Channel catfish, Ictalurus punctatus, cyclophilin A and B cDNA characterization and expression analysis

Effects of dietary carbohydrate/lipid ratios on non-specific immune responses, antioxidant capacity, hepatopancreas and intestines histology, and expression of TLR-MAPK/NF-κB signaling pathway-related genes of Procambarus clarkii

To investigate the effects of dietary carbohydrate/lipid (CHO: L) ratios on non-specific immune responses, antioxidant capacity, and expression of TLR-MAPK/NF-κB signaling pathway-related genes of red swamp crayfish (Procambarus clarkii). Four isonitrogenous and isoenergetic diets containing different CHO: L ratios were formulated. The results showed that the group with a CHO: L ratio of 5.94 had better growth performance (P < 0.05). The highest T-AOC, CAT, and SOD activities and the lowest MDA content in hemolymph and hepatopancreas were observed in the group with a CHO: L ratio of 5.94 (P < 0.05). The lowest activities of ALT, AST, ACP, AKP, and ALB in the hemolymph were observed in CHO: L ratio 5.94 group (P < 0.05), while the highest LZM activity, TP, and GLB content were observed in CHO: L 5.94 group (P < 0.05). The highest mRNA expression levels of tlr3, myd88, and mapk3, and the lowest mRNA expression levels of nf-kb α, nf-kb β, nf-kb p105, and traf6 were observed in the CHO: L of 5.94 group (P < 0.05). The highest mRNA expression levels of immune-related genes were observed in the CHO: L of 5.94 group (P < 0.05). Overall, these results indicated that the optimum dietary CHO: L ratio is vital in promoting growth and enhancing antioxidants and immunity to maintain red swamp crayfish's intestinal and hepatopancreas health status. In conclusion, the diets with a CHO:L ratio of 5.94 (approximately 36.23% carbohydrate and 6.10% lipid) is optimal for juvenile red swamp crayfish's physiological condition and health status.

Function and association analysis of Cyclophilin A gene with resistance to Edwardsiella ictaluri in yellow catfish

Edwardsiella ictaluri (E. ictaluri) is one of the main bacterial pathogens in catfish which has caused serious economic loss to yellow catfish (Pelteobagrus fulvidraco) in China. In our previous work, we demonstrated that CypA was up-regulated at the early stage of E. ictaluri infection in yellow catfish and displayed strong chemotactic activity for leukocytes in vitro. However, the effect of CypA on E. ictaluri is unknown in vivo. Therefore, two homozygous transgenic zebrafish lines expressing yellow catfish CypA (TG-CypA-1 and TG-CypA-2) were generated. After challenged with E. ictaluri at a dose of 1.0 × 10⁴ CFU per adult fish, both two transgenic lines exhibited a higher resistance to bacterial infection than the wildtype zebrafish. Herein, CypA gene in E. ictaluri-challenged yellow catfish was screened for presence of polymorphisms by sequencing and six single nucleotide polymorphisms (SNPs) were identified. SNP association analysis revealed that 528T/C SNP in the first intron was significantly different in disease-susceptible and -resistant groups, which was confirmed in two independent populations of yellow catfish. Moreover, the relative expression of CypA in the resistant group (CC genotype in 528T/C SNP) was significantly higher than that in the susceptible group (TT genotype in 528T/C SNP) in different immune organs of yellow catfish including spleen, head kidney, body kidney and liver. Our results reveal the potential function of CypA in host defense to bacterial infection and suggest the SNP marker in CypA gene associated with the resistance to E. ictaluri may facilitate the selective breeding of disease-resistant yellow catfish in the future.

Effects of hesperidin on the growth performance, antioxidant capacity, immune responses and disease resistance of red swamp crayfish (Procambarus clarkii)

We evaluated the effects of hesperidin on the nonspecific immunity, antioxidant capacity and growth performance of red swamp crayfish (Procambarus clarkii). A total of 900 healthy crayfish were randomly divided into six groups: the control group (fed the basal diet) and the HES25, HES50, HES75, HES100 and HES150 groups, which were fed the basal diet supplemented with 25, 50, 75, 100 and 150 mg kg^-1 hesperidin, respectively. The feeding experiment lasted 8 weeks. The results indicated that compared with the control group, the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin had a decreased feed conversion ratio (FCR) and increased final body weight (FBW), specific growth rate (SGR) and weight gain (WG) (P < 0.05). The protein carbonyl content (PCC), reactive oxygen species (ROS) level and malondialdehyde (MDA) level in the hepatopancreas and hemocytes were significantly lower, while the total antioxidant capacity (T-AOC), glutathione peroxidase (GPx) activity, and superoxide dismutase (SOD) activity were significantly higher in the crayfish groups supplemented with 50-150 mg kg^-1 hesperidin than in the control group. Supplementation with 50-150 mg kg^-1 hesperidin significantly increased the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), lysozyme (LZM), and phenoloxidase (PO) compared with the control group (P < 0.05); upregulated the mRNA expression of cyclophilin A (CypA), extracellular copper-zinc superoxide dismutase (ecCuZnSOD), GPxs, crustin, astacidin, Toll3 and heat shock protein 70 (HSP70) (P < 0.05); and decreased crayfish mortality following white spot syndrome virus (WSSV) infection. These findings indicate that dietary hesperidin supplementation at an optimum dose of 50-150 mg kg^-1 may effectively improve nonspecific immunity, antioxidant capacity and growth performance in crayfish.

Spodoptera litura cyclophilin A is required for Microplitis bicoloratus bracovirus-induced apoptosis during insect cellular immune response

Microplitis bicoloratus bracovirus (MbBV) is a polydnavirus found in the parasitic wasp M. bicoloratus. Although MbBV is a known inducer of apoptosis in host hemocytes, the mechanism by which this occurs remains elusive. In this study, we found that expression of cyclophilin A (CypA) was significantly upregulated in Spodoptera litura hemocytes at 6-day post-parasitization. Similar results were reported in High Five cells (Hi5 cells) infected by MbBV, suggesting that the upregulation of CypA is linked to MbBV infection in insect cells. cDNA encoding CypA was cloned from parasitized hemocytes of S. litura, and bioinformatic analyses showed that S. litura CypA belongs to the cyclophilin family of proteins. Overexpression of S. litura CypA in Hi5 cells revealed that the protein promotes MbBV-induced apoptosis in vitro. Conversely, suppression of the expression and activity of CypA protein significantly rescued the apoptotic phenotype observed in MbBV-infected Hi5 cells, suggesting that it plays a key role in this process. MbBV infection also promoted the cytoplasmic-nuclear translocation of CypA in Hi5 cells. Taken together, these results suggest that MbBV infection upregulates the expression of CypA, which is required for MbBV-mediated apoptosis. Our findings provide insight into the role that CypA plays in insect cellular immune response.

Molecular identification and expression analysis of a novel cyclophilin a gene in the red swamp crayfish, Procambarus clarkii

Cyclophilin A (Cyp A) is the main intracellular receptor of cyclosporin A (CsA) belonging to the immunophilin family, which is known as an effective immunosuppressive drug. This study aimed to gain insights into the structure and biological function of cyclophilin A in the red swamp crayfish, Procambarus clarkii (PcCypA). We cloned PcCypA by homology cloning and anchored polymerase chain reaction (PCR), and assessed its mRNA and protein expression levels in different tissues using quantitative real-time PCR and western blot analysis, respectively. The full-length DNA contained a 5' untranslated region (UTR) comprising 108 base pairs (bp), an open reading frame of 495 bp encoding a polypeptide of 164 amino acids with an estimated molecular mass of 17.3 kDa, and a 3' UTR of 281 bp including a significant poly(A) plus tail sequence. The predicted amino acid sequence of PcCypA shared high identity with CypA in other organisms. PcCypA transcripts were detected in the hepatopancreas, gill, heart, muscle, testis, and ovary of crayfish, with the highest expression levels in the heart. Western blot analysis found one 17-kDa band in all of the tissues examined, except for the ovary. Molecular identification and expression analysis of PcCypA will facilitate further studies of the immune defense mechanisms in red swamp crayfish, and provide new insights into freshwater invertebrate immunology.

Chemotactic Activity of Cyclophilin A in the Skin Mucus of Yellow Catfish (Pelteobagrus fulvidraco) and Its Active Site for Chemotaxis

Fish skin mucus is a dynamic barrier for invading pathogens with a variety of anti-microbial enzymes, including cyclophilin A (CypA), a multi-functional protein with peptidyl-prolyl cis/trans isomerase (PPIase) activity. Beside various other immunological functions, CypA induces leucocytes migration in vitro in teleost. In the current study, we have discovered several novel immune-relevant proteins in yellow catfish skin mucus by mass spectrometry (MS). The CypA present among them was further detected by Western blot. Moreover, the CypA present in the skin mucus displayed strong chemotactic activity for yellow catfish leucocytes. Interestingly, asparagine (like arginine in mammals) at position 69 was the critical site in yellow catfish CypA involved in leucocyte attraction. These novel efforts do not only highlight the enzymatic texture of skin mucus, but signify CypA to be targeted for anti-inflammatory therapeutics.

Molecular cloning and functional characterization of cyclophilin A in yellow catfish (Pelteobagrus fulvidraco)

Cyclophilin A (CypA) is a ubiquitously expressed protein which involves in diverse pathological conditions including infection and inflammation. In this report, a CypA gene (designated as YC-CypA) was cloned from yellow catfish (Pelteobagrus fulvidraco) which is an important cultured fish species in Asian countries. The open reading frame (ORF) of YC-CypA encoded a polypeptide of 164 amino acids with calculated molecular weight of 17.70 kDa. The deduced amino acid sequences of the YC-CypA shared highly conserved structures with CypAs from the other species, indicating that YC-CypA should be a new member of the CypA family. Full-length YC-CypA protein was expressed in Escherichia coli and specific polyclonal antibody against YC-CypA was generated. The YC-CypA protein showed chemotactic activity by transwell migration assay. The mRNA and protein of YC-CypA could be detected in all examined tissues with relatively higher mRNA level in spleen and higher protein level in head kidney, respectively. The temporal expression patterns of YC-CypA, IL-1β and TNF-α mRNAs were analyzed in the liver, spleen and head kidney post of Edwardsiella ictaluri infection. By immunohistochemistry assay, slight enhancement of YC-CypA protein was observed in the liver, spleen, body kidney and head kidney of yellow catfish infected with E. ictaluri. In conclusion, YC-CypA of yellow catfish showed chemotactic activity in vitro and might have been involved in cytokines secretion in yellow catfish during the infection of E. ictaluri.

Conformational plasticity of an enzyme during catalysis: intricate coupling between cyclophilin A dynamics and substrate turnover

Enzyme catalysis is central to almost all biochemical processes, speeding up rates of reactions to biological relevant timescales. Enzymes make use of a large ensemble of conformations in recognizing their substrates and stabilizing the transition states, due to the inherent dynamical nature of biomolecules. The exact role of these diverse enzyme conformations and the interplay between enzyme conformational dynamics and catalysis is, according to the literature, not well understood. Here, we use molecular dynamics simulations to study human cyclophilin A (CypA), in order to understand the role of enzyme motions in the catalytic mechanism and recognition. Cyclophilin A is a tractable model system to study using classical simulation methods, because catalysis does not involve bond formation or breakage. We show that the conformational dynamics of active site residues of substrate-bound CypA is inherent in the substrate-free enzyme. CypA interacts with its substrate via conformational selection as the configurations of the substrate changes during catalysis. We also show that, in addition to tight intermolecular hydrophobic interactions between CypA and the substrate, an intricate enzyme-substrate intermolecular hydrogen-bonding network is extremely sensitive to the configuration of the substrate. These enzyme-substrate intermolecular interactions are loosely formed when the substrate is in the reactant and product states and become well formed and reluctant to break when the substrate is in the transition state. Our results clearly suggest coupling among enzyme-substrate intermolecular interactions, the dynamics of the enzyme, and the chemical step. This study provides further insights into the mechanism of peptidyl-prolyl cis/trans isomerases and the general interplay between enzyme conformational dynamics and catalysis.

Molecular cloning and characterization of two isoforms of cyclophilin A gene from Venerupis philippinarum

Cyclophilin A (CypA) is a ubiquitously distributed intracellular protein belonging to the immunophilin family, which is recognized as the cell receptor for the potent immunosuppressive drug cyclosporine A. In the present study, two isoforms of cyclophilin A gene (named as VpCypA1 and VpCypA2) were isolated and characterized from Venerupis philippinarum by RACE approaches. Both VpCypA1 and VpCypA2 possessed all conserved features critical for the fundamental structure and function of CypA, indicating that the two isoforms of cyclophilin A should be new members of CypA family. The expression of VpCypA2 mRNA in haemocytes was significantly up-regulated and the highest expression level was detected at 96 h post-infection with 7.7-fold increase compared with that in the blank group. On the contrary, the relative expression level of VpCypA1 mRNA was down-regulated rapidly at 6 h post-infection and reached 0.4-fold of the control group. They exhibited different expression profile and identical effect of immune modulation, which might suggest the two VpCypA isoforms exert their function in a manner of synergy. These results provide valuable information for further exploring the roles of cyclophilin A in the immune responses of V. philippinarum.

Proteome reference map of the skin mucus of Atlantic cod (Gadus morhua) revealing immune competent molecules

The skin mucosal proteome of Atlantic cod (Gadus morhua) was mapped using a 2D PAGE, LC-MS/MS coupled approach. Mucosal proteins from naive fish were identified primarily by similarity searches across various cod EST databases. The identified proteins were clustered into 8 groups based on gene ontology classification for biological process. Most of the proteins identified from the gel are hitherto unreported for cod. Galectin-1, mannan binding lectin (MBL), serpins, cystatin B, cyclophilin A, FK-506 binding protein, proteasome subunits (alpha-3 and -7), ubiquitin, and g-type lysozyme are considered immune competent molecules. Five of the aforementioned proteins were cloned and their tissue distribution was analysed by RT-PCR.

Development of genomic resources in support of sequencing, assembly, and annotation of the catfish genome

Major progress has been made in catfish genomics including construction of high-density genetic linkage maps, BAC-based physical maps, and integration of genetic linkage and physical maps. Large numbers of ESTs have been generated from both channel catfish and blue catfish. Microarray platforms have been developed for the analysis of genome expression. Genome repeat structures are studied, laying grounds for whole genome sequencing. USDA recently approved funding of the whole genome sequencing project of catfish using the next generation sequencing technologies. Generation of the whole genome sequence is a historical landmark of catfish research as it opens the real first step of the long march toward genetic enhancement. The research community needs to be focused on aquaculture performance and production traits, take advantage of the unprecedented genome information and technology, and make real progress toward genetic improvements of aquaculture brood stocks.

Sequence analysis, characterization and mRNA distribution of channel catfish (Ictalurus punctatus Rafinesque, 1818) chemokine (C-X-C motif) receptor 4 (CXCR4) cDNA

Chemokine receptor CXCR4, a member of the G protein-coupled receptor superfamily, binds selectively CXCL12. This protein plays many important roles in immunological as well as pathophysiological functions. In this study, we identified and characterized the channel catfish CXCR4 transcript. The full-length nucleic acid sequence of channel catfish CXCR4 cDNA comprised of 1994 nucleotides, including an open reading frame, which appears to encode a putative peptide of 357 amino acid residues with a calculated molecular mass of 40.1kDa. By comparison with the human counterpart, the channel catfish CXCR4 peptide can be divided into domains, including seven transmembrane domains, four cytoplasmic domains, and four extracellular domains. The CXCR4 transcript was detected in spleen, anterior kidney, liver, intestine, skin and gill of all catfish examined in this study. Because four CXCL of channel catfish have been identified, the result provides valuable information for further exploring the channel catfish chemokine signalling pathways and their roles in immune responses to infection.

Channel catfish (Ictalurus punctatus Rafinesque, 1818) tetraspanin membrane protein family: identification, characterization and expression analysis of CD63 cDNA

CD63, known as lysosome associated membrane protein 3 (LAMP-3), is a member of the tetraspanin integral membrane protein family. This protein plays many important roles in immuno-physiological functions. In this communication, we report the identification, characterization, and expression analysis of the channel catfish CD63 transcript. The complete nucleic acid sequence of channel catfish CD63 cDNA was comprised of 1159 nucleotides, including an open reading frame, which appears to encode a putative peptide of 237-amino-acid residues. Like other tetraspanin proteins, the channel catfish CD63 peptide can be divided into domains, including four transmembrane domains, three intracellular domains, and one of each small and large extracellular loops. The channel catfish CD63 peptide shares 52-55% identity among fish counterparts, but only 43-46% identity among mammalian counterparts. The characteristic Cys-Cys-Gly motif and four Cys residues in the large extracellular loop were conserved. The channel catfish CD63 transcript was detected by RT-PCR in spleen, anterior kidney, liver, intestine, skin and gill. This result provides important information for further elucidating CD63 functions in channel catfish.

Channel catfish (Ictalurus punctatus Rafinesque, 1818) CD156a (ADAM metallopeptidase domain 8): cDNA clone, characterization and expression in tissues

CD156a, also known as a disintegrin and metalloprotease domain 8 (ADAM-8), is a type 1 transmembrane glycoprotein of the ADAM family. This protein plays important roles in immune and other physiological functions. In this communication, the channel catfish CD156a cDNA was characterized and its expression in various tissues was determined. The full-length of channel catfish CD156a cDNA had 3035 nucleotides, including an open reading frame which appears to encode an 850 amino acid peptide with a calculated molecular mass of 94.6kDa. The peptide had three potential N-glycosylation sites. By comparison with other species, the degree of homology of the CD156a amino acid sequences ranged from 31.6% (vs. chicken CD156a) to 59.5% (vs. zebrafish CD156a). The channel catfish CD156a peptide could be structurally divided into nine domains. Several canonical features for CD156a functions were conserved in channel catfish. The CD156a transcript was detected by two-step RT-PCR in anterior kidney and gill, suggesting that CD156a may be involved in the innate immune response in channel catfish. Reagents for further elucidating the immune functions of channel catfish CD156a are under development.

Functional annotation and analysis of expressed sequence tags from the hepatopancreas of mitten crab (Eriocheir sinensis)

Due to its popularity as a traditional food, intensive harvesting of the mitten crab (Eriocheir sinensis) is common and has lead to an increase in disease incidence, resulting in catastrophic losses to crab aquaculture. The hepatopancreas of E. sinensis is not only an important digestive organ but also an indispensable immune organ. We constructed a nonnormalized cDNA library from the hepatopancreas of E. sinensis and acquired 3,297 high-quality expressed sequence tags representing 1,178 unigenes. More than half of these unigenes were novel genes for this species; the remaining had homologs in public databases, which is of great importance for future functional research. We also investigated the association of these genes with immune processes for insight into one of the main functions of the hepatopancreas besides metabolism. Despite the relatively low sampling scalar of our cDNA library, we were able to demonstrate several important properties of the hepatopancreatic transcriptome and identified numerous genes that were closely associated with immune responses. These results might serve as the basis for an in-depth genomics study of E. sinensis, including transcriptome analysis, physical mapping, and whole genome sequencing.

Characterization and tissue expression of channel catfish (Ictalurus punctatus Rafinesque, 1818) ubiquitin carboxyl-terminal hydrolase L5 (UCHL5) cDNA

The ubiquitin-proteasome cycle is a complex, non-lysosomal biochemical process for intracellular protein degradation. This process involves many enzymes. One enzyme involved in this process is ubiquitin carboxyl-terminal hydrolase L5 (UCHL5), which deubiquitylates the polyubiquitin chain into ubiquitin. In this report, we isolated, sequenced, and characterized the channel catfish UCHL5 cDNA. The complete nucleic acid sequence of the channel catfish UCHL5 cDNA is comprised of 1,357 nucleotides, including an open reading frame, which appears to encode a putative peptide of 329 amino acid residues. The estimated molecular mass and pI of this peptide are 37.6 kDa and 4.84 at pH 7.0, respectively. The degree of conservation of the channel catfish UCHL5 amino acid sequence in comparison to other species ranged from 85% (vs. mouse) to 92% (vs. zebrafish and spotted green pufferfish). The channel catfish UCHL5 transcript was detected by RT-PCR in spleen, head kidney, liver, intestine, skin and gill, suggesting the UCHL5 transcript is constitutively expressed. This research provides important information for further elucidating UCHL5 in the channel catfish ubiquitin-proteasome pathway.

Channel catfish, Ictalurus punctatus, cysteine proteinases: cloning, characterisation and expression of cathepsin H and L

The antigen recognition by the host immune system is a complex biochemical process that requires a battery of enzymes. Cathepsins are one of the enzyme superfamilies involved in antigen degradation. We observed the up-regulation of catfish cathepsin H and L transcripts during the early stage of Edwardsiella ictaluri infection in preliminary studies, and speculated that cathepsin H and L may play roles in infection. We identified, sequenced and characterized the complete channel catfish cathepsin H and L cDNAs, which comprised 1415 and 1639 nucleotides, respectively. The open reading frames of cathepsin H appeared to encode a protein of 326-amino acid residues, which that of cathepsin L encoded a protein of 336 amino acids. The degree of conservation of the channel catfish cathepsin H and L amino acid sequences in comparison to other species ranged from 61% to 77%, and 67% to 85%, respectively. The catalytic triad and substrate binding sites are conserved in cathepsin H and L amino acid sequences. The cathepsin L transcript was expressed in all tissues examined, while the cathepsin H was expressed in restricted tissues. These results provide important information for further exploring the roles of channel catfish cathepsins in antigen processing.

Channel catfish, Ictalurus punctatus Rafinesque 1818, tetraspanin membrane protein family: characterization and expression analysis of CD81 cDNA

CD81, also known as the target of an antiproliferative antibody 1 (TAPA-1) in human, is a member of tetraspanin integral membrane protein family. This protein plays many important roles in immune and other physiological functions. In this report, we characterized and analyzed expression of the channel catfish CD81 transcript. The full-length of channel catfish CD81 cDNA comprised of 1130 nucleotides, including an open reading frame which appears to encode a putative peptide of 234 amino acid residues. By comparison with the human counterpart, the channel catfish CD81 peptide could be divided into domains, including four transmembrane domains, three intracellular domains, and one of each small and large extracellular loops. The degree of conservation of the channel catfish CD81 amino acid sequence to that of mammalian counterparts ranged from 65% to 67%. The large extracellular domain shows the least conservation between fish and mammals. However, the characteristic Cys(159)-Cys(160)-Gly(161) motif and Cys(176/188) in this domain were conserved. The channel catfish CD81 transcript was detected by RT-PCR in spleen, head kidney, liver, intestine, skin and gill. This result provides important information for further elucidating CD81 functions in channel catfish.

A cyclophilin A inducible expressed in gonad of zhikong scallop Chlamys farreri

Cyclophilin A (CypA), a receptor for the immunosuppressive agent cyclosporin A (CsA), is a cis-trans peptidyl-prolyl isomerase (PPIase) which accelerates the cis-trans isomerization of prolyl-peptide bonds, interacts with a variety of proteins and therefore regulates their activities. One CypA (designated CfCypA) cDNA was cloned from Chlamys farreri by expressed sequence tag (EST) and rapid amplification of cDNA ends (RACE) techniques. The full-length cDNA of CfCypA consisted of 1,248 nucleotides with a canonical polyadenylation signal sequence AATAAA, a poly (A) tail, and an open reading frame (ORF) of 495 nucleotides encoding a polypeptide of 164 amino acids. The deduced amino acid sequence shared high similarity with CypA from the other species, indicating that CfCypA should be a new member of the CypA family. Quantitative real-time (RT) PCR was employed to assess the mRNA expression of CfCypA in various tissues and its temporal expression in haemocytes and gonad of scallops challenged with Vibrio anguillarum. The mRNA transcripts of CfCypA could be detected in all the examined tissues with highest expression level in gonad. After bacterial challenge, the expression level of CfCypA was almost unchanged in haemocytes, but up-regulated in gonad and increased to the peak (22.59-fold; P < 0.05) at 4 h post-injection, and then dropped to the original level at 8 h post-injection. These results indicated that CfCypA was constitutive expressed in haemocytes, but could be induced in gonad, and perhaps played a critical role in response to the bacterial challenge in gonad.

Molecular cloning, sequencing and characterization of channel catfish (Ictalurus punctatus, Rafinesque 1818) cathepsin S gene

Cathepsin S is a lysosomal cysteine endopeptidase of the papain family. Our preliminary results showed the up-regulation of cathepsin S (CTSS) transcript during the early stage of Edwardsiella ictaluri infection, leading us to speculate that CTSS may play a role in infection. In this report, we identified, sequenced and characterized the channel catfish CTSS cDNA. Total RNA from tissues was isolated and cDNA libraries were constructed by the rapid amplification cDNA end (RACE) method. The gene-specific primers in conjunction with the RACE primers were used to PCR amplify 5'- and 3'-ends of the CTSS transcript. The complete channel catfish CTSS cDNA comprised 1530 nucleotides including a 96-nucleotide 5'-untranslated region (UTR), a 990-nucleotide open reading frame and a 444-nucleotide 3'-UTR. The open reading frame appears to encode a protein of 329 amino-acid residues with calculated molecular mass of 36.7kDa and pI of 5.96. The degree of conservation of the channel catfish CTSS amino-acid sequence in comparison to other species ranged from 56.6 to 68.5%. These results provide important information for further exploring the roles of channel catfish CTSS in antigen processing.