Cloning and sequencing of caspase 6 in rainbow trout, Oncorhynchus mykiss, and analysis of its expression under conditions known to induce apoptosis

Impact of different levels of handling on Solea senegalensis culture: effects on growth and molecular markers of stress

Aquaculture routine practices may cause stress induction on the fish and compromise their welfare affecting the production. This experiment aimed to evaluate the potential links between handling during culture with stress responses and growth on Senegalese sole (Solea senegalensis). We worked with two fish cohorts in terms of initial body weight and culture stage: Trial 1 included specimens in the fattening stage (226 ± 4.96 g) and Trial 2 animals in the pre-fattening stage (27.20 ± 0.44 g). The tested culture protocol, which lasted 6 and 4 months for Trial 1 and 2, respectively, mainly reduced handling-derived stressors in the experimental tanks via lowering routine samplings to a minimum. This decrease of the handling-derived stress was reflected in both trials with lower concentration of circulating cortisol in blood plasma from the experimental fish when compared to controls. Moreover, the proposed protocol promoted higher growth in the fish cultured in the less disturbing protocol in Trial 2. Higher specific growth rates and mean body weight and length were reported. In order to further explore the potential beneficial effects of our protocol, we studied the musculoskeletal from Trial 2 gene expression of key genes regulating glucocorticoid signaling pathway and apoptosis: glucocorticoid receptors 1 and 2 (gr1, gr2), heat shock protein 90 AA (hsp90aa), and caspase 6 (casp6). In line with the cortisol reduced level in this trial, gr1, hsp90aa, and casp6 genes showed lower expression in the samples coming from the experimental group. The findings of this study provide valuable information to the aquaculture industry for the management of Solea senegalensis stress and welfare.

Expression Analysis of the Caspase10 from Olive Flounder (Paralichthys olivaceus) against Viral Hemorrhagic Septicemia Virus (VHSV) Challenge

The caspase10 encodes an initiating caspase that plays an important role in the maintaining the cellular homeostasis by regulating the steps involved in the immune response and cell death. We investigated the expression of caspase10 during the different developmental stages and in olive flounder tissues. Caspase10 increased in the late stage of the formation of immune tissue, and high expression was observed in the gills, kidney, skin, and spleen. The current study analyzed the expressional changes of caspase10 in olive flounder infected with viral hemorrhagic septicemia virus (VHSV). One of the major causes of mass mortality, VHSV infection in olive flounder attributes to significant expression of caspase10 in the gills, spleen, skin, and kidneys. The results indicate a close association of caspase10 expression with the immune response to VHSV infection in olive flounder. The observations could form the basis data for exploration of other fish immune system.

miR-34a Regulates the Activity of HIF-1a and P53 Signaling Pathways by Promoting GLUT1 in Genetically Improved Farmed Tilapia (GIFT, Oreochromis niloticus) Under Hypoxia Stress

In fish under hypoxia stress, homeostasis can become imbalanced, leading to tissue and organ damage and decreased survival. Therefore, it is useful to explore the molecular and physiological regulation mechanisms that function in fish under hypoxia stress. The microRNA miR-34a is involved in fat and glycogen metabolism, and in apoptosis. In this study, we first verified that GLUT1, the gene encoding glucose transporter 1, is a potential target gene of miR-34a in genetically improved farmed tilapia (GIFT, Oreochromis niloticus) by dual luciferase reporter assays. Then, we clarified the regulatory relationship between miR-34a and GLUT1 by qRT-PCR analyses. We analyzed the regulatory effects of knockdown or promotion of GLUT1 expression in vitro and in vivo in GIFT under hypoxia stress. The results confirm that GLUT1 is a target gene of miR-34a in GIFT. Down-regulation of miR-34a significantly promoted GLUT1 expression. Knockdown of GLUT1 reduced the glycogen content in GIFT liver cells, inhibited HIF-1a gene expression, up-regulated the expression of genes involved in P53 signaling pathways (P53 and CASPASE-3 genes), and accelerated hepatocyte apoptosis under hypoxia stress. Compared with the control group, the group injected in the tail vein with miR-34a antagomir showed up-regulated expression of GLUT1 in the liver, increased liver glycogen content at 96 h of hypoxia stress, down-regulated expression of P53 and CASPASE-3, and decreased serum aspartate aminotransferase and alanine aminotransferase enzyme activities. Our results provide information about the molecular regulation mechanism of miRNAs and their target genes in fish during the response to hypoxia stress.

Down-regulation of corticosteroid receptor in leucocytes of stressed rainbow trout

The relationship between stress and immunosuppression was investigated in peripheral blood leucocytes (PBL) in rainbow trout, with reference to corticosteroid receptor (CR) expression and responses to cortisol- and/or lipopolysaccharide (LPS)-administration. Confinement stress in shallow water resulted in a sustained elevation of plasma cortisol, whereas lysozyme and immunoglobin levels were suppressed. Significant increases in mRNA levels of caspase-6 and insulin-like growth factor (IGF)-I were observed in PBL isolated from stressed fish. Confinement stress also suppressed proinflammatory cytokine, interleukin (IL)-1β, expression in PBL. There were decreasing tendencies for the mRNA levels of CRs in PBL of stressed fish. In-vitro treatment of cortisol and LPS on isolated PBL from unstressed trout increased both IL-1 β and CR mRNA expression. However, in PBL from stressed fish, cortisol and LPS treatment increased IL-1 β but not CR mRNA levels. Proliferative activities estimated as in-vitro incorporation of bromodeoxyuridine (BrdU) were decreased by cortisol in PBL from the unstressed and stressed fish groups; however, LPS-stimulated proliferation was observed only in the unstressed fish. Ratios of apoptotic PBL quantified as cell fragmentation using an automated cell counter were increased by cortisol in both groups; however, LPS-stimulated apoptosis was observed only in the stressed fish. Our study reveals cortisol has immune-suppressive effects in stressed fish, irrespective of CR down-regulation and desensitization. The complexity of immune-endocrine interaction is shown by the stress-induced attenuation of LPS effects.

Modulation of posterior intestinal mucosal proteome in rainbow trout (Oncorhynchus mykiss) after Yersinia ruckeri infection

Yersinia ruckeri is the causative agent of enteric redmouth disease in salmonids. In fish, the intestine represents an important site of nutrient uptake, host–pathogen interactions, and defense. The posterior intestine can be inflamed, reddened, and filled with an opaque, yellowish fluid during Y. ruckeri infection. Herein, we report an investigation on the proteome alteration in the posterior intestinal mucosa of rainbow trout (Oncorhynchus mykiss) after exposure to Y. ruckeri. The intestinal mucosal proteins were identified and quantified by a shotgun proteomic approach by applying data-independent quantification with sequential windowed acquisition of all theoretical mass spectra (SWATH). A total of 437 proteins were found to be differentially up- or downregulated in the posterior intestine. Gene ontology of upregulated proteins pointed to their involvement into exopeptidase, endopeptidase, and hydrolase activities, while the downregulated proteins were involved in lipid metabolism, actin binding, and translation processes. Additionally, upregulated proteins were predicted to be involved in lysosome, oxidative phosphorylation, and metabolic pathways, while downregulated proteins were implicated in focal adhesion, regulation of actin cytoskeleton, protein digestion and absorption pathways. This study showed that Y. ruckeri infection can alter protein abundance involved in serine-type carboxypeptidase, cysteine and aspartic-type endopeptidases, metallopeptidases, antioxidant defense, calcium ion binding, glycolytic and carbohydrate metabolic processes in the proteome of the intestinal mucosa of rainbow trout.

Glucocorticoid receptor in ayu (Plecoglossus altivelis): Genomic and non-genomic effects on monocytes/macrophages function

The glucocorticoid receptor (GR) is an important feedback regulator of the hypothalamic-pituitary-interrenal (HPI) axis. However, there are a limited number of studies focused on host-pathogen interactions in which an association between GR and immune response has been evaluated in monocytes/macrophages (MO/MФ) after being challenged with highly pathogenic bacteria. Here, we cloned the cDNA sequence of the glucocorticoid receptor (PaGR) gene from ayu fish. The PaGR transcript was expressed in all tissues, and changes in expression were observed in immune tissues and MO/MФ after live Vibrio anguillarum infection. Subsequently, PaGR was expressed and purified to prepare anti-PaGR antibodies. We analyzed the subcellular localization of PaGR. PaGR was expressed not only in the intracellular space but also in the plasma membrane. PaGR activation decreased the expression of pro-inflammatory cytokines and increased the expression of anti-inflammatory cytokines. However, PaGR activation suppressed the phagocytosis activity of V. anguillarum-infected ayu MO/MФ via a non-genomic pathway. Interestingly, PaGR activation could enhance MO/MФ bacterial killing capability and apoptosis. Therefore, PaGR may modulate the immune response in ayu MO/MФ by genomic and non-genomic pathways.

Characterization of the responses of the caspase 2, 3, 6 and 8 genes to immune challenges and extracellular ATP stimulation in the Japanese flounder (Paralichthys olivaceus)

BACKGROUND

Caspases are a family of conserved intracellular cysteine-dependent aspartate-specific cysteine proteases that play important roles in regulating cell death and inflammation. Our previous study revealed the importance of the inflammatory caspase 1 gene in extracellular ATP-mediated immune signaling in Japanese flounder, Paralichthys olivaceus. To explore the potential roles of other caspases in P. olivaceus innate immunity, we extended our study by characterizing of the responses of four additional P. olivaceus caspase genes, termed JfCaspase 2, 3, 6 and 8, to inflammatory challenge and extracellular ATP stimulation.

RESULTS

Sequence analysis revealed that the domain structures of all the Japanese flounder caspase proteins are evolutionarily conserved. Quantitative real-time PCR analysis showed that the JfCaspase 2, 3, 6 and 8 genes were expressed ubiquitously but at unequal levels in all examined Japanese flounder normal tissues. In addition, the basal gene expression levels of JfCaspase 2, 3, 6 and 8 were higher than those of JfCaspase 1 in both Japanese flounder head kidney macrophages (HKMs) and peripheral blood leukocytes (PBLs). Furthermore, immune challenge experiments showed that the inflammatory stimuli LPS and poly(I:C) significantly modulated the expression of the JfCaspase 2, 3, 6 and 8 genes in Japanese flounder immune cells. Finally, DNA fragmentation, associated with increased extracellular ATP-induced JfCaspase 2, 3, 6 and 8 gene expression and enzymatic activity, was inhibited by the caspase inhibitor Z-VAD-FMK in the HKMs.

CONCLUSION

Our findings demonstrate broad participation of multiple caspase genes in response to inflammatory stimulation in Japanese flounder immune cells and provide new evidence for the involvement of caspase(s) in extracellular ATP-induced apoptosis in fish.

A novel caspase-6 from sea cucumber Holothuria leucospilota: Molecular characterization, expression analysis and apoptosis detection

In this study, a novel caspase-6 named HLcaspase-6 was identified from sea cucumber Holothuria leucospilota. The full-length cDNA of HLcaspase-6 is 2195 bp in size, containing a 126 bp 5'-untranslated region (UTR), a 1043 bp 3'-UTR and a 1026 bp open reading frame (ORF) encoding a protein of 341 amino acids with a deduced molecular weight of 38.57 kDa. HLcaspase-6 contains the common signatures of the caspase family, including the conserved pentapeptide motif QACRG, as well as the P20 and P10 domains. In addition, HLcaspase-6 contains a short pro-domain. HLcaspase-6 mRNA is ubiquitously expressed in all tissues examined, with the highest transcript level in the intestine, followed by coelomocytes. In in vitro experiments, the expression of HLcaspase-6 mRNA in coelomocytes was significantly up-regulated by lipopolysaccharides (LPS) or polyriboinosinic-polyribocytidylic acid [poly (I:C)] challenge, suggesting that HLcaspase-6 might play important roles in the innate immune defense of sea cucumber against bacterial and viral infections. Moreover, we further confirmed that overexpression of HLcaspase-6 could induce apoptosis and activate the p53 signal pathway.

Effects of thermal stress on the expression of glucocorticoid receptor complex linked genes in Senegalese sole (Solea senegalensis): Acute and adaptive stress responses

The present study examined the short and mid-term effects of a rise in temperature from 18°C to 24°C on the expression of genes related to the stress response regulation in juveniles of Senegalese sole, Solea senegalensis. The animals were exposed to a temperature increase of 6°C, after 1month of acclimation at 18°C. After this process, samples of different tissues were collected from a total of 96 fish at four sampling points: 1h, 24h, 3days and 1week. The transcript levels of a set of genes involved in the stress response such as glucocorticoid receptors 1 and 2, corticotrophin-releasing factor, corticotrophin-releasing factor binding proteins, proopiomelanocortin A and B, and cellular stress defense (heat shock protein 70, 90AA and 90AB) were quantified at these sampling points. Additionally, blood samples were also taken to measure the circulating plasma cortisol concentration. Thermal stress induced by increasing temperature prompted an elevation of plasma cortisol levels in juvenile Senegalese sole after 1h as a short-term response, and a consecutive increase after one week, as a mid-term response. Senegalese sole seemed to respond positively in terms of adaptive mechanisms, with a rapid over-expression of grs and hsps in liver and brain, significantly higher after one hour post stress, denoting the fast and acute response of those tissues to a rapid change on temperature. The ratio hsp90/gr also increased 24h after thermal shock, ratio proposed to be an adaptive mechanism to prevent proteosomal degradation of GR. As a mid-term response, the elevation of brain crfbp gene expression one week after thermal shock could be an adaptive mechanism of negative feedback on HPI axis. Taken together, these data suggested an initial up-regulation of the glucocorticoid receptor complex linked genes in response to a temperature increase in Senegalese sole, with heat shock protein 90 potentially being a regulatory factor for the glucocorticoid receptor in the presence of cortisol.

Apoptosis in fish: environmental factors and programmed cell death

Apoptosis, a form of programmed cell death, is a critical component in maintaining homeostasis and growth in all tissues and plays a significant role in immunity and cytotoxicity. In contrast to necrosis or traumatic cell death, apoptosis is a well-controlled and vital process characterized mainly by cytoplasmic shrinkage, chromatin condensation, DNA fragmentation, membrane blebbing and apoptotic bodies. Our understanding of apoptosis is partly based on observations in invertebrates but mainly in mammals. Despite the great advantages of fish models in studying vertebrate development and diseases and the tremendous interest observed in recent years, reports on apoptosis in fish are still limited. Although apoptotic machinery is well conserved between aquatic and terrestrial organisms throughout the history of evolution, some differences exist in key components of apoptotic pathways. Core parts of apoptotic machinery in fish are virtually expressed as equivalent to the mammalian models. Some differences are, however, evident, such as the extrinsic and intrinsic pathways of apoptosis including lack of a C-terminal region in the Fas-associated protein with a death domain in fish. Aquatic species inhabit a complex and highly fluctuating environment, making these species good examples to reveal features of apoptosis that may not be easily investigated in mammals. Therefore, in order to gain a wider view on programmed cell death in fish, interactions between the main environmental factors, chemicals and apoptosis are discussed in this review. It is indicated that apoptosis can be induced in fish by exposure to environmental stressors during different stages of the fish life cycle.

Molecular cloning and characterization of four caspases members in Apostichopus japonicus

The caspase family representing aspartate-specific cysteine proteases have been demonstrated to possess key roles in apoptosis and immune response. We previously demonstrated that LPS challenged Apostichopus japonicus coelomocyte could significantly induced apoptosis in vitro. However, apoptosis related molecules were scarcely investigated in this economic species. In the present work, we cloned and characterized four members caspase family from A. japonicus (designated as Ajcaspase-2, Ajcaspase-3, Ajcaspase-6, and Ajcaspase-8, respectively) by RACE. Multiple sequence alignment and structural analysis revealed that all Ajcaspases contained the conservative CASC domain at C terminal, in which some unique features for each Ajcaspase made them different from each other. These specific domains together with phylogenetic analysis supported that all these four identified proteins belonged to novel members of apoptotic signaling pathway in sea cucumber. Tissue distribution analysis revealed that four Ajcaspase genes were constitutively expressed in all examined tissues. The expression of Ajcaspase-2 was tightly correlated with that of Ajcaspase-8 in each detected tissues. Ajcaspase-3 and Ajcaspase-6 transcripts were both highly expressed in immune tissue of coelomocytes. Furthermore, the Vibrio splendidus challenged sea cucumber coelomocytes could significantly up-regulate the mRNA expressions of four genes. The expression levels of Ajcaspase-2 and Ajcaspase-8 were relative earlier than those of Ajcaspase-6 and Ajcaspase-3, respectively, which could be inferred that Ajcapase-2 might directly modulate Ajcaspase-6, and Ajcaspase-8 initiate the expression of Ajcaspase-3. The induce expressions differed among each Ajcaspase depending upon their roles such as initiator or effector caspase. All our results demonstrated that four Ajcaspases present diversified functions in apoptotic cascade signaling pathway of sea cucumber under immune response.

Expression profile of six stress-related genes and productive performances of fast and slow growing broiler strains reared under heat stress conditions

High temperature is one of the prominent environmental factors causing economic losses to the poultry industry as it negatively affects growth and production performance in broiler chickens. We used One Step TaqMan real time RT-PCR (reverse transcription polymerase chain reaction) technology to study the effects of chronic heat stress on the expression of genes codifying for the antioxidative enzymes superoxide dismutase (SOD), and catalase (CAT), as well as for heat shock protein (HSP) 70, HSP90, glucocorticoid receptor (NR3C1), and caspase 6 (CASP6) in the liver of two different broiler genetic strains: Red JA Cou Nu Hubbard (CN) and Ross 508 Aviagen (RO). CN is a naked neck slow growing broiler intended for the free range and/or organic markets, whereas RO is selected for fast growing. We also analysed the effect of chronic heat stress on productive performances, and plasma corticosterone levels as well as the association between transcriptomic response and specific SNPs (single nucleotide polymorphisms) in each genetic strain of broiler chickens. RO and CN broilers, 4 weeks of age, were maintained for 4 weeks at either 34 °C or 22 °C. The results demonstrated that there was a genotype and a temperature main effect on the broilers' growth from the 4th to the 8th week of age, but the interaction effect between genotype and temperature resulted not statistically significant. By considering the genotype effect, fast growing broilers (RO) grew more than the slow growing ones (CN), whereas by considering the temperature effect, broilers in unheated conditions grew more than the heat stressed ones. Corticosterone levels increased significantly in the blood of heat stressed broilers, due to the activation of the HPA (hypothalamic-pituitary-adrenocortical axis). Carcass yield at slaughter was of similar values in the 4 cohorts (genotype/temperature combinations or treatment groups), ranging from 86.5 to 88.6%, whereas carcass weight was negatively influenced by heat stress in both broiler strains. Heat stress affected gene expression by downregulating CASP6 and upregulating CAT transcript levels. HSPs, SOD and NR3C1 mRNA levels remained unaffected by heat stress. The differences found in the mRNA copies of CASP6 gene could be partly explained by SNPs.

Effect of infectious hypodermal and haematopoietic necrosis virus (IHHNV) infection on caspase 3c expression and activity in freshwater prawn Macrobrachium rosenbergii

Caspase 3c (MrCasp3c) was sequenced from the freshwater giant prawn Macrobrachium rosenbergii using Illumina Solexa Genome Analyzer Technique. MrCasp3c consisted of 2080 bp nucleotide encoded 521 polypeptide with an estimated molecular mass of 59 kDa. MrCasp3c sequence contains caspase family p20 domain profile and caspase family p10 domain profile at 236-367 and 378-468 respectively. The quantitative real time PCR analysis revealed a broad expression of MrCasp3c with the highest expression in haemocyte and the lowest in stomach. The expression of MrCasp3c after challenge with the infectious hypodermal and haematopoietic necrosis virus (IHHNV) was tested in haemocyte. In addition, MrCasp3c was expressed in Escherichia coli by prokaryotic expression plasmid pMAL-c2x. The enzyme activity of MrCasp3c was also found to be up-regulated by IHHNV in haemocyte and hepatopancreas tissues. This study suggested that MrCasp3c may be an effector caspase associated with the induction of apoptosis which is potentially involved in the immune defence of M. rosenbergii.

Molecular cloning and characterisation of the rock bream, Oplegnathus fasciatus, Fas (CD95/APO-1), and its expression analysis in response to bacterial or viral infection

Fas belongs to the tumour necrosis factor (TNF) receptor superfamily and can transmit a death signal leading to apoptosis. In the present study, we isolated the full-length cDNA for rock bream (Oplegnathus fasciatus) Fas (RbFas). The full-length RbFas cDNA was 1770 bp long and contained an open reading frame of 957 bp that encoded 319 amino acid residues with a predicted molecular mass of 35.1 kDa. The 319 amino-acid predicted RbFas sequence is homologous to other Fas sequences, contains three cysteine-rich domains and a death domain (DD) and two potential N-glycosylation sites. Expression of RbFas mRNA was detected in nine different tissues from healthy rock bream and was the highest in red blood cells. In analyses of mitogen-stimulated RbFas expression in peripheral blood leucocytes, expression of RbFas mRNA was observed between 1 and 36 h after stimulation with LPS, and 1 and 3 h stimulation with poly I:C. In the case of bacterial injection, the RbFas transcript peaked 6 h after injection in both the kidney and the spleen. Otherwise, the RbFas transcript peaked after 1 h in spleen and 6 h in kidney following injection with RSIV.

A novel Fas ligand in mollusk abalone: molecular characterization, immune responses and biological activity of the recombinant protein

Fas ligand is a member of the TNF superfamily that plays an important role by inducing apoptosis and homeostasis of immune responses. The gene encoding Fas ligand was isolated from a disk abalone (Haliotis discus discus) cDNA library, denoted as the AbFas ligand. It contains an 1832bp transcript with a 945bp open reading frame, encoding 315 amino acids. The AbFas ligand showed characteristic transmembrane and TNF family signature domains. The deduced amino acid comparison showed that the AbFas ligand exhibits 22.0, 16.1 and 14.5% identities to human Fas ligand, TNF-alpha, and lymphotoxin (LT-alpha), respectively. Phylogenetic analysis indicates that the AbFas ligand belongs to the invertebrate TNF family and it is closely related to vertebrate Fas ligand counterparts. Quantitative real-time PCR analysis results showed that the AbFas ligand transcripts were constitutively expressed in abalone hemocytes, gills, mantle, muscle, digestive tract and digestive gland in a tissue-specific manner. By immune stimulation, AbFas ligand mRNA was significantly (p<0.05) up-regulated after infection with a mixture of bacteria (Vibrio alginolyticus, Vibrio parahemolyticus, and Listeria monocytogenes), viral haemorrhagic septicaemia virus (VHSV), and lipopolysaccharide (LPS) in abalone gills. The recombinant AbFas ligand was over-expressed in Escherichia coli (E. coli) and purified using a pMAL protein fusion system. This recombinant AbFas ligand showed its biological activity by inducing both superoxide anion (O(2-) and H(2)O(2) in human THP-1 cells in concentration-dependant manner. Correlating the AbFas ligand transcriptional up-regulation against bacteria, virus and LPS with the biological activity of its recombinant protein, we could suggest that the abalone Fas ligand may control microbial infection by inducing O(2-), H(2)O(2) and other ROS.

Caspases: evolutionary aspects of their functions in vertebrates

Caspases (cysteine-dependent aspartyl-specific protease) belong to a family of cysteine proteases that mediate proteolytic events indispensable for biological phenomena such as cell death and inflammation. The first caspase was identified as an executioner of apoptotic cell death in the worm Caenorhabditis elegans. Additionally, a large number of caspases have been identified in various animals from sponges to vertebrates. Caspases are thought to play a pivotal role in apoptosis as an evolutionarily conserved function; however, the number of caspases that can be identified is distinct for each species. This indicates that species-specific functions or diversification of physiological roles has been cultivated through caspase evolution. Furthermore, recent studies suggest that caspases are also involved in inflammation and cellular differentiation in mammals. This review highlights vertebrate caspases in their universal and divergent functions and provides insight into the physiological roles of these molecules in animals.

Fish as model systems for the study of vertebrate apoptosis

Apoptosis is a process of pivotal importance for multi-cellular organisms and due to its implication in the development of cancer and degenerative disease it is intensively studied in humans and mammalian model systems. Invertebrate models of apoptosis have been well-studied, especially in C. elegans and D. melanogaster, but as these are evolutionarily distant from mammals the relevance of findings for human research is sometimes limited. Presently, a non-mammalian vertebrate model for studying apoptosis is missing. However, in the past few years an increasing number of studies on cell death in fish have been published and thus new model systems may emerge. This review aims at highlighting the most important of these findings, showing similarities and dissimilarities between fish and mammals, and will suggest topics for future research. In addition, the outstanding usefulness of fish as research models will be pointed out, hoping to spark future research on this exciting, often underrated group of vertebrates.

Caspases - an update

Caspases belong to a family of highly conserved aspartate-specific cysteine proteases and are members of the interleukin-1beta-converting enzyme family, present in multicellular organisms. The caspase gene family consists of 15 mammalian members that are grouped into two major sub-families, namely inflammatory caspases and apoptotic caspases. The apoptotic caspases are further subdivided into two sub-groups, initiator caspases and executioner caspases. The caspases form a caspase-cascade system that plays the central role in the induction, transduction and amplification of intracellular apoptotic signals for cell fate determination, regulation of immunity, and cellular proliferation and differentiation. The substrates of apoptotic caspases have been associated with cellular dismantling, while inflammatory caspases mediate the proteolytic activation of inflammatory cytokines. The activation of this delicate caspase-cascade system and its functions are regulated by a variety of regulatory molecules, such as the inhibitor of apoptosis protein (IAP), FLICE, calpain, and Ca(2+). Based on the available literature we have reviewed and discussed the members of the caspase family, caspase-cascade system, caspase-regulating molecules and their apoptotic and non-apoptotic functions in cellular life and death. Also recent progress in the molecular structure and physiological role of non-mammalian caspases such as paracaspases, metacaspases and caspase-like-protease family members are included in relation to that of mammalian species.

Molecular cloning, expression, and functional analysis of caspase-10 from Japanese flounder Paralichthys olivaceus

We isolated and sequenced caspase-10 cDNA and gene from Japanese flounder, Paralichthys olivaceus. The Japanese flounder (JF)-caspase-10 cDNA consisted of 2282 bp and encoded 495 amino acid residues. The characteristic death effector domains (DEDs) of caspases were observed in JF-caspase-10 as well as the three aspartic acid residues (D-186, -382 and -392), which are potential cleavage sites for the large and small subunit structures. The amino acid residue (His-325) and pentapeptide (QACQG), which are involved in catalytic activity, were absolutely conserved in Japanese flounder-caspase-10. JF-caspase-10 gene has a length of 6.6 kb and consists of 11 exons and 10 introns similar to that of human. The strong expression of JF-caspase-10 mRNA was detected in the gills, peripheral blood leukocytes, spleen and posterior kidney, while the weak expression was observed in the head kidney, heart, intestine, skin and stomach. The over-expression analysis of JF-caspase-10 in Japanese flounder cell line HINAE was shown to induce apoptosis 24h post-transfection using TUNEL assay.

Molecular cloning, characterization, expression and functional analysis of Japanese flounder Paralichthys olivaceus Fas ligand

We isolated and sequenced Fas ligand cDNA and its gene from Japanese flounder (JF), Paralichthys olivaceus. The JF-Fas ligand cDNA consisted of 1016 bp and encoded 230 amino acid residues. The identities of the deduced amino acid sequence of the JF-Fas ligand to human Fas ligand, Tumor necrosis factor-alpha and Lymphotoxin-alpha were 26.1%, 24.5% and 23.0%, respectively. A proline-rich domain (PRD) that is important for localization of the protein was found in the N-terminal region, and two cysteine residues, which form a disulfide bond, were conserved. The JF-Fas ligand gene has a length of 1.8 kb and consists of four exons and three introns. The length of the JF-Fas ligand second intron is shorter than that in the human and pig Fas ligand genes. However, the organization of the exons and introns is similar to that of mammals. RT-PCR was conducted for 12 tissues, and expression of JF-Fas ligand mRNA was detected in the kidney, thymus, gills, stomach and spleen. The recombinant JF-Fas ligand prepared in an Escherichia coli protein expression system showed cytotoxic activity against Japanese flounder cell line HINAE and caused the fragmentation of genomic DNA. The cytotoxic activity was measured by MTT assay. These results indicate that fish possess a Fas ligand system.

In vivo effects of thyroid hormone, corticosteroids and prolactin on cell proliferation and apoptosis in the anterior intestine of the euryhaline mudskipper (Periophthalmus modestus)

We have previously shown that anterior intestinal epithelium of the euryhaline mudskipper (Periophthalmus modestus) undergoes apoptosis during seawater (SW) acclimation, whereas elevated cell proliferation was observed in freshwater (FW)-acclimated fish. To understand the possible endocrine regulation of the gastrointestinal cell turnover during salinity acclimation, we examined the ratios of apoptotic and proliferating cells in the anterior intestine of one-third SW-acclimated mudskipper treated with triiodothyronine (T3), cortisol, 11-deoxycorticosterone (DOC, the putative teleostean mineralocorticoid), or prolactin (PRL). In situ nick end labeling of genomic DNA (TUNEL) and immunohistochemistry of proliferating cells nuclear antigen (PCNA) were used as indicators of apoptosis and cell proliferations, respectively. Cortisol significantly elevated apoptosis (P<0.05) in the epithelia and connective tissues and also stimulated the epithelial cell proliferation (P<0.05). PRL induced epithelial cell proliferation (P<0.05), but did not affect apoptotic status of the intestinal epithelium. Neither T3 nor DOC had any impact on cell proliferation or apoptosis. Together, our results suggest a role for cortisol and PRL in the regulation of anterior intestinal epithelial turnover during salinity acclimation in this species.

First molecular cloning and characterisation of caspase-9 gene in fish and its involvement in a gram negative septicaemia

Caspase-9 is an initiator caspase in the apoptotic process whose function is to activate effector caspases that are downstream in the mitochondrial pathway of apoptosis. This work reports for the first time the complete sequencing and characterisation of caspase-9 in fish. A 1924bp cDNA of sea bass caspase-9 was obtained, consisting of 1308bp open reading frame coding for 435 amino acids, 199bp of the 5'-UTR and 417bp of the 3'-UTR including a canonical polyadenilation signal 10 nucleotides upstream the polyadenilation tail. The sequence retains the pentapeptide active-site motif (QACGG) and the putative cleavage sites at Asp(121), Asp(325) and Asp(343). The sequence of sea bass caspase-9 exhibits a very close homology to the sequences of caspase-9 from other vertebrates, particularly with the putative caspases-9 of Danio rerio and Tetraodon nigroviridis (77.5 and 75.4% similarity, respectively), justifying the fact that the phylogenetic analysis groups these species together with sea bass. The sea bass caspase-9 gene exists as a single copy gene and is organised in 9 introns and 10 exons. The sea bass caspase-9 showed a basal expression in all the organs analysed, although weaker in spleen. The expression of sea bass caspase-9 in the head kidney of sea bass infected with the Photobacterium damselae ssp. piscicida (Phdp) strain PP3, showed increased expression from 0 to 12h returning to control levels at 24h. Caspase-9 activity was detected in Phdp infected sea bass head kidney from 18 to 48h post-infection, when the fish were with advanced septicaemia.

Cloning and characterization of the executioner caspases 3, 6, 7 and Hsp70 in hyperthermic Atlantic salmon (Salmo salar) embryos

Hyperthermia during embryogenesis has been reported to induce deformities in Atlantic salmon (Salmo salar). To examine the involvement of executioner caspases in hyperthermia-induced cell-death in a poikilotherm vertebrate species, five genes encoding caspase-3,-6, and -7 were cloned from Atlantic salmon, and the expression was studied in thermal stressed salmon embryos. The salmon genome contained two genetically distinct variants of both salmon caspase-3 and caspase-6 that is likely the result of two independent chromosome or genome duplications. Whereas only partial caspase-3A encoding sequences were isolated, the full-length caspase-3B cDNA encodes the inactive proenzyme of 279 amino acids (aa) consisting of an N-terminal prodomain and the large and the small subunit. The salmon caspase-6A and caspase-6B proenzymes include an additional linker region between the two subunits. The deduced salmon caspase-7 consists of only 245 aa and lacks the prodomain and part of the large subunit similar to the predicted caspase-7 of the puffer fish Tetraodon sp.. Increased apoptotic activity as evidenced by cleavage of nuclear DNA was demonstrated in salmon embryos incubated at 18-20 degrees C for 84 h after acclimatization at 8 degrees C. Hyperthermia-induced activation of the executioner caspases was indicated by the increased mRNA levels of caspase-3B, caspase-6A/B and caspase-7 after 54 h heat exposure as quantified by real-time RT-PCR. The 2-2.5 fold increase in the mRNA expression of the heat shock protein Hsp70 gene coincided with the peak mRNA values of the executioner caspases. Whole-mount in situ hybridization of the salmon embryo identified caspase-7 mRNA in the lens exclusively, while caspase-3B and caspase-6A/B were expressed in multiple tissues of exposed and control embryos. Interestingly, cardiac expression of caspase-6A/B was only identified in heat stressed embryos. Altogether, these results shed light on evolutionary aspects of the executioner caspases in vertebrates and their expression in salmon embryos exposed to hyperthermia. In particular, the heat sensitive caspase-6 expression in the embryonic heart is of interest since cardiac malformations are an emergent problem in salmon aquaculture.

Cloning, characterization and expression analysis of interleukin-10 from the zebrafish (Danio rerion)

Cytokines are proteins produced by many different cells of the immune system and play a significant role in initiating and regulating the inflammatory process. In this research, an important cytokine, interleukin-10 (IL-10) gene, has been identified and characterized from zebrafish (Danio rerio) genome database. Zebrafish IL-10 is located within a 2690 bp fragment and contains five exons and four introns, sharing the same organization with mammalian IL-10 genes. An open reading frame of 543 bp was found to encode a putative 180 amino acid protein with a signal peptide of 22 amino acids, which shares 29.7-80.9 % homology with amino acid sequences of other known IL-10. The signature motif of IL-10 is also conserved in zebrafish IL-10. The predicted transcript was finally confirmed by sequencing of cDNA clones. Multi-tissue reverse transcriptase PCR (RT-PCR) was performed to examine the tissue distribution and expression regulation of this gene in seven organs of normal and lipopolysaccharide (LPS) stimulation zebrafish. The results demonstrated that this gene was expressed slightly in normal kidney, gill and gut, no expression was detected in other four tissues. The expression was clearly upregulated after LPS stimulation. Using the ideal zebrafish model, further study of IL-10 characterization and function may provide insight on the understanding of the innate immune system.

Identification and characterization of a FasL-like protein and cDNAs encoding the channel catfish death-inducing signaling complex

To elucidate cytolytic mechanisms in the channel catfish, lysates from catfish lymphoid and fibroblast cell lines were screened by Western blot analysis using a panel of antibodies reactive with components of the mammalian apoptotic pathway. Strong reactivity with three proteins (approximate Mr 70,000, 37,000, and 15,000) was seen using an antibody targeted to mammalian Fas ligand (FasL). The sizes of the two smaller proteins are consistent with their tentative designation as membrane-bound (37,000 Mr) and soluble (15,000 Mr) FasL. Treatments known to induce FasL in mammalian systems (e.g., PMA/calcium ionophore, UV-irradiation) induced expression of the 37,000- Mr protein in catfish T-cell lines. Moreover, expression of the 37,000- Mr protein in clonal T cells was up-regulated by increasing cell density. At the nucleotide level, homologues of Fas receptor (FasR), FADD, and caspase 8 were identified and characterized. These gene products likely constitute the teleost equivalent of the death-inducing signaling complex (DISC). FADD was constitutively expressed in all (T, B, macrophage, and fibroblast) cell lines examined as well as in peripheral blood lymphocytes (PBL), whereas FasR and caspase 8 were expressed in all cell lines except CCO, a FasL-positive fibroblast line. In contrast to FasL, expression of FasR and caspase 8 was inversely proportional to cell density. Collectively these studies identified four membrane-proximal proteins involved in the initiation of apoptosis in channel catfish and suggest that mechanisms of cell-mediated cytotoxicity in teleosts are similar to those used by mammals.

A short-term in vitro gill culture system to study the effects of toxic (copper) and non-toxic (cortisol) stressors on the rainbow trout, Oncorhynchus mykiss (Walbaum)

A short-term (24 h) method of gill filament culture system was developed to predict the effects of environmental contamination and stress in fish. Gill culture system containing two or three rainbow trout gill filaments in sterile glutamine supplemented Leibovitz 15 (L-15) media was submitted for 24 h to six different treatments: (i) CONT (control, medium only); (ii) CORT (cortisol, 0.28 microM cortisol); (iii) BLOCK (glucocorticoid receptor blocker, 14 microM RU 486); (iv) CORT+BLOCK (cortisol and blocker, 0.28 microM cortisol+14 microM RU 486); (v) CORT+CU (cortisol and copper, 100 microM CuSO4+0.28 microM cortisol); (vi) CU (copper, 100 microM CuSO4). After 24 h, the overall gill structure and cellular components resembled those of salmonids in vivo. Lactate dehydrogenase (LDH) activity in the culture media increased in the CORT+CU and CU groups but was significantly lower in the CORT+CU compared to CU group. Apoptotic cells increased in the CORT and CORT+BLOCK. The numbers of glucocorticoid (GR) receptor-positive cells were lower in the CU group. This short-term culture system seems to be suitable for studying the effects of both external and internal stress effectors (toxicants and hormones respectively), as it contains all cell types found in the gills and the cells give similar biological response as in vivo.

Effects of prolactin and growth hormone on proliferation and survival of cultured trout leucocytes

The in vitro effects of prolactin (PRL) and growth hormone (GH) on the proliferation and survival of leucocytes isolated from the blood of the rainbow trout (Oncorhynchus mykiss) were examined, with special reference to the immunosuppression by cortisol. Both PRL and GH induced a mitogenic effect in trout leucocytes. Contrary, the frequencies of annexin V-positive apoptotic cells and propidium iodide-positive dead cells were decreased by the administration of PRL, but were uninfluenced by GH. Administration of cortisol suppressed the mitotic activity and induced cell death of leucocytes. PRL inhibited the decrease in mitosis and the increase in cell death due to cortisol. GH significantly assisted recovery of cortisol-suppressed mitosis but did not influence the survival of leucocytes. These results suggest that PRL and GH are involved in the maintenance of specific immune functions in fish through a prevention of immunosuppression by cortisol.

Non-specific cytotoxic cell receptor (NCCRP)-1 type gene in tilapia (Oreochromis niloticus): its cloning and analysis

Non specific cytotoxic cells are natural killer cell equivalent in teleosts. These cells are known to mediate innate immune responses in fishes. In this study, from tilapia, a non-specific cytotoxic cell receptor protein (NCCRP) like cDNA composed of 960 bps with a 12 bps 5' UTR, 702 bps open reading frame and 246 bps 3' UTR has been cloned. The predicted gene product is 233 amino acid with a molecular weight of 26.6 kDa and pI of 6.07. The gene has a typical F-box associated domain, which harbors the antigen binding region, implicated in formation of conjugates with target cells necessary for killing. By semi-quantitative RT-PCR studies, the expression level of NCCRP-1 was highest in liver followed by head kidney, spleen and intestine. Low expression levels were recorded in brain, gill and heart. Lowest expression of transcripts was in the skin. As evidenced by in situ hybridisation the NCCRP-1 transcripts were expressed on lymphocyte like cells as well as neutrophils.

Molecular identification and expression analysis of tumor necrosis factor in channel catfish (Ictalurus punctatus)

A tumor necrosis factor (TNF) alpha-like gene, encoding a propeptide of 230 amino acids and a mature (soluble) peptide of 162 amino acids, was identified in channel catfish (Ictalurus punctatus). While the catfish protein shared features in common with both mammalian TNFalpha and TNFbeta homologs, overall sequence identity/similarity was slightly higher vs. TNFalpha genes when mature TNF sequences were compared. Phylogenetic analysis placed catfish and other fish TNF sequences within their own cluster apart from mammalian TNFalpha and beta genes, and supported the suggestion that TNFalpha and beta genes separated after the divergence of mammals and teleosts. In contrast to trout and carp, but similar to flounder, catfish TNF was present as a single copy gene. Expression studies demonstrated that catfish TNFalpha mRNA was present in all tested tissues (i.e. liver, spleen, head kidney, mesonephros, gill, thymus, and PBLs) from an unstimulated fish. Moreover, catfish TNF was constitutively expressed in actively proliferating, but otherwise unstimulated, macrophage (42TA) and T cell (G14D; TS32.17) lines, but not in B cell (1G8 or 3B11) or fibroblast lines. TNF expression was upregulated in PBLs, and in G14D and 42TA cells, but not in 3B11 cells, by PMA/calcium ionophore treatment. These results demonstrate that a catfish homolog of TNFalpha has been identified, and indicate that catfish TNFalpha is expressed in catfish in a manner similar to that seen in mammals.

Cloning, characterization and expression analysis of interleukin-10 from the common carp, Cyprinus carpio L

Interleukin (IL)-10 was cloned from the common carp (Cyprinus carpio L.) using IL-10 primers from carp head kidney following stimulation with concanavalin A and lipopolysaccharide. The cDNA consisted of a 1096 bp sequence containing a 55 bp 5' untranslated region and a 498 bp 3' untranslated region. An open reading frame of 543 bp encoded a putative 180 amino acid protein with a putative signal peptide of 22 amino acids. The signature motif of IL-10 is conserved in carp sequence. A 2083 bp genomic sequence of carp IL-10 was found to contain five exons interrupted by four introns. With the exception of much more compact introns, the genomic structure was similar to that of mammalian IL-10. By homology, phylogeny and genomic analyses, the carp gene cloned was designated as IL-10. Carp IL-10 was expressed in head, kidney, liver, spleen and intestine during the resting phase. The gene was also expressed in head kidney and liver following in vitro stimulation with lipopolysaccharide.

Gyrodactylus derjavini infection elicits IL-1beta expression in rainbow trout skin

Specific gene expression of the pro-inflammatory cytokine IL-1beta and the type II IL-1beta receptor (IL-1RII, 'decoy receptor') was studied in skin of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) fry during infection with the ectoparasitic monogenean Gyrodactylus derjavini Mikailov, 1975. Cytokine expression was studied in both primary and secondary infections using a semi-quantitative RT-PCR technique. Generally, low levels of specific IL-1beta1, IL-1beta2 and IL-1RII gene transcription were found in uninfected hosts. In contrast, a clear induction of both IL-1beta isoforms could be observed during the initial phases of primary G. derjavini infections. A less obvious induction of IL-1beta expression was seen in secondary infections imposed just after recovery from the priming infection. However, challenge infections given one-month post full recovery of the primary infections did not elicit transcription levels above those seen in skin samples from uninfected hosts. Despite this, hosts carrying a secondary infection elicited a stronger response toward G. derjavini thus expelling parasites quicker than their nai;ve counterparts. When induced, indications of a more tight regulation of the IL-1beta1 isoform compared to IL-1beta2 could be observed. Increased expression of IL-1RII was seen later during the course of a primary infection and could be involved in the observed down regulation of IL-1, especially the beta1 isoform. The current study represents the first example of cytokine expression in fish induced by an ectoparasitic infection and indicates the importance of localised mucosal immune reactions in responses of fish towards gyrodactylids.

Molecular cloning and expression analysis of a novel caspase recruitment domain protein (CARD) in common carp Cyprinus carpio L

A novel caspase recruitment domain protein (CARD) was isolated from common carp Cyprinus carpio L. by expressed sequence tag analysis. This gene consist of a 2016 bp open reading frame and untranslated regions, which is putatively translated to a protein of 535 amino acid residues. The gene harbors domains (CARD and Coiled-coil domain), which are conserved in proteins of CARD family. The CARD domain have carp was similar to human CARD9 with 72.4% identity. Expression analysis revealed that CARD gene of carp (carp-CARD) expressed in normal tissues of head kidney, spleen, liver, heart and brain. Here we demonstrated that the expression of carp-CARD increased by cortisol treatment in all the tissues and had a high and long lasting expression in cortisol treated spleen.

Induction of apoptosis in frog virus 3-infected cells

The ability of frog virus 3 (FV3), the type species of the family Iridoviridae, to induce apoptosis was examined by monitoring DNA cleavage, chromatin condensation, and cell-surface expression of phosphotidylserine (PS) in fathead minnow (FHM) and baby hamster kidney (BHK) cells. In productively infected FHM cells, DNA fragmentation was first noted at 6-7 h postinfection and was clearly seen by 17 h postinfection, while chromatin condensation was detected at 8.5 h postinfection. As with some other viruses, FV3-induced apoptosis did not require de novo viral gene expression as both heat-inactivated and UV-inactivated virus readily triggered DNA fragmentation in FHM cells. Moreover, FV3-induced apoptosis was blocked in FHM cells by the pan-caspase inhibitor Z-VAD-FMK, suggesting that virus infection triggers programmed cell death through activation of the caspase cascade. FV3 infection also triggered apoptosis in BHK cells as monitored by TUNEL and annexin V binding assays. To determine whether FV3, similar to other large DNA viruses, encoded proteins that block or delay apoptosis, mock- and FV3-infected FHM cells were osmotically shocked and assayed for DNA fragmentation 3 hours later. DNA fragmentation was clearly seen whether or not shocked cells were previously infected with FV3, indicating that infection with FV3 did not block apoptosis induced by osmotic shock in FHM cells. The above results demonstrate that iridoviruses triggered apoptosis and that the induction of programmed cell death did not require viral gene expression. However, it remains to be determined if virion attachment to target cells is sufficient to induce cell death, or if apoptosis is triggered directly or indirectly by one or more virion-associated proteins.

Evolution of interleukin-1beta

All jawed vertebrates possess a complex immune system, which is capable of anticipatory and innate immune responses. Jawless vertebrates possess an equally complex immune system but with no evidence of an anticipatory immune response. From these findings it has been speculated that the initiation and regulation of the immune system within vertebrates will be equally complex, although very little has been done to look at the evolution of cytokine genes, despite well-known biological activities within vertebrates. In recent years, cytokines, which have been well characterised within mammals, have begun to be cloned and sequenced within non-mammalian vertebrates, with the number of cytokine sequences available from primitive vertebrates growing rapidly. The identification of cytokines, which are mammalian homologues, will give a better insight into where immune system communicators arose and may also reveal molecules, which are unique to certain organisms. Work has focussed on interleukin-1 (IL-1), a major mediator of inflammation which initiates and/or increases a wide variety of non-structural, function associated genes that are characteristically expressed during inflammation. Other than mammalian IL-1beta sequences there are now full cDNA sequences and genomic organisations available from bird, amphibian, bony fish and cartilaginous fish, with many of these genes having been obtained using an homology cloning approach. This review considers how the IL-1beta gene has changed through vertebrate evolution and whether its role and regulation are conserved within selected non-mammalian vertebrates.

Oxygen-dependent cellular functions--why fishes and their aquatic environment are a prime choice of study

Owing to the variability of oxygen tension in aquatic, especially the freshwater environment, oxygen has been a major force in the evolution of fishes. Their long evolutionary history, and the present different oxygen requirements between species, and acclimatory responses to hypoxic and hyperoxic conditions make fishes prime models in the study of oxygen-dependent cellular functions and their regulation. In the present article oxygen-dependent membrane transport, cellular signalling, energy metabolism, gene expression and apoptosis are reviewed with an emphasis on available results on fish. Available data on oxygen sensing are described and examples on the cascade from sensing oxygen to its physiological effects are given. From the data it is clear that hitherto fish have not been utilised in the study of oxygen-dependent cellular regulation as much as their evolutionary history and present oxygen requirements would give possibilities to. Even more generally, oxygen has hitherto seldom been a carefully controlled key variable in experimental cell biology.