Molecular cloning and expression of a Toll receptor in the giant tiger shrimp, Penaeus monodon

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.

Activation of PmRelish from Penaeus monodon by yellow head virus

Humoral innate immune response against pathogenic infection is partly responsible by the Imd pathway in which a transcription factor Relish relays the infection signals to the nuclei for the expression of antimicrobial proteins. A PmRelish gene which encoded a protein of 1195 amino acids was cloned. The PmRelish was constitutively expressed in all tissues tested and mostly up-regulated upon YHV infection. In hemocytes, the PmRelish expression was up-regulated upon Vibrio harveyi, yellow head virus (YHV) and white spot syndrome virus (WSSV) challenges. Using dsRNA silencing of PmRelish gene, it was shown that the expression of penaeidin5 but not anti-lipopolysaccharide factor ALFPm3, crustinPm1 and penaeidin3 was under the regulation of Imd pathway. Under PmRelish silencing, the shrimp were more susceptible to infection by YHV with the 50% survival rate reduced from about 72 h to 42 h. The PmRelish was detected in the cytoplasm of all the hemocytes from both uninfected and YHV-infected shrimp. The accumulation of activated PmRelish in the nuclei was not clearly observed but the activated PmRelish was detected in the YHV-infected hemocytes by Western blot analysis. Thus, the PmRelish and, hence, the Imd pathway respond to the YHV infection.

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.

A novel Toll like receptor with two TIR domains (HcToll-2) is involved in regulation of antimicrobial peptide gene expression of Hyriopsis cumingii

Animal Toll-like receptors (TLRs) are involved in innate immunity. Toll proteins are generally transmembrane proteins. In this study, an atypical Toll-like receptor (HcToll-2) was identified from the triangle-shell pearl mussel Hyriopsis cumingii, which belongs to phylum Mollusca. Unlike the typical Toll like receptors with extracellular leucine-rich repeats (LRRs), transmembrane, and intracellular Toll/interleukin-1 receptor (TIR) domains, HcToll-2 has two homologous TIR domains located at the C-terminal (designated as HcTIR1 and HcTIR2) and lacks a transmembrane domain. Phylogenetic analysis showed that HcTIR1 was clustered with TIR of sea anemone Toll, and HcTIR2 was clustered with TIR of Drosophila Toll. HcToll-2 mRNA could be detected in the hepatopancreas and was upregulated after challenge with Escherichia coli and Staphylococcus aureus. Recombinant HcLRR protein with GST tag could bind to bacteria and also to LPS and PGN. Over-expression of both HcTIR1 and HcTIR2 induced drosomycin genes in Drosophila S2 cells. RNAi analysis showed that HcToll-2 was required for the expression of theromacin, which is a cysteine-rich antimicrobial peptide (AMP) gene. This research is the first report of an atypical Toll-like receptor HcToll-2 involved in antibacterial immunity through induction of AMP expression.

Functional analysis of Fenneropenaeus chinensis anti-lipopolysaccharide factor promoter regulated by lipopolysaccharide and (1,3)-β-D-glucan

Current knowledge on cis-regulatory elements of immune genes of shrimp is poor. In this study, the genomic sequence of the Fenneropenaeus chinensis anti-lipopolysaccharide factor (ALFFc) gene was obtained by using PCR and genome walking techniques, and the promoter was identified. The ALFFc gene contained three exons interrupted by two introns. Immune-related transcription factor binding sites recognized by nuclear factor-kappa B, octamer binding protein 1, GATA binding factor 1 and specificity protein 1 were identified in the regin from +1 to -702. The activity of ALFFc promoter was analyzed in insect sf9 cell lines. The putative promoter sequence of pALF-702 drive the expression of reporter EGFP gene successfully by adding lipopolysaccharide or (1,3)-β-D-glucan, but the shorter promoter sequence pALF-318 is only by (1,3)-β-D-glucan. The results pointed out that these transcription elements might contribute to the differences in promoter of ALFFc. Our results would provide supports for future studies to identify the functional transcription elements in the ALF promoter and to expand our knowledge on regulation of innate immune genes in Chinese shrimp.

Molecular cloning and characterization of a Toll receptor gene from Macrobrachium rosenbergii

Toll receptors are cell surface molecules acting as pattern recognition receptors (PRRs) that have been implicated in the signaling pathway of innate immune responses. In this study, the full-length cDNA of a Toll receptor gene of Macrobrachium rosenbergii, designated MrToll, was successfully isolated using designed degenerate primers and the rapid amplification of cDNA ends (RACE). The MrToll gene sequence contained an open reading frame (ORF) of 2799 nucleotides encoding a protein of 932 amino acid residues. The protein contained distinct structural motifs of the Toll-like receptor (TLR) family, including an extracellular domain containing 15 leucine-rich repeats (LRRs), a transmembrane segment of 23 amino acids, and a cytoplasmic Toll/interleukin-1R (TIR) domain of 139 residues. Phylogenetic analysis revealed that MrToll and Toll receptor of Marsupenaeus japonicus (MjToll) evolved closely. However, the MrToll ORF demonstrated only 48-49% identity with shrimp Toll1, suggesting that MrToll isolated from a palaemonid shrimp might belong to a novel class of Toll receptors in shrimp. The transcripts of the MrToll gene were constitutively expressed in various tissues, with high levels in hemocytes, the stomach and muscle. A reverse transcriptase PCR assay demonstrated that the expression patterns of MrToll were distinctly modulated after Aeromonas caviae stimulation, with significant enhancement at 3-12 h post-challenge and a decline to basal levels at 24 h post-challenge. In addition, when MrToll-silenced shrimp were challenged with A. caviae, there was a significant increase in mortality and bacterial CFU counts. These results suggest that MrToll might be involved in host innate defense, especially against the pathogen A. caviae.

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.

Identification and functional studies of Akirin, a potential positive nuclear factor of NF-κB signaling pathways in the Pacific white shrimp, Litopenaeus vannamei

As conserved nuclear factors, Akirins play critical roles in regulating antimicrobial peptides (AMPs) transcription downstream of NF-κB dependent signaling pathways in insects and mammals. However, no any functional studies was reported in penaeid shrimp. The identification and functional analysis of Akirin in the Pacific white shrimp, Litopenaeus vannamei were made in this research. The 833 nucleotides cDNA of Litopenaeus vannamei Akirin (LvAkirin) was obtained with an open reading frame of 639 bp, which encodes a putative protein of 212 amino acids. The molecular weight of LvAkirin is about 23.7 kDa with theoretical pI of 9.05. Two predicted nuclear localization signals (NLSs) were found and amino acid sequence alignments showed that Akirins are highly conserved between insects and mammals. The constitutive expression of LvAkirin mRNA was confirmed in all the examined tissues and high level appeared in testis followed by hemocytes and gill. LvAkirin mRNA was strongly induced in response to Vibrio parahaemolyticus infection. Silencing LvAkirin by dsRNA significantly reduced the expression of NF-κB dependent anti-lipopolysaccharide factor, crustin and penaeidin3a as well as transcription factors, Dorsal and Relish post Vibrio anguillarum (V. anguillarum) and Micrococcus lysodeikticus (M. lysodeikticus) challenge. Antibacterial activities of shrimp plasma was analyzed and high cumulative mortality was found in LvAkirin-silenced shrimps post bacteria challenge. Hence, we proposed LvAkirin might function as a positive nuclear factor of NF-κB dependent signaling pathways in shrimp innate immunity.

Identification, characterization, and functional analysis of Tube and Pelle homologs in the mud crab Scylla paramamosain

Tube and Pelle are essential components in Drosophila Toll signaling pathway. In this study, we characterized a pair of crustacean homologs of Tube and Pelle in Scylla paramamosain, namely, SpTube and SpPelle, and analyzed their immune functions. The full-length cDNA of SpTube had 2052 bp with a 1578 bp open reading frame (ORF) encoding a protein with 525 aa. A death domain (DD) and a kinase domain were predicted in the deduced protein. The full-length cDNA of SpPelle had 3825 bp with a 3420 bp ORF encoding a protein with 1140 aa. The protein contained a DD and a kinase domain. Two conserved repeat motifs previously called Tube repeat motifs present only in insect Tube or Tube-like sequences were found between these two domains. Alignments and structure predictions demonstrated that SpTubeDD and SpPelleDD significantly differed in sequence and 3D structure. Similar to TubeDD, SpTubeDD contained three common conserved residues (R, K, and R) on one surface that may mediate SpMyD88 binding and two common residues (A and A) on the other surface that may contribute to Pelle binding. By contrast, SpPelleDD lacked similar conservative residues. SpTube, insect Tube-like kinases, and human IRAK4 were found to be RD kinases with an RD dipeptide in the kinase domain. SpPelle, Pelle, insect Pelle-like kinases, and human IRAK1 were found to be non-RD kinases lacking an RD dipeptide. Both SpTube and SpPelle were highly expressed in hemocytes, gills, and hepatopancreas. Upon challenge, SpTube and SpPele were significantly increased in hemocytes by Gram-negative or Gram-positive bacteria, whereas only SpPelle was elevated by White Spot Syndrome Virus. The pull-down assay showed that SpTube can bind to both SpMyD88 and SpPelle. These results suggest that SpTube, SpPelle, and SpMyD88 may form a trimeric complex involved in the immunity of mud crabs against both Gram-negative and Gram-positive bacteria.

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.

Beta-glucan: an ideal immunostimulant in aquaculture (a review)

The major hindrance in the development and sustainability of aquaculture industry is the occurrence of various diseases in the farming systems. Today, preventive and management measures are central concern to overcome such outbreak of diseases. Immunostimulants are considered as an effective tool for enhancing immune status of cultured organisms. Among different immunostimulants used in aquaculture practices, β-glucan is one of the promising immunostimulant, which is a homopolysaccharide of glucose molecule linked by the glycoside bond. It forms the major constituents of cell wall of some plants, fungi, bacteria, mushroom, yeast, and seaweeds. Major attention on β-glucan was captivated with the gain in knowledge on its receptors and the mechanism of action. The receptor present inside the animal body recognizes and binds to β-glucan, which in turn renders the animal with high resistance and enhanced immune response. This review highlights β-glucan as an immunostimulant, its effective dosages, and route of administration and furthermore provides an outline on role of β-glucan in enhancing growth, survival, and protection against infectious pathogens pertaining to fishes and shellfishes. Study also summarizes the effect of β-glucan on its receptors, recognition of proteins, immune-related enzymes, immune-related gene expression and their mechanisms of action.

An IκB homologue (FcCactus) in Chinese shrimp Fenneropenaeus chinensis

This study firstly reports the characterization of a functional IκB homologue, FcCactus in Chinese shrimp Fenneropenaeus chinensis. The full length cDNA of FcCactus consists of a 1359 bp open reading frame (ORF) encoding a 453 amino acid protein with a predicted molecular weight (MW) of 48.46 kDa and theoretical pI of 5.23. Phylogenetic analysis and multiple alignments revealed that the deduced amino acid sequence of FcCactus cDNA had high similarities to Cactus or IκB reported in seven other arthropods. Genomic DNA sequence of FcCactus was also obtained with a length of more than 17698 bp and constituted of seven exons and six introns. Analysis on 5'-upstream regulatory region of its DNA sequence revealed that it contained the core promoter sequence with the TATA-box and transcription start site existing in it; furthermore, various transcription factor binding sites (HSF, Hb, BR-C Z, Dfd, CF2-II, Croc, Ttk, Dorsal, and c-Rel) were predicted. Spatial expression profiles showed that FcCactus mRNA had the highest expression level in muscle, hemocytes, heart and lymphoid organ. Gram-positive bacteria (Micrococcus lysodeikticus) and Gram-negative bacteria (Vibrio anguillarium) injection to shrimp caused the modulation of FcCactus at the transcription level. DsRNAi (double-strand RNA interference) approach was used to study the function of FcCactus and the data showed that FcCactus could regulate the expression of different antimicrobial peptides (AMPs) and antiviral factor (AV). The present data showed that FcCactus might play important roles in regulating the immune response of shrimp.

Signaling pathways regulating innate immune responses in shrimp

The first line of defense against microbial infections in animals is innate immune response which triggers diverse humoral and cellular activities via signal transduction pathways. Toll, IMD and JAK/STAT pathways are regarded as the main pathways regulating the immune response of invertebrates. This paper reviews the main progress of the investigation on the immune response to pathogen's infection in shrimp and supposes that these three signal pathways exist in shrimp. Most of the components (proteins or genes) involved in Toll pathway of Drosophila have been cloned also in shrimp which suggested the existence of Toll pathway in shrimp. The data update shows that the Toll pathway of shrimp is responsive not only to Gram-positive bacteria, Gram-negative bacteria, but also to WSSV. Challenge of WSSV can lead to the variation of transcription level of all identified components in shrimp Toll pathway, which supported that Toll pathway in shrimp played important roles during WSSV infection. Two major homologs to the components of IMD pathway of Drosophila, IMD and Relish, have been identified in shrimp, which indicated that IMD pathway should be existed in shrimp and might play important roles in regulating the immune response of shrimp to bacteria and virus infection. Relish in IMD pathway and dorsal in Toll pathway of shrimp were both involved in the immune response of shrimp to bacteria and virus infection, which implied that these two pathways are not completely separated during the immune response of shrimp. The transcription of STAT in shrimp was modulated after WSSV infection, which suggested that a putative JAK/STAT pathway might exist in shrimp and be very important to virus infection. Study on the signaling pathway regulating the immune response in shrimp could help us to understand the innate immune system, and would provide instructions to shrimp disease control. Obviously, to get more clear ideas about the innate immunological pathways in shrimp, more solid functional studies should be done in the future.

Reprint of: Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

Pattern recognition receptors acting in innate immune system of shrimp against pathogen infections

Invertebrates, including shrimp, have developed very complicated innate immune system against pathogens. Much work has been performed on the innate immunity of shrimp, including immune recognition, signal transduction, effector molecules and antiviral responses due to its great economic value. Pattern recognition is the first step of innate immunity. Pattern recognition receptors (PRRs) sense the presence of infection and activate immune responses. The studies on shrimp PRRs revealed the recognition mechanism of shrimp at a certain degree. To date, 11 types of pattern recognition receptors (PRRs) have been identified in shrimp, namely, β-1,3-glucanase-related proteins, β-1,3-glucan-binding proteins, C-type lectins, scavenger receptors, galectins, fibrinogen-related proteins, thioester-containing protein, Down syndrome cell adhesion molecule, serine protease homologs, trans-activation response RNA-binding protein and Toll like receptors. A number of PRRs have been functionally studied and have been found to have different binding specificities and immune functions. The present review aims to summarize the current knowledge on the PRRs of shrimp.

A novel myeloid differentiation factor 88 homolog, SpMyD88, exhibiting SpToll-binding activity in the mud crab Scylla paramamosain

Myeloid differentiation factor 88 (MyD88) is an essential regulator in the Toll or Toll-like receptor (TLR) signaling pathway. In the current study, we characterized a novel crustacean MyD88 homolog, SpMyD88, and analyzed its binding activity with SpToll. The full-length cDNA sequence of SpMyD88 is 2933 bp, with a 1419 bp open reading frame encoding a 472-amino acid protein. No signal peptide was predicted. A death domain (residues 19-103), a Toll/interleukin-1 receptor (TIR) domain (residues 156-297), and a C-terminal extension (CTE) domain (residues 298-472) were also found. In a phylogenetic tree constructed with MyD88 homologs from both invertebrates and vertebrates, arthropod MyD88s including SpMyD88 formed a cluster containing a unique CTE domain. SpToll shared the highest identity with human TLR4. These two receptors were grouped into a cluster of a tree constructed based on the conserved TIR domains. SpToll also had a close relationship with other shrimp TLRs that possess potential antibacterial activity. SpMyD88 was highly expressed in the hemocytes, gills, hepatopancreas, and eye stalks. Upon challenge with Vibrio harveyi, both SpMyD88 and SpToll were significantly increased in the hemocytes, whereas only SpMyD88 was elevated by Staphylococcus aureus. In addition, a pull-down assay demonstrated that SpMyD88 showed a binding activity with SpToll. These results suggest that SpMyD88 and SpToll are involved in the defense system of mud crabs against Gram-negative bacteria.

Insights into the antiviral functions of the RNAi machinery in penaeid shrimp

Over the last decade, RNA interference pathways have emerged in eukaryotes as critical regulators of many diverse biological functions including, among others, transcriptional gene regulation, post-transcriptional gene silencing, heterochromatin remodelling, suppression of transposon activity, and antiviral defences. Although this gene silencing process has been reported to be relatively well conserved in species of different phyla, there are important discrepancies between plants, invertebrates and mammals. In penaeid shrimp, the existence of an intact and functional RNAi machinery is supported by a rapidly growing body of evidence. However, the extent to which this process participates to the host immune responses remains poorly defined in this non-model organism. This review summarizes our current knowledge of RNAi mechanisms in shrimp and focuses on their implication in antiviral activities and shrimp immune defences.

Identification and expression analysis of two Toll-like receptor genes from sea cucumber (Apostichopus japonicus)

Toll-like receptors (TLRs) are a family of type I integral membrane glycoproteins which play pivotal roles in innate immunity. In this study, two TLRs named AjTLR3 and AjToll were cloned from sea cucumber (Apostichopus japonicus). The full-length cDNA sequences of AjTLR3 and AjToll are 3484 bp and 4211 bp, with an open reading frame (ORF) of 2679 bp and 2853 bp, encoding 892 and 950 amino acids, respectively. Both AjTLR3 and AjToll are composed of a leucine-rich repeat (LRR) domain, a transmembrane (TM) domain and an intracellular Toll/interleukin-1 receptor (TIR) domain. Evolution analysis revealed that AjTLR3 and AjToll were clustered with the vertebrate-like TLRs (V-TLRs) and the protostome-like TLRs (P-TLRs), respectively. These two genes were widely expressed in all five tested tissues (body wall, coelomocytes, tube feet, intestine and respiratory tree), but showed different expression patterns. The significantly up-regulated expressions of AjTLR3 and AjToll after peptidoglycan (PGN), lipopolysaccharides (LPS), Zymosan A and polyinosinic-polycytidylic acid (PolyI:C) challenges suggested that they were functionally involved in the immune responses to the Cram-positive bacteria, Gram-negative bacteria, fungi and double-stranded RNA (dsRNA) viruses, respectively.

Validation of reference genes for real-time PCR of reproductive system in the black tiger shrimp

Gene expression of reproductive system of the black tiger shrimp (Peneaus monodon) has been widely studied to address poor maturation problem in captivity. However, a systematic evaluation of reference genes in quantitative real-time PCR (qPCR) for P. monodon reproductive organs is lacking. In this study, the stability of four potential reference genes (18s rRNA, GAPDH, β-actin, and EF1-α) was examined in the reproductive tissues in various conditions using bioinformatic tools: NormFinder and geNorm. For NormFinder, EF1-α and GAPDH ranked first and second as the most stable genes in testis groups whereas GAPDH and EF1-α were for ovaries from wild-caught broodstock and domesticated groups. EF1-α and β-actin ranked first and second for the eyestalk ablated ovaries. For geNorm, EF1-α and GAPDH had the best stability in all testis and ovaries from domesticated groups whereas EF1-α and β-actin were the best for ovaries from wild-caught and eyestalk ablated groups. Moreover, the expression levels of two well-known reproductive genes, Dmc1 and Vitellogenin, were used to validate these reference genes. When normalized to EF1-α, the expected expression patterns were obtained in all cases. Therefore, this work suggests that EF1-α is more versatile as reference genes in qPCR analysis for reproductive system in P. monodon.

Virus-binding proteins and their roles in shrimp innate immunity

Disease outbreaks caused by viral pathogens constitute a major limitation to development of the shrimp aquaculture industry. Many research have been conducted to better understand how host shrimp respond to viral infections with the aim of using the gained knowledge to develop better strategies for disease management and control. One approach has been to study the interactions between host and viral proteins, and particularly host virus-binding proteins that might play an important role in the viral infection process. Within the past five years, increasing numbers of virus-binding proteins (VBPs) have been reported in shrimp. Characterization of these molecules has emphasized on their potential therapeutic applications by demonstrating their activities in inhibition of viral replication via in vivo neutralization assay. However, signaling to induce innate antiviral immune responses as a consequence of binding between viral proteins and VBPs remain to be fully elucidated.

Expression profile of toll-like receptor 2 mRNA in selected tissues of shark (Chiloscyllium sp.)

Sharks are a species of delight for immunologists from the evolutionary perspective since it is considered as the first species to have evolved the adaptive immune responses in addition to the innate immune system. One of the components of the highly conserved innate immune system is the toll-like receptors (TLR) which has a conserved overall protein structure throughout deuterostome evolution. There is no report that demonstrates the expression of these receptors in sharks. In this study we successfully amplified a 270 bp amplicon using a degenerate primer design strategy that corresponded to the Toll/IL-1 receptor (TIR) domain of TLR2 (GenBank ID: JF792813). BLAST analysis revealed a maximum nucleotide identity of 87% and 76% with the TLR2 of higher mammals and teleost fishes respectively. Domain prediction revealed a TIR structure between 1 and 87 amino acids that had a maximum identity of 58% and 76% with TLR2 - TIR protein of teleost fishes and higher mammals respectively. Phylogenetic analysis revealed a closer clustering of the shark TIR sequence with those from human, cattle, goat, sheep and chicken than with other fish species. Basal expression levels of the TLR2-TIR mRNA were found to be significantly higher in kidneys followed by fins, spleen and intestinal spiral valve (ISV). In tissues such as spleen and kidney the expression of the TLR2-TIR mRNA could be localized to lymphoid and macrophages like cells and tubular epithelial cells respectively. In-vivo exposure of sharks to peptidoglycan (TLR 2 ligand) resulted in 9 folds higher expression of TLR2-TIR mRNA in gills followed by 5 folds in the fins. However, when inoculated with a TLR ligand pool, the expression levels significantly increased to 12 fold in skin followed by epigonal, kidneys and ISV. These findings not only support the presence of the TLRs in sharks but also their induction upon exposure to specific ligands. Further studies are needed to identify their numbers, their ligand specificity and downstream cytokine responses.

Cloning and characterisation of the SpToll gene from green mud crab, Scylla paramamosain

Toll/Toll-like receptors (TLRs), one of the most important pattern recognition receptors (PRRs), play a crucial role in innate immune responses in both invertebrates and vertebrates. In this study, we cloned and characterised a Toll gene from Scylla paramamosain (SpToll). Bioinformatic analysis predicted that SpToll contained one open reading frame of 3018bp and encoded a single-pass transmembrane domain protein of 1005 amino acids. Further, SpToll could be clustered into one branch along with other arthropod Tolls in a phylogenetic tree. SpToll transcripts could be detected by RT-PCR from all tissues examined including the heart, gill, hepatopancreas, stomach, intestine, muscle, eyestalk and hemocytes. Infection by Vibrio parahemolyticus up-regulated SpToll mRNA expression in hemocytes after 48h. The profile of single nucleotide polymorphisms (SNPs) in the leucine-rich repeats (LRRs) domain of SpToll in three healthy crabs was then evaluated. Two hundred and twenty SNPs with a frequency of about 1.0-4.0% were identified in hemocyte DNA/cDNA. Surprisingly, the adenine to guanine transition at position 1372 (c.1372A>G) had a frequency of about 50%. Finally, the results showed that challenge with V. parahemolyticus stimulated the appearance of two sets of SNPs in crabs. More importantly, the c.1372A>G mutation could contribute to a low mortality after V. parahemolyticus infection and introduce variation of charge and secondary structure into the SpToll polypeptide. In summary, these studies suggested a novel Toll homologue in crab and identified a SNP with potential pathogen-resistant activities. The result will be important for the investigation of crab immune defense mechanisms.

Molecular cloning and tissue distribution of the Toll receptor in the black tiger shrimp, Penaeus monodon

The black tiger shrimp (Penaeus monodon) is economically important in many parts of the world, including Thailand. Shrimp immunity is similar to that of other invertebrate organisms; it consists of an innate immunity system. Toll or Toll-like receptors (TLRs) play an essential role in recognizing the cleaved form of the cytokine Spätzle, which is processed by a series of proteolytic cascades activated by secreted recognition molecules. We isolated a full-length Toll receptor from P. monodon. The cloned full-length sequence of the PmToll cDNA consists of 4144 nucleotides, containing a 5'-UTR with 366 nucleotides, a 3'-terminal UTR with 985 nucleotides, with a classical polyadenylation signal sequence AATAAA, a poly A-tail with 27 nucleotides, and an open reading frame coding for 931 amino acids. The deduced amino acid sequence of PmToll is a typical type I membrane domain protein, characteristic of TLR functional domains. It includes a putative signal peptide, an extracellular domain consisting of leucine-rich repeats, flanked by cysteine-rich motifs, a single-pass transmembrane portion, and a cytoplasmic TLR domain. PmToll was expressed in all tissues tested, including gill, hemocytes, heart, hepatopancreas, lymphoid organs, muscle, nerve, pleopod, stomach, testis, and ovary. The deduced amino acid of PmToll is closely related to that of other shrimp Tolls, especially FcToll. Further studies elucidating the mechanism of action of Tolls will be of benefit for understanding the defense mechanisms of this economically important aquatic species.

Molecular cloning, characterization and expression analysis of two novel Tolls (LvToll2 and LvToll3) and three putative Spätzle-like Toll ligands (LvSpz1-3) from Litopenaeus vannamei

Toll-like receptor-mediated NF-κB pathways are essential for inducing immune related-gene expression in the defense against bacterial, fungal and viral infections in insects and mammals. Although a Toll receptor (LvToll1) was cloned in Litopenaeus vannamei, relatively little is known about other types of Toll-like receptors and their endogenous cytokine-like ligand, Spätzle. Here, we report two novel Toll-like receptors (LvToll2 and LvToll3) and three Spätzle-like proteins (LvSpz1-3) from L. vannamei. LvToll2 has 1009 residues with an extracellular domain containing 18 leucine-rich repeats (LRRs) and a cytoplasmic Toll/interleukin-1 receptor (TIR) domain of 139 residues. LvToll3 is 1244 residues long with an extracellular domain containing 23 LRRs and a cytoplasmic TIR domain of 138 residues. The Spätzle-like proteins LvSpz1, LvSpz2 and LvSpz3 are 237, 245 and 275 residues in length, respectively, and all of them have a putative C-terminal cystine-knot domain. In Drosophila Schneider 2 (S2) cells, LvToll1 and LvToll3 were localized to the membrane and cytoplasm, and LvToll2 was confined to the cytoplasm. In Drosophila S2 cells, LvToll2 could significantly activate the promoters of NF-κB-pathway-controlled antimicrobial peptide genes, whereas LvToll1 and LvToll3 had no effect on them. LvSpz1 exerted some degree of inhibition on the promoter activities of Drosophila Attacin A and L. vannamei Penaeidin4. LvSpz3 also inhibited the Drosophila Attacin A promoter, but LvSpz2 could only slightly activate it. LvToll1, LvToll2 and LvToll3 were constitutive expressed in various tissues, while LvSpz1, LvSpz2 and LvSpz3 exhibited tissue-specific expression in the epithelium, eyestalk, intestine, gill and muscle. In the gill, after Vibrio alginolyticus challenge, LvToll1 was upregulated, but LvToll2 and LvToll3 showed no obvious changes. LvSpz1 and LvSpz3 were also strongly induced by V. alginolyticus challenge, but LvSpz2 only showed a slight downregulation. In the gill, after white spot syndrome virus (WSSV) challenge, LvToll1, LvToll2, LvToll3, LvSpz1 and LvSpz3 were upregulated, but LvSpz2 showed no obvious change, except for a slight downregulation at 12h post-injection of WSSV. These findings might be valuable in understanding the innate immune signal pathways of shrimp and enabling future studies on the host-pathogen interactions in V. alginolyticus and WSSV infections.

Shrimp molecular responses to viral pathogens

From almost negligible amounts in 1970, the quantity of cultivated shrimp (~3 million metric tons in 2007) has risen to approach that of the capture fishery and it constitutes a vital source of export income for many countries. Despite this success, viral diseases along the way have caused billions of dollars of losses for shrimp farmers. Desire to reduce the losses to white spot syndrome virus in particular, has stimulated much research since 2000 on the shrimp response to viral pathogens at the molecular level. The objective of the work is to develop novel, practical methods for improved disease control. This review covers the background and limitations of the current work, baseline studies and studies on humoral responses, on binding between shrimp and viral structural proteins and on intracellular responses. It also includes discussion of several important phenomena (i.e., the quasi immune response, viral co-infections, viral sequences in the shrimp genome and persistent viral infections) for which little or no molecular information is currently available, but is much needed.

A primitive Toll-like receptor signaling pathway in mollusk Zhikong scallop Chlamys farreri

As a member of pattern-recognition receptors (PRRs), the Toll-like receptor (TLR) and its signaling pathway play pivotal roles in recognizing various pathogen-associated molecular patterns (PAMPs), and buildup the front-line against invading pathogens. In the present study, the sequence features and mRNA expression profiles of five key genes involved in TLR signal pathway were characterized, and their functions in the immune responses were also investigated in order to validate the TLR signaling pathway and its potential roles in the immune defense of Zhikong scallop Chlamys farreri. These five genes, including CfTLR, CfMyD88, CfTRAF6, CfIκB and CfNFκB, exhibited significant similarity with their homologues from other model organisms, and contained the typical motifs. A strong interaction between the TIR domain from CfTLR and CfMyD88 protein was revealed via ELISA assays. The mRNA transcripts of these five genes were all up-regulated after LPS stimulation, indicating that they were involved in the immune response against LPS. When CfTLR expression was inhibited by RNAi technology, the mRNA expression level of CfMyD88, CfTRAF6, CfIκB, CfNFκB and G-type lysozyme were all decreased, while those of superoxide dismutase and catalase were increased. After Listonella anguillara challenge, the apoptosis level of those CfTLR-suppressed scallops was significantly lower than that in control groups (p<0.05) at the beginning of bacteria challenge, while the cumulative mortality was significantly higher than that of control groups (p<0.05). These results collectively favored that a rather canonical MyD88-dependent TLR pathway existed in scallop and this pathway was involved in immune signaling to active the diverse downstream reaction including anti-oxidant, anti-bacteria and apoptosis.

Differential profiles of gene expression in grouper Epinephelus coioides, infected with Singapore grouper iridovirus, revealed by suppression subtractive hybridization and DNA microarray

Suppression subtractive hybridization (SSH) was used to generate a subtracted cDNA library enriched with gene transcripts differentially expressed in the spleen of orange-spotted grouper Epinephelus coioides after 5 days of infection with Singapore grouper iridovirus (SGIV). In the forward and reverse-subtracted libraries, 260 and 153 non-redundant expressed sequence tags (EST), respectively, were identified. These annotated genes responding to SGIV infection were grouped into eight gene categories related to immunity, cell structure, transcription-translation, cell signalling, metabolism, mitochondrial proteins, ribosomal proteins and unknown or hypothetical proteins. A DNA microarray containing all the differentially expressed genes was constructed, and the gene expression patterns in different tissues were investigated in virus-infected E. coioides. Of these genes, four associated with the infection processes were identified and further investigated by quantitative real-time PCR. These results provide new insights into the molecular basis of host-pathogen interactions in E. coioides, and will help the development of control strategies against SGIV infection.

Identification and functional study of a shrimp Dorsal homologue

Rel/NF-kappaB transcription factors play central roles in induction and regulation of innate immune responses. Here, identification and functional analysis of LvDorsal, a Dorsal homologue from the Pacific white shrimp Litopenaeus vannamei, were described. The full-length cDNA of LvDorsal is 2204bp with an open reading frame that encodes 400 amino acids. The deduced LvDorsal contains a conserved Rel homology domain (RHD), an IPT (Ig-like, plexins and transcription factors) domain and a nucleus localization signal, suggesting that it belongs to the class II NF-kappaB. RT-PCR analysis showed that LvDorsal mRNAs were expressed in all the tissues tested, including gill, epidermis, hemocytes, intestine, stomach, eyestalk, brain, hepatopancreas, muscle, heart and pyloric caecum. Immunofluorescence assay showed that recombinant LvDorsal was translocated into the nucleus of Drosophila S2 cells. Electrophoretic mobility shift assay illustrated that recombinant LvDorsal RHD from S2 cells bound specifically with D. melanogaster kappaB motifs. Additionally, the dual-luciferase reporter assays indicated that LvDorsal could transactivate the reporter gene controlled by the 5' flanking region of shrimp penaeidin-4 and Drosophila attacin genes, suggesting that LvDorsal can regulate the transcription of shrimp penaeidin-4 gene. Study of LvDorsal will help us to better understand shrimp immunity and may help to obtain more effective methods to prevent shrimp diseases.

A clip domain serine proteinase plays a role in antibacterial defense but is not required for prophenoloxidase activation in shrimp

The clip domain serine proteinases (clip-SPs) play critical roles in the signaling processes during embryonic development and in the innate immunity of invertebrates. In the present study, we identified a homolog of the clip-SP, designated as PmClipSP1, by searching the Penaeus monodon EST database (http://pmonodon.biotec.or.th), and using RACE-PCR to obtain the complete gene which contained a 1101bp open reading frame encoding 366 amino acids with a 25 amino acid signal peptide. The deduced PmClipSP1 protein sequence, which shares a predicted structural similarity to the clip-SPs of other arthropod species, appears to possess a clip domain at the N-terminus and an enzymatically active serine proteinase domain at the C-terminus. Tissue distribution analyses revealed that, at the transcript level, PmClipSP1 is mainly expressed in shrimp hemocytes, whilst temporal gene expression analyses showed that the hemocyte PmClipSP1 transcript levels were upregulated at 3h and downregulated at 6-48h following systemic Vibrio harveyi infection. RNAi-mediated silencing of the PmClipSP1 gene, by injection of double-stranded RNA (dsRNA) corresponding to the PmClipSP1 gene into shrimp, significantly reduced PmClipSP1 transcript levels, but neither significantly altered the other clip-SP and clip-SPH transcript levels nor reduced the total phenoloxidase (PO) enzyme activity in shrimp hemocytes, compared to the levels seen in the GFP dsRNA control, suggesting that PmClipSP1 is not involved in the proPO system. However, suppression of the PmClipSP1 gene led to a significant increase in the number of viable bacteria in the hemolymph (approximately 2.4-fold) and in the mortality rate (59%) of shrimp systemically infected with V. harveyi. These findings suggest that PmClipSP1 plays a role in the antibacterial defense mechanism of P. monodon shrimp.

RNAi knock-down of the Litopenaeus vannamei Toll gene (LvToll) significantly increases mortality and reduces bacterial clearance after challenge with Vibrio harveyi

In this study, we used real-time PCR to simultaneously monitor the responses of 12 key genes of the shrimp innate immune system in Litopenaeus vannamei after challenge with Vibrio harveyi. In the proPO activating system, we found that proPO was up-regulated (3.3x control at 36hpi). The hemolymph clotting genes transglutaminase (TGase) and clotting protein were also up-regulated, as were 5 genes in the antimicrobial peptide system (ALF, Crustin, Lyz, PEN2 and PEN4), with only PEN3 showing no significant changes. In the antioxidant defense system, SOD was slightly elevated while GPx was substantially down-regulated. In the pattern recognition receptor system, at 24hpi, the Toll gene (LvToll) showed the highest relative increase in expression level of all the investigated genes (15x greater than the sterile seawater control). In the second part of this study, when LvToll was knocked down by RNAi silencing, there was no effect on either survival rates or bacterial number in unchallenged shrimp. There was also no difference in mortality rates between control shrimp and LvToll-silenced shrimp when these two groups were challenged with a viral pathogen (white spot syndrome virus; WSSV). However, when LvToll-silenced shrimp were challenged by V. harveyi, there was a significant increase in mortality and bacterial CFU counts. We note that the increase in bacterial CFU count occurred even though treatment with EGFP dsRNA had the opposite effect of reducing the CFU counts. We conclude that LvToll is an important factor in the shrimp innate immune response to acute V. harveyi infection, but not to WSSV.

Identification and molecular characterization of a Spätzle-like protein from Chinese shrimp (Fenneropenaeus chinensis)

In invertebrates, the Toll signaling pathway is important for activation of antimicrobial peptides in the innate immune system. Activation of the Toll pathway requires binding of Toll with its ligand Spätzle. Here we described a Spätzle-like protein, designated as Fc-Spz, from hemocytes of Chinese shrimp, Fenneropenaeus chinensis. The deduced amino acid sequence of Fc-Spz shares 54% identity with Spätzle-like protein of salmon louse (Lepeophtheirus salmonis). Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR), quantitative real time PCR, and Western blot analyses were carried out to analyze the expression pattern and distribution profile of Fc-Spz in shrimp after challenged with bacteria and virus. The results showed that Fc-Spz mRNA was up-regulated in all the tissues tested in shrimp injected with Vibrio anguillarum and white spot syndrome virus (WSSV). The C-terminal active Fc-Spz domain (114 residues) was expressed in Escherichia coli and purified by affinity chromatography. The recombinant Fc-Spz C-114 was injected into crayfish (Procambarus clarkii) to determine the expression levels of several antimicrobial peptide genes. The results showed that recombinant Fc-Spz C-114 could up-regulate crustin 2 expression in crayfish. These results suggest that Fc-Spz may play a role in the innate immune defence of Chinese shrimp and crayfish.

Antiviral immunity in crustaceans

Viral diseases of shrimp have caused negative effects on the economy in several countries in Asia, South America and America, where they have numerous shrimp culture industries. The studies on the immunity of shrimp and other crustaceans have mainly focused on general aspects of immunity and as a consequence little is known about the antiviral responses in crustaceans. The aim of this review is to update recent knowledge of innate immunity against viral infections in crustaceans. Several antiviral molecules have been isolated and characterized recently from decapods. Characterization and identification of these molecules might provide a promising strategy for protection and treatment of these viral diseases. In addition dsRNA-induced antiviral immunity is also included.

Lack of evidence for Litopenaeus vannamei Toll receptor (lToll) involvement in activation of sequence-independent antiviral immunity in shrimp

Injection of non-specific dsRNA initiates a broad-spectrum innate antiviral immune response in the Pacific white shrimp, Litopenaeus vannamei, however, the receptor involved in recognition of this by-product of viral infections remains unknown. In vertebrates, dsRNA sensing is mediated by a class of Toll-like receptors (TLRs) and results in activation of the interferon system. Because a TLR (lToll) was recently characterized in L. vannamei, we investigated its potential role in dsRNA recognition. We showed that injection of non-specific RNA duplexes did not modify lToll gene expression. A reverse genetic approach was therefore implemented to study its role in vivo. Silencing of lToll did not impair the ability of non-specific dsRNA to trigger protection from white spot syndrome virus and did not increase the shrimp susceptibility to viral infection, when compared to controls. In contrast, gene-specific dsRNA injected to specifically silence lToll expression activated an antiviral response. These data strongly suggest that shrimp lToll plays no role in dsRNA-induced antiviral immunity.

Application of nucleic-acid-based therapeutics for viral infections in shrimp aquaculture

Viral infections are one of the major reasons for the huge economic losses in shrimp farming. The control of viral diseases in shrimp remains a serious challenge for the shrimp aquacultural industry, with major pathogens, such as the white spot syndrome virus, yellow head virus, Taura syndrome virus, hepatopancreatic parvovirus, and baculoviruses, being geographically widespread. In the absence of a true adaptive immune response system in invertebrates such as shrimp, one of the alternative and more specific approaches to counteract viral infections in shrimp could be the use of molecular-based gene transfer technologies, such as RNA interference (RNAi). The RNAi mechanism is initiated by double-stranded RNAs (dsRNAs), which are fragmented into shorter 21-23 nucleotides of short interfering RNAs (siRNAs) by a type III endonuclease, the Dicer. RNAi, which is mediated by small interfering RNA (siRNA), results in the sequence-specific post-transcriptional silencing of a target gene. This gene-silencing mechanism is universally conserved and is a well-known phenomenon that exists in many eukaryotes, including invertebrates. It has been recently extended to shrimp as an important potential tool in viral disease prevention. RNAi technology shows considerable promise as a therapeutic approach and efficient strategy for shrimp virus control in the aquaculture industry. Further progress in understanding the mechanism of siRNAs at the molecular level, as well as strategies to achieve their tightly regulated, stable, prolonged and tissue-specific expression in an effective manner, will definitely revolutionize therapeutic approaches for counteracting viral diseases of shrimp. In the present review, the recent development and potential use of RNAi in combating shrimp viral infections is discussed.

Comparison of gene expression profiles of Fenneropenaeus chinensis challenged with WSSV and Vibrio

Microarray technique was used to analyze the gene expression profiles of shrimp when they were challenged by WSSV and heat-inactivated Vibrio anguillarum, respectively. At 6 h post challenge (HPC), a total of 806 clones showed differential expression profile in WSSV-challenged samples, but not in Vibrio-challenged samples. The genes coding energy metabolism enzyme and structure protein were the most downregulated elements in 6 h post WSSV-challenged (HPC-WSSV) tissues. However, a total of 155 clones showed differential expression in the Vibrio-challenged samples, but not in WSSV-challenged samples. Serine-type endopeptidase and lysosome-related genes were the most upregulated elements in tissues 6 h post Vibrio challenge (HPC-Vibrio). Totally, 188 clones showed differential expression in both 6 and 12 HPC-WSSV and HPC-Vibrio samples. Most of the differentially expressed genes (185/188) were downregulated in the samples of 12 HPC-WSSV, whereas upregulated in the samples at 6 and 12 HPC-Vibrio and 6 HPC-WSSV. The expression profiles of three differentially expressed genes identified in microarray hybridization were analyzed in hemocytes, lymphoid organ, and hepatopancreas of shrimp challenged by WSSV or Vibrio through real-time PCR. The results further confirmed the microarray hybridization results. The data will provide great help for us in understanding the immune mechanism of shrimp responding to WSSV or Vibrio.

A key gene of the RNA interference pathway in the black tiger shrimp, Penaeus monodon: identification and functional characterisation of Dicer-1

RNA interference (RNAi) is an evolutionarily conserved mechanism by which double-stranded RNA (dsRNA) initiates post-transcriptional silencing of homologous genes. Here we report the amplification and characterisation of a full length cDNA from black tiger shrimp (Penaeus monodon) that encodes the bidentate RNAase III Dicer, a key component of the RNAi pathway. The full length of the shrimp Dicer (Pm Dcr1) cDNA is 7629bp in length, including a 5' untranslated region (UTR) of 130bp, a 3' UTR of 77bp, and an open reading frame of 7422bp encoding a polypeptide of 2473 amino acids with an estimated molecular mass of 277.895kDa and a predicted isoelectric point of 4.86. Analysis of the deduced amino acid sequence indicated that the mature peptide contains all the seven recognised functional domains and is most similar to the mosquito (Aedes aegypti) Dicer-1 sequence with a similarity of 34.6%. Quantitative RT-PCR analysis showed that Pm Dcr1 mRNA is most highly expressed in haemolymph and lymphoid organ tissues (P<0.05). However, there was no correlation between Pm Dcr1 mRNA levels in lymphoid organ and the viral genetic loads in shrimp naturally infected with gill-associated virus (GAV) and Mourilyan virus (P>0.05). Treatment with synthetic dsRNA corresponding to Pm Dcr1 sequence resulted in knock-down of Pm Dcr1 mRNA expression in both uninfected shrimp and shrimp infected experimentally with GAV. Knock-down of Pm Dcr1 expression resulted in more rapid mortalities and higher viral loads. These data demonstrated that Dicer is involved in antiviral defence in shrimp.

Identification of cDNA encoding Toll receptor, MjToll gene from kuruma shrimp, Marsupenaeus japonicus

Toll receptors are cell-surface receptors acting as pattern recognition receptors (PRRs) that are involved in the signaling pathway for innate immunity activation and are genetically conserved from insects to mammals. Tolls from penaeid shrimp are found in white leg shrimp Litopenaeus vannamei (lToll) and black tiger shrimp Penaeus monodon (PmToll). However, the molecular ligand-recognition patterns and identification of these penaeid Toll classes remain unknown. Here, we report cDNA cloning of a new type of Toll receptor gene (MjToll) from kuruma shrimp, Marsupenaeus japonicus, and the modulation of expression by immunostimulation. The full length cDNA of MjToll gene has 3095 nucleotides coding for a putative protein of 1009 amino acids. The MjToll gene is constitutively expressed in the gill, gut, lymphoid organ, heart, hematopoietic organ, hemocyte, ventral abdominal nerve cord, eyestalk neural ganglia and brain tissues. The MjToll gene expression was significantly increased (76-fold) as compared to a control in lymphoid organ stimulated with peptidoglycan at 12h, in vitro. lToll gene showed high similarity to PmToll gene with 96.9% identity; however, MjToll gene exhibited a percentage identity of 59% with that of penaeid Toll homologues. Therefore, this suggests that the identified MjToll gene belongs to the other class of Toll receptors in shrimp.