Molecular characterization and expression analysis of Cathepsin B and L cysteine proteases from rock bream (Oplegnathus fasciatus)

Proteomics and phosphoproteomics analysis identifies liver immune protein markers in large yellow croakers (Larimichthys crocea) fed a soybean oil-based diet

Dietary fish oil (FO) replacement has led to an inflammatory response in fish species. This study aimed to identify immune-related proteins in the liver tissue of fish fed a FO-based or soybean oil (SO)-based diet. By conducting proteomics and phosphoproteomics analyses, a total of 1601 differentially expressed proteins (DEPs) and 460 differentially abundant phosphorylated proteins (DAPs) were identified, respectively. Enrichment analysis revealed immune-related proteins involved in bacterial infection, pathogen identification, cytokine production, and cell chemotaxis. The mitogen-activated protein kinase (MAPK) pathway exhibited significant alterations in both protein and phosphorylation levels, with several hub DEPs and DAPs associated with MAPK pathway and leukocyte transendothelial migration being notable. In vitro experiments indicated that linolenic acid (LNA), derived from SO, inhibited the expression of NF-E2-related factor 2 (Nrf2), but increased the expression of signaling proteins linked to nuclear factor κB (NF-κB) and MAPK pathways. Transwell assays indicated that treatment of liver cells with LNA promoted macrophage migration. Collectively, the results showed that the SO-based diet upregulated the expression of NF-κB signaling-related proteins and activated the MAPK pathway, promoting immune cell migration. These findings provide novel insights for developing effective solutions to alleviate health problems caused by dietary high levels of SO inclusion.

Cathepsin H and cathepsin B of Cynoglossus semilaevis are involved in anti-bacterial immunity against Edwardsiella tarda

Cathepsin H and Cathepsin B are two lysosomal cysteine proteases participating in various physiological processes including immune responses. In fish, the functional roles of Cathepsin H and Cathepsin B during bacterial infection are less understood. In a previous work, we characterized a Cathepsin B homologue (CsCatB) of half-smooth tongue sole (Cynoglossus semilaevis), an economically valuable fish species in China. In this report, we identified a Cathepsin H homologue (CsCatH) from C. semilaevis. In healthy tongue sole, the transcriptional expression of CsCatH was detected in nine different tissues. Laser scanning confocal microscopic analysis showed that ectopically expressed CsCatH and CsCatB were co-localized with the lysosome. Upon infection by Edwardsiella tarda, a significant fish pathogen which caused a severe fish disease termed edwardsiellosis, the expressions of CsCatH and CsCatB were remarkedly upregulated. The knockdown of CsCatH and CsCatB significantly increased the replication of E. tarda and mitigated E. tarda-induced apoptosis in tongue sole tissues. These findings revealed the importance of CsCatH and CsCatB in anti-bacterial immunity of tongue sole.

Comparative analysis of two cathepsin L genes in Asiatic hard clam (Meretrix meretrix): Similar in sequence features, different in expression profiles

Cathepsin L is widely found in eukaryotes and prokaryotes, and it plays important roles in innate immunity. In the present study, we cloned two cathepsin L genes (designated as MmCTSL1 and MmCTSL2, respectively) from Asiatic hard clam (Meretrix meretrix). The complete sequence of MmCTSL1 cDNA contained a 5' untranslated region (UTR) of 31 bp, a 3' UTR of 228 bp with a poly (A) tail, and an open reading frame (ORF) of 1005 bp encoding 334 amino acids with predicted molecular weight of 37.5 kDa and theoretical isoelectric point of 5.27, and contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W27 to F87), and a papain family cysteine protease domain (from L118 to T333). The complete sequence of MmCTSL2 cDNA contained a 5' UTR of 50 bp, a 3' UTR of 162 bp with a poly (A) tail, and an ORF of 996 bp encoding a polypeptide of 331 amino acids with predicted molecular weight of 36.8 kDa and theoretical isoelectric point of 7.07. It contained a signal peptide (from M1 to A16), a protease inhibitor I29 family domain (from W30 to F89), and a papain family cysteine protease domain (from L115 to T330). Real-time quantitative PCR analysis demonstrated that MmCTSL1 and MmCTSL2 were widely expressed in all the tested tissues, including adductor muscle, foot, gill, hemocytes, hepatopancreas and mantle, with the highest mRNA expression level in hepatopancreas and hemocytes, respectively. After Vibrio splendidus challenge, the mRNA expression levels of MmCTSL1 and MmCTSL2 in hemocytes and hepatopancreas were both significantly up-regulated with different expression profiles. In hemocytes, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks (3.4-fold and 13.0-fold compared with the control, respectively) at 12 h after bacterial challenge, and MmCTSL2 responds earlier than MmCTSL1. In hepatopancreas, the expression levels of MmCTSL1 and MmCTSL2 reached their respective peaks at 6 h (9.0-fold compared with the control) and 24 h (2.8-fold compared with the control) after bacterial challenge, meaning that MmCTSL1 responds earlier than MmCTSL2. At the same time, whether in hepatopancreas or hemocytes, MmCTSL1 persist for a while after the bacterial challenge peak, while MmCTSL2 would quickly return to the initial level after the bacterial challenge peak. These results indicate that cathepsin L may be involved in the immune process of hard clam against V. splendidus with different potential roles.

Characteristics of cathepsin members and expression responses to poly I:C challenge in Pacific cod (Gadus macrocephalus)

Cathepsins are major lysosomal enzymes that participate in necessary physiological processes, including protein degradation, tissue differentiation, and innate or adaptive immune responses. According to their proteolytic activity, vertebrate cathepsins are classified as cysteine proteases (cathepsins B, C, F, H, K, L, O, S, V, W, and X or Z), aspartic proteases (cathepsin D and E), and serine proteases (cathepsin A and G). Several cathepsins were reported in teleosts, however, no cathepsin gene has been identified from Pacific cod so far. In the present study, a total of 13 cathepsin genes were identified for Pacific cod. The evolutionary path of each cathepsin gene was demonstrated via analysis of phylogenetic trees, multiple alignments, conserved domains, motif compositions, and tertiary structures. Tissue distribution analysis showed that all cathepsin genes were ubiquitously expressed in eight healthy tissues but they exhibited diverse levels of expression. Several cathepsin genes were found to be highly expressed in the kidney, spleen, head kidney and liver, whereas low or modest levels were detected in the gills, skin, intestines, and heart. Temporal-specific expression of cathepsins in early developmental stages of Pacific cod were also conducted. CTSK, S, F, and Z were highly expressed at 1 dph and 5 dph and decreased later, while CTSL, L1, and L.1 transcript levels gradually increased in a time-dependent manner. Additionally, the expression profiles of cathepsin genes in Pacific cod were evaluated in the spleen and liver after poly I:C challenge. The results indicated that all cathepsin genes were significantly upregulated upon poly I:C stimulation, suggesting that they play key roles in antiviral immune responses in Pacific cod. Our findings establish a foundation for future exploration of the molecular mechanisms of cathepsins in modulating antiviral immunity in Pacific cod.

Bioactivity of orange-spotted grouper (Epinephelus coioides) cathepsin L: Proteolysis of bacteria and regulation of the innate immune response

Cathepsin L (CTSL) is a cysteine endopeptidase involved in protein degradation mainly in lysosomes. Following activation in an acidic environment, it plays a key role in a variety of physiological, immunological, and pathological processes. The biological function of CTSL in teleost remains unclear. Immunohistochemical analysis revealed that CTSL was expressed mainly in lymphoid organs, head kidney, trunk kidney, and liver, which particularly was expressed in leukocyte-like cells. We performed two forms of recombinant CTSL (rCTSL and rTCTSL) derived from orange-spotted grouper (Epinephelus coioides) to elucidate the role of CTSL in teleost innate immunity, based on differences in immune-related gene expression. We determined that rCTSL has a proteolytic function whereas rTCTSL does not. Under CTSL activation, we observed increases in IL-1β, IL-6, IL-12, IFNγ, CCL-1, CCL-3, epinecidin-1, lysozyme, and IgM. The bacteriolytic activity of rCTSL was more pronounced against Gram-positive bacteria than Gram-negative bacteria. Our findings indicate CTSL plays multiple roles in the reactions of innate immunity.

Functional characterization of cathepsin B and its role in the antimicrobial immune responses in golden pompano (Trachinotus ovatus)

Cathepsin B (CTSB) is one of the typical representatives of cysteine protease family. It has the activity of both exopeptidase and endopeptidase. It plays an important role in antigen presentation, degradation, apoptosis, inflammatory response and physiological process of many diseases. In this study, CTSB of Trachinotus ovatus (TroCTSB) was cloned, and its structure and function were analyzed. The results showed that the coding region of TroCTSB was 993 bp, encoding 330 amino acid residues. The homology analysis showed that the amino acid sequence of TroCTSB was similar to that in other teleosts and mammals (68.69%-88.48%). Under normal physiological conditions, TroCTSB was widely distributed in various tissues with the highest expression level in stomach, followed by liver, and the lowest expression level in blood. The optimal pH and temperature of purified recombinant protein rTroCTSB were 5.5 and 40 °C, respectively. The toxicity test of metal ions showed that Fe²⁺, Cu²⁺, Ca²⁺ and Zn²⁺ could all inhibit the activity of TroCTSB, with Zn²⁺ ranking the first. In addition, after Edwardsiella tarda infection, the expression of TroCTSB was significantly up-regulated in liver, spleen and head kidney. The overexpression of TroCTSB significantly inhibited the infection of E. tarda in golden pompano tissues, and the knockdown of TroCTSB remarkably promoted the reproduction of E. tarda in golden pompano tissues in vivo. This study suggests that TroCTSB was involved in the antibacterial immune response of T. ovatus, and provided a reference for further research in elucidating the resistance mechanism of TroCTSB.

Identification and molecular profiling of a novel homolog of cystatin C from rock bream (Oplegnathus fasciatus) evidencing its transcriptional sensitivity to pathogen infections

Cystatins are reversible inhibitors of cysteine proteases which show an omnipresent distribution in the life on earth. Although, cystatins with mammalian origin were well characterized and their roles in physiology were reported in details, those from teleostean origin are still underrepresented in literature. However, role of cystatins in fish physiology and immune defense is highlighted in few recent reports. In this study, a cystatin C holmologue from rock bream (Oplegnathus fasciatus); termed RbCytC was identified and molecularly characterized. The complete coding sequence of RbCytC was 387 bp in length, which codes for a polypeptide with 129 amino acids, including a signal peptide of 19 amino acids. The consensus cystatin family signatures including a G residue, turning up towards the N-terminus region, QVVAG motif, locating at the middle of the sequence and the PW motif at the c terminal region was found to be well conserved in RbCytC. Phylogenetic analysis using different cystatin counterparts affirmed the close evolutionary relationship of RbCytC with its teleostan homologs which belong to family 2 cystatins. The predicted molecular model of RbCytC resembled most of the structural features of empirically elucidated tertiary structures for chicken egg white cystatin. According to the qPCR assays, RbCytC showed detectable expression in all fish tissues used in the experiment, with markedly pronounced expression level in liver. Moreover, its basal mRNA expression was up-regulated in liver and spleen tissues by experimental rock bream iridovirus infection, whereas down regulated in the same tissues, post live Edwardsiella tarda injection. Collectively, outcomes of our study validate the structural homology of RbCytC with known cystatin C similitudes, especially those of teleosts and suggest its potential roles in proteolytic processes of rock bream physiology as well as in host immune defense mechanisms.

Pathogenic infection and immune-related gene expression of Chinese sturgeon (Acipenser sinensis) challenged by Citrobacter freundii

Citrobacter freundii is one of the important bacterial diseases responsible for disease outbreaks to wild and cultured fishes globally. However, no known empirical research has focused on exploring relationships between immune response after C. freundii infection in sturgeons. In this study, C. freundii was isolated and identified from artificially breeding Chinese sturgeon, and global measurement of transcriptome response to C. freundii infection in head-kidney and spleen of A. sinensis were conducted to the acknowledgement of the potential mechanisms of pathogen-host interaction triggered by the bacterial infection. In total, differentially expressed genes which significantly associated with immune responses were found to be participated in antigen processing and presentation (MHC I, MHC II, HspA1, Hsp90A, Hsp70, CTSL, and CTSE), and acute phase response (serotransferrin and CP), as well as changing of other immune-related cytokine, such as chemokine and interferon, which proving their reacting and regulatory role during the response of thehost against C. freundii infection in fish. C. freundii can cause serious disease in sturgeon species was first reported in this study, and innate immune responses to C. freundii infection in this study will be conducive to understand the defense mechanisms and making appropriate prevention strategies in A. sinensis aquaculture operations.

Role of major histocompatibility complex II antigen-presentation pathway genes in orange-spotted grouper infected with Cryptocaryon irritans

Cryptocaryon irritans, a pathogen model for fish mucosal immunity, causes skin mucosal and systematic humoral immune response. Where and how MHC II antigen presentation occurs in fish infected with C. irritans remain unknown. In this study, the full-length cDNA of the grouper cysteine protease CTSS was cloned. The expression distributions of six genes (CTSB, CTSL, CTSS, GILT, MHC IIA and MHC IIB) involved in MHC II antigen presentation pathway were tested. These genes were highly expressed in systematic immune tissues and skin and gill mucosal-associated immune tissues. All six genes were upregulated in skin at most time points. Five genes expected CTSS was upregulated in spleen at most time points. CTSB, CTSL and MHC IIA were upregulated in the gill and head kidney at some time points. These results indicate that the presentation of MHC II antigen intensively occurred in local infected skin and gill. Spleen, not head kidney, had the most extensive systematic antigen presentation. In skin, six genes most likely peaked at day 2, earlier than in spleen (5-7 days), marking an earlier skin antibody peak than any recorded in serum previously. This significant and earlier mucosal antigen presentation indicates that specific immune response occurs in local mucosal tissues.

Seasonal changes of hydrolytic enzyme activities in the skin mucus of rainbow trout, Oncorhynchus mykiss at different body sizes

The innate immune factors in the skin mucus of fish are affected by the ecological and physiological conditions such as developmental stage and seasonal cycle. The aim of this study was to investigate the seasonal changes in soluble protein and the hydrolytic enzyme activities of the skin mucus of rainbow trout including lysozyme, alkaline phosphatase (ALP) and proteases at different body sizes. Skin mucus samples were collected over three consecutive season periods including winter, spring and late summer. In each season, sampling was performed separately from three different weight groups including 2-20 g (W1), 100-200 g (W2) and 400-600 g (W3) fish. Our results showed a significant increase of soluble protein in all three weight groups from winter to spring when water temperature elevated from 9 °C to 14 °C. Moreover lysozyme activity was remarkably elevated in W1 fish from winter to late summer. In all three seasons, the activity of lysozyme was significantly decreased along with increasing the fish size. Contrary to lysozyme, the activity of proteases and ALP showed a decreasing trend from winter to late summer. A significant positive correlation was found between the proteases and ALP activity, proposing that both proteases and ALP might have important synergic roles in the mucosal innate immune function of rainbow trout. Moreover, using reverse transcription PCR (RT-PCR) analysis of some proteases genes including cathepsin-L and cathepsin-D, we demonstrated that the proteases are transcribed and likely synthesized in epidermal mucus cells of rainbow trout. The present study confirmed seasonal changes of hydrolytic enzyme activities in the skin mucus of rainbow trout across all three weight groups, with the highest variation in juvenile fish.

Transcriptome changes for Nile tilapia (Oreochromis niloticus) in response to alkalinity stress

Nile tilapia is an important economic fish in the world because of its fast growth, high meat yield and strong adaptability. It is more adaptable to high alkalinity than common freshwater fish and provides valuable material for developing alkaline-tolerant strains and understanding the adaptation mechanism of fish to extreme environmental stress. In this study, we employed high throughput RNA sequencing to reveal the tissues (gill, kidney and liver) transcriptome differences of O. niloticus at different carbonate alkalinities (FW, AW40 and AW60). A total of 1,369,381,790 raw reads were obtained, including 496,441,232 reads in FW group, 437,907,696 reads in AW40 and 435,032,862 reads in AW60. In addition, 484,555,626 reads in gill, 451,618,224 reads in kidney and 433,207,940 reads in liver. A large number of stress-regulated changes were detected comprehensively. We focused on 3 significantly change pathways (steroid biosynthesis, drug metabolism and protein digestion/absorption) and 17 DEGs (HMG-CoA reductase, UDP-glucuronosyltransferase, and carbonic anhydrase etc.) which were shared among compared groups (AW40 vs FW, AW60 vs FW, AW40 vs 60 AW60) in gill, kidney and liver, respectively. These pathways/genes are sensitive to alkalinity stress and crucial to the alkalinity adaptation of tilapia. Overall, we found a large number of candidate genes, which encode important regulators of stress tolerance and ultimately contribute to future alkaline-tolerant fish breeding. Among these genes, lipid metabolism (involving signal transduction), detoxification and immune related genes are more prominent to the response and adaptability of fish to alkalinity stress.

Transcriptome and metabolome analyses of Coilia nasus in response to Anisakidae parasite infection

Parasites from the family Anisakidae are capable of infecting a range of marine fish species worldwide. Coilia nasus, which usually feeds and overwinters in coastal waters and spawns in freshwater, is highly susceptible to infection by Anisakidae. In this study, we used scanning electron microscopes to show that C. nasus infected by Anisakidae exhibited damage and fibrosis of the liver tissue. To better understand host immune reaction and metabolic changes to Anisakidae infection, we used a combination of transcriptomic and metabolomic method to characterize the key genes and metabolites, and the signaling pathway regulation of C. nasus infected by Anisakidae. We generated 62,604 unigenes from liver tissue and identified 391 compounds from serum. Of these, Anisakidae infection resulted in significant up-regulation of 545 genes and 28 metabolites, and significant down-regulation of 416 genes and 37 metabolites. Seventy-four of the 961 differentially expressed genes were linked to immune response, and 1, 2-Diacylglycerol, an important immune-related metabolite, was significantly up-regulated after infection. Our results show activation of antigen processing and presentation, initiation of the T cell receptor signaling pathway, disruption of the TCA cycle, and changes to the amino acid and Glycerolipid metabolisms, which indicate perturbations to the host immune system and metabolism following infection. This is the first study describing the immune responses and metabolic changes in C. nasus to Anisakidae infection, and thus improves our understanding of the interaction mechanisms between C. nasus and Anisakidae. Our findings will be useful for future research on the population ecology of C. nasus.

Detoxification and Immune Transcriptomic Response of the Gill Tissue of Bay Scallop (Argopecten irradians) Following Exposure to the Algicide Palmitoleic Acid

Palmitoleic acid (PA) is an effective algicide against Alexandrium tamarense. However, the toxicological mechanism of PA exposure is unclear. The transcript abundance and differentially expressed genes (DEGs) in gills of bay scallop were investigated following 80 mg/L PA exposure up to 48 h using the Illumina HiSeq 4000 deep-sequencing platform with the recommended read length of 100 bp. De novo assembly of paired-end reads yielded 62,099 unigenes; 5414 genes were identified as being significantly increased, and 4452 were decreased. Based on gene ontology classification and enrichment analysis, the ‘cellular process’, ‘metabolic process’, ‘response to stimulus’, and ‘catalytic process’ with particularly high functional enrichment were revealed. The DEGs, which are related to detoxification and immune responses, revealed that acid phosphatase, fibrinogen C domain-containing protein, cyclic AMP-responsive element-binding protein, glutathione reductase, ATP-binding cassette, nuclear factor erythroid 2-related factor, NADPH2:quinone reductase, and cytochrome P450 4F22, 4B1, and 2C8-related gene expression decreased. In contrast, some genes related to glutathione S-transferase, C-type lectin, superoxide dismutase, toll-like receptors, and cytochrome P450 2C14, 2U1, 3A24 and 4A2 increased. The results of current research will be a valuable resource for the investigation of gene expression stimulated by PA, and will help understanding of the molecular mechanisms underlying the scallops’ response to PA exposure.

Identification and expression of cathepsin B from the freshwater mussel Cristaria plicata

Cathepsin B plays crucial roles in host immune defense against pathogen infection. In present study, a cathepsin B gene from the freshwater mussel, Cristaria plicata (CpCathB) was cloned and characterized. The full-length cDNA of CpCathB was 1825 bp, and contained a 5' untranslated region (UTR) of 36 nucleotides, an open reading frame (ORF) of 1044 bp and a 3' UTR of 745 bp with a poly (A) tail. The deduced CpCathB protein was encoded as a preproenzyme with 347 amino acid residues and predicted molecular weight of 38.55 kDa. Sequence alignment revealed that CpCathB protein shared 56% - 60.7% identity comparison with other species. The predicted tertiary structure of CpCathB protein was highly similar to that of human. The CpCathB mRNA was expressed in hemocytes, hepatopancreas, adductor muscle, gills and mantle tissues of healthy mussels, and the highest expression level was in hepatopancreas. The transcripts of CpCathB were increased in hemocytes and hepatopancreas from mussels after Aeromonas hydrophila challenge. Moreover, the recombinant CpCathB was expressed in the Escherichia coli Rosetta-gami (DE3) strain. The maximum titer of the anti-CpCathB polyclonal antibodies was 1:640,000.The CpCathB protein had a higher expression in hepatopancreas and mantle and a lower level in hemocytes.

Molecular cloning and functional characterization of cathepsin B from Nile tilapia (Oreochromis niloticus)

Cathepsin B (CatB) has been widely known for its hydrolytic ability and involvement in the innate immunity. However, the mechanism of CatB from teleosts participating in immunoregulation remains poorly understood; and the sequence of CatB from Nile tilapia (NtCatB) has not been cloned and characterized. In this study, the coding sequence of NtCatB was cloned, and then characterized by bioinformatic analysis and heterologous expression. The deduced amino acid sequence (330-aa) of NtCatB contains the representative features of CatB. Quantitative real-time PCR revealed the extensive mRNA expression of NtCatB in six tissues of healthy Nile tilapia, and its transcription level was significantly up-regulated after Streptococcus agalactiae challenge. NtCatB may interact with some immunological function proteins and take part in the regulatory pathway. These results suggest that NtCatB is likely to be involved in the immune reaction. The mature region (residues 79-328, mNtCatB) of NtCatB was cloned and transferred to pET-28a for expressing the recombinant protein. The purified recombinant mNtCatB was verified with the activity of 992.34 U mg^-1 min^-1 under the optimal condition using a substrate hydrolyzing assay. The recombinant cystatin-A1-like can effectively inhibit the activity of the recombinant mNtCatB, and their binding form was predicted by molecular docking. Our results contribute to elucidating the immunological functions of NtCatB.

Molecular characterization and gene expression of cathepsin L in Nile tilapia (Oreochromis niloticus)

Cathepsin L (CatL) has been widely known for its involvement in the innate immunity. However, it still remains poorly understand how CatL modulates the immune system of teleosts. Moreover, the CatL of Nile tilapia (NtCatL) has not been cloned or characterized. In this study, the gene encoding NtCatL was cloned, and was characterized by bioinformatics analysis, heterologous expression and protease activity assay. The coding sequence of NtCatL is 1017 bp in length and encodes 338 amino acid residues with a predicted molecular weight of 38.487 kDa and a theoretical isoelectric point of 5.79. NtCatL possesses the features of a typical cathepsin L, including one signal peptide, one propeptide region, and one papain family cysteine protease domain containing four active site residues (Gln¹³⁵, Cys¹⁴¹, His²⁸¹, and Asn³⁰⁵). The prediction of protein-protein interaction shows that NtCatL may interact with some functional proteins for realizing an immune function. Real-time quantitative PCR revealed the widespread transcriptional expression of NtCatL in six tissues of healthy Nile tilapia, and the NtCatL mRNA is significantly up-regulated after Streptococcus agalactiae challenge. These results suggest that NtCatL is likely to be involved in the immune reaction of Nile tilapia. Recombinant proteins from the mature domain (residues 117-337) of NtCatL were obtained by heterologous expression using pET28a and Rosetta (DE3) competent cells. A protein product with the high purity was obtained by using TALON Superflow purification rather than adopting HisTrap HP columns. The protease activity of the recombinant protein was verified by using a substrate hydrolyzing assay. This work has cloned and characterized the CatL from Nile tilapia for the first time, and contributes to elucidating the immunological functions of CatL.

Molecular cloning and functional characterization of cathepsin B from the sea cucumber Apostichopus japonicus

Cathepsin B (CTSB), a member of lysosomal cysteine protease, is involved in multiple levels of physiological and biological processes, and also plays crucial roles in host immune defense against pathogen infection in vertebrates. However, the function of CTSB within the innate immune system of invertebrates, particularly in marine echinoderms, has been poorly documented. In this study, the immune function of CTSB in Apostichopus japonicus (designated as AjCTSB), a commercially important and disease vulnerable aquaculture specie, was investigated by integrated molecular and protein approaches. A 2153 bp cDNA representing the full-length of AjCTSB was cloned via overlapping ESTs and RACE fragments. AjCTSB contained an open reading frame of 999 bp encoding a secreted protein of 332 amino acid residues with a predicted molecular mass of 36.8 kDa. The deduced amino acid of AjCTSB shared a typical activity center containing three conserved amino acid residues (Cys¹⁰⁸, His²⁷⁷ and Asn²⁹⁷). Phylogenetic tree analysis also supported that AjCTSB was a new member of CTSB family with clustering firstly with invertebrate CTSBs. Quantitative real time PCR analysis revealed that AjCTSB was ubiquitously expressed in all examined tissues with the highest levels in intestine. The Vibrio splendidus challenged sea cucumber and LPS-exposed coelomocytes could both significantly boost the expression of AjCTSB. Moreover, the purified recombinant AjCTSB exhibited dose-dependent CTSB activities at the concentration ranged from 0 to 0.24 μg μL^-1. Further functional analysis indicated that coelomocytes apoptosis was significantly inhibited by 0.16-fold in vivo and the apoptosis execution Ajcaspase 3 was extremely reduced in Apostichopus japonicus coelomocytes treated with specific AjCTSB siRNA. Collectively, all these results suggested that AjCTSB was an important immune factor and might be served as apoptosis enhancers in pathogen challenged sea cucumber.

Cathepsin L of the sea cucumber Apostichopus japonicus-molecular characterization and transcriptional response to Vibrio splendidus infection

Cathepsin L, a lysosomal endopeptidase, has been noted for its involvement in the innate immune response in invertebrates. Here, the cathepsin L cDNA of the sea cucumber Apostichopus japonicus (AjCatL) is identified from an EST library and then cloned by the rapid amplification of the cDNA ends (RACE) PCR. The full-length cDNA is 1678 bp long containing an open reading frame (ORF) of 1002 bp, an 80 bp 5' UTR and a 599 bp 3' UTR. The cDNA encodes 333 amino acid residues with a predicted molecular mass of 37.07 kDa and a theoretical isoelectric point (pI) of 5.01. The full-length AjCatL contains three active sites of eukaryotic thiol (cysteine) protease at positions 133-144, 278-288 and 295-314. Analysis of the predicted tertiary structure of prepro-CatL (17-333 aa) and mature-CatL (116-333 aa) reveals that the propeptide region (17-115 aa) blocks access to the substrate-binding cleft. Phylogenetic analysis shows that the AjCatL is clustered together with two other CatLs from Strongylocentrotus purpuratus. The enzymatic activity of AjCatL was verified using a substrate hydrolyzing assay with recombinant mAjCatL. Further analysis of real time-PCR demonstrates that the expression of AjCatL mRNA is significantly up-regulated in the coelomocytes in cases of infection with the common bacterial pathogen, Vibrio splendidus. This suggests that the AjCatL is likely to be involved in the immune response.

Identification, mRNA expression profiling and activity characterization of cathepsin L from red drum (Sciaenops ocellatus)

Cathepsin L is a cysteine protease with a papain-like structure. It is known to be implicated in multiple processes of mammalian immune response to pathogen infection. In teleost fish, the functionality of cathepsin L is less understood. In this work, we characterized a cathepsin L homologue (designated as SoCatL) from red drum Sciaenops ocellatus, an important farmed fish species in China. SoCatL possesses a typical domain arrangement characteristic of cathepsin L, which comprises a proregion and a protease domain with four catalytically essential residues (Gln137, Cys143, His282 and Asn302) conserved in various organisms. SoCatL shares moderate sequence identities with mammalian cathepsin L and relatively high sequence identities with teleost cathepsin L. Phylogenetic analysis revealed that SoCatL is evolutionally close to fish cathepsin L, especially those belonging to the Perciformes order. The homology model of SoCatL was discovered to exhibit a structure resembling human cathepsin L. Transcriptional expression of SoCatL was found ubiquitous in tissues and enhanced after experimental infection with a bacterial pathogen. Recombinant SoCatL purified from Escherichia coli (designated as rSoCatL) displayed apparent proteolytic activity, which was optimal at 50 °C and pH 7.0. The activity of rSoCatL required the catalytic residue Cys143 and was severely reduced by cathepsin inhibitor. These results suggest that SoCatL is a teleost cathepsin L homologue which functions as a cysteine protease and is likely to participate in the host immune response against bacterial infection.

Cathepsin S, but not cathepsin L, participates in the MHC class II-associated invariant chain processing in large yellow croaker (Larimichthys crocea)

Two cysteine proteases, cathepsin S (CatS) and cathepsin L (CatL), have been identified as the key enzymes involved in the processing of invariant chain (Ii chain) in mammals. However, little is known about the roles of fish cathepsins in the Ii chain processing. In this study, large yellow croaker cathepsin S (LycCatS) and L (LycCatL) were identified and characterized. Based on the sequence comparison and phylogenetic analysis, both LycCatS and LycCatL are highly conserved to their counterparts in teleost. These two cathepsins were constitutively expressed in all tissues and immune-related cells tested, although at different levels. Both recombinant LycCatS (rLycCatS) and LycCatL (rLycCatL) possess the typical cysteine protease activity. Like other mammalian endopeptidase cathepsins, rLycCatS and rLycCatL could be autocatalytically activated to remove propeptides and release active mature peptides. On the other hand, the autocatalytic activation of rLycCatL could be inhibited by recombinant large yellow croaker Ii chain (rLyc-TR-Ii), but the autocatalytic activation of rLycCatS was not affected by rLyc-TR-Ii. Furthermore, the activated rLycCatS can efficiently process rLyc-TR-Ii in a stepwise manner in vitro, while the activated rLycCatL can not. These data indicate that cathepsin S may be the main cathepsin involved in the Ii chain processing in bony fish.

Identification and mucosal expression analysis of cathepsin B in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish (skin, gill and intestine) constitute the primary line of defense against pathogen invasion. Although the importance of fish mucosal surfaces as the first barriers against pathogens cannot be overstated, the knowledge of teleost mucosal immunity are still limited. Cathepsin B, a lysosomal cysteine protease, is involved in multiple levels of physiological and biological processes, and playing crucial roles for host immune defense against pathogen infection. In this regard, we identified the cathepsin B (ctsba) of channel catfish and investigated the expression patterns of the ctsba in mucosal tissues following Edwardsiella ictaluri and Flavobacterium columnare challenge. Here, catfish ctsba gene was widely expressed in all examined tissues with the lowest expression level in muscle, and the highest expression level in trunk kidney, followed by spleen, gill, head kidney, intestine, liver and skin. In addition, the phylogenetic analysis showed the catfish ctsba had the strongest relationship to zebrafish. Moreover, the ctsba showed a general trend of up-regulated in mucosal tissues following both Gram-negative bacterial challenge. Taken together, the increased expression of ctsba in mucosal surfaces indicated the protective function of ctsba against bacterial infection, and the requirement for effective clearance of invading bacteria. Further studies are needed, indeed, to expand functional characterization and examine whether ctsba may play additional physiological and biological roles in catfish mucosal tissues.

Mucosal expression signatures of two Cathepsin L in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish are the first line of host defense against various pathogens. The mucosal immune responses are the most critical events to prevent pathogen attachment and invasion. Cathepsins are a group of peptidases that involved in different levels of immune responses, but the knowledge of the roles of Cathepsin in mucosal immune responses against bacterial infection are still lacking. Therefore, in the present study we characterized the Cathepsin L gene family in channel catfish, and profiled their expression levels after challenging with two different Gram-negative bacterial pathogens. Here, two Cathepsin L genes were identified from channel catfish and were designated CTSL1a and CTSL.1. Comparing to other fish species, the catfish CTSL genes are highly conserved in their structural features. Phylogenetic analysis was conducted to confirm the identification of CTSL genes. Expression analysis revealed that the CTSL genes were ubiquitously expressed in all tested tissues. Following infection, the CTSL genes were significantly induced at most timepoints in mucosal tissues. But the expression patterns varied depending on both pathogen and tissue types, suggesting that CTSL genes may exert disparate functions or exhibit distinct tissue-selective roles in mucosal immune responses. Our findings here, clearly revealed the key roles of CTSL in catfish mucosal immunity; however, further studies are needed to expand functional characterization and examine whether CTSL may also play additional physiological roles in catfish mucosal tissues.

Genome-wide identification and transcript profile of the whole cathepsin superfamily in the intertidal copepod Tigriopus japonicus

Modulation of expression of cathepsins in innate immune response has previously been reported in mollusks and large crustaceans including crabs, lobsters, and shrimps in response to immune challenges. However, similar responses in copepods and the related cathepsin members remain under-investigated. To understand molecular and innate immune responses in the intertidal copepod Tigriopus japonicus, we identified the full spectra of cathepsin members (2 aspartyl proteases, 18 cysteine proteases, and 4 serine proteases) and also analyzed transcriptional expression of cathepsin (Tj-cathepsin) genes in developmental stages, lipopolysaccharide (LPS)- and two Vibrio species-exposed T. japonicus. The transcriptional levels of most Tj-cathepsin genes were highly increased during the molting transition from the nauplius to the copepodid stages. LPS treatment induced innate immune response via significant transcriptional increase of serine cathepsin (e.g., cathepsin As) members with induction of several cysteine cathepsin genes. However, Tj-aspartyl cathepsin E-like and a novel cysteine cathepsin were slightly reduced in response to LPS exposure. Interestingly, Vibrio species showed very low transcriptional sensitivity in the expression of entire cathepsins, while LPS induced several cathepsin gene-involved primitive immune responses in T. japonicus. In this paper, we discuss how whole cathepsin expression profiling can be linked to host defense mechanism to better understand and uncover the underlying mechanism of copepods' innate immunity.

Molecular cloning, characterization and expression analysis of cathepsin O in silkworm Bombyx mori related to bacterial response

Cathepsins are the main members of the cysteine family and play important roles in immune response in vertebrates. The Cathepsin O of Bombyx mori (BmCathepsin O) was cloned from the hemocytes by the rapid amplification of cDNA ends (RACE). The genomic DNA was 6131bp long with a total of six exons and five introns. Its pre-mRNA was spliced to generate two spliceosomes. By comparisons with other reported cathepsins O, it was concluded that the identity between them ranged from 29 to 39%. Expression analysis indicated that BmCathepsin O was specific-expressed in hemocytes, and highly expressed at the 4th molting and metamorphosis stages. Immunofluorescence assay and qRT-PCR showed that BmCathepsin O was expressed in granulocytes and plasmatocytes. Interestingly, BmCathepsin O was significantly up-regulated after stimulated by 20-hydroxyecdysone (20-E) in vivo, which suggested that BmCathepsin O may be regulated by 20E. Moreover, activation of BmCathepsin O was also observed in hemocytes challenged by Escherichia coli, indicating its potential involvement in the innate immune system of silkworm, B. mori. In summary, our studies provide a new insight into the functional features of Cathepsin O.

Molecular characterization of the cathepsin B of turbot (Scophthalmus maximus)

Cathepsin B is an enzymatic protein belonging to the peptidase C1 family. It is involved in diverse physiological and pathological functions that include immune response. In this study, we identified and characterized a cathepsin B homolog (SmCatB) from turbot (Scophthalmus maximus). SmCatB is composed of 330 amino acid residues and possesses typical domain architecture of cathepsin B, which contains a propeptide region and a cysteine protease domain, and the latter processes four conserved residues (Q101, C107, H277, and N297) in the active site. SmCatB shares 80.6-87.6% overall sequence identities with the cathepsin B of a number of teleost. SmCatB expression was detected in a wide range of tissues and upregulated by bacterial infection in a time-dependent manner. Recombinant SmCatB (rSmCatB-WT) purified from Escherichia coli exhibited apparent protease activity, which was optimal at 50 °C and pH 5.5. Compared to rSmCatB-WT, the mutant proteins rSmCatB-C107S, rSmCatB-H277A, and rSmCatB-N297A, which bear C107S, H277A, and N297A mutations, respectively, were significantly reduced in protease activity, with the highest reduction observed with rSmCatB-N297A. These results indicate that SmCatB is a bioactive protease that depends on the conserved structural features and that SmCatB is involved in pathogen-induced immune response.

Comparative genomic of the teleost cathepsin B and H and involvement in bacterial induced immunity of miiuy croaker

Cathepsins are a family of lysosomal proteases play different roles at physiological and pathological states and present in almost all animals as well as other organisms. Cathepsins B and H are both cysteine proteases of cathepsins. Cathepsin B and H have been studied playing parts in protein degradation/turnover, antigen presentation/processing and hormone maturation in mammals. However, little is known about the structures and functions of cathepsin B and H in teleosts. In the present study, we identified and characterized the full-length miiuy croaker (Miichthys miiuy) cathepsin B and H genes. The sequence analysis results showed that both cathepsin B and H contain the characteristics of papain family with a signal peptide, propeptide and mature peptide regions. The comparison of the genomic organizations and locations indicated the conserved synteny and mild evolution in the cathepsin B and H genes adjacent regions. In addition, the gene synteny analysis showed that miiuy croaker cathepsin B has a closer relationship to stickleback and fugu than to cave fish and zebrafish, and cathepsin H was most similar with the 2 subtype in tilapia and fugu. By phylogenetic analysis, miiuy croaker cathepsin B and H were all assigned to cysteine proteases, and with a close relationship to Salmo salar cathepsin B and Oplegnathus fasciatus cathepsin H, respectively. Quantitative real-time RT-PCR analysis results confirmed that cathepsin B and H genes expressed ubiquitously in all tested healthy tissues from miiuy croaker. Furthermore, up-regulated expression of the cathepsin B and H transcripts in liver, spleen and kidney after exposure upon Vibrio anguillarum suggested that they may play important roles in innate immune response and antigen processing of miiuy croaker.

Identification of cathepsin B from large yellow croaker (Pseudosciaena crocea) and its role in the processing of MHC class II-associated invariant chain

In teleost, cathepsin B has been identified from several species and shown to play roles in the host immune response during pathogen challenge. However, the mechanism of how cathepsin B modulates the immune response in teleosts remains poorly understood. In this study, we identified and characterized cathepsin B (LycCatB) and invariant chain (LycIi) from the large yellow croaker (Pseudosciaena crocea). Sequence comparison and phylogenetic analysis indicated that LycCatB and LycIi are highly conserved within teleosts. Quantitative RT-PCR analysis showed that LycCatB mRNA was widely expressed in all examined tissues. We then recombinantly expressed LycCatB and Lyc-TR-Ii (transmembrane domain removed Ii chain) in Pichia pastoris and Escherichiacoli, respectively. The recombinant LycCatB (rLycCatB) can hydrolyze the substrate Z-FR-AMC with a Km value of 40.68μM. Furthermore, co-incubation of rLycCatB with rLyc-TR-Ii led to an efficient cleavage of rLyc-TR-Ii in a time-dependant manner. These results indicated that cathepsin B may be involved in MHC class II-associated Ii processing in large yellow croaker, and provide new information helping to elucidate the immunological functions of teleost cathepsin B.

Gene expression of pro- and anti-apoptotic proteins in rock bream (Oplegnathus fasciatus) infected with megalocytivirus (family Iridoviridae)

Viruses belonging to the genus Megalocytivirus cause diseases in marine fishes primarily in East and Southeast Asian countries. Rock bream iridovirus (RBIV), which is a member of the Megalocytivirus genus, causes severe mass mortalities in rock beam (Oplegnathus fasciatus) in Korea. In this study, we assessed apoptosis-related gene expression patterns in Megalocytivirus-infected rock bream in high mortality and low mortality conditions to determine important apoptosis-related factors, which may affect fish survival/or death. In the high mortality group (100% mortality at 15 dpi), significantly high levels of perforin, granzyme, Fas ligand and caspase 9 expression (5.6-, 10.2-, 13.4- and 4.2-fold, respectively) were observed in the kidney at 8 dpi. Basal expression levels of Fas and caspase 3 were observed at 8 d (1.5-/0.7-fold) and 10 dpi (1.3-/0.6-fold), accompanied by heavy viral loads (8.12 × 10(6)-2.21 × 10(7)/μl). Inhibitor of apoptosis 1 (IAP1) was highly expressed (3.5- to 4.8-fold) at 1 d and 4 dpi; however, IAP1 was reduced when fish died at 8 d and 10 dpi (1.7- to 2.0-fold), which was not significantly different from that of the control group. A similar expression pattern was observed in the low mortality group (18% expected mortality at 30 dpi), which was characterised by a delayed lower magnitude of expression with lower viral loads than the high mortality group. Perforin, granzyme and Fas ligand expression was significantly higher in the low mortality group than in the control group at several sampling points until 30 dpi. Fas and caspases 8, 9 and 3 expression levels showed no statistical significance until 30 dpi. In the low mortality group, significantly higher IAP1 expression compared with the control was observed at 10 d (2.2-fold), 20 d (3.6-fold) and 22 dpi (2.0-fold). In summary, perforin- and granzyme-related apoptosis initiation signals were activated; however, the Fas-induced apoptosis pathway did not efficiently respond. Upregulated IAP1 in RBIV-infected rock bream, which was reported for the first time in this study, exhibited inhibited apoptotic responses in RBIV-infected fish. Although it remains unclear whether apoptosis inhibition aids or impedes fish survival, our data clearly show that the apoptotic response is inhibited in RBIV-infected rock bream.

Characterization of cathepsin B gene from orange-spotted grouper, Epinephelus coioides involved in SGIV infection

The lysosomal cysteine protease cathepsin B of papain family is a key regulator and signaling molecule that involves in various biological processes, such as the regulation of apoptosis and activation of virus. In the present study, cathepsin B gene (Ec-CB) was cloned and characterized from orange-spotted grouper, Epinephelus coioides. The full-length Ec-CB cDNA was composed of 1918 bp and encoded a polypeptide of 330 amino acids with higher identities to cathepsin B of teleosts and mammalians. Ec-CB possessed typical cathepsin B structural features including an N-terminal signal peptide, the propeptide region and the cysteine protease domain which were conserved in other cathepsin B sequences. Phylogenetic analysis revealed that Ec-CB was most closely related to Lutjanus argentimaculatus. RT-PCR analysis showed that Ec-CB transcript was expressed in all the examined tissues which abundant in spleen, kidney and gill. After challenged with Singapore grouper iridovirus (SGIV) stimulation, the mRNA expression of cathepsin B in E. coioides was up-regulated at 24 h post-infection. Subcellular localization analysis revealed that Ec-CB was distributed predominantly in the cytoplasm. When the fish cells (GS or FHM) were treated with the cathepsin B specific inhibitor CA-074Me, the occurrence of CPE induced by SGIV was delayed, and the viral gene transcription was significantly inhibited. Additionally, SGIV-induced typical apoptosis was also inhibited by CA-074Me in FHM cells. Taken together, our results demonstrated that the Ec-CB might play a functional role in SGIV infection.

Immune gene discovery in the crucian carp Carassius auratus

The crucian carp Carassius auratus (Cyprinidae) is one of the important fish species in aquaculture. Although the crucian carp has several economic benefits, their immune system and gene information have not been investigated in depth as yet. Here, we performed the transcriptome analysis of C. auratus using the pyrosequencing method and selected several immune-related genes. Of unigenes obtained in this species, we identified a number of immune system-related genes (e.g. adhesive protein, antimicrobial protein, apoptosis- and cell cycle-related protein, cellular defense effector, immune regulator, pattern recognition protein, protease, protease inhibitor, reduction/oxidation-related protein, signal transduction-related protein and stress protein) that are potentially useful for studies on fish immunity. To be of public and practical use, we designed primer pairs of each gene from the crucian carp for real-time RT-PCR application and tested the amplicon identity of entire gene sets with the total RNA sample. For comparative analysis, we measured tissue-preferential transcript profiles of selected genes. This study will be helpful to extend our knowledge on the immune system of the crucian carp in comparative aspects and to develop the crucian carp as a potential model organism for aquatic quality monitoring in fish farming.

Genomic structure and immunological response of an STAT4 family member from rock bream (Oplegnathus fasciatus)

The Janus tyrosine kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway plays a critical role in host defense against viral and bacterial infections. STAT proteins are a group of transcription factors that translocate into the nucleus and are critical for the induction of many genes crucial for the allergic cascade and immune defense. In the present study, a member of the STAT4 family was identified from rock bream (RbSTAT4) at the genomic level, and its transcriptional regulation in response to different pathological stimuli under in vivo conditions was investigated. The genomic sequence of RbSTAT4 is approximately 15.6 kb in length, including a putative core promoter region and 24 exons interrupted by 23 introns. Bioinformatics analysis of RbSTAT4 identified the presence of typical and conserved features of the STAT4 family, including the STAT_int domain, STAT alpha domain, STAT bind domain, linker domain, SH2 domain, and transcriptional activation domain. According to the phylogenetic analysis, RbSTAT4 exhibited the closest evolutionary proximity with the STAT4 member from mandarin fish (Siniperca chuatsi). The RbSTAT4 transcript in healthy rock breams was detected to have ubiquitous expression in 11 different tissues examined, where liver and spleen tissues showed moderate expressions compared with the highest expression level detected in gill tissue. The time-course in vivo immune stimulation of rock bream with lipopolysaccharide, poly I:C, live Edwardsiella tarda, and rock bream iridovirus caused significant transcriptional regulation of the RbSTAT4 expression in gill, head kidney, and spleen tissues, suggesting that RbSTAT4 is involved in immune regulation mechanisms and/or signaling cascades, orchestrating against both bacterial and viral pathogens.

Identification of cathepsin B in the razor clam Sinonovacula constricta and its role in innate immune responses

Cathepsin B, a lysosomal cysteine protease, has drawn much attention in vertebrates. However, very little is known about the functions of cathepsin B in bivalves. In this study, we identified the cathepsin B gene in the razor clam Sinonovacula constricta. The protein has a typical cysteine protease structure, comprising a 15-residue putative signal peptide, a 75-residue propeptide and a 249-residue mature domain. In the mature domain, there is an occluding loop, an oxyanion hole (Gln) and a catalytic triad (Cys, His and Asn). The cathepsin B gene is expressed in a wide range of tissues but appears to exhibit greatest level of expression in the liver. During the early developmental stages, the transcript could be detected widely. After the clam was infected with Vibrio anguillarum, the expression of the cathepsin B gene showed the most significant up-regulation in the liver and mantle tissues at 8h after infection. The fact that bacterial infection can induce the expression of the cathepsin B transcript suggests that cathepsin B could play an important role in the innate immunity of clams.

Molecular characterization and expression analysis of four cathepsin L genes in the razor clam, Sinonovacula constricta

Cathepsin L (CTSL) is a lysosomal cysteine protease involved in immune responses in vertebrates. However, few studies exist regarding the role of cathepsin L in bivalves. In this study, we isolated and characterized four cathepsin L genes from the razor clam Sinonovacula constricta, referred to as CTSL1, CTSL2, CTSL3 and CTSL4. These four genes contained typical papain-like cysteine protease structure and enzyme activity sites with ERWNIN-like and GNFD-like motifs in the proregion domain and an oxyanion hole (Gln) and a catalytic triad (Cys, His and Asn) in the mature domain. Expression analysis of the four transcripts revealed a tissue-specific pattern with high expression of CTSL1 and CTSL3 in liver and gonad tissues and high expression of CTSL2 and CTSL4 in liver and gill tissues. During the developmental stages, the four transcripts showed the highest expression in the juvenile stage; however, CTSL3 had a much higher expression level than the other three transcripts during embryogenesis. The four transcripts showed significant changes in expression as early as 4 h or 8 h after infection with Vibrio anguillarum. The fact that bacterial infection can induce expression of the four CTSL transcripts suggests that these transcripts are important components of the innate immunity system of the clam.

A preliminary study of differentially expressed genes of the scallop Chlamys farreri against acute viral necrobiotic virus (AVNV)

The scallop Chlamys farreri is one of the most important aquaculture species in northern coastal provinces. However, the sustainable development of scallop industry is currently threatened by a notorious pathogen named as acute viral necrobiotic virus (AVNV), which often causes mass mortality of the animals. Despite that great attention has been focused on this novel pathogen, little knowledge about the host-virus interactions is available. In this study, suppression subtractive hybridization (SSH) was employed to identify the up-regulated differentially expressed genes in the hemocytes of C. farreri challenged by AVNV. A forward subtracted cDNA library was finally constructed and 288 positive colonies representing differentially genes were screened to perform sequencing. A total of 275 ESTs were used for further analysis using bioinformatics tools after vector screening, among which 167 ESTs could be finally identified, with significant match (E values <1 × 10(-3)) to the deposited genes (proteins) in the corresponding databases. These genes could be classified into ten categories according to their Gene Ontology annotations of biological processes and molecular functions, i.e. cell defense and homeostasis (13.82%), cellular protein metabolic process (14.90), cellular metabolism (13.09%), cytoskeletal or cellular component (5.82%), transcription regulation or RNA processing (2.18%), cell division (meiosis)/apoptosis (2.18%), DNA metabolic process and repair (1.45%), cell adhesion/signaling (1.09%), microsatellite (0.73%), and ungrouped or unknown functions (6.88). The possible biological significance of some novel genes (mainly immune and homeostasis related genes) in the host response to AVNV were discussed. This study is the first global analysis of differentially expressed genes in hemocytes from AVNV-infected C. farreri, and in addition to increasing our understanding of the molecular pathogenesis of this virus-associated scallop disease, the results presented here should provide new insights into the molecular basis of host-pathogen interactions in C. farreri.

Macrobrachium rosenbergii cathepsin L: molecular characterization and gene expression in response to viral and bacterial infections

Cathepsin L (MrCathL) was identified from a constructed cDNA library of freshwater prawn Macrobrachium rosenbergii. MrCathL full-length cDNA is 1161 base pairs (bp) with an ORF of 1026bp which encodes a polypeptide of 342 amino acid (aa) long. The eukaryotic cysteine proteases, histidine and asparagine active site residues were identified in the aa sequence of MrCathL at 143-154, 286-296 and 304-323, respectively. The pair wise clustalW analysis of MrCathL showed the highest similarity (97%) with the homologous cathepsin L from Macrobrachium nipponense and the lowest similarity (70%) from human. Phylogenetic analysis revealed two distinct clusters of the invertebrates and vertebrates cathepsin L in the phylogenetic tree. MrCathL and cathepsin L from M. nipponense were clustered together, formed a sister group to cathepsin L of Penaeus monodon, and finally clustered to Lepeophtheirus salmonis. High level of (P<0.05) MrCathL gene expression was noticed in haemocyte and lowest in eyestalk. Furthermore, the MrCathL gene expression in M. rosenbergii was up-regulated in haemocyte by virus [M. rosenbergii nodovirus (MrNV) and white spot syndrome baculovirus (WSBV)] and bacteria (Vibrio harveyi and Aeromonas hydrophila). The recombinant MrCathL exhibited a wide range of activity in various pH between 3 and 10 and highest at pH 7.5. Cysteine proteinase (stefin A, stefin B and antipain) showed significant influence (100%) on recombinant MrCathL enzyme activity. The relative activity and residual activity of recombinant MrCathL against various metal ions or salts and detergent tested at different concentrations. These results indicated that the metal ions, salts and detergent had an influence on the proteinase activity of recombinant MrCathL. Conclusively, the results of this study imply that MrCathL has high pH stability and is fascinating object for further research on the function of cathepsin L in prawn innate immune system.

Expression characterization and activity analysis of a cathepsin B from Pacific abalone Haliotis discus hannai

Cathepsin B (EC 3.4.22.1) is a member of lysosomal cysteine protease and has a papain-like fold. In mammals, it is involved in protein degradation and other physiological processes including immune response. However, little is known about the function of cathepsin B in mollusks. In this study, we identified and analyzed a cathepsin B homolog (HdCatB) from Pacific abalone (Haliotis discus hannai), an economically important mollusk species cultured in East Asia. HdCatB is composed of 336 amino acid residues and its mature form is predicted to start at residue 86. HdCatB possesses typical domain architecture of cathepsin B and contains a propeptide region and a cysteine protease domain, the latter containing the four active site residues (Q108, C114, H282, and N302) that are conserved in many different organisms. HdCatB shares 40-60% overall sequence identities with the cathepsin Bofa number of vertebrates and invertebrates and is phylogenetically very close to mollusk cathepsin B. Quantitative real time RT-PCR analysis revealed that HdCatB expression occurred in multiple tissues and was upregulated by bacterial infection. Recombinant HdCatB purified from Escherichia coli exhibited apparent protease activity, which was optimal at 45 °C and pH 6.0. These results indicate that HdCatB is a bioactive protease that is likely to be implicated in the immune response of abalone during bacterial infection.

Cathepsin L in the orange-spotted grouper, Epinephelus coioides: molecular cloning and gene expression after a Vibrio anguillarum challenge

The orange-spotted grouper, Epinephelus coioides, is an important fish maricultured in many Asian countries. In the present study, the full-length cDNA of cathepsin L, an immunity related gene of fishes, was isolated from E. coioides using rapid amplification of cDNA ends (RACE). It is 1,443 bp in length, including an open reading frame (ORF) of 1,011 bp. The open reading frame encoded a preproprotein of 336 amino acids (aa), which consisted of a signal peptide of 16 aa, a proregion peptide of 98 aa and a mature peptide of 222 aa. The preproprotein contained an oxyanion hole (Gln), a catalytic triad formed by Cys, His and Asn, and the conserved ERWNIN, GNFD and GCNGG motifs, all characteristic of cathepsin L. Homology analysis revealed that the deduced amino acid sequence of E. coioides cathepsin L shared 80.1-94.8 % identity with those of reported fishes. Tissue-dependent mRNA expression analysis showed that the cathepsin L transcript was expressed in all the examined tissues of the healthy E. coioides, being highest in the liver and moderate in the heart, gonad and intestine. After Vibrio anguillarum stimulation, the mRNA expression of cathepsin L in E. coioides was significantly increased in the skin, fin, gills, liver, blood, spleen, head kidney and intestine, with the highest observed in the spleen (10.6-fold) at 12 h post-injection and the next in blood (7.5-fold) at 8 h post-injection. These results provided initial information for further studies on the physiological and immunological roles of the cathepsin L gene in the orange-spotted grouper.