A clip domain serine protease (cSP) from the Chinese mitten crab Eriocheir sinensis: cDNA characterization and mRNA expression

Bacterial recognition and inhibition activities of an LRR-only protein in the Chinese mitten crab, Eriocheir sinensis

LRR-only protein (LRRop) is an important class of immune molecules that function as pattern recognition receptor in invertebrates, however, the bacterial inhibitory activity of this proteins remain largely unknown. Herein, a novel LRRop was cloned from Eriocheir sinensis and named as EsLRRop2. The EsLRRop2 consists of six LRR motifs and formed a horseshoe shape three-dimension structure. EsLRRop2 was mainly expressed in intestine and hepatopancreas. The transcripts of EsLRRop2 in the intestine and hepatopancreas were induced by Vibrio parahaemolyticus and Staphylococcus aureus, and displayed similar transcriptional profiles. The expression levels of EsLRRop2 responded more rapidly and highly to V. parahaemolyticus than S. aureus in the intestine and hepatopancreas. Although the basal expression level of EsLRRop2 in hemocytes was relatively low, its transcripts in hemocytes were significantly induced by V. parahaemolyticus and S. aureus. The recombinant proteins of EsLRRop2 (rEsLRRop2) displayed a wide range of binding spectrum against vibrios, including V. parahaemolyticus, V. alginolyticus, and V. harveryi. The rEsLRRop2 showed dose- and time-dependent inhibitory activity against V. parahaemolyticus and S. aureus, and it could agglutinate the two bacteria. Furthermore, the inhibitory activities of rEsLRRop2 against V. parahaemolyticus, V. alginolyticus, V. harveryi and S. aureus was slightly affected by pH and salinity, and the rEsLRRop2 displayed the strongest inhibitory activity against all the three vibrios when the salinity was 20 ‰ and pH was 8.0. Collectively, these results elucidate the bacterial binding and inhibitory activities of EsLRRop2, and provide theoretical foundations for the application of rEsLRRop2 in prevention and control of vibrio diseases in aquaculture.

Expression characteristics and inhibitory activity of a leucine-rich repeat (LRR)-only protein in the Chinese mitten crab, Eriocheir sinensis

The leucine-rich repeat (LRR) domain is a crucial structure in a variety of immune related proteins and displays multiple immune functions. In this study, the open reading frame (ORF) of an LRR-only protein was cloned from the Chinese mitten crab, Eriocheir sinensis (EsLRRop1). The protein sequence of EsLRRop1 contained seven LRR motifs, three LRR-TYP motifs and an LRRCT motif. Tissue distribution exhibited that EsLRRop1 mainly expressed in nervous tissues including thoracic ganglion, eyestalk and brain while showed relatively lower transcriptional level in hemocyte. Based on the above expression characteristics, the responses of EsLRRop1 to the challenge of Vibrio parahaemolyticus and Staphylococcus aureus were tested. The result showed that the transcript of EsLRRop1 in thoracic ganglion and eyestalk up-regulated after being challenged with S. aureus, while it decreased post injection with V. parahaemolyticus. The transcript of EsLRRop1 in hemocytes up-regulated sharply at 3 h and decreased at 12 h and 24 h after being challenged with V. parahaemolyticus, while it decreased at 12 h and 24 h post injection with S. aureus. The recombinant protein of EsLRRop1 (His-EsLRRop1) displayed binding activities to V. alginolyticus, V. harveyi, V. parahaemolyticus, S. aureus, Corynebacterium glutamicum and Micrococcus lysodeikticus as well as lipopolysaccharide (LPS) and peptidoglycan (PGN). Moreover, the His-EsLRRop1 exhibited inhibitory activity against V. parahaemolyticus and V. harveyi with minimum inhibitory concentration (MIC) of 3.57-7.14 μM and 7.14-14.28 μM, respectively. These results provide theoretical basis for the application of EsLRRop1 in inhibiting bacteria in aquaculture practice.

A trypsin-like serine protease domain of masquerade gene in crayfish Procambarus clarkii could activate prophenoloxidase and inhibit bacterial growth

Masquerade (Mas) is a secreted trypsin-like serine protease (SPs) and involved in immune response in some arthropods. However, according to previous studies, Mas presents different functional activities. In the present study, the functional mechanisms of Mas in crayfish Procambarus clarkii immune defense were studied. A fragment cDNA sequence of PcMas was identified and characterized. From the structural analysis, it contains a trypsin-like serine protease domain. The highest expression level of PcMas was detected in hepatopancreas. The infection of A. hydrophila could induce the expression of PcMas, while the WSSV infection did not cause changes in the expression of PcMas. Through the prokaryotic expression system, the PcMas protein was expressed in E. coli. It was verified that PcMas can bind to bacteria in vitro and inhibit the growth of the bacteria. By dsRNA interference with the expression of PcMas, the decrease expression of PcMas led to a decrease in the activity of phenoloxidase in hemolymph and an increase of mortality caused by A. hydrophila infection. The injection of recombinant protein can enhance the activity of phenoloxidase and reduce mortality caused by A. hydrophila infections. Therefore, the present study confirmed that PcMas could improve the body's immune response to eliminate bacterial pathogens by binding with bacteria and activating the prophenoloxidase system. The results will enrich the molecular mechanisms of crustaceans immune defense.

An ShK-domain serine protease of Eriocheir sinensis regulates the PO activity to resist Spiroplasma eriocheiris infection

A novel serine protease contains two ShK-domain was found from the Chinese mitten crab Eriocheir sinensis (EsShK-SP). The full-length EsShK-SP cDNA is 1927 bp and contains a 1260-bp open reading frame encoding a protein of 420 amino acids, including a signal peptide, two ShK domain, and Tryp-SPC domain. Quantitative real-time PCR showed that EsShK-SP was expressed mainly in the hemocytes, gills, intestine, and nerve, but weakly in heart, muscle, and hepatopancreas. After infected with Spiroplasma eriocheiris, the expression of EsShK-SP was significantly up-regulated from 1 d to 9 d. The Tryp-SPC domain was ligated with pGEX-4T-1 vector and prokaryotic expressed to obtain recombinant protein rSPC. When rSPC and S. eriocheiris stimulated the hemocytes of E. sinensis, the PO activity was significantly up-regulated. The subcellular localization revealed that recombinant EsShK-SP was mainly located in the cytoplasm of Drosophila S2 cells. Both absolute real-time PCR and confocal laser scanning microscope results showed that over-expression of EsShK-SP in S2 cells could decrease the copy number of S. eriocheiris. Meanwhile, the over-expression of EsShK-SP also increased the PO activity and cell viability of S2 cells. After EsShK-SP RNA interference using dsRNA, the expression levels of proPO and activity of PO decreased significantly from 48 h to 96 h. The knockdown of EsShK-SP by RNAi resulted in the copy number of S. eriocheiris in the EsShK-SP silenced group was significantly increased compared to the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in the EsShK-SP-dsRNA group. The above results indicated that EsShK-SP plays an important immune role during E. sinensis against S. eriocheiris through regulation of the proPO system.

Research progress in innate immunity of freshwater crustaceans

Invertebrates lack adaptive immunity and innate immunity plays important roles in combating foreign invasive pathogens. Freshwater crustaceans, which are invertebrates, depend completely on their innate immune system. In recent years, many immune-related molecules in freshwater crustaceans, as well as their functions, have been identified. Three main immune signaling pathways, namely, Toll, immune deficiency (IMD), and Janus kinase-signal transducer activator of transcription (JAK/STAT) pathways, were found in freshwater crustaceans. A series of pattern recognition receptors (PRRs), including Toll receptors, lectins, lipopolysaccharide and β-1,3-glucan binding protein, scavenger receptors, Down syndrome cell adhesion molecules, and thioester-containing proteins, were reported. Prophenoloxidase activation system and antimicrobial peptide synthesis are two important immune effector systems. These components are involved in the innate immunity of freshwater crustaceans, and they function in the innate immune defense against invading pathogens. This review mainly summarizes innate immune signaling pathways, PRRs, and effector molecules in freshwater crustaceans.

Functional characterization of two clip-domain serine proteases in the swimming crab Portunus trituberculatus

Clip domain serine proteases (cSPs), a family of multifunctional proteins, play a crucial role in innate immune system. Here, we report the functional characterization of two clip domain serine proteases (PtcSP1 and PtcSP3) from the swimming crab Portunus trituberculatus. The recombinant N-terminal clip domains and the C-terminal SP-like domains of PtcSP1 and PtcSP3 were expressed in Escherichia coli system, and assayed for various biological functions: protease activity, antimicrobial activity, bacterial clearance and microbial-binding activity. The recombinant SP-like domains of PtcSP1 and PtcSP3 exhibited trypsin-like protease activity, while their recombinant clip domains showed strong antibacterial activity and could bind to bacteria and yeast, suggesting the potential roles of PtcSP1 and PtcSP3 in immune defense and pattern recognition. Unlike PtcSP3, PtcSP1 revealed the opsonic activity as shown by a higher bacterial clearance rate of Vibrio alginolyticus coated with the combination of the recombinant clip domain and SP-like domain of PtcSP1 as compared with V. alginolyticus only. Knockdown of PtcSP1 or PtcSP3 by RNA interference resulted in a significant decrease of total phenoloxidase (PO) activity in crab, suggesting that PtcSP1 and PtcSP3 are involved in the proPO system. In addition, suppression of PtcSP1 or PtcSP3 changed the expression of PtALFs and complement-like components. All these findings suggest that PtcSP1 and PtcSP3 are multifunctional immune molecules and perform different protective functions in crab defense.

JAK/STAT signalling regulates antimicrobial activities in Eriocheir sinensis

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signalling pathway plays a significant role in immune responses to pathogens. In invertebrates, three core components (Domeless, Hopscotch and STAT92E) of the JAK/STAT pathway were first identified in Drosophila melanogaster. In the present study, we report the cloning and characterisation of DOME, JAK and STAT from Eriocheir sinensis. EsDOME, EsJAK and EsSTAT are 1299, 1110 and 794 amino acid proteins encoded by 4200, 3333 and 2385 bp open reading frames, respectively. Bioinformatics analysis revealed that all three share specific domains with corresponding functions. Quantitative real-time PCR showed that all three components were highly expressed in various tissues including the gill, hepatopancreas and hemocytes. Moreover, EsDOME, EsJAK and EsSTAT were upregulated significantly in hemocytes after bacterial challenge. In addition, the JAK/STAT signalling pathway positively regulates antimicrobial peptide expression during the antibacterial immune response. Thus, the JAK/STAT pathway plays a critical role in bacterial immune responses in E. sinensis.

GenDiS database update with improved approach and features to recognize homologous sequences of protein domain superfamilies

Since proteins evolve by divergent evolution, proteins with distant homology to each other may or may not bear similar functions. Improved computational approaches are required to recognize distant homologues that are functionally similar. One of the methods of assigning function to sequences is to use profiles derived from sequences of known structure. We describe an update of the Genomic Distribution of protein structural domain Superfamilies (GenDiS) database, namely GenDiS+, which provides a projection of SCOP superfamily members on the sequence space (NR database, NCBI). The sequences are validated using structure-based sequence alignment profiles and domain and full-length sequence alignments. GenDiS+ is a `tour de force’ for detecting homologues within around 160 000 taxonomic identifiers, starting from nearly 11 000 domains of known structure. Features, like full-sequence alignment and phylogeny, domain sequence alignment and phylogeny, list of associated structural and sequence domains with strength of interactions, links to databases like Pfam, UniProt and ModBase and list of sequences with a PDB structure, are provided.

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 clip domain serine protease regulates the expression of proPO and hemolymph clotting in mud crab, Scylla paramamosain

The clip domain serine proteinases (clip-SPs) play vital roles in embryonic development and in various innate immune functions in invertebrates such as antimicrobial activity, cell adhesion, hemolymph clotting, pattern recognition and regulation of the prophenoloxidase system. However, little is known about the role of the clip domain serine proteinase in Scylla paramamosain (designated SpcSP) immunity. In the present study, we cloned a clip-SP from S. paramamosain hemocytes using rapid amplification of cDNA end (RACE) approach. The full-length cDNA of SpcSP was 1823 bp, containing a 5' untranslated region (UTR) of 334 bp, an open reading frame of 1122 bp, and a 3' UTR of 367 bp. The open reading frame encoded a polypeptide of 373 amino acids with a calculated molecular weight of 39.7 kDa and an isoelectric point of 6.64. Structurally, SpcSP has a predicted 21-residue signal peptide and possessed the characteristic features of the clip domain family of serine proteases, namely one clip domain in the amino-terminal with six highly conserved cysteine residues and one enzyme active serine proteinase domain in the carboxyl-terminal with a highly conserved catalytic triad (His¹⁵⁶, Asp²²⁶, Ser³²¹). Phylogenetic analysis showed that SpcSP was clustered together with PtcSP (clip domain serine proteinase from Portunus trituberculatus). Quantitative real-time PCR (qPCR) analysis showed that the mRNA of SpcSP was constitutively expressed at different levels in all tested tissues in untreated S. paramamosain, with hemocytes and skin expressing the most. The transcriptional level of SpcSP in hemocytes was significantly up-regulated upon challenge with V. parahaemolyticus and LPS, indicating its involvement in antibacterial immune response. Indirect immunofluorescence analysis showed that SpcSP was expressed in the cytoplasm of all three hemocyte cell types (hyaline, semigranular and granular cells). Further, recombinant SpcSP protein exhibited strong binding ability and has antimicrobial activity against both Gram-positive and Gram-negative bacteria as well as fungi. Moreover, knockdown of SpcSP resulted in increased hemolymph clotting time and decreased the mRNA expression of SpproPO mRNA in hemocytes. These findings therefore suggest that SpcSP plays an important role in the antimicrobial defense mechanism of S. paramamosain by regulating the expression of SpproPO and hemolymph clotting in S. paramamosain.

Identification of a clip domain serine proteinase involved in immune defense in Chinese mitten crab Eriocheir sinensis

Clip-domain serine proteinase is an important serine proteinase family involved in many biological processes, which is only found in invertebrates. In the present study, the full-length cDNA of a clip domain serine proteinase (designed as EsCDSP) gene was cloned from Chinese mitten crab Eriocheir sinensis using rapid amplification of cDNA ends (RACE) technique. It was of 1488 bp with an open reading frame (ORF) of 1134 bp encoding a polypeptide of 377 amino acids. There were a signal peptide, a clip domain, and a Tryp_SPc domain in the deduced amino acid sequence of EsCDSP. Highly conserved cysteine residues were identified in the clip domain and Tryp_SPc domain. EsCDSP shared similarities of 40%-61% with CDSPs from Penaeus monodon (ACP19562.1), Scylla paramamosain (CCW43200.1), Drosophila melanogaster (NP_649734.2) and Delia antiqua (AAW57295.1). It was clustered with other CDSPs from crabs in the phylogenetic tree. EsCDSP transcript was highly expressed in hemocytes and it could response to the stimulations of Vibro anguillarum and Pichia pastoris. rEsCDSP could activate proPO system and significantly increase the PO activity of HLS. In addition, rEsCDSP could bond to Aeromonas hydrophila, Vibro anguillarum and Vibro alginolyticus, and reduced the mortality rate causing by pathogen infection. All the results suggested that EsCDSP was an important immune response participator involved in activation of the proPO system of crab.

Functional characterization of hemocytes from Chinese mitten crab Eriocheir sinensis by flow cytometry

Hemocytes comprise a diversity of cell types with functional and structural heterogeneity, and they play key roles in the host defense of invertebrates. In the present study, the hemocytes from Chinese mitten crab Eriocheir sinensis were directly separated into two groups by flow cytometry. The hemocytes in P1 group were full of round and abundant granules with deeply staining cytoplasm, while P2 hemocytes were more diverse with a wide range of sizes and less granularity. Both P1 and P2 hemocytes exhibited phagocytic ability, but the phagocytic rate of P1 hemocytes increased which was significantly higher than that of P2 hemocytes after LPS stimulations. The levels of ROS production and intracellular Calcium as well as lysosome content were higher in P1 hemocytes than that in P2 hemocytes under both normal and immune-activated situations. The genes involved in phagocytosis, antimicrobial and antioxidant activities were mainly expressed in P1 hemocytes, while the genes involved in proPO activation system were highly expressed in P2 hemocytes. These results collectively suggested that P1 hemocytes were the main immunocompetent hemocytes in Chinese mitten crab and P2 hemocytes mainly participated in proPO activation system.

A chymotrypsin-like serine protease from Portunus trituberculatus involved in pathogen recognition and AMP synthesis but not required for prophenoloxidase activation

Clip domain serine proteases (clip-SPs) play critical roles in various immune responses in arthropods, such as hemolymph coagulation, antimicrobial peptide (AMP) synthesis, cell adhesion and melanization. In the present study, we report the molecular and functional characterization of a clip domain serine protease (PtcSP2) from the swimming crab Portunus trituberculatus. The N-terminal clip domain and the C-terminal SP-like domain of PtcSP2 were expressed in Escherichia coli system, and assayed for their activities. Sequence similarity and phylogenetic analysis revealed that PtcSP2 may belong to the chymotrypsin family, which was confirmed by protease activity assay of the recombinant SP-like domain. The clip domain of PtcSP2 exhibited strong antibacterial activity and microbial-binding activity, suggesting the potential role in immune defense and recognition. Knockdown of PtcSP2 by RNA interference could significantly reduce PtcSP2 transcript levels, but neither decrease the total phenoloxidase (PO) activity in crab nor significantly alter the expression levels of serine protease inhibitors PtPLC and PtSerpin. These results indicate that PtcSP2 is not involved in the proPO system. However, suppression of PtcSP2 led to a significant change in the expression of AMP genes PtALFs and PtCrustin but not PtALF5. All these findings suggest that PtcSP2 is a multifunctional chymotrypsin-like serine protease and may participate in crab innate immunity by its antibacterial activity, immune recognition or regulation of AMP expression.

Identification of a novel clip domain serine proteinase (Sp-cSP) and its roles in innate immune system of mud crab Scylla paramamosain

Clip domain serine proteinases and their homologs are involved in the innate immunity of invertebrates. To identify the frontline defense molecules against pathogenic infection, we isolated a novel clip domain serine proteinase (Sp-cSP) from the hemocytes of mud crab Scylla paramamosain. The full-length 1362 bp Sp-cSP contains a 1155 bp open reading frame (ORF) encoding 384 amino acids. Multiple alignment analysis showed that the putative amino acid sequence of Sp-cSP has about 52% and 51% identity with Pt-cSP2 (AFA42360) and Pt-cSP3 (AFA42361) from Portunus trituberculatus, respectively, while the similarity with other cSP sequences was lower than 30%. However, all cSP sequences possess a conserved clip domain at the N-terminal and a Tryp-SPc domain at the C-terminal. The genomic organization of Sp-cSP consists of nine exons and eight introns, with some introns containing one or more tandem repeats. RT-PCR results indicated that Sp-cSP transcripts were predominantly expressed in the subcuticular epidermis, muscle and mid-intestine, but barely detectable in the brain and heart. Further, Sp-cSP transcripts were significantly up-regulated after challenge with lipopolysaccharides (LPS), Vibrio parahaemolyticus, polyinosinic polycytidylic acid (PolyI:C) or white spot syndrome virus (WSSV). Moreover, in vitro, the recombinant Sp-cSP revealed a strong antimicrobial activity against a Gram-positive (Staphylococcus aureus) and four Gram-negative (V. parahaemolyticus, Vibrio alginolyticus, Escherichia coli, Aeromonas hydrophila) bacteria in a dose-dependent manner. Taken together, the acute-phase response to immune challenges and the antimicrobial activity assay indicate that Sp-cSP is a potent immune protector and plays an important role in host defense against pathogen invasion in S. paramamosain.

Characterization and expression analysis of chymotrypsin after bacterial challenge in the mud crab, Scylla paramamosain

Chymotrypsin is one of the serine proteases families that have various biological functions. A chymotrypsin gene was isolated from hepatopancreas of the mud crab, Scylla paramamosain (designated SpCHY) in this study. The full-length cDNA of SpCHY contained 942 nucleotides with a polyadenylation sequence and encoded a peptide of 270 amino acids with a signal peptide of 17 amino acids. The SpCHY gene contains seven exons, six introns, a TATA box and several transcription factor binding sites that were found in 5’-promoter region which is 1221 bp in length. Real-time quantitative PCR analysis indicated that the expression level of SpCHY mRNA in hepatopancreas was significantly higher than that in other tissues. Immunocytochemistry and in situ hybridization exhibited the CHY-like reactivity presented in resorptive cells of the hepatopancreas. After bacterial challenge with Vibrio alginolyticus, the expression level of SpCHY mRNA was extremely up-regulated at 3 h in hepatopancreas. Our results suggest that SpCHY might play an important role in the mud crab’s immune response.

Identification and characterization of Tube in the Chinese mitten crab Eriocheir sinensis

As a key component of the Toll signaling pathway, Tube plays central roles in many biological activities, such as survival, development and innate immunity. Tube has been found in shrimps, but has not yet been reported in the crustacean, Eriocheir sinensis. In this study, we cloned the full-length cDNA of the adaptor Tube for the first time from E. sinensis and designated the gene as EsTube. The full-length cDNA of EsTube was 2247-bp with a 1539-bp open reading frame (ORF) encoding a 512-amino acid protein. The protein contained a 116-residue death domain (DD) at its N-terminus and a 272-residue serine/threonine-protein kinase domain (S_TKc) at its C-terminus. Phylogenetic analysis clustered EsTube initially in one group with other invertebrate Tube and Tube-like proteins, and then with the vertebrate IRAK-4 proteins, finally with other invertebrate Pelle proteins. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis results showed that EsTube was highly expressed in the ovary and testis, and moderately expressed in the thoracic ganglia and stomach. EsTube was expressed at all selected stages and was highly expressed in the spermatid stage (October, testis) and the stage III-2 (November, ovary). EsTube was differentially induced after injection of lipopolysaccharides (LPS), peptidoglycan (PG) or zymosan (β-1,3-glucan). Our study indicated that EsTube might possess multiple functions in immunity and development in E. sinensis.

Transcriptome profiling analysis on whole bodies of microbial challenged Eriocheir sinensis larvae for immune gene identification and SNP development

To study crab immunogenetics of individuals, newly hatched Eriocheir sinensis larvae were stimulated with a mixture of three pathogen strains (Gram-positive bacteria Micrococcus luteus, Gram-negative bacteria Vibrio alginolyticus and fungi Pichia pastoris; 10⁸ cfu·mL^-1). A total of 44,767,566 Illumina clean reads corresponding to 4.52 Gb nucleotides were generated and assembled into 100,252 unigenes (average length: 1,042 bp; range: 201-19,357 bp). 17,097 (26.09%) of 65,535 non-redundant unigenes were annotated in NCBI non-redundant protein (Nr) database. Moreover, 23,188 (35.38%) unigenes were assigned to three Gene Ontology (GO) categories, 15,071 (23.00%) to twenty-six Clusters of orthologous Groups (COG) and 8,574 (13.08%) to six Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, respectively. Numerous genes were further identified to be associated with multiple immune pathways, including Toll, immune deficiency (IMD), janus kinase (JAK)-signal transducers and activators of transcription (STAT) and mitogen-activated protein kinase (MAPK) pathways. Some of them, such as tumor necrosis factor receptor associated factor 6 (TRAF6), fibroblast growth factor (FGF), protein-tyrosine phosphatase (PTP), JNK-interacting protein 1 (JIP1), were first identified in E. sinensis. TRAF6 was even first discovered in crabs. Additionally, 49,555 single nucleotide polymorphisms (SNPs) were developed from over 13,309 unigenes. This is the first transcriptome report of whole bodies of E. sinensis larvae after immune challenge. Data generated here not only provide detail information to identify novel genes in genome reference-free E. sinensis, but also facilitate our understanding on host immunity and defense mechanism of the crab at whole transcriptome level.

Two novel Toll genes (EsToll1 and EsToll2) from Eriocheir sinensis are differentially induced by lipopolysaccharide, peptidoglycan and zymosan

Tolls/Toll-like receptors (TLRs) play an essential role in initiating innate immune responses against pathogens and are found throughout the insect kingdom but have not yet been reported in the crustacean, Eriocheir sinensis. For this purpose, we cloned two novel Toll genes from E. sinensis, EsToll1 and EsToll2. The full-length cDNA of EsToll1 was 3963 bp with a 3042-bp open reading frame (ORF) encoding a 1013-amino acid protein. The extracellular domain of this protein contains 17 leucine-rich repeats (LRRs) and a 139-residue cytoplasmic Toll/interleukin-1 receptor (TIR) domain. The cDNA full-length of EsToll2 was 4419 bp with a 2667-bp ORF encoding an 888-amino acid protein with an extracellular domain containing 10 LRRs and a 139-residue cytoplasmic TIR domain. By phylogenetic analysis, EsToll1 and EsToll2 clustered into one group together with Tolls from other crustaceans. Quantitative RT-PCR analysis demonstrated that a) both EsToll1 and EsToll2 were constitutively expressed in all tested crab tissues; b) EsToll1 and EsToll2 were differentially induced after injection of lipopolysaccharides (LPS), peptidoglycan (PG) or zymosan (GLU). Importantly, EsToll2 expression was significantly upregulated at almost all time intervals post-challenge with LPS, PG and GLU. Our study indicated that EsToll1 and EsToll2 are differentially inducibility in response to various PAMPs, suggesting their involvement in a specific innate immune recognition mechanism in E. sinensis.

Cloning and characterization of a clip domain serine protease and its homolog (masquerade) from Eriocheir sinensis

Serine proteinases (SPs) or SP homologs (SPHs) including clip domain SPs (cSPs) or SPHs (cSPHs) play critical roles in digestion, embryonic development, hemolymph coagulation, and melanization. In this study, one cSP (EscSP) and one SPH, similar to Drosophila masquerade (EsMas), were identified from hepatopancreas of the Chinese mittern crab Eriocheir sinensis. They both possess the clip domains at the N-terminal, EscSP has only one clip domain, but EsMas has seven clip domains. One SP or SP-like domain was at the C-terminal of EscSP and EsMas respectively. In contrast to EscSP, absence of a catalytic residue of Ser resulted in the loss of SP activity of EsMas. Tissue distribution analysis showed that EscSP mRNA was mainly expressed in hepatopancreas, nerve and eyestalk tissue; whereas the EsMas transcript was mainly distributed in eyestalk, muscle, nerve and hemocytes. EscSP in hemocytes showed significant increase after a lipopolysaccharide (LPS) or peptidoglycan (PGN) challenge. However, down-regulation of EsMas was observed in hemocytes challenged by LPS from 2 to 24 h, by contrast EsMas could be induced by PGN challenge at 2 and 24 h. All these findings indicated that EscSP and EsMas might be involved in the innate immune defenses in E. sinensis.

Identification and characterization of a serine protease inhibitor Esserpin from the Chinese mitten crab Eriocheir sinensis

Serine protease inhibitors (serpins) represent an expanding superfamily of endogenous inhibitors that regulate proteolytic events and involve in a variety of physiological processes. A serine protease inhibitor, namely Esserpin, was identified from Chinese mitten crab Eriocheir sinensis based on expressed sequence tag (EST) analysis. The full-length cDNA of Esserpin was of 2367 bp, including an open reading frame (ORF) of 1371 bp encoding a polypeptide of 456 amino acids with estimated molecular mass of 49.95 kDa and theoretical isoelectric point of 6.03. A putative signal peptide of 23 amino acids and a classical serpin domain were identified in Esserpin. The deduced amino acid sequence of Esserpin shared homology with serpins from Fenneropenaeus chinensis and Pacifastacus leniusculus. The mRNA transcripts of Esserpin could be detected in all the examined tissues including heart, gill, hemocytes, muscle, gonad and hepatopancreas, and the highest expression level was present in gonad. After the crabs were challenged by Vibrio anguillarum and Pichia pastoris, the expression levels of Esserpin transcripts in hemocytes were significantly up-regulated, and peaked at 24 h (5.18-fold of blank group, P < 0.05) and 3 h (2.87-fold of blank group, P < 0.05), respectively. The functional activity of Esserpin was investigated by recombination and expression of the cDNA fragment encoding its mature peptide in Escherichia coli BL21 (DE3)-pLysS. The recombinant Esserpin (rEsserpin) could inhibit trypsin activities in a dose-dependent manner, and it could lead to 100% inhibition of trypsin activities under the concentration of 873.76 nM, while there was no evident inhibition of chymotrypsin observed with rEsserpin. Moreover, rEsserpin inhibited the growth of E. coli at the final concentration of 1747.52 nM, and it also significantly depressed (P < 0.05) the phenoloxidase activity in the plasma at the final concentration of 873.76 nM. These results indicated that Esserpin was a homologue of serpin in crab and it could be induced after immune stimulation and mediate immune response possibly via the inhibition of bacterial growth and the regulation of prophenoloxidase-activating system.

Three clip domain serine proteases (cSPs) and one clip domain serine protease homologue (cSPH) identified from haemocytes and eyestalk cDNA libraries of swimming crab Portunus trituberculatus

Four genes including three clip domain serine proteases (PtcSP1, PtcSP2 and PtcSP3) and one clip domain serine protease homologue (PtcSPH) of the swimming crab Portunus trituberculatus (Decapoda: Brachyura: Portunidae) were characterized based on analysis of expressed sequence tags from haemocytes and eyestalk cDNA libraries. The relative four peptidases, which share high structural similarity to the clip-SPs of other arthropod species, appeared to possess a clip domain at the N-terminus and an enzymatically active serine protease domain at the C-terminus except PtcSPH for its second catalytic residue Asp. (D) replaced by Ala (A). Alignment among the four full-sequences showed that PtcSP2 and PtcSP3 had the highest identical score (58%) while the similarity of other sequences was lower than 24%. The mRNA transcripts of PtcSPs and PtcSPH could be detected widely in all the examined tissues with remarkable different expression levels. The temporal expressions of PtcSPs and PtcSPH demonstrated different time-dependent expression pattern post Vibrio alginolyticus, Micrococcus luteus, and Pichia pastoris challenge. Especially, the expression of PtcSPH transcripts showed greater change against V. alginolyticus compared with the other two microorganisms. These findings suggest that PtcSPs and PtcSPH play different roles in the antibacterial defence mechanism of P. trituberculatus crab.

Molecular cloning, characterization and expression analysis of cathepsin A gene in Chinese mitten crab, Eriocheir sinensis

Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, function in immune response in vertebrates; however, their function within the innate immune system of invertebrates remains largely unknown. Therefore, we investigated the immune functionality of cathepsin A (catA) in Chinese mitten crab (Eriocheir sinensis), a commercially important and disease vulnerable aquaculture species. The full length catA cDNA (2200 bp) was cloned via PCR based upon an initial expressed sequence tag (EST) isolated from a hepatopancreatic cDNA library. The catA cDNA contained a 1398 bp open reading frame (ORF) that encoded a putative 465 amino acid (aa) protein. Comparisons with other reported vertebrate cathepsins sequences revealed percent identity range from 48 to 51%. CatA mRNA expression in E. sinensis was (a) tissue-specific, with the highest expression observed in gill and (b) responsive in hemocytes to a Vibrio anguillarum challenge, with peak exposure observed 12 h post-injection. Collectively, data demonstrate the successful isolation of catA from the Chinese mitten crab, and its involvement in the innate immune system of an invertebrate.