A Dorsal homolog (FcDorsal) in the Chinese shrimp Fenneropenaeus chinensis is responsive to both bacteria and WSSV challenge

MicroRNA sequencing analysis reveals immune responses in hepatopancreas of Fenneropenaeus penicillatus under white spot syndrome virus infection

White Spot Disease is one of the most harmful diseases of the red tail shrimp, which can cause devastating economic losses due to the highest mortality up to 100% within a few days. MicroRNAs (miRNAs) are large class of small noncoding RNAs with the ability to post-transcriptionally repress the translation of target mRNAs. MiRNAs are considered to have a significant role in the innate immune response of crustaceans, particularly in relation to antiviral defense mechanisms. Numerous crustacean miRNAs have been verified to be required in host immune defense against viral infection, however, till present, the miRNAs functions of F. penicillatus defense WSSV infection have not been studied yet. Here in this study, for the first time, miRNAs involved in the F. penicillatus immune defense against WSSV infection were identified using high-throughput sequencing platform. A total of 432 miRNAs were obtained including 402 conserved miRNAs and 30 novel predicted miRNAs. Comparative analysis between the WSSV-challenged group and the control group revealed differential expression of 159 microRNAs in response to WSSV infection. Among these, 48 were up-regulated and 111 were down-regulated. Ten candidate MicroRNAs associated with immune activities were randomly selected for qRT-PCR analysis, which confirming the expression profiling observed in the MicroRNA sequencing data. As a result, most differentially expressed miRNAs were down-regulated lead to increase the expression of various target genes that mediated immune reaction defense WSSV infection, including genes related to signal transduction, Complement and coagulation cascade, Phagocytosis, and Apoptosis. Furthermore, the genes expression of the key members in Toll and Imd signaling pathways and apoptotic signaling were mediated by microRNAs to activate host immune responses including apoptosis against WSSV infection. These results will help to understand molecular defense mechanism against WSSV infection in F. penicillatus and to develop an effective WSSV defensive strategy in shrimp farming.

Kruppel homolog 1 modulates ROS production and antimicrobial peptides expression in shrimp hemocytes during infection by the Vibrio parahaemolyticus strain that causes AHPND

Shrimp aquaculture has been seriously affected by acute hepatopancreatic necrosis disease (AHPND), caused by a strain of Vibrio parahaemolyticus that carries the Pir toxin plasmids (V. parahaemolyticus (AHPND)). In this study, the transcription factor, Kruppel homolog 1-like of Peneaus vannamei (PvKr-h1), was significantly induced in shrimp hemocytes after V. parahaemolyticus (AHPND) challenge, suggesting that PvKr-h1 is involved in shrimp immune response. Knockdown of PvKr-h1 followed by V. parahaemolyticus (AHPND) challenge increased bacterial abundance in shrimp hemolymph coupled with high shrimp mortality. Moreover, transcriptome and immunofluorescence analyses revealed that PvKr-h1 silencing followed by V. parahaemolyticus (AHPND) challenge dysregulated the expression of several antioxidant-related enzyme genes, such as Cu-Zu SOD, GPX, and GST, and antimicrobial peptide genes, i.e., CRUs and PENs, and reduced ROS activity and nuclear translocation of Relish. These data reveal that PvKr-h1 regulates shrimps' immune response to V. parahaemolyticus (AHPND) infection by suppressing antioxidant-related enzymes, enhancing ROS production and promoting nuclei import of PvRelish to stimulate antimicrobial peptide genes expression.

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.

Effects of Compound Feed Attractants on Growth Performance, Feed Utilization, Intestinal Histology, Protein Synthesis, and Immune Response of White Shrimp (Litopenaeus Vannamei)

To investigate the effects of compound attractants on the growth performance, feed utilization, intestinal morphology, protein synthesis, and immune response of Litopenaeus vannamei, the following seven diets were formulated: a positive control (P), a negative control (N), and five diets with compound attractants which were labeled as A, B, C, D, and E, each with four of five tested attractants (yeast extract, squid visceral powder, fish soluble, and squid paste, shrimp paste), respectively. Shrimp (0.71 ± 0.00 g) were distributed to seven groups of four replicates and fed for 7 weeks. Results showed that the final body weight, feed intake, specific growth rate, and weight gain of shrimp in the B and D groups were the greatest. Hemolymph total antioxidant capacity of shrimp in the B, D, and E groups reached the highest level. In the hepatopancreas, the activity of total nitric oxide synthase, malondialdehyde content, the expression levels of sod, myd88, eif4e2, and raptor in shrimp fed the B diet were the highest, and the highest levels of dorsal and relish were observed in the C group. In the intestine, intestinal muscle thickness and expression levels of toll and eif2α in the C group were the highest, while the highest expression level of sod and relish occurred in the B group. In summary, the B and E diets promoted the feed intake, growth performance and the antioxidant enzyme activity of L. vannamei. The C diet enhanced the protein synthesis of shrimp. Regression analysis indicated that the WG and FI of shrimp were increased as the dietary inclusion levels of squid paste and shrimp paste increased, while they were decreased as the dietary inclusion levels of yeast extract and fish soluble increased.

The ECSIT Mediated Toll3-Dorsal-ALFs Pathway Inhibits Bacterial Amplification in Kuruma Shrimp

The Toll signaling pathway plays an important role in animal innate immunity. However, its activation and signal transmission greatly differ across species and need to be investigated. Shrimp farming is a worldwide economic activity affected by bacterial disease from the 1990s, which promoted research on shrimp immunity. In this study, we first proved that, among the three identified Toll receptors in Marsupenaeus japonicus kuruma shrimp, Toll 3 plays a pivotal role in initiating the antibacterial response in vivo, especially upon anti-Staphylococcus aureus infection. Further research showed that this result was due to the activation of the Dorsal transcription factor, which induced the expression of two anti-lipopolysaccharide factors (Alfs). Moreover, the evolutionarily conserved signaling intermediate in Toll pathways, ECSIT, was proved to be needed for signal transmission from Toll 3 to Dorsal and the expression of anti-lipopolysaccharide factors. Finally, the mortality assay showed that a Toll3-ECSIT-Dorsal-Alf axis was functional in the anti-S.aureus immunity of M. japonicus shrimp. The results provide new insights into the function and signal transduction of the Toll pathway in aquatic species and offer basic knowledge for shrimp disease control and genetic breeding.

Identification and function of an Arasin-like peptide from Litopenaeus vannamei

Antimicrobial peptides (AMPs) play an important role in the host defense system of shrimps. In this study, an Arasin-like peptide, named as LvArasin-like, was identified from the hemocytes of the pacific white shrimp, Litopenaeus vannamei. The complete open reading frame (ORF) of LvArasin-like was 213 bp, encoding 70 amino acid residues with a predicted molecular mass of 5.68 kDa and a theoretical isoelectric point (pI) of 6.73. The predicted peptide consisted of a signal peptide, an N-terminal Pro/Arg-rich domain, and a C-terminal cysteine-rich domain. LvArasin-like expression was most abundant in the gills and was up-regulated in hemocytes after LPS or Poly I:C injection as well as challenges by Vibrio parahaemolyticus or Staphylococcus aureus infection. In the heterologous expression system, LvArasin-like protein (rLvArasin-like) was recombinantly expressed in the forms of a dimer or both a monomer and dimer. The rLvArasin-like could directly bind to gram-positive and gram-negative bacteria and exhibited broad-spectrum antimicrobial activity towards them, with 50 % of minimal inhibitory concentrations (MIC50) of 6.25-50 μM. Moreover, dsRNA-mediated knockdown of LvArasin-like enhanced the susceptibility of shrimp to V. parahaemolyticus. In addition, the transcriptional level of LvArasin-like was downregulated when silencing of the transcription factors LvDorsal and LvRelish using RNAi in vivo. All of these results suggest that LvArasin-like is involved in host defense against bacterial infection. Therefore, it is a potential therapeutic agent for disease control in shrimp aquaculture.

Transcriptome analysis reveals the molecular mechanisms of heterosis on thermal resistance in hybrid abalone

BACKGROUND

Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive.

RESULTS

Heterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone.

CONCLUSION

More alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.

Anthraquinone extract from Rheum officinale Bail improves growth performance and Toll-Relish signaling-regulated immunity and hyperthermia tolerance in freshwater prawn Macrobrachium nipponense

This study was aimed to investigate the facilitation of anthraquinone extract on growth performance, immunity, and antioxidant capacity of the oriental river prawn (Macrobrachium nipponense), and whether it could ameliorate the hyperthermia stress. A 12-week rearing experiment was conducted with 0, 125, 250, 500, and 1000 mg kg^-1 anthraquinone extract from Rheum officinale Bail-supplemented diets (AE0, AE125, AE250, AE500, and AE1000), and followed a 48-h thermal stress with 32℃ incubation. Results indicate AE250 and AE500 significantly improved the growth performance and feed utilization, the optimum level was estimated to be 251.22 mg kg^-1 based on the regression analysis of special growth ratio (SGR). Meanwhile, AE250 and AE500 improved antioxidant enzyme activity and immune-related protein concentration of iNOS-NO signaling. Under thermal stress, AE250 and AE500 improved the heat tolerance, and Toll-Relish signaling was active to the resistance. These results indicate anthraquinone extract could be used as an effective immunostimulant to improve growth performance, physiological balance and protect organism form environmental hyperthermia stress. This may provide insights for immunostimulant development in aquaculture production.

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.

The involvement of crustaceans toll-like receptors in pathogen recognition

Crustacean species are considered as a major sector in the aquaculture industry that plays a fundamental role in the world's economy. However, with a wide range of various epidemic diseases in the industry, studies of immune-related genes such as toll-like receptor genes are of great importance. Recently, the TLR in crustacean species has been described to perform a vital role in defense of crustacean against the pathogens. Meanwhile, many TLR genes from crustacean were characterized, and their contribution discovered in innate immunity against several pathogens. This review was aimed to present an overview of the crustacean TLRs including structural features that contained three major domains: a leucine-rich repeat (LRR) domains, a transmembrane area (TM), and a conserved region called Toll/interleukin-1 receptor (TIR) domain. The tissue distribution patterns of TLR genes, which act as a guide for future research on which TLR gene or genes that can be expressed, at which tissue or tissues. We also described recent works on the expression of the TLR gene that evaluated the immune function after pathogen stimulation in shrimp, crab, and crayfish. Furthermore, we recommended a prospective for future investigation plan that might contribute to the development and management systems in the global crustacean aquaculture industry. Lastly, we assumed that a clear understanding of the expression pattern and biological function of crustacean TLR genes could serve as a baseline for future immunological studies.

Isolation and transcriptome analysis of three subpopulations of shrimp hemocytes reveals the underlying mechanism of their immune functions

Hemocytes in shrimp play important roles in innate immune responses against pathogens. Although three types of hemocytes including hyalinocytes, semi-granulocytes and granulocytes were identified based on their morphological characters in penaeid shrimp, knowledge about the molecular basis of their functions in the immunity is still very limited. In the present study, three subpopulations of hemocytes were firstly separated by Percoll gradient centrifugation, and their transcriptomes were analyzed. The data showed that significantly differential gene expression patterns existed in different types of hemocytes. The genes encoding phagocytic receptors, lectins and actin cytoskeleton involved in phagocytosis were highly expressed in hyalinocytes, while genes involved in the humoral immunity signaling pathways were highly expressed in semi-granulocytes, and genes encoding prophenoloxidase (proPO)-activating enzyme and serine proteases involved in proPO system activation were highly expressed in granulocytes. Further flow cytometry analysis indicated that hyalinocytes were the main hemocytes subpopulation responsible for ingesting foreign fluorescent beads, and this ingestion process mainly depends on the endocytic way of macropinocytosis. These data provide valuable information for understanding the molecular basis of distinct shrimp hemocytes subpopulations of shrimp in cellular and humoral immunity.

The NF-κB family member dorsal plays a role in immune response against Gram-positive bacterial infection in mud crab (Scylla paramamosain)

The NF-κB family is a set of evolutionarily conserved transcription factors that play central roles in various biological events. Dorsal is an invertebrate NF-κB family member that is essential for the regulation of immune responses. In the current study, the Dorsal gene from Scylla paramamosain (SpDorsal) was identified, which showed high homology to other crustacean Dorsal proteins. Expression of SpDorsal was highest in hemocytes and could be significantly changed after immune stimulations. In expression vector-transfected S2 cells, SpDorsal was mainly localized in the cytoplasm and could be efficiently translocated into the nucleus upon immune stimulations with the Gram-positive bacteria Staphylococcus aureus and poly (I:C), but not the Gram-negative bacteria Vibrio parahaemolyticus. As a transcription factor, SpDorsal could activate the promoter of S. paramamosain Hyastatin (SpHyastatin) in vitro, while S. paramamosain Cactus (SpCactus), a homolog of IκB, could interact with SpDorsal to prevent its nuclear translocation and inhibit its transcription factor activity. Silencing of SpDorsal in vivo using RNAi strategy significantly increased the mortality of crabs infected with S. aureus but not that with V. parahaemolyticus. These indicated that the SpDorsal signaling pathway could be mainly implicated in immune responses against Gram-positive bacterial infection in S. paramamosain.

Effects of dopamine on immune signaling pathway factors, phagocytosis and exocytosis in hemocytes of Litopenaeus vannamei

Dopamine (DA) is an important neuroendocrine factor, which can act as neurotransmitter and neurohormone. In this study, we explored the immune defense mechanism in Litopenaeus vannamei with injection of dopamine at 10^-7 and 10^-6 mol shrimp^-1, respectively. The genes expressions of dopamine receptor (DAR), G proteins (Gs, Gi, Gq), phagocytosis and exocytosis-related proteins, as well as intracellular signaling pathway factors, and immune defense parameters were measured. Results showed that mRNA expression levels of dopamine receptor D4 (D4), Gi, nuclear transcription factors and exocytosis-related proteins decreased significantly and reached the minimum at 3 h, while the genes expressions of Gs, Gq and phagocytosis-related proteins reached the highest and lowest levels at 3 h and 6 h, respectively. The second messenger synthetases increased significantly in treatment groups within 3 h. Simultaneously, the second messengers and protein kinases shared a similar trend, which were significantly elevated and reached the peak value at 3 h. Ultimately lead to the total hemocyte count (THC), proPO activity and phagocytic activity decreased significantly, reaching minimum values at 3 h, 3 h and 6 h, respectively. While PO activity showed obvious peak changes, which maximum value reached at 3 h. These results suggested that DA receptor could couple with G protein after DA injection and might regulate immunity through cAMP-PKA, DAG-PKC or CaM pathway.

TmDorX2 positively regulates antimicrobial peptides in Tenebrio molitor gut, fat body, and hemocytes in response to bacterial and fungal infection

Dorsal, a member of the nuclear factor-kappa B (NF-κB) family of transcription factors, is a critical downstream component of the Toll pathway that regulates the expression of antimicrobial peptides (AMPs) against pathogen invasion. In this study, the full-length ORF of Dorsal was identified from the RNA-seq database of the mealworm beetle Tenebrio molitor (TmDorX2). The ORF of TmDorX2 was 1,482 bp in length, encoding a polypeptide of 493 amino acid residues. TmDorX2 contains a conserved Rel homology domain (RHD) and an immunoglobulin-like, plexins, and transcription factors (IPT) domain. TmDorX2 mRNA was detected in all developmental stages, with the highest levels observed in 3-day-old adults. TmDorX2 transcripts were highly expressed in the adult Malpighian tubules (MT) and the larval fat body and MT tissues. After challenging the larvae with Staphylococcus aureus and Escherichia coli, the TmDorX2 mRNA levels were upregulated 6 and 9 h post infection in the whole body, fat body, and hemocytes. Upon Candida albicans challenge, the TmDorX2 mRNA expression were found highest at 9 h post-infection in the fat body. In addition, TmDorX2-knockdown larvae exposed to E. coli, S. aureus, or C. albicans challenge showed a significantly increased mortality rate. Furthermore, the expression of 11 AMP genes was downregulated in the gut and fat body of dsTmDorX2-injected larvae upon E. coli challenge. After C. albicans and S. aureus challenge of dsTmDorX2-injected larvae, the expression of 11 and 10 AMPs was downregulated in the gut and fat body, respectively. Intriguingly, the expression of antifungal transcripts TmTenecin-3 and TmThaumatin-like protein-1 and -2 was greatly decreased in TmDorX2-silenced larvae in response to C. albicans challenge, suggesting that TmDorX2 regulates antifungal AMPs in the gut in response to C. albicans infection. The AMP expression profiles in the fat body, hemocytes, gut, and MTs suggest that TmDorX2 might have an important role in promoting the survival of T. molitor larvae against all mentioned pathogens.

Effects of crustacean hyperglycemic hormone (CHH) on regulation of hemocyte intracellular signaling pathways and phagocytosis in white shrimp Litopenaeus vannamei

Shrimps like other arthropods rely on innate immune system, and may have some form of adaptive immunity in defending against pathogens. Phagocytosis is one of the oldest cellular processes, serving as a development process, a feeding mechanism and especially as a key defense reaction in innate immunity of all multicellular organisms. It is confirmed that crustacean hyperglycemic hormone (CHH) is one of the most important neuropeptides produced by Neuro-endocrine Immune (NEI) regulatory network, which undertakes important roles in various biological processes, especially in immune function and stress response. In this study, the recombinant Litopenaeus vannamei CHH (rLvCHH) was obtained from a bacterial expression system and the intracellular signaling pathways involved in the mechanism of phagocytosis after rLvCHH injection was investigated. The results showed that the contents of adenylyl cyclase (AC), phospholipase C (PLC) and calmodulin (CaM) in hemocytes were increased significantly after rLvCHH injection. Furthermore, the mRNA expression levels of NF-kB family members (relish and dorsal) and phagocytosis-related proteins in hemocytes were basically overexpressed after rLvCHH stimulation, while the expression level of NF-kB repressing factor (NKRF) gene was down-regulated significantly. Eventually, the total hemocyte count and phagocytic activity of hemocyte were dramatically enhanced within 3 h. Collectively, these results indicate that shrimps L. vannamei could carry out a simple but 'smart' NEI regulation through the action of neuroendocrine factors, which could couple with their receptors and trigger the downstream signaling pathways during the phagocytic responses of hemocytes.

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.

Identification and function of penaeidin 3 and penaeidin 5 in Fenneropenaeus merguiensis

Antimicrobial peptides (AMPs) participate in immune defenses of invertebrate, vertebrate and plant species. As a kind of AMPs, penaeidins play important roles in innate immunity of shrimp. In this study, two penaeidin homologues termed FmPEN3 and FmPEN5 were cloned and identified from Fenneropenaeus merguiensis for the first time. The complete open reading frames (ORFs) of FmPEN3 and FmPEN5 were 216 bp and 240 bp, encoding 71 and 79 amino acids, respectively. Both FmPEN3 and FmPEN5 contain an N-terminal proline-rich domain (PRD) and a C-terminal cysteine-rich domain (CRD). The genome structure of FmPEN3 and FmPEN5 genes both consist of 2 exons and 1 intron. qPCR analysis showed that FmPEN3 was constitutively expressed but FmPEN5 transcripts were found only in hemocytes, gills, epidermis, nerve and pyloric cecum. The FmPEN3 and FmPEN5 expression were responsive to Vibrio parahaemolyticus and Micrococcus lysodeikticus infection and their transcription levels were downregulated by RNAi silencing of the transcription factors FmDorsal and FmRelish. In addition, recombinant proteins of FmPEN3 (rFmPEN3) and FmPEN5 (rFmPEN5) were successfully expressed in E. coli. The antibacterial assays revealed that rFmPEN3 and rFmPEN5 could inhibit the growth of M. lysodeikticus but only rFmPEN5 could inhibit the growth of V. parahaemolyticus in vitro. In summary, the results presented in this study indicated the functions of FmPEN3 and FmPEN5 played in anti-bacterial immunity of F. merguiensis, providing some insights into the function of AMPs in shrimp.

The crab Relish plays an important role in white spot syndrome virus and Vibrio alginolyticus infection

Relish is a transcription factor and forms an important part of the immune deficiency signaling pathway. In the current study, a Relish homolog was cloned from the hemolymph of Scylla paramamosain using RT-PCR and RACE. The full length cDNA of Relish consists of 4263 base pairs (bp), including a 3552 bp open reading frame encoding a 1184 amino acid protein. The data showed that Relish was highly expressed in the gonad and digestive organs of S. paramamosain. Furthermore, the expression of Relish was up-regulated by infection with white spot syndrome virus (WSSV) or Vibrio alginolyticus. When Relish was knocked down, immune genes such as Janus Kinase, signal transducer and activator of transcription, crustin antimicrobial peptide, prophenoloxidase, C-type-lectin and myosin-II-essential-light-chain-like-protein were significantly down-regulated (P < 0.01), and Toll-like receptor was significantly up-regulated (P < 0.01) in hemocytes. The mortality of WSSV-infected or V. alginolyticus-infected crabs was enhanced following Relish knockdown. Thus, Relish is very important in the progression of WSSV and V. alginolyticus infection. It was found that Relish knockdown caused the highest level of apoptosis in the disease-free group, and higher levels of apoptosis in the WSSV group and V. alginolyticus group compared with that in the control group. Knockdown of Relish influenced the activity of phenoloxidase (PO) and superoxide dismutase (SOD), and total hemocyte count (THC) following WSSV or V. alginolyticus infection, indicating that Relish plays a regulatory role in the immune response to WSSV or V. alginolyticus infection in crabs. Thus, we conclude that Relish may anticipate host defense mechanisms against pathogen infection by affecting apoptosis, THC, PO activity and SOD activity.

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

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

A cytosolic sensor, PmDDX41, mediates antiviral immune response in black tiger shrimp Penaeus monodon

DEAD (Asp-Glu-Ala-Asp)-box polypeptide 41 (DDX41), a receptor belonging to the DExD family, has recently been identified as an intracellular DNA sensor in vertebrates. Here, we report on the identification and functional characterization of PmDDX41, the first cytosolic DNA sensor in shrimp. By searching a Penaeus monodon expressed sequence tag (EST) database (http://pmonodon.biotec.or.th), three cDNA fragments exhibiting similarity to DDX41 in various species were identified and assembled, resulting in a complete open reading frame of PmDDX41 that contains 1863-bp and encodes a putative protein of 620 amino acids. PmDDX41 shares 83% and 79% similarity to DDX41 homolog from the bee Apis florea and fruit fly Drosophila melanogaster, respectively and contains three conserved domains in the protein: DEADc domain, HELICc domain, and zinc finger domain. The transcript of PmDDX41 was detected in all tested tissues and was up-regulated upon infection with a DNA virus, white spot syndrome virus (WSSV). However, PmDDX41 mRNA expression was not significantly changed and down-regulated in response to a bacterium, Vibrio harveyi, or an RNA virus, yellow head virus (YHV), respectively, compared with the control phosphate-buffered saline-injected shrimp. Furthermore, the suppression of PmDDX41 by dsRNA-mediated gene silencing resulted in more rapid death of WSSV-infected shrimp and a significant decrease in the mRNA expression levels of several immune-related genes (PmIKKβ, PmIKKɛ, PmRelish, PmCactus, PmDorsal, PmPEN3, PmPEN5, and ALFPm6). These results suggest that PmDDX41 is involved in the antiviral response, probably via a DNA-sensing pathway that is triggered through the IκB kinase complex and leads to the activation of several immune-related genes.

Shrimp humoral responses against pathogens: antimicrobial peptides and melanization

Diseases have caused tremendous economic losses and become the major problem threatening the sustainable development of shrimp aquaculture. The knowledge of host defense mechanisms against invading pathogens is essential for the implementation of efficient strategies to prevent disease outbreaks. Like other invertebrates, shrimp rely on the innate immune system to defend themselves against a range of microbes by recognizing and destroying them through cellular and humoral immune responses. Detection of microbial pathogens triggers the signal transduction pathways including the NF-κB signaling, Toll and Imd pathways, resulting in the activation of genes involved in host defense responses. In this review, we update the discovery of components of the Toll and Imd pathways in shrimp and their participation in the regulation of shrimp antimicrobial peptide (AMP) synthesis. We also focus on a recent progress on the two most powerful and the best-studied shrimp humoral responses: AMPs and melanization. Shrimp AMPs are mainly cationic peptides with sequence diversity which endues them the broad range of activities against microorganisms. Melanization, regulated by the prophenoloxidase activating cascade, also plays a crucial role in killing and sequestration of invading pathogens. The progress and emerging research on mechanisms and functional characterization of components of these two indispensable humoral responses in shrimp immunity are summarized and discussed. Interestingly, the pattern recognition protein (PRP) crosstalk is evidenced between the proPO activating cascade and the AMP synthesis pathways in shrimp, which enables the innate immune system to build up efficient immune responses.

A role of tumor susceptibility gene 101 (TSG101) in innate immune response of crayfish Procambarus clarkii

Tumor susceptibility gene 101 (TSG101) is a multi-functional gene involved in cell growth and proliferation in vertebrates. However, its role in the innate immune response of crustaceans remains unclear. Here, a TSG101 gene was identified in crayfish Procambarus clarkii with an open reading frame of 1320 bp that encoded a predicted 48.3-kDa protein highly homologous to those in other invertebrates. TSG101 mRNA was highly expressed in stomach and hepatopancreas, and its expression was induced significantly in different tissues (hemocytes, gills and intestine) by lipopolysaccharide (LPS) and polyinosinic:polycytidylic acid (poly I: C) with various expression patterns. Recombinant TSG101 protein was expressed in Escherichia coli, and a possible protein-protein interaction between TSG101 and hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) was explored by far-western blotting. RNA interference of TSG101 affected the gene expression of members of the Toll pathway. These results suggest that TSG101 is involved in the innate immune responses of P. clarkii.

Activation of Toll Pathway Is Different between Kuruma Shrimp and Drosophila

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

cDNA cloning and expression analysis of a phosphopyruvate hydratase gene from the chinese shrimp Fenneropenaeus chinensis

In the present study a cDNA encoding a phosphopyruvate hydratase (enolase) was cloned from the muscle of the Chinese shrimp (Fenneropenaeus chinensis) and named as FcEnolase. The cDNA of FcEnolase encoded a protein of 434 amino acid residues with a molecular mass 47.22 kDa. The residues 342-355 constituted the signature motif "LLLKVNQIGSVTES". A SNP locus (C96T) in the ORF at 96 bp was identified. The results showed that the FcEnolase was a conserved gene. In the normal F. chinensis, the mRNA level in the muscle was much higher (P < 0.05) than the mRNA level in the gill and hepatopancreas. To verify the mRNA level of FcEnolase in the F. chinensis post WSSV infection, a real-time RT-PCR was performed. In the WSSV-infected F. chinensis, the FcEnolase mRNA level was significantly (P < 0.05) up-regulated in the muscle at 12 and 24 h post challenge (hpc) to approximately 2.7-fold and 2.7-fold the mRNA level in the controls, respectively. The FcEnolase mRNA level in the gill was significantly (P < 0.05) down-regulated at 6 hpc to approximately 0.3-fold the mRNA level in the control, followed by a significant (P < 0.05) up-regulation at 12 hpc to approximately 2.8-fold the mRNA level in the control. There was no obvious change of FcEnolase mRNA level in the hepatopancreas during the infection process. The expression profile coincided with the fact that WSSV primarily infects the tissues of muscle and gill, but hardly infects hepatopancreas. To verify the protein level of FcEnolase post WSSV infection, a Western blot was performed. The FcEnolase protein level in the muscle at 24 hpc significantly (P < 0.05) increased to approximately 2.1-fold the level in the control. These results showed the characterization of FcEnolase and suggested that the FcEnolase might be involved in the response of F. chinensis to WSSV infection.

In vivo activity and the transcriptional regulatory mechanism of the antimicrobial peptide SpHyastatin in Scylla paramamosain

A new gene homologous to the reported antimicrobial peptide (AMP) hyastatin from Hyas araneus was screened in the SSH library constructed from the hemocytes of Scylla paramamosain, and named SpHyastatin. In vivo study showed that SpHyastatin was predominantly expressed in hemocytes of S. paramamosain. With the challenge of either Vibrio parahaemolyticus or lipopolysaccharide (LPS), SpHyastatin showed a positive response, meaning that it was probably involved in the immune reaction against bacterial infection in vivo. A distinctive feature of SpHyastatin in comparison with six other known AMPs tested was that SpHyastatin could maintain a higher transcription level from megalopas to the adult crab, indicating a potential consistent resistance against pathogens conferred by this peptide existing in the blood circulation of crabs. RNA interference assay was performed to inhibit SpHyastatin transcription in vivo and the result demonstrated that silencing SpHyastatin mRNA transcripts could decrease the survival rate of crabs challenged with V. parahaemolyticus. To further understand the molecular mechanisms that regulate SpHyastatin expression, a 576 bp 5'-flanking sequence of SpHyastatin was obtained using genome walking. Here, we focused our experiments on investigating the roles of the putative NF-κB binding site in LPS-mediated transcriptional regulation of the SpHyastatin gene using endothelial progenitor cells and Hela cells. Luciferase reporter analyses demonstrated that the putative NF-κB element acted as a positive regulatory element and was essential for the induction of SpHyastatin promoter by LPS. These results should shed light on the in vivo functional property and the molecular mechanism of regulation for the crab AMP SpHyastatin.

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

Nuclear factor-kappa B (NF-κB) pathways play important roles in innate immune responses. In this study, we identified a dorsal homolog (MrDorsal) from freshwater prawn Macrobrachium rosenbergii. The full-length cDNA of MrDorsal comprised 2533 bp with an open reading frame of 1986 bp, which encoded a peptide of 661 amino acid residues. Amino acid sequence analysis showed that MrDorsal contains a Rel homolog domain and an IPT/TIG (i.e., Ig-like, plexin, and transcription factors) domain. The signature sequence of dorsal protein FRYMCEG existed in the deduced amino acid sequence. Sequence analysis showed that MrDorsal shared high similarities with Dorsal from invertebrate species. MrDorsal was abundant in the hemocytes and gills of healthy prawns but minute levels were detected in other tissues. The expression of MrDorsal was significantly upregulated 48 h after the white spot syndrome virus (WSSV-) challenge. Knockdown of MrDorsal using double-stranded RNA could suppress the transcription of crustin genes (MrCrustin2 and MrCrustin4) in gills of prawns after 48 h of the WSSV challenge. Results indicated that MrDorsal was involved to regulate the expression of crustin genes and it might play potential important roles during WSSV infection.

Isolation and expression analysis of an MAPKK gene from Fenneropenaeus chinensis in response to white spot syndrome virus infection

Mitogen-activated kinase kinase (MAPKK) is an important gene involved in the host-virus interaction process. To obtain a better understanding of MAPKK in the interaction process between the Chinese shrimp Fenneropenaeus chinensis and white spot syndrome virus (WSSV), we cloned the sequence of an MAPKK cDNA from F. chinensis (FcMAPKK) and investigated the effect of FcMAPKK on WSSV infection. The results showed that the FcMAPKK gene contained a 1227 bp open reading frame (ORF), which encoded a highly conserved protein with a serine/threonine protein kinase catalytic (S_TKc) domain. The deduced amino acid sequence of FcMAPKK shared identities between 11.9 and 92.6% with MAPKKs from vertebrate, invertebrate, plant and fungus species. The FcMAPKK was expressed in all the examined tissues in the normal F. chinensis. FcMAPKK expression level was highest in the hepatopancreas where it was approximately 2.6-fold the expression level in the gill, and lowest in the muscle where it was approximately 0.3-fold the expression level in the hepatopancreas. The FcMAPKK expression levels in the muscle, gill, and hepatopancreas were all changed post WSSV challenge. The FcMAPKK expression was significantly (P < 0.01) up-regulated in the muscle of F. chinensis at 48 h post WSSV infection. The WSSV began to replicate quickly in the normal F. chinensis at 48 h post infection, while the WSSV replication in the U0126-treated F. chinensis could be significantly (P < 0.05) inhibited. The results suggested that FcMAPKK might be involved in the WSSV infection process, and hijacking of FcMAPKK might be required for WSSV replication in F. chinensis.

Proteomic analysis by iTRAQ in red claw crayfish, Cherax quadricarinatus, hematopoietic tissue cells post white spot syndrome virus infection

To elucidate proteomic changes of Hpt cells from red claw crayfish, Cherax quadricarinatus, we have carried out isobaric tags for relative and absolute quantitation (iTRAQ) of cellular proteins at both early (1 hpi) and late stage (12 hpi) post white spot syndrome virus (WSSV) infection. Protein database search revealed 594 protein hits by Mascot, in which 17 and 30 proteins were present as differentially expressed proteins at early and late viral infection, respectively. Generally, these differentially expressed proteins include: 1) the metabolic process related proteins in glycolysis and glucogenesis, DNA replication, nucleotide/amino acid/fatty acid metabolism and protein biosynthesis; 2) the signal transduction related proteins like small GTPases, G-protein-alpha stimulatory subunit, proteins bearing PDZ- or 14-3-3-domains that help holding together and organize signaling complexes, casein kinase I and proteins of the MAP-kinase signal transduction pathway; 3) the immune defense related proteins such as α-2 macroglobulin, transglutaminase and trans-activation response RNA-binding protein 1. Taken together, these protein information shed new light on the host cellular response against WSSV infection in a crustacean cell culture.

Co-expression of Dorsal and Rel2 Negatively Regulates Antimicrobial Peptide Expression in the Tobacco Hornworm Manduca sexta

Nuclear factor κB (NF-κB) plays an essential role in regulation of innate immunity. In mammals, NF-κB factors can form homodimers and heterodimers to activate gene expression. In insects, three NF-κB factors, Dorsal, Dif and Relish, have been identified to activate antimicrobial peptide (AMP) gene expression. However, it is not clear whether Dorsal (or Dif) and Relish can form heterodimers. Here we report the identification and functional analysis of a Dorsal homologue (MsDorsal) and two Relish short isoforms (MsRel2A and MsRel2B) from the tobacco hornworm, Manduca sexta. Both MsRel2A and MsRel2B contain only a Rel homology domain (RHD) and lack the ankyrin-repeat inhibitory domain. Overexpression of the RHD domains of MsDorsal and MsRel2 in Drosophila melanogaster S2 and Spodoptera frugiperda Sf9 cells can activate AMP gene promoters from M. sexta and D. melanogaster. We for the first time confirmed the interaction between MsDorsal-RHD and MsRel2-RHD, and suggesting that Dorsal and Rel2 may form heterodimers. More importantly, co-expression of MsDorsal-RHD with MsRel2-RHD suppressed activation of several M. sexta AMP gene promoters. Our results suggest that the short MsRel2 isoforms may form heterodimers with MsDorsal as a novel mechanism to prevent over-activation of antimicrobial peptides.

Identification and molecular characterization of dorsal and dorsal-like genes in the cyclopoid copepod Paracyclopina nana

To date, knowledge of the immune system in aquatic invertebrates has been reported in only a few model organisms, even though all metazoans have an innate immune system. In particular, information on the copepod's immunity and the potential role of key genes in the innate immune systems is still unclear. In this study, we identified dorsal and dorsal-like genes in the cyclopoid copepod Paracyclopina nana. In silico analyses for identifying conserved domains and phylogenetic relationships supported their gene annotations. The transcriptional levels of both genes were slightly increased from the nauplius to copepodid stages, suggesting that these genes are putatively involved in copepodid development of P. nana. To examine the involvement of both genes in the innate immune response and under stressful conditions, the copepods were exposed to lipopolysaccharide (LPS), different culture densities, salinities, and temperatures. LPS significantly upregulated mRNA expressions of dorsal and dorsal-like genes, suggesting that both genes are transcriptionally sensitive in response to immune modulators. Exposure to unfavorable culture conditions also increased mRNA levels of dorsal and dorsal-like genes. These findings suggest that transcriptional regulation of the dorsal and dorsal-like genes would be associated with environmental changes in P. nana.

Analysis on the expression and function of syndecan in the Pacific white shrimp Litopenaeus vannamei

Syndecan is considered to be a multifunctional protein which functions as a cell surface receptor involved in cell adhesion, migration, cytoskeleton organization and differentiation. Previous bioinformatic analysis has revealed that syndecan in shrimp might interact with white spot syndrome virus (WSSV). In the present study, we experimentally studied the function of syndecan in shrimp immunity. The syndecan from Litopenaeus vannamei (LvSDC) was cloned and analyzed. The full-length cDNA of LvSDC was 1005 bp, consisting of 59 bp 5'-UTR, 253 bp 3'-UTR, and 693 bp open reading frame encoding 230 amino acids. LvSDC consisted of an extracellular domain (ED), a transmembrane domain (TM) and a cytoplasmic domain (CD). TM and CD shared high similarities with those of syndecan proteins from other species. LvSDC was ubiquitously expressed in all tested tissues, with the highest level in Oka. After WSSV challenge, the transcription level of LvSDC in Oka was apparently up-regulated. Recombinant LvSDC protein and its rabbit polyclonal antibody were prepared for detecting the location of LvSDC in hemocytes using immunocytochemistry approach. Data showed that LvSDC mainly located at the cell membrane and the cytoplasm of hemocytes. After silencing of LvSDC with siRNA, the WSSV copy numbers and mortality of shrimp after WSSV infection were both significantly decreased. These data provide useful information for understanding the immune mechanism of shrimp to WSSV infection.

Microarray Analysis of Immunity Against WSSV in Response to Injection of Non-specific Long dsRNA in Kuruma Shrimp, Marsupenaeus japonicus

Injection of shrimp with non-specific double-stranded RNA (dsRNA) of diverse lengths, sequences, and base compositions is known to induce non-specific immunity and protect against lethal disease, although the mechanisms are unclear. Previous shrimp studies examined the effects of non-specific RNA on particular pathways, while their global effects have not been examined. To understand the global effects of non-specific RNA in shrimp, we injected kuruma shrimp (Marsupenaeus japonicus) with a dsRNA and a small interfering RNA (siRNA) that is not specific to any gene in the shrimp genome and then examined global gene expression at 24 and 48 h with a microarray. For the non-specific RNA, we chose double-stranded green fluorescent protein (dsGFP) and siGFP because they are commonly used as mock controls and their effects on shrimp have not yet been studied. Injection of PBS was used as a control. The microarray results showed that many genes were up-regulated and some were down-regulated by dsGFP. In addition, dsGFP injection increased survival following WSSV challenge. The changes in expression for several genes were confirmed by quantitative PCR. The up-regulated genes included genes for eight immune-related proteins: c-type lectin 2, hemocyte homeostasis-associated protein, viral responsive protein, fibrinogen-related protein 1, sid-1 like protein, argonaute 2, Dicer 2, and heat shock protein 90. These results show that injection of shrimp with non-specific dsRNA hinders viral accumulation and prevents significant mortalities.

Recent insights into host-pathogen interaction in white spot syndrome virus infected penaeid shrimp

Viral disease outbreaks are a major concern impeding the development of the shrimp aquaculture industry. The viral disease due to white spot syndrome virus (WSSV) observed in early 1990s still continues unabated affecting the shrimp farms and cause huge economic loss to the shrimp aquaculture industry. In the absence of effective therapeutics to control WSSV, it is important to understand viral pathogenesis and shrimp response to WSSV at the molecular level. Identification and molecular characterization of WSSV proteins and receptors may facilitate in designing and development of novel therapeutics and antiviral drugs that may inhibit viral replication. Investigations into host-pathogen interactions might give new insights to viral infectivity, tissue tropism and defence mechanism elicited in response to WSSV infection. However, due to the limited information on WSSV gene function and host immune response, the signalling pathways which are associated in shrimp pathogen interaction have also not been elucidated completely. In the present review, the focus is on those shrimp proteins and receptors that are potentially involved in virus infection or in the defence mechanism against WSSV. In addition, the major signalling pathways involved in the innate immune response and the role of apoptosis in host-pathogen interaction is discussed.

RNA-seq analysis of Macrobrachium rosenbergii hepatopancreas in response to Vibrio parahaemolyticus infection

Background

The Malaysian giant freshwater prawn, Macrobrachium rosenbergii, is an economically important crustacean worldwide. However, production of this prawn is facing a serious threat from Vibriosis disease caused by Vibrio species such as Vibrio parahaemolyticus. Unfortunately, the mechanisms involved in the immune response of this species to bacterial infection are not fully understood. We therefore used a high-throughput deep sequencing technology to investigate the transcriptome and comparative expression profiles of the hepatopancreas from this freshwater prawn infected with V. parahaemolyticus to gain an increased understanding of the molecular mechanisms underlying the species’ immune response to this pathogenic bacteria.

Result

A total of 59,122,940 raw reads were obtained from the control group, and 58,385,094 reads from the Vibrio-infected group. Via de novo assembly by Trinity assembler, 59,050 control unigenes and 73,946 Vibrio-infected group unigenes were obtained. By clustering unigenes from both libraries, a total of 64,411 standard unigenes were produced. The standard unigenes were annotated against the NCBI non-redundant, Swiss-Prot, Kyoto Encyclopaedia of Genes and Genome pathway (KEGG) and Orthologous Groups of Proteins (COG) databases, with 19,799 (30.73%), 16,832 (26.13%), 14,706 (22.83%) and 7,856 (12.19%) hits respectively, giving a final total of 22,455 significant hits (34.86% of all unigenes). A Gene Ontology (GO) analysis search using the Blast2GO program resulted in 6,007 unigenes (9.32%) being categorized into 55 functional groups. A differential gene expression analysis produced a total of 14,569 unigenes aberrantly expressed, with 11,446 unigenes significantly up-regulated and 3,103 unigenes significantly down-regulated. The differentially expressed immune genes fall under various processes of the animal immune system.

Conclusion

This study provided an insight into the antibacterial mechanism in M. rosenbergii and the role of differentially expressed immune genes in response to V. parahaemolyticus infection. Furthermore, this study has generated an abundant list of transcript from M.rosenbergii which will provide a fundamental basis for future genomics research in this field.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-015-0052-6) contains supplementary material, which is available to authorized users.

Toll-pathway in tiger shrimp (Penaeus monodon) responds to white spot syndrome virus infection: evidence through molecular characterisation and expression profiles of MyD88, TRAF6 and TLR genes

The Toll-pathway plays key roles in regulating the innate immune response in invertebrates. Myeloid differentiation factor 88 (MyD88) and Tumour necrosis factor receptor (TNFR)-associated factor 6 (TRAF6) are key molecules in this signalling pathway. To investigate the role of Toll-pathway in innate immune response of shrimp, Penaeus monodon, MyD88 (PmMyD88) and TRAF6 (PmTRAF6) were identified and characterised. PmMyD88 cDNA is 1716 bp long with an open reading frame (ORF) of 1449 bp encoding a putative protein of 482 amino acids, with a death domain, a TIR domain and C-terminal extension domain. PmTRAF6 cDNA is 2563 bp long with an ORF of 1785 bp (594 amino acids) with an N-terminal RING-type zinc finger domain, two TRAF-type zinc finger domains, a coiled region and a MATH domain. In healthy shrimp, PmMyD88, PmTRAF6 and PmToll were detected in 15 tissues with the highest expression in midgut, eyestalk and lymphoid organ, respectively. Responses of these genes to WSSV in experimentally-infected P. monodon as well as in cultured haemocytes and also effect of poly I:C on the gene expression in vitro was investigated at six time-points in seven tissues. PmToll showed significant up-regulation at all time-points of infection in six tissues and until 24 h post-infection in vitro. However, poly I:C-induced haemocytes showed up-regulation of the gene until 48 h post-exposure. WSSV caused significant up-regulation of PmMyD88 in most of the tissues tested. The virus challenge as well as poly I:C induction in vitro also resulted in significant up-regulation of the gene. Up-regulated expression of PmTRAF6 was detected in haemocytes and lymphoid organ at late stage of infection. In vitro virus challenge showed significant up-regulation of PmTRAF6 at almost all time-points whereas no significant change in the expression was observed on poly I:C induction. The responses of these key genes, observed in the present study, suggest that Toll-pathway as a whole may play a crucial role in the immune response against viruses in shrimp.

Gene structure, cDNA characterization and RNAi-based functional analysis of a myeloid differentiation factor 88 homolog in Tenebrio molitor larvae exposed to Staphylococcus aureus infection

Myeloid differentiation factor 88 (MyD88), an intracellular adaptor protein involved in Toll/Toll-like receptor (TLR) signal processing, triggers activation of nuclear factor-kappaB (NF-κB) transcription factors. In the present study, we analyzed the gene structure and biological function of MyD88 in a coleopteran insect, Tenebrio molitor (TmMyD88). The TmMyD88 gene was 1380 bp in length and consisted of five exons and four introns. The 5'-flanking sequence revealed several putative transcription factor binding sites, such as STAT-4, AP-1, cJun, cfos, NF-1 and many heat shock factor binding elements. The cDNA contained a typical death domain, a conservative Toll-like interleukin-1 receptor (TIR) domain, and a C-terminal extension (CTE). The TmMyD88 TIR domain showed three significantly conserved motifs for interacting with the TIR domain of TLRs. TmMyD88 was grouped within the invertebrate cluster of the phylogenetic tree and shared 75% sequence identity with the TIR domain of Tribolium castaneum MyD88. Homology modeling of the TmMyD88 TIR domain revealed five parallel β-strands surrounded by five α-helices that adopted loop conformations to function as an adaptor. TmMyD88 expression was upregulated 7.3- and 4.79-fold after 12 and 6h, respectively, of challenge with Staphylococcus aureus and fungal β-1,3 glucan. Silencing of the TmMyD88 transcript by RNA interference led to reduced resistance of the host to infection by S. aureus. These results indicate that TmMyD88 is required for survival against Staphylococcus infection.

eIF2α of Litopenaeus vannamei involved in shrimp immune response to WSSV infection

The alpha subunit of Eukaryotic Initiation Factor 2 (eIF2α) is a key translation regulator that plays an important role in cellular stress responses, which including virus infection. To investigate whether WSSV infection can activate the PERK-eIF2α pathway, the eIF2α in shrimp Litopenaeus vannamei, designed as LveIF2α, was analyzed. The LveIF2α, a 332-amino acid polypeptide, shares a high degree of similarity with eIF2α from other species, having two eIF2α protein signatures at the 13-88 aa and 192-243 aa. The WSSV challenge experiment showed that the protein level of the total LveIF2α was decreased after infection, while the phosphorylation of LveIF2α has no significant change, which indicated that the phosphorylation ratio of LveIF2α was increased after infection. Furthermore, inhibitor treatment led to a significant decrease of WSSV loads. Moreover, the Binding immunoglobulin protein (BiP), an endoplasmic reticulum (ER) stress sensor, and PERK were also investigated during virus infection and it was shown that they were both up-regulated. Taken together, these results suggested that WSSV infection can induce ER stress and activated the unfolded protein response (UPR), and the PERK-eIF2α pathway is important for innate immune during WSSV infection in shrimp.

The responsive expression of a chitinase gene in the ridgetail white prawn Exopalaemon carinicauda against Vibrio anguillarum and WSSV challenge

Chitinases are essential enzymes for crustaceans and participates in several biological processes, such as nutrient digestion, morphogenesis, pathogenesis, and pathogen defense. In the present study, the full-length cDNA of Chi (named EcChi) was cloned from the hemocytes of ridgetail white prawn Exopalaemon carinicauda by rapid amplification of cDNA ends methods. The full-length cDNA of EcChi was 1,319 bp, including contains a 5'-untranslated region (UTR) of 42 bp, 3'-UTR of 101 bp with a poly (A) tail, an open-reading frame of 1,176 bp, encoding a 391-amino acid polypeptide with the predicted molecular weight of 43.71 kDa and estimated isoelectric point of 4.78. Sequence analysis revealed that the conserved chitinases family 18 active site was predicted in the amino acid sequence of EcChi. BLAST analysis revealed that amino acids of EcChi shared high identity (61-77 %) with that of other crustaceans. Quantitative real-time PCR analysis indicated that EcChi could be detected in all the tested tissues, and strongly expressed in hepatopancreas of E. carinicauda. After challenged with Vibrio anguillarum and WSSV, EcChi transcripts both in hemocytes and hepatopancreas increased significantly in the first 3 h, respectively. These results indicated that EcChi might be involved in the innate immune responses to V. anguillarum and WSSV in E. carinicauda.

Litopenaeus vannamei NF-κB is required for WSSV replication

Many viruses can hijack the host cell NF-κB as part of their life cycle, diverting NF-κB immune regulatory functions to favor their replications. There were several reports on the functions of Litopenaeus vannamei NF-κB (LvNF-κB) in White spot syndrome virus (WSSV) replication in vitro. Here, we studied the relationship between LvNF-κB family protein Dorsal (LvDorsal) and Relish (LvRelish) with WSSV replication in vivo. The expressions of LvDorsal and LvRelish were significantly upregulated by WSSV challenge. Virus loads and expression of viral envelope protein VP28 in LvDorsal or LvRelish silencing shrimps were significantly lower than the control shrimps injected with EGFP-dsRNA or PBS after challenge with 1×10(5) copies WSSV/shrimp. In addition to the LvDorsal activation of WSV069 (ie1) and WSV303 promoter that we have reported, LvRelish can also activate WSV069 (ie1) and WSV303 promoter by dual luciferase reporter assays through screening 40 WSSV gene promoters that have putative multiple NF-κB binding sites. The promoter activity of the WSV069 (ie1) by LvDorsal activation was significantly higher than that by LvRelish activation. WSSV replication in LvDorsal, LvRelish or WSV303 silencing shrimps were significantly inhibited. These results indicate that the L. vannamei NF-κB family proteins LvDorsal and LvRelish expressions are significantly activated by WSSV challenge and WSSV replication partially relied on the activations of LvDorsal and LvRelish in vivo.

Bioinformatic prediction of WSSV-host protein-protein interaction

WSSV is one of the most dangerous pathogens in shrimp aquaculture. However, the molecular mechanism of how WSSV interacts with shrimp is still not very clear. In the present study, bioinformatic approaches were used to predict interactions between proteins from WSSV and shrimp. The genome data of WSSV (NC_003225.1) and the constructed transcriptome data of F. chinensis were used to screen potentially interacting proteins by searching in protein interaction databases, including STRING, Reactome, and DIP. Forty-four pairs of proteins were suggested to have interactions between WSSV and the shrimp. Gene ontology analysis revealed that 6 pairs of these interacting proteins were classified into “extracellular region” or “receptor complex” GO-terms. KEGG pathway analysis showed that they were involved in the “ECM-receptor interaction pathway.” In the 6 pairs of interacting proteins, an envelope protein called “collagen-like protein” (WSSV-CLP) encoded by an early virus gene “wsv001” in WSSV interacted with 6 deduced proteins from the shrimp, including three integrin alpha (ITGA), two integrin beta (ITGB), and one syndecan (SDC). Sequence analysis on WSSV-CLP, ITGA, ITGB, and SDC revealed that they possessed the sequence features for protein-protein interactions. This study might provide new insights into the interaction mechanisms between WSSV and shrimp.

Transcriptional profiles of Rel/NF-κB, inhibitor of NF-κB (IκB), and lipopolysaccharide-induced TNF-α factor (LITAF) in the lipopolysaccharide (LPS) and two Vibrio sp.-exposed intertidal copepod, Tigriopus japonicus

The immune system and the role of immunity-related genes have rarely been studied in copepods, even though copepods have a primitive immune response system and also have a potential in pathogen transport higher trophic levels. In this study, we firstly cloned and characterized three core immune genes such as nuclear factor κB (NF-κB), inhibitor of NF-κB (IκB), and lipopolysaccharide-induced TNF-α factor (LITAF) genes in the intertidal copepod Tigriopus japonicus. Several in silico analyses based on conserved domains, motifs, and phylogenetic relationships were supporting their annotations. To investigate the immune-related role of three genes, we exposed lipopolysaccharide (LPS) and two Vibrio sp. to T. japonicus. After exposure of different concentrations of LPS and two Vibrio sp., transcripts of TJ-IκB and TJ-LITAF genes were significantly elevated during the time course in a dose-dependent manner, while TJ-NF-κB transcripts were not significantly changed during exposure. These findings demonstrated that the copepod T. japonicus has a conserved immunity against infection.

Immunostimulatory activity of sulfated galactans isolated from the red seaweed Gracilaria fisheri and development of resistance against white spot syndrome virus (WSSV) in shrimp

Sulfated galactans (SG) were isolated from the red seaweed Gracilaria fisheri (G. fisheri). Chemical analysis revealed SG contains sulfate (12.7%) and total carbohydrate (42.2%) with an estimated molecular mass of 100 kDa. Structure analysis by NMR and FT-IR spectroscopy revealed that SG is a complex structure with a linear backbone of alternating 3-linked β-D-galactopyranose and 4-linked 3,6-anhydrogalactose units with partial 6-O-methylate-β-D-galactopyranose and with sulfation occurring on C4 of D-galactopyranose and C6 of L-galactopyranose units. SG treatment enhanced immune parameters including total haemocytes, phenoloxidase activity, superoxide anions and superoxide dismutase in shrimp Penaeus monodon. Shrimp fed with Artemia salina enriched with SG (100 and 200 μg ml(-1)) and inoculated with white spot syndrome virus (WSSV) showed a significantly lower mortality rate and lower viral VP 28 amplification and expression than control. The results suggest that SG from G. fisheri exhibits immune stimulatory and antiviral activities that could protect P. monodon from WSSV infection.

Molecular cloning and expression analysis of a dorsal homologue from Eriocheir sinensis

Dorsal as a crucial component of Toll signaling pathway, played important roles in induction and regulation of innate immune responses. In this study, we cloned a NF-κB-like transcription factor Dorsal from Eriocheir sinensis and designated it as EsDorsal. The full-length cDNA of EsDorsal was 2493 bp with a 2022-bp open reading frame (ORF) encoding a 673-amino acid protein. This protein contained a 171-residue conserved Rel homology domain (RHD) and a 102-residue Ig-like, plexins and transcription factors domain (IPT). By phylogenetic analysis, EsDorsal was clustered into one group together with other invertebrate Dorsals or NF-κBs, and then clustered with vertebrate NF-κBs. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis results showed that (a) EsDorsal had higher expression level in immune organs; (b) EsDorsal differentially induced after injection of lipopolysaccharides (LPS), peptidoglycan (PG) or zymosan (GLU). Importantly, EsDorsal was more responsive to LPS than GLU and PG. Collectively, EsDorsal was differentially inducibility in response to various PAMPs, suggesting its involvement in a specific innate immune regulation in E. sinensis.

Screening of genes regulated by Relish in Chinese shrimp Fenneropenaeus chinensis

Relish is a key NF-κB transcription factor in the innate immunity. Learning the function of Relish in regulating the related genes of shrimp will be helpful to understand the shrimp immunity. In the present study, RNA interference (RNAi) and suppression subtractive hybridization (SSH) techniques were combined together to identify the genes regulated by Relish. A forward SSH library represents the genes whose transcription was regulated by Relish, and the reverse SSH library represents the genes whose transcription was up-regulated after Relish was silenced in shrimp responsive to Vibrio anguillarium (VA) stimulation. In the forward library, 43 unique genes were identified, and in the reverse library, 57 genes were identified. The expression of ten differentially expressed genes, including early cuticle protein5 (ECP5), Toll-like receptor protein (TLRP), antiviral factor (AV), C-type lectin receptor (CLR), thrombospondin (TSP), S-adenosylmethionine synthetase (SAMS), carcinolectin 5b-5 (CL5b-5), QM protein (QMP), heat shock protein 67B2 (HSP67B2), and Thioredoxin-related protein 14 (TRP14) were further confirmed by real-time PCR. The present data provides us a wide view to understand the function of Relish gene in the innate immunity of shrimp.

De novo whole transcriptome analysis of the fish louse, Argulus siamensis: first molecular insights into characterization of Toll downstream signalling molecules of crustaceans

Argulus siamensis is a major ectoparasitic pathogen of freshwater fish capable of causing substantial economic loss. None of the available control measures have been able to address the problem of argulosis resourcefully. To combat this pathogen effectively, it is necessary to have a comprehensive understanding of its life processes with information on various genes involved. The transcriptome studies can generate introductory information about genes participating in physiological processes of the parasite which could be targeted for their control. In this study, the transcriptome sequencing of A. siamensis was performed on Illumina HiSeq 2000 platform which generated 75,126,957 high quality reads. A total of 46,352 transcript contigs were assembled with average length of 1211bp and N50 length of 2302bp. In total, 19,290 CDS including 184 novel CDS and 59,019 open reading frames (ORFs) were identified from the assembled contigs. Gene ontology and Kyoto Encylopedia of Genes and Genomes pathway analysis were performed to classify contigs into their functional categories and regulation pathways. Additionally, 1171 simple sequence repeats were identified from the assembled contigs. Further, twelve contigs with high similarity with downstream molecules of the mammalian toll like receptor (TLR) pathway were validated by their inductive expressions in response to lipopolysaccharide (LPS) of Gram negative bacteria, Escherichia coli and Gram positive bacteria, Staphylococcus aureus. The transcriptome of an ectoparasite A. siamensis was sequenced, assembled, annotated, and the downstream signalling molecules of Toll pathway characterized. The transcriptome data generated will facilitate studies on functional genomics that will subsequently be applied for vaccine development and other control strategies against the parasite.

A new shrimp peritrophin-like gene from Exopalaemon carinicauda involved in white spot syndrome virus (WSSV) infection

Peritrophin was first separated from insect peritrophic membrane (PM), and it played an important role in stimulating the digestion of food and protecting insects from invasion by microorganisms. In this study, a full-length cDNA of a new peritrophin-like protein (EcPT) was cloned from the ridgetail white shrimp Exopalaemon carinicauda, which was an excellent experimental animal for shrimp. The full length cDNA comprised 1235 bp including an 873 bp open reading frame encoding 291 amino acids. The deduced amino acid sequence contained a segment of signal peptide and three conserved chitin binding type 2 domains (ChtBD2) characterized by having a 6-cysteine motif. Tissue expression analysis revealed that EcPT was mainly expressed in stomach and gills, which were also the two main target tissues of WSSV infection. The transcription levels of EcPT in both stomach and gills were found to have significantly changed upon WSSV infection by real-time PCR. Silencing EcPT by dsRNA interference led to higher survival rate of shrimp against WSSV challenge, which suggested that EcPT might be involved in WSSV infection.