide factor expression in Macrobrachium nipponense during WSSV infection

White spot syndrome virus (WSSV), a double-stranded DNA virus, is harmful in aquaculture. The signal transducer and activator of transcription (STAT) has been shown to play a role during host infection with the virus, but the exact mechanism by which it acts is unclear. In this study, three STAT isoforms (MnSTAT1, MnSTAT2, and MnSTAT3) were identified in Macrobrachium nipponense. The full-length sequence of MnSTAT1 was 3336 bp, with 2259 bp open reading frame (ORF), encoding a 852 amino acids protein. The full-length sequence of MnSTAT2 was 2538 bp, and the ORF was 2391 bp, encoding 796 amino acids. The full-length sequence of MnSTAT3 sequence was 2618 bp, and the ORF was 2340 bp, encoding 779 amino acids. MnSTAT1-3 is produced by alternative last exon. MnSTAT1-3 all contain a STAT_int, a STAT_alpha, a STAT_bind, and a SH2 structure. MnSTAT1-3 are widely expressed in various tissues tested. The expression levels of MnSTAT1-3 in the intestine of M. nipponense were upregulated at multiple time points following WSSV stimulation. The expression of seven anti-lipopolysaccharide factors (ALFs) was significantly reduced with the knockdown of MnSTATs during WSSV infection. Results showed that MnSTATs regulated the expression of intestinal ALFs and was involved in the innate immunity against WSSV of M. nipponense.

A Mannose Receptor from Litopenaeus vannamei Involved in Innate Immunity by Pathogen Recognition and Inflammation Regulation

Mannose receptor, as a member of the C-type lectin superfamily, is a non-canonical pattern recognition receptor that can internalize pathogen-associated ligands and activate intracellular signaling. Here, a mannose receptor gene, LvMR, was identified from the Pacific white shrimp Litopenaeus vannamei. LvMR encoded a signal peptide, a fibronectin type II (FN II) domain, and two carbohydrate-recognition domains (CRDs) with special EPS and FND motifs. LvMR transcripts were mainly detected in the hepatopancreas, and presented a time-dependent response after pathogen challenge. The recombinant LvMR (rLvMR) could bind to various PAMPs and agglutinate microorganisms in a Ca²⁺-dependent manner with strong binding ability to _D-mannose and N-acetyl sugars. The knockdown of LvMR enhanced the expression of most NF-κB pathway genes, inflammation and redox genes, while it had no obvious effect on the transcription of most phagocytosis genes. Moreover, the knockdown of LvMR caused an increase in reactive oxygen species (ROS) content and inducible nitric oxide synthase (iNOS) activity in the hepatopancreas after Vibrio parahaemolyticus infection. All these results indicate that LvMR might perform as a PRR in immune recognition and a negative regulator of inflammation during bacterial infection.

A novel C-type lectin for Litopenaeus vannamei involved in the innate immune response against Vibrio infection

C-type lectins (CTLs), as a member of pattern recognition receptors, play a vital role in the innate immune response of invertebrates to eliminate micro-invaders. In this study, a novel CTL of Litopenaeus vannamei, namely, LvCTL7, was successfully cloned, with an open reading frame of 501 bp and a capability to encode 166 amino acids. Blast analysis showed that the amino acid sequence similarity between LvCTL7 and MjCTL7 (Marsupenaeus japonicus) was 57.14%. LvCTL7 was mainly expressed in hepatopancreas, muscle, gill and eyestalk. Vibrio harveyi can significantly affect LvCTL7 expression level in hepatopancreases, gills, intestines and muscles (p < 0.05). LvCTL7 recombinant protein can bind to Gram-positive bacteria (Bacillus subtilis) and Gram-negative bacteria (Vibrio parahaemolyticus and V. harveyi). It can cause the agglutination of V. alginolyticus and V. harveyi, but it had no effect on Streptococcus agalactiae and B. subtilis. The expression levels of SOD, CAT, HSP 70, Toll 2, IMD and ALF genes in the challenge group added with LvCTL7 protein were more stable than those in the direct challenge group (p < 0.05). Moreover, knockdown of LvCTL7 by double-stranded RNA interference downregulated the expression levels of genes (ALF, IMD and LvCTL5) that protect against bacterial infection (p < 0.05). These results indicated that LvCTL7 had microbial agglutination and immunoregulatory activity, and it was involved in the innate immune response against Vibrio infection in L. vannamei.

Alternative splicing derived invertebrate variable lymphocyte receptor displays diversity and specificity in immune system of crab Eriocheir sinensis

Variable lymphocyte receptors (VLRs) play vital roles in adaptive immune system of agnathan vertebrate. In the present study, we first discover a novel VLR gene, VLR2, from an invertebrate, the Chinese mitten crab, Eriocheir sinensis. VLR2 has ten different isoforms formed via alternative splicing, which is different from that in agnathan vertebrate with the assembly of LRR modules. The longest isoform, VLR2-L, responds to Gram-positive bacteria Staphylococcus aureus challenge specifically, while shows no response to Gram-negative bacteria Vibrio parahaemolyticus challenge, confirmed by recombinant expression and bacterial binding experiments. Interestingly, VLR2s with short LRRs regions (VLR2-S8 and VLR2-S9) tend to bind to Gram-negative bacteria rather than Gram-positive bacteria. Antibacterial activity assay proves six isoforms of VLR2 have pluralistic antibacterial effects on bacteria which were never reported in invertebrate. These results suggest that the diversity and specificity of VLR2 resulted from alternative splicing and the length of the LRRs region. This pathogen-binding receptor diversity will lay the foundation for the study of immune priming. Furthermore, studying the immune function of VLR2 will provide a new insight into the disease control strategy of crustacean culture.

New insight of variable lymphocyte receptor-likes in anti-bacteria activity from Eriocheir sinensis

The Chinese mitten crab, Eriocheir sinensis, is a vital freshwater aquaculture species in China, however, is also facing various crab disease threats. In the present study, we identify three novel variable lymphocyte receptor-like (VLR-like) genes-VLR-like1, VLR-like3 and VLR-like4-from E. sinensis, which play vital roles in adaptive immune system of agnathan vertebrates. The bacterial challenge, bacterial binding and antibacterial-activity experiments were applied to study immune functions of VLR-likes, and the transcriptomic data from previous E. sinensis bacterial challenge experiments were analyzed to speculate the possible signaling pathway. VLR-like1 and VLR-like4 can respond to Staphylococcus aureus challenge and inhibit S. aureus specifically. VLR-like1 and VLR-like4 possess broad-spectrum bacteria-binding ability whereas VLR-like3 do not. VLR-likes in E. sinensis could associate with the Toll-like receptor (TLR) signaling pathway. The above results suggest that VLR-likes defend against bacteria invasion though exerting anti-bacteria activity, and probably connect with the TLR signaling pathway. Furthermore, studying the immune functions of these VLR-likes will provide a new insight into the disease control strategy of crustacean culture.

Comparative study of five anti-lipopolysaccharide factor genes in Litopenaeus vannamei

Anti-lipopolysaccharide factors (ALFs) are a family of common innate immune effectors in crustaceans, and they exhibit broad spectrum antimicrobial activity. In this study, we identified and characterized five novel ALF genes (designated as LvALF1-5) from the Pacific white shrimp (Litopenaeus vannamei) to investigate their potential immune functions. The amino acid sequence alignments showed that LvALFs contained two conserved cysteine residues, a hydrophobic N-terminal region, and the conserved signature sequence W(T/K)CPG(S)WT(A). They all shared high similarity with previously reported ALFs and were clearly novel members of the ALF family. The mRNA transcripts of LvALFs were most highly expressed in hemocytes and the hepatopancreas. After shrimp were stimulated with Vibrio parahaemolyticus or white spot syndrome virus, expression of the LvALFs was significantly induced in hemocytes and the hepatopancreas with various expression profiles. Recombinant proteins of LvALFs exhibited potent bacteriostatic activity in vitro. Together, these results suggest that LvALF1-5 participate in the immune response of Pacific white shrimp against invading pathogens.

New insights into the regulation mechanism of red claw crayfish (Cherax quadricarinatus) hepatopancreas under air exposure using transcriptome analysis

Red claw crayfish (Cherax quadricarinatus) is an important freshwater shrimp species worldwide with enormous economic value. Waterless transportation is an inherent feature of red claw crayfish transportation. However, the high mortality of red claw crayfish is a severe problem in the aquaculture of crayfish after waterless transportation. In this study, we investigated the responses of the hepatopancreas from the red claw crayfish undergoing air exposure stress and normal conditions on transcriptome levels. We used Illumina-based RNA sequencing (RNA-Seq) to perform a transcriptome analysis from the hepatopancreas of red claw crayfish challenged by air exposure. An average of 57,148,800 clean reads per library was obtained, and 33,567 unigenes could be predicted and classified according to their homology with matches in the National Center for Biotechnology Information (NCBI) non-redundant protein sequences (Nr), Gene Ontology (GO), a manually annotated and reviewed protein sequence database (Swiss-Prot), protein families (Pfam), Clusters of Orthologous Groups (COG) of proteins, and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. 690 and 3407 differentially expressed genes (DEGs) were identified between the two stress stages of the red claw crayfish. More DEGs were identified in 12 h, indicating that gene expressions were largely changed at 12 h. Some immune-related pathways and genes were identified according to KEGG and GO enrichment analysis. A total of 12 DEGs involved in immune response and trehalose mechanism were verified by quantitative real-time-polymerase chain reaction (qRT-PCR). The results indicated that the red claw crayfish might counteract the stress of air exposure at the transcriptomic level by increasing expression levels of antioxidant-, immune-, and trehalose metabolism-related genes. These transcriptome results from the hepatopancreas provide significant insights into the influence mechanism of air exposure to the trehalose mechanism and immune response in the red claw crayfish.

Oral administration of Synechococcus sp. PCC7942 trans-vp19 and trans-vp (19+28) genes improve the immune and antioxidant capacity in Procambarus clarkii under white spot syndrome virus stress

This study aimed to evaluate antioxidant capacity and protection from white spot syndrome virus (WSSV) challenge of Procambarus clarkii fed trans-vp19 and trans-vp (19 + 28) genes of Synechococcus sp. PCC7942 (Syn7942). P. clarkii were fed transgenic cyanobacteria continuously for 7 days, and then infected with WSSV after 12 h starvation. The daily mortality in each group was measured for 10 days and hepatopancreas and muscle of P. clarkii were examined for enzymes phenoloxidase (PO) activity, catalase (CAT) activity, glutathione peroxidase (GSH-px) activity, and malondialdehyde (MDA) concentration after immunization and viral challenge at different times. Compared with the WSSV-infected crayfish in positive control group (challenge and no vaccination) and wild type group (challenge, feeding wild-type Syn7942), vp19 group (challenge, feeding Syn7942 trans-vp19 gene) and vp (19 + 28) group [challenge, feeding Syn7942 trans-vp (19 + 28) genes] significantly improved the survival rate from 0% to 60% and 56.7%, respectively. Consistently, significantly greater PO, CAT, and GSH-px activity and significantly lower MDA concentration in the vp19 and vp (19 + 28) groups compared to the control group. These results demonstrate that the trans-vp19 and trans-vp (19 + 28) gene of Syn7942 significantly facilitated the immune and antioxidant capacity of crayfish. Therefore, the trans-vp19 and trans-vp (19 + 28) genes of Syn7942 could provide protection for crayfish as an anti-WSSV oral medication.

Dietary supplementation of synbiotic Leuconostoc mesenteroide B4 and dextran improves immune regulation and disease resistance of Penaeus vannamei against Vibrio parahaemolyticus

White shrimp (Penaeus vannamei) is an important culture species in Taiwan but often encounters disease infection by Vibrio parahaemolyticus that cause acute hepatopancreatic necrosis disease (AHPND). This study investigates the effects of dietary supplementation of Leuconostoc mesenteroide B4 and its fermentate (dextran) on the immune response, intestinal morphology, disease resistance, and immune-related gene expression in white shrimp. In comparison to the control group, the shrimp fed with a diet containing B4+dextran (10⁷ CFU B4/g feed and 0.05% dextran) for 14, 28, 42 and 56 days had a significantly higher feed efficiency, weight gain and specific growth rate. A significantly higher villus height in the intestine and higher survival rate after challenging with V. parahaemolyticus was recorded for the B4+dextran group. Flow cytometry analysis demonstrated that the group that had ingested B4+dextran had a higher total hemocyte count and a higher proportion of semi-granulocytes, but a lower percentage of granulocytes compared to the control group. The shotgun metagenomic results in the midgut revealed that Leuco. mesenteroides was barely found in the midgut of the shrimp, suggesting that this microbe and its transient presence in the midgut is not the direct mechanism underlying the improved shrimp growth in the treated sample. Instead, dextran, a key ingredient in the B4 fermentate, on the dynamic of the microbial populations in shrimp, possibly promoting the diversity of gut microbes, especially the beneficial microbes, and thereby rendering protection against AHPND. In terms of comparing the gene expression between the control and synbiotic groups, pre- and post-bacterial challenge, a higher expression level of immune genes was mostly found in the B4+dextran group after challenging it with V. parahaemolyticus (group B4+dextran-VP) in the hepatopancreas and hemocyte. In contrast, the transcript level of immune-related genes was found to be higher in the B4+dextran group than other combinations in the midgut. Taken together, this study found that dietary addition of synbiotic Leuco. mesenteroides B4 and dextran can improve the growth performance, intestinal morphology and microbiome, regulation of immune genes and disease resistance against V. parahaemolyticus infection in white shrimp.

Single-cell RNA-seq uncovered hemocyte functional subtypes and their differentiational characteristics and connectivity with morphological subpopulations in Litopenaeus vannamei

Hemocytes play central roles in shrimp immune system, whereas whose subclasses have not yet been completely defined. At present, the morphological classification of hemocytes is inadequate to classify the complete hemocyte repertoire and elucidate the functions and differentiation and maturation processes. Based on single-cell RNA sequencing (scRNA-seq) of hemocytes in healthy Litopenaeus vannamei, combined with RNA-FISH and flow cytometric sorting, we identified three hemocyte clusters including TGase+ cells, CTL+ cells and Crustin+ cells, and further determined their functional properties, potential differentiation trajectory and correspondence with morphological subpopulations. The TGase+ cells were mainly responsible for the coagulation, exhibiting distinguishable characteristics of hyalinocyte, and appeared to be developmentally arrested at an early stage of hemocyte differentiation. The CTL+ cells and Crustin+ cells arrested at terminal stages of differentiation mainly participated in recognizing foreign pathogens and initiating immune defense responses, owning distinctive features of granule-containing hemocytes. Furthermore, we have revealed the functional sub-clusters of three hemocyte clusters and their potential differentiation pathways according to the expression of genes involved in cell cycle, cell differentiation and immune response, and the successive differentiation and maturation of hyalinocytes to granule-containing hemocytes have also mapped. The results revealed the diversity of shrimp hemocytes and provide new theoretical rationale for hemocyte classification, which also facilitate systematic research on crustacean immunity.

Molecular identification and functional analysis of a tumor necrosis factor superfamily gene from Chinese mitten crab (Eriocheir sinensis)

Tumor necrosis factor (TNF) is one of the most important cytokines involved in various biological processes in vertebrates and invertebrates. In the present study, a new member of the TNF superfamily (named EsTNFSF) was identified from the Chinese mitten crab (Eriocheir sinensis). The full-length cDNA of EsTNFSF is 2462 bp and encodes a polypeptide with 499 amino acids. The deduced EsTNFSF protein contained a transmembrane region and a conserved extracellular C-terminal TNF domain. Phylogenetic analysis indicated that EsTNFSF was closely related to other TNFSFs from crustaceans. Quantitative real-time PCR analysis showed that EsTNFSF was expressed in all the tissues examined, and the highest expression was found in the hepatopancreas. The mRNA levels of EsTNFSF in hemocytes underwent a time-dependent and variable degree of enhancement after stimulation with lipopolysaccharide, peptidoglycan, Staphylococcus aureus, and Vibrio parahaemolyticus. Functionally, EsTNFSF knockdown by siRNA suppressed the transcriptional levels of c-Jun N-terminal kinase and two antimicrobial peptides, anti-lipopolysaccharide factor and crustin. Furthermore, purified recombinant EsTNFSF protein accelerated the bacterial clearance in vivo and inhibited the growth of V. parahaemolyticus and S. aureus in vitro. The results revealed that EsTNFSF, as an inducible immune response gene, plays a crucial role in the antibacterial immune defense of E. sinensis.

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.

A C-type lectin containing two carbohydrate recognition domains participates in the antibacterial response by regulating the JNK pathway and promoting phagocytosis

C-type lectins (CTLs) are important immune-related molecules in crustaceans. However, the immunologic mechanism by which CTLs eliminate invading pathogens is still unclear. In this study, we studied the antimicrobial mechanism of a CTL containing two carbohydrate recognition domains (DClec). After Aeromonas hydrophila challenge, several antimicrobial peptides (ALF1, ALF4, ALF5 and lys-i2) were upregulated. The transcript levels of ALF1, ALF4 and ALF5 were downregulated after A. hydrophila challenge in groups with DClec interference or inhibition compared with the control group. Similar results were obtained after c-Jun N-terminal kinase (JNK) interference. This finding indicates that DClec might regulate the JNK signalling pathway and subsequently adjust antimicrobial peptide (AMP) expression. Additionally, we found that DClec was secreted into the hemolymph. Recombinant protein DClec (rDClec) agglutinated gram-positive or gram-negative bacteria. Both rDClec and the native DClec in hemolymph bound to different bacteria. In this process, Ca²⁺ promoted the rDClec bacterial binding ability. After DClec interference, the phagocytosis ability of hemocytes was lower than that of the control group. Therefore, DClec can facilitate bacterial elimination by promoting AMPs expression and hemocyte phagocytosis.

A New Crustin Gene Homolog SpCrus8 Identified in Scylla paramamosain Exerting In Vivo Protection Through Opsonization and Immunomodulation

Crustins are the most abundant class of antimicrobial peptides in crustaceans and are essential for protecting animals from infection. Among them, type II crustins usually exhibit potent antimicrobial activity. Interestingly, in this study, a newly identified type II crustin gene homolog (named SpCrus8) from mud crab Scylla paramamosain, the recombinant proteins of which (rSpCrus8 and rTrx-SpCrus8) showed no obvious antibacterial effects, but could significantly reduce the bacterial load in crab hemolymph and improve the survival rate of crabs infected with Vibrio alginolyticus. The immune-related function of SpCrus8 and the underlying mechanism deserve further investigation. It was found that the SpCrus8 gene was widely distributed in various tissues of adult crabs. In the hepatopancreas of crabs infected with V. alginolyticus or Staphylococcus aureus, transcripts of the SpCrus8 gene were remarkably induced, indicating that the SpCrus8 gene was involved in the immune response to bacterial infection in vivo. In addition, rSpCrus8 and rTrx-SpCrus8 had strong binding activity not only to microbial surface components (lipopolysaccharide, lipoteichoic acid, peptidoglycan, and glucan), but also to the tested bacteria (S. aureus, Pseudomonas aeruginosa and V. alginolyticus). Notably, rSpCrus8 and rTrx-SpCrus8 could significantly promote hemocyte phagocytosis. After rSpCrus8 and rTrx-SpCrus8 treatment, a large number of fluorescent microspheres were observed to aggregate into clusters and be phagocytosed by multiple hemocytes, while hemocytes in the control group phagocytosed only individual microspheres, indicating that SpCrus8 played an important role in opsonization. When the SpCrus8 gene was knocked down, the expression levels of the key phagocytosis-related genes SpRab5 and SpRab7 were significantly downregulated, as well as the IMD signaling pathway genes SpIKKβ and SpRelish, and another crustin gene SpCrus5. Correspondingly, all the SpIKKβ, SpRelish and SpCrus5 genes were significantly upregulated after rSpCrus8 treatment, suggesting that SpCrus8 might be involved in the immunomodulation of S. paramamosain. Taken together, this study revealed the immune-related functions of the SpCrus8 gene in opsonization and regulation, which will help us further understand the role of the crustin gene family in the immune system of mud crabs and provide new insights into the function of type II crutins.

Control of vibriosis in shrimp through the management of the microbiota and the immune system

Shrimp aquaculture is constantly threatened by recurrent outbreaks of diseases caused by pathogenic bacteria of the genus Vibrio. Acute hepatopancreatic necrosis disease (AHPND) is one of the most aggressive vibriosis reported to date in the shrimp industry. AHPND provokes massive mortalities, causing economic losses with strong social impacts. Control of vibriosis requires the application of multifactorial strategies. This includes vibrio exclusion, shrimp microbiota, particularly in the digestive tract, and shrimp health management through immune stimulation. This paper reviews these two strategies for the prophylactic control of vibriosis. First, we describe the devastating effects of AHPND and the cellular and humoral effectors of the shrimp immune system to cope with this pathology. Secondly, the mechanisms of action of probiotics and their positive impacts are highlighted, including their immunostimulant effects and their role in the balance of the shrimp microbiota. Finally, we reviewed immunostimulants and prebiotics polysaccharides that together with probiotics act benefiting growth, feed efficiency and the microbiota of the digestive tract of farmed shrimp.

Shrimp thrombospondin (TSP): presence of O-β1,4 N-acetylglucosamine polymers and its function in TSP chain association in egg extracellular matrix

We characterized the existence of O-β(1,4)-GlcNAc polymers (β1,4GNP) that were anchored on the O-linked glycosylation sites of shrimp thrombospondin (pmTSP-II). There were five putative β1,4GNP linkages on the epithelial growth factor-like domain of pmTSP-II. Antibody against O-β-GlcNAc (CTD110.6) was used to prove the existence of linear and complex β1,4GNP. The antibody well reacted with linear chito-triose, -tetraose and -pentaose conjugated with phosphatidylethanolamine lipid. The immunoreactivity could also be detected with a complex β1,4GNP within pmTSP-II (at MW > 250 kDa). Upon denaturing the protein with SDS-PAGE buffer, the size of pmTSP-II was shifted to be 250 kDa, approximately 2.5 folds larger than the deduced molecular mass of pmTSP-II (110 kDa), suggesting additional association of pmTSP-II apart from its known disulfide bridging. This was confirmed by chitinase digestion on pmTSP-II protein leading to the subsequent smaller protein bands at 110–170 kDa in time- and concentration-dependent manners. These bands well reacted with CTD110.6 antibody and disappeared after extensive chitinase hydrolysis. Together, we believe that β1,4GNP on pmTSP-II serve the function in an inter-chain association to provide structural architecture of egg extracellular matrix, a novel function of pmTSP-II in reproductive biology.

Comprehensive Transcriptomic and Metabolomic Analysis of the Litopenaeus vannamei Hepatopancreas After WSSV Challenge

Litopenaeus vannamei is the major farmed shrimp species worldwide. White spot disease due to white spot syndrome virus (WSSV) is severely affecting shrimp worldwide, causing extensive economic losses in L. vannamei culture. This is the first study that applied combined transcriptomic and metabolomic analysis to study the effects on the L. vannamei hepatopancreas after WSSV challenge. Our transcriptomic data revealed differentially expressed genes (DEGs) associated with immunity, apoptosis, the cytoskeleton and the antioxidant system in the hepatopancreas of L. vannamei. Metabolomic results showed that WSSV disrupts metabolic processes including amino acid metabolism, lipid metabolism and nucleotide metabolism. After challenged by WSSV, immune-related DEGs and differential metabolites (DMs) were detected in the hepatopancreas of L. vannamei, indicating that WSSV may damage the immune system and cause metabolic disorder in the shrimp. In summary, these results provide new insights into the molecular mechanisms underlying L. vannamei's response to WSSV.

Long-read RNA sequencing of Pacific abalone Haliotis discus hannai reveals innate immune system responses to environmental stress

Haliotis discus hannai is a commercially important mollusk species, and the abalone aquaculture sector has been jeopardized by deteriorating environmental circumstances such as bacterial infection and thermal stress during the hot summers. However, due to a paucity of genetic information, such as transcriptome resources, our understanding of their stress adaptation is restricted. In this research, using single-molecule long-read (SMRT) sequencing technology, a library composed of ten tissues (i.e., haemocytes, gills, muscle, hepatopancreas, digestive tract, mantle, mucous gland, ovary, testis and head) was constructed and sequenced. In all, 41,855 high-quality unique transcripts, among which 24,778 were successfully annotated. Additionally, 13,463 SSRs, 1,169 transcription factors, and 18,124 lncRNAs were identified in H. discus hannai transcriptome. Furthermore, multiple immune-related transcripts were identified according to KEGG annotation, and a portion of these transcripts were mapped into several classical immune-related pathways, including the PI3K-AKT signaling pathway and Toll-like receptor signaling pathway. Additionally, 24 typical sequences related to the immunity pathway were detected by RT-PCR; the results showed that most of the immune-related genes showed significantly high expression at 72 h after bacterial challenges and thermal stress, especially the expression level of genes in gills was significantly higher than that in haemocytes under V. parahaemolyticus stress at 24 h. At the same time. The analysis of alternative splicing identified several innate immunity-related functions genes, including CD109 and caspase 2. These results suggest that the complex immune system, particularly the powerful innate immunity system, was crucial for H. discus hannai response to numerous environmental challenges.

Characterization of the Dual Functions of LvCrustinVII from Litopenaeus vannamei as Antimicrobial Peptide and Opsonin

Crustin are a family of antimicrobial peptides that play an important role in protecting against pathogens infection in the innate immune system of crustaceans. Previously, we identified several novel types of crustins, including type VI and type VII crustins. However, their immune functions were still unclear. In the present study, the immune function of type VII crustin LvCrustinVII were investigated in Litopenaeus vannamei. LvCrustinVII was wildly expressed in all tested tissues, with relatively high expression levels in hepatopancreas, epidermis and lymphoid organ. Upon Vibrio parahaemolyticus infection, LvCrustinVII was significantly upregulated in hepatopancreas. Recombinant LvCrustinVII (rLvCrustinVII) showed strong inhibitory activities against Gram-negative bacteria Vibrio harveyi and V. parahaemolyticus, while weak activities against the Gram-positive bacteria Staphylococcus aureus. Binding assay showed that rLvCrustinVII could bind strongly to V. harveyi and V. parahaemolyticus, as well as the cell wall components Glu, LPS and PGN. In the presence of Ca²⁺, rLvCrustinVII could agglutinate V. parahaemolyticus and enhance hemocyte phagocytosis. The present data partially illustrate the immune function of LvCrustinVII, which enrich our understanding on the functional mechanisms of crustins and provide useful information for application of this kind of antimicrobial peptides.

Impact of imidacloprid exposure on the biochemical responses, transcriptome, gut microbiota and growth performance of the Pacific white shrimp Litopenaeus vannamei

The widespread use of neonicotinoid insecticides, such as imidacloprid, in agriculture is one of the key factors for the drop in the survival of invertebrates, including decapod crustaceans. However, there is currently a lack of comprehensive studies on the chronic toxicity mechanisms in decapod crustaceans. Here, the concentration-dependent effects of imidacloprid on the physiology and biochemistry, gut microbiota and transcriptome of L. vannamei , and the interaction between imidacloprid, gut microbiota and genes were studied. Imidacloprid caused oxidative stress, leading to reduced growth and to immunity and tissue damage in L. vannamei . Imidacloprid increased the gut pathogenic microbiota abundance and broke the steady state of the gut microbiota interaction network, resulting in microbiota function disorders. Chronic imidacloprid exposure induced overall transcriptome changes in L. vannamei . Specifically, imidacloprid caused a large number of differentially expressed genes (DEGs) to be significantly downregulated. The inhibition of autophagy-related pathways revealed the toxic process of imidacloprid to L. vannamei . The changes in phase I and II detoxification gene expression clarified the formation of a detoxification mechanism in L. vannamei . The disturbance of circadian rhythm (CLOCK) caused by imidacloprid is one of the reasons for the increase in gut pathogenic microbiota abundance.

Cloning, expression and function analysis of trehalose-6-phosphate synthase gene from Marsupenaeus japonicu

Trehalose is an important disaccharide that plays an important role in extreme environmental conditions. Trehalose-6-phosphate synthase (TPS) gene is the key gene for trehalose synthesis in Marsupenaeus japonicus. In this study, a TPS gene was isolated and characterized from M. japonicus. The full-length cDNA of TPS gene of M. japonicus (MjTPS) was 3308 bp, encoding 844 amino acids. The protein of the deduced MjTPS contained a glycol_transf_20 domain and a trehalose_PPase domain. The mRNA expression level of MjTPS was the highest in hepatopancreas. The further analysis found that MjTPS gene expression was up-regulated in a short time under low-salinity and high-nitrite stress, indicating that MjTPS gene had certain resistance to low-salinity and high-nitrite stress. Compared with the control group, both the expression of MjTPS and the trehalose content significantly decreased from 3 h to 24 h after MjTPS gene interference,. After RNAi, the mortality of M. japonicus increased, the expression level of MjTPS and the synthesis of downstream products decreased under low-salinity and high-nitrite stress, and what's more, the expression of immune genes PMO25, ERP, CD, HSP90, HSP70, HSP60, HMC and CLEC2 were significantly changed, implying that MjTPS might be participated in the immune response of M. japonicus. In addition, MjTPS gene silencing could affect the expression of CHI1 and CHS, suggesting that MjTPS might be involved in molting behavior of M. japonicus. These results provide new information for further studying the function of trehalose-6-phosphate synthase in shrimp.

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

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

BigPEN, an antimicrobial peptide of penaeidin family from shrimp Litopenaeus vannamei with membrane permeable and DNA binding activity

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LvBigPEN, a member of penaeidins from L. vannamei, was regulated by host AP-1 signaling pathway.

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LvBigPEN could bind to both Gram-negative bacteria and Gram-positive bacteria.

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LvBigPEN could destroy bacterial cells and bind to DNA.

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LvBigPEN played an important role in defense against V. parahaemolyticus infection.

Penaeidins are members of an antimicrobial peptide (AMP) family that have broad anti-microbial activities only found in penaeid shrimps. The LvBigPEN, a member of penaeidins from shrimp Litopenaeus vannamei, has showed antiviral activity against white spot syndrome virus (WSSV) in our previous report. However, whether LvBigPEN possesses potential anti-bacterial activities is still unknown. Herein, we found that the LvBigPEN played an important role in restricting the infection of Vibrio parahaemolyticus, a natural and Gram-negative bacteria pathogen in shrimp. The transcription of LvBigPEN was strongly induced after V. parahaemolyticus challenge. RNA interference (RNAi) mediated knockdown of LvBigPEN showed that LvBigPEN had a potential antibacterial function against V. parahaemolyticus. Microorganism binding assays indicated that rLvBigPEN could bind to both Gram-negative bacteria and Gram-positive bacteria. Transmission electron microscopy (TEM) analysis showed its ability to destroy bacterial cells in vitro. Besides, in a gel retardation assay, rLvBigPEN could bind to plasmid DNA and bacteria (V. parahaemolyticus) genomic DNA in a concentration-dependent manner. Moreover, the AP-1 pathway could participate in the transcription of LvBigPEN by the dual luciferase reporter assays. Taken together, these results suggested that LvBigPEN possessed the antibacterial activity against V. parahaemolyticus and may be alternative agents for the prevention and treatment of diseases caused by V. parahaemolyticus.

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

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

Molecular and functional characterization of mitochondrial manganese superoxide dismutase from Macrobrachium rosenbergii during bacterial infection

Superoxide dismutases (SODs) are the main antioxidant enzymes involved in alleviating oxidative stress. Although mitochondrial manganese SOD (mMnSOD) has been reported to be correlated with the immune response in crustaceans, its biological properties and role in the immune response remain unclear. Here, we cloned the Macrobrachium rosenbergii mMnSOD (MrmMnSOD), analyzed its activity and expression pattern under Staphylococcus aureus and Vibrio parahaemolyticus infection, and further explored its possible mechanism during antibacterial immune response. The results showed that both enzyme activity and the expression of MrmMnSOD were significantly up-regulated by bacterial infection. MrmMnSOD knockdown made the prawn susceptible to Vibrio infection, which increased the mortality rate and the number of bacteria in haemocytes. The bacterial agglutination assay confirmed that MrmMnSOD decreases bacterial abundance via agglutination. Overall, this work identified antibacterial function of MrmMnSOD in the immune response. In addition to contributing to immunological theory, these findings aid disease prevention and control in crustacean aquaculture.

Two fibrinogen-related proteins (FREPs) in the razor clam (Sinonovacula constricta) with a broad recognition spectrum and bacteria agglutination activity

Fibrinogen-related proteins (FREPs) that contain only the fibrinogen-related domain are likely involved in pathogen recognition. In this study, we identified two FREPs from the razor clam (Sinonovacula constricta), called ScFREP-1 and ScFREP-2, and investigated their roles in the immune response. Both ScFREP-1 and ScFREP-2 contained a fibrinogen-related domain at the C-terminal. ScFREP-1 and ScFREP-2 mRNAs were detected in all adult clam tissues tested, with the highest expression levels in the gill and mantle, respectively. Their expression levels were significantly upregulated after microbe infection. Recombinant ScFREPs could bind Gram-positive and Gram-negative bacteria as well as some pathogen-associated molecular patterns (PAMPs), and they could agglutinate those bacteria. These results showed that ScFREPs functioned as potential pattern recognition receptors to mediate immune response by recognizing PAMPs and agglutinating invasive microbes.

Dorsal regulates the expression of two phage lysozymes acquired via horizontal gene transfer in triangle sail mussel Hyriopsis cumingii

Dorsal is a Rel/NF-κB transcription factor, which forms a key part of the Toll pathway. Lysozyme is a ubiquitous enzyme that degrades bacterial cell walls. In this study, a Dorsal homolog was cloned and characterized from triangle sail mussel Hyriopsis cumingii, namely, HcDorsal. Dorsal consisted of 3041 bp, including a 1938 bp open reading frame encoding a 645 amino acid protein. The deduced HcDorsal protein contained a Rel homology domain and an Ig-like, plexin, transcription factor domain. Analysis of expression patterns showed that HcDorsal was highly expressed in the hepatopancreas of H. cumingii. The expression level of HcDorsal continuously increased after Vibrio parahaemolyticus stimulation. When HcDorsal was knocked down by siRNA interference, two phage lysozyme genes (HcLyso1 and HcLyso2) obtained by horizontal gene transfer were significantly downregulated in hemocytes of mussels. Furthermore, knockdown of HcLyso1 and HcLyso2 could weaken V. parahaemolyticus clearance ability. Recombinant HcLyso1 and HcLyso2 proteins accelerated the bacterial clearance in vivo in mussels and evidently inhibited the growth of V. parahaemolyticus. These results suggested that HcDorsal could be activated after V. parahaemolyticus stimulation and then modulate the immune response through the transcriptional regulation of HcLyso1 and HcLyso2, thereby playing a protective role in mussels.

Hepatopancreatic transcriptome analysis and humoral immune factor assays in red claw crayfish (Cherax quadricarinatus) provide insight into innate immunomodulation under Vibrio parahaemolyticus infection

Red claw crayfish (Cherax quadricarinatus) is an economically and nutritionally important specie. We aimed to assess the immunostimulatory response to C. quadricarinatus infection with Vibrio parahaemolyticus. After determining the LD50, we infected C. quadricarinatus and examined the differential expression profiles of hepatopancreas transcriptional genes, and observed the temporal changes of hepatopancreas pathological sections and serum immunoenzymatic activities at different time points to reveal the infection mechanism of V. parahaemolyticus and the immune detoxification mechanism of the organism. The results showed that V. parahaemolyticus infection with C. quadricarinatus caused hepatopancreas injury and the immune enzyme activity of the organism changed with time delay. Transcriptome analysis of 47,338 single genes obtained by RNA sequencing and de nove transcriptome assembly identified a total of 3678 differentially expressed genes (P < 0.05) in the expression profiles of susceptible and normal animals for comparative analysis, and 2516 differentially expressed genes (P < 0.05) in the expression profiles of asymptomatic (infection-resistant) and normal animals. GO and KEGG and analyses revealed immune-related pathways under V. parahaemolyticus infection, including Vibrio cholerae infection, phagosome, lysozyme, oxidative phosphorylation, antigen processing and presentation, apoptosis, and Toll-like receptor signaling, as well as significant differences in the expression patterns of related immune genes at different times (P < 0.05). These new experimental results reveal the molecular response of the hepatopancreas to V. parahaemolyticus infection and the corresponding adaptive mechanisms, thus further revealing the pathogenesis due to bacterial infection in the aquatic environment, and providing a reference for further understanding of microbial-host interactions in aquatic systems.

iTRAQ-based quantitative proteomic analysis of differentially expressed proteins in the hepatopancreas of Litopenaeus vannamei after WSSV infection

White spot syndrome virus (WSSV) is the most destructive virus among invertebrates. In this study, we analyzed the immune response after WSSV infection in Pacific white shrimp Litopenaeus vannamei using isobaric tags for relative and absolute quantitation (iTRAQ). We identified 325 differentially expressed proteins (DEPs) in the hepatopancreas of L. vannamei. Among them, 212 were up-regulated proteins, and several of them might be related to immunity (e.g. arginine kinase and peroxiredoxin). Of the 113 down-regulated proteins, some were related to immunity (e.g. cathepsin C and cathepsin L) and others to the antioxidant defense process (e.g. glutathione peroxidase and catalase). One down-regulated DEP (C7M84_014268) and 3 up-regulated DEPs (C7M84_003456, C7M84_020702, and C7M84_007135) were randomly selected and analyzed using parallel reaction monitoring. This study is an important step for a comprehensive understanding of the immune relationship between L. vannamei and WSSV and provides valuable information for the prevention of viral diseases in the crustacean aquaculture industry.

A C-Type Lectin Highly Expressed in Portunus trituberculatus Intestine Functions in AMP Regulation and Prophenoloxidase Activation

A C-type lectin (PtCLec2) from Portunus trituberculatus was identified for characterization of its role in defense and innate immunity. PtCLec2 contains a single carbohydrate-recognition domain (CRD) with a conserved QPD motif, which was predicted to have galactose specificity. The mRNA expression of PtCLec2 was predominantly detected in intestine and increased rapidly and significantly upon pathogen challenge. The recombinant PtCLec2 (rPtCLec2) could bind various microorganisms and PAMPs with weak binding ability to yeast and PGN. It agglutinated the tested Gram-negative bacteria (Vibrio alginolyticus and Pseudomonas aeruginosa), Gram-positive bacteria (Staphylococcus aureus and Micrococcus luteus), and rabbit erythrocytes in the presence of exogenous Ca²⁺, and these agglutination activities were suppressed by LPS, d-galactose, and d-mannose. Further, rPtCLec2 enhanced phagocytosis and clearance of V. alginolyticus, and displayed inhibitory activities against the tested bacteria. Knockdown of PtCLec2 decreased the transcription of two phagocytosis genes (PtArp and PtMyosin), three prophenoloxidase (proPO) system-related genes (PtPPAF, PtcSP1, and PtproPO), six antimicrobial peptides (AMPs) (PtALF4-7, PtCrustin1, and PtCrustin3), and PtRelish but upregulated the expression levels of PtJNK, PtPelle, and PtTLR. These results collectively indicate that PtCLec2 might perform its immune recognition function via binding and agglutination, and mediate pathogen elimination via regulating hemocyte phagocytosis, AMP synthesis, and proPO activation.

The identification of a nuclear factor Akirin with regulating the expression of antimicrobial peptides in red swamp crayfish (Procambarus clarkii)

Akirin is a highly conserved nuclear factor among different species. It is closely related to skeletal muscle development, innate immune response, and tumorigenesis in a variety of animals. In invertebrates, Akirin is mainly involved in gene transcription and NF-κB dependent natural immune response. In the present study, a nuclear factor Akirin was identified from Procambarus clarkii. The Akirin protein of crayfish consists of 204 amino acids and is conserved among its family members, especially the nuclear localization signal peptide motif (KRRR). PcAkirin was highly expressed in stomach, intestines, and hepatopancreas. After A. hydrophila challenge, the transcription level of Akirin significantly increased in hemocyte and hepatopancreas. In addition, the recombinant Akirin protein was produced successfully and helpful to resist WSSV infection by increasing the expression level of some immune related genes. On the contrary, after interfering with Akirin gene by dsRNA, the crayfish increased the sensitivity to A. hydrophila and WSSV infections. The results are more obvious in the accumulated mortality of P. clarkii infected with A. hydrophila and WSSV. All these results suggested that Akirin played a significant role in innate immune responses and protected it from WSSV and bacterial infection in crayfish.

Dietary Supplementation of Brown Seaweed and/or Nucleotides Improved Shrimp Performance, Health Status and Cold-Tolerant Gene Expression of Juvenile Whiteleg Shrimp during the Winter Season

This study was aimed to evaluate the efficiency of Sargassumpolycystum and nucleotides- supplemented diets to improve immune response and cold-tolerance of juvenile Litopenaeus vannamei. Four treatments were evaluated: T1, the control, shrimp received only a basal diet; T2, a basal diet with 500 ppm nucleotides; T3, a basal diet with 500 ppm S.polycystum powdered; T4, a basal diet with 500 ppm nucleotides and 500 ppm S.polycystum powdered. Shrimp were fed experimental diets for 56 days. Results revealed shrimp fed T4 diet exhibited the best significant improvement in water quality, survival, growth, and feed utilization indices followed by T2, and T3, while T1 showed the worst values. Additionally, nonspecific immune responses (phagocytosis (%), lysozyme, phenoloxidase, super oxide dismutase (SOD) activity, total nitric oxide) were improved with 1.7-3.2-fold in T4 higher than T1. Histomorphology of hepatopancreas in T4 showed the most increased activation of the hepatic glandular duct system compared with the other treatments. Moreover, nucleotides/seaweed-supplemented diets upregulated relative expression of cMnSOD, Penaeidin4, and heat shock protein70 (HSP70) genes, while translationally controlled tumor protein (TCTP) was downregulated. In conclusion, the synergistic effects of both S. polycystum and nucleotides have many advantages as a growth promoter, immunostimulant, antimicrobial, and cold-tolerant stimulant to L. vannamei.

B-type allatostatin modulates immune response in hepatopancreas of the mud crab Scylla paramamosain

B-type allatostatin (AST-B) is a pleiotropic neuropeptide, widely found in arthropods. However, the information about its immune effect in crustaceans is unknown. In this study, we identified the nervous tissue as the main site for Sp-AST-B expression, while its receptor gene (Sp-AST-BR) is widely expressed in various tissues, including the hepatopancreas. This suggests the peptide's potential role in diverse physiological processes in the mud crab Scylla paramamosain. In situ hybridization revealed that Sp-AST-BR is mainly localized in the F-cell of hepatopancreas. Furthermore, we found a significant up-regulation of Sp-AST-BR transcripts in the hepatopancreas following exposure to lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid (Poly (I:C)). Results from in vitro and in vivo experiments revealed that treatment with a synthetic AST-B peptide mediated significant upregulation in expression of AST-BR, nuclear factor-κB (NF-κB) pathway components (Dorsal and Relish), pro-inflammatory cytokine (IL-16) and antimicrobial peptides (AMPs) in the hepatopancreas. In addition, AST-B treatment mediated significant elevation of nitric oxide (NO) production and enhanced the bacteriostasis capacity of the hepatopancreas tissue in vitro. Taken together, these findings reveal the existence of a basic neuroendocrine-immune (NEI) network in crabs, and indicate that AST-B could couple with its receptor to trigger downstream signaling pathways and induce immune responses in the hepatopancreas.

Function of the MOB kinase activator-like 1 in the innate immune defense of the oriental river prawn (Macrobrachium nipponense)

The monopolar spindle one binder (MOB) protein, a key signal transducer of the Hippo signaling pathway, is involved in growth control and cancer. In this study, a new MOB kinase activator-like 1 of the oriental river prawns, Macrobrachium nipponense, (MnMOB1) was isolated and characterized. The open reading frame of MnMOB1 consisted of 651 nucleotides that encoded 216 amino acid residues and contained the Mob1_phocein domain. Phylogenetic analysis revealed that MnMOB1 clustered together with the MOB1 from Penaeus vannamei. The distribution of MnMOB1 expression in various tissues of normal prawn revealed that the MnMOB1 expression was highest in the hepatopancreas followed by those in the intestines, gill, heart, stomach, and hemocytes. In prawns challenged with Staphylococcus aureus and Vibrio parahaemolyticus, the expression levels of MnMOB1 in the hepatopancreas, gills, and intestine were upregulated. Furthermore, the expression levels of crustins and anti-lipopolysaccharide factors in prawn injected with S. aureus and V. parahaemolyticus and MnMOB1 knockdown were significantly decreased relative to those in the control group. These findings indicated that MnMOB1 is involved in the regulation of antimicrobial peptide expression and plays a crucial role in the innate immunity of M. nipponense.

Identification of a group D anti-lipopolysaccharide factor (ALF) from kuruma prawn (Marsupenaeus japonicus) with antibacterial activity against Vibrio parahaemolyticus

Anti-lipopolysaccharide factor (ALF), which belongs to the antimicrobial peptide (AMP) family, has become a relatively new weapon to combat severe infections and has been demonstrated to be active against bacteria, fungi and some viruses. In the present study, a new ALF of group D (MjALF-D; GenBank accession No. MN416688) from Marsupenaeus japonicus was detected. MjALF-D encodes a polypeptide with 124 aa, and the peptide contains a 26-residue signal peptide and a lipopolysaccharide-binding domain (LBD). The structure of MjALF-D was found to consist of three α-helices, four β-sheets and random coils. qRT-PCR analysis revealed that MjALF-D expression was primarily observed in the stomach and was universally upregulated in both the gill and stomach after challenge by lipopolysaccharide (LPS) and Vibrio parahaemolyticus. Moreover, rMjALF-D can inhibit the growth of V. parahaemolyticus. rMjALF-D could destroy the bacterial membrane and lead to cytoplasmic leakage investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which may be the mechanism by which rMjALF-D inhibits V. parahaemolyticus. Additionally, rMjALF-D showed distinct binding or antibacterial ability after direct incubation with V. parahaemolyticus or bacterial genomic DNA and a certain effect on the protein expression of it. Together, these results indicated that rMjALF-D possessed the antibacterial activity against V. parahaemolyticus and the potential involvement in the innate immune response of M. japonicus.

The sterol regulatory element binding protein homolog of Penaeus vannamei modulates fatty acid metabolism and immune response

The sterol regulatory element binding proteins (SREBPs) transcription factors family, which regulate the expression of genes involved in cellular lipid metabolism and homeostasis, have recently been implicated in various physiological and pathophysiological processes such as immune regulation and inflammation in vertebrates. Consistent with other invertebrates, we identified a single SREBP ortholog in Penaeus vannamei (designated PvSREBP) with transcripts ubiquitously expressed in tissues and induced by lipopolysaccharide (LPS), Vibrio parahaemolyticus and Streptococcus iniae. In vivo RNA interference (RNAi) of PvSREBP attenuated the expression of several fatty acid metabolism-related genes (i.e., cyclooxygenase (PvCOX), lipoxygenase (PvLOX), fatty acid binding protein (PvFABP) and fatty acid synthase (PvFASN)), which consequently decreased the levels of total polyunsaturated fatty acids (ΣPUFAs). In addition, PvSREBP silencing decreased transcript levels of several immune-related genes such as hemocyanin (PvHMC) and trypsin (PvTrypsin), as well as genes encoding for heat-shock proteins (i.e., PvHSP60, PvHSP70 and PvHSP90). Moreover, in silico analysis revealed the presence of SREBP binding motifs on the promoters of most of the dysregulated genes, while shrimp depleted of PvSREBP were more susceptible to V. parahaemolyticus infection. Collectively, we demonstrated the involvement of shrimp SREBP in fatty acids metabolism and immune response, and propose that PvSREBP and PvHMC modulate each other through a feedback mechanism to establish homeostasis. The current study is the first to show the dual role of SREBP in fatty acid metabolism and immune response in invertebrates and crustaceans.

A novel C-type lectin with a YPD motif from Portunus trituberculatus (PtCLec1) mediating pathogen recognition and opsonization

C-type lectins are a superfamily of Ca²⁺-dependent carbohydrate-recognition proteins that function as pattern recognition receptors (PRRs) in innate immune system. In this study, a new C-type lectin was identified from the swimming crab Portunus trituberculatus (PtCLec1). The full-length cDNA of PtCLec1 was 873 bp encoding 176 amino acids. The predicted PtCLec1 protein contained a signal peptide and a single carbohydrate-recognition domain with a special YPD motif. The PtCLec1 transcripts were mainly detected in hepatopancreas and its relative expression levels were significantly up-regulated after the challenges of Vibrio alginolyticus, Micrococcus luteus and Pichia pastoris. The recombinant PtCLec1 (rPtCLec1) could bind all the tested pathogen-associated molecular patterns (PAMPs), including lipopolysaccharides (LPS), peptidoglycan (PGN) and glucan (GLU), and microorganisms, including V. alginolyticus, V. parahaemolyticus, Pseudomonas aeruginosa, Staphylococcus aureus, M. luteus and P. pastoris. It also exhibited strong activity to agglutinate bacteria and yeast in a Ca²⁺-dependent manner, and such agglutinating activity could be inhibited by d-galactose and LPS. Moreover, rPtCLec1 revealed antimicrobial activity against the tested Gram-negative (V. alginolyticus, V. parahaemolyticus and P. aeruginosa) and Gram-positive bacteria (S. aureus and M. luteus), and promoted the clearance of V. alginolyticus in vivo and hemocyte phagocytosis in vitro. Knockdown of PtCLec1 could down-regulate the expression of phagocytosis-related genes, but enhance the expression levels of prophenoloxidase (proPO) system-related genes, mannose-binding lectin (MBL), antimicrobial peptides (AMPs), MyD88 and Relish. All these results indicate that PtCLec1 might act as a PRR in immune recognition and an opsonin in pathogen elimination.

The red swamp crayfish, Procambarus clarkii cathepsin C, participates in the innate immune response to the viral and bacterial pathogens

The cathepsin C, a lysosomal cysteine protease, involves the modulation of immune and inflammatory responses in living organisms. However, the knowledge on cathepsin C in red swamp crayfish (Procambarus clarkii), a freshwater crustacean with economic values, remained unclear. In the present study, we provide identification and molecular characterization of cathepsin C from P. clarkii. (Hereafter Pc-cathepsin C). The Pc-cathepsin C cDNA contained a 1356 bp open reading frame that encoded a protein of 451 amino acid residues. The deduced amino acid sequence comprised of cathepsin C exclusion domain and pept_C1 domain, and also catalytic residues (Cys²⁴⁸, His³⁹⁵ and Asn⁴¹⁷). Analysis of the transcriptional patterns of the Pc-cathepsin C gene revealed that it was broadly distributed in various tissues of P. clarkii, and it was more abundant in the hepatopancreas and gut. Following a challenge with viral and bacterial pathogen-associated molecular patterns, the expression of Pc-cathepsin C was strongly enhanced at different time points. The knockdown of Pc-cathepsin C, altered the expression of immune-responsive genes, suggesting its immunoregulatory role in P. clarkii. This study has identified and provided the immunoregulatory function of Pc-cathepsin C, which will contribute to further investigation of the molecular mechanism of cathepsin C in crustaceans.

Characterization of a chitinase-1 gene (PtCht-1) from a marine crab Portunus trituberculatus and its response to immune stress

Chitinases play an important role in many biological processes in crustaceans, including molting, digestion, and immunity. In order to further explore the immune defense mechanism of chitinase in Portunus trituberculatus, the PtCht-1 gene was cloned by RACE (rapid-amplification of cDNA ends). This cDNA with a full length of 1910 bp, and an ORF (open reading frame) 1749 bp, coded for 582 amino acid residues and was classified into P. trituberculatus chitinase GH18-group4. It had the typical structural characteristics of GH18 chitinase family. Real-time PCR was used to analyze the expression of PtCht-1 in different tissues, molting stages, after pathogen infection, and low salinity (11‰). PtCht-1 was expressed in all tissues, with the highest expression in the hepatopancreas. In the hepatopancreas of different molting stages, the expression level decreased successively during post-molt stages (A/B), pre-molt stage (D) and inter-molt stage (C). Under normal circumstances, after artificial infection with WSSV and Vibrio parahaemolyticus, the expression of PtCht-1 in hepatopancreas reached the maximum at 48 h, and in hemolymph at 72 h and 24 h, respectively. Overall PtCht-1 expression was up-regulated compared with the control group. Low salinity stress significantly inhibited the expression of PtCht-1, up to 42 folds. Under low salinity stress, the time when WSSV infection reached the peak was markedly delayed by at least 24 h. The results of this study indicate that PtCht-1, as an immune factor, is likely involved in pathogen defense of P. trituberculatus, the immune function of which may be inhibited to some extent after low salinity stress.

Comprehensive expression analysis of the beta integrin from Penaeus monodon indicating its participation in innate immunity and ammonia nitrogen stress response

The aim of the present study was to investigate the function of the beta integrin (PmItgb) in Penaeus monodon. The 3011 bp cDNA sequence of PmItgb was cloned from P. monodon using rapid amplification of cDNA ends (RACE) PCR. Phylogenetic tree analyses indicated that the amino acid sequence of PmItgb should be merged into Fenneropenaeus chinensis (93%). Quantitative real-time PCR (q RT-PCR) revealed that PmItgb mRNA was highly expressed in the hemocytes. In addition, with regard to developmental stages, PmItgb showed significantly higher expression in oosperm, nauplius IV, zoea I and III, and post larval stages than that in other development stages. PmItgb expression in the shrimp epidermis was higher in the postmolt (B) stage, and lower in other molting stages. We also found that Vibrio harveyi and V. anguillarum challenge enhanced PmItgb expression in the hepatopancreas and gills. When PmItgb was inhibited, innate immunity-related genes such as ALF, crustin 1, crustin 7, penaeidin 3, and penaeidin 5 were significantly down-regulated. Furthermore, we demonstrated that PmItgb knock-down by specific dsRNA reduced bacterial clearance. In high ammonia nitrogen concentrations, PmItgb was significantly up-regulated in the hepatopancreas and gills. After PmItgb was silenced, the rate of mortality owing to high ammonia nitrogen concentrations decreased; the expression of related anti-apoptotic genes was up-regulated, and that of the apoptotic genes was slightly down-regulated. These results suggested that PmItgb may be involved in shrimp innate immunity and mediate apoptosis of hepatopancreatic cells induced by high ammonia nitrogen environments.