Genomic organisation of rainbow trout, Oncorhynchus mykiss TGF-beta

Importance of prebiotics in aquaculture as immunostimulants. Effects on immune system of Sparus aurata and Dicentrarchus labrax

Infectious diseases in fish represent a major problem for the aquaculture field as they produce extensive damages and loss. Over the last few years, with increased development of the aquaculture industry, different methods have been used to contrast these pathologies. Common interest has led to the use of components (as additives in diets) that could contrast diseases without causing any negative impact on the environment. These components are represented by prebiotics, probiotics, and plant extracts. In this review, the effects of prebiotics are described. Prebiotics are indigestible fibres fermented by gut enzymes and commensal bacteria, whose beneficial effects are due to the by-products generated from fermentation. The influence of pre-biotics on the immune system of fish is called immunosaccharides. Mannanoligosaccharides (MOS), Fructooligosaccharides (FOS) and Inulin act at different levels in the innate immune response. For example, through phagocytosis, lysozyme activity, and the complement system activity, an increase in fish growth and an amelioration of their health status is brought about. In this review, the use of prebiotics in aquaculture, such as immunostimulants, has been highlighted: particularly in two teleost fish species, Sparus aurata and Dicentrarchus labrax. The results demonstrate that the road is still long and further studies are required, but the use of prebiotics, individually or coupled together, can open the doors to pioneering a new model of alternative components to antimicrobial agents.

Differential immune gene expression profiles in susceptible and resistant full-sibling families of Atlantic salmon (Salmo salar) challenged with infectious pancreatic necrosis virus (IPNV)

This study aims to identify at the expression level the immune-related genes associated with IPN-susceptible and resistant phenotypes in Atlantic salmon full-sibling families. We have analyzed thirty full-sibling families infected by immersion with IPNV and then classified as resistant or susceptible using a multivariate survival analysis based on a gamma-Cox frailty model and the Kaplan-Meier mortality curves. In four families within each group head kidneys were pooled for real-time PCR and one-color salmon-specific oligonucleotide microarray (21K) analysis at day 1 and 5 post-infection. Transcripts involved in innate response (IL-6, IFN-α), antigen presentation (HSP-70, HSP-90, MHC-I), TH1 response (IL-12, IFN-γ, CRFB6), immunosuppression (IL-10, TGF-β1) and leukocyte activation and migration (CCL-19, CD18) showed a differential expression pattern between both phenotypes, except in IL-6. In susceptible families, except for IFN-γ, the expressions dropped to basal values at day 5 post-infection. In resistant families, unlike susceptible families, levels remained high or increased (except for IL-6) at day 5. Transcriptomic analysis showed that both families have a clear differential expression pattern, resulting in a marked down-regulation in immune related genes involved in innate response, complement system, antigen recognition and activation of immune response in IPN-resistant. Down-regulation of genes, mainly related to tissue differentiation and protein degradation metabolism, was also observed in resistant families. We have identified an immune-related gene patterns associated with susceptibility and resistance to IPNV infection of Atlantic salmon. This suggests that a limited immune response is associated with resistant fish phenotype to IPNV challenge while a highly inflammatory but short response is associated with susceptibility.

The cytokine networks of adaptive immunity in fish

Cytokines, produced at the site of entry of a pathogen, drive inflammatory signals that regulate the capacity of resident and newly arrived phagocytes to destroy the invading pathogen. They also regulate antigen presenting cells (APCs), and their migration to lymph nodes to initiate the adaptive immune response. When naive CD4+ T cells recognize a foreign antigen-derived peptide presented in the context of major histocompatibility complex class II on APCs, they undergo massive proliferation and differentiation into at least four different T-helper (Th) cell subsets (Th1, Th2, Th17, and induced T-regulatory (iTreg) cells in mammals. Each cell subset expresses a unique set of signature cytokines. The profile and magnitude of cytokines produced in response to invasion of a foreign organism or to other danger signals by activated CD4+ T cells themselves, and/or other cell types during the course of differentiation, define to a large extent whether subsequent immune responses will have beneficial or detrimental effects to the host. The major players of the cytokine network of adaptive immunity in fish are described in this review with a focus on the salmonid cytokine network. We highlight the molecular, and increasing cellular, evidence for the existence of T-helper cells in fish. Whether these cells will match exactly to the mammalian paradigm remains to be seen, but the early evidence suggests that there will be many similarities to known subsets. Alternative or additional Th populations may also exist in fish, perhaps influenced by the types of pathogen encountered by a particular species and/or fish group. These Th cells are crucial for eliciting disease resistance post-vaccination, and hopefully will help resolve some of the difficulties in producing efficacious vaccines to certain fish diseases.

Two dynamin-2 genes are required for normal zebrafish development

Dynamin-2 (DNM2) is a large GTPase involved in clathrin-mediated endocytosis and related trafficking pathways. Mutations in human DNM2 cause two distinct neuromuscular disorders: centronuclear myopathy and Charcot-Marie-Tooth disease. Zebrafish have been shown to be an excellent animal model for many neurologic disorders, and this system has the potential to inform our understanding of DNM2-related disease. Currently, little is known about the endogenous zebrafish orthologs to human DNM2. In this study, we characterize two zebrafish dynamin-2 genes, dnm2 and dnm2-like. Both orthologs are structurally similar to human DNM2 at the gene and protein levels. They are expressed throughout early development and in all adult tissues examined. Knockdown of dnm2 and dnm2-like gene products resulted in extensive morphological abnormalities during development, and expression of human DNM2 RNA rescued these phenotypes. Our findings suggest that dnm2 and dnm2-like are orthologs to human DNM2, and that they are required for normal zebrafish development.

Cloning and expression analysis of the transforming growth factor-beta receptors type 1 and 2 in the rainbow trout Oncorhynchus mykiss

Transforming growth factor-β (TGF-β) binding to the TGF-β type I (TGFBR1) and type II (TGFBR2) receptors delivers a plethora of cell-type specific effects. Moreover, the responses to TGF-β are tuned by regulatory mechanisms at the receptor level itself. To further elucidate TGF-β family signal transduction in teleosts, we therefore cloned the first complete set of a putative TGF-β receptor complex in salmonids. Rainbow trout TGFBR1 and TGFBR2 are transmembrane proteins with a serine/threonine kinase domain and are highly conserved within vertebrates. High expression levels in muscle and brain indicate regulation of the TGF-β system in muscular and nervous systems. Lipopolysaccharide (LPS) induced expression of both receptor chains in RTgill cells while bacterial and viral mimics modulated the two receptors inversely in head kidney (HK) macrophages. In addition, T cell mitogens lowered receptor levels in HK leukocytes. These data provide the first insights into TGF-β type I and II receptor modulation during immune responses in teleost fish.

Identification of a novel transforming growth factor-beta (TGF-beta6) gene in fish: regulation in skeletal muscle by nutritional state

Background

The transforming growth factor-β (TGF-β) family constitutes of dimeric proteins that regulate the growth, differentiation and metabolism of many cell types, including that of skeletal muscle in mammals. The potential role of TGF-βs in fish muscle growth is not known.

Results

Here we report the molecular characterization, developmental and tissue expression and regulation by nutritional state of a novel TGF-β gene from a marine fish, the gilthead sea bream Sparus aurata. S. aurata TGF-β6 is encoded by seven exons 361, 164, 133, 111, 181, 154, and 156 bp in length and is translated into a 420-amino acid peptide. The exons are separated by six introns: >643, 415, 93, 1250, 425 and >287 bp in length. Although the gene organization is most similar to mouse and chicken TGF-β2, the deduced amino acid sequence represents a novel TGF-β that is unique to fish that we have named TGF-β6. The molecule has conserved putative functional residues, including a cleavage motif (RXXR) and nine cysteine residues that are characteristic of TGF-β. Semi-quantitative analysis of TGF-β6 expression revealed differential expression in various tissues of adult fish with high levels in skin and muscle, very low levels in liver, and moderate levels in other tissues including brain, eye and pituitary. TGF-β6 is expressed in larvae on day of hatching and increases as development progresses. A fasting period of five days of juvenile fish resulted in increased levels of TGF-β6 expression in white skeletal muscle compared to that in fed fish, which was slightly attenuated by one injection of growth hormone.

Conclusion

Our findings provide valuable insights about genomic information and nutritional regulation of TGF-β6 which will aid the further investigation of the S. aurata TGF-β6 gene in association with muscle growth. The finding of a novel TGF-β6 molecule, unique to fish, will contribute to the understanding of the evolution of the TGF-β family of cytokines in vertebrates.

Stress-related hormones modulate cytokine expression in the head kidney of gilthead seabream (Sparus aurata)

Neuro-endocrine and immune systems closely interact in fish, and their regulation is crucial for the maintenance of good health of cultured fish. We have used the seabream head kidney to study whether stress-related hormones can modulate the immune response. For this purpose, the effects of adrenaline, adrenocorticotropic hormone (ACTH) and cortisol on the expression of pro-inflammatory cytokines (TNF-alpha, IL-1beta, IL-6) and the anti-inflammatory cytokine TGF-beta1 were determined by means of quantitative real-time PCR on isolated head kidney cells. ACTH (150 ng mL(-1)) caused an acute increase of TNF-alpha and IL-6 mRNA levels as well as an inhibition of IL-1beta expression. The expression of the anti-inflammatory cytokine TGF-beta1 was also increased, although in a lower extent. Adrenaline (1 muM) early effects were only clear inhibiting IL-1beta expression but not TNF-alpha, IL-6 or TGF-beta1 mRNA levels, while a longer exposure to the hormone inhibited all cytokines. Moreover, cortisol (50 and 100 ng mL(-1)) reduced the expression of all cytokines in a dose-dependent manner. Bacterial lipopolysaccharide (LPS) stimulated IL-1beta expression and inhibited that of the anti-inflammatory TGF-beta1, although it was ineffective on TNF-alpha and IL-6. In addition, adrenaline and cortisol decreased the LPS-stimulated IL-1beta expression, further demonstrating their previously reported anti-inflammatory effects. The combination of ACTH and LPS, on the other hand, did not affect LPS-stimulated IL-1beta expression but was effective increasing TNF-alpha expression. Taking all these results in consideration, we conclude that the expression of pro- and anti-inflammatory cytokines in the seabream head kidney is highly influenced by stress-related hormones, thus indicating an important role for the endocrine system in the modulation of the immune response in teleost fish.

Decreased expression of TGF-beta, GILT and T-cell markers in the early stages of soybean enteropathy in Atlantic salmon (Salmo salar L.)

This study investigated the early expression of T-cell markers and genes potentially involved in the induction of soybean meal (SBM) enteropathy in the distal intestine (DI) of Atlantic salmon (Salmo salar L.). Quantitative PCR was used to study the expression of CD3, CD8beta, transforming growth factor beta (TGF-beta), interferon-gamma-inducible lysosomal thiol reductase (GILT) and interleukin-1beta (IL-1beta) in salmon fed SBM for 1, 3 and 7 days using fish fed fishmeal as controls. In the same tissue, the morphological development of SBM enteropathy was evaluated by routine histology and the presence of T cells was mapped by immunohistochemistry. TGF-beta was significantly down-regulated on all days of feeding SBM. GILT was significantly down-regulated on days 3 and 7 compared to day 1. A depression in the expression of T-cell markers was observed on day 3 whereas increased densities of T cells were observed at the base of mucosal folds after 7 days of feeding SBM. Down-regulation of GILT and TGF-beta may lead to sensitization of intraepithelial lymphocytes and failure to maintain normal mucosal integrity in the DI. These responses are implicated in the pathogenesis of SBM enteropathy in Atlantic salmon.

Expression profiles of cytokines released in intestinal epithelial cells of the rainbow trout, Oncorhynchus mykiss, in response to bacterial infection

To determine whether fish intestinal epithelial cells (IECs) contribute to mucosal immunity, we established a method for isolating IECs from the rainbow trout Oncorhynchus mykiss and examined cytokine production in these cells. Components of the intestinal epithelium were released by incubation of intestinal pieces with 1mM dithiothreitol (DTT)/ethylenediamine tetraacetic acid (EDTA). The IEC-rich fraction (purity >90%; survival rate approximately 95%) was obtained by centrifugation on a 35%/40% Percoll gradient, followed by magnetic cell sorting using an anti-trout IgM antiserum. The gene expression profiles of 14 cytokines in trout IECs were investigated after culturing the cells for 6h with or without the pathogenic bacterium Aeromonas salmonicida. Trout IECs could produce several cytokines, of which IL-1beta and TNFalpha2 were upregulated when the cells were stimulated with live A. salmonicida. Immunohistochemical analyses with the anti-trout TNF antibody confirmed that the TNF protein was present in the IECs of trout that were intra-anally challenged with live A. salmonicida. These results show that trout IECs are an important trigger of the intestinal immune system. Further, formalin-killed A. salmonicida, conditioned medium of this bacterium, or live nonpathogenic Escherichia coli could not upregulate the expression of these cytokines. These results indicate that the production of inflammatory cytokines by IECs is caused by the adhesion of A. salmonicida, but is not due to only simple ligand-receptor interactions between the surface molecules of IECs and the bacterium or in response to bacterial secretions.

Cell markers and determinants in fish immunology

Despite the impressive increase in the cloning and expression of genes encoding fish immunoregulatory molecules, the knowledge on "in vivo" and "in vitro" functional immunology of the corresponding peptide products is still at an initial stage. This is partly due to the lacking of specific markers for immunoregulatory peptides, that represent an indispensible tool to dissect immune reactions and to trace the fate of cellular events downstream of the activation. In this review we summarise the available information on functional immune activities of some teleost species and discuss the obtained data in an evolutionary and applied context.

Construction and analysis of a secreting expression vector for fish cells

A new expression plasmid (pcDNA3-LP) was designed to produce and secrete proteins in fish cells by fusion with the rainbow trout TGF-beta leader peptide. The luciferase reporter gene was used to test the secreting ability of this vector. Secreting (pcDNA3-LP-LUC) and non-secreting (pcDNA3-LUC) constructs were made and compared in transient transfection experiments in salmonid (RTG-2) and cyprinid (EPC) cell lines. The amount of luciferase secreted into the supernatants of RTG-2 or EPC cells transiently transfected with pcDNA3-LP-LUC relative to cells transfected with pcDNA3-LUC was 7- and 85-fold, respectively. Two stable clones of EPC transfected with pcDNA3-LUC and four clones transfected with pcDNA3-LP-LUC were isolated. Approximately 90% of the total luciferase activity produced was secreted by stable EPC clones containing pcDNA3-LP-LUC whereas only 5% of total activity was secreted by clones containing pcDNA3-LUC. The two constructs were injected intra-muscularly into rainbow trout and the luciferase activity present in the serum of fish determined. The luciferase activity in serum from fish injected with pcDNA3-LP-LUC was 2.7-fold higher (P<0.05) than that fish injected with pcDNA3-LUC. This new vector opens up opportunities in fish DNA vaccinology and in the production of fish recombinant proteins.

Molecular characterisation of sea bream (Sparus aurata) transforming growth factor beta1

A transforming growth factor beta1 (TGF beta1) full length cDNA was characterised and sequenced from the head kidney of sea bream (Sparus aurata) previously challenged with a nodavirus. The cloned cDNA of 1778bp contains a predicted open reading frame of 379 amino acids, which includes the mature peptide region of 112 amino acids. The regulating region of the peptide possesses four potential N-linked glycosylation sites (N-X-T/S), as well as an RGD integrin binding site, an RKKR tetrabasic cut site and nine conserved cysteines all characteristic of the TGF beta superfamily. Compared to other teleost TGF beta1 genes, the sea bream TGF beta1 is most closely related to hybrid striped bass (Moronesaxatilis xM. chrysops) TGF beta1 (80% amino acid identity). The genomic organisation of TGF beta1 was determined through the generation of contiguous PCR clones. The sea bream TGF beta1 gene is approximately 3.6kb in length and consists of five coding regions. Two introns are absent in comparison to the genomic organisation of rainbow trout Oncorhynchus mykiss TGF beta1, whilst an additional intron not present in other sequenced TGF beta genes, but present in the trout TGF beta1 gene, is conserved in sea bream.A reverse transcription polymerase chain reaction (RT-PCR) assay was developed to study TGF beta expression in different sea bream tissues. Constitutive TGF beta1 expression was detected in the liver, brain, muscle, kidney, heart, gills and spleen of sea bream, as well as in head kidney macrophages and blood leucocytes.

Induction of nitric oxide and respiratory burst response in activated goldfish macrophages requires potassium channel activity

Potassium channel activity is important for modulating mammalian macrophage antimicrobial functions. The involvement of potassium channels in mediation of immune cell function in lower vertebrates, such as teleost, has not been explored. Since relatively little is known about the types of potassium channels present in fish macrophages, pharmacological blockers with broad ranges of activity were tested: 4-aminopyridine (4-AP), quinine, and tetraethylammonium chloride (TEA). The potassium channel blockers inhibited reactive nitrogen intermediates (RNI) and reactive oxygen intermediates (ROI) production by goldfish macrophages activated with bacterial lipopolysaccharide (LPS) and/or macrophage activating factor (MAF)-containing supernatants. Quinine was the most potent inhibitor with an IC(50) of 50 microM, while the other blockers, 4-AP and TEA, had IC(50) of 1.2 and 0.6mM, respectively. A reversible depolarization of the goldfish macrophage plasma membrane potential (Vm) was observed following treatments with potassium channel blockers, and was related to transcriptional changes in the inducible nitric oxide synthase gene (iNOS). Down-regulation of antimicrobial activities and depolarization of the goldfish macrophage plasma membrane were not a consequence of reduced cell number or viability, suggesting that potassium channels are required for generation of appropriate goldfish macrophage antimicrobial functions.

Isolation and characterization of As60A, a transforming growth factor-beta gene, from the malaria vector Anopheles stephensi

We have isolated the first mosquito member of the TGF-beta superfamily, As60A. As60A is a single copy gene, approximately 5 kb in length and encodes eight exons. Here we report the isolation and characterization of two of four transcripts produced from this gene. The transcripts As60A(1)and As60A(2)encode related 5'UTR/exon 1 sequences. As60A is most similar to the 60A genes from Drosophila and is thus a member of the Dpp/BMP subfamily of the TGF-beta superfamily. The splice junction of intron 2 is conserved among As60A, BMP2, BMP4, Tc-Dpp, Bm-tgh-1, TGF-beta1 and Dpp. Intron 2 also contains three putative binding sites for a Dorsal/Gambif1 transcription factor. The large number of introns and the conservation of intron 2 indicate that As60A is relatively ancient compared to the other arthropod TGF-beta genes. We also propose that As60A plays a role in the mosquito immune response to Plasmodium infection.

Biochemical and functional characterisation of macrophage stimulating factors secreted by mitogen-induced goldfish kidney leucocytes

Mitogen-stimulated goldfish kidney leucocytes secrete a number of different macrophage activation factors (MAF) that induce profound physiological changes in macrophages. MAF produced by goldfish kidney leucocytes was characterised using fast performance liquid chromatography (FPLC) and bioassays that measured MAF-induced respiratory burst (RB) and nitric oxide (NO) responses of activated macrophages. Mitogen-induced fish kidney leucocyte supernatants were fractionated using gel permeation FPLC (GP-FPLC) and the ability of different fractions to induce NO or RB measured. A MAF of M(r) 50 kD, that induced a potent nitric oxide response in both a long-term goldfish macrophage cell line (GMCL) and in in vitro-derived fish kidney macrophages (IVDKM) was identified. The GP-FPLC partially purified 50 kD MAF activity occasionally induced significantly higher nitric oxide production than that of the crude MAF preparations. This increase in the NO-inducing activity was due to segregation of the 50 kD MAF from a novel macrophage deactivating molecule of M(r) 10-12 kD present in crude MAF preparations. This 10-12 kD molecule was shown to inhibit nitric oxide production in cytokine-activated goldfish macrophages. Mitogen-induced fish kidney leucocyte supernatants contained two distinct MAFs that induced the respiratory burst in GMCL and IVDKM: the 50 kD and 30 kD proteins. The partially purified 30 kD MAF primed goldfish macrophage for increased RB activity after only 6 h of treatment, and continued to augment the RB activity after 24 h of stimulation. In contrast, the GP-FPLC partially purified 50 kD molecule also primed the RB after only 6 h of stimulation, but subsequently deprimed the RB after 24 h of stimulation, an effect similar to that observed for crude MAF preparations. The 50 kD MAF activity was further purified using chromatofocusing FPLC (C-FPLC) using basic pH gradients and was shown to consist of two distinct NO-inducing molecules (> pI 9.3). Mitogen-stimulated fish kidney leucocytes secrete several factors that profoundly affect the anti-microbial responses of teleost macrophages and which undoubtedly are responsible for regulating teleost macrophage function in vivo.

Cloning and sequencing hybrid striped bass (Morone saxatilis x M. chrysops) transforming growth factor-beta (TGF-beta), and development of a reverse transcription quantitative competitive polymerase chain reaction (RT-qcPCR) assay to measure TGF-beta mRNA of teleost fish

A transforming growth factor (TGF)-beta was isolated and cloned from hybrid striped bass (Morone saxatilis x M. chrysops) anterior kidney mononuclear cells. This isolate (Genbank accession number AF140363) contains an open reading frame of 1146 bases coding for a 382 amino acid protein most similar to rainbow trout TGF-beta (57.3 and 78.6% identity with precursor and active protein, respectively) and rat TGF-beta 1 (41.1 and 68.8% identity with precursor and active protein, respectively). Consensus primers were demonstrated to amplify specifically by polymerase chain reaction (PCR), a TGF-beta segment from 14 species of teleost fish comprising 10 taxonomic families in 7 orders. A reverse transcription quantitative competitive polymerase chain reaction (RT-qcPCR) assay was devised to measure TGF-beta mRNA expression in teleost fish. Higher levels of TGF-beta mRNA expression were detected in mononuclear cells of peripheral blood than from spleen or anterior kidney.

TGF-beta3 exists in bony fish

A partial nucleotide sequence of transforming growth factor-beta3 (TGF-beta3) has been isolated from the Siberian sturgeon (Acipenser baeri), rainbow trout (Oncorhynchus mykiss) and European eel (Anguilla anguilla), confirming a ubiquitous presence in the ray-finned (Actinopterygian) bony fish. The bony fish TGF-beta3 is highly conserved, with some 83-84% nucleotide identity (coding region) and 90-95% predicted amino acid identity to known homeotherm TGF-beta3's. Far lower homologies are apparent with other known TGF-beta isoforms in fish (e.g. 64-66% and 81-82% amino acid identity to trout TGF-beta 1/5 and carp TGF-beta2 respectively). Phylogenetic tree analysis showed that the fish TGF-beta3's clustered with the known homeotherm TGF-beta3's. The relatively tight clustering of TGF-beta1, TGF-beta2 and TGF-beta3 was in contrast to the TGF-beta5's, which are clearly a more heterogenous group.

Inhibition of macrophage activity by mitogen-induced goldfish leukocyte deactivating factor

Macrophage activating and deactivating cytokines have been characterized in mammalian systems but little is known about these immunoregulatory molecules in fish. Using gel permeation and chromatofocusing fast performance liquid chromatography (GP-FPLC and C-FPLC) we partially purified a macrophage deactivating factor (MDF) from mitogen-induced goldfish kidney leukocytes. Inhibition of the macrophage-derived nitric oxide (NO) response induced by this MDF was time-, dose- and temperature-dependent. Macrophages pre-treated for 6 or 24 h with MDF before activation with macrophage activating factors (MAF) and/or bacterial lipopolysaccharide (LPS) exhibited a down-regulation in their NO response, while those treated with MDF 24 h after activation with MAF and LPS did not. MDF treatment also impaired the NO response of goldfish macrophages infected with the mammalian protozoan parasite Leishmania major. These results suggest that MDF exhibits its inhibitory effect downstream of the converging intracellular pathways induced by LPS and/or L. major. The novel teleost MDF has an approximate Mr of 15 kD and a pI < 4, and is the first endogenous molecule of teleosts known to down regulate macrophage antimicrobial responses.