A tailless Dscam from Eriocheir sinensis diversified by alternative splicing

A member of the immunoglobulin superfamily lrig-1 might be involved in the immune priming of Scylla paramamosain in response to the infection and re-infection by Vibrio parahaemolyticus

A member of the immunoglobulin superfamily designated leucine-rich repeats and immunoglobulin-like domains protein-1 (lrig-1) encoding a protein with 1109 amino acids with a characteristic IGc2 domain was identified from the transcriptome data of mud crab Scylla paramamosain. Lrig-1 contained: one signaling peptide; one LRR_NT domain; nine LRR domains; three LRR_TYP domains; one LRR_CT domain; three IGc2 regions; one transmembrane region; C-terminal cytoplasmic tail. lrig-1 was widely expressed in all tissues of mud crab and was responsive in hemocytes to first and second Vibrio parahaemolyticus infections. lrig-1 knockdown mediated by RNAi repressed expression of several antimicrobial peptides significantly. Its orthologs in 19 crustacean species were identified and showed high conservation. These results suggest that lrig-1 have a vital role in mud crabs against V. parahaemolyticus infection through expression of multiple antimicrobial peptides. The results obtained in the present study imply the potential roles the lrig-1 played in immune priming in crabs.

An immunoglobulin superfamily member (CgIgIT2) functions as immune inhibitory receptor to inhibit the inflammatory cytokine expressions in Crassostrea gigas

Immune inhibitory receptors are increasingly acknowledged as potent regulators of immune response, which inhibit the overactivation of immune system and play an important role in maintaining immune homeostasis. In the present study, a novel immunoglobulin superfamily member (CgIgIT2) was identified from the Pacific oyster, Crassostrea gigas. The protein sequence of CgIgIT2 contained one signal peptide, four Ig domains, one fibronectin type III domain, one transmembrane domain, and a cytoplasmic tail with two intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs) and one immunoreceptor tyrosine-based switch motif (ITSM). The mRNA transcripts of CgIgIT2 were widely expressed in all the tested tissues, including haemolymph, gill, mantle, adductor muscle, labial palp, gonad and hepatopancreas, with the highest expression in haemolymph. The mRNA expressions of CgIgIT2 in haemocytes increased significantly at 24, 48 and 72 h after Vibrio splendidus stimulation. The positive green signals of CgIgIT2 protein were mainly detected in granulocytes of haemocytes, which were 1.27-fold and 2.15-fold (p < 0.05) higher than that of semi-granulocytes and agranulocytes, respectively. And CgIgIT2 was mainly located in the membrane and cytoplasm of haemocytes. The recombinant protein of CgIgIT2-4 × Ig (rCgIgIT2-4 × Ig) exhibited binding activity towards multiple pathogen-associated molecular patterns (PAMPs), including lipopolysaccharides (LPS), peptidoglycan (PGN), mannose (MAN) and polyinosinic-polycytidylic acid (Poly (I: C)) with the highest affinity for LPS. rCgIgIT2-4 × Ig could also bind Gram-negative bacteria (V. splendidus, V. anguillarum, Escherichia coli), Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis), and fungi (Pichia pastoris). In the blocking assay with anti-CgIgIT2 antibody, the mRNA expressions of interleukins (CgIL17-1, CgIL17-3 and CgIL17-6) and tumor necrosis factors (CgTNF-1 and CgTNF-2) in haemocytes all increased significantly at 12 h after V. splendidus stimulation. These results suggested that CgIgIT2 could function as an inhibitor receptor to bind different PAMPs and microbes, as well as inhibit the mRNA expressions of multiple inflammatory cytokines in oysters.

The extracellular non-variable region of Dscam promotes bacterial clearance by promoting phagocytosis of hemocytes in Eriocheir sinensis

As the most typical example of mRNA variable splicing, Down Syndrome Cell Adhesion Molecule (Dscam) can produce a large number of mRNA isomers. It plays an important role not only in the nervous system, but also in the immune system. In Eriocheir sinensis, the extracellular region of Dscam has three variable domains, which can produce 25, 34 and 18 exons and encode the N-terminal region of immunoglobulin (Ig) 2 and Ig3 domains, and the entire Ig7 domain, respectively. In addition to three variable domains, the extracellular non-variable region of Dscam also includes many Ig domains and fibronectin type III (FNIII) domains. However, the role of the extracellular non-variable region function of Dscam in the immune defense of E. sinensis is unclear. In this study, we focused on the role of the extracellular non-variable region of Dscam in crab immune defense. The results indicate that the extracellular non-variable region of Dscam can bind bacteria and has bacteriostatic function. At the same time, the extracellular non-variable region of Dscam can also directly promote bacterial clearance by promoting phagocytosis of hemocytes.

Immunological functional differentiation of two transmembrane variants of Dscam in Chinese mitten crab

Down syndrome cell adhesion molecule (Dscam), also called hypervariable Dscam (Dscam-hv), is an important player in arthropod alternative splicing that connects neurons and immune regulation, acting as a pathogen-specific recognition molecule. Dscam-hv has two forms: transmembrane (TM) Dscam (mDscam) and soluble Dscam (sDscam). Herein, we investigated two transmembrane variants of mDscam resulting from alternative splicing of the transmembrane domain, focusing on differences in their immune regulation. We characterized the Dscam[TM1] and Dscam[TM2] genes of Chinese mitten crab (Eriocheir sinensis) through bioinformatics analysis. Both genes are expressed in the gill, intestine, and other immune tissues. Following gram-positive and gram-negative bacteria stimulation, EsDscam[TM1] and EsDscam[TM2] mRNA expression levels increased significantly in hemocytes. Sequencing showed that EsDscam[TM1] was more abundant in hemocytes than EsDscam[TM2]. Additionally, the two subtypes differ in their regulation of antimicrobial peptides, the proportion of exon 33 carried, and bacterial phagocytosis.

Full-length transcriptome analysis provides new insights into the innate immune system of Marsupenaeus japonicus

As invertebrates, shrimp are generally thought to solely rely on their innate immune system to combat invading pathogens. Recently, an increasing number of studies have revealed that the innate immune response of invertebrates exhibits diversity and specificity based on their diverse immune molecules. Herein, a full-length transcriptome analysis of several immune-related tissues (hepatopancreas, gill, hemocytes, stomach and intestine) in the kuruma shrimp (Marsupenaeus japonicus) was conducted to identify immune-related molecules with a focus on transcript variations. In total, 11,222 nonredundant full-length transcripts with an N50 length of 5174 were obtained, and most of these transcripts (94.84%) were successfully annotated. In addition, a total of 147 long noncoding RNAs (lncRNAs) were also predicted. Importantly, transcript variants of several vital immune-related genes were observed, including twenty-five alpha-2-macroglobulins (α2-Ms), ten Toll-like receptors (TLRs), six C-type lectins (CTLs), five M-type lectins (MTLs) and three Down syndrome cell adhesion molecules (Dscams). Furthermore, 509 nonredundant full-length transcripts were predicted to be generated from alternative splicing (AS) events, which contribute to the diversity of immune molecules. Overall, our study provides valuable data on the full-length transcripts of M. japonicus, which will facilitate the exploration of immune molecules in this species. Moreover, numerous transcript variants of immune molecules detected in this study provide clues for further investigating the diversity and specificity of the innate immune response in shrimp.

Enhanced Immune Protection of Mud Crab Scylla paramamosain in Response to the Secondary Challenge by Vibrio parahaemolyticus

“Immune priming” plays a vital part in the immune system of invertebrates, protecting against recurrent infections by pathogens, and can provide some ideas for the prevention and treatment of invertebrate diseases. Many invertebrates have been demonstrated recently to have immune priming, but the relevant mechanisms are not known. Expression of immune system–related genes in the hemocytes and hepatopancreas of the mud crab (Scylla paramamosain) before and after repeated stimulation with Vibrio parahaemolyticus were analyzed by real-time fluorescence quantitative polymerase chain reaction. Some molecules that may participate in the immune priming of S. paramamosain were screened out, and their possible roles in immune priming were interpreted. Crabs injected first with heat-killed V. parahaemolyticus (HkVp group) or physiologic (0.9%) saline (PS group) were rechallenged at 168 h with live V. parahaemolyticus (HkVp+Vp group and PS+Vp group, respectively). The log-rank test shows a significant difference in survival rate between the HkVp+Vp group and the other groups after the ICH (p < 0.05). Expression of genes involved in the toll-like receptor (TLR) signaling pathway and some antimicrobial peptide genes were detected. By, respectively, comparing gene quantification at different time points in hemocytes and the hepatopancreas, the molecules that may play a part in the early stage of the immune priming of S. paramamosain in the hemocytes are found to be down syndrome cell adhesion molecule (Dscam), Hyastatin, Cactus, Arasin, antilipopolysaccharide factor 3 (ALF3), ALF4, ALF5, and ALF6 as well as later acting molecules, such as Crustin, Dorsal, Pelle, and myeloid differentiation factor 88 (MyD88). The molecules that functioned throughout the entire period are TLR and Spaetzle. In the hepatopancreas, the molecules that may play a part in the early stages of immune priming are Dscam, Hyastatin, Arasin, ALF6, Pelle, Spaetzle, Dorsal and, in the later stage, ALF4. The molecules that functioned throughout the entire period are TLR, Crustin, Cactus, MyD88, ALF3, and ALF5. In summary, the immune function of S. paramamosain is enhanced after it receives the same repetitive stimulation by V. parahaemolyticus, indicating immune priming in S. paramamosain. Our study enriches research on immune priming in invertebrates and lays the foundation for further studies revealing the molecular mechanism of immune priming in crabs.

Peculiarities of innate immune memory in crustaceans

Classical characteristic of the innate immune system is the lack of ability to build up immunological memory, contrast to the adaptive immune system that is capable of "remembering" antigens, and rapidly mount a greater magnitude of immune response upon subsequent exposure to the same antigens. Peculiarly, immunological memory of innate immunity is evidenced in invertebrates. At least three different memory phenomena have been described, namely sustained unique response, recalled response, and immune shift. Studies attended to decipher the mechanistic biology of the innate immune memory reveals the role of epigenetics, which modulates the response of immune memory, and the heritability of immune memory to subsequent generations. A parthenogenetic Artemia model demonstrated successful transgenerational epigenetic inheritance of resistance trait against Vibrio campbellii. Following, the role of invertebrate hemocytes and Down syndrome cell adhesion molecule (Dscam) in innate immune memory is reviewed. While there is no vertebrate antibody homolog found in invertebrates, Dscam was found to resemble the functionality of vertebrate antibody. Insight of Dscam as immune factor was illustrated further in the current review.

A CCL25 chemokine functions as a chemoattractant and an immunomodulator in black rockfish, Sebastes schlegelii

Chemokines are small cytokines that are classified into four groups, one of which is called CC chemokines. In the present study, the full-length cDNA of a CCL25 chemokine was identified from black rockfish, Sebastes schlegelii (named as SsCCL25) by EST (expressed sequence tag) analysis. The cDNA of SsCCL25 consisted of a 5-terminal untranslated region (UTR) of 74 bp, a 3-UTR of 882 bp with a poly (A) tail, and an open reading frame (ORF) of 303 bp encoding a polypeptide of 100 amino acids with the putative molecular mass of 11.5 kDa. There was a SCY domain in the deduced amino acid sequence of SsCCL25. The phylogenetic relationships and syntenic analyses provided evidences for the identities of SsCCL25 with CCL25 group. The mRNA transcripts of SsCCL25 were expressed in all detected tissues and dominantly in liver, muscle and gill. Moreover, after Vibrio anguillarum stimulation, the mRNA expression levels of SsCCL25 were significantly up-regulated at 24 h (p < 0.05) in the liver and during 4-8 h (p < 0.05) in the spleen. Recombinant SsCCL25 protein induced chemotaxis of both control and LPS-stimulated peripheral blood leukocytes (PBL) and enhanced their resistance to bacterial infection in a dose-dependent manner. Furthermore, rSsCCL25 showed significant inhibitory effect on V. anguillarum and Edwardsiella tarda growth. All these results collectively indicated that SsCCL25 might contribute to the defense against microbe infection and function as a chemoattractant in black rockfish.

Dscam in immunity: A question of diversity in insects and crustaceans

In insects and crustaceans, thousands of Down syndrome cell adhesion molecules (Dscam) can be generated by alternative splicing of variable exons from a single-locus gene, Dscam-hv. This extraordinarily versatile gene (38,016 protein isoforms produced in Drosophila) was first proposed to be involved in exon guidance and subsequently implicated in immunity as a hypervariable immune molecule. Almost 20 y after discovery of Dscam-hv, there have been many studies in insects and crustaceans regarding roles of Dscam in immunity, with many similarities and concurrently, many differences. Here, we review the current status of Dscam-hv, presented as a comparison of similarities and differences in insects and crustaceans and discuss hypotheses of Dscam functions in immunity.

The gene structure and hypervariability of the complete Penaeus monodon Dscam gene

Using two advanced sequencing approaches, Illumina and PacBio, we derive the entire Dscam gene from an M2 assembly of the complete Penaeus monodon genome. The P. monodon Dscam (PmDscam) gene is ~266 kbp, with a total of 44 exons, 5 of which are subject to alternative splicing. PmDscam has a conserved architectural structure consisting of an extracellular region with hypervariable Ig domains, a transmembrane domain, and a cytoplasmic tail. We show that, contrary to a previous report, there are in fact 26, 81 and 26 alternative exons in N-terminal Ig2, N-terminal Ig3 and the entirety of Ig7, respectively. We also identified two alternatively spliced exons in the cytoplasmic tail, with transmembrane domains in exon variants 32.1 and 32.2, and stop codons in exon variants 44.1 and 44.2. This means that alternative splicing is involved in the selection of the stop codon. There are also 7 non-constitutive cytoplasmic tail exons that can either be included or skipped. Alternative splicing and the non-constitutive exons together produce more than 21 million isoform combinations from one PmDscam locus in the P. monodon gene. A public-facing database that allows BLAST searches of all 175 exons in the PmDscam gene has been established at http://pmdscam.dbbs.ncku.edu.tw/.

The Enhanced Immune Protection in Chinese Mitten Crab Eriocheir sinensis Against the Second Exposure to Bacteria Aeromonas hydrophila

Accumulating evidences suggest that the enhanced immune responses and increased protection against bacteria-induced mortality can be initiated after the primary exposure to various microbial communities and their components in various organisms including commercially valuable crustaceans. In the present study, the survival rate and immune responses of Chinese mitten crab Eriocheir sinensis were determined after an immune priming (IP) with formalin-killed Aeromonas hydrophila and an immune challenge (ICH) with the same but live pathogen (Ah group). A group in which the animals received a salt injection prior to challenge was maintained as control (Ns group). In the present study, it was shown that an IP with killed A. hydrophila can significantly protect the crabs against the ICH with a lethal dose of the live pathogen. The increased survival was associated with elevated rate and duration of phagocytosis. The antibacterial activity of the serum was significantly increased in Ah group compared to that in Ns group. Significant changes of phenoloxidase (PO) activities were also found between Ah and Ns group but not in Ah group between IP and ICH. No significant changes of lysozyme were found in Ah and NS group during the whole experiment except 3 h after IP. In addition, the levels of transcripts and protein of Dscam were increased in hemocytes of the crabs from Ah group. All the results suggested that a primary immune priming with a particular killed pathogen could induce an enhanced immunity in crabs when they were encountered secondly with the same live pathogen. The evidences of elevated immune protections in crabs would contribute to better understand the mechanism of immune priming in invertebrates.

Transcriptomic analysis of immune-related genes in the lipopolysaccharide-stimulated hepatopancreas of the mudflat crab Helice tientsinensis

The mudflat crab Helice tientsinensis is one of the most economically important aquaculture species in China. Nevertheless, it is susceptible to various diseases caused by viruses, bacteria and rickettsia-like organisms. A better understanding of the immune system and genes related to the responses to bacterial and viral infection is required. Herein, the hepatopancreas transcriptome of H. tientsinensis was analyzed by comparing control and lipopolysaccharide (LPS)-stimulated RNA-Seq data, yielding 91,885,038 bp and 13.78 Gb of clean reads. Following assembly and annotation, 93,207 unigenes with an average length of 883 bp were identified, of which 31,674 and 13,700 were annotated in Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases, respectively. Following LPS, 4845 differentially expressed genes (DEGs) were identified, of which 2491 and 2354 were up- and down-regulated, respectively. To further investigate immune-related DEGs, KEGG enrichment analysis identified immune response pathways, most notably the peroxisome and Toll-like receptor signaling pathways. Quantitative real time-PCR (qRT-PCR) confirmed the up-regulation of a random selection of DEGs. This systematic transcriptomic analysis of the innate immune pathway in H. tientsinensis expands our understanding of the immune system in crabs.

A hypervariable immunoglobulin superfamily member from Crassostrea gigas functions as pattern recognition receptor with opsonic activity

Immunoglobulin superfamily (IgSF), an extensive collection of proteins possessing at least one immunoglobulin-like (Ig-like) domain, performs a wide range of functions in recognition, binding or adhesion process of cells. In the present study, a cysteine-rich motif associated immunoglobulin domain containing protein (designated CgCAICP-1) was identified in Pacific oyster Crassostrea gigas. The deduced protein sequence of CgCAICP-1 contained 534 amino acidresidues, with three Ig domains which were designated as IG1, IG2 and IG3, and a cysteine-rich motif between the first and second Ig domain. The mRNA transcripts of CgCAICP-1 were highly expressed in hemocytes and up-regulated significantly (p < 0.05) after the stimulation of lipopolysaccharides (LPS), but not peptidoglycan (PGN). The recombinant CgCAICP-1 protein (rCgCAICP-1) exhibited binding activity to various pathogen-associated molecular patterns (PAMPs) including LPS, PGN, mannose (Man) and D-galactose (D-Gal), and microorganisms including Vibrio splendidus, Escherichia coli, Staphylococcus aureus, Micrococcus luteus and Pichia pastoris. The phagocytic rates of oyster hemocytes towards Gram-negative bacteria V. splendidus and Gram-positive bacteria M. luteus were significantly enhanced (p < 0.05) after pre-incubation of microbes with rCgCAICP-1. Furthermore, the transcripts of CgCAICP-1 exhibited high level of polymorphism among individuals. The ratio of nonsynonymous and synonymous distances (dN/dS) for AA'BCC'D strands of IG1 (the possible binding sites 1, pbs1) across all allelic variants was 2.09 (p < 0.05), while the ratio for the non-pbs regions was less than 1.0. The 1248 bp fragment amplified from the 5' end of CgCAICP-1 open reading frame (ORF) from 24 transcript variants could be divided artificially into seven regions of 50 elements, and all of the allelic variants might be derived from these elements by point mutation and recombination processes. These results collectively suggested that CgCAICP-1 might function as an important pattern recognition receptor (PRR) to recognize various PAMPs and facilitated the phagocytosis of oyster hemocytes towards both Gram-positive and Gram-negative bacteria. Diverse isoforms of CgCAICP-1 were generated through point mutation and recombination processes and maintained by balancing selection, which would provide a broader spectrum of interaction surface and be associated with immune resistance of oysters to infectious pathogens.

Characterize a typically Dscam with alternative splicing in mud crab Scylla paramamosain

As a member of the immunoglobulin superfamily, Down syndrome cell adhesion molecule (Dscam) could function in the innate immunity of invertebrates. Recently, it is shown that arthropod Dscams play similar functions as antibodies in the adaptive immune system. Dscam could produce thousands of isoforms by alternative splicing and specifically bind to various pathogens. In the present study, we cloned the first Dscam from mud crab Scylla paramamosain (SpDscam), with full-length cDNA 7363 bp containing an open reading frame (ORF) of 6069bp and encoding 2022 amino acids, which had typical domain architecture as other arthropods, i.e., 10 immunoglobulin domains (Ig), 6 fibronectin type 3 domains (FN III), transmembrane and cytoplasmic tail. Quantitative real-time PCR revealed that SpDscam was highly expressed in brain, skin, muscle, intestine and hepatopancreas, but weakly expressed in hemolymph, heart and gill. SpDscam had three alternative splicing regions, located at the N-terminal of Ig2 and Ig3 as well as on the whole Ig7. In these regions, 32, 41 and 14 exons were detected, together with the two exon types of transmembrane domain, indicating SpDscam could potentially encode at least 36,736 unique isoforms. SpDscam induced by Vibrio parahaemolyticus challenge had strong binding ability to V. parahaemolyticus. Further, SpDscam induced by V. parahaemolyticus possessed a clearance of V. parahaemolyticus in S. paramamosain. Collectively, the results indicated SpDscam was a hypervariable pattern-recognition receptor (PRR) by alternative splicing in innate immunity system of mud crab S. paramamosain.

Dscam1 in Pancrustacean Immunity: Current Status and a Look to the Future

The Down syndrome cell adhesion molecule 1 (Dscam1) gene is an extraordinary example of diversity: by combining alternatively spliced exons, thousands of isoforms can be produced from just one gene. So far, such diversity in this gene has only been found in insects and crustaceans, and its essential part in neural wiring has been well-characterized for Drosophila melanogaster. Ten years ago evidence from D. melanogaster showed that the Dscam1 gene is involved in insect immune defense and work on Anopheles gambiae indicated that it is a hypervariable immune receptor. These exciting findings showed that via processes of somatic diversification insects have the possibility to produce unexpected immune molecule diversity, and it was hypothesized that Dscam1 could provide the mechanistic underpinnings of specific immune responses. Since these first publications the quest to understand the function of this gene has uncovered fascinating insights from insects and crustaceans. However, we are still far from a complete understanding of how Dscam1 functions in relation to parasites and pathogens and its full relevance for the immune system. In this Hypothesis and Theory article, we first briefly introduce Dscam1 and what we know so far about how it might function in immunity. By focusing on seven questions, we then share our sometimes contrasting thoughts on what the evidence tells us so far, what essential experiments remain to be done, and the future prospects, with the aim to provide a multiangled view on what this fascinating gene has to do with immune defense.

Down syndrome cell adhesion molecule 1: testing for a role in insect immunity, behaviour and reproduction

Down syndrome cell adhesion molecule 1 (Dscam1) has wide-reaching and vital neuronal functions although the role it plays in insect and crustacean immunity is less well understood. In this study, we combine different approaches to understand the roles that Dscam1 plays in fitness-related contexts in two model insect species. Contrary to our expectations, we found no short-term modulation of Dscam1 gene expression after haemocoelic or oral bacterial exposure in Tribolium castaneum, or after haemocoelic bacterial exposure in Drosophila melanogaster. Furthermore, RNAi-mediated Dscam1 knockdown and subsequent bacterial exposure did not reduce T. castaneum survival. However, Dscam1 knockdown in larvae resulted in adult locomotion defects, as well as dramatically reduced fecundity in males and females. We suggest that Dscam1 does not always play a straightforward role in immunity, but strongly influences behaviour and fecundity. This study takes a step towards understanding more about the role of this intriguing gene from different phenotypic perspectives.

Reprint of "review of Dscam-mediated immunity in shrimp and other arthropods"

Although true adaptive immunity is only found in vertebrates, there is increasing evidence that shrimp and other arthropods exhibit immune specificity and immune memory. The invertebrate immune response is now called "innate immunity with specificity" or "immune priming", and its underlying mechanisms are still unclear. However, while vertebrate antibodies have no invertebrate homolog, the Down syndrome cell adhesion molecule (Dscam), which is a hypervariable protein created by alternative splicing, can function as a pathogen-specific recognizing molecule in arthropods. Here we review our current understanding of the Dscam-mediated immune responses in arthropods, especially in shrimp, and show that Dscam may be involved in both general innate immunity and the pathogen-specific immune response.

Review of Dscam-mediated immunity in shrimp and other arthropods

Although true adaptive immunity is only found in vertebrates, there is increasing evidence that shrimp and other arthropods exhibit immune specificity and immune memory. The invertebrate immune response is now called "innate immunity with specificity" or "immune priming", and its underlying mechanisms are still unclear. However, while vertebrate antibodies have no invertebrate homolog, the Down syndrome cell adhesion molecule (Dscam), which is a hypervariable protein created by alternative splicing, can function as a pathogen-specific recognizing molecule in arthropods. Here we review our current understanding of the Dscam-mediated immune responses in arthropods, especially in shrimp, and show that Dscam may be involved in both general innate immunity and the pathogen-specific immune response.

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.