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Jonathan J Ewbank

Publications and source records attributed to Jonathan J Ewbank.

16 recordsLinked to original sources
PubMed2006

Infection in a dish: high-throughput analyses of bacterial pathogenesis.

Diverse aspects of host-pathogen interactions have been studied using non-mammalian hosts such as Dictyostelium discoideum, Caenorhabditis elegans, Drosophila melanogaster and Danio rerio for more than 20 years. Over the past two years, the use of these model hosts to dissect bacterial virulence mechanisms has been expanded to include the important human pathogens Vibrio cholerae and Yersinia pestis. Innovative approaches using these alternative hosts have also been developed, enabling the isolation of new antimicrobials through screening large libraries of compounds in a C. elegans Enterococcus faecalis infection model. Host proteins required by Mycobacterium and Listeria during their invasion and intracellular growth have been uncovered using high-throughput dsRNA screens in a Drosophila cell culture system, and immune evasion mechanisms deployed by Pseudomonas aeruginosa during its infection of flies have been identified. Together, these reports further illustrate the potential and relevance of these non-mammalian hosts for modelling many facets of bacterial infection in mammals.

Animals↗
PubMed2006

A semi-automated high-throughput approach to the generation of transposon insertion mutants in the nematode Caenorhabditis elegans.

The generation of a large collection of defined transposon insertion mutants is of general interest to the Caenorhabditis elegans research community and has been supported by the European Union. We describe here a semi-automated high-throughput method for mutant production and screening, using the heterologous transposon Mos1. The procedure allows routine culture of several thousand independent nematode strains in parallel for multiple generations before stereotyped molecular analyses. Using this method, we have already generated >17 500 individual strains carrying Mos1 insertions. It could be easily adapted to forward and reverse genetic screens and may influence researchers faced with making a choice of model organism.

Animals↗
PubMed2006

A generalized transducing phage (phiIF3) for the genomically sequenced Serratia marcescens strain Db11: a tool for functional genomics of an opportunistic human pathogen.

A bacteriophage (phiIF3) capable of mediating generalized transduction in Serratia marcescens strain Db11 has been isolated and characterized. The genome of this Serratia strain has recently been sequenced and is likely to become the reference strain for S. marcescens researchers. phiIF3 is most likely a virulent phage, which can transduce markers at frequencies of 10(-6) transductants per p.f.u. It has a lipopolysaccharide receptor and was determined to have a latent period of 50 min and a burst size of approximately 100 phages. The phage DNA was resistant to digestion with restriction enzymes. Electron microscopy showed phiIF3 to be a member of the family Myoviridae. This is the first report of a generalized transducing phage able to infect Db11 and this phage will be a valuable tool for functional genomic analysis of the pathogen host.

Bacteriophages↗
PubMed2005

XNP-1/ATR-X acts with RB, HP1 and the NuRD complex during larval development in C. elegans.

Mutations in the XNP/ATR-X gene cause several X-linked mental retardation syndromes in humans. The XNP/ATR-X gene encodes a DNA-helicase belonging to the SNF2 family. It has been proposed that XNP/ATR-X might be involved in chromatin remodelling. The lack of a mouse model for the ATR-X syndrome has, however, hampered functional studies of XNP/ATR-X. C. elegans possesses one homolog of the XNP/ATR-X gene, named xnp-1. By analysing a deletion mutant, we show that xnp-1 is required for the development of the embryo and the somatic gonad. Moreover, we show that abrogation of xnp-1 function in combination with inactivation of genes of the NuRD complex, as well as lin-35/Rb and hpl-2/HP1 leads to a stereotyped block of larval development with a cessation of growth but not of cell division. We also demonstrate a specific function for xnp-1 together with lin-35 or hpl-2 in the control of transgene expression, a process known to be dependent on chromatin remodelling. This study thus demonstrates that in vivo XNP-1 acts in association with RB, HP1 and the NuRD complex during development.

Animals↗
PubMed2004

Diversity and specificity in the interaction between Caenorhabditis elegans and the pathogen Serratia marcescens.

BACKGROUND: Co-evolutionary arms races between parasites and hosts are considered to be of immense importance in the evolution of living organisms, potentially leading to highly dynamic life-history changes. The outcome of such arms races is in many cases thought to be determined by frequency dependent selection, which relies on genetic variation in host susceptibility and parasite virulence, and also genotype-specific interactions between host and parasite. Empirical evidence for these two prerequisites is scarce, however, especially for invertebrate hosts. We addressed this topic by analysing the interaction between natural isolates of the soil nematode Caenorhabditis elegans and the pathogenic soil bacterium Serratia marcescens. RESULTS: Our analysis reveals the presence of i) significant variation in host susceptibility, ii) significant variation in pathogen virulence, and iii) significant strain- and genotype-specific interactions between the two species. CONCLUSIONS: The results obtained support the previous notion that highly specific interactions between parasites and animal hosts are generally widespread. At least for C. elegans, the high specificity is observed among isolates from the same population, such that it may provide a basis for and/or represent the outcome of co-evolutionary adaptations under natural conditions. Since both C. elegans and S. marcescens permit comprehensive molecular analyses, these two species provide a promising model system for inference of the molecular basis of such highly specific interactions, which are as yet unexplored in invertebrate hosts.

Animals↗
PubMed2004

TLR-independent control of innate immunity in Caenorhabditis elegans by the TIR domain adaptor protein TIR-1, an ortholog of human SARM.

Both plants and animals respond to infection by synthesizing compounds that directly inhibit or kill invading pathogens. We report here the identification of infection-inducible antimicrobial peptides in Caenorhabditis elegans. Expression of two of these peptides, NLP-29 and NLP-31, was differentially regulated by fungal and bacterial infection and was controlled in part by tir-1, which encodes an ortholog of SARM, a Toll-interleukin 1 receptor (TIR) domain protein. Inactivation of tir-1 by RNA interference caused increased susceptibility to infection. We identify protein partners for TIR-1 and show that the small GTPase Rab1 and the f subunit of ATP synthase participate specifically in the control of antimicrobial peptide gene expression. As the activity of tir-1 was independent of the single nematode Toll-like receptor, TIR-1 may represent a component of a previously uncharacterized, but conserved, innate immune signaling pathway.

Amino Acid Sequence↗
PubMed2004

Immunity in Caenorhabditis elegans.

Until very recently it was not known whether the invertebrate Caenorhabditis elegans was capable of mounting a specific immune response to protect itself from pathogens. It has only just become clear that this simple nematode in fact possesses a complex innate immune system, involving multiple signalling pathways and an armoury of antimicrobial proteins and peptides. Genetic and microarray approaches are now revealing the molecular cross-talk that exists between the different signalling cascades.

Animals↗
PubMed2004

Evolution of the innate immune system: the worm perspective.

Simple model organisms that are amenable to comprehensive experimental analysis can be used to elucidate the molecular genetic architecture of complex traits. They can thereby enhance our understanding of these traits in other organisms, including humans. Here, we describe the use of the nematode Caenorhabditis elegans as a tractable model system to study innate immunity. We detail our current understanding of the worm's immune system, which seems to be characterized by four main signaling cascades: a p38 mitogen-activated protein kinase, a transforming growth factor-beta-like, a programed cell death, and an insulin-like receptor pathway. Many details, especially regarding pathogen recognition and immune effectors, are only poorly characterized and clearly warrant further investigation. We additionally speculate on the evolution of the C. elegans immune system, taking into special consideration the relationship between immunity, stress responses and digestion, the diversification of the different parts of the immune system in response to multiple and/or coevolving pathogens, and the trade-off between immunity and host life history traits. Using C. elegans to address these different facets of host-pathogen interactions provides a fresh perspective on our understanding of the structure and complexity of innate immune systems in animals and plants.

Amino Acid Sequence↗
PubMed2004

Genetic models in pathogenesis.

To decipher the complexity of host-pathogen interactions the widest possible range of model hosts and of analytical methods is required. As some virulence mechanisms and certain host responses have been conserved throughout evolution, even simple organisms can be used as model hosts to help our understanding of infectious diseases. The availability of molecular genetic tools and a cooperative community of researchers are pivotal to the emergence of model systems. In this review, we first summarize the genetic screens that can be used to identify pathogen virulence factors, then we present a comparative overview of existing or emerging genetically tractable host models.

Animals↗
PubMed2003

Virulence factors of the human opportunistic pathogen Serratia marcescens identified by in vivo screening.

The human opportunistic pathogen Serratia marcescens is a bacterium with a broad host range, and represents a growing problem for public health. Serratia marcescens kills Caenorhabditis elegans after colonizing the nematode's intestine. We used C.elegans to screen a bank of transposon-induced S.marcescens mutants and isolated 23 clones with an attenuated virulence. Nine of the selected bacterial clones also showed a reduced virulence in an insect model of infection. Of these, three exhibited a reduced cytotoxicity in vitro, and among them one was also markedly attenuated in its virulence in a murine lung infection model. For 21 of the 23 mutants, the transposon insertion site was identified. This revealed that among the genes necessary for full in vivo virulence are those that function in lipopolysaccharide (LPS) biosynthesis, iron uptake and hemolysin production. Using this system we also identified novel conserved virulence factors required for Pseudomonas aeruginosa pathogenicity. This study extends the utility of C.elegans as an in vivo model for the study of bacterial virulence and advances the molecular understanding of S.marcescens pathogenicity.

Animals↗
PubMed2003

Caenorhabditis elegans: an emerging genetic model for the study of innate immunity.

Invaluable insights into how animals, humans included, defend themselves against infection have been provided by more than a decade of genetic studies that have used fruitflies. In the past few years, attention has also turned to another simple animal model, the nematode worm Caenorhabditis elegans. What exactly have we learned from the work in Drosophila? And will research with C. elegans teach us anything new about our response to pathogen attack?

Animals↗
PubMed2003

[A worm's life].

Despite its relative anatomic simplicity, the nematode Caenorhabditis elegans (C. elegans) is a complex multicellular organism. In this review, we describe studies that have contributed to a better understanding of certain aspects of the worm's physiology. We focus on the cellular and molecular basis of the interaction between C. elegans and its environment, including its sensory capacities, the intrinsic biological clock that governs the speed of its life, and on some of the factors that control its life span. We also outline very recent findings that have demonstrated the existence of an innate immune system in C. elegans. Finally, we highlight a number of novel techniques that are transforming the worm from a largely genetic model system into an attractive organism for functional genomic studies.

Animals↗
PubMed2002

Inducible antibacterial defense system in C. elegans.

The term innate immunity refers to a number of evolutionary ancient mechanisms that serve to defend animals and plants against infection. Genetically tractable model organisms, especially Drosophila, have contributed greatly to advances in our understanding of mammalian innate immunity. Essentially, nothing is known about immune responses in the nematode Caenorhabditis elegans. Using high-density cDNA microarrays, we show here that infection of C. elegans by the Gram-negative bacterium Serratia marcescens provokes a marked upregulation of the expression of many genes. Among the most robustly induced are genes encoding lectins and lysozymes, known to be involved in immune responses in other organisms. Certain infection-inducible genes are under the control of the DBL-1/TGFbeta pathway. We found that dbl-1 mutants exhibit increased susceptibility to infection. Conversely, overexpression of the lysozyme gene lys-1 augments the resistance of C. elegans to S. marcescens. These results constitute the first demonstration of inducible antibacterial defenses in C. elegans and open new avenues for the investigation of evolutionary conserved mechanisms of innate immunity.

Animals↗
PubMed2002

Tackling both sides of the host-pathogen equation with Caenorhabditis elegans.

If one is interested in dissecting the complex interactions that exist between host and pathogen, the nematode worm Caenorhabditis elegans is perhaps not the first model host that comes to mind. In this review I will introduce 'the worm' and try to show how it is, in fact, well suited to the identification of universal virulence factors and holds great promise for the study of conserved mechanisms of innate immunity.

Animals↗
PubMed2002

Diverse bacteria are pathogens of Caenorhabditis elegans.

Practically and ethically attractive as model systems, invertebrate organisms are increasingly recognized as relevant for the study of bacterial pathogenesis. We show here that the nematode Caenorhabditis elegans is susceptible to a surprisingly broad range of bacteria and may constitute a useful model for the study of both pathogens and symbionts.

Aeromonas hydrophila↗