Molecular cloning, characterization and expression analysis of cathepsin D gene from turbot Scophthalmus maximus

A novel function by cathepsin D in degradation of nucleic acids

Cathepsin D (CTSD) is an aspartic endopeptidase, however, we found that it was also capable of enzymatic digestion of nucleic acids (NAs). The purpose of this study was to investigate the basic properties of CTSD enzymatic activity on NAs, and explore the degradation mechanism. The results showed that NAs were efficiently digested between pH 3.0 and 5.0, and the optimum pH was 3.5. CTSD exhibited optimum activity at the temperature of 50°C. The degradation rate was improved with an increased CTSD concentration, and NAs were digested to an enzyme concentration of 0.001%, at which point, NAs were no longer digested. Ca2+ and Mg2+ at low concentrations of 5 mM promoted the digestion remarkably. As the protein substrate for CTSD, both Hb and BSA had no effect on DNA degradation, even when the molar ratio of protein:DNA was 104:1. Kinetic parameters of Km and kcat/Km value were (42 ± 1) μM and (1.62 ± 0.1) × 10-2 s-1mM-1 respectively, using real-time quantitative PCR (RT-PCR). Specially, pepstatin A which is the specific aspartic protease inhibitor exhibited inhibitory effect on NA digestion by CTSD as well, suggesting that the catalytic active site of CTSD for NAs might be the same as protein. A brief degradation mechanism is discussed. The present study may change the cognition of CTSD specificity for substrate and contribute greatly to enzymology of CTSD.

Bactericidal permeability-increasing protein/LPS-binding protein (BPI/LBP) enhances resistance of golden pompano Trachinotus ovatus against bacterial infection

Antimicrobial peptides are crucial components of innate immunity against microbial invasions. As a kind of antimicrobial peptides, bactericidal permeability-increasing protein (BPI)/lipopolysaccharide-binding protein (LBP) play vital roles in defending the host against gram-negative bacteria. In the current study, a novel BPI/LBP from Trachinotus ovatus (TroBPI/LBP) was characterized. The full length of TroBPI/LBP cDNA sequence is 1434 bp, which contained 477 amino acids. Multiple amino acid alignments of TroBPI/LBP shows 34.07%-84.49% identity with other fish BPI/LBP. Similar to other BPI/LBP, TroBPI/LBP also possesses an N-terminal signal peptide, a BPI/LBP/CETP N-terminal domain, and a BPI/LBP/CETP C-terminal domain. In vitro, the recombinant protein of TroBPI/LBP showed effective bacterial depression activity and binding activity to gram-negative bacteria. In vivo, TroBPI/LBP was constitutively expressed in tested tissues, and the highest expression level was in liver. Following Vibrio alginolyticus stimulation, the mRNA expression of TroBPI/LBP was significantly upregulated in immune-related tissues, and peaked at 12 h post-infection, which confirmed that TroBPI/LBP was highly sensitive to V. alginolyticus stimuli. Furthermore, functional analyses showed that the overexpression of TroBPI/LBP could enhance the ability of fish to against V. alginolyticus infection, and the knockdown of TroBPI/LBP significantly diminished bacterial clearance capacity post-infection. Therefore, these results suggest that TroBPI/LBP may play an important role in host defense against bacterial infection.

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.

Cathepsin D Plays a Vital Role in Macrobrachium nipponense of Ovary Maturation: Identification, Characterization, and Function Analysis

The oriental river prawn Macrobrachium nipponense is an economically important aquacultural species. However, its aquaculture is negatively impacted by the rapid sexual maturation of female M. nipponense. The fast sexual maturation produces a large number of offspring which leads to a reduction in resilience, a low survival rate, and an increased risk of hypoxia, this in turn, seriously affects the economic benefits of prawn farming. Cathepsin D is a lysosomal protease involved in the ovarian maturation of M. nipponense. In the current study, the cDNA of the gene encoding cathepsin D (Mn-CTSD) was cloned from M. nipponense. The total length was 2391 bp and consisted of an open reading frame (ORF) of 1158 bp encoding 385 amino acids. Sequence analysis confirmed the presence of conserved N-glycosylation sites and characteristic sequences of nondigestive cathepsin D. The qPCR analysis indicated that Mn-CTSD was highly expressed in all tissues tested, most significantly in the ovaries, whereas in situ hybridization showed that expression occurred mainly in oocyte nuclei. Analysis of its expression during development showed that Mn-CTSD peaked during the O-IV stage of ovarian maturation. For the RNAi interference experiment, female M. nipponense specimens in the ovary stage I were selected. Injection of Mn-CTSD double-stranded (ds)RNA into female M. nipponense decreased the expression of Mn-CTSD in the ovaries, such that the Gonad Somatic Index (GSI) of the experimental group was significantly lower than that of the control group (1.79% versus 4.57%; p < 0.05). Ovary development reached the O-III stage in 80% of the control group, compared with 0% in the experimental group. These results suggest that Mn-CTSD dsRNA inhibits ovarian maturation in M. nipponense, highlighting its important role in ovarian maturation in this species and suggesting an approach to controlling ovarian maturation during M. nipponense aquaculture.

Genome-Wide Identification, Evolutionary Analysis, and Expression Patterns of Cathepsin Superfamily in Black Rockfish (Sebastes schlegelii) following Aeromonas salmonicida Infection

Cathepsins are lysosomal cysteine proteases belonging to the papain family and play crucial roles in intracellular protein degradation/turnover, hormone maturation, antigen processing, and immune responses. In the present study, 18 cathepsins were systematically identified from the fish S. schlegelii genome. Phylogenetic analysis indicated that cathepsin superfamilies are categorized into eleven major clusters. Synteny and genome organization analysis revealed that whole-genome duplication led to the expansion of S. schlegelii cathepsins. Evolutionary rate analyses indicated that the lowest Ka/Ks ratios were observed in CTSBa (0.13) and CTSBb (0.14), and the highest Ka/Ks ratios were observed in CTSZa (1.97) and CTSZb (1.75). In addition, cathepsins were ubiquitously expressed in all examined tissues, with high expression levels observed in the gill, intestine, head kidney, and spleen. Additionally, most cathepsins were differentially expressed in the head kidney, gill, spleen, and liver following Aeromonas salmonicida infection, and their expression signatures showed tissue-specific and time-dependent patterns. Finally, protein–protein interaction network (PPI) analyses revealed that cathepsins are closely related to a few immune-related genes, such as interleukins, chemokines, and TLR genes. These results are expected to be valuable for comparative immunological studies and provide insights for further functional characterization of cathepsins in fish species.

Functional Analysis of the Cathepsin D Gene Response to SGIV Infection in the Orange-Spotted Grouper, Epinephelus coioides

(1) Background: Lysosomal aspartic protease Cathepsin D (CD) is a key regulator and signaling molecule in various biological processes including activation and degradation of intracellular proteins, the antigen process and programmed cell death. However, the function of fish CD in virus infection remains largely unknown. (2) Methods: The functions of the CD gene response to SGIV infection was determined with light microscopy, reverse transcription quantitative PCR, Western blot and flow cytometry. (3) Results: In this study, Ec-Cathepsin D (Ec-CD) was cloned and identified from the orange-spotted grouper, Epinephelus coioides. The open reading frame (ORF) of Ec-CD consisted of 1191 nucleotides encoding a 396 amino acid protein with a predicted molecular mass of 43.17 kDa. Ec-CD possessed typical CD structural features including an N-terminal signal peptide, a propeptide region and a mature domain including two glycosylation sites and two active sites, which were conserved in other CD sequences. Ec-CD was predominantly expressed in the spleen and kidneys of healthy groupers. A subcellular localization assay indicated that Ec-CD was mainly distributed in the cytoplasm. Ec-CD expression was suppressed by SGIV stimulation and Ec-CD-overexpressing inhibited SGIV replication, SGIV-induced apoptosis, caspase 3/8/9 activity and the activation of reporter gene p53 and activating protein-1 (AP-1) in vitro. Simultaneously, Ec-CD overexpression obviously restrained the activated mitogen-activated protein kinase (MAPK) pathways, including extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). In addition, Ec-CD overexpression negatively regulated the transcription level of pro-inflammatory cytokines and activation of the NF-κB promotor. (4) Conclusions: Our findings revealed that the Ec-CD possibly served a function during SGIV infection.

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.

Characterization of the cathepsin D in Procambarus clarkii and its biological role in innate immune responses

Cathepsin D belongs to aspartic protease family, produced in the rough endoplasmic reticulum, and then transported to lysosomes, where it participates in various physiological processes. Despite its importance, only a few reports available on the functional role of cathepsin D in crustaceans. Herein, we cloned a cDNA fragment of cathepsin D from the hepatopancreas of the red swamp crayfish, Procambarus clarkii (Pc-cathepsin D) for the first time. It included 1158 base pairs open reading frame, encoding a protein of 385 amino acids. Multiple alignment analysis confirmed the presence of aspartic proteinase active sites and N glycosylation sites. Pc-cathepsin D mRNA expression was high in the gills followed by gut, heart, hepatopancreas of P. clarkii. At different time points post-infection with lipopolysaccharides, peptidoglycan, or polyinosinic polycytidylic acid, Pc-cathepsin D mRNA expression significantly enhanced compared with the control group. Knockdown of the Pc-cathepsin D by double-stranded RNA, strikingly, changed the expression of all the tested P. clarkii immune-associated genes, including Pc-Toll, Pc-lectin, Pc-cactus, Pc-anti-lipopolysaccharide factor, Pc-phospholipase, and Pc-sptzale. Altogether, these results suggest that Pc-cathepsin D is needed to confer innate immunity against microbial pathogens by modulating the expression of crucial transcripts that encode immune-associated genes.

First report of cathepsin E in a teleost (Korean rose bitterling, Rhodeus uyekii): Molecular characterisation and tissue distribution

We isolated and characterised a cDNA encoding the aspartic protease cathepsin E (CTSE) in Korean rose bitterling, Rhodeus uyekii. The full-length Rhodeus uyekii CTSE (RuCTSE) cDNA (1396 bp) contains an open reading frame of 1218 bp, encoding 405 amino acids. Alignment of multiple CTSE protein sequences revealed that two of the aspartyl protease active site residues and a disulphide bond were well-conserved among the other CTSE sequences. Phylogenetic analysis revealed that RuCTSE is most closely related to freshwater fish cathepsin E. RuCTSE is widely expressed in the liver, spleen, ovary, testis, brain, eye, intestine, muscle, fin, stomach, and kidney. This first report of teleost CTSE will provide important information related to the identification of other cathepsin E genes in various fish species and will serve as a useful molecular tool to help clarify biological activities in other teleosts.

The effect of Triaenophorus nodulosus (Cestoda: Bothriocephalidea) infection on some biochemical parameters of the liver of Perca fluviatilis

Natural infection of 2 to 6-year-old perch with the cestode parasites Triaenophorus nodulosus was shown to have minor effects on the studied components of the antioxidant defense system, nucleic acids degradation, and carbohydrate metabolism enzymes in the liver of the fish. The level of infection of 1-4 parasite larvae per fish observed in wild population of perch was shown to be moderate in terms of its effect on the health of the host fish. The activity of hepatic enzymes β-galactosidase, β-glucosidase, cathepsin D, and glutathione S-transferase showed different responses in infected males and females, which indicates different potential resistance of fish to the stress exposure between genders.

Effects of different light spectra on embryo development and the performance of newly hatched turbot (Scophthalmus maximus) larvae

Light is a key environmental factor that synchronizes various life stages from embryo development to sexual maturation in fish. For turbot, light spectra have the most influence at the larval and juvenile stages. In the current study, differences in the development of embryos and the performance of newly hatched turbot larvae exposed to five different spectra: full spectrum (LDF), blue (LDB, peak at 450 nm), green (LDG, peak at 533 nm), orange (LDO, peak at 595 nm) and red (LDR, peak at 629 nm), were examined. At 62.8 h post fertilization, a higher number of embryos exposed to short-wavelengths (LDG and LDB) had developed a heartbeat in comparison with embryos exposed to other wavelengths. Larvae exposed to the green spectrum had higher malformation rates than larvae exposed to the other spectra, indicating that larvae exposed to green light may have significantly reduced survival rates. The results of non-specific immunity parameters showed that the mRNA expression levels of cathepsin D (CTSD), cathepsin F (CTSF), catalase (CAT) and metallothionein (MT) in larvae exposed to LDB were significantly higher than those exposed to other spectra, but CAT activity in larvae exposed to LDB was significantly lower than larvae exposed to the other spectra. There was no significant difference in MT activity in larvae exposed to the five different spectra. The mRNA expression level of lysozyme (LZM) in larvae exposed to LDR was significantly higher than other spectra, while there was no significant difference in LZM activity observed in larvae exposed to LDR, LDG, LDB and LDF. The difference of the enzyme activity of total superoxide dismutase (T-SOD) was not significant among larvae exposed to the five spectra. mRNA expression of the heat shock protein 70 (HSP70) was significantly higher in newly hatched larvae exposed to LDB, LDR and LDG, indicating that larvae exposed to LDB, LDG and LDR exhibited a stress response. The mRNA expression level of the insulin-like growth factor-1 (IGF-1) and growth parameters in the newly hatched larvae exposed to the different spectra were not significantly different. The results of the present study indicate that LDO and LDF should be used for embryo incubation and newly hatched larvae when rearing turbot. This study provides a theoretical basis for optimizing the incubation light environment for fertilized turbot eggs, promoting immunity and reducing stress responses in newly hatched larvae.

Molecular identification and function analysis of bactericidal permeability-increasing protein/LPS-binding protein 1 (BPI/LBP1) from turbot (Scophthalmus maximus)

Bactericidal permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) play important roles in host antimicrobial defense. In the present study, we identified one isoform of BPI/LBP gene from turbot (Scophthalmus maximus), designated as SmBPI/LBP1. The full-length cDNA sequence of SmBPI/LBP1 was 1826 bp, which encoding one secreted protein with 480 amino acid residues. Structurally, the SmBPI/LBP1 showed high similarity to its homologs from other vertebrates or invertebrates, which all contained a signal peptide, a BPI/LBP/CETP N-terminal with a LPS-binding domain, and a BPI/LBP/CETP C-terminal domain. The deduced amino acid sequences of SmBPI/LBP1 shared significant similarity to BPI/LBP of Seriola lalandi dorsalis (71%) and Paralichthys olivaceus (69%). Phylogentic analysis further supported that SmBPI/LBP1 act as a new member of vertebrate BPI/LBP family. SmBPI/LBP1 was ubiquitously expressed in all tested tissues, with the highest expression level in spleen tissue. The mRNA expression of SmBPI/LBP1 in spleen and kidney were significantly up-regulated after Vibrio vulnificus challenge. Finally, the recombinant SmBPI/LBP1 showed high affinity to lipopolysaccharide, followed by peptidoglycan and lipoteichoic acid, which is the ubiquitous component of Gram-negative or Gram-positive bacteria. These results indicated that SmBPI/LBP1 probably played important roles in immune response against bacteria infection.

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.

Natural Resistance Associated Macrophage Protein Is Involved in Immune Response of Blunt Snout Bream, Megalobrama amblycephala

The natural resistance-associated macrophage protein gene (Nramp), has been identified as one of the significant candidate genes responsible for modulating vertebrate natural resistance to intracellular pathogens. Here, we identified and characterized a new Nramp family member, named as maNramp, in the blunt snout bream. The full-length cDNA of maNramp consists of a 153 bp 5′UTR, a 1635 bp open reading frame encoding a protein with 544 amino acids, and a 1359 bp 3′UTR. The deduced protein (maNRAMP) possesses the typical structural features of NRAMP protein family, including 12 transmembrane domains, three N-linked glycosylation sites, and a conserved transport motif. Phylogenetic analysis revealed that maNRAMP shares the significant sequence consistency with other teleosts, and shows the higher sequence similarity to mammalian Nramp2 than Nramp1. It was found that maNramp expressed ubiquitously in all normal tissues tested, with the highest abundance in the spleen, followed by the head kidney and intestine, and less abundance in the muscle, gill, and kidney. After lipopolysaccharide (LPS) stimulation, the mRNA level of maNramp was rapidly up-regulated, which reached a peak level at 6 h. Altogether, these results indicated that maNramp might be related to fish innate immunity and similar to mammalian Nramp1 in function.

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

Cathepsin D (CTSD, EC 3.4.23.5) belongs to aspartic protease family, which is located in lysosomes and is distributed in diverse tissues and cells. CTSD has a wide variety of physiological functions, owing to its proteolytic activity in degradating proteins and peptides. In the current study, the full length cDNA of sea cucumber (Apostichopus japonicus) cathepsin D (AjCTSD) was firstly cloned, then the association between AjCTSD and sea cucumber autolysis was investigated. The full length cDNA of AjCTSD was 2896 bp, with an open reading frame (ORF) for 391 amino acids. AjCTSD was widely expressed in body wall, muscle and intestine; the expression level was the highest in intestine, followed by muscle and body wall. Compared to fresh tissues, AjCTSD expression levels were significantly increased in all examined autolytic tissues. The purified recombinant AjCTSD promoted the degradation of sea cucumber muscle. In conclusion, AjCTSD contributed to sea cucumber muscle autolysis.

Ameliorative effect of vitamin E on hepatic oxidative stress and hypoimmunity induced by high-fat diet in turbot (Scophthalmus maximus)

This study was conducted to examine the effects of vitamin E on growth performance, oxidative stress and non-specific immunity of turbot (Scophthalmus maximus) fed with high-fat diet. Results showed that high-fat diet significantly increased hepatosomatic index, viscerosomatic index, hepatic malondialdehyde level and decreased catalase and superoxide dismutase activities, whereas final weight, specific growth rate and survival rate remained unchanged. Meanwhile, nitro blue tetrazolium positive leucocytes of head kidney, respiratory burst activity in head-kidney macrophage, phagocytic index and serum lysozyme activity were significantly reduced after feeding with high-fat diet. Furthermore, fish fed with high-fat diet promoted higher expression of heat shock protein (hsp70, hsp90), and inhibited expression of complement component 3 (c3) in the liver and tumor necrosis factor-α (tnf-α), interleukine 1β (il-1β), toll like receptor 22 (tlr-22) in the spleen and head-kidney, respectively. However, simultaneous supplementation with 480 mg kg^-1 vitamin E protected turbot against high-fat diet-induced hepatic oxidative stress, hypoimmunity through attenuating lipid peroxidation, renewing antioxidant enzymes activities and nonspecific immune responses, and modulating the expression of stress protein (hsp70, hsp90) and immune-related genes (c3, tnf-α, il-1β, tlr-22). In conclusion, the obtained results indicate the vitamin E as a wildly used functional feed additive contributes potentially to alleviate high-fat diet-induced hepatic oxidative stress and hypoimmunity, maintain the health, and improve the broodstock management for turbot.

Identification and characterization of a novel Toll-like receptor 4 homologue in blunt snout bream, Megalobrama amblycephala

Toll-like receptors (TLRs) are central players in the innate immune system in response to a wide range of pathogen infection. Among various TLRs, TLR4 plays a key role in recognition of bacterial lipopolysaccharides (LPS). In the present study, we identified and characterized a novel TLR4 homologue (maTLR4b) in blunt snout bream (Megalobrama amblycephala) which was significantly distinct from previously reported M. amblycephala TLR4 (tentatively named maTLR4a). The results showed that the complete cDNA sequence of maTLR4b was 3261 bp with an open reading frame encoding a polypeptide of 820 amino acids, and that its genomic sequence was 3793 bp, which had 3 exons. Structurally, the deduced maTLR4b protein showed a typical TLR domain architecture, including a signal peptide, eight leucine-rich repeats (LRRs) in the extracellular region, a transmembrane domain, and a Toll-Interleukin 1 receptor (TIR) domain in the cytoplasmic region. Phylogenetic analysis revealed that all TLR4s from teleost fish formed a monophyletic clade. Both maTLR4a and maTLR4b were divided into two distinct branches, and showed the highest level of similarity with the grass carp TLR4.2 and TLR4.4 homologue, respectively. MaTLR4b was constitutively expressed in all healthy tissues tested although at different levels. After LPS stimulation, the expression levels were significantly up-regulated in spleen, and peaked at 4 h between maTLR4a and maTLR4b, but with a distinct and complementary expression patterns. Taken together, these results suggested that maTLR4b is indeed a functional homologue of TLR4 in other species, which may play vital role in innate immune.

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.

Identification and expression analysis on bactericidal permeability-increasing protein/lipopolysaccharide-binding protein of blunt snout bream, Megalobrama amblycephala

Bactericidal permeability-increasing protein (BPI) and lipopolysaccharide-binding protein (LBP) belong to the lipid transfer protein/lipopolysaccharide-binding protein family and play a critical role in the innate immune response to Gram-negative bacteria. In the present study, a novel BPI/LBP from blunt snout bream, Megalobrama amblycephala (maBPI/LBP) was isolated by RACE techniques. The open reading frame (ORF) of maBPI/LBP gene encoded a polypeptide of 474 amino acids with a putative 18-aa hydrophobic signal peptide. Structurally, the maBPI/LBP showed highly similar to those of BPI/LBPs from invertebrate and teleost, LBPs and BPIs from mammal, which contained an N-terminal BPI/LBP/CETP domain BPI1 with a LPS-binding domain, a C-terminal BPI/LBP/CETP domain BPI2, and proline-rich domain. The homologous identities of deduced amino acid sequences displayed that the maBPI/LBP possessed significant similarity (96.61% and 90.07%) with those of grass carp and common carp, respectively. The recombinant protein of maBPI/LBP showed effectively kill Gram-negative bacteria. The maBPI/LBP gene was expressed in a wide range of normal tested tissues, with the highest expression levels in the kidney. The experiments revealed that the mRNA expression of maBPI/LBP in spleen considerably up-regulated from 2 h to 8 h post LPS stimulation, and peaked rapidly at 2 h (7.40-fold, P < 0.05), which confirmed that maBPI/LBP was the absolute sensitive to LPS stimulation. Furthermore, the level of maBPI/LBP mRNA expression reached the maximum for a second time at 24 h after LPS stimulation. These results suggested that maBPI/LBP was a constitutive and inducible acute-phase protein contributing to the host immune defense against pathogenic bacterial infection in M. amblycephala. This study will further our understanding of the function of BPI/LBP and the molecular mechanism of innate immunity in teleost.

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.

Effect of dietary vitamin E on the growth performance and nonspecific immunity in sub-adult turbot (Scophthalmus maximus)

This study investigated the growth performance and non-specific immunity in sub-adult turbot fed with graded levels of vitamin E (0, 120, 240, 480 and 960 mg kg(-1)) for 15 weeks. Results showed that the final weight, specific growth rate, nitro blue tetrazolium positive leucocytes of head kidney, phagocytic index, serum lysozyme activity and superoxide dismutase activity significantly increased with increasing vitamin E levels. The highest values were recorded in the diet with 480 mg kg(-1) vitamin E. However, no significant differences in the hepatosomatic index, viscerosomatic index and survival rate were found among all dietary treatment. Furthermore, the expression levels of complement component 3 (C3), tumor necrosis factor-α (TNF-α) and interleukine 1β (IL-1β) were significantly upregulated in the fish feed with the vitamin E-supplemented diets. Compared with the basal diet, the diet supplemented with 480 mg kg(-1) vitamin E significantly augmented the mRNA expression of IL-1β, TNF-α in the spleen and head-kidney, C3 in the liver, respectively. In conclusion, the obtained results indicate the basal diet supplemented with moderate dietary vitamin E (480 mg kg(-1)) increased the growth, nonspecific immune responses, and expression levels of some immune-related genes in sub-adult turbot. These observations suggest that optimal dietary vitamin E can promote the growth, maintain the health and improve the broodstock management for turbot.

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.

A developmental hepatotoxicity study of dietary bisphenol A in Sparus aurata juveniles

Previous studies in rats have indicated that a diet enriched with Bisphenol A adversely effects metabolism and reproductive success. In rats exposed to BPA by maternal gavage, alteration in the developmental programming, higher obesity rates and reproductive anomalies were induced. Starting with this evidence, the aim of this study was to provide important insights on the effects induced by a BPA enriched diet, on the reproductive physiology and metabolism of juvenile fish, simulating the scenario occurring when wild fish fed on prey contaminated with environmental BPA. Seabream was chosen as model, as it is one of the primary commercial species valued by consumers and these results could provide important findings on adverse effects that could be passed on to humans by eating contaminated fish. A novel method for measuring BPA in the food and water by affinity chromatography was developed. Analysis of signals involved in reproduction uncovered altered levels of vtg and Zp, clearly indicating the estrogenic effect of BPA. Similarly, BPA up-regulated catd and era gene expression. A noteworthy outcome from this study was the full length cloning of two vtg encoding proteins, namely vtgA and vtgB, which are differently modulated by BPA. Cyp1a1 and EROD activity were significantly downregulated, confirming the ability of estrogenic compounds to inhibit the detoxification process. GST activity was unaffected by BPA contamination, while CAT activity was down regulated. These results collectively confirm the estrogenic effect of BPA and provide additional characterization of novel vtg genes in Sparus aurata.

Cloning, characterisation, and expression analysis of the cathepsin D gene from rock bream (Oplegnathus fasciatus)

Cathepsins are lysosomal cysteine proteases belonging to the papain family, members of which play important roles in normal metabolism for the maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin D (RbCTSD) cDNAs were identified by expressed sequence tag analysis of a lipopolysaccharide-stimulated rock bream liver cDNA library. The full-length RbCTSD cDNA (1644 bp) contained an open reading frame of 1191 bp encoding 396 amino acids. Alignment analysis revealed that the active sites and N-glycosylation sites of the deduced protein were well conserved. Phylogenetic analysis revealed that RbCTSD is most closely related to the Mi-iuy croaker (Miichthys miiuy) cathepsin D. RbCTSD was ubiquitously expressed in all the examined tissues, predominantly in muscle and kidneys. RbCTSD mRNA expression was also examined in several tissues under conditions of bacterial and viral challenge. All examined tissues of fish infected with Edwardsiella tarda (E. tarda), Streptococcus iniae (S. iniae), and red sea bream iridovirus (RSIV) showed significant increases in RbCTSD expression compared with the control. In the kidney and spleen, RbCTSD mRNA expression was markedly upregulated following infection with all tested pathogens. These findings indicate that RbCTSD plays an important role in the innate immune response of rock bream. Furthermore, these results provide important information for the identification of other cathepsin D genes in various fish species.

Characterization and expression of sweetfish (Pleco glossus altivelis) cathepsin D

Cathepsin D (CTSD) is a lysosomal acidic endoproteinase that plays an important role in immune response. In this study, we obtained sweetfish (Plecoglossus altivelis) CTSD (PaCTSD) via de-novo transcriptome sequencing of sweetfish macrophages. The full length cDNA sequence of PaCTSD was 1 955 bp encoding a propeptide of 397 amino acids. The deduced protein had a calculated molecular weight of 43.17 × 10³. Multiple alignment with other known CTSD amino acid sequences revealed amino acid conservation through the teleosts. Phylogenetic tree analysis showed that PaCTSD grouped tightly with other fish CTSD, and was close to that of Atlantic salmon and rainbow trout. Subsequently, PaCTSD was prokaryotically expressed and refolded by the urea gradient method on a nickel-nitrilotriacetic acid column. Enzyme activity analysis showed that PaCTSD exhibited pH-dependent proteolytic activity. Quantitative real-time PCR showed that PaCTSD mRNA was expressed in all detected tissues in healthy sweetfish. The highest expression was observed in the spleen and white blood cells, followed by liver, head-kidney, kidney, intestine, gill, and muscle. After Listonella anguillarum infection, PaCTSD transcripts were up-regulated significantly in liver, spleen, white blood cells, and head-kidney of sweetfish. In summary, PaCTSD has proteolytic activity and is closely involved in the immune response of sweetfish.

Changes in digestive enzyme activities during larval development of leopard grouper (Mycteroperca rosacea)

The leopard grouper is an endemic species of the Mexican Pacific with an important commercial fishery and good aquaculture potential. In order to assess the digestive capacity of this species during the larval period and aid in the formulation of adequate weaning diets, this study aimed to characterize the ontogeny of digestive enzymes during development of the digestive system. Digestive enzymes trypsin, chymotrypsin, acid protease, leucine-alanine peptidase, alkaline phosphatase, aminopeptidase N, lipase, amylase and maltase were quantified in larvae fed live prey and weaned onto a formulated microdiet at 31 days after hatching (DAH) and compared with fasting larvae. Enzyme activity for trypsin, lipase and amylase were detected before the opening of the mouth and the onset of exogenous feeding, indicating a precocious development of the digestive system that has been described in many fish species. The intracellular enzyme activity of leucine-alanine peptidase was high during the first days of development, with a tendency to decrease as larvae developed, reaching undetectable levels at the end of the experimental period. In contrast, activities of enzymes located in the intestinal brush border (i.e., aminopeptidase and alkaline phosphatase) were low at the start of exogenous feeding but progressively increased with larval development, indicating the gradual maturation of the digestive system. Based on our results, we conclude that leopard grouper larvae possess a functional digestive system at hatching and before the onset of exogenous feeding. The significant increase in the activity of trypsin, lipase, amylase and acid protease between 30 and 40 DAH suggests that larvae of this species can be successfully weaned onto microdiets during this period.

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.

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 characterisation and expression analysis of the cathepsin H gene from rock bream (Oplegnathus fasciatus)

Cathepsins are lysosomal cysteine proteases belonging to the papain family, whose members play important roles in normal metabolism for the maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin H (RbCTSH) cDNAs were identified by expressed sequence tag analysis of a lipopolysaccharide-stimulated rock bream liver cDNA library. The full-length RbCTSH cDNA (1326 bp) contained an open reading frame of 978 bp encoding 325 amino acids. The presence of an ERFNIN-like motif was predicted in the propeptide region of RbCTSH. Furthermore, multiple alignments showed that the EPQNCSAT region was well conserved among other cathepsin H sequences. Phylogenetic analysis revealed that RbCTSH is most closely related to Nile tilapia cathepsin H. RbCTSH was expressed significantly in the intestine, spleen, head kidney and stomach. RbCTSH mRNA expression was also examined in several tissues under conditions of bacterial and viral challenge. All examined tissues of fish infected with Edwardsiella tarda, Streptococcus iniae and red sea bream iridovirus (RSIV) showed significant increases in RbCTSH expression compared to the control. In the kidney and spleen, RbCTSH mRNA expression was upregulated markedly following infection with bacterial pathogens. These findings indicate that RbCTSH plays an important role in the innate immune response of rock bream. Furthermore, these results provide important information for the identification of other cathepsin H genes in various fish species.

Differential gene expression profile of the calanoid copepod, Pseudodiaptomus annandalei, in response to nickel exposure

To better understand the underlying mechanisms of reactions of copepods exposed to elevated level of nickel, the suppression subtractive hybridization (SSH) was used to elucidate the response of the copepod Pseudodiaptomus annandalei to nickel exposure at the gene level. P. annandale is one of a few copepod species that can be cultured relatively easy under laboratory condition, and it is considered to be a potential model species for toxicity study. In the present study, P. annandalei were exposed to nickel at a concentration of 8.86 mgL(-1) for 24h, after which the RNA was prepared for SSH using unexposed P. annandalei as drivers. A total of 474 clones on the middle scale in the SSH library were sequenced. Among these genes, 129 potential functional genes were recognized based on the BLAST searches in NCBI and Uniprot databases. These genes were then categorized into nine groups in association with different biological processes using AmiGO against the Gene Ontology database. Of the 129 genes, 127 translatable DNA sequences were predicted to be proteins, and the putative amino acid sequences were searched for conserved domains (CD) and proteins using the CD-Search service and BLASTp. Among 129 genes, 119 (92.2%) were annotated to be involved in different biological processes, while 10 genes (7.8%) were classified as an unknown-function gene group. To further confirm the up-regulation of differentially expressed genes, the quantitative real time PCR were performed to test eight randomly selected genes, in which five of them, i.e. α-tubulin, ribosomal protein L13, ferritin, separase and Myohemerythrin-1, exhibited clear up-regulation after nickel exposure. In addition, MnSOD was further studied for the differential expression pattern after nickel exposure and the results showed that MnSOD had a time- and dose-dependent expression pattern in the copepod after nickel exposure. To the best of our knowledge, this is the first attempt to investigate the toxicity effects of nickel on a copepod at molecular level.

Molecular cloning, characterization and expression of cathepsin D from grass carp (Ctenopharyngodon idella)

Cathepsin D is a lysosomal aspartic proteinase which participates in various degradation functions within the cell. In this current study, we cloned and characterized the complete cDNA of grass carp cathepsin D through 5'- and 3'-RACE. The cathepsin D contained a 56 bp 5' terminal untranslated region (5'-UTR), a 1197 bp open reading frame encoding 398 amino acids, and a 394 bp 3'-UTR. Grass carp cathepsin D shared high similarity with those from other species, and showed the highest amino acid identity of 91% to Danio rerio. Unlike many other organisms, the grass carp cathepsin D contains only one N-glycosylation site closest to the N-terminal. Real-time quantitative RT-PCR demonstrated that Cathepsin D expressed in all twelve tissues (bladder, brain, liver, heart, gill, muscle, fin, eye, intestines, spleen, gonad and head kidney). The relative expression levels of Cathepsin D in gonad and liver were 26.58 and 24.95 times as much as those in fin, respectively. The expression level of Cathepsin D in muscle approximately 16-fold higher, in intestines and spleen were 12-fold higher. The cathepsin D expression showed an upward trend during embryonic development. After challenged with Aeromonas hydrophil, the expression of grass carp cathepsin D gene showed significant changes in the four test tissues (liver, head kidney, spleen and intestines). The fact that the bacterial infection can obviously improve the cathepsin D expression in immune-related organs, may suggest that cathepsin D plays an important role in the innate immune response of grass carp.

Molecular identification and expression analysis of two distinct BPI/LBPs (bactericidal permeability-increasing protein/LPS-binding protein) from rock bream, Oplegnathus fasciatus

We identified two cDNAs designated as RbBPI/LBP-1 and RbBPI/LBP2, respectively, which were identified by expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The two cDNA displayed 36.9% identity at the translated amino acid level. Despite the low level of identity between the two genes, high conservation was seen in the BPI/LBP/CETP N-terminal, LPS-binding, the proline-rich central and the BPI/LBP/CETP C-terminal domains. The full-length RbBPI/LBP-1 cDNA (1945 bp) contained an open reading frame (ORF) of 1431 bp encoding 476 amino acids. The full-length RbBPI/LBP-2 cDNA was 2652 bp in length and contained an ORF of 1422 bp encoding 473 amino acids. RbBPI/LBP-1 was significantly expressed in the spleen, liver, intestine and gill. On the other hand, RbBPI/LBP-2 showed significant expression in the kidney, peripheral blood leukocytes, and spleen. Real-time RT-PCR was used to examine RbBPI/LBP-1 and RbBPI/LBP-2 mRNA expression in kidney under conditions of bacterial and viral challenge. Experimental infection of rock bream with Streptococcus iniae, Edwardsiella tarda, and red sea bream iridovirus resulted in significant increases in RbBPI/LBP-1 and RbBPI/LBP-2 mRNA levels in the kidneys, however, the increases in transcription was seen at different time points.

Identification and expressional analysis of two cathepsins from half-smooth tongue sole (Cynoglossus semilaevis)

Cathepsins are a family of lysosomal proteases that play an important role in protein degradation, antigen presentation, apoptosis, and inflammation. Cathepsins are divided into three groups, i.e., cysteine protease, serine protease, and aspartic protease. Cathepsin D and cathepsin L, which are aspartic protease and cysteine protease respectively, have been identified in a number of teleosts; however, the immunological relevance of fish cathepsins is largely unknown. In this study, we cloned and analyzed the expression profiles of a cathepsin D (CsCatD) and a cathepsin L (CsCatL) homologs from half-smooth tongue sole (Cynoglossus semilaevis). CsCatD is composed of 396 amino acid residues and shares 67.6-88.4% overall sequence identities with fish and human cathepsin D. Structurally CsCatD possesses an aspartic endopeptidase domain, which contains two conserved aspartic acid residues that form the catalytic site. CsCatL is 336 residues in length and shares 64.7-90.2% overall sequence identities with fish and human cathepsin L. CsCatL has an N-terminal cathepsin propeptide inhibitor domain followed by a Papain family cysteine protease domain, the latter containing four conserved catalytic residues: Gln-133, Cys-139, His-279, and Asn-303. Recombinant CsCatL purified from Escherichia coli exhibited apparent protease activity. Quantitative real time RT-PCR analysis detected constitutive expression of CsCatD and CsCatL in multiple tissues, with the lowest level found in heart and the highest level found in liver. Experimental challenge of tongue sole with the bacterial pathogen Vibrio anguillarum and megalocytivirus caused significant inductions of both CsCatD and CsCatL expression in kidney and spleen in time-dependent manners. Immunization of the fish with a subunit vaccine also enhanced CsCatD and CsCatL expression in the first week post-vaccination. These results suggest involvement of CsCatD and CsCatL in host immune reactions to bacterial and viral infections and in the process of antigen-induced immune response.

Molecular identification and expression analysis of cathepsins O and S from rock bream, Oplegnathus fasciatus

Cathepsins are lysosomal cysteine proteases belonging to the papain family, members of which play important roles in normal metabolism for maintenance of cellular homeostasis. Rock bream (Oplegnathus fasciatus) cathepsin O and S (RbCTSO and RbCTSS, respectively) cDNAs were identified by expressed sequence tag (EST) analysis of a lipopolysaccharide (LPS)-stimulated rock bream liver cDNA library. The full-length RbCTSO cDNA (1698 bp) contained an open reading frame (ORF) of 1017 bp encoding 338 amino acids. The full-length RbCTSS cDNA was 1401 bp in length and contained an ORF of 1014 bp encoding 337 amino acids. RbCTSO was significantly expressed in the liver, peripheral blood lymphocytes (PBLs) and spleen. On the other hand, RbCTSS showed significant expression in the liver, trunk kidney, muscle and gills. Real-time RT-PCR was used to examine RbCTSO and RbCTSS mRNA expression in several tissues (kidney, spleen, liver and gill) under conditions of bacterial and viral challenge. Experimental infection of rock bream with Streptococcus iniae and red sea bream iridovirus (RSIV) resulted in significant increases in RbCTSO and RbCTSS mRNA levels in the tissues.

Molecular characterization and expression analysis of the channel catfish cathepsin D genes

Cathepsin D is a lysosomal aspartic proteinase that participates in various degradation functions of the cell. In this study, we characterized the cathepsin D genes in channel catfish and found two genes encoding catfish cathepsin D, referred to as cathepsin D1 and D2 genes. These two genes are highly similar in genomic structure and organization, sharing a moderate level of amino acid sequence similarity (56%). Genomic Southern analysis suggested the presence of a single copy of each of the cathepsin D1 and D2 genes. Phylogenetic analysis provided strong evidence that two cathepsin D genes are present in most of the teleost lineage, with cathepsin D2 likely having been lost in some higher vertebrate lineages. The catfish cathepsin D1 and D2 genes are expressed in virtually all the 11 tested tissues (brain, gill, heart, head kidney, trunk kidney, intestine, liver, muscle, skin, spleen, and stomach) on the transcript level, but appear to exhibit greater levels of expression in immune-related tissues and organs. Upon infection with Edwardsiella ictaluri, the expression of the catfish cathepsin D genes showed the most significant changes in liver and head kidney, with time points and magnitude of transcript changes varying between the two genes. We additionally examined bacterially-mediated changes of expression in gill, intestine, and trunk kidney. The fact that bacterial infection can induce expression of the cathepsin D genes and that they appeared to be expressed naturally at higher levels in immune-related organs may suggest that they are an important component of the innate immune response of catfish against bacterial infections.

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

Cathepsins are lysosomal cysteine proteases of the papain family that play an important role in intracellular protein degradation and turn over within the lysosomal system. In the present study, full-length sequences of cathepsin B (RbCathepsin B) and L (RbCathepsin L) were identified after transcriptome sequencing of rock bream Oplegnathus fasciatus mixed tissue cDNA. Cathepsin B was composed of 330 amino acid residues with 36 kDa predicted molecular mass. RbCathepsin L contained 336 amino acid residues encoding for a 38 kDa predicted molecular mass protein. The sequencing analysis results showed that both cathepsin B and L contain the characteristic papain family cysteine protease signature and active sites for the eukaryotic thiol proteases of cysteine, asparagine and histidine. In addition, RbCathepsin L contained EF hand Ca(2+) binding and cathepsin propeptide inhibitor domains. The rock bream cathepsin B and L showed the highest amino acid identity of 90 and 95% to Lutjanus argentimaculatus cathepsin B and Lates calcarifer cathepsin L, respectively. By phylogenetic analysis, cathepsin B and L exhibited a high degree of evolutionary relationship to respective cathepsin family members of the papain superfamily. Quantitative real-time RT-PCR analysis results confirmed that the expression of cathepsin B and L genes was constitutive in all examined tissues isolated from un-induced rock bream. Moreover, activation of RbCathepsin B and L mRNA was observed in both lipopolysaccharide (LPS) and Edwardsiella tarda challenged liver and blood cells, indicating a role of immune response in rock bream.

Cloning and expression of stearoyl-CoA desaturase 1 (SCD-1) in the liver of the Sichuan white goose and landes goose responding to overfeeding

The EST sequence of goose (Anser cygnoides) Stearoyl-CoA desaturase 1(SCD-1) was obtained from a subtractive cDNA library. To further investigate the role of SCD-1 in lipid metabolism in geese, 5'-RACE and 3'-RACE were carried out in this study to obtain the complete cDNA sequence of goose SCD-1, which contained a 29-bp 5' UTR, a 1074-bp open reading frame (ORF) encoding 357 amino acids, and a 125-bp 3' UTR. The expression of SCD-1 was measured in several tissues, and the effects of overfeeding on the expression of SCD-1 were studied. The results of real time RT-PCR demonstrated that, compared to the brain, goose SCD-1 mRNA was more abundant in the liver. Overfeeding markedly increased the mRNA expression of SCD-1 in the liver of Sichuan White and Landes geese, and gene expression was markedly higher in the Sichuan White goose than in the landes goose. The mRNA abundance of SCD-1 in the liver had significant positive correlations with triacylglycerol (TG) content in liver lipids and in the levels of plasma insulin and very low-density lipoproteins (VLDL) levels in Sichuan white geese. However, the mRNA abundance of SCD-1 in the livers of Landes geese had only significant positive correlations with the TG content in liver lipids. In conclusion, SCD-1 is not only critical for hepatic steatosis in geese but is also important for the difference in lipid deposition in the livers of the two breeds.

Cathepsin B differential expression and enzyme processing and activity during Fundulus heteroclitus embryogenesis

The role of lysosomal proteases such as cathepsin B (Ctsb) and one of the paralogs of cathepsin L (Ctsla) during yolk metabolism in fish oocytes is well established. However, the function of Ctsb during embryogenesis, particularly in marine teleosts, has been poorly documented. In this study, the spatio-temporal expression of Ctsb and Ctsla, their enzymatic activities, and the processing of the Ctsb and its cellular localization, was investigated in developing embryos of the killifish (Fundulus heteroclitus). Both fhctsb and fhctsla transcript levels, as well as cathepsin B- and L-like activities, gradually increased in embryos from the 2-4 cell stage up to 7 days post-fertilization. During the morula to gastrula transition an increase of the active FhCtsb single chain form was followed by a rise in cathepsin B activity, which were apparently regulated by post-transcriptional mechanisms. During neurulation, a 8-fold increase in cathepsin B activity was accompanied by a more moderate increase in cathepsin L activity, which was 6-fold enhanced by 7 dpf. These increased catalytic activities were well-correlated to changes in the electrophoretic pattern of yolk proteins and a strong expression of fhctsb and its protein product in the yolk syncytial layer. The increase of cathepsin B activity was further correlated with an increment of the relative amount of the FhCtsb single and double chain forms, both active forms of FhCtsb. These results suggest that FhCtsb may be involved in the mechanisms underlying the onset of gastrulation in F. heteroclitus embryos, and may play complementary roles with FhCtsla during yolk metabolism.

Cathepsin D from the hepatopancreas of the cuttlefish (Sepia officinalis): purification and characterization

Cathepsin D from the hepatopancreas of cuttlefish ( Sepia officinalis ) was purified to homogeneity by precipitation with ammonium sulfate (30-60%, w/v), Sephadex G-100 gel filtration, Mono-S cation-exchange chromatography, Sephadex G-75 gel filtration, and Mono-S FPLC with a 54-fold increase in specific activity and 17% recovery. The molecular weight of the purified cathepsin D was estimated to be 37.5 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On the basis of the native-PAGE and hemoglobin zymography, the purified protease appeared as a single band. The optimum pH and temperature for the cathepsin D activity were pH 3.0 and 50 °C, respectively, using hemoglobin as a substrate. The purified enzyme was completely inhibited by pepstatin A; however, no inhibition was observed with phenylmethylsulfonyl fluoride and ethylenediaminetetraacetic acid. Moreover, the activity was strongly inhibited by SDS and molybdate and enhanced by ATP. The purified cathepsin D was activated by Mg(2+), Ni(2+), Zn(2+), Cu(2+), Cd(2+), Sr(2+), and Co(2+) ions, whereas it was not affected by Na(+), K(+), and Ca(2+) ions. The N-terminal amino acid sequence of the first 13 amino acids of the purified cathepsin D was APTPEPLSNYMDA. S. officinalis cathepsin D, which showed high homology with cathepsin D from marine vertebrates and invertebrates, had a Pro residue at position 6 and a Ser residue at position 8, where Thr and Lys are common in all marine vertebrates cathepsins D. S. officinalis cathepsin D showed high efficiency for the hydrolysis of myofibrillar proteins extracted from cuttlefish muscle.

cDNA cloning, characterization, and expression analysis of the Rac1 gene from Scophthalmus maximus

Rac1 is a small GTP-binding protein that belongs to the Rho small GTPases, which are important signaling molecules that regulate the dynamics of the actin cytoskeleton and mediate changes in cell morphology and motility. The EST sequence of Rac1 from turbot (Scophthalmus maximus L.) was obtained from a subtractive cDNA library previously. In this study, the full-length cDNA sequence of turbot Rac1 was obtained, which was 2420 nucleotides (nt) encoding a protein of 192 amino acids, with a putative molecular weight of 21.3 kDa. At the amino-acid level, turbot Rac1 was highly conserved to previously characterized GTPases of Rac sub-family, and was nearly identical to human Rac1 (95.3% identity). Quantitative real-time PCR demonstrated that the Rac1 was constitutively expressed in all tissues examined, but at different levels. Upon challenge with Vibrio harveyi, the expression level of Rac1 fluctuated in the liver at different time points. In the head kidney, its expression level decreased to the lowest at 4 h, and then increased to the background level at 24 h. The remarkable degree of evolutionary conservation observed in turbot Rac1 primary structure together with its changing in expression level upon challenge suggested a functionally important role for this Rho family member in the immune response.

Identification of a cathepsin D potentially involved in H2A cleavage from scallop Chlamys farreri

We report here a cDNA and its deduced amino acid sequence encoding a cathepsin D-like, aspartic protease from Chlamys farreri (denoted as CfCD) by expressed sequence tag and rapid amplification of cDNA ends techniques. The cDNA of CfCD consisted of 1,810 nucleotides with a canonical polyadenylation signal sequence AATAAA and a polyA tail, encoding a short signal peptide of 18 amino acids, a pro-enzyme peptide of 29 amino acid residues, and a mature enzyme of 349 residues. The deduced amino acid sequence of CfCD was significant homology to CDs from human, fish and invertebrates. Two conserved catalytic motifs (VFDTGSSNLWV and AIADTGTSLLVG) and two potential N-glycosylation sites were also identified in the deduced amino acid sequence of CfCD. All this characteristics indicated CfCD should be a member of CDs family. The mRNA spatial expression of CfCD in mantle, gonad, gill, hemocytes, hepatopancreas and adductor muscle was examined by quantitative real-time PCR. mRNA transcripts of CfCD could be detected in all tissues with the highest expression level in hepatopancreas. After 8 h Vibrio anguillarum challenge, the expression level of CfCD changed significantly in all examined tissues except mantle (P = 0.183) and hemocytes (P = 0.069). The information generated in the present study would be helpful for future studies aiming at investigating the detailed functions of cathepsin D from marine invertebrates.