Identification and real-time imaging of a myc-expressing neutrophil population involved in inflammation and mycobacterial granuloma formation in zebrafish

Towards a new combination therapy for tuberculosis with next generation benzothiazinones

The benzothiazinone lead compound, BTZ043, kills Mycobacterium tuberculosis by inhibiting the essential flavo-enzyme DprE1, decaprenylphosphoryl-beta-D-ribose 2-epimerase. Here, we synthesized a new series of piperazine-containing benzothiazinones (PBTZ) and show that, like BTZ043, the preclinical candidate PBTZ169 binds covalently to DprE1. The crystal structure of the DprE1-PBTZ169 complex reveals formation of a semimercaptal adduct with Cys387 in the active site and explains the irreversible inactivation of the enzyme. Compared to BTZ043, PBTZ169 has improved potency, safety and efficacy in zebrafish and mouse models of tuberculosis (TB). When combined with other TB drugs, PBTZ169 showed additive activity against M. tuberculosis in vitro except with bedaquiline (BDQ) where synergy was observed. A new regimen comprising PBTZ169, BDQ and pyrazinamide was found to be more efficacious than the standard three drug treatment in a murine model of chronic disease. PBTZ169 is thus an attractive drug candidate to treat TB in humans.

Subject Categories Microbiology, Virology & Host Pathogen Interaction; Pharmacology & Drug Discovery

Automated processing of zebrafish imaging data: a survey

Due to the relative transparency of its embryos and larvae, the zebrafish is an ideal model organism for bioimaging approaches in vertebrates. Novel microscope technologies allow the imaging of developmental processes in unprecedented detail, and they enable the use of complex image-based read-outs for high-throughput/high-content screening. Such applications can easily generate Terabytes of image data, the handling and analysis of which becomes a major bottleneck in extracting the targeted information. Here, we describe the current state of the art in computational image analysis in the zebrafish system. We discuss the challenges encountered when handling high-content image data, especially with regard to data quality, annotation, and storage. We survey methods for preprocessing image data for further analysis, and describe selected examples of automated image analysis, including the tracking of cells during embryogenesis, heartbeat detection, identification of dead embryos, recognition of tissues and anatomical landmarks, and quantification of behavioral patterns of adult fish. We review recent examples for applications using such methods, such as the comprehensive analysis of cell lineages during early development, the generation of a three-dimensional brain atlas of zebrafish larvae, and high-throughput drug screens based on movement patterns. Finally, we identify future challenges for the zebrafish image analysis community, notably those concerning the compatibility of algorithms and data formats for the assembly of modular analysis pipelines.

Zebrafish scube1 (signal peptide-CUB (complement protein C1r/C1s, Uegf, and Bmp1)-EGF (epidermal growth factor) domain-containing protein 1) is involved in primitive hematopoiesis

scube1 (signal peptide-CUB (complement protein C1r/C1s, Uegf, and Bmp1)-EGF domain-containing protein 1), the founding member of a novel secreted and cell surface SCUBE protein family, is expressed predominantly in various developing tissues in mice. However, its function in primitive hematopoiesis remains unknown. In this study, we identified and characterized zebrafish scube1 and analyzed its function by injecting antisense morpholino-oligonucleotide into embryos. Whole-mount in situ hybridization revealed that zebrafish scube1 mRNA is maternally expressed and widely distributed during early embryonic development. Knockdown of scube1 by morpholino-oligonucleotide down-regulated the expression of marker genes associated with early primitive hematopoietic precursors (scl) and erythroid (gata1 and hbbe1), as well as early (pu.1) and late (mpo and l-plastin) myelomonocytic lineages. However, the expression of an early endothelial marker fli1a and vascular morphogenesis appeared normal in scube1 morphants. Overexpression of bone morphogenetic protein (bmp) rescued the expression of scl in the posterior lateral mesoderm during early primitive hematopoiesis in scube1 morphants. Biochemical and molecular analysis revealed that Scube1 could be a BMP co-receptor to augment BMP signaling. Our results suggest that scube1 is critical for and functions at the top of the regulatory hierarchy of primitive hematopoiesis by modulating BMP activity during zebrafish embryogenesis.

Modeling innate immune response to early Mycobacterium infection

In the study of complex patterns in biology, mathematical and computational models are emerging as important tools. In addition to experimental approaches, these modeling tools have recently been applied to address open questions regarding host-pathogen interaction dynamics, including the immune response to mycobacterial infection and tuberculous granuloma formation. We present an approach in which a computational model represents the interaction of the Mycobacterium infection with the innate immune system in zebrafish at a high level of abstraction. We use the Petri Net formalism to model the interaction between the key host elements involved in granuloma formation and infection dissemination. We define a qualitative model for the understanding and description of causal relations in this dynamic process. Complex processes involving cell-cell or cell-bacteria communication can be modeled at smaller scales and incorporated hierarchically into this main model; these are to be included in later elaborations. With the infection mechanism being defined on a higher level, lower-level processes influencing the host-pathogen interaction can be identified, modeled, and tested both quantitatively and qualitatively. This systems biology framework incorporates modeling to generate and test hypotheses, to perform virtual experiments, and to make experimentally verifiable predictions. Thereby it supports the unraveling of the mechanisms of tuberculosis infection.

Using myc genes to search for stem cells in the ciliary margin of the Xenopus retina

The ciliary marginal zone (CMZ) of fish and frog retinas contains cells that proliferate throughout postembryonic development as the retina grows with increasing body size, indicating the presence of stem cells in this region. However, neither the location nor the molecular identity of retinal stem cells has been identified. Here, we show in Xenopus that c-myc and n-myc are sequentially expressed both during development and in the post-embryonic retina. The c-myc+/n-myc- cells near the extreme periphery of the CMZ cycle more slowly and preferentially retain DNA label compared to their more central cmyc+/n-myc+ neighbors which cycle rapidly and preferentially dilute DNA label. During retinal development c-myc is functionally required earlier than n-myc, and n-myc expression depends on earlier c-myc expression. The expression of c-myc but not n-myc in the CMZ depends on growth factor signaling. Our results suggest that c-myc+/n-myc- cells in the far peripheral CMZ are candidates for a niche-dependent population of retinal stem cells that give rise to more centrally located and rapidly dividing n-myc+ progenitors of more limited proliferative potential. Analysis of homologues of these genes in the zebrafish CMZ suggests that the transition from c-myc to n-myc expression might be conserved in other lower vertebrates whose retinas growth throughout life.

Innate immune response to Streptococcus iniae infection in zebrafish larvae

Streptococcus iniae causes systemic infection characterized by meningitis and sepsis. Here, we report a larval zebrafish model of S. iniae infection. Injection of wild-type S. iniae into the otic vesicle induced a lethal infection by 24 h postinfection. In contrast, an S. iniae mutant deficient in polysaccharide capsule (cpsA mutant) was not lethal, with greater than 90% survival at 24 h postinfection. Live imaging demonstrated that both neutrophils and macrophages were recruited to localized otic infection with mutant and wild-type S. iniae and were able to phagocytose bacteria. Depletion of neutrophils and macrophages impaired host survival following infection with wild-type S. iniae and the cpsA mutant, suggesting that leukocytes are critical for host survival in the presence of both the wild-type and mutant bacteria. However, zebrafish larvae with impaired neutrophil function but normal macrophage function had increased susceptibility to wild-type bacteria but not the cpsA mutant. Taking these findings together, we have developed a larval zebrafish model of S. iniae infection and have found that although neutrophils are important for controlling infection with wild-type S. iniae, neutrophils are not necessary for host defense against the cpsA mutant.

Maternal pak4 expression is required for primitive myelopoiesis in zebrafish

Transcripts of pak4, the zebrafish ortholog of p21-activated kinase 4 (PAK4), are most abundant in the egg and fall to low levels by the end of gastrulation, after which expression is essentially ubiquitous. Translation of maternal mRNA into pak4 protein is first detectable at high stage (3.3hpf). Splice-blocking morpholino oligonucleotides (MOs) were used to prevent zygotic pak4 expression. This had no discernable effect on development through larval stages. In contrast, a translation-blocking MO, alone or in combination with the splice MOs, resulted in a complex lethal phenotype. In addition to disrupted somite development and other morphogenetic abnormalities, the knockdown of maternal pak4 expression led to alterations in regulatory gene expression in the primitive hematopoietic domains, leading to deficiencies in granulocyte and leukocyte lineages. At least some of the effects of pak4 knockdown on gene expression could be mimicked by treatment with actin depolymerization agents, suggesting a mechanistic link between regulation of microfilament dynamics by pak4 and regulation of gene expression in primitive myeloid cell differentiation.

Activation of NF-κB protein prevents the transition from juvenile ovary to testis and promotes ovarian development in zebrafish

Testis differentiation in zebrafish involves juvenile ovary to testis transformation initiated by an apoptotic wave. The molecular regulation of this transformation process is not fully understood. NF-κB is activated at an early stage of development and has been shown to interact with steroidogenic factor-1 in mammals, leading to the suppression of anti-Müllerian hormone (Amh) gene expression. Because steroidogenic factor-1 and Amh are important for proper testis development, NF-κB-mediated induction of anti-apoptotic genes could, therefore, also play a role in zebrafish gonad differentiation. The aim of this study was to examine the potential role of NF-κB in zebrafish gonad differentiation. Exposure of juvenile zebrafish to heat-killed Escherichia coli activated the NF-κB pathways and resulted in an increased ratio of females from 30 to 85%. Microarray and quantitative real-time-PCR analysis of gonads showed elevated expression of NF-κB-regulated genes. To confirm the involvement of NF-κB-induced anti-apoptotic effects, zebrafish were treated with sodium deoxycholate, a known inducer of NF-κB or NF-κB activation inhibitor (NAI). Sodium deoxycholate treatment mimicked the effect of heat-killed bacteria and resulted in an increased proportion of females from 25 to 45%, whereas the inhibition of NF-κB using NAI resulted in a decrease in females from 45 to 20%. This study provides proof for an essential role of NF-κB in gonadal differentiation of zebrafish and represents an important step toward the complete understanding of the complicated process of sex differentiation in this species and possibly other cyprinid teleosts as well.

Neutrophil-delivered myeloperoxidase dampens the hydrogen peroxide burst after tissue wounding in zebrafish

Prompt neutrophil arrival is critical for host defense immediately after injury [1-3]. Following wounding, a hydrogen peroxide (H(2)O(2)) burst generated in injured tissues is the earliest known leukocyte chemoattractant [4]. Generating this tissue-scale H(2)O(2) gradient uses dual oxidase [4] and neutrophils sense H(2)O(2) by a mechanism involving the LYN Src-family kinase [5], but the molecular mechanisms responsible for H(2)O(2) clearance are unknown [6]. Neutrophils carry abundant amounts of myeloperoxidase, an enzyme catalyzing an H(2)O(2)-consuming reaction [7, 8]. We hypothesized that this neutrophil-delivered myeloperoxidase downregulates the high tissue H(2)O(2) concentrations that follow wounding. This was tested in zebrafish using simultaneous fluorophore-based imaging of H(2)O(2) concentrations and leukocytes [4, 9-11] and a new neutrophil-replete but myeloperoxidase-deficient mutant (durif). Leukocyte-depleted zebrafish had an abnormally sustained wound H(2)O(2) burst, indicating that leukocytes themselves were required for H(2)O(2) downregulation. Myeloperoxidase-deficient zebrafish also had abnormally sustained high wound H(2)O(2) concentrations despite similar numbers of arriving neutrophils. A local H(2)O(2)/myeloperoxidase interaction within wound-recruited neutrophils was demonstrated. These data demonstrate that leukocyte-delivered myeloperoxidase cell-autonomously downregulates tissue-generated wound H(2)O(2) gradients in vivo, defining a new requirement for myeloperoxidase during inflammation. Durif provides a new animal model of myeloperoxidase deficiency closely phenocopying the prevalent human disorder [7, 12, 13], offering unique possibilities for investigating its clinical consequences.

Non-invasive imaging of disseminated candidiasis in zebrafish larvae

Disseminated candidiasis caused by the pathogen Candida albicans is a clinically important problem in hospitalized individuals and is associated with a 30 to 40% attributable mortality(6). Systemic candidiasis is normally controlled by innate immunity, and individuals with genetic defects in innate immune cell components such as phagocyte NADPH oxidase are more susceptible to candidemia(7-9). Very little is known about the dynamics of C. albicans interaction with innate immune cells in vivo. Extensive in vitro studies have established that outside of the host C. albicans germinates inside of macrophages, and is quickly destroyed by neutrophils(10-14). In vitro studies, though useful, cannot recapitulate the complex in vivo environment, which includes time-dependent dynamics of cytokine levels, extracellular matrix attachments, and intercellular contacts(10, 15-18). To probe the contribution of these factors in host-pathogen interaction, it is critical to find a model organism to visualize these aspects of infection non-invasively in a live intact host. The zebrafish larva offers a unique and versatile vertebrate host for the study of infection. For the first 30 days of development zebrafish larvae have only innate immune defenses(2, 19-21), simplifying the study of diseases such as disseminated candidiasis that are highly dependent on innate immunity. The small size and transparency of zebrafish larvae enable imaging of infection dynamics at the cellular level for both host and pathogen. Transgenic larvae with fluorescing innate immune cells can be used to identify specific cells types involved in infection(22-24). Modified anti-sense oligonucleotides (Morpholinos) can be used to knock down various immune components such as phagocyte NADPH oxidase and study the changes in response to fungal infection(5). In addition to the ethical and practical advantages of using a small lower vertebrate, the zebrafish larvae offers the unique possibility to image the pitched battle between pathogen and host both intravitally and in color. The zebrafish has been used to model infection for a number of human pathogenic bacteria, and has been instrumental in major advances in our understanding of mycobacterial infection(3, 25). However, only recently have much larger pathogens such as fungi been used to infect larva(5, 23, 26), and to date there has not been a detailed visual description of the infection methodology. Here we present our techniques for hindbrain ventricle microinjection of prim(25) zebrafish, including our modifications to previous protocols. Our findings using the larval zebrafish model for fungal infection diverge from in vitro studies and reinforce the need to examine the host-pathogen interaction in the complex environment of the host rather than the simplified system of the Petri dish(5).

Neutrophil reverse migration becomes transparent with zebrafish

The precise control of neutrophil-mediated inflammation is critical for both host defense and the prevention of immunopathology. In vivo imaging studies in zebrafish, and more recently in mice, have made the novel observation that neutrophils leave a site of inflammation through a process called neutrophil reverse migration. The application of advanced imaging techniques to the genetically tractable, optically transparent zebrafish larvae was critical for these advances. Still, the mechanisms underlying neutrophil reverse migration and its effects on the resolution or priming of immune responses remain unclear. Here, we review the current knowledge of neutrophil reverse migration, its potential roles in host immunity, and the live imaging tools that make zebrafish a valuable model for increasing our knowledge of neutrophil behavior in vivo.

Pathogen recognition and activation of the innate immune response in zebrafish

The zebrafish has proven itself as an excellent model to study vertebrate innate immunity. It presents us with possibilities for in vivo imaging of host-pathogen interactions which are unparalleled in mammalian model systems. In addition, its suitability for genetic approaches is providing new insights on the mechanisms underlying the innate immune response. Here, we review the pattern recognition receptors that identify invading microbes, as well as the innate immune effector mechanisms that they activate in zebrafish embryos. We compare the current knowledge about these processes in mammalian models and zebrafish and discuss recent studies using zebrafish infection models that have advanced our general understanding of the innate immune system. Furthermore, we use transcriptome analysis of zebrafish infected with E. tarda, S. typhimurium, and M. marinum to visualize the gene expression profiles resulting from these infections. Our data illustrate that the two acute disease-causing pathogens, E. tarda and S. typhimurium, elicit a highly similar proinflammatory gene induction profile, while the chronic disease-causing pathogen, M. marinum, induces a weaker and delayed innate immune response.

Live imaging reveals differing roles of macrophages and neutrophils during zebrafish tail fin regeneration

Macrophages and neutrophils are the pivotal immune phagocytes that enter the wound after tissue injury to remove the cell debris and invaded microorganisms, which presumably facilitate the regrowth of injured tissues. Taking advantage of the regeneration abilities of zebrafish and the newly generated leukocyte-specific zebrafish lines with labeling of both leukocyte lineages, we assessed the behaviors and functions of neutrophils and macrophages during tail fin regeneration. Live imaging showed that within 6 hours post amputation, the inflammatory stage, neutrophils were the primary cells scavenging apoptotic bodies and small cell debris, although they had limited phagocytic capacity and quickly underwent apoptosis. From 6 hours post amputation on, the resolution and regeneration stage, macrophages became the dominant scavengers, efficiently resolving inflammation and facilitating tissue remodeling and regrowth. Ablation of macrophages but not neutrophils severely impaired the inflammatory resolution and tissue regeneration, resulting in the formation of large vacuoles in the regenerated fins. In contrast, removal of neutrophils slightly accelerates the regrowth of injured fin. Our study documents the differing behaviors and functions of macrophages and neutrophils during tissue regeneration.

Unexpected link between lipooligosaccharide biosynthesis and surface protein release in Mycobacterium marinum

The mycobacterial cell envelope is characterized by the presence of a highly impermeable second membrane, which is composed of mycolic acids intercalated with different unusual free lipids, such as lipooligosaccharides (LOS). Transport across this cell envelope requires a dedicated secretion system for extracellular proteins, such as PE_PGRS proteins, which are specific mycobacterial proteins with polymorphic GC-rich sequence (PGRS). In this study, we set out to identify novel components involved in the secretion of PE_PGRS proteins by screening Mycobacterium marinum transposon mutants for secretion defects. Interestingly, most mutants were not affected in secretion but in the release of PE_PGRS proteins from the cell surface. These mutants had insertions in a gene cluster associated with LOS biosynthesis. Lipid analysis of these mutants revealed a role at different stages of LOS biosynthesis for 10 novel genes. Furthermore, we show that regulatory protein WhiB4 is involved in LOS biosynthesis. The absence of the most extended LOS molecule, i.e. LOS-IV, and a concomitant accumulation of LOS-III was already sufficient to reduce the release of PE_PGRS proteins from the mycobacterial cell surface. A similar effect was observed for major surface protein EspE. These results show that the attachment of surface proteins is strongly influenced by the glycolipid composition of the mycobacterial cell envelope. Finally, we tested the virulence of a LOS-IV-deficient mutant in our zebrafish embryo infection model. This mutant showed a marked increase in virulence as compared with the wild-type strain, suggesting that LOS-IV plays a role in the modulation of mycobacterial virulence.

Mesoporous silica nanoparticles as a compound delivery system in zebrafish embryos

Silica nanoparticles can be efficiently employed as carriers for therapeutic drugs in vitro. Here, we use zebrafish embryos as a model organism to see whether mesoporous silica nanoparticles (MSNPs) can be incorporated to deliver compounds in vivo. We injected 35-40 nL (10 mg/mL) of custom-synthesized, fluorescently-tagged 200 nm MSNPs into the left flank, behind the yolk sac extension, of 2-day-old zebrafish embryos. We tracked the distribution and translocation of the MSNPs using confocal laser scanning microscopy. Some of the particles remained localized at the injection site, whereas others entered the bloodstream and were carried around the body. Embryo development and survival were not significantly affected by MSNP injection. Acridine orange staining revealed that MSNP injections did not induce significant cell death. We also studied cellular immune responses by means of lysC::DsRED2 transgenic embryos. MSNP-injected embryos showed infiltration of the injection site with neutrophils, similar to controls injected with buffer only. In the same embryos, counterstaining with L-plastin antibody for leukocytes revealed the same amount of cellular infiltration of the injection site in embryos injected with MSNPs or with buffer only. Next, we used MSNPs to deliver two recombinant cytokines (macrophage colony-stimulating factor and receptor for necrosis factor ligand) to zebrafish embryos. These proteins are known to activate cells involved in bone remodeling, and this can be detected with the marker tartrate-resistant acid phosphatase. Coinjection of these proteins loaded onto MSNPs produced a significant increase in the number of tartrate-resistant acid phosphatase-positive cells after 2-3 days of injection. Our results show that MSNPs can be used to deliver bioactive compounds into zebrafish larvae without producing higher mortality or gross evidence of teratogenicity.

Runx1 regulates embryonic myeloid fate choice in zebrafish through a negative feedback loop inhibiting Pu.1 expression

Proper cell fate choice in myelopoiesis is essential for generating correct numbers of distinct myeloid subsets manifesting a wide spectrum of subset-specific activities during development and adulthood. Studies have suggested that myeloid fate choice is primarily regulated by transcription factors; however, new intrinsic regulators and their underlying mechanisms remain to be elucidated. Zebrafish embryonic myelopoiesis gives rise to neutrophils and macrophages and represents a promising system to derive new regulatory mechanisms for myeloid fate decision in vertebrates. Here we present an in vivo study of cell fate specification during zebrafish embryonic myelopoiesis through characterization of the embryos with altered Pu.1, Runx1 activity alone, or their combinations. Genetic analysis shows that low and high Pu.1 activities determine embryonic neutrophilic granulocyte and macrophage fate, respectively. Inactivation and overexpression of Runx1 in zebrafish uncover Runx1 as a key embryonic myeloid fate determinant that favors neutrophil over macrophage fate. Runx1 is induced by high Pu.1 level and in turn transrepresses pu.1 expression, thus constituting a negative feedback loop that fashions a favorable Pu.1 level required for balanced fate commitment to neutrophils versus macrophages. Our findings define a Pu.1-Runx1 regulatory loop that governs the equilibrium between distinct myeloid fates by assuring an appropriate Pu.1 dosage.

Retinoic acid signaling plays a restrictive role in zebrafish primitive myelopoiesis

Retinoic acid (RA) is known to regulate definitive myelopoiesis but its role in vertebrate primitive myelopoiesis remains unclear. Here we report that zebrafish primitive myelopoiesis is restricted by RA in a dose dependent manner mainly before 11 hpf (hours post fertilization) when anterior hemangioblasts are initiated to form. RA treatment significantly reduces expressions of anterior hemangioblast markers scl, lmo2, gata2 and etsrp in the rostral end of ALPM (anterior lateral plate mesoderm) of the embryos. The result indicates that RA restricts primitive myelopoiesis by suppressing formation of anterior hemangioblasts. Analyses of ALPM formation suggest that the defective primitive myelopoiesis resulting from RA treatment before late gastrulation may be secondary to global loss of cells for ALPM fate whereas the developmental defect resulting from RA treatment during 10–11 hpf should be due to ALPM patterning shift. Overexpressions of scl and lmo2 partially rescue the block of primitive myelopoiesis in the embryos treated with 250 nM RA during 10–11 hpf, suggesting RA acts upstream of scl to control primitive myelopoiesis. However, the RA treatment blocks the increased primitive myelopoiesis caused by overexpressing gata4/6 whereas the abolished primitive myelopoiesis in gata4/5/6 depleted embryos is well rescued by 4-diethylamino-benzaldehyde, a retinal dehydrogenase inhibitor, or partially rescued by knocking down aldh1a2, the major retinal dehydrogenase gene that is responsible for RA synthesis during early development. Consistently, overexpressing gata4/6 inhibits aldh1a2 expression whereas depleting gata4/5/6 increases aldh1a2 expression. The results reveal that RA signaling acts downstream of gata4/5/6 to control primitive myelopoiesis. But, 4-diethylamino-benzaldehyde fails to rescue the defective primitive myelopoiesis in either cloche embryos or lycat morphants. Taken together, our results demonstrate that RA signaling restricts zebrafish primitive myelopoiesis through acting downstream of gata4/5/6, upstream of, or parallel to, cloche, and upstream of scl.

Zebrafish: model for the study of inflammation and the innate immune response to infectious diseases

The zebrafish (Danio rerio) has been extensively used in biomedical research as a model to study vertebrate development and hematopoiesis and recently, it has been adopted into varied fields including immunology. After fertilization, larvae survive with only the innate immune responses because adaptive immune system is morphologically and functionally mature only after 4-6 weeks postfertilization. This temporal separation provides a suitable system to study the vertebrate innate immune response in vivo, independently from the adaptive immune response. The transparency of early life stages allows a useful real-time visualization. Adult zebrafish which have complete (innate and adaptative) immune systems offer also advantages over other vertebrate infection models: small size, relatively rapid life cycle, ease of breeding, and a growing list of molecular tools for the study of infectious diseases. In this review, we have tried to give some examples of the potential of zebrafish as a valuable model in innate immunity and inflammation studies.

Long-term stimulation of trout head kidney cells with the cytokines MCSF, IL-2 and IL-6: gene expression dynamics

The production of salmonid leukocyte cell lines from primary cell cultures has been attempted on several occasions, however, to date only monocyte/macrophage like cell lines exist (e.g. RTS-11 and SHK-1 cells). With the increasing number of cytokines discovered in fish in recent years, many of which are growth factors for leukocytes, we now have the possibility of using these molecules to promote leukocyte development and differentiation in culture. We have generated stable cell lines transfected with a variety of plasmids expressing cytokines (Interleukin (IL)-2, IL-6 and Macrophage Colony Stimulating Factor (MCSF)), in order to produce conditioned media rich in these cytokines. The cytokine-conditioned media were used to assess their activity and ability to support the growth of primary head kidney (HK) leukocyte cultures. Here, we describe a series of experiments aimed to determine which cell population(s) of primary HK cultures is supported and will grow in conditioned media containing MCSF, IL-2 or IL-6. For a period of 5 weeks, cells were incubated at 22°C and media were changed every 3-4 days. Samples were taken at different time points, from freshly isolated HK cells (T0), one week post-stimulation (1-WPS), 3-WPS and 5-WPS for RNA extraction. A variety of cell lineage markers (MCSF Receptor 2 (MCSFR2) for macrophages, CD4 and CD8a for T cells and IgM heavy chain for B cells) were then analysed by real-time qPCR to study the cell population dynamics as influenced by the different recombinant cytokines in the cultures. We show here that whilst MCSF appears to drive macrophage differentiation and maintenance, IL-2 and IL-6 seem to preferentially drive lymphocyte differentiation.

In vivo real-time visualization of leukocytes and intracellular hydrogen peroxide levels during a zebrafish acute inflammation assay

Following injury, the inflammatory response directs the host immune cells to the wound to maintain tissue integrity and combat pathogens. The recruitment of immune cells to inflammatory sites is achieved through the establishment of a variety of signal gradients. Using a zebrafish embryo injury model, it was recently demonstrated that, upon injury, cells at the wound margin rapidly produce hydrogen peroxide (H(2)O(2)) which serves as an early paracrine signal to leukocytes. This chapter provides a method for performing in vivo time-lapse fluorescence microscopy to visualize leukocyte behaviors and wound-produced H(2)O(2) simultaneously in single zebrafish embryos during an acute inflammatory response. Protocols are included for inducing a robust, reproducible acute inflammatory response, for rapidly mounting immobilized embryos for time-lapse imaging, and for computing ratiometric data from the images of embryos expressing the genetically encoded H(2)O(2) sensor fluorophore HyPer. General issues to consider when designing multichannel fluorescent imaging are discussed, including particular considerations to note when monitoring intracellular H(2)O(2) concentration dynamics using HyPer.

Evolutionary history of c-myc in teleosts and characterization of the duplicated c-myca genes in goldfish embryos

c-Myc plays an important role during embryogenesis in mammals, but little is known about its function during embryonic development in teleosts. In addition, the evolutionary history of c-myc gene in teleosts remains unclear, and depending on the species, a variable number of gene duplicates exist in teleosts. To gain new insight into c-myc genes in teleosts, the present study was designed to clarify the evolutionary history of c-myc gene(s) in teleosts and to subsequently characterize DNA methylation and early embryonic expression patterns in a cyprinid fish. Our results show that a duplication of c-myc gene occurred before or around the teleost radiation, as a result of the teleost-specific whole genome duplication giving rise to c-myca and c-mycb in teleosts and was followed by a loss of the c-mycb gene in the Gasterosteiforms and Tetraodontiforms. Our data also demonstrate that both c-myc genes previously identified in carp and goldfish are co-orthologs of the zebrafish c-myca. These results indicate the presence of additional c-myca duplication in Cyprininae. We were able to identify differences between the expression patterns of the two goldfish c-myca genes in oocytes and early embryos. These differences suggest a partial sub-functionalization of c-myca genes after duplication. Despite differences in transcription patterns, both of the c-myca genes displayed similar DNA methylation patterns during early development and in gametes. Together, our results clarify the evolutionary history of the c-myc gene in teleosts and provide new insight into the involvement of c-myc in early embryonic development in cyprinids.

Identification of vimentin- and elastin-like transcripts specifically expressed in developing notochord of Atlantic salmon (Salmo salar L.)

The notochord functions as the midline structural element of all vertebrate embryos, and allows movement and growth at early developmental stages. Moreover, during embryonic development, notochord cells produce secreted factors that provide positional and fate information to a broad variety of cells within adjacent tissues, for instance those of the vertebrae, central nervous system and somites. Due to the large size of the embryo, the salmon notochord is useful to study as a model for exploring notochord development. To investigate factors that might be involved in notochord development, a normalized cDNA library was constructed from a mix of notochords from ∼500 to ∼800 day°. From the 1968 Sanger-sequenced transcripts, 22 genes were identified to be predominantly expressed in the notochord compared to other organs of salmon. Twelve of these genes were found to show expressional regulation around mineralization of the notochord sheath; 11 genes were up-regulated and one gene was down-regulated. Two genes were found to be specifically expressed in the notochord; these genes showed similarity to vimentin (acc. no GT297094) and elastin (acc. no GT297478). In-situ results showed that the vimentin- like transcript was expressed in both chordocytes and chordoblasts, whereas the elastin- like transcript was uniquely expressed in the chordoblasts lining the notochordal sheath. In salmon aquaculture, vertebral deformities are a common problem, and some malformations have been linked to the notochord. The expression of identified transcripts provides further insight into processes taking place in the developing notochord, prior to and during the early mineralization period.

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.

Mediator subunit 12 is required for neutrophil development in zebrafish

Hematopoiesis requires the spatiotemporal organization of regulatory factors to successfully orchestrate diverse lineage specificity from stem and progenitor cells. Med12 is a regulatory component of the large Mediator complex that enables contact between the general RNA polymerase II transcriptional machinery and enhancer bound regulatory factors. We have identified a new zebrafish med12 allele, syr, with a single missense mutation causing a valine to aspartic acid change at position 1046. Syr shows defects in hematopoiesis, which predominantly affect the myeloid lineage. Syr has identified a hematopoietic cell-specific requirement for Med12, suggesting a new role for this transcriptional regulator.

Lung neutrophils facilitate activation of naive antigen-specific CD4+ T cells during Mycobacterium tuberculosis infection

Initiation of the adaptive immune response to Mycobacterium tuberculosis occurs in the lung-draining mediastinal lymph node and requires transport of M. tuberculosis by migratory dendritic cells (DCs) to the local lymph node. The previously published observations that 1) neutrophils are a transiently prominent population of M. tuberculosis-infected cells in the lungs early in infection and 2) that the peak of infected neutrophils immediately precedes the peak of infected DCs in the lungs prompted us to characterize the role of neutrophils in the initiation of adaptive immune responses to M. tuberculosis. We found that, although depletion of neutrophils in vivo increased the frequency of M. tuberculosis-infected DCs in the lungs, it decreased trafficking of DCs to the mediastinal lymph node. This resulted in delayed activation (CD69 expression) and proliferation of naive M. tuberculosis Ag85B-specific CD4 T cells in the mediastinal lymph node. To further characterize the role of neutrophils in DC migration, we used a Transwell chemotaxis system and found that DCs that were directly infected by M. tuberculosis migrated poorly in response to CCL19, an agonist for the chemokine receptor CCR7. In contrast, DCs that had acquired M. tuberculosis through uptake of infected neutrophils exhibited unimpaired migration. These results revealed a mechanism wherein neutrophils promote adaptive immune responses to M. tuberculosis by delivering M. tuberculosis to DCs in a form that makes DCs more effective initiators of naive CD4 T cell activation. These observations provide insight into a mechanism for neutrophils to facilitate initiation of adaptive immune responses in tuberculosis.

Live imaging of disseminated candidiasis in zebrafish reveals role of phagocyte oxidase in limiting filamentous growth

Candida albicans is a human commensal and a clinically important fungal pathogen that grows in both yeast and hyphal forms during human infection. Although Candida can cause cutaneous and mucosal disease, systemic infections cause the greatest mortality in hospitals. Candidemia occurs primarily in immunocompromised patients, for whom the innate immune system plays a paramount role in immunity. We have developed a novel transparent vertebrate model of candidemia to probe the molecular nature of Candida-innate immune system interactions in an intact host. Our zebrafish infection model results in a lethal disseminated disease that shares important traits with disseminated candidiasis in mammals, including dimorphic fungal growth, dependence on hyphal growth for virulence, and dependence on the phagocyte NADPH oxidase for immunity. Dual imaging of fluorescently marked immune cells and fungi revealed that phagocytosed yeast cells can remain viable and even divide within macrophages without germinating. Similarly, although we observed apparently killed yeast cells within neutrophils, most yeast cells within these innate immune cells were viable. Exploiting this model, we combined intravital imaging with gene knockdown to show for the first time that NADPH oxidase is required for regulation of C. albicans filamentation in vivo. The transparent and easily manipulated larval zebrafish model promises to provide a unique tool for dissecting the molecular basis of phagocyte NADPH oxidase-mediated limitation of filamentous growth in vivo.

A high-throughput screen for tuberculosis progression

One-third of the world population is infected with Mycobacterium tuberculosis and multi-drug resistant strains are rapidly evolving. The noticeable absence of a whole organism high-throughput screening system for studying the progression of tuberculosis is fast becoming the bottleneck in tuberculosis research. We successfully developed such a system using the zebrafish Mycobacterium marinum infection model, which is a well-characterized model for tuberculosis progression with biomedical significance, mimicking hallmarks of human tuberculosis pathology. Importantly, we demonstrate the suitability of our system to directly study M. tuberculosis, showing for the first time that the human pathogen can propagate in this vertebrate model, resulting in similar early disease symptoms to those observed upon M. marinum infection. Our system is capable of screening for disease progression via robotic yolk injection of early embryos and visual flow screening of late-stage larvae. We also show that this system can reliably recapitulate the standard caudal vein injection method with a throughput level of 2,000 embryos per hour. We additionally demonstrate the possibility of studying signal transduction leading to disease progression using reverse genetics at high-throughput levels. Importantly, we use reference compounds to validate our system in the testing of molecules that prevent tuberculosis progression, making it highly suited for investigating novel anti-tuberculosis compounds in vivo.

Simultaneous intravital imaging of macrophage and neutrophil behaviour during inflammation using a novel transgenic zebrafish

The zebrafish is an outstanding model for intravital imaging of inflammation due to its optical clarity and the ability to express fluorescently labelled specific cell types by transgenesis. However, although several transgenic labelling myeloid cells exist, none allow distinction of macrophages from neutrophils. This prevents simultaneous imaging and examination of the individual contributions of these important leukocyte subtypes during inflammation. We therefore used Bacterial Artificial Chromosome (BAC) recombineering to generate a transgenic Tg(fms:GAL4.VP16)i186 , in which expression of the hybrid transcription factor Gal4-VP16 is driven by the fms (CSF1R) promoter. This was then crossed to a second transgenic expressing a mCherry-nitroreductase fusion protein under the control of the Gal4 binding site (the UAS promoter), allowing intravital imaging of mCherry-labelled macrophages. Further crossing this compound transgenic with the neutrophil transgenic Tg(mpx:GFP)i114 allowed clear distinction between macrophages and neutrophils and simultaneous imaging of their recruitment and behaviour during inflammation. Compared with neutrophils, macrophages migrate significantly more slowly to an inflammatory stimulus. Neutrophil number at a site of tissue injury peaked around 6 hours post injury before resolving, while macrophage recruitment increased until at least 48 hours. We show that macrophages were effectively ablated by addition of the prodrug metronidazole, with no effect on neutrophil number. Crossing with Tg(Fli1:GFP)y1 transgenic fish enabled intravital imaging of macrophage interaction with endothelium for the first time, revealing that endothelial contact is associated with faster macrophage migration. Tg(fms:GAL4.VP16)i186 thus provides a powerful tool for intravital imaging and functional manipulation of macrophage behaviour during inflammation.

Infectious disease modeling and innate immune function in zebrafish embryos

The major cell types of the innate immune system, macrophages and neutrophils, develop during the first two days of zebrafish embryogenesis. The interaction of these immune cells with pathogenic microbes can excellently be traced in the optically transparent zebrafish embryos. Various tools and methods have recently been developed for visualizing and isolating the zebrafish embryonic innate immune cells, for establishing infections by different micro-injection techniques, and for analyzing the host innate immune response following microbial recognition. Here we provide practical guidelines for the application of these methodologies and review the current state of the art in zebrafish infectious disease research.

mpeg1 promoter transgenes direct macrophage-lineage expression in zebrafish

Macrophages and neutrophils play important roles during the innate immune response, phagocytosing invading microbes and delivering antimicrobial compounds to the site of injury. Functional analyses of the cellular innate immune response in zebrafish infection/inflammation models have been aided by transgenic lines with fluorophore-marked neutrophils. However, it has not been possible to study macrophage behaviors and neutrophil/macrophage interactions in vivo directly because there has been no macrophage-only reporter line. To remove this roadblock, a macrophage-specific marker was identified (mpeg1) and its promoter used in mpeg1-driven transgenes. mpeg1-driven transgenes are expressed in macrophage-lineage cells that do not express neutrophil-marking transgenes. Using these lines, the different dynamic behaviors of neutrophils and macrophages after wounding were compared side-by-side in compound transgenics. Macrophage/neutrophil interactions, such as phagocytosis of senescent neutrophils, were readily observed in real time. These zebrafish transgenes provide a new resource that will contribute to the fields of inflammation, infection, and leukocyte biology.

Irf8 regulates macrophage versus neutrophil fate during zebrafish primitive myelopoiesis

In vertebrates, myeloid cells comprise polymorphonuclear and mononuclear lineages that arise from 2 successive waves of development: a transitory primitive wave giving rise to limited myeloid cells during embryonic stage and a definitive wave capable of producing myeloid cells throughout the fetal and adult life. One key unresolved question is what factors dictate polymorphonuclear versus mononuclear lineage fates during myelopoiesis. Here we show that during zebrafish embryogenesis interferon regulatory factor-8 (irf8) is expressed specifically in macrophages but not neutrophils. Suppression of Irf8 function in zebrafish causes a depletion of macrophages and an enhanced output of neutrophils but does not affect the overall number, proliferation, and survival of primitive myeloid cells. These data indicate that the skewed myeloid lineage development in Irf8 knockdown embryos results from a cell-fate switching. Such a conclusion is further supported by the observation showing that overexpression of Irf8 promotes macrophage formation at the expense of neutrophil development. Genetic epistasis analysis reveals that Irf8 acts downstream of Pu.1 but is insufficient to promote macrophage development in the absence of Pu.1. Our findings demonstrate that Irf8 is a critical determinant for neutrophil versus macrophage fate choice during zebrafish primitive myelopoiesis.

Transcriptome analysis of Traf6 function in the innate immune response of zebrafish embryos

TRAF6 is a key player at the cross-roads of development and immunity. The analysis of its in vivo molecular function is a great challenge since severe developmental defects and early lethality caused by Traf6 deficiency in knock-out mice interfere with analyses of the immune response. In this study we have used a new strategy to analyze the function of Traf6 in a zebrafish-Salmonella infectious disease model. In our approach the effect of a Traf6 translation-blocking morpholino was titrated down to avoid developmental defects and the response to infection under these conditions was studied using the combination of microarray analysis and whole transcriptome deep sequencing. Transcriptome profiling of the traf6 knock-down allowed the identification of a gene set whose responsiveness during infection is highly dependent on Traf6. Expression trend analysis based on the resulting datasets identified nine clusters of genes with characteristic transcription response profiles, demonstrating Traf6 has a dynamic role as a positive and negative regulator. Among the Traf6-dependent genes was a large set of well known anti-microbial and inflammatory genes. Additionally, we identified several genes which were not previously linked to a response to microbial infection, such as the fertility hormone gene gnrh2 and the DNA-damage regulated autophagy modulator 1 gene dram1. With the use of the zebrafish embryo model we have now analyzed the in vivo function of Traf6 in the innate immune response without interference of adaptive immunity.

Eosinophils in the zebrafish: prospective isolation, characterization, and eosinophilia induction by helminth determinants

Eosinophils are granulocytic leukocytes implicated in numerous aspects of immunity and disease. The precise functions of eosinophils, however, remain enigmatic. Alternative models to study eosinophil biology may thus yield novel insights into their function. Eosinophilic cells have been observed in zebrafish but have not been thoroughly characterized. We used a gata2:eGFP transgenic animal to enable prospective isolation and characterization of zebrafish eosinophils, and demonstrate that all gata2(hi) cells in adult hematopoietic tissues are eosinophils. Although eosinophils are rare in most organs, they are readily isolated from whole kidney marrow and abundant within the peritoneal cavity. Molecular analyses demonstrate that zebrafish eosinophils express genes important for the activities of mammalian eosinophils. In addition, gata2(hi) cells degranulate in response to helminth extract. Chronic exposure to helminth- related allergens resulted in profound eosinophilia, demonstrating that eosinophil responses to allergens have been conserved over evolution. Importantly, infection of adult zebrafish with Pseudocapillaria tomentosa, a natural nematode pathogen of teleosts, caused marked increases in eosinophil number within the intestine. Together, these observations support a conserved role for eosinophils in the response to helminth antigens or infection and provide a new model to better understand how parasitic worms activate, co-opt, or evade the vertebrate immune response.

Macrophage-specific gene functions in Spi1-directed innate immunity

The Spi1/Pu.1 transcription factor plays a crucial role in myeloid cell development in vertebrates. Despite extensive studies of Spi1, the controlled gene group remains largely unknown. To identify genes dependent on Spi1, we used a microarray strategy using a knockdown approach in zebrafish embryos combined with fluorescence-activated cell sorting of myeloid cells from transgenic embryos. This approach of using knockdowns with specific green fluorescent protein-marked cell types was highly successful in identifying macrophage-specific genes in Spi1-directed innate immunity. We found a gene group down-regulated on spi1 knockdown, which is also enriched in fluorescence-activated cell-sorted embryonic myeloid cells of a spi1:GFP transgenic line. This gene group, representing putative myeloid-specific Spi1 target genes, contained all 5 previously identified Spi1-dependent zebrafish genes as well as a large set of novel immune-related genes. Colocalization studies with neutrophil and macrophage markers revealed that genes cxcr3.2, mpeg1, ptpn6, and mfap4 were expressed specifically in early embryonic macrophages. In a functional approach, we demonstrated that gene cxcr3.2, coding for chemokine receptor 3.2, is involved in macrophage migration to the site of bacterial infection. Therefore, based on our combined transcriptome analyses, we discovered novel early macrophage-specific marker genes, including a signal transducer pivotal for macrophage migration in the innate immune response.

Burkholderia cenocepacia creates an intramacrophage replication niche in zebrafish embryos, followed by bacterial dissemination and establishment of systemic infection

Bacteria belonging to the "Burkholderia cepacia complex" (Bcc) often cause fatal pulmonary infections in cystic fibrosis patients, yet little is know about the underlying molecular mechanisms. These Gram-negative bacteria can adopt an intracellular lifestyle, although their ability to replicate intracellularly has been difficult to demonstrate. Here we show that Bcc bacteria survive and multiply in macrophages of zebrafish embryos. Local dissemination by nonlytic release from infected cells was followed by bacteremia and extracellular replication. Burkholderia cenocepacia isolates belonging to the epidemic electrophoretic type 12 (ET12) lineage were highly virulent for the embryos; intravenous injection of <10 bacteria of strain K56-2 killed embryos within 3 days. However, small but significant differences between the clonal ET12 isolates K56-2, J2315, and BC7 were evident. In addition, the innate immune response in young embryos was sufficiently developed to control infection with other less virulent Bcc strains, such as Burkholderia vietnamiensis FC441 and Burkholderia stabilis LMG14294. A K56-2 cepR quorum-sensing regulator mutant was highly attenuated, and its ability to replicate and spread to neighboring cells was greatly reduced. Our data indicate that the zebrafish embryo is an excellent vertebrate model to dissect the molecular basis of intracellular replication and the early innate immune responses in this intricate host-pathogen interaction.

Characterization of zebrafish larval inflammatory macrophages

Zebrafish have emerged as a powerful model system to study leukocyte recruitment and inflammation. Here we characterize the morphology and function of inflammatory macrophages in zebrafish larvae. These macrophages can be distinguished from neutrophils by immunolabeling of L-Plastin without MPO co-expression and by an elongated morphology. Live imaging of transgenic zMPO:GFP larvae demonstrate that GFP(lo) macrophages migrate to wounds by extension of thin pseudopods and carry out phagocytosis of tissue debris, and FACS analysis of leukocyte markers indicates expression of CSF1R in these macrophages. These findings identify distinct functional and morphological characteristics of inflammatory macrophages in zebrafish larvae.

Identification of phagocytic cells, NK-like cytotoxic cell activity and the production of cellular exudates in the coelomic cavity of adult zebrafish

Coelomic cavity (CC) cells of mature zebrafish harvested by lavage with media or trypsin-EDTA contained 0.80-1.20 x 10(5) and 2.0-3.5 x 10(5) cells, respectively. Media lavage was composed of granulocytes (60-80%), lymphocytes (10-20%), and NCC (4-10%). Granulocytes had large electron dense cytoplasmic paracrystalline granules and a segmented nucleus; they expressed plastin-1, myeloid specific peroxidase and MCSF mRNA; and they were NCAMP-1(+). Lymphocytes had B- and T-cell specific mRNA and were NCAMP-1(-) and NCCRP-1(-). NCC were 3 microm, NCAMP-1(+) and NCCRP-1(+) and did not express B- and T-cell specific mRNA. Additionally, trypsin lavage contained monocytes (marginated chromatin, low nuclear:cytoplasm ratio, sparse cytosolic granules) and macrophages (non-segmented nuclei, no margination of chromatin, abundant electron dense granules). E. coli injected into the CC were phagocytosed in a dose and time dependent fashion by granulocytes, monocytes and macrophages. NCC lysed mammalian target cells and NCAMP-1 expressing hybridoma cells in redirected lysis assays.

Using in vivo zebrafish models to understand the biochemical basis of neutrophilic respiratory disease

Neutrophilic inflammation in the lung protects against infectious disease, and usually resolves spontaneously after removal of the inflammatory stimulus. However, much lung disease is caused by a failure of resolution of neutrophilic inflammation. Our laboratory is seeking an understanding of the biochemical basis of inflammation resolution, using the zebrafish model system. Zebrafish larvae are transparent, allowing visualization of GFP (green fluorescent protein)-labelled leucocytes during inflammation in vivo, and they can be readily manipulated by a range of forward and reverse genetic techniques. This combination of advantages makes zebrafish a powerful tool for the study of in vivo inflammatory processes. Using this model, we have visualized the process of inflammation resolution in vivo, and identified a role for apoptosis in this process. In addition, we have performed a forward genetic screen for mutants with defective resolution of inflammation, and reverse genetic experiments examining the influence of candidate genes on inflammation resolution. We have established a platform for screening for compounds with anti-inflammatory activity, which has yielded a number of interesting leads. Looking forward to succeed in the future, we are working at combining mutants, transgenes and pharmacological agents to dissect the biochemical basis of inflammation resolution, and to identify compounds that might be used to treat patients with respiratory disease.

The epithelial cell adhesion molecule EpCAM is required for epithelial morphogenesis and integrity during zebrafish epiboly and skin development

The aberrant expression of the transmembrane protein EpCAM is associated with tumor progression, affecting different cellular processes such as cell–cell adhesion, migration, proliferation, differentiation, signaling, and invasion. However, the in vivo function of EpCAM still remains elusive due to the lack of genetic loss-of-function studies. Here, we describe epcam (tacstd) null mutants in zebrafish. Maternal-zygotic mutants display compromised basal protrusive activity and epithelial morphogenesis in cells of the enveloping layer (EVL) during epiboly. In partial redundancy with E-cadherin (Ecad), EpCAM made by EVL cells is further required for cell–cell adhesion within the EVL and, possibly, for proper attachment of underlying deep cells to the inner surface of the EVL, thereby also affecting deep cell epiboly movements. During later development, EpCAM per se becomes indispensable for epithelial integrity within the periderm of the skin, secondarily leading to disrupted morphology of the underlying basal epidermis and moderate hyper-proliferation of skin cells. On the molecular level, EVL cells of epcam mutant embryos display reduced levels of membranous Ecad, accompanied by an enrichment of tight junction proteins and a basal extension of apical junction complexes (AJCs). Our data suggest that EpCAM acts as a partner of E-cadherin to control adhesiveness and integrity as well as plasticity and morphogenesis within simple epithelia. In addition, EpCAM is required for the interaction of the epithelia with underlying cell layers.

EpCAM is a well-established marker for carcinomas of epithelial origin and a potential target for immunotherapy. In vitro analyses have implicated EpCAM in a plethora of different cellular processes, such as adhesion, motility, proliferation, differentiation, and signaling. Strikingly, depending on the context, EpCAM displayed rather opposite effects, either promoting or attenuating cell–cell adhesion versus cell migration and tissue invasion, a phenomenon described as the “double-face” of EpCAM. However, the in vivo relevance of its different effects remained largely unclear. Here, we present the first genetic analysis of EpCAM function in vivo, based on loss-of-function mutants in the zebrafish. As it is in mammals, zebrafish EpCAM is expressed in simple epithelia. Mutant embryos display defects both in epithelial morphogenesis and in epithelial integrity. Reduced epithelial morphogenesis is accompanied, and possibly caused, by an extension of apical junctional complexes and compromised basal protrusive activity. Furthermore, mutant epithelia display alterations in the relative abundance of adherence junction versus tight junction components. In addition, EpCAM tightly cooperates with E-cadherin and has a previously unrecognized trans effect on the morphogenesis and integrity of underlying cell layers. Cell differentiation and proliferation in EpCAM mutants are not, or only secondarily, affected. During later development and adulthood, EpCAM is largely dispensable, reinforcing its suitability as a target for anti-carcinoma immunotherapy with minimal side effects.

The ENTH domain protein Clint1 is required for epidermal homeostasis in zebrafish

Epidermal hyperproliferation and inflammation are hallmarks of the human condition psoriasis. Here, we report that a zebrafish line with a mutation in the cargo adaptor protein Clint1 exhibits psoriasis-like phenotypes including epithelial hyperproliferation and leukocyte infiltration. Clint1 is an ENTH domain-containing protein that binds SNARE proteins and functions in vesicle trafficking; however, its in vivo function in animal models has not been reported to date. The clint1 mutants exhibit chronic inflammation characterized by increased Interleukin 1beta expression, leukocyte infiltration, bidirectional trafficking and phagocytosis of cellular debris. The defects in clint1 mutants can be rescued by expression of zebrafish clint1 and can be phenocopied with clint1-specific morpholinos, supporting an essential role for Clint1 in epidermal development. Interaction studies suggest that Clint1 and Lethal giant larvae 2 function synergistically to regulate epidermal homeostasis. Accordingly, clint1 mutants show impaired hemidesmosome formation, loss of cell-cell contacts and increased motility suggestive of epithelial to mesenchymal transition. Taken together, our findings describe a novel function for the ENTH domain protein Clint1 in epidermal development and inflammation and suggest that its deficiency in zebrafish generates a phenotype that resembles the human condition psoriasis.

Transcriptome profiling and functional analyses of the zebrafish embryonic innate immune response to Salmonella infection

Due to the clear separation of innate immunity from adaptive responses, the externally developing zebrafish embryo represents a useful in vivo model for identification of innate host determinants of the response to bacterial infection. Here we performed a time-course transcriptome profiling study and gene ontology analysis of the embryonic innate immune response to infection with two model Salmonella strains that elicit either a lethal infection or an attenuated response. The transcriptional response to infection with both the lethal strain and the avirulent LPS O-Ag mutant strain showed clear conservation with host responses detected in other vertebrate models and human cells, including induction of genes encoding cell surface receptors, signaling intermediates, transcription factors, and inflammatory mediators. Furthermore, our study led to the identification of a large set of novel immune response genes and infection markers, the future functional characterization of which will support vertebrate genome annotation. From the time series and bacterial strain comparisons, matrix metalloproteinase genes, including mmp9, were among the most consistent infection-responsive genes. Purified Salmonella flagellin also strongly induced mmp9 expression. Using knockdown analysis, we showed that this gene was downstream of the zebrafish homologs of the flagellin receptor TLR5 and the adaptor MyD88. Additionally, flagellin-mediated induction of other inflammation markers, including il1b, il8, and cxcl-C1c, was reduced upon Tlr5 knockdown as well as expression of irak3, a putative negative TLR pathway regulator. Finally, we showed that induction of il1b, mmp9, and irak3 requires Myd88-dependent signaling, while ifn1 and il8 were induced Myd88 independently during Salmonella infection.

Fate mapping embryonic blood in zebrafish: multi- and unipotential lineages are segregated at gastrulation

Vertebrate hematopoiesis first produces primitive (embryonic) lineages and ultimately generates the definitive (adult) blood. Whereas definitive hematopoiesis may produce many diverse blood types via a common multipotent progenitor, primitive hematopoiesis has been thought to produce only erythrocytes or macrophages via progenitors that are unipotent for single blood lineages. Using a variety of in vivo cell-tracing techniques, we show that primitive blood in zebrafish derives from two different progenitor types. On the dorsal gastrula, blood progenitors are unipotential cells that divide infrequently, populate the rostral blood islands, and differentiate into macrophages. In contrast, on the ventral gastrula, blood progenitors are multipotential cells with rapid cell cycles; populate the intermediate cell mass; and differentiate into erythrocytes, neutrophils, and thrombocytes. Our results demonstrate the existence of primitive hematopoietic progenitors that are segregated very early in development and that are specified to produce either a unipotent or a multipotent blood cell lineage.

Cell-mediated immune responses in tuberculosis

Tuberculosis is primarily a disease of the lung, and dissemination of the disease depends on productive infection of this critical organ. Upon aerosol infection with Mycobacterium tuberculosis (Mtb), the acquired cellular immune response is slow to be induced and to be expressed within the lung. This slowness allows infection to become well established; thus, the acquired response is expressed in an inflammatory site that has been initiated and modulated by the bacterium. Mtb has a variety of surface molecules that interact with the innate response, and this interaction along with the autoregulation of the immune response by several mechanisms results in less-than-optimal control of bacterial growth. To improve current vaccine strategies, we must understand the factors that mediate induction, expression, and regulation of the immune response in the lung. We must also determine how to induce both known and novel immunoprotective responses without inducing immunopathologic consequences.