Structural and functional diversification in the teleost S100 family of calcium-binding proteins

Molecular Actors of Inflammation and Their Signaling Pathways: Mechanistic Insights from Zebrafish

Inflammation is a hallmark of the physiological response to aggressions. It is orchestrated by a plethora of molecules that detect the danger, signal intracellularly, and activate immune mechanisms to fight the threat. Understanding these processes at a level that allows to modulate their fate in a pathological context strongly relies on in vivo studies, as these can capture the complexity of the whole process and integrate the intricate interplay between the cellular and molecular actors of inflammation. Over the years, zebrafish has proven to be a well-recognized model to study immune responses linked to human physiopathology. We here provide a systematic review of the molecular effectors of inflammation known in this vertebrate and recapitulate their modes of action, as inferred from sterile or infection-based inflammatory models. We present a comprehensive analysis of their sequence, expression, and tissue distribution and summarize the tools that have been developed to study their function. We further highlight how these tools helped gain insights into the mechanisms of immune cell activation, induction, or resolution of inflammation, by uncovering downstream receptors and signaling pathways. These progresses pave the way for more refined models of inflammation, mimicking human diseases and enabling drug development using zebrafish models.

An adult zebrafish model for adherent-invasive Escherichia coli indicates protection from AIEC infection by probiotic E. coli Nissle

Adherent-invasive Escherichia coli (AIEC) is an opportunistic pathogen associated with major inflammatory bowel disease, Crohn disease, and ulcerative colitis. Unfavorable conditions push commensal AIEC to induce gut inflammation, sometimes progressing to inflammation-induced colon cancer. Recently, zebrafish have emerged as a useful model to study human intestinal pathogens. Here, a zebrafish model to study AIEC infection was developed. Bath inoculation with AIEC resulted in colonization and tissue disruption in the zebrafish intestine. Gene expression of pro-inflammatory markers including interleukin-1β (IL-1β), tumor necrosis factor alpha (TNFα), interferon-γ (IFNγ), and S100A-10b (akin to human calprotectin) in the zebrafish intestine was significantly induced by AIEC infection. The probiotic E. coli Nissle 1917 (EcN) was tested as a therapeutic and prophylactic against AIEC infection and reduced AIEC colonization, tissue damage, and pro-inflammatory responses in zebrafish. Furthermore, EcN diminished the propionic-acid-augmented hyperinfection of AIEC in zebrafish. Thus, this study shows the efficacy of EcN against AIEC in an AIEC-zebrafish model.

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AIEC can colonize, invade, and induce inflammation in the zebrafish gut

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Probiotic E. coli Nissle can protect zebrafish from AIEC infection

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EcN is effective both prophylactically and therapeutically against AIEC-induced IBD

Intranasal delivery of SARS-CoV-2 spike protein is sufficient to cause olfactory damage, inflammation and olfactory dysfunction in zebrafish

Anosmia, loss of smell, is a prevalent symptom of SARS-CoV-2 infection. Anosmia may be explained by several mechanisms driven by infection of non-neuronal cells and damage in the nasal epithelium rather than direct infection of olfactory sensory neurons (OSNs). Previously, we showed that viral proteins are sufficient to cause neuroimmune responses in the teleost olfactory organ (OO). We hypothesize that SARS-CoV-2 spike (S) protein is sufficient to cause olfactory damage and olfactory dysfunction. Using an adult zebrafish model, we report that intranasally delivered SARS-CoV-2 S RBD mostly binds to the non-sensory epithelium of the olfactory organ and causes severe olfactory histopathology characterized by loss of cilia, hemorrhages and edema. Electrophysiological recordings reveal impaired olfactory function to both food and bile odorants in animals treated intranasally with SARS-CoV-2 S RBD. However, no loss of behavioral preference for food was detected in SARS-CoV-2 S RBD treated fish. Single cell RNA-Seq of the adult zebrafish olfactory organ indicated widespread loss of olfactory receptor expression and inflammatory responses in sustentacular, endothelial, and myeloid cell clusters along with reduced numbers of T_regs. Combined, our results demonstrate that intranasal SARS-CoV-2 S RBD is sufficient to cause structural and functional damage to the zebrafish olfactory system. These findings may have implications for intranasally delivered vaccines against SARS-CoV-2.

Rodlet cells in kidney of goldfish (Carassius auratus, Linnaeus 1758): A light and confocal microscopy study

Rodlet cells (RCs) have always been an enigma for scientists. RCs have been given a variety of activities over the years, including ion transport, osmoregulation, and sensory function. These cells, presumably as members of the granulocyte line, are present only in teleosts and play a role in the innate immune response. RCs are migratory cells found in a variety of organs, including skin, vascular, digestive, uropoietic, reproductive, and respiratory systems, and present distinct physical properties that make them easily recognizable in tissues and organs. The development of RCs can be divided into four stages: granular, transitional, mature, and ruptured, having different morphological characteristics. Our study aims to characterize the different stages of these cells by histomorphological and histochemical techniques. Furthermore, we characterized these cells at all stages with peroxidase and fluorescence immunohistochemical techniques using different antibodies: S100, tubulin, α-SMA, piscidin, and for the first time TLR-2. From our results, the immunoreactivity of these cells to the antibodies performed may confirm that RCs play a role in fish defense mechanisms, helping to expand the state of the art on immunology and immune cells of teleosts.

The Calcium Binding Protein S100A11 and Its Roles in Diseases

The calcium binding protein S100 family in humans contains 21 known members, with each possessing a molecular weight between 10 and 14 kDa. These proteins are characterized by a unique helix-loop-helix EF hand motif, and often form dimers and multimers. The S100 family mainly exists in vertebrates and exerts its biological functions both inside cells as a calcium sensor/binding protein, as well as outside cells. S100A11, a member of the S100 family, may mediate signal transduction in response to internal or external stimuli and it plays various roles in different diseases such as cancers, metabolic disease, neurological diseases, and vascular calcification. In addition, it can function as chemotactic agent in inflammatory disease. In this review, we first detail the discovery of S100 proteins and their structural features, and then specifically focus on the tissue and organ expression of S100A11. We also summarize its biological activities and roles in different disease and signaling pathways, providing an overview of S100A11 research thus far.

Divalent cations influence the dimerization mode of murine S100A9 protein by modulating its disulfide bond pattern

S100A9, with its congener S100A8, belongs to the S100 family of calcium-binding proteins found exclusively in vertebrates. These two proteins are major constituents of neutrophils. In response to a pathological condition, they can be released extracellularly and become alarmins that induce both pro- and anti-inflammatory signals, through specific cell surface receptors. They also act as antimicrobial agents, mainly as a S100A8/A9 heterocomplex, through metal sequestration. The mechanisms whereby divalent cations modulate the extracellular functions of S100A8 and S100A9 are still unclear. Importantly, it has been proposed that these ions may affect both the ternary and quaternary structure of these proteins, thereby influencing their physiological properties. In the present study, we report the crystal structures of WT and C80A murine S100A9 (mS100A9), determined at 1.45 and 2.35 Å resolution, respectively, in the presence of calcium and zinc. These structures reveal a canonical homodimeric form for the protein. They also unravel an intramolecular disulfide bridge that stabilizes the C-terminal tail in a rigid conformation, thus shaping a second Zn-binding site per S100A9 protomer. In solution, mS100A9 apparently binds only two zinc ions per homodimer, with an affinity in the micromolar range, and aggregates in the presence of excess zinc. Using mass spectrometry, we demonstrate that mS100A9 can form both non-covalent and covalent homodimers with distinct disulfide bond patterns. Interestingly, calcium and zinc seem to affect differentially the relative proportion of these forms. We discuss how the metal-dependent interconversion between mS100A9 homodimers may explain the versatility of physiological functions attributed to the protein.

Marking vertebrates langerhans cells, from fish to mammals

Langerhans cells (LCs) are specialized dendritic cells (DCs) that play a defense role in recognizing foreign antigens, in tissue where antigenic exposures occur, as in the skin and mucous membranes. LCs are able to continuously move within the tissues thanks to dendritic contraction and distension performing their surveillance and/or phagocytosis role. These cells are characterized by the presence of Birbeck granules in their cytoplasm, involved in endocytosis. LCs have been characterized in several classes of vertebrates, from fish to mammals using different histological and molecular techniques. The aim of the present review is to define the state of art and the need of information about immunohistochemical markers of LCs in different classes of vertebrates. The most used immunohistochemical (IHC) markers are Langerin/CD207, CD1a, S-100 and TLR. These IHC markers are described in relation to their finding in different vertebrate classes with phylogenetical considerations. Among the four markers, Langerin/CD207 and TLR have the widest spectrum of cross reactivity in LCs.

Transcriptomic responses of S100 family to bacterial and viral infection in zebrafish

The S100 family proteins are a group of small acidic polypeptides and have diverse functions in regulating many aspects of physiological processes. They are structurally conserved and possess two EF-hands which are central for calcium-mediated functions. In this study, 14 S100 cDNA sequences were determined in zebrafish and their genomic organizations confirmed. Re-analyzing the gene synteny of the S100 loci identified two major S100 loci in Chr16 and Chr19 which share remarkable conservation with the S100 locus in human Chr1, suggesting they may have evolved from a single locus during the teleost specific whole genome duplication event. It appears that the homologues of human S100G and S100P have been lost in zebrafish. Expression analysis reveals that S100W, ICN1 and ICN2 are markedly expressed in embryos. Further, the transcripts of S100 genes are relatively abundant in mucosal tissues such as gills and gut. Intraperitoneal injection of poly(I:C) resulted in up-regulation of most S100 genes in the gut and spleen, with highest induction of S100V2 and S100Z detected. In fish challenged with spring viremia of carp virus (SVCV), expression of most S100 family genes was increased in the spleen between day 1 and 7 post infection, with consistent induction seen for the S100A1, S100A10b, S100B, S100ICN1, S100T, S100U, S100V1 and S100Z. Interestingly, intraperitoneal injection of Edwardsiella tarda down-regulated S100 expression in the gut but resulted in induction in the spleen. The results demonstrate that the S100 family genes are differentially modulated by bacterial and viral pathogens in zebrafish.

Characterization of the fish ovarian stroma during the spawning season: Cytochemical, immunohistochemical and ultrastructural studies

The changes in the ovarian stroma of the fish during their spawning season become it an excellent biological model for studies on cellular and vascular elements due to the intense tissue remodeling in fish occur naturally throughout this critical period. The present study aims to investigate the cellular and vascular components of the ovarian stroma of Redbelly tilapia during the spawning season by conventional, immunohistochemical stains as well as to detect the ultrastructural characteristics for each stromal component. The histological examinations revealed a series of blood vessels with special structures, include throttle artery, glomus, spirally oriented arterioles, modified arteries, and veins as well as arteriovenous anastomosis. Various types of cells were detected in the stroma include; telocytes, rodlet cells, mast cells, eosinophils, neutrophils, lymphocytes, fibroblasts, macrophages, melanocytes, adipocytes, dendritic cells, and endocrine (steroidogenic, interstitial) cells. Moreover, these stromal cells showed a broad range of staining affinity against c-kit, desmin, and s100-protein. Bundles of nerve fibers were detected between the follicles. This study exposed various cellular and vascular components with distinct functions in the ovary of Redbelly tilapia during the spawning season.

Otoferlin Depletion Results in Abnormal Synaptic Ribbons and Altered Intracellular Calcium Levels in Zebrafish

The protein otoferlin plays an essential role at the sensory hair cell synapse. Mutations in otoferlin result in deafness and depending on the species, mild to strong vestibular deficits. While studies in mouse models suggest a role for otoferlin in synaptic vesicle exocytosis and endocytosis, it is unclear whether these functions are conserved across species. To address this question, we characterized the impact of otoferlin depletion in zebrafish larvae and found defects in synaptic vesicle recycling, abnormal synaptic ribbons, and higher resting calcium concentrations in hair cells. We also observed abnormal expression of the calcium binding hair cell genes s100s and parvalbumin, as well as the nogo related proteins rtn4rl2a and rtn4rl2b. Exogenous otoferlin partially restored expression of genes affected by endogenous otoferlin depletion. Our results suggest that in addition to vesicle recycling, depletion of otoferlin disrupts resting calcium levels, alters synaptic ribbon architecture, and perturbs transcription of hair cells specific genes during zebrafish development.

Habitat Partitioning and its Possible Genetic Background Between Two Sympatrically Distributed Eel Species in Taiwan

The geographical distributions of the Japanese eel (Anguilla japonica) and Giant-mottled eel (A. marmorata) overlap in many regions in East Asia and therefore suffer from interspecific competition in the same rivers. After a long period of adaptation, the Japanese eel and Giant-mottled eel may exhibit habitat partitioning in the rivers to diminish the interspecific competition between them. In this study, we conducted a field investigation in the Fengshan River in Taiwan to survey the habitat distributions of the Japanese eel and Giant-mottled eel throughout a river. Moreover, we investigated whether their habitat distributions are related to their swimming and upstream migration. Thus, the mRNA expression levels of several candidate genes that may be associated with the swimming and upstream migration of eel were examined in the glass eels of the Japanese eel and Giant-mottled eel. Field investigation indicated that the Japanese eel mainly inhabited the lower and middle reaches of the Fengshan River, but the Giant- mottled eel was distributed over the middle to upper reaches. The mRNA expression levels of fMYH, dio2, gria3, and neurod1 were higher in the Giant-mottled eel than in the Japanese eel, implying that Giant- mottled eels might have better swimming bursts and more active upstream migration than Japanese eels. These results suggest that there is a habitat partition at which these two eel species coexist in a river, and their habitat distributions may be linked to their swimming bursts and upstream migration. Determining the habitat distributions of freshwater eels is important for developing applicable plans for eel conservation and resource management.

Convergent vomeronasal system reduction in mammals coincides with convergent losses of calcium signalling and odorant-degrading genes

The vomeronasal system (VNS) serves crucial functions for detecting olfactory clues often related to social and sexual behaviour. Intriguingly, two of the main components of the VNS, the vomeronasal organ (VNO) and the accessory olfactory bulb, are regressed in aquatic mammals, several bats and primates, likely due to adaptations to different ecological niches. To detect genomic changes that are associated with the convergent reduction of the VNS, we performed the first systematic screen for convergently inactivated protein-coding genes associated with convergent VNS reduction, considering 106 mammalian genomes. Extending previous studies, our results support that Trpc2, a cation channel that is important for calcium signalling in the VNO, is a predictive molecular marker for the presence of a VNS. Our screen also detected the convergent inactivation of the calcium-binding protein S100z, the aldehyde oxidase Aox2 that is involved in odorant degradation, and the uncharacterized Mslnl gene that is expressed in the VNO and olfactory epithelium. Furthermore, we found that Trpc2 and S100z or Aox2 are also inactivated in otters and Phocid seals for which no morphological data about the VNS are available yet. This predicts a VNS reduction in these semi-aquatic mammals. By examining the genomes of 115 species in total, our study provides a detailed picture of how the convergent reduction of the VNS coincides with gene inactivation in placental mammals. These inactivated genes provide experimental targets for studying the evolution and biological significance of the olfactory system under different environmental conditions.

Evolution of S100A3 and PAD3, two important genes for mammalian hair

Hair is one of the defining characteristics of mammals. The hair shaft has a two-layer structure comprising the cortex, which is the inner layer and is composed of cortical cells, and the cuticle, which is the outermost layer. S100 calcium-binding protein A3 (S100A3) is expressed at high levels in the human hair cuticle. Arginine 51 of S100A3 protein is citrullinated specifically by peptidylarginine deiminase 3 (PAD3), and this citrullination is related to maturation of the cuticle. However, the detailed evolutionary processes of S100A3 and PAD3 during mammalian evolution are unknown. Here, we show that nonsynonymous changes in S100A3 accelerated in the common ancestral branch of mammals, probably as a result of positive selection that returned after the acquisition of hair cuticle-specific function in mammals. Later, pseudogenisation or nonfunctionalisation of S100A3 and PAD3 occurred in some species, such as the cetaceans. Our results show that positive selection and relaxation of the functional constraints of genes played important roles in the evolution of mammalian hair.

Evaluating the Effects of Various Decalcification Protocols on Immunohistochemical Staining in Zebrafish (Danio rerio)

Fixation and decalcification can alter protein structure in tissues, influencing the efficacy of primary antibodies routinely used in immunohistochemical (IHC) staining. Histologic examination of zebrafish requires both processes, making staining and analysis potentially challenging. Here, we investigated the effects of common fixation and decalcification protocols on IHC staining in zebrafish. We also identified zebrafish-reactive and -specific antibodies for use in research and diagnostics. For several of the antibodies, time spent in Dietrich's fixative containing 2% glacial acetic acid or 3.4% formaldehyde followed by decalcification with ethylenediaminetetraacetic acid (EDTA) significantly impacted IHC staining quality, particularly regarding staining intensity. Protocols utilizing shorter fixation times produced higher-quality stains. In addition, individual markers were variably affected by the type of fixative. Dietrich's fixative significantly reduced staining quality for the "neural" markers: glial fibrillar acidic protein, chromogranin A, S100. A negative time-dependent effect of fixation on staining quality was found for several antibodies: muscle actin (Dietrich's only), cytokeratin AE1/AE3, chromogranin, and S100. Neither decalcification protocol had a statistically significant negative time-dependent effect on staining quality. Based on our results, we suggest shorter fixation and decalcification protocols to best preserve IHC staining quality as well as recommend deliberate selection of the fixative used depending on the protein of interest.

Effects of high-soy diet on S100 gene expression in liver and intestine of rainbow trout (Oncorhynchus mykiss)

The current study examines expression of S100 genes, a group of calcium-sensing proteins poorly characterized in fishes. In mammals, these proteins are known to play roles beyond calcium-signaling, including mediation of inflammatory processes. Some S100 proteins also serve as biomarkers for a variety of autoinflammatory conditions. It is well known that salmonids exhibit varying degrees of intestinal enteritis when exposed to alternative feed ingredients containing antinutritional factors, with soybean meal (SBM) being one of the best characterized. The etiology of soy-caused distal enteritis isn't entirely understood but displays similar histopathological alterations to the gut observed in human mucosal inflammatory bowel diseases. We sought to determine if teleost S100 genes show a concomitant response like that observed in mammals, utilizing rainbow trout fed high-soy diets as a model for intestinal inflammation. We examined expression of fourteen known salmonid S100 genes in the liver, first segment of the mid-intestine (proximal intestine), and second segment of the mid-intestine (distal intestine). After 12 weeks on a high-soy diet containing 40% SBM, we observed upregulation of several S100 genes in the distal intestine (S100I2, A10a, V1, V2, and W), no changes in the proximal intestine, and downregulation of S100V2 in the liver. Overall, our results provide further knowledge of the expression of S100 genes and provide targets for future research regarding inflammatory processes in the rainbow trout gut.

Transcriptomic Analysis of Zebrafish TDP-43 Transgenic Lines

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive neurodegenerative disorder that affects both upper and lower motor neurons, leading to muscle atrophy with spasticity and eventual death in 3-5 years after the disease onset. More than 50 mutations linked to ALS have been found in the gene TARDBP, encoding the protein TDP-43 that is the predominant component of neuronal inclusions in ALS. TDP-43 is an RNA binding protein with glycine-rich domains that binds to more than 6,000 RNAs in the human brain. However, ALS-related mutations do not appear to affect the function of these genes, indicating that a toxic gain-of-function may occur. We generated transgenic zebrafish lines expressing human TDP-43, either the wild-type form or the ALS-causative G348C mutation identified in a subset of ALS patients, with the transgene expression driven by an inducible heat shock promoter in order to bypass a potential early mortality. The expression of the mutant but not the wild-type human TDP-43 in zebrafish embryos induced a reduction of the locomotor activity in response to touch compared to controls and moderate axonopathy of the motor neurons of the spinal cord, with premature branching of the main axonal branch, recapitulating previous results obtained by mRNA injections. We used these lines to investigate transcriptomic changes due to the presence of mutant TDP-43 using RNA sequencing and have found 159 genes that are differentially expressed compared to control, with 67 genes up-regulated and 92 genes down-regulated. These transcriptomic changes are in line with recent transcriptomic data obtained in mouse models, indicating that these zebrafish transgenic lines are adequate to further study TDP-43-related ALS.

The tegumental allergen-like proteins of Schistosoma mansoni: A biochemical study of SmTAL4-TAL13

Schistosoma mansoni, like other trematodes, expresses a number of unusual calcium binding proteins which consist of an EF-hand domain joined to a dynein light chain-like (DLC-like) domain by a flexible linker. These proteins have been implicated in host immune responses and drug binding. Three members of this protein family from S. mansoni (SmTAL1, SmTAL2 and SmTAL3) have been well characterised biochemically. Here we characterise the remaining family members from this species (SmTAL4-13). All of these proteins form homodimers and all except SmTAL5 bind to calcium and manganese ions. SmTAL9, 10 and 11 also bind to magnesium ions. The antischistosomal drug, praziquantel interacts with SmTAL4, 5 and 8. Some family members also bind to calmodulin antagonists such as chlorpromazine and trifluoperazine. Molecular modelling suggests that all ten proteins adopt similar overall folds with the EF-hand and DLC-like domains folding discretely. Bioinformatics analyses suggest that the proteins may fall into two main categories: (i) those which bind calcium ions reversibly at the second EF-hand and may play a role in signalling (SmTAL1, 2, 8 and 12) and (ii) those which bind calcium ions at the first EF-hand and may play either signalling or structural roles (SmTAL7, 9, 10 and 13). The remaining proteins include those which do not bind calcium ions (SmTAL3 and 5) and three other proteins (SmTAL4, 6 and 11). The roles of these proteins are less clear, but they may also have structural roles.

Transcriptomic Analysis of Zebrafish TDP-43 Transgenic Lines

Amyotrophic lateral sclerosis (ALS) is a late-onset progressive neurodegenerative disorder that affects both upper and lower motor neurons, leading to muscle atrophy with spasticity and eventual death in 3-5 years after the disease onset. More than 50 mutations linked to ALS have been found in the gene TARDBP, encoding the protein TDP-43 that is the predominant component of neuronal inclusions in ALS. TDP-43 is an RNA binding protein with glycine-rich domains that binds to more than 6,000 RNAs in the human brain. However, ALS-related mutations do not appear to affect the function of these genes, indicating that a toxic gain-of-function may occur. We generated transgenic zebrafish lines expressing human TDP-43, either the wild-type form or the ALS-causative G348C mutation identified in a subset of ALS patients, with the transgene expression driven by an inducible heat shock promoter in order to bypass a potential early mortality. The expression of the mutant but not the wild-type human TDP-43 in zebrafish embryos induced a reduction of the locomotor activity in response to touch compared to controls and moderate axonopathy of the motor neurons of the spinal cord, with premature branching of the main axonal branch, recapitulating previous results obtained by mRNA injections. We used these lines to investigate transcriptomic changes due to the presence of mutant TDP-43 using RNA sequencing and have found 159 genes that are differentially expressed compared to control, with 67 genes up-regulated and 92 genes down-regulated. These transcriptomic changes are in line with recent transcriptomic data obtained in mouse models, indicating that these zebrafish transgenic lines are adequate to further study TDP-43-related ALS.

A review of S100 protein family in lung cancer

S100 protein family, representing 25 relatively small calcium binding proteins, has been reported to be involved in multiple stages of tumorigenesis and progression. These proteins are considered having potential value to be adopted as novel biomarkers in the detection and accurate prediction of many kinds of tumors, including lung cancer. As the one having the highest morbidity and mortality among all cancers, lung carcinoma is still occult for detection, especially at early stage. S100 proteins take participation in the lung neoplasia through playing intracellular and/or extracellular functions, therefore getting involved in a variety of biological processes such as differentiation, proliferation, and migration. A few members have also been testified to modulate TGF-β/Smad-3 mediated transcriptional activity of target genes involved in tumor promotion. In addition to that, a number of proteins in this family have already been reported to experience an abnormal trend in lung cancer at cell, serum and tissue levels. Thus, S100 proteins may serve as effective biomarkers for suspected or already diagnosed lung cancer patients. In future, S100 protein family might be applied as therapeutic targets in clinical treatment of lung cancer. In this review, we firstly summed up the biological and clinical evidence connecting S100 proteins and lung cancer, which has not been summarized before.

Multiple Evolutionary Origins of Ubiquitous Cu2+ and Zn2+ Binding in the S100 Protein Family

The S100 proteins are a large family of signaling proteins that play critical roles in biology and disease. Many S100 proteins bind Zn2+, Cu2+, and/or Mn2+ as part of their biological functions; however, the evolutionary origins of binding remain obscure. One key question is whether divalent transition metal binding is ancestral, or instead arose independently on multiple lineages. To tackle this question, we combined phylogenetics with biophysical characterization of modern S100 proteins. We demonstrate an earlier origin for established S100 subfamilies than previously believed, and reveal that transition metal binding is widely distributed across the tree. Using isothermal titration calorimetry, we found that Cu2+ and Zn2+ binding are common features of the family: the full breadth of human S100 paralogs-as well as two early-branching S100 proteins found in the tunicate Oikopleura dioica-bind these metals with μM affinity and stoichiometries ranging from 1:1 to 3:1 (metal:protein). While binding is consistent across the tree, structural responses to binding are quite variable. Further, mutational analysis and structural modeling revealed that transition metal binding occurs at different sites in different S100 proteins. This is consistent with multiple origins of transition metal binding over the evolution of this protein family. Our work reveals an evolutionary pattern in which the overall phenotype of binding is a constant feature of S100 proteins, even while the site and mechanism of binding is evolutionarily labile.

Cloning and characterization of two duplicated interleukin-17A/F2 genes in common carp (Cyprinus carpio L.): Transcripts expression and bioactivity of recombinant IL-17A/F2

Interleukin-17 (IL-17) plays an important role in inflammation and host defense in mammals. In this study, we identified two duplicated IL-17A/F2 genes in the common carp (Cyprinus carpio) (ccIL-17A/F2a and ccIL-17A/F2b), putative encoded proteins contain 140 amino acids (aa) with conserved IL-17 family motifs. Expression analysis revealed high constitutive expression of ccIL-17A/F2s in mucosal tissues, including gill, skin and intestine, their expression could be induced by Aeromonas hydrophila, suggesting a potential role in mucosal immunity. Recombinant ccIL-17A/F2a protein (rccIL-17A/F2a) produced in Escherichia coli could induce the expression of proinflammatory cytokines (IL-1β) and the antimicrobial peptides S100A1, S100A10a and S100A10b in the primary kidney in a dose- and time-dependent manner. Above findings suggest that ccIL-17A/F2 plays an important role in both proinflammatory and innate immunity. Two duplicated ccIL-17A/F2s showed different expression level with ccIL-17A/F2a higher than b, comparison of two 5' regulatory regions indicated the length from anticipated promoter to transcriptional start site (TSS) and putative transcription factor binding site (TFBS) were different. Promoter activity of ccIL-17A/F2a was 2.5 times of ccIL-17A/F2b which consistent with expression results of two genes. These suggest mutations in 5'regulatory region contributed to the differentiation of duplicated genes. To our knowledge, this is the first report to analyze 5'regulatory region of piscine IL-17 family genes.

Role of S100 Proteins in Colorectal Carcinogenesis

The family of S100 proteins represents 25 relatively small (9-13 kD) calcium binding proteins. These proteins possess a broad spectrum of important intracellular and extracellular functions. Colorectal cancer is the third most common cancer in men (after lung and prostate cancer) and the second most frequent cancer in women (after breast cancer) worldwide. S100 proteins are involved in the colorectal carcinogenesis through different mechanisms: they enable proliferation, invasion, and migration of the tumour cells; furthermore, S100 proteins increase angiogenesis and activate NF-κβ signaling pathway, which plays a key role in the molecular pathogenesis especially of colitis-associated carcinoma. The expression of S100 proteins in the cancerous tissue and serum levels of S100 proteins might be used as a precise diagnostic and prognostic marker in patients with suspected or already diagnosed colorectal neoplasia. Possibly, in the future, S100 proteins will be a therapeutic target for tailored anticancer therapy.

Identification of sensory hair-cell transcripts by thiouracil-tagging in zebrafish

Background

Sensory hair cells are exquisitely sensitive to mechanical stimuli and as such, are prone to damage and apoptosis during dissections or in vitro manipulations. Thiouracil (TU)-tagging is a noninvasive method to label cell type-specific transcripts in an intact organism, thereby meeting the challenge of how to analyze gene expression in hair cells without the need to sort cells. We adapted TU-tagging to zebrafish to identify novel transcripts expressed in the sensory hair cells of the developing acoustico-lateralis organs.

Methods

We created a transgenic line of zebrafish expressing the T.gondii uracil phospho-ribosyltransferase (UPRT) enzyme specifically in the hair cells of the inner ear and lateral line organ. RNA was labeled by exposing 3 days post-fertilization (dpf) UPRT transgenic larvae to 2.5 mM 4-thiouracil (4TU) for 15 hours. Following total RNA isolation, poly(A) mRNA enrichment, and purification of TU-tagged RNA, deep sequencing was performed on the input and TU-tagged RNA samples. 

Results

Analysis of the RNA sequencing data revealed the expression of 28 transcripts that were significantly enriched (adjusted p-value < 0.05) in the UPRT TU-tagged RNA relative to the input sample. Of the 25 TU-tagged transcripts with mammalian homologs, the expression of 18 had not been previously demonstrated in zebrafish hair cells. The hair cell-restricted expression for 17 of these transcripts was confirmed by whole mount mRNA in situ hybridization in 3 dpf larvae.

Conclusions

The hair cell-restricted pattern of expression of these genes offers insight into the biology of this receptor cell type and may serve as useful markers to study the development and function of sensory hair cells. In addition, our study demonstrates the utility of TU-tagging to study nascent transcripts in specific cell types that are relatively rare in the context of the whole zebrafish larvae.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2072-5) contains supplementary material, which is available to authorized users.

Combinatorial analysis of calcium-binding proteins in larval and adult zebrafish primary olfactory system identifies differential olfactory bulb glomerular projection fields

In the zebrafish (Danio rerio) olfactory epithelium, the calcium-binding proteins (CBPs) calretinin and S100/S100-like protein are mainly expressed in ciliated or crypt olfactory sensory neurons (OSNs), respectively. In contrast parvalbumin and calbindin1 have not been investigated. We present a combinatorial immunohistological analysis of all four CBPs, including their expression in OSNs and their axonal projections to the olfactory bulb in larval and adult zebrafish. A major expression of calretinin and S100 in ciliated and crypt cells, respectively, with some expression of S100 in microvillous cells is confirmed. Parvalbumin and calbindin1 are strongly expressed in ciliated and microvillous cells, but not in crypt cells. Moreover, detailed combinatorial double-label experiments indicate that there are eight subpopulations of zebrafish OSNs: S100-positive crypt cells (negative for all other three CBPs), parvalbumin only, S100 and parvalbumin, parvalbumin and calbindin1, and parvalbumin and calbindin1 and calretinin-positive microvillous OSNs, as well as a major parvalbumin and calbindin1 and calretinin, and minor parvalbumin and calbindin1 and calretinin-only-positive ciliated OSN populations. CBP-positive projections to olfactory bulb are consistent with previous reports of ciliated OSNs projecting to dorsal and ventromedial glomerular fields and microvillous OSNs to ventrolateral glomerular fields. We newly describe parvalbumin-positive fibers to the mediodorsal field which is calretinin free, with its anterior part showing additionally calbindin1-positive fibers, but absence thereof in the posterior part, indicating an origin from microvillous OSNs in both parts. One singular glomerulus (mdG2) exhibits S100 and parvalbumin-positive fibers, apparently originating from all crypt cells plus some microvillous OSNs. Arguments for various olfactory labeled lines are discussed.

Divergent immunity and energetic programs in the gills of migratory and resident Oncorhynchus mykiss

Divergent life history strategies occur in steelhead or rainbow trout Oncorhynchus mykiss, and many populations produce both migrant (anadromous fish that move to the ocean after rearing) and resident (do not migrate and remain in fresh water) individuals. Mechanisms leading to each type are only partially understood; while the general tendency of a population is heritable, individual tendency may be plastic, influenced by local environment. Steelhead hatchery programmes aim to mitigate losses in wild stocks by producing trout that will migrate to the ocean and not compete with wild trout for limited freshwater resources. To increase our understanding of gill function in these migratory or resident phenotypes, here we compare gill transcriptome profiles of hatchery-released fish either at the release site (residents) or five river kilometres downstream while still in full fresh water (migrants). To test whether any of these genes can be used as predictive markers for smoltification, we compared these genes between migrant-like and undifferentiated trout while still in the hatchery in a common environment (prerelease). Results confirmed the gradual process of smoltification, and the importance of energetics, gill remodelling and ion transport capacity for migrants. Additionally, residents overexpressed transcripts involved in antiviral defences, potentially for immune surveillance via dendritic cells in the gills. The best smoltification marker candidate was protein s100a4, expression of which was highly correlated with Na(+) , K(+) ATPase (NKA) activity and smolt-like morphology in pre- and postrelease trout gills.

Immunohistochemical characterization of the crypt neurons in the olfactory epithelium of adult zebrafish

The fish sensory epithelium contains three types of sensory cells denominated ciliated, microvillous, and crypt neurons. Each one differs from the other in its morphological, ultrastructural and molecular features, as well as in their projections to the central nervous system. Crypt neurons are present in both bony and cartilaginous fish and can be identified on the basis of their morphology and the expression of some specific proteins and genes. In this study we have investigated the morphology of crypt neurons, as well as the occurrence and co-localization of S100 protein, calretinin and TRPV4, three proposed markers for crypt cells, in the olfactory epithelium of adult zebrafish (Danio rerio) using double immunofluorescence associated to laser confocal microscopy. A sparse population of superficial S100 protein positive cells was detected being identified as crypt neurons. The calretinin immunoreactive cells were more abundant, occasionally resembling the morphology of the crypt cells but never displaying co-localization of both proteins. The TRPV4 positive cells differed in morphology from crypt cells, thus excluding the occurrence of TRPV4 in those cells. These results demonstrate that only S100 protein immunoreactivity can be used to identify crypt cells. Because some calretinin positive cells showed localization and morphology similar to the crypt cells of the sensory epithelium, the occurrence of two subtypes of crypt cells, S100 protein and calretinin positive, cannot be excluded. The significance of these findings remains to be elucidated.

Zebrafish crypt neurons project to a single, identified mediodorsal glomerulus

Crypt neurons are a third type of olfactory receptor neurons with a highly unusual "one cell type--one receptor" mode of expression, the same receptor being expressed by the entire population of crypt neurons. Attempts to identify the target region(s) of crypt neurons have been inconclusive so far. We report that TrkA-like immunoreactivity specifically labeled somata, axons, and terminals of zebrafish crypt neurons and reveal a single glomerulus, mdg2 of the dorsomedial group, as target glomerulus of crypt neurons. Injection of a fluorescent tracing dye into the mdg2 glomerulus retrogradely labeled mostly crypt neurons, as assessed by quantitative morphometry, whereas no crypt neurons were found after injections in neighboring glomeruli. Our data provide strong evidence that crypt neurons converge onto a single glomerulus, and thus form a labeled line consisting of a single sensory cell type, a single olfactory receptor and a single target glomerulus.

Evolution of the S100 family of calcium sensor proteins

The S100s are a large group of Ca(2+) sensors found exclusively in vertebrates. Transcriptomic and genomic data from the major radiations of mammals were used to derive the evolution of the mammalian S100s genes. In human and mouse, S100s and S100 fused-type proteins are in a separate clade from other Ca(2+) sensor proteins, indicating that an ancient bifurcation between these two gene lineages has occurred. Furthermore, the five genomic loci containing S100 genes have remained largely intact during the past 165 million years since the shared ancestor of egg-laying and placental mammals. Nonetheless, interesting births and deaths of S100 genes have occurred during mammalian evolution. The S100A7 loci exhibited the most plasticity and phylogenetic analyses clarified relationships between the S100A7 proteins encoded in the various mammalian genomes. Phylogenetic analyses also identified four conserved subgroups of S100s that predate the rise of warm-blooded vertebrates: A2/A3/A4/A5/A6, A1/A10/A11/B/P/Z, A13/A14/A16, and A7s/A8/A9/A12/G. The similarity between genomic location and phylogenetic clades suggest that these subfamilies arose by a series of tandem gene duplication events. Examination of annotated S100s in lower vertebrates suggests that the ancestral S100 was a member of the A1/A10/A11/B/P/Z subgroup and arose near the emergence of vertebrates approximately 500 million years ago.

Crypt neurons express a single V1R-related ora gene

Both ciliated and microvillous olfactory sensory neuron populations express large families of olfactory receptor genes. However, individual neurons generally express only a single receptor gene according to the "one neuron-one receptor" rule. We report here that crypt neurons, the third type of olfactory neurons in fish species, use an even more restricted mode of expression. We recently identified a novel olfactory receptor family of 6 highly conserved G protein-coupled receptors, the v1r-like ora genes. We show now that a single member of this family, ora4 is expressed in nearly all crypt neurons, whereas the other 5 ora genes are not found in this cell type. Consistent with these findings, ora4 is never coexpressed with any of the remaining 5 ora genes. Furthermore, several lines of evidence indicate the absence of any other olfactory receptor families in crypt neurons. These results suggest that the vast majority of the crypt neuron population may select one and the same olfactory receptor gene, a "one cell type-one receptor" mode of expression. Such an expression pattern is familiar in the visual system, with rhodopsin as the sole light receptor of rod photoreceptor cells, but unexpected in the sense of smell.

Identification of a new cartilage-specific S100-like protein up-regulated during endo/perichondral mineralization in gilthead seabream

Calcium ions and calcium-binding proteins play a major role in many cellular processes, in particular skeletogenesis and bone formation. We report here the discovery of a novel S100 protein in fish and the analysis of its gene expression patterns. A 648-bp full-length cDNA encoding an 86-amino acid S100-like calcium-binding protein was identified through the subtractive hybridization of a gilthead seabream (Sparus aurata) cDNA library constructed to identify genes associated with in vitro mineralization. Deduced protein lacks an identifiable signal peptide and exhibits two EF-hand motifs characteristic of S100 proteins. Phylogenetic and bioinformatic analyses of S100 sequences suggested that gilthead seabream protein represents a novel and fish-specific member of the S100 protein family. Expression of S100-like gene was up-regulated during the in vitro mineralization of bone-derived cell lines and during seabream development, from larvae throughout adulthood, reflecting skeletogenesis. Restriction of S100-like gene expression to chondrocytes of cartilaginous tissues undergoing endo/perichondral mineralization in juvenile fish further confirmed the mineralogenic role of the protein in fish and emphasized the potential of S100-like as a marker of mineralizing cartilage in developing fish.

Ion regulation in fish gills: recent progress in the cellular and molecular mechanisms

Fish encounter harsh ionic/osmotic gradients on their aquatic environments, and the mechanisms through which they maintain internal homeostasis are more challenging compared with those of terrestrial vertebrates. Gills are one of the major organs conducting the internal ionic and acid-base regulation, with specialized ionocytes as the major cells carrying out active transport of ions. Exploring the iono/osmoregulatory mechanisms in fish gills, extensive literature proposed several models, with many conflicting or unsolved issues. Recent studies emerged, shedding light on these issues with new opened windows on other aspects, on account of available advanced molecular/cellular physiological approaches and animal models. Respective types of ionocytes and ion transporters, and the relevant regulators for the mechanisms of NaCl secretion, Na(+) uptake/acid secretion/NH(4)(+) excretion, Ca(2+) uptake, and Cl(-) uptake/base secretion, were identified and functionally characterized. These new ideas broadened our understanding of the molecular/cellular mechanisms behind the functional modification/regulation of fish gill ion transport during acute and long-term acclimation to environmental challenges. Moreover, a model for the systematic and local carbohydrate energy supply to gill ionocytes during these acclimation processes was also proposed. These provide powerful platforms to precisely study transport pathways and functional regulation of specific ions, transporters, and ionocytes; however, very few model species were established so far, whereas more efforts are needed in other species.

Differential bulbar and extrabulbar projections of diverse olfactory receptor neuron populations in the adult zebrafish (Danio rerio)

Immunohistochemical methods were used to characterize the expression of two calcium-binding proteins, calretinin (CR) and S100, in the olfactory rosette of the adult zebrafish. These proteins are expressed in different sets of sensory neurons, and together represent a large proportion of these cells. Double immunofluorescence for CR and Gα(olf) protein, and CR immunoelectron microscopy, indicated that most CR-immunoreactive (ir) cells were ciliary neurons. Differential S100- and CR-ir projections to glomerular fields of the olfactory bulb were also observed, although these projections overlap in some glomeruli. Application of the carbocyanine dye DiI to either S100-ir or CR-ir glomerular regions led to labeling of cells mostly similar to S100-ir and CR-ir neurons, respectively. Instead, these bulbar regions project to similar telencephalic targets. On the other hand, antibodies against keyhole limpet hemocyanin (KLH)-stained numerous sensory cells in the olfactory rosette, including cells that were CR- and S100-negative. This antiserum also stained most primary bulbar projections and revealed extrabulbar olfactory primary projections coursing to the ventral area of the telencephalon through the medial olfactory tract. This extrabulbar projection was confirmed by tract-tracing with DiI. A loose association of this extrabulbar primary olfactory projection and the catecholaminergic populations of the ventral area was also observed with double tyrosine hydroxylase/KLH-like immunohistochemistry. Comparison between KLH-like-ir pathways and the structures revealed by FMRFamide immunohistochemistry (a marker of terminal ganglion cells and fibers) indicated that the KLH-like-ir extrabulbar projection was different from the terminal nerve system. The significance of the extrabulbar olfactory projection of zebrafish is discussed.

Onset and dynamic expression of S100 proteins in the olfactory organ and the lateral line system in zebrafish development

In the zebrafish olfactory epithelium, three morphologically distinct olfactory neurons express different marker proteins. We utilize this feature to access developmental dynamics of one of the neuron types, the crypt cells, to determine whether they are differentiated at a stage similar to other olfactory neurons. Immunohistochemical studies using an S100 antibody that specifically recognizes crypt cells showed that S100-positive cells appear in olfactory rosettes as early as at 2day postfertilization (dpf). However, some of the rosettes did not have any S100-positive cells until 4 dpf. The number of S100-positive cells in individual rosettes increased steadily over the next 3days before it decreased significantly. There were 7.8 S100-positive cells per rosettes on average in larvae at 7 dpf. The number reduced to 2.2 at 9 dpf. A recovery to a pre-reduction level was detected in 12 dpf larvae. We also observed S100-positive cells in neuromasts of the lateral line system in 2 dpf larvae, suggesting that the crypt cells and sensory cells in the neuromasts have similar onsets of differentiation. Our data have provided a time line of differentiation of crypt cells in development of the olfactory system and demonstrated that this type of cell is differentiated at a stage similar to ciliated and microvillous olfactory neurons. A nonlinear growth trajectory of the crypt cell population in the first nine days of zebrafish development implicates a possible functional significance of crypt cells in early life stages of zebrafish.

Molecular level interactions of S100A13 with amlexanox: inhibitor for formation of the multiprotein complex in the nonclassical pathway of acidic fibroblast growth factor

S100A13 and acidic fibroblast growth factor (FGF1) are involved in a wide array of important biological processes, such as angiogenesis, cell differentiation, neurogenesis, and tumor growth. Generally, the biological function of FGF1 is to recognize a specific tyrosine kinase on the cell surface and initiate the cell signal transduction cascade. Amlexanox (2-amino-7-isopropyl-5-oxo-5H-[1]benzopyrano[2,3-b]pyridine-3-carboxylic acid) is an antiallergic drug that binds S100A13 and FGF1 and inhibits the heat shock induced release of S100A13 and FGF1. In the present study, we investigated the interaction of amlexanox with S100A13 using various biophysical techniques, including isothermal titration calorimetry, fluorescence spectrophotometry, and multidimensional NMR spectroscopy. We report the three-dimensional solution structure of the S100A13-amlexanox complex. These data show that amlexanox binds specifically to the FGF1-S100A13 interface and prevents the formation of the FGF1-releasing complex. In addition, we demonstrate that amlexanox acts as an antagonist of S100A13 by binding to its FGF1 binding site and subsequently inhibiting the nonclassical pathway of these proteins. This inhibition likely results in the ability of amlexanox to antagonize the angiogenic and mitogenic activity of FGF1.

The chicken leukocyte receptor complex encodes a family of different affinity FcY receptors

Chicken Ig-like receptors (CHIR) form a large family in the leukocyte receptor complex on microchromosome 31 with inhibitory, activating, and bifunctional receptors. Recently, we characterized CHIR-AB1 as a high-affinity, primordial FcY receptor. Given that the CHIR family represents a multigene family, it is plausible that more than a single receptor binds to IgY. Therefore, after comparing CHIR-AB1-like sequences in databases, we cloned CHIR-AB1 homologues from two individual chickens representing the lines M11 and R11 with primers binding to highly conserved regions. In both lines this approach yielded 18 different CHIR-AB amino acid versions, with one sequence out of each line that was identical with the previously characterized B19 CHIR-AB1 Ig domain and two additional R11-M11 identical sequence pairs. All M11-derived CHIR-AB homologues were then expressed as soluble human Ig fusion proteins. Following standardization of the fusion protein concentration with an ELISA, the IgY, IgM, and IgA binding activities were determined by ELISA. Six fusion proteins recognized IgY, whereas none bound to IgM and IgA. The affinities of selected fusion proteins were determined using surface plasmon resonance yielding an equilibrium binding constant between 25 nM for high binders and 260 nM for low binders. Sequence comparisons and subsequent mutational analysis of selected residues identified five amino acids that are potentially involved in IgY binding. These results imply that multiple FcY receptors of variable affinity are encoded by the CHIR locus and that different chicken lines may express both unique as well as highly conserved FcY receptors.

Positive Darwinian selection and the birth of an olfactory receptor clade in teleosts

Trace amine-associated receptors (TAARs) in mammals recently have been shown to function as olfactory receptors. We have delineated the taar gene family in jawless, cartilaginous, and bony fish (zero, 2, and >100 genes, respectively). We conclude that taar genes are evolutionary much younger than the related OR and ORA/V1R olfactory receptor families, which are present already in lamprey, a jawless vertebrate. The 2 cartilaginous fish genes appear to be ancestral for 2 taar classes, each with mammalian and bony fish (teleost) representatives. Unexpectedly, a whole new clade, class III, of taar genes originated even later, within the teleost lineage. Taar genes from all 3 classes are expressed in subsets of zebrafish olfactory receptor neurons, supporting their function as olfactory receptors. The highly conserved TAAR1 (shark, mammalian, and teleost orthologs) is not expressed in the olfactory epithelium and may constitute the sole remnant of a primordial, nonolfactory function of this family. Class III comprises three-fourths of all teleost taar genes and is characterized by the complete loss of the aminergic ligand-binding motif, stringently conserved in the other 2 classes. Two independent intron gains in class III taar genes represent extraordinary evolutionary dynamics, considering the virtual absence of intron gains during vertebrate evolution. The d(N)/d(S) analysis suggests both minimal global negative selection and an unparalleled degree of local positive selection as another hallmark of class III genes. The accelerated evolution of class III teleost taar genes conceivably might mark the birth of another olfactory receptor gene family.

The fifth class of Galpha proteins

All alpha-subunits of vertebrate heterotrimeric G proteins have been classified into 4 major classes, Gs, Gi, Gq, and G12, which possess orthologs already in sponges, one of the earliest animal phyla to evolve. Here we report the discovery of the fifth class of Galpha protein, Gv, ancient like the other 4 classes, with members already in sponges, and encoded by 1-2 gnav genes per species. Gv is conserved across the animal kingdom including vertebrates, arthropods, mollusks, and annelids, but has been lost in many lineages such as nematodes, fruit fly, jawless fish, and tetrapods, concordant with a birth-and-death mode of evolution. All Gv proteins contain 5 G-box motifs characteristic of GTP-binding proteins and the expected acylation consensus sites in the N-terminal region. Sixty amino acid residues are conserved only among Gv, suggesting that they may constitute interaction sites for Gv-specific partner molecules. Overall Gv homology is high, on average 70% amino acid identity among vertebrate family members. The d(N)/d(S) analysis of teleost gnav genes reveals evolution under stringent negative selection. Genomic structure of vertebrate gnav genes is well conserved and different from those of the other 4 classes. The predicted full ORF of zebrafish gnav1 was confirmed by isolation from cDNA. RT-PCR analysis showed broad expression of gnav1 in adult zebrafish and in situ hybridization demonstrated a more restricted expression in larval tissues including the developing inner ear. The discovery of this fifth class of Galpha proteins changes our understanding of G protein evolution.

Transcriptional biomarkers and mechanisms of copper-induced olfactory injury in zebrafish

Metals such as copper disrupt olfactory function in fish. Unfortunately, little is understood of the molecular consequences of copper olfactory impairment, thus hindering the development of relevant diagnostic tools of olfactory injury. To address this critical data gap, we analyzed gene expression within olfactory tissues of adult zebrafish exposed to CuCl2 (6, 16, 40 ppb) for 24 h. Transcriptional markers of copper impairment within the entire olfactory system were identified and specific genes of interest (e.g., S100a, parvalbumin 8, olfactory marker protein, and calbindin 2-like protein) were confirmed with quantitative real-time PCR. In addition, we performed gene set analysis (GSA) using both a priori and custom pathways of gene sets specifically targeting the olfactory signal transduction (OST) pathway. These analyses revealed down-regulated gene sets related to calcium channels and ion transport, g-proteins, and olfactory receptors. Collectively, these data demonstrate that copper causes a depression of transcription of key genes within the OST pathway and elsewhere within olfactory tissues, likely resulting in an olfactory system less responsive to odorants. Further, these data provide a mechanistic explanation in support of earlier studies of functional olfactory impairment in fish following copper exposure.