Evolution of the zebrafish model: from development to immunity and infectious disease

High-Quality Indigo Naturalis Obtained with Automatic Foam Separation

Indigo Naturalis is not only an ancient plant dye but also a famous herbal medicine with antibacterial, anti-inflammatory, and anticancer properties. In traditional processes, thousands of manual stirring separate the high-quality Indigo Naturalis from the crude pulp system. However, this method is time-consuming and labor-intensive, resulting in an unstable quality and low yield, which cannot meet the requirements of modern industrial production. In this study, foam-separation technology was used to increase the industrial applicability of high-quality Indigo Naturalis. The process parameters were optimized based on the content of active ingredients, skin irritation effects, and antioxidative stress activity. The results showed that the optimal process of the foam separation achieved the liquid level difference of 40 cm and the foaming intensity of 0.35 MPa. Compared with the original sample, the indigo and indirubin contents in purified Indigo Naturalis were 1.6 and 3 times higher, the total ash content decreased from 86 to 70%, the pH value decreased from 12.18 to 9.71, and the leachate doubled. Animal experiments suggested the significantly reduced irritation (p < 0.01) and enhanced antioxidative stress activity (p < 0.01) of Indigo Naturalis after foam separation. Therefore, the foam-separation equipment developed in this study enabled the refinement of active ingredients in Indigo Naturalis, which greatly improved the production efficiency and quality.

Internal Temperatures of Packaging for Overnight Cross-country Shipping of Zebrafish (Danio Rerio)

As the use of zebrafish (Danio rerio) as a research model continues to rise, so too will the shipping and sharing of zebrafish strains across collaborating institutions. If done incorrectly, shipping can result in significant mortality, welfare concerns, and loss of valuable resources for researchers and research institutions. Here we introduce a novel method to track temperatures of zebrafish containers during shipping and show that internal packaging temperatures are directly affected by the external temperatures. We used temperature logging Thermochron iButtons to track the temperatures of 2 packages containing adult zebrafish that were shipped overnight from Dallas, TX to Columbus, OH during winter following recommended fish shipping guidelines. We found that the external packaging of both boxes of fish were exposed to temperatures that had previously been shown to be lethal to zebrafish. However, internal temperatures and, more specifically, water temperature, stayed within 24.0 to 26.5^°C during shipment, resulting in 100% survival of adult zebrafish. This novel method of tracking packaging temperatures of live fish during shipping can help to inform fish health status on arrival.

Comparative bioactivity profile of phospholipids from three marine byproducts based on the zebrafish model

Phospholipids (PLs) are important components of physiological metabolism in animals and plants, and they have been widely used in clinical treatment, cosmetics, and industry. With the development of marine resources, marine PLs rich in polyunsaturated fatty acids have attracted increasing attention. As important marine resources, shrimp heads (SH), codfish roe (CR), and squid gonads (SG) contain a high PL content. The antithrombotic, antistroke, anti-inflammatory, pro-angiogenic, and cardioprotective activities of PLs from SH, CR, and SG were evaluated and compared using the in vivo zebrafish model. The results showed that the PL extracts of SH, CR, and SG had significant biological activities, which lays a theoretical foundation for the development and utilization of PLs in marine byproducts in the future, providing a new choice for the prevention of inflammatory and cardiovascular diseases. PRACTICAL APPLICATIONS: In this experiment, phospholipids in seafood from different sources were extracted, and their biological activities were comprehensively evaluated and compared using the zebrafish model to lay a foundation for the development of cardiovascular drugs, health food, special medicinal food, and other effective components. The utilization of marine byproducts not only makes full use of resources, but it also protects the environment.

Brain-localized and Intravenous Microinjections in the Larval Zebrafish to Assess Innate Immune Response

Creating a robust and controlled infection model is imperative for studying the innate immune response. Leveraging the particular strengths of the zebrafish model system, such as optical transparency, ex utero development, and large clutch size, allows for the development of methods that yield consistent and reproducible results. We created a robust model for activation of innate immunity by microinjecting bacterial particles or live bacteria into larval zebrafish, unlike previous studies which largely restricted such manipulations to embryonic stages of zebrafish. The ability to introduce stimuli locally or systemically at larval stages provides significant advantages to examine host response in more mature tissues as well as the possibility to interrogate adaptive immunity at older larval stages. This protocol describes two distinct modes of microinjection to introduce lipopolysaccharide (LPS) or bacteria into the living larval zebrafish: one localized to the brain, and another into the bloodstream via the caudal vein plexus. Graphic abstract: Schematic shows the two distinct modes of larval zebrafish microinjection, either in the brain parenchyma or in the blood stream intravenously. Reagents introduced into the zebrafish to assess immune response are depicted in the "injection components" as described in the protocol.

Mathematical Mirroring for Identification of Local Symmetry Centers in Microscopic Images Local Symmetry Detection in FIJI

Symmetry is omnipresent in nature and we encounter symmetry routinely in our everyday life. It is also common on the microscopic level, where symmetry is often key to the proper function of core biological processes. The human brain is exquisitely well suited to recognize such symmetrical features with ease. In contrast, computational recognition of such patterns in images is still surprisingly challenging. In this paper we describe a mathematical approach to identifying smaller local symmetrical structures within larger images. Our algorithm attributes a local symmetry score to each image pixel, which subsequently allows the identification of the symmetrical centers of an object. Though there are already many methods available to detect symmetry in images, to the best of our knowledge, our algorithm is the first that is easily applicable in ImageJ/FIJI. We have created an interactive plugin in FIJI that allows the detection and thresholding of local symmetry values. The plugin combines the different reflection symmetry axis of a square to get a good coverage of reflection symmetry in all directions. To demonstrate the plugins potential, we analyzed images of bacterial chemoreceptor arrays and intracellular vesicle trafficking events, which are two prominent examples of biological systems with symmetrical patterns.

Streptococcus suis biofilm: regulation, drug-resistance mechanisms, and disinfection strategies

Streptococcus suis (S. suis) is a major swine pathogen and an important zoonotic agent. Like most pathogens, the ability of S. suis to form biofilms plays a significant role in its virulence and drug resistance. A better understanding of the mechanisms involved in biofilm formation by S. suis as well as of the methods to efficiently remove and kill biofilm-embedded bacteria can be of high interest for the prevention and treatment of S. suis infections. The aim of this literature review is to update our current knowledge of S. suis biofilm formation, regulatory mechanisms, drug-resistance mechanisms, and disinfection strategies.

β-Glucan-Producing Pediococcus parvulus 2.6: Test of Probiotic and Immunomodulatory Properties in Zebrafish Models

Lactic acid bacteria synthesize exopolysaccharides (EPS), which could benefit the host's health as immunomodulators. Furthermore, EPS could protect bacteria against gastrointestinal stress, favoring gut colonization, thus protecting the host against pathogenic infections. Pediococcus parvulus 2.6, produces a 2-substituted (1,3)-β-D-glucan and, in this work, its probiotic properties as well as the immunomodulatory capability of its EPS have been investigated using Danio rerio (zebrafish). To this end and for a comparative analysis, P. parvulus 2.6 and its isogenic β-glucan-non-producing 2.6NR strain were fluorescently labeled by transfer of the pRCR12 plasmid, which encodes the mCherry protein. For the in vivo studies, there were used: (i) a gnotobiotic larvae zebrafish model for bacterial colonization, pathogen competition, and evaluation of the β-glucan immunomodulation capability and (ii) a transgenic (mpx:GFP) zebrafish model to determine the EPS influence in the recruitment of neutrophils under an induced inflammation. The results revealed a positive effect of the β-glucan on colonization of the zebrafish gut by P. parvulus, as well as in competition of the bacterium with the pathogen Vibrio anguillarum in this environment. The larvae treatment with the purified β-glucan resulted in a decrease of expression of genes encoding pro-inflammatory cytokines. Moreover, the β-glucan had an anti-inflammatory effect, when it was evaluated in an induced inflammation model of Tg(mpx:GFP) zebrafish. Therefore, P. parvulus 2.6 and its EPS showed positive health properties in in vivo fish models, supporting their potential usage in aquaculture.

Infection and adaption-based proteomic changes of Streptococcus suis serotype 2 in a pig model

Streptococcus suis (S. suis) is an emerging zoonotic agent that is responsible for significant economic losses to the porcine industry worldwide. However, most research regarding the pathogenic mechanisms has used in vitro cultures of S. suis, which may not provide an accurate representation of the in vivo biological activities. In this study, 188 differential abundance S. suis proteins were identified in in vivo samples obtained from the blood of the infected pigs. These were compared with in vitro samples by a Tandem Mass Tags (TMT) experiment. Thus, a virulence associated network was established using the enriched differential abundance proteins (obtained via bioinformatics analysis in this study) and the previously reported putative virulence factors associated with in vivo infection. One of the most important up-regulated hubs in this network, adhE (an acetaldehyde-CoA/alcohol dehydrogenase) was found. Furthermore, knocking out adhE in S. suis serotype 2 strain ZY05719 decreased virulence. Cell culture experiments and far-western blot analysis showed that adhE is involved in adhesion to Caco-2 cells; Hsp60 could be one of the receptors for this protein.

SIGNIFICANCE

This study is a systematical research to identify in vivo regulated virulence associated proteins of S. suis in pigs. It constructs a network consisting of in vivo infection related factors for the first time to get to know the coordinated actions of a multitude of factors that lead to host pathogenicity and filter the most important hubs. The individual factors that contribute to infection is also identified. A novel differential protein adhE which is one of the most important hubs of this network and is up-regulated in abundance in vivo is found to moonlight as an important adhesion by binding Hsp60 and finally contributes to virulence.

EPSP of L. casei BL23 Protected against the Infection Caused by Aeromonas veronii via Enhancement of Immune Response in Zebrafish

Aquaculture is the fastest-growing food production sector in the world, and it supplies nearly 50% of the global food fish supply. However, disease outbreaks have become a major problem in the fish farming industry. The beneficial contribution of probiotic bacteria to aquatic animals' health has been widely described, and they have been widely used in aquaculture for disease control and growth promotion. However, the action of probiotic bacterial components and mechanisms underlying protection against pathogens afforded by probiotic bacteria remain poorly understood. In the present study, we pre-colonized zebrafish larvae (before hatching) with 17 potential probiotic bacterial strains and screened for those possessing anti-infective effects against Aeromonas veronii. We found that Lactobacillus casei BL23 significantly increased the survival of zebrafish larvae upon A. veronii infection. Using a germ-free (GF) zebrafish model and gut microbiota transplant experiment, we showed that L. casei BL23 per se has anti-infective effects in zebrafish larvae, which does not involve microbiota. Furthermore, we identified an exopolysaccharide-protein complex (EPSP) extracted from L. casei BL23 cells, which consisted of a 40-45 KD size protein and an exopolysaccharide composed of α-Rha, α-Glc, β-GlcNAc, and β-GalNAc. EPSP significantly increased the survival rate of GF zebrafish at a dose of 10-20 μg/ml after A. veronii infection (P < 0.01). In addition, the EPSP induced a higher expression of TLR1 and TLR2, and modulated the expression profile of pro-inflammatory and anti-inflammatory cytokines in zebrafish liver (ZFL) cells. Our data indicated that the anti-infective effect of EPSP from L. casei BL23 was mediated by enhancement of immune responses in zebrafish, which might involve the TLR1/TLR2 signal pathway.

Sensitive biomarkers identification for differentiating Cd and Pb induced toxicity on zebrafish embryos

Cadmium (Cd) and lead (Pb) are naturally existing heavy metals that pose significant health risks. The present study aims to identify sensitive biomarkers for differentiating the toxicities induced by Cd and Pb and for providing clues for the early prediction of toxicity and environmental risk assessment. Indicators related to oxidative stress and inflammatory responses in zebrafish treated with Cd and Pb over time (from 24hpf to 96hpf) were compared. Furthermore, endpoints such as embryo lethality and teratogenicity were detected. Then, several related genes involved in oxidative stress and inflammatory responses characterizing both Cd and Pb exposure, along with key molecules in the MAPKs pathway, were compared at the mRNA level, allowing the selection of the most sensitive and informative biomarkers. Significant increases in reactive oxygen species (ROS) production were observed in zebrafish exposed to Cd and Pb. Cd and Pb exposure induced developmental toxicity, influencing survival rate, hatching rate, larval growth, and heart rate and causing abnormal embryonic development. Similar trends in SOD1 and SOD2 gene expression were induced by Cd and Pb, while nuclear factor erythroid-2 related factor 2 (Nrf2) gene expression responded differently to each metal. In addition, Cd and Pb induced a delayed activation of the CAT and HO-1 genes, with no apparent change in the 24hpf and 48hpf groups. Genes related to immunotoxicity were activated significantly in a time-dependent manner, and these genes exhibited different sensitivities to Cd and Pb. MAPKs pathway genes were also activated in a time-dependent manner, and the expression of these genes showed different effects under Cd and Pb treatment. In summary, the present works have identified some potential sensitive biomarkers. The Nrf2 gene is a potential biomarker to differentiate Pb-induced toxicity from that of Cd, and the IFN-γ gene may be used as a sensitive biomarker for evaluating the risk of Pb contamination. We found that the timeline of MAPKs pathway activation helped to differentiate these two metals toxicities. Furthermore, Pb induced the early activation of ERK2/3 and JNK1, while p38 MAPKs showed delayed activation with no apparent change in the 24hpf group. Cd induced an early activation of ERK2 and a delayed activation of p38a, p38b, ERK3 and JNK1, indicating that the JNK1 pathway is sensitive to Pb exposure, while the p38 pathway may be susceptible to Cd. This work contributes to sensitive biomarker identification and early environmental risk evaluation for chemicals as well as toxicity prediction.

Treatment of Francisella infections via PLGA- and lipid-based nanoparticle delivery of antibiotics in a zebrafish model

We tested the efficiency of 2 different antibiotics, rifampicin and oxolinic acid, against an established infection caused by fish pathogen Francisella noatunensis ssp. orientalis (F.n.o.) in zebrafish. The drugs were tested in the free form as well as encapsulated into biodegradable nanoparticles, either polylactic-co-glycolic acid (PLGA) nanoparticles or nanostructured lipid carriers. The most promising therapies were PLGA-rifampicin nanoparticles and free oxolinic acid; the PLGA nanoparticles significantly delayed embryo mortality while free oxolinic acid prevented it. Encapsulation of rifampicin in both PLGA and nanostructured lipid carriers enhanced its efficiency against F.n.o. infection relative to the free drug. We propose that the zebrafish model is a robust, rapid system for initial testing of different treatments of bacterial diseases important for aquaculture.

Identification and characterization of the zebrafish glutathione S-transferase Pi-1

Zebrafish has in recent years emerged as a popular vertebrate model for use in pharmacological and toxicological studies. While there have been sporadic studies on the zebrafish glutathione S-transferases (GSTs), the zebrafish GST gene superfamily still awaits to be fully elucidated. We report here the identification of 15 zebrafish cytosolic GST genes in NCBI GenBank database and the expression, purification, and enzymatic characterization of the zebrafish cytosolic GST Pi-1 (GSTP1). The cDNA encoding the zebrafish GSTP1 was cloned from a 3-month-old female zebrafish, expressed in Eschelichia coli host cells, and purified. Purified GSTP1 displayed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene as a representative substrate. The enzymatic characteristics of the zebrafish GSTP1, including pH-dependency, effects of metal cations, and kinetic parameters, were studied. Moreover, the expression of zebrafish GSTP1 at different developmental stages during embryogenesis, throughout larval development, onto maturity was examined.

Rhein attenuates inflammation through inhibition of NF-κB and NALP3 inflammasome in vivo and in vitro

Rhein is an important component in traditional Chinese herbal medicine formulations for gastrointestinal disorders, including inflammatory bowel diseases such as ulcerative colitis. In this study, we investigated the beneficial effects of rhein in inflammation models in the transgenic zebrafish line TG (corolla eGFP), in which both macrophages and neutrophils express eGFP and RAW264.7 macrophages. We found that the tail-cutting-induced migration of immune cells was significantly reduced in transgenic zebrafish treated with rhein. In addition, the production of proinflammatory cytokines, including IL-6, IL-1β, and tumor necrosis factor-α, were significantly reduced in lipopolysaccharide (LPS)-induced RAW264.7 macrophages treated with rhein. Parallel to the inhibition of proinflammatory cytokines, rhein significantly reduced phosphorylation levels of NF-κB p65 and inducible nitric oxide synthase, as well as COX-2 protein expression levels. Furthermore, rhein significantly reduced NALP3 and cleaved IL-1β expression in LPS + ATP-induced RAW264.7 macrophages. Thus, the present study demonstrates that rhein may exhibit its anti-inflammatory action via inhibition of NF-κB and NALP3 inflammasome pathways.

Expression pattern and functional analysis of fundc1 in rare minnow (Gobiocypris rarus)

Fundc1 is a mitochondrial outer membrane protein and plays important roles in mitochondria fission and hypoxia-induced mitophagy in mammalian cells. However, there is no relevant report of fundc1 in fish. In the present study, we cloned a 942bp fundc1 cDNA from rare minnow. The cDNA, designated as Grfundc1 cDNA, contains an open reading frame (ORF) of 459bp which encodes a polypeptide of 152 amino acid residues. Comparisons of deduced amino acid sequences demonstrated that Grfundc1 was highly homologous with those of other vertebrates. RT-PCR and real time PCR detection revealed that the transcripts of Grfundc1 were not detectable in the unfertilized eggs and had high levels at blastula and gastrula stages. Whole mount in situ hybridization analysis observed that Grfundc1 was ubiquitously expressed at early stage and later riched in specific regions, such as brain, branchial arch, eye and somite during embryogenesis. Grfundc1 was expressed in all the tissues of rare minnow adult, including brain, liver, gill, eyes, heart, kidney, intestine, muscle, testis and ovary. The expression of Grfundc1 in the brain, gill, heart and eye of rare minnow adult was significantly down-regulated by hypoxia. Similar hypoxic response was observed in the rare minnow embryos at 48hpf following hypoxia exposure. Functional analysis showed that knockdown of Grfundc1 significantly caused defects in the body axis and dorsal neural tissues of rare minnow embryos. These results indicate that Grfundc1 may play important roles in embryogenesis in fish.

The Zebrafish as a Model for Human Bacterial Infections

The development of the zebrafish (Danio rerio) infectious disease model has provided new insights and information into pathogenesis. Many of these new discoveries would not have been possible using a typical mammalian model. The advantages of using this model are many and in the last 15 years the model has been exploited for the analysis of many different pathogens. Here, we describe in detail how to perform a bacterial infection using either the adult zebrafish or zebrafish larvae using microinjection. Multiple methods of analysis are described that can be used to address specific questions pertaining to disease progression and the interactions with the immune system.

SBP2 plays an important role in the virulence changes of different artificial mutants of Streptococcus suis

Comparative proteomics analysis using the proteomes of the two mutants with different virulence found a promising putative virulence factor, SBP2, which can bind fibronectin and laminin.

Micrometam C Protects against Oxidative Stress in Inflammation Models in Zebrafish and RAW264.7 Macrophages

Micrometam C is a core of novel marine compound isolated from the mangrove associates Micromelum falcatum. In this study, we investigated the protective effects of micrometam C in inflammation models in the transgenic zebrafish line Tg (corola: eGFP) and RAW264.7 macrophages. We found that micrometam C significantly suppressed the migration of immune cells in tail-cutting-induced inflammation in transgenic zebrafish and reduced lipopolysaccharide (LPS)-induced reactive oxygen species (ROS) in both zebrafish and macrophages. In addition, micrometam C also restored LPS-induced reduction of endogenous antioxidants, such as catalase (CAT), glutathione (GSH) and superoxide dismutase (SOD). The protective effects of micrometam C were in parallel to its inhibition of NADPH oxidase and nuclear factor-kappa-binding (NF-κB) activity. Thus, the present results demonstrate that micrometam C protects against LPS-induced inflammation possibly through its antioxidant property.

Induction of mild enterocolitis in zebrafish Danio rerio via ingestion of Vibrio anguillarum serovar O1

Vibrio anguillarum is the etiological agent of a fatal hemorrhagic disease known as vibriosis that affects a wide range of fish species, causing severe economic losses. Several investigations have been carried out to elucidate the virulence mechanisms of this pathogen and to develop rapid detection techniques and effective disease-prevention strategies. The aim of our study was to evaluate the most effective way to induce mild enteritis in a fish model, in order to allow further applications. The experiments were carried out using 2 methods of administration of V. anguillarum serotype O1 to adult zebrafish Danio rerio: via intraperitoneal injection and via ingestion of infected Artemia nauplii. The results showed that the intraperitoneal administration often caused massive fish death due to severe systemic involvement. In our experiments, the effect of intraperitoneal infection was evident 48 h post infection, with cumulative mortality within 7 d post infection with severe histopathological changes in kidney hematopoietic tissue and in the intestine. In contrast, oral infection via Artemia did not show systemic involvement and only a moderate degree of inflammatory influx of the mucosa, a partial recovery at 12 d post infection, and no mortality. For these reasons, oral infection with live food appears to be the most effective method to induce mild enteritis with a local inflammatory response.

Nonspecific cytotoxic cell antimicrobial protein (NCAMP-1): a novel alarmin ligand identified in zebrafish

Cells from the coelomic cavity of adult zebrafish (zf) were used to study the alarmin-like activities of nonspecific cytotoxic cell antimicrobial protein-1 (NCAMP-1). Immunohistochemistry studies using polyclonal anti-NCAMP-1 identified constitutive NCAMP-1 in epithelial cells of the zf anterior kidney, in liver parenchyma and in the lamina propria of the intestine. NCAMP-1 was also located in the cytosol of mononuclear cells in these tissues. Cytosolic NCAMP-1 was detected in a diverse population of coelomic cells (CC) using confocal microscopy and polyclonal anti-NCAMP-1 staining. Large mononuclear and heterophil-like CC had intracellular NCAMP-1. These studies indicated that NCAMP-1 is constitutively found in epithelial cells and in ZFCC. To establish a relationship between NCAMP-1 and the alarmin functions of ATP, a stimulation-secretion model was initiated using zf coelomic cells (ZFCC). ZFCCs treated with the alarmin ATP secreted NCAMP-1 into culture supernatants. Treatment of ZFCC with either ATP or NCAMP-1 activated purinergic receptor induced pore formation detected by the ZFCC uptake of the dye YO-PRO-1. ATP induced YO-PRO-1 uptake was inhibited by antagonists oxidized-ATP, KN62, or CBB. These antagonists did not compete with NCAMP-1 induced YO-PRO-1 uptake. Binding of ZFCC by both ATP and NCAMP-1 produced an influx of Ca²⁺. Combined treatment of ZFCC with ATP and NCAMP-1 increased target cell cytotoxicity. Individually NCAMP-1 or ATP treatment did not produce target cell damage. Similar to ATP, NCAMP-1 activates cellular pore formation, calcium influx and cytotoxicity.

Zebrafish liver (ZFL) cells are able to mount an anti-viral response after stimulation with Poly (I:C)

The zebrafish (Danio rerio) is a widely used model species for biomedical research and is also starting to be a model for aquaculture research. The ZFL cell line, established from zebrafish liver, has been mostly used in toxicological and ecotoxicological studies. However, no studies have previously characterised this cell line in regard to its immunological response. The aim of this work was to study the gene expression response of the ZFL cell line after incubation with different prototypical immune stimuli, such as lipopolysaccharide (LPS), peptidoglycan (PGN), zymosan, and with a special focus on the dsRNA Poly (I:C). Using PCR, microarrays, and confocal microscopy we have explored the response of the ZFL cells against Poly (I:C). This study shows that the ZFL is able to uptake very efficiently the Poly (I:C) and mount a strong anti-viral response. We can conclude that ZFL could be used not only in toxicological studies, but also in studying anti-viral responses in zebrafish.

Functional characterization of chitinase-3 reveals involvement of chitinases in early embryo immunity in zebrafish

The function and mechanism of chitinases in early embryonic development remain largely unknown. We show here that recombinant chitinase-3 (rChi3) is able to hydrolyze the artificial chitin substrate, 4-methylumbelliferyl-β-D-N,N',N″-triacetylchitotrioside, and to bind to and inhibit the growth of the fungus Candida albicans, implicating that Chi3 plays a dual function in innate immunity and chitin-bearing food digestion in zebrafish. This is further corroborated by the expression profile of Chi3 in the liver and gut, which are both immune- and digestion-relevant organs. Compared with rChi3, rChi3-CD lacking CBD still retains partial capacity to bind to C. albicans, but its enzymatic and antifungal activities are significantly reduced. By contrast, rChi3-E140N with the putative catalytic residue E140 mutated shows little affinity to chitin, and its enzymatic and antifungal activities are nearly completely lost. These suggest that both enzymatic and antifungal activities of Chi3 are dependent on the presence of CBD and E140. We also clearly demonstrate that in zebrafish, both the embryo extract and the developing embryo display antifungal activity against C. albicans, and all the findings point to chitinase-3 (Chi3) being a newly-identified factor involved in the antifungal activity. Taken together, a dual function in both innate immunity and food digestion in embryo is proposed for zebrafish Chi3. It also provides a new angle to understand the immune role of chitinases in early embryonic development of animals.

The biofilm mode of life boosts the anti-inflammatory properties of Lactobacillus

The predominant form of life for microorganisms in their natural habitats is the biofilm mode of growth. The adherence and colonization of probiotic bacteria are considered as essential factors for their immunoregulatory function in the host. Here, we show that Lactobacillus casei ATCC334 adheres to and colonizes the gut of zebrafish larvae. The abundance of pro-inflammatory cytokines and the recruitment of macrophages were low when inflammation was induced in probiotic-fed animals, suggesting that these bacteria have anti-inflammatory properties. We treated human macrophage-differentiated monocytic THP-1 cells with supernatants of L. casei ATCC334 grown in either biofilm or planktonic cultures. TNF-α production was suppressed and the NF-κB pathway was inhibited only in the presence of supernatants from biofilms. We identified GroEL as the biofilm supernatant compound responsible, at least partially, for this anti-inflammatory effect. Gradual immunodepletion of GroEL demonstrated that the abundance of GroEL and TNF-α were inversely correlated. We confirmed that biofilm development in other Lactobacillus species affects the immune response. The biofilms supernatants of these species also contained large amounts of GroEL. Thus, our results demonstrate that the biofilm enhances the immunomodulatory effects of Lactobacillus sp. and that secreted GroEL is involved in this beneficial effect.

Complement system in zebrafish

Zebrafish is recently emerging as a model species for the study of immunology and human diseases. Complement system is the humoral backbone of the innate immune defense, and our knowledge as such in zebrafish has dramatically increased in the recent years. This review summarizes the current research progress of zebrafish complement system. The global searching for complement components in genome database, together with published data, has unveiled the existence of all the orthologues of mammalian complement components identified thus far, including the complement regulatory proteins and complement receptors, in zebrafish. Interestingly, zebrafish complement components also display some distinctive features, such as prominent levels of extrahepatic expression and isotypic diversity of the complement components. Future studies should focus on the following issues that would be of special importance for understanding the physiological role of complement components in zebrafish: conclusive identification of complement genes, especially those with isotypic diversity; analysis and elucidation of function and mechanism of complement components; modulation of innate and adaptive immune response by complement system; and unconventional roles of complement-triggered pathways.

Studying the immune response to human viral infections using zebrafish

Humans and viruses have a long co-evolutionary history. Viral illnesses have and will continue to shape human history: from smallpox, to influenza, to HIV, and beyond. Animal models of human viral illnesses are needed in order to generate safe and effective antiviral medicines, adjuvant therapies, and vaccines. These animal models must support the replication of human viruses, recapitulate aspects of human viral illnesses, and respond with conserved immune signaling cascades. The zebrafish is perhaps the simplest, most commonly used laboratory model organism in which innate and/or adaptive immunity can be studied. Herein, we will discuss the current zebrafish models of human viral illnesses and the insights they have provided. We will highlight advantages of early life stage zebrafish and the importance of innate immunity in human viral illnesses. We will also discuss viral characteristics to consider before infecting zebrafish with human viruses as well as predict other human viruses that may be able to infect zebrafish.

Zebrafish as a model for zoonotic aquatic pathogens

Aquatic habitats harbor a multitude of bacterial species. Many of these bacteria can act as pathogens to aquatic species and/or non-aquatic organisms, including humans, that come into contact with contaminated water sources or colonized aquatic organisms. In many instances, the bacteria are not pathogenic to the aquatic species they colonize and are only considered pathogens when they come into contact with humans. There is a general lack of knowledge about how the environmental lifestyle of these pathogens allows them to persist, replicate and produce the necessary pathogenic mechanisms to successfully transmit to the human host and cause disease. Recently, the zebrafish infectious disease model has emerged as an ideal system for examining aquatic pathogens, both in the aquatic environment and during infection of the human host. This review will focus on how the zebrafish has been used successfully to analyze the pathogenesis of aquatic bacterial pathogens.

Establishment of three Francisella infections in zebrafish embryos at different temperatures

Francisella spp. are facultative intracellular pathogens identified in increasingly diverse hosts, including mammals. F. noatunensis subsp. orientalis and F. noatunensis subsp. noatunensis infect fish inhabiting warm and cold waters, respectively, while F. tularensis subsp. novicida is highly infectious for mice and has been widely used as a model for the human pathogen F. tularensis. Here, we established zebrafish embryo infection models of fluorescently labeled F. noatunensis subsp. noatunensis, F. noatunensis subsp. orientalis, and F. tularensis subsp. novicida at 22, 28, and 32°C, respectively. All infections led to significant bacterial growth, as shown by reverse transcription-quantitative PCR (RT-qPCR), and to a robust proinflammatory immune response, dominated by increased transcription of tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β). F. noatunensis subsp. orientalis was the most virulent, F. noatunensis subsp. noatunensis caused chronic infection, and F. tularensis subsp. novicida showed moderate virulence and led to formation of relatively small granuloma-like structures. The use of transgenic zebrafish strains with enhanced green fluorescent protein (EGFP)-labeled immune cells revealed their detailed interactions with Francisella species. All three strains entered preferentially into macrophages, which eventually assembled into granuloma-like structures. Entry into neutrophils was also observed, though the efficiency of this event depended on the route of infection. The results demonstrate the usefulness of the zebrafish embryo model for studying infections caused by different Francisella species at a wide range of temperatures and highlight their interactions with immune cells.

Identifying proteins in zebrafish embryos using spectral libraries generated from dissected adult organs and tissues

Spectral libraries provide a sensitive and accurate method for identifying peptides from tandem mass spectra, complementary to searching genome-derived databases or sequencing de novo. Their application requires comprehensive libraries including peptides from low-abundant proteins. Here we describe a method for constructing such libraries using biological differentiation to "fractionate" the proteome by harvesting adult organs and tissues and build comprehensive libraries for identifying proteins in zebrafish (Danio rerio) embryos and larvae (an important and widely used model system). Hierarchical clustering using direct comparison of spectra was used to prioritize organ selection. The resulting and publicly available library covers 14,164 proteins, significantly improved the number of peptide-spectrum matches in zebrafish developmental stages, and can be used on data from different instruments and laboratories. The library contains information on tissue and organ expression of these proteins and is also applicable for adult experiments. The approach itself is not limited to zebrafish but would work for any model system.

Adult zebrafish model for pneumococcal pathogenesis

Streptococcus pneumoniae (pneumococcus) is a leading cause of community acquired pneumonia, septicemia, and meningitis. Due to incomplete understanding of the host and bacterial factors contributing to these diseases optimal treatment and prevention methods are lacking. In the present study we examined whether the adult zebrafish (Danio rerio) can be used to investigate the pathophysiology of pneumococcal diseases. Here we show that both intraperitoneal and intramuscular injections of the pneumococcal strain TIGR4 cause a fulminant, dose-dependent infection in adult zebrafish, while isogenic mutant bacteria lacking the polysaccharide capsule, autolysin, or pneumolysin are attenuated in the model. Infection through the intraperitoneal route is characterized by rapid expansion of pneumococci in the bloodstream, followed by penetration of the blood-brain barrier and progression to meningitis. Using Rag1 mutant zebrafish, which are devoid of somatic recombination and thus lack adaptive immune responses, we show that clearance of pneumococci in adult zebrafish depends mainly on innate immune responses. In conclusion, this study provides evidence that the adult zebrafish can be used as a model for a pneumococcal infection, and that it can be used to study both host and bacterial factors involved in the pathogenesis. However, our results do not support the use of the zebrafish in studies on the role of adaptive immunity in pneumococcal disease or in the development of new pneumococcal vaccines.

Characterization of four heat-shock protein genes from Nile tilapia (Oreochromis niloticus) and demonstration of the inducible transcriptional activity of Hsp70 promoter

Heat-shock proteins (Hsps), known as stress proteins and extrinsic chaperones, play important roles in the folding, translocation, and refolding/degradation of proteins. In this study, we identified four Hsps in Nile tilapia (Oreochromis niloticus), which display conserved Hsp characteristics in their predicted amino acid sequences. Further analyses on the structures, homology, and phylogenetics revealed that the four Hsps belong to Hsp70 family. One of them does not contain introns and is named Hsp70, while all the other three contain introns and are named Hsc70-1, Hsc70-2, and Hsc70-3. Expressions of the four Hsp proteins were observed in all examined tissues. Six hours after infection of Streptococcus agalactiae in Nile tilapia, the expression of Hsp70 was significantly increased in the liver, head kidney, spleen and gill, while Hsc70s' expression was unchanged in all examined tissues except the head kidney that showed significantly reduced expression of both Hsc70-2 and Hsc70-3. These results suggest that Hsp70 may participate in the defense against S. agalactiae infection. We then isolated the promoter of Hsp70 gene and inserted it into the donor plasmid of Tgf2 transposon system containing green fluorescent protein (GFP) gene. The plasmid was microinjected into zebrafish embryos, where the expression of GFP was induced by heat shock, S. agalactiae immersion challenge, indicating that the isolated Hsp70 promoter has transcriptional activity and is inducible by both heat shock and bacterial challenge. This promoter may facilitate the future construction of disease-resistant transgenic fish. The work also contributes to the further study of immune response of tilapia after bacterial infection.

Assessing Pseudomonas virulence with nonmammalian host: zebrafish

In the last years, the zebrafish (Danio rerio) has become an important vertebrate animal model to study host-pathogen interactions, especially in its embryonic stage. The presence of a fully developed innate immune system in the first days of embryogenesis, the facility of obtaining and manipulating large numbers of embryos, the optical transparency of the embryos that allow the direct visualization of bacterial infections, a wide range of genetic tools, and extensive mutant resources and collections of transgenic reporter lines are important advantages of the zebrafish-embryo model. Pseudomonas aeruginosa is able to lethally infect zebrafish embryos when the amount of cells injected exceeds the phagocytic capacity of the embryo. Different studies have proved the suitability of zebrafish embryos as a model to analyze P. aeruginosa infection. Here we describe the detailed protocols to establish a P. aeruginosa infection in zebrafish embryos and to image the interaction of the bacterium with this host with fluorescent microscopy.

Transcriptional analysis of the Streptococcus pyogenes salivaricin locus

The sal lantibiotic locus plays an important role in the virulence of Streptococcus pyogenes. Our transcriptional analysis of the sal locus provides new information on the complex regulation of this operon. Transcription of the operon is regulated by a promoter upstream of the operon and by a second internal promoter upstream of the salKRZ genes. Here we identify the location of the internal promoter and provide information on how this promoter is autoregulated by proteins within the locus. We determined by primer extension that the salKR promoter is located within the salY gene and identified several regulatory regions important for expression. The higher activity of the promoter in a salKR deletion strain indicates a role in repression by the SalR response regulator. Further, this promoter had higher activity in a salA deletion strain, implicating corepression or a signaling role for the SalA peptide. Finally, we demonstrate that this promoter can be controlled by host factors. Analysis of transcriptional regulation of this locus provides a better understanding of the function of the sal locus in S. pyogenes pathogenesis.

Verification of intraovum transmission of a microsporidium of vertebrates: Pseudoloma neurophilia infecting the Zebrafish, Danio rerio

Direct transmission from parents to offspring, referred to as vertical transmission, occurs within essentially all major groups of pathogens. Several microsporidia (Phylum Microsporidia) that infect arthropods employ this mode of transmission, and various lines of evidence have suggested this might occur with certain fish microsporidia. The microsporidium, Pseudoloma neurophilia, is a common pathogen of the laboratory zebrafish, Danio rerio. We previously verified that this parasite is easily transmitted horizontally, but previous studies also indicated that maternal transmission occurs. We report here direct observation of Pseudoloma neurophilia in the progeny of infected zebrafish that were reared in isolation, including microscopic visualization of the parasite in all major stages of development. Histological examination of larval fish reared in isolation from a group spawn showed microsporidian spores in the resorbing yolk sac of a fish. Infections were also observed in three of 36 juvenile fish. Eggs from a second group spawn of 30 infected fish were examined using a stereomicroscope and the infection was observed from 4 to 48 hours post-fertilization in two embryos. Intraovum infections were detected in embryos from 4 of 27 pairs of infected fish that were spawned based on qPCR detection of P. neurophilia DNA. The prevalence of intraovum infections from the four spawns containing infected embryos was low (∼1%) based on calculation of prevalence using a maximum likelihood analysis for pooled samples. Parasite DNA was detected in the water following spawning of 11 of the infected pairs, suggesting there was also potential for extraovum transmission in these spawning events. Our study represents the first direct observation of vertical transmission within a developing embryo of a microsporidian parasite in a vertebrate. The low prevalence of vertical transmission in embryos is consistent with observations of some other fish pathogens that are also readily transmitted by both vertical and horizontal routes.

Transcriptome profiling reveals Th17-like immune responses induced in zebrafish bath-vaccinated with a live attenuated Vibrio anguillarum

Background

A candidate vaccine, live attenuated Vibrio anguillarum developed in our laboratory could prevent vibriosis of fish resulted from V. anguillarum and V. alginolyticus. To elucidate the molecular mechanisms underlying the vaccine protection, we used microarray technology to compare the spleen transcriptomes of bath-vaccinated and unvaccinated zebrafish at 28 days post vaccination.

Principal Findings

A total of 2164 genes and transcripts were differentially expressed, accounting for 4.9% of all genes represented on the chip. In addition to iron metabolism related to the innate immunity and the signaling pathways, these differentially expressed genes also involved in the adaptive immunity, mainly including the genes associated with B and T cells activation, proliferation and expansion. Transcription profiles of Th17-related transcription factors, cytokines and cytokine receptors during 35 days post-vaccination implied that Th17 cells be activated in bath-vaccinated zebrafish.

Conclusion/Significance

The transcriptome profiling with microarray revealed the Th17-like immune response to bath-vaccination with the live attenuated V. anguillarum in zebrafish.

Evaluation of zebrafish brain development using optical coherence tomography

The zebrafish is a well-established model system used to study and understand various human biological processes. The present study used OCT to investigate growth of the adult zebrafish brain. Twenty zebrafish were studied, using their standard lengths as indicators of their age. Zebrafish brain aging was evaluated by analyzing signal attenuation rates and texture features in regions of interest (ROIs). Optical scattering originates from light interaction with biological structures. During development, the zebrafish brain gains cells. Signal attenuation rate, therefore, increases with increasing zebrafish brain age. This study's analyses of texture features could not identify aging in zebrafish brain. These results, therefore, indicated that the OCT signal attenuation rate can indicate zebrafish brain aging, and its analysis provides a more effective means of observing zebrafish brain aging than texture features analysis. Using OCT system could further increase the technique's potential for recognition and monitoring of zebrafish brain development.

Viral diseases in zebrafish: what is known and unknown

Naturally occurring viral infections have the potential to introduce confounding variability that leads to invalid and misinterpreted data. Whereas the viral diseases of research rodents are well characterized and closely monitored, no naturally occurring viral infections have been characterized for the laboratory zebrafish (Danio rerio), an increasingly important biomedical research model. Despite the ignorance about naturally occurring zebrafish viruses, zebrafish models are rapidly expanding in areas of biomedical research where the confounding effects of unknown infectious agents present a serious concern. In addition, many zebrafish research colonies remain linked to the ornamental (pet) zebrafish trade, which can contribute to the introduction of new pathogens into research colonies, whereas mice used for research are purpose bred, with no introduction of new mice from the pet industry. Identification, characterization, and monitoring of naturally occurring viruses in zebrafish are crucial to the improvement of zebrafish health, the reduction of unwanted variability, and the continued development of the zebrafish as a model organism. This article addresses the importance of identifying and characterizing the viral diseases of zebrafish as the scope of zebrafish models expands into new research areas and also briefly addresses zebrafish susceptibility to experimental viral infection and the utility of the zebrafish as an infection and immunology model.

Identification of a novel collagen type І-binding protein from Streptococcus suis serotype 2

Streptococcus suis, a major pathogen of pigs, is an emerging zoonotic agent that causes meningitis and septic shock. cbp40 is a putative virulent gene that has been identified using suppression subtractive hybridization performed on the virulent S. suis serotype 2 strain HA9801 and the avirulent S. suis serotype 2 strain T15. Based on predicted protein features showing a shared conserved domain with the collagen-binding protein Cna of Staphylococcus aureus, Cbp40 is likely to function as a direct mediator of collagen adhesion. Here, the cbp40 gene was cloned and the recombinant protein purified. Western blotting using swine convalescent sera confirmed its role as an immunogenic protein. Collagen binding activity could be detected by western affinity blot and ELISA. Conversely, deletion of the cbp40 gene reduced bacterial adhesion to HEp-2 cells, capacity for biofilm formation, and virulence in a zebrafish infection model. The response of the bEnd.3 cell line to infection with the S. suis serotype 2 strain ZY05719 and the cbp40-knockout strain was evaluated using gene expression arrays. The differentially expressed genes were involved in inflammatory and immune responses, leukocyte adhesion and heterophilic cell adhesion. Collectively, these data suggest that Cbp40 plays an important role as an extracellular matrix adhesion protein that interacts with host cells during infection.

In vivo screening of zebrafish microRNA responses to bacterial infection and their possible roles in regulating immune response genes after lipopolysaccharide stimulation

Micro (mi)RNAs are abundant small noncoding RNAs found in plants and animals, the regulatory functions of which are not fully understood in fish. To identify potential miRNAs, we screened an miRNA microarray with total RNA from zebrafish infected with Vibrio harveyi and another from uninfected zebrafish. Six miRNAs were obtained from the microarray screening. We studied miRNA expression patterns of 2 miRNAs (miR-122 and miR-194) after bacterial infection of transgenic zebrafish (containing tilapia hepcidin (TH)2-3) and non-transgenic zebrafish from which the 2 miRNAs were obtained from the microarray experiment. The results indicated that miR-122 and miR-194 were higher in PBS-injected zebrafish compared with TH2-3 zebrafish or wild-type (WT) zebrafish after V. harveyi infection. Overexpression of miRNAs (miR-122, miR-192, and miR-194a) was seen in zebrafish liver (ZFL) cells after lipopolysaccharide (LPS) treatment and in untreated fish. Our results showed that after 24 h of doxycycline treatment without LPS stimulation, interleukin (IL)-22, lysozyme, toll-like receptor (TLR)1, TLR3, TLR4a, and tumor necrosis factor (TNF)-α gene expressions were, respectively, upregulated by ~14-, 22-, 2.2-, 13-, 200-, and 38-fold in miR-122-transfected compared with non-transfected (WT) ZFL cells. In cells transfected with miR-192 and treated with LPS after 8-12 h, IL-22, lysozyme, TLR1, TLR3, TLR4a, and TNF-α expressions significantly differed between WT and miR-192-overexpressing ZFL cells. However, we observed significantly higher IL-22 expression levels after 12 h of LPS treatment in miR-192-transfected ZFL cells compared with non-transfected cells. In contrast, IL-22, lysozyme, and TNF-α were markedly upregulated (>100-fold) after miR-194a transfection and overexpression in ZFL cells and treatment with LPS. Our cloning and expression analyses indicated that miR-122, miR-192, and miR-194a play important roles in zebrafish immunology.

A new zebrafish model of oro-intestinal pathogen colonization reveals a key role for adhesion in protection by probiotic bacteria

The beneficial contribution of commensal bacteria to host health and homeostasis led to the concept that exogenous non-pathogenic bacteria called probiotics could be used to limit disease caused by pathogens. However, despite recent progress using gnotobiotic mammal and invertebrate models, mechanisms underlying protection afforded by commensal and probiotic bacteria against pathogens remain poorly understood. Here we developed a zebrafish model of controlled co-infection in which germ-free zebrafish raised on axenic living protozoa enabled the study of interactions between host and commensal and pathogenic bacteria. We screened enteric fish pathogens and identified Edwardsiella ictaluri as a virulent strain inducing a strong inflammatory response and rapid mortality in zebrafish larvae infected by the natural oro-intestinal route. Using mortality induced by infection as a phenotypic read-out, we pre-colonized zebrafish larvae with 37 potential probiotic bacterial strains and screened for survival upon E. ictaluri infection. We identified 3 robustly protective strains, including Vibrio parahaemolyticus and 2 Escherichia coli strains. We showed that the observed protective effect of E. coli was not correlated with a reduced host inflammatory response, nor with the release of biocidal molecules by protective bacteria, but rather with the presence of specific adhesion factors such as F pili that promote the emergence of probiotic bacteria in zebrafish larvae. Our study therefore provides new insights into the molecular events underlying the probiotic effect and constitutes a potentially high-throughput in vivo approach to the study of the molecular basis of pathogen exclusion in a relevant model of vertebrate oro-intestinal infection.

Roles of inflammatory caspases during processing of zebrafish interleukin-1β in Francisella noatunensis infection

The interleukin-1 family of cytokines are essential for the control of pathogenic microbes but are also responsible for devastating autoimmune pathologies. Consequently, tight regulation of inflammatory processes is essential for maintaining homeostasis. In mammals, interleukin-1 beta (IL-1β) is primarily regulated at two levels, transcription and processing. The main pathway for processing IL-1β is the inflammasome, a multiprotein complex that forms in the cytosol and which results in the activation of inflammatory caspase (caspase 1) and the subsequent cleavage and secretion of active IL-1β. Although zebrafish encode orthologs of IL-1β and inflammatory caspases, the processing of IL-1β by activated caspase(s) has never been examined. Here, we demonstrate that in response to infection with the fish-specific bacterial pathogen Francisella noatunensis, primary leukocytes from adult zebrafish display caspase-1-like activity that results in IL-1β processing. Addition of caspase 1 or pancaspase inhibitors considerably abrogates IL-1β processing. As in mammals, this processing event is concurrent with the secretion of cleaved IL-1β into the culture medium. Furthermore, two putative zebrafish inflammatory caspase orthologs, caspase A and caspase B, are both able to cleave IL-1β, but with different specificities. These results represent the first demonstration of processing and secretion of zebrafish IL-1β in response to a pathogen, contributing to our understanding of the evolutionary processes governing the regulation of inflammation.

Zebrafish (Danio rerio) larvae as a system to test the efficacy of polysaccharides as immunostimulants

The present study was carried out to examine the use of zebrafish (Danio rerio) as a preliminary screening model for testing the effect of potential immunostimulant substances on the innate immune system. β-Glucan, a polysaccharide used widely as an immunostimulant, was used as a representative molecule and tested on zebrafish embryos and larvae. The efficacy of the molecule was evaluated by determining the differential expression of some selected genes related to the immune system by RT-qPCR. Larvae from 72 hours post fertilization were found at the optimal developmental stage for assessing the expression of the selected genes. To verify if the β-glucan entered the larvae and therefore was responsible for the effects produced, the molecule was labeled fluorescently to check its localization by using microscopy. For estimating the effects of β-glucan on gene expression, zebrafish embryos and larvae were immersed in three different concentrations of β-glucan (50, 100, and 150 μg/mL) using five different exposure times. A stronger gene induction was observed when longer times of exposure and older larvae were used. The most evident effects of β-glucan were the overexpression of the genes TNFα, MPO, TRF, and LYZ. Moreover, slight changes in MPO expression were detected using a transgenic line of zebrafish (MPO::GFP), and a temporal increase in resistance against Vibrio anguillarum was found after β-glucan immersion. The assay used in this study permits the testing potential of immunostimulants in a simple and cost-effective way.

PROTEOMICS in aquaculture: applications and trends

Over the last forty years global aquaculture presented a growth rate of 6.9% per annum with an amazing production of 52.5 million tonnes in 2008, and a contribution of 43% of aquatic animal food for human consumption. In order to meet the world's health requirements of fish protein, a continuous growth in production is still expected for decades to come. Aquaculture is, though, a very competitive market, and a global awareness regarding the use of scientific knowledge and emerging technologies to obtain a better farmed organism through a sustainable production has enhanced the importance of proteomics in seafood biology research. Proteomics, as a powerful comparative tool, has therefore been increasingly used over the last decade to address different questions in aquaculture, regarding welfare, nutrition, health, quality, and safety. In this paper we will give an overview of these biological questions and the role of proteomics in their investigation, outlining the advantages, disadvantages and future challenges. A brief description of the proteomics technical approaches will be presented. Special focus will be on the latest trends related to the aquaculture production of fish with defined nutritional, health or quality properties for functional foods and the integration of proteomics techniques in addressing this challenging issue.

The inhibitory effect of environmental ammonia on Danio rerio LPS induced acute phase response

Ammonia is a toxic by-product of amino acid catabolism and a common environmental pollutant that has been associated with increased disease susceptibility in fish although the mechanism is not well understood. We addressed the hypothesis that elevated environmental ammonia acts by impairing the acute phase response (APR). Specifically, we determined the impact of sub-lethal acute (24 h) and chronic (14 d) ammonia exposure on acute phase protein gene expression in zebrafish (Danio rerio) in response to a challenge with bacterial lipopolysaccharide (LPS: i.p. 10 μg/g after 24h). A panel of LPS-responsive genes (SAA, HAMP, LECT2, Hp and IL1β) were identified and evaluated by real-time quantitative PCR. Ammonia was found to impair induction of SAA, HAMP and LECT2 by 50-90%. Both short (15 min, 1h and 24h) and long-term (14 days) exposure to high environmental ammonia concentrations significantly elevated whole-body cortisol levels compared with control fish. Our results reveal for the first time that exposure to high environmental levels of ammonia suppresses the innate immune response in fish. We hypothesize that high environmental ammonia-mediated elevation of cortisol levels in zebrafish may be playing a key role in this immunosuppression, while the mechanisms involved remains to be elucidated.

Characterization and functional analysis of atl, a novel gene encoding autolysin in Streptococcus suis

Streptococcus suis serotype 2 (S. suis 2) is an important swine and human pathogen responsible for septicemia and meningitis. A novel gene, designated atl and encoding a major autolysin of S. suis 2 virulent strain HA9801, was identified and characterized in this study. The Atl protein contains 1,025 amino acids with a predicted molecular mass of 113 kDa and has a conserved N-acetylmuramoyl-l-alanine amidase domain. Recombinant Atl was expressed in Escherichia coli, and its bacteriolytic and fibronectin-binding activities were confirmed by zymography and Western affinity blotting. Two bacteriolytic bands were shown in the sodium dodecyl sulfate extracts of HA9801, while both were absent from the atl inactivated mutant. Cell chains of the mutant strain became longer than that of the parental strain. In the autolysis assay, HA9801 decreased to 20% of the initial optical density (OD) value, while the mutant strain had almost no autolytic activity. The biofilm capacity of the atl mutant was reduced ∼30% compared to the parental strain. In the zebrafish infection model, the 50% lethal dose of the mutant strain was increased up to 5-fold. Furthermore, the adherence to HEp-2 cells of the atl mutant was 50% less than that of the parental strain. Based on the functional analysis of the recombinant Atl and observed effects of atl inactivation on HA9801, we conclude that Atl is a major autolysin of HA9801. It takes part in cell autolysis, separation of daughter cells, biofilm formation, fibronectin-binding activity, cell adhesion, and pathogenesis of HA9801.

Documented and potential research impacts of subclinical diseases in zebrafish

The zebrafish (Danio rerio) has become a very important animal model in biomedical research. In contrast with other models, such as mice, there has been relatively little documentation or control of subclinical disease in zebrafish research facilities. Several infectious and noninfectious conditions are consistently detected by histopathology in apparently healthy D. rerio. The most commonly observed infectious agent in zebrafish is Pseudoloma neurophilia, which is a microsporidian organism that targets the central nervous system, peripheral nerves, and occasionally other tissues. Mycobacteriosis, caused by Mycobacterium chelonae and other species, is also a frequent finding. Less commonly encountered agents include Pseudocapillaria tomentosa, which can cause extensive proliferative enteritis, and a myxozoan (Myxidium sp.) that inhabits the urinary tract but appears to cause few if any pathological changes. Noninfectious diseases that are often clinically unapparent in zebrafish include hepatic megalocytosis, bile and pancreatic ductal proliferation, and neoplasms of the ultimobranchial gland, gastrointestinal tract, and testis. To date, there is little information on the degree to which these conditions may impact research in subclinically affected fish, but there is reason to believe that they should be considered as potentially significant causes of nonprotocol variation in experiments. Therefore, it is imperative that research facilities monitor their stocks for the presence of these occult diseases and be aware of their existence when interpreting study results. Furthermore, for underlying disease conditions that cannot be readily eradicated, it is essential to determine the physiological and immunological changes that they elicit in zebrafish. Understanding the cause, modes of transmission, and distribution of the pathogens would provide useful information for the development of control and prevention strategies.

The giant danio (D. aequipinnatus) as a model of cardiac remodeling and regeneration

The paucity of mammalian adult cardiac myocytes (CM) proliferation following myocardial infarction (MI) and the remodeling of the necrotic tissue that ensues, result in non-regenerative repair. In contrast, zebrafish (ZF) can regenerate after an apical resection or cryoinjury of the heart. There is considerable interest in models where regeneration proceeds in the presence of necrotic tissue. We have developed and characterized a cautery injury model in the giant danio (GD), a species closely related to ZF, where necrotic tissue remains part of the ventricle, yet regeneration occurs. By light and transmission electron microscopy (TEM), we have documented four temporally overlapping processes: (1) a robust inflammatory response analogous to that observed in MI, (2) concomitant proliferation of epicardial cells leading to wound closure, (3) resorption of necrotic tissue and its replacement by granulation tissue, and (4) regeneration of the myocardial tissue driven by 5-EDU and [(3) H]thymidine incorporating CMs. In conclusion, our data suggest that the GD possesses robust repair mechanisms in the ventricle and can serve as an important model of cardiac inflammation, remodeling and regeneration.

Comparison of static immersion and intravenous injection systems for exposure of zebrafish embryos to the natural pathogen Edwardsiella tarda

Background

The zebrafish embryo is an important in vivo model to study the host innate immune response towards microbial infection. In most zebrafish infectious disease models, infection is achieved by micro-injection of bacteria into the embryo. Alternatively, Edwardsiella tarda, a natural fish pathogen, has been used to treat embryos by static immersion. In this study we used transcriptome profiling and quantitative RT-PCR to analyze the immune response induced by E. tarda immersion and injection.

Results

Mortality rates after static immersion of embryos in E. tarda suspension varied between 25-75%, while intravenous injection of bacteria resulted in 100% mortality. Quantitative RT-PCR analysis on the level of single embryos showed that expression of the proinflammatory marker genes il1b and mmp9 was induced only in some embryos that were exposed to E. tarda in the immersion system, whereas intravenous injection of E. tarda led to il1b and mmp9 induction in all embryos. In addition, microarray expression profiles of embryos subjected to immersion or injection showed little overlap. E. tarda-injected embryos displayed strong induction of inflammatory and defense genes and of regulatory genes of the immune response. E. tarda-immersed embryos showed transient induction of the cytochrome P450 gene cyp1a. This gene was also induced after immersion in Escherichia coli and Pseudomonas aeruginosa suspensions, but, in contrast, was not induced upon intravenous E. tarda injection. One of the rare common responses in the immersion and injection systems was induction of irg1l, a homolog of a murine immunoresponsive gene of unknown function.

Conclusions

Based on the differences in mortality rates between experiments and gene expression profiles of individual embryos we conclude that zebrafish embryos cannot be reproducibly infected by exposure to E. tarda in the immersion system. Induction of il1b and mmp9 was consistently observed in embryos that had been systemically infected by intravenous injection, while the early transcriptional induction of cyp1a and irg1l in the immersion system may reflect an epithelial or other tissue response towards cell membrane or other molecules that are shed or released by bacteria. Our microarray expression data provide a useful reference for future analysis of signal transduction pathways underlying the systemic innate immune response versus those underlying responses to external bacteria and secreted virulence factors and toxins.

Host-pathogen interactions made transparent with the zebrafish model

The zebrafish holds much promise as a high-throughput drug screening model for immune-related diseases, including inflammatory and infectious diseases and cancer. This is due to the excellent possibilities for in vivo imaging in combination with advanced tools for genomic and large scale mutant analysis. The context of the embryo’s developing immune system makes it possible to study the contribution of different immune cell types to disease progression. Furthermore, due to the temporal separation of innate immunity from adaptive responses, zebrafish embryos and larvae are particularly useful for dissecting the innate host factors involved in pathology. Recent studies have underscored the remarkable similarity of the zebrafish and human immune systems, which is important for biomedical applications. This review is focused on the use of zebrafish as a model for infectious diseases, with emphasis on bacterial pathogens. Following a brief overview of the zebrafish immune system and the tools and methods used to study host-pathogen interactions in zebrafish, we discuss the current knowledge on receptors and downstream signaling components that are involved in the zebrafish embryo’s innate immune response. We summarize recent insights gained from the use of bacterial infection models, particularly the Mycobacterium marinum model, that illustrate the potential of the zebrafish model for high-throughput antimicrobial drug screening.

The zebrafish brain in research and teaching: a simple in vivo and in vitro model for the study of spontaneous neural activity

Recently, the zebrafish (Danio rerio) has been established as a key animal model in neuroscience. Behavioral, genetic, and immunohistochemical techniques have been used to describe the connectivity of diverse neural circuits. However, few studies have used zebrafish to understand the function of cerebral structures or to study neural circuits. Information about the techniques used to obtain a workable preparation is not readily available. Here, we describe a complete protocol for obtaining in vitro and in vivo zebrafish brain preparations. In addition, we performed extracellular recordings in the whole brain, brain slices, and immobilized nonanesthetized larval zebrafish to evaluate the viability of the tissue. Each type of preparation can be used to detect spontaneous activity, to determine patterns of activity in specific brain areas with unknown functions, or to assess the functional roles of different neuronal groups during brain development in zebrafish. The technique described offers a guide that will provide innovative and broad opportunities to beginner students and researchers who are interested in the functional analysis of neuronal activity, plasticity, and neural development in the zebrafish brain.