Characterization and expression analyses of anti-apoptotic Bcl-2-like genes NR-13, Mcl-1, Bcl-X1, and Bcl-X2 in Atlantic cod (Gadus morhua)

Polystyrene microplastics induce myocardial inflammation and cell death via the TLR4/NF-κB pathway in carp

Microplastics (MPs) have attracted widespread attention as an emerging environmental pollutant. Especially in aquatic ecosystems, the harm of MPs to aquatic animals has increasingly become a severe environmental problem. In this study, we constructed a carp polystyrene microplastics (PS-MPs) exposure model to explore the damage and mechanism of PS-MPs exposure to carp myocardial tissue. The results of H&E, TUNEL, and AO/EB staining showed that PS-MPs exposure could induce inflammation, apoptosis, and necrosis in carp myocardial tissue and cardiomyocytes. In addition, our study explored the targeting relationship between PS-MPs and TLR4 and found that PS-MPs exposure could significantly increase the expression of TLR4 pathway-related factors. As the concentration of PS-MPs increased, the NF-κB pathway and inflammation-related factors increased dose-dependent. In addition, myocardial injury induced by exposure to PS-MPs was predominantly apoptotic, accompanied by necrosis. In short, our data suggest that PS-MPs cause damage to myocardial tissue via the TLR4\NF-κB pathway. The above findings enrich the theory of toxicological studies on PS-MPs and provide an essential reference for aquaculture.

Molecular characterization and expression analysis of B-cell lymphoma-2 protein in Amphiprion clarkii and its role in virus infections

Amphiprion clarkii is increasingly being used as a captive-bred ornamental fish in South Korea. However, its breeding has recently been greatly hindered by destructive diseases due to pathogens. B-cell lymphoma-2 (Bcl2), a mitochondrial apoptosis regulatory gene involved in immune responses, has not been investigated in anemonefish, including A. clarkii. Herein, we aimed to annotate Bcl2 in the A. clarkii transcriptome and examined its role against virus infections. Sequence analysis indicated that Bcl2 in A. clarkii (AcBcl2) contained all four Bcl-2 homology domains. The structure of AcBcl2 closely resembled those of previously analyzed anti-apoptotic Bcl2 proteins in mammals. Expression analysis showed that the highest level of AcBcl2 was expressed in blood. AcBcl2 expression in the blood was downregulated within 24 hpi when challenged with immune stimulants poly I:C and lipopolysaccharides. AcBcl2 reduced poly I:C-induced cell death. The propagation of viral hemorrhagic septicemia virus (VHSV) was higher in the presence of AcBcl2. Cell mortality was higher in AcBcl2 when transfected cells were infected with VHSV, and a higher viral transcript was observed compared to their respective controls. In conclusion, AcBcl2 is an anti-apoptotic protein, and its activity may facilitate the propagation of VHSV.

Evolutionary conservation of a regulative pathway of erythropoiesis in Poikilothermic vertebrates

Apoptosis, programmed cell death, plays a central role in haematopoiesis. Mature erythrocytes of non-mammalian vertebrates maintain a permanent nucleus; these cells can undergo apoptosis (eryptosis), as do other somatic cells of a given non-mammalian vertebrate. In this study, we have investigated the expression and subcellular distribution of Bcl-2, Bcl-X_L and Bax proteins in the maturation phases and after X-ray irradiation of nucleated erythrocytes of Torpedo marmorata and Caretta caretta and the effect of X-ray irradiation on nucleated circulating erythrocytes of Torpedo marmorata. The cellular distribution of proteins was detected in erythrocytes by using immunocytochemistry at light microscopy and immunoelectron microscopy. The electrophoretic separation and immunoblotting of pro- and anti-apoptotic proteins of immature and mature erythroid cells was performed too, after X-ray irradiation of torpedoes. The results of the immunocytochemical analyses show an increase, in the expression level of Bax in mature as compared to young erythrocytes and a corresponding decrease of Bcl-2 and Bcl-X_L. This maturation pattern of Bax, Bcl-2 and Bcl-X_L was abrogated in X-ray irradiated torpedo erythrocytes. On the basis of these observations, Bax, Bcl-2 and Bcl-X_L seems to play a role in the erythropoiesis of Torpedo marmorata Risso and in Caretta caretta. In conclusion, the same apoptotic proteins of somatic cells appear to be conserved in circulating nucleated erythrocytes thus suggesting to play a role in the maturation of these cells.

Effects of exposure in utero to buprenorphine on oxidative stress and apoptosis in the hippocampus of rat pups

The study investigated the effect of buprenorphine (BUP) on oxidative indices and gene expression of apoptotic molecules in the hippocampus of neonates during the fetal stage. BUP (1 or 0.5 mg/kg) was subcutaneously administrated to pregnant rat dams. After parturition, the pups were maintained to the end of breastfeeding period, then hippocampi were assessed for oxidative stress indices [glutathione (GSH), thiobarbituric acid reactive substances (TBARS), superoxide dismutase (SOD), total antioxidant capacity (TAC)] and mRNA expression of apoptotic markers (Bax, Bcl2 and caspase 3). Our data indicated that BUP (0.5 mg/kg) administration during gestation significantly increased GSH and TAC concentrations in the hippocampus of pups versus control group (p < 0.05). BUP (0.5 and 1 mg/kg) administration significantly elevated the expression levels of Bcl2 in the hippocampus of neonates compared with controls. BUP injection (0.5 and 1 mg/kg) to pregnant rats markedly reduced the expression levels of caspase 3 in the hippocampus of neonates in BUP 0.5 group (p < 0.01) and BUP 1 group (p < 0.05) versus the controls. Our study indicated that BUP may potentiate antioxidant system and inhibit apoptosis and oxidative stress in the hippocampus of neonates received this drug during the fetal stage.

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BUP at low doses may potentiate antioxidant system.

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BUP at low dose may inhibit oxidative stress.

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BUP at low dose may act as an anti-apoptotic agent.

Inhibition of ER Stress by 2-Aminopurine Treatment Modulates Cardiomyopathy in a Murine Chronic Chagas Disease Model

Trypanosoma cruzi infection results in debilitating cardiomyopathy, which is a major cause of mortality and morbidity in the endemic regions of Chagas disease (CD). The pathogenesis of Chagasic cardiomyopathy (CCM) has been intensely studied as a chronic inflammatory disease until recent observations reporting the role of cardio-metabolic dysfunctions. In particular, we demonstrated accumulation of lipid droplets and impaired cardiac lipid metabolism in the hearts of cardiomyopathic mice and patients, and their association with impaired mitochondrial functions and endoplasmic reticulum (ER) stress in CD mice. In the present study, we examined whether treating infected mice with an ER stress inhibitor can modify the pathogenesis of cardiomyopathy during chronic stages of infection. T. cruzi infected mice were treated with an ER stress inhibitor 2-Aminopurine (2AP) during the indeterminate stage and evaluated for cardiac pathophysiology during the subsequent chronic stage. Our study demonstrates that inhibition of ER stress improves cardiac pathology caused by T. cruzi infection by reducing ER stress and downstream signaling of phosphorylated eukaryotic initiation factor (P-elF2α) in the hearts of chronically infected mice. Importantly, cardiac ultrasound imaging showed amelioration of ventricular enlargement, suggesting that inhibition of ER stress may be a valuable strategy to combat the progression of cardiomyopathy in Chagas patients.

Identification of a Bcl-xL homolog from orange-spotted grouper (Epinephelus coioides) involved in SGIV-induced nonapoptotic cell death

Bcl-2 family proteins play essential roles in modulating immune response and controlling cells' fate. Bcl-xL is one of anti-apoptotic protein in this family. In this study, a new Bcl-xL homolog (EcBcl-xL) was identified and characterized from orange-spotted grouper, Epinephelus coioides. EcBcl-xL encoded a 221 amino acid peptides that shared 86% identity to Larimichthys crocea Bcl-xL protein, contained four conserved BH domains and one transmembrane region. The predicted three-dimensional structure of EcBcl-xL was similar with Homo sapiens Bcl-xL. EcBcl-xL widely expressed in all tested tissues with highest expression in head kidney. Its expression level was significantly up-regulated after SGIV infection in vivo. Furthermore, overexpression of EcBcl-xL could inhibit SGIV-induced nonapoptotic cell death and suppressed viral genes transcriptions in GS cells. Our findings suggested that EcBcl-xL might play a role during virus infection through modulating SGIV-induced nonapoptotic cell death.

Transcriptome profiling of the antiviral immune response in Atlantic cod macrophages

A study was conducted to determine the transcriptome response of Atlantic cod (Gadus morhua) macrophages to the viral mimic, polyriboinosinic polyribocytidylic acid (pIC), using a 20K Atlantic cod microarray platform and qPCR. We identified 285 significantly up-regulated and 161 significantly down-regulated probes in cod macrophages 24 h after pIC stimulation. A subset of 26 microarray-identified transcripts was subjected to qPCR validation using samples treated with pIC or phosphate-buffered saline (control) over time (3, 6, 12, 24, 48 h), and 77% of them showed a significant response to pIC. The microarray and qPCR analyses in this study showed that pIC induced the expression of cod macrophage transcripts involved in RLR- and TLR-dependent pathogen recognition (e.g. tlr3, tlr7, mda5 and lgp2), as well as signal transducers (e.g. stat1 and nfkbia) and transcription activators (e.g. irf7 and irf10) in the MyD88-independent and dependent signalling pathways. Several immune effectors (e.g. isg15s, viperin, herc4, mip2 and ccl13) were significantly up-regulated in pIC-stimulated cod macrophages. The expression of some transcripts (e.g. irf7, irf10, viperin) was significantly up-regulated by pIC as early as 12 h. All pIC-induced transcripts had peak expression at either 24 h (e.g. tlr7, irf7, mip2) or 48 h (e.g. tlr3, lgp2, stat1). This study suggests possible roles of both vertebrate-conserved (e.g. tlr3 as an up-regulated gene) and fish-specific (tlr22g as a down-regulated gene) receptors in dsRNA recognition, and the importance of conserved and potentially fish-specific interferon stimulated genes in cod macrophages.

Identification, characterization and functional analysis of anti-apoptotic protein BCL-2-like gene from pufferfish, Takifugu obscurus, responding to bacterial challenge

Apoptosis plays a crucial role in many biological processes, including development, cellular homeostasis and immune responses. The BCL-2 family is a key regulator of the mitochondrial response to apoptotic signals in the intrinsic pathway. In this study, we identified and characterized the cDNA and expression pattern of pufferfish BCL-2 (PfBCL-2). The full-length cDNA of PfBCL-2 was 1412 bp with an open reading frame of 657 bp encoding a putative protein of 219 amino acids (Accession no: KP898414). The calculated molecular mass of the PfBCL-2 was 24.2 kDa with a predicted isoelectric point of 5.27. The deduced PfBCL-2 protein exhibited four highly conserved BCL-2 homology domains, suggesting that PfBCL-2 may play a similar role in the apoptotic-signaling pathway as in other species. Real-time PCR results showed that PfBCL-2 transcript was expressed in a wide range of tissues but exhibited the greatest level of expression in blood. Transcriptional responses of PfBCL-2 exhibited different spatial and temporal expression profiles in liver and blood after bacterial infection. PfBcl-2 transcript was significantly up-regulated in liver at 6, 12, 24 and 48 h (with maximum induction at 48 h) and was up-regulated in blood at 3, 6, 12 and 24 h (with maximum induction at 12 h). Meanwhile, recombinant PfBCL-2 fused with His6 tag was efficiently expressed in Escherichia coli BL21 (DE3) and purified using Ni-nitrilotriacetic acid resin. Western blot analysis indicated that its protein level appeared to be elevated during the initial bacterial infection. These results suggest that PfBCL-2 plays important roles in immune responses against bacteria challenge.

Identification and functional characterization of two Bcl-2 family protein genes in Zhikong scallop Chlamys farreri

Apoptosis plays significant roles in maintenance of homeostasis, immune defense and development. The Bcl-2 family proteins are important regulators of the intrinsic apoptosis. In the study, we have characterized a Bcl-2-like gene (named CfBcl-2) and a Bax-like gene (named CfBax) from the Zhikong scallop Chlamys farreri. The full-length of the CfBcl-2 cDNA is 944 nucleotides (nt) encoding a putative protein of 225 amino acid residues (aa) that contains four Bcl-2 homology (BH) domains, and the CfBax cDNA is 505 nt encoding a putative protein of 115 aa that contains three Bcl-2 BH domains. Sequence and phylogenetic analysis demonstrate that CfBcl-2 and CfBax present typical domain organization of the corresponding Bcl-2 related proteins and are more similar and clustered with their homologues of other molluscs. The two genes are ubiquitously expressed in six tissues of C. farreri, with the highest expression level of CfBcl-2 in adductor muscle and highest expression level of CfBax in gill. The expressions of CfBcl-2 and CfBax in hemocytes were both significantly up-regulated after an in vivo exposure of scallops to air, injection with lipopolysaccharide and infection with acute viral necrobiotic disease virus, and the expression patterns of the two genes after the three treatments vary in different change magnitude and up-regulation timespan. Yeast two-hybrid assay reveals a direct interaction between the CfBcl-2 and CfBax proteins. These results indicate that the CfBcl-2 and CfBax may participate in the apoptosis-based stress and immune responses against noxious stimulation.

An anti-apoptotic B-cell lymphoma-2 (BCL-2) from Channa striatus: Sequence analysis and delayed and advanced gene expression in response to fungal, bacterial and poly I:C induction

B-cell lymphoma-2 (BCL-2) is a suppressor of apoptosis and inhibits the caspase dependent apoptosis pathway. In this study, we report molecular characterization of a cDNA sequence encoded of BCL-2 from striped murrel, Channa striatus. A partial cDNA sequence of CsBCL-2 was identified from the striped murrel cDNA library during annotation. Subsequently, the full length CsBCL-2 cDNA sequence was obtained by an internal sequencing method using a forward primer. The sequence contains 699 nucleotide base pairs which encode 232 amino acid residues. The domain and motif analysis revealed that the CsBCL-2 polypeptide consists of BCL-2 homologous domain BH4 at the N-terminal region between 4 and 21 and the BCL-2 homologous domains BH1, BH2 and BH3 between 87 and 187. The CsBCL-2 polypeptide sequence does not have a signal peptide region, but it consists of two novel transmembrane regions at 134-152 and 209-226. The sequence analysis showed that the CsBCL-2 has highest sequence identity (70%) with BCL-2 like protein 1 (BCL-2 L1) from pufferfish Takifugu rubripes. The phylogenetic analysis showed that the CsBCL-2 was situated in the BCL-2 L1 fish clade. The secondary analysis showed that the CsBCL-2 protein consists of 132 amino acid residues in the α-helical region and 100 amino acid residues in the random coil region. The validated 3D structure of CsBCL-2 showed the active residues Gly(135) and Arg(136) in the 7th α-helical position, whereas Trp(178) is in the 9th α-helical region. CsBCL-2 mRNA transcription is predominately present in spleen and is upregulated upon being induced with fungus Aphanomyces invadans, bacteria Aeromonas hydrophila, Escherichia coli LPS, Laminaria digitata beta-1,3-glucan and poly I:C. Overall, the CsBCL-2 mRNA transcription results indicate the potential involvement of CsBCL-2 in immune system of C. striatus. However, further research at proteomic level is necessary to examine these predictions.

Development of a bacterial challenge test for gnotobiotic Nile tilapia Oreochromis niloticus larvae

Gastrointestinal microbiota have an important impact on fish health and disease, stimulating interest in a better understanding of how these gastrointestinal microbial communities are composed and consequently affect host fitness. In this respect, probiotic microorganisms have been extensively used in recent aquaculture production. To study the use of probiotics in the treatment of infectious diseases, the establishment of a method of experimental infection to obtain consistent results for mortality and infection in challenge tests is important. In pathogen-screening tests, 4 candidate pathogenic bacteria strains (Edwardsiella ictaluri gly09, E. ictaluri gly10, E. tarda LMG2793 and Streptococcus agalactiae LMG15977) were individually tested on xenic Nile tilapia larvae. Only Edwardsiella strains delivered via Artemia nauplii, with or without additional pathogen delivery via the culture water, led to increased mortality in fish larvae. A gnotobiotic Nile tilapia larvae model system was developed to provide a research tool to investigate the effects and modes-of-action of probiotics under controlled conditions. A double disinfection procedure using hydrogen peroxide and sodium hypochlorite solution was applied to the fish eggs, which were subsequently incubated in a cocktail of antibiotic and antifungal agents. In the gnotobiotic challenge test, E. ictaluri gly09R was added to the model system via Artemia nauplii and culture water, resulting in a significant mortality of the gnotobiotic fish larvae. The developed gnotobiotic Nile tilapia model can be used as a tool to extend understanding of the mechanisms involved in host-microbe interactions and to evaluate new methods of disease control.

Two molluscan BCL-2 family members from Manila clam, Ruditapes philippinarum: molecular characterization and immune responses

Apoptosis based immune responses are important component of host defense in mollusks. In this study, we have identified two novel molluscan BCL-2 cDNAs from Manila clam, Ruditapes philippinarum and named as RpBCL-2A and RpBCL-2B. There were four and three highly conserved BCL-2 homology (BH) regions in RpBCL-2A and RpBCL-2B, respectively suggesting these two genes could be different isoforms of anti-apoptotic BCL-2 family. Phylogenetic results revealed that Manila clam BCL-2 genes were clustered closely with invertebrate BCL-2 members. It gives evidence of their common origin and conserved features of invertebrate BCL-2 family. RpBCL-2A and 2B were expressed in tissue-specific manner showing the highest and lowest level of expression in gills and hemocytes, respectively. However there was no clear expression profile difference between two genes. After Vibrio tapetis challenge, transcriptional responses of RpBCL-2A and RpBCL-2B were induced in gills and hemocytes with high variation that could be due to effects of immune reactions of other host defense molecules.

The restricted binding repertoire of Bcl-B leaves Bim as the universal BH3-only prosurvival Bcl-2 protein antagonist

B-cell lymphoma-2 (Bcl-2) proteins mediate intrinsic-, or mitochondrial-, initiated apoptosis. We have investigated the structure and function of the least characterized Bcl-2 family member, Bcl-B, solving the crystal structure of a Bcl-B:Bim complex to 1.9 Å resolution. Bcl-B is distinguished from other Bcl-2 family members through an insertion of an unstructured loop between helices α5 and α6. Probing Bcl-B interactions with Bcl-2 homology (BH)3 motifs using a combination of biophysical- and cell-based assays revealed a unique BH3-only protein binding profile. Bcl-B has high-affinity interactions with Bim and Bik only. Our results not only delineate the mode of action of Bcl-B but also complete our understanding of the specific interactions between BH3-only proteins and their prosurvival Bcl-2 counterparts. Notably, we conclude that Bim is the universal prosurvival antagonist as no other BH3-only protein binds all six prosurvival proteins and that Mcl-1 and Bcl-x_L form a distinct prosurvival dyad.

Immune gene expression in trout cell lines infected with the fish pathogenic oomycete Saprolegnia parasitica

The oomycete Saprolegnia parasitica causes significant losses in the aquaculture industry, mainly affecting salmon, trout and catfish. Since the ban of malachite green, effective control measures are currently not available prompting a re-evaluation of the potential for immunological intervention. In this study, the immune response of salmonid cells is investigated at the transcript level, by analysis of a large set of immune response genes in four different rainbow trout cell lines (RTG-2, RTGill, RTL and RTS11) upon infection with S. parasitica. Proinflammatory cytokine transcripts were induced in all four cell lines, including IL-1β1, IL-8, IL-11, TNF-α2, as well as other components of the innate defences, including COX-2, the acute phase protein serum amyloid A and C-type lectin CD209a and CD209b. However, differences between the four cell lines were found. For example, the fold change of induction was much higher in the epithelial RTL and macrophage-like RTS11 cell lines compared to the fibroblast cell lines RTG-2 and RTGill. Several antimicrobial peptides (AMPs) were also up-regulated in response to Saprolegnia infection, including hepcidin and cathelicidin 1 (rtCATH1) and 2 (rtCATH2). An rtCATH2 peptide was synthesised and tested for activity and whilst it showed no killing activity for zoospores, it was able to delay sporulation of S. parasitica. These results demonstrate that particular immune genes are up-regulated in response to S. parasitica infection and that AMPs may play a crucial role in the first line of defence against oomycetes in fish.

Gene expression profiles of the spleen, liver, and head kidney in turbot (Scophthalmus maximus) along the infection process with Aeromonas salmonicida using an immune-enriched oligo-microarray

We evaluated the expression profiles of turbot in the spleen, liver, and head kidney across five temporal points of the Aeromonas salmonicida infection process using an 8 × 15 K Agilent oligo-microarray. The microarray included 2,176 different fivefold replicated gene probes designed from a turbot 3' sequenced EST database. We were able to identify 471 differentially expressed (DE) genes (17.3% of the whole microarray), 223 in the spleen, 246 in the liver, and 125 in the head kidney, in at least one of the five temporal points sampled for each organ. Most of these genes could be annotated (83.0%) and functionally categorized using Gene Ontology terms (69.1%) after the additional sequencing of DE genes from the 5' end. Many DE genes were related to innate and acquired immune functions in accordance to previous studies with this pathogen in other fish species. A high proportion of DE genes were organ specific (77.1%), but their associated GO functions were rather similar in the three organs. The most striking difference in functional distribution was observed between the up- and down-regulated gene groups. Up-regulated genes were mostly associated to key immune functions while down-regulated ones mainly involved metabolism- and transport-related genes. Genetic response appeared clustered in groups of genes with similar expression profiles along the temporal series. The spleen showed the most clustering while the liver and head kidney displayed a higher diversification. The information obtained will aid to understand the turbot immune response and will specifically be valuable to develop strategies of defense to A. salmonicida to achieve more resistant broodstocks for turbot industry.

Mcl-1 and YY1 inhibition and induction of DR5 by the BH3-mimetic Obatoclax (GX15-070) contribute in the sensitization of B-NHL cells to TRAIL apoptosis

The pan Bcl-2 family antagonist Obatoclax (GX15-070), currently in clinical trials, was shown to sensitize TRAIL-resistant tumors to TRAIL-mediated apoptosis via the release of Bak and Bim from Mcl-1 or Bcl-2/Bcl-XL complexes or by the activation of Bax, though other mechanisms were not examined. Herein, we hypothesize that Obatoclax-mediated sensitization to TRAIL apoptosis may also result from alterations of the apoptotic pathways. The TRAIL-resistant B-cell line Ramos was used as a model for investigation. Treatment of Ramos cells with Obatoclax significantly inhibited the expression of several members of the Bcl-2 family, dissociated Bak from Mcl-1 and inhibited the NFκB activity. Cells treated with Mcl-1 siRNA were sensitized to TRAIL apoptosis. We examined whether the sensitization of Ramos to TRAIL by Obatoclax resulted from signaling of the DR4 and/or DR5. Transfection with DR5 siRNA, but not with DR4 siRNA, sensitized the cells to apoptosis following treatment with Obatoclax and TRAIL. The signaling via DR5 correlated with Obatoclax-induced inhibition of the DR5 repressor Yin Yang 1 (YY1). Transfection with YY1 siRNA sensitized the cells to TRAIL apoptosis following treatment with Obatoclax and TRAIL. Overall, the present findings reveal a new mechanism of Obatoclax-induced sensitization to TRAIL apoptosis and the involvement of the inhibition of NFκB activity and downstream Mcl-1 and YY1 expressions and activities.

Transcriptome responses to heat stress in the nucleated red blood cells of the rainbow trout (Oncorhynchus mykiss)

The retention of a nucleus in the mature state of fish red blood cells (RBCs) and the ability to easily collect and manipulate blood in nonterminal experiments make blood an ideal tissue on which to study the cellular stress response in fish. Through the use of the cGRASP 16K salmonid microarray, we investigated differences in RBC global gene transcription in fish held under control conditions (11°C) and exposed to heat stress (1 h at 25°C followed by recovery at 11°C). Repeated blood sampling (via a dorsal aorta cannula) enables us to examine the individual stress response over time. Samples were taken preheat stress (representing individual control) and at 4 and 24 h postheat stress (representing early and late transcriptional regulation). Approximately 3,000 microarray features had signal above threshold when hybridized with RBC RNA-derived targets, and cannulation did not have a detectable effect on RBC mRNA expression at the investigated time points. Genes involved in the stress response, immune response, and apoptosis were among those showing the highest dysregulation during both early and late transcriptional regulation. Additionally, genes related to the differentiation and development of blood cells were transcriptionally upregulated at the 24 h time point. This study provides a broader understanding of the mechanisms underpinning the stress response in fish and the discovery of novel genes that are regulated in a stress specific manner. Moreover, salmonid transcripts that are consistently dysregulated in blood in response to heat stress are potential candidates of nonlethal biomarkers of exposure to this particular stressor.