101
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Rathore N, Matta H, Chaudhary PM. An evolutionary conserved pathway of nuclear factor-kappaB activation involving caspase-mediated cleavage and N-end rule pathway-mediated degradation of IkappaBalpha. J Biol Chem 2004; 279:39358-65. [PMID: 15252032 DOI: 10.1074/jbc.m406712200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The Drosophila nuclear factor-kappaB (NF-kappaB)-like transcription factor Relish is activated by an endoproteolytic cleavage step mediated by the Drosophila caspase Dredd. We have examined the contribution of the caspase cascade to NF-kappaB activation via TRAIL, a mammalian tumor necrosis factor family ligand that is a potent activator of caspases. Our results demonstrate that TRAIL activates NF-kappaB in two phases as follows: an early caspase independent phase and a late caspase dependent phase. The late phase of the TRAIL-induced NF-kappaB is critically dependent on caspase 8 and can be blocked by pharmacological and genetic inhibitors of caspase 8 activation, such as benzyloxycarbonyl-VAD-fluoromethyl ketone, benzyloxycarbonyl-IETD-fluoromethyl ketone, and small interfering RNA targeting caspase 8 and FADD. Whereas caspase 3 is required for TRAIL-induced apoptosis, it is not involved in TRAIL-induced NF-kappaB activation. The late phase of TRAIL-induced NF-kappaB activation involves caspase mediated cleavage of IkappaBalpha between Asp(31) and Ser(32) residues to generate an N-terminal truncated fragment that is degraded by the proteasome via the N-end rule pathway. Our results demonstrate that caspases play an evolutionarily conserved role as regulated entry points to the N-end rule pathway and in NF-kappaB activation in mammalian cells.
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Affiliation(s)
- Nisha Rathore
- Hamon Center for Therapeutic Oncology Research, Texas 75390-8593, USA
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102
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Foley E, O'Farrell PH. Functional dissection of an innate immune response by a genome-wide RNAi screen. PLoS Biol 2004; 2:E203. [PMID: 15221030 PMCID: PMC434151 DOI: 10.1371/journal.pbio.0020203] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2004] [Accepted: 05/04/2004] [Indexed: 12/18/2022] Open
Abstract
The innate immune system is ancient and highly conserved. It is the first line of defense and the only recognizable immune system in the vast majority of metazoans. Signaling events that convert pathogen detection into a defense response are central to innate immunity. Drosophila has emerged as an invaluable model organism for studying this regulation. Activation of the NF-kappaB family member Relish by the caspase-8 homolog Dredd is a central, but still poorly understood, signaling module in the response to gram-negative bacteria. To identify the genes contributing to this regulation, we produced double-stranded RNAs corresponding to the conserved genes in the Drosophila genome and used this resource in genome-wide RNA interference screens. We identified numerous inhibitors and activators of immune reporters in a cell culture model. Epistatic interactions and phenotypes defined a hierarchy of gene action and demonstrated that the conserved gene sickie is required for activation of Relish. We also showed that a second gene, defense repressor 1, encodes a product with characteristics of an inhibitor of apoptosis protein that inhibits the Dredd caspase to maintain quiescence of the signaling pathway. Molecular analysis revealed that Defense repressor 1 is upregulated by Dredd in a feedback loop. We propose that interruption of this feedback loop contributes to signal transduction.
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MESH Headings
- Amino Acid Sequence
- Animals
- Blotting, Western
- Caspase 8
- Caspases/metabolism
- Cell Line
- Drosophila
- Drosophila Proteins/metabolism
- Epistasis, Genetic
- Gene Expression Regulation
- Gene Library
- Genes, Reporter
- Genome
- Image Processing, Computer-Assisted
- Immunity, Innate
- Insect Proteins/metabolism
- Microscopy, Fluorescence
- Models, Biological
- Models, Genetic
- Molecular Sequence Data
- NF-kappa B/metabolism
- Phenotype
- RNA Interference
- RNA, Double-Stranded/metabolism
- Sequence Homology, Amino Acid
- Signal Transduction
- Transcription Factors/metabolism
- Up-Regulation
- beta-Galactosidase/metabolism
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Affiliation(s)
- Edan Foley
- 1Department of Biochemistry and Biophysics, University of California, San FranciscoSan Francisco, CaliforniaUnited States of America
| | - Patrick H O'Farrell
- 1Department of Biochemistry and Biophysics, University of California, San FranciscoSan Francisco, CaliforniaUnited States of America
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103
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Abstract
In recent years, the innate immune system has emerged from the shadow of adaptive immune responses as a major area of research in its own right. One of the most significant model systems that has been used to investigate this phenomenon has been the fruit fly, Drosophila melanogaster. Exploration of the differential immune response presented by Drosophila led to the discovery of important signalling events and transduction pathways, which were thereafter shown to be specific for the type of infecting pathogen. These factors and pathways were subsequently found to have homologues in many other organisms, including those with adaptive immune responses. In light of the present status of studies in innate immunity, this review describes the current state of understanding of the Drosophila immune response.
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Affiliation(s)
- Phil Irving
- Institut de Biologie Moléculaire et Cellulaire du CNRS. 15, Strasbourg, France
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104
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Montagnani C, Kappler C, Reichhart JM, Escoubas JM. Cg-Rel, the first Rel/NF-kappaB homolog characterized in a mollusk, the Pacific oyster Crassostrea gigas. FEBS Lett 2004; 561:75-82. [PMID: 15013754 DOI: 10.1016/s0014-5793(04)00124-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2003] [Accepted: 12/30/2003] [Indexed: 11/24/2022]
Abstract
We report here the identification and functional characterization of Cg-Rel, a gene encoding the Crassostrea gigas homolog of Rel/NF-kappaB transcription factors found in insects and mammals. Sequence and phylogenetic analysis showed that Cg-Rel shares the structural organization of Rel/NF-kappaB transcription factors of class II. It includes a Rel homology domain as well as a C-terminal transactivation domain (TD). Overexpression of Cg-Rel in the Drosophila S2 cell line activated the expression of a NF-kappaB-dependent reporter gene, whereas transfection with a Cg-Rel construct containing a C-terminal deletion of the TD or using a reporter gene with mutated kappaB binding sites failed to activate expression. These results suggest that Cg-Rel is a functional member of the Rel family of transcription factors, making this the sixth structurally homologous component of the Rel/NF-kappaB pathway characterized in C. gigas. Based on homology to other invertebrates' Rel/NF-kappaB cascade, the function of the oyster pathway may serve to regulate genes involved in innate defense and/or development. These findings serve to highlight a potentially important regulatory pathway to the study of oyster immunology, hence allowing comparison of the immune system in vertebrates and invertebrates, an important key issue to understand its evolution.
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Affiliation(s)
- C Montagnani
- Laboratoire de Défense et Résistance chez les Invertébrés Marins (DRIM) (IFREMER, CNRS, UMII), Université de Montpellier II, 2 place Eugène Bataillon, CC80, 34095 Montpellier, France
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105
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Salvesen GS, Abrams JM. Caspase activation - stepping on the gas or releasing the brakes? Lessons from humans and flies. Oncogene 2004; 23:2774-84. [PMID: 15077141 DOI: 10.1038/sj.onc.1207522] [Citation(s) in RCA: 194] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The central components of the execution phase of apoptosis in worms, flies, and humans are members of the caspase protease family. Work in Drosophila and mammalian systems has revealed a web of interactions that govern the activity of these proteases, and two fundamental control points have been identified. These are zymogen activation - the process that converts a latent caspase into its active form, and inhibition of the resulting active protease. In humans, the driving force for caspase activity is activation of the zymogens, but in Drosophila, a major thrust is derepression of caspase inhibitors. In this review, we consider evidence for these two distinct events in terms of the regulation of caspase activity. This sets the scene for therapy to reinstate the normal death mechanisms that have been overcome in a cancer cell's quest for immortality.
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Affiliation(s)
- Guy S Salvesen
- Program in Apoptosis and Cell Death Research, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, CA 92122, USA.
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106
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Park JM, Brady H, Ruocco MG, Sun H, Williams D, Lee SJ, Kato T, Richards N, Chan K, Mercurio F, Karin M, Wasserman SA. Targeting of TAK1 by the NF-kappa B protein Relish regulates the JNK-mediated immune response in Drosophila. Genes Dev 2004; 18:584-94. [PMID: 15037551 PMCID: PMC374239 DOI: 10.1101/gad.1168104] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The molecular circuitry underlying innate immunity is constructed of multiple, evolutionarily conserved signaling modules with distinct regulatory targets. The MAP kinases and the IKK-NF-kappa B molecules play important roles in the initiation of immune effector responses. We have found that the Drosophila NF-kappa B protein Relish plays a crucial role in limiting the duration of JNK activation and output in response to Gram-negative infections. Relish activation is linked to proteasomal degradation of TAK1, the upstream MAP kinase kinase kinase required for JNK activation. Degradation of TAK1 leads to a rapid termination of JNK signaling, resulting in a transient JNK-dependent response that precedes the sustained induction of Relish-dependent innate immune loci. Because the IKK-NF-kappa B module also negatively regulates JNK activation in mammals, thereby controlling inflammation-induced apoptosis, the regulatory cross-talk between the JNK and NF-kappa B pathways appears to be broadly conserved.
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Affiliation(s)
- Jin Mo Park
- Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, School of Medicine, University of California, San Diego, La Jolla, 92093-0636, USA
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107
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Wajant H, Scheurich P. Analogies between Drosophila and mammalian TRAF pathways. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2004; 34:47-72. [PMID: 14979664 DOI: 10.1007/978-3-642-18670-7_3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A central event in innate immunity is the activation of the NF-kappaB signaling pathway and up-regulation of NF-kappaB-dependent defense genes. Attack of mammals as well as of insects by microorganisms leads, among other things, to the activation of receptors of the Toll-like receptor group. Various adaptor proteins involving members of the TNF receptor-associated factor (TRAF) family channel these receptor-generated signals to conserved intracellular kinase cascades that finally lead to the activation of NF-kappaB and JNK. In vertebrates, TRAF proteins link these pathways also to IL-1R-related molecules and members of the TNF receptor superfamily, which orchestrate a variety of immunoregulatory processes of the innate but also of the adaptive immune system. In this review, we will focus on the similarities but also the differences in TRAF-dependent signaling pathways of mammals and insects.
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Affiliation(s)
- H Wajant
- Department of Molecular Internal Medicine, Medical Polyclinic, University Würzburg, Röntgenring 11, 97070 Würzburg, Germany
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108
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Abstract
Because of the evolutionary conservation of innate mechanisms of host defense, Drosophila has emerged as an ideal animal in which to study the genetic control of immune recognition and responses. The discovery that the Toll pathway is required for defense against fungal infection in Drosophila was pivotal in studies of both mammalian and Drosophila immunity. Subsequent genetic screens in Drosophila to isolate additional mutants unable to induce humoral responses to infection have identified and ordered the function of components of two signaling cascades, the Toll and Imd pathways, that activate responses to infection. Drosophila blood cells also contribute to host defense through phagocytosis and signaling, and may carry out a form of self-nonself recognition that is independent of microbial pattern recognition. Recent work suggests that Drosophila will be a useful model for dissecting virulence mechanisms of several medically important pathogens.
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Affiliation(s)
- Catherine A Brennan
- Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer, New York, New York 10021, USA
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109
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Levy F, Bulet P, Ehret-Sabatier L. Proteomic Analysis of the Systemic Immune Response of Drosophila. Mol Cell Proteomics 2004; 3:156-66. [PMID: 14645501 DOI: 10.1074/mcp.m300114-mcp200] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Improvements in two-dimensional gel electrophoresis, mass spectrometry, and bioinformatics provide new tools to characterize proteins involved in a physiological process, such as the immune response of the insect model Drosophila melanogaster. Profiling of the proteins present in the hemolymph (insect blood) of noninfected flies versus flies infected with bacteria or fungi was performed by two-dimensional gel electrophoresis, silver or Coomassie staining, and image analysis. Through this differential analysis, more than 70 out of 160 spots were up- or down-regulated by at least 5-fold after microbial infection. Coomassie staining, in-gel digestion, and database searches yielded the identity of a series of proteins that are directly involved in the Drosophila immune system. This included proteases, protease inhibitors, and recognition molecules such as prophenoloxydase-activating enzymes, serpins, and Gram-negative binding protein-like. Proteins with a potential function in the immune response were also identified, such as an odorant binding protein, peptidylglycine alpha-hydroxylating monooxygenase, and transferrin, affording new candidates for further investigation of innate immune mechanisms. Moreover, several molecules resulting from the cleavage of proteins were detected after the fungal infection. Altogether, this first differential proteomic analysis of the immune response of Drosophila paves the way for the study of proteins affected during innate immunity.
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Affiliation(s)
- Francine Levy
- Institut de Biologie Moléculaire et Cellulaire, 15 rue René Descartes, 67084 Strasbourg Cedex, France
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110
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Ryu JH, Nam KB, Oh CT, Nam HJ, Kim SH, Yoon JH, Seong JK, Yoo MA, Jang IH, Brey PT, Lee WJ. The homeobox gene Caudal regulates constitutive local expression of antimicrobial peptide genes in Drosophila epithelia. Mol Cell Biol 2004; 24:172-85. [PMID: 14673153 PMCID: PMC303351 DOI: 10.1128/mcb.24.1.172-185.2004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In Drosophila melanogaster, although the NF-kappaB transcription factors play a pivotal role in the inducible expression of innate immune genes, such as antimicrobial peptide genes, the exact regulatory mechanism of the tissue-specific constitutive expression of these genes in barrier epithelia is largely unknown. Here, we show that the Drosophila homeobox gene product Caudal functions as the innate immune transcription modulator that is responsible for the constitutive local expression of antimicrobial peptides cecropin and drosomycin in a tissue-specific manner. These results suggest that certain epithelial tissues have evolved a unique constitutive innate immune strategy by recruiting a developmental "master control" gene.
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Affiliation(s)
- Ji-Hwan Ryu
- Division of Molecular Life Science and Center for Cell Signaling Research, Ewha Womans University, Seoul, South Korea
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111
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Abstract
Toll receptors are type I transmembrane proteins that play important roles in development and immunity in animals. Comparison of the genomes of mouse and human on one side and of the fruitfly Drosophila and the mosquito Anopheles (two dipteran insects) on the other, revealed that the four species possess a similar number of Toll receptors (approximately 10). However, phylogenetic analyses indicate that the families of Toll receptors expanded independently in insects and mammals. We review recent results on these receptors, which point to differences in the activation and signaling between Tolls in insects and Toll-like receptors (TLRs) in mammals. Whereas mammalian TLRs appear to be solely dedicated to host-defense, insect Tolls may be predominantly linked to other functions, probably developmental.
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Affiliation(s)
- Jean-Luc Imler
- Institut de Biologie Moléculaire et Cellulaire, CNRS, 15 rue René Descartes, 67000 Strasbourg, France.
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112
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Abstract
Drosophila mounts a potent host defence when challenged by various microorganisms. Analysis of this defence by molecular genetics has now provided a global picture of the mechanisms by which this insect senses infection, discriminates between various classes of microorganisms and induces the production of effector molecules, among which antimicrobial peptides are prominent. An unexpected result of these studies was the discovery that most of the genes involved in the Drosophila host defence are homologous or very similar to genes implicated in mammalian innate immune defences. Recent progress in research on Drosophila immune defence provides evidence for similarities and differences between Drosophila immune responses and mammalian innate immunity.
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Affiliation(s)
- Jules A Hoffmann
- Institut de Biologie Moléculaire et Cellulaire du CNRS, 67084 Strasbourg Cedex, France.
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113
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Silverman N, Zhou R, Erlich RL, Hunter M, Bernstein E, Schneider D, Maniatis T. Immune Activation of NF-κB and JNK Requires Drosophila TAK1. J Biol Chem 2003; 278:48928-34. [PMID: 14519762 DOI: 10.1074/jbc.m304802200] [Citation(s) in RCA: 197] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of the Drosophila immune response activates NF-kappaB and JNK signaling pathways. For example, infection by Gram-negative bacteria induces the Imd signaling pathway, leading to the activation of the NF-kappaB-like transcription factor Relish and the expression of a battery of genes encoding antimicrobial peptides. Bacterial infection also activates the JNK pathway, but the role of this pathway in the immune response has not yet been established. Genetic experiments suggest that the Drosophila homolog of the mammalian MAPK kinase kinase, TAK1 (transforming growth factor beta-activated kinase 1), activates both the JNK and NF-kappaB pathways following immune stimulation. In this report, we demonstrate that Drosophila TAK1 functions as both the Drosophila IkappaB kinase-activating kinase and the JNK kinase-activating kinase. However, we found that JNK signaling is not required for antimicrobial peptide gene expression but is required for the activation of other immune inducible genes, including Punch, sulfated, and malvolio. Thus, JNK signaling appears to play an important role in the cellular immune response and the stress response.
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Affiliation(s)
- Neal Silverman
- Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
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114
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Abstract
The innate immune system in drosophila and mammals senses the invasion of microorganisms using the family of Toll receptors, stimulation of which initiates a range of host defense mechanisms. In drosophila antimicrobial responses rely on two signaling pathways: the Toll pathway and the IMD pathway. In mammals there are at least 10 members of the Toll-like receptor (TLR) family that recognize specific components conserved among microorganisms. Activation of the TLRs leads not only to the induction of inflammatory responses but also to the development of antigen-specific adaptive immunity. The TLR-induced inflammatory response is dependent on a common signaling pathway that is mediated by the adaptor molecule MyD88. However, there is evidence for additional pathways that mediate TLR ligand-specific biological responses.
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Affiliation(s)
- Kiyoshi Takeda
- Department of Host Defense, Research Institute for Microbial Diseases, Osaka University, Suita Osaka 565-0871, Japan.
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115
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Carroll PM, Dougherty B, Ross-Macdonald P, Browman K, FitzGerald K. Model systems in drug discovery: chemical genetics meets genomics. Pharmacol Ther 2003; 99:183-220. [PMID: 12888112 DOI: 10.1016/s0163-7258(03)00059-7] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Animal model systems are an intricate part of the discovery and development of new medicines. The sequencing of not only the human genome but also those of the various pathogenic bacteria, the nematode Caenorhabditis elegans, the fruitfly Drosophila, and the mouse has enabled the discovery of new drug targets to push forward at an unprecedented pace. The knowledge and tools in these "model" systems are allowing researchers to carry out experiments more efficiently and are uncovering previously hidden biological connections. While the history of bacteria, yeast, and mice in drug discovery are long, their roles are ever evolving. In contrast, the history of Drosophila and C. elegans at pharmaceutical companies is short. We will briefly review the historic role of each model organism in drug discovery and then update the readers as to the abilities and liabilities of each model within the context of drug development.
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Affiliation(s)
- Pamela M Carroll
- Department of Applied Genomics, Bristol-Myers Squibb, Pennington NJ 08534, USA
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116
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Kim MS, Byun M, Oh BH. Crystal structure of peptidoglycan recognition protein LB from Drosophila melanogaster. Nat Immunol 2003; 4:787-93. [PMID: 12845326 DOI: 10.1038/ni952] [Citation(s) in RCA: 161] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2003] [Accepted: 06/06/2003] [Indexed: 11/08/2022]
Abstract
The family of peptidoglycan recognition proteins (PGRPs) are associated with the recognition of the peptidoglycan of microbes and subsequent activation of signaling pathways for immune response. Here the crystal structure of Drosophila PGRP-LB is determined at a resolution of 2.0 A and shows an active-site cleft with a zinc cage. Poor conservation of surface residues at the cleft predicts a widely varying individual specificity of PGRPs for molecular patterns on microbial cell walls. At the back of this cleft is a putatively conserved distinctive groove. The location and mainly hydrophobic nature of the groove indicate that the back face serves for subsequent signaling after clustering of PGRP molecules by binding to polymeric cell wall components.
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Affiliation(s)
- Min-Sung Kim
- Center for Biomolecular Recognition and Division of Molecular and Life Science, Department of Life Science, Pohang University of Science and Technology, Pohang, Kyungbuk, 790-784, Korea
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117
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Hetru C, Troxler L, Hoffmann JA. Drosophila melanogaster antimicrobial defense. J Infect Dis 2003; 187 Suppl 2:S327-34. [PMID: 12792847 DOI: 10.1086/374758] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The Drosophila melanogaster host defense is complex but remarkably efficient. It is a multifaceted response to a variety of fungal, bacterial, and parasitic invaders. Current knowledge is discussed on recognition of infectious microorganisms and on the activation of intracellular signaling cascades that concur with the expression of numerous immune-responsive genes, among which, to date, the most prominent appear to encode potent antimicrobial peptides.
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Affiliation(s)
- Charles Hetru
- Institut de Biologie Moléculaire et Cellulaire, UPR9022 du Centre National de la Recherche Scientifique, Strasbourg, France
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118
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Stoven S, Silverman N, Junell A, Hedengren-Olcott M, Erturk D, Engstrom Y, Maniatis T, Hultmark D. Caspase-mediated processing of the Drosophila NF-kappaB factor Relish. Proc Natl Acad Sci U S A 2003; 100:5991-6. [PMID: 12732719 PMCID: PMC156314 DOI: 10.1073/pnas.1035902100] [Citation(s) in RCA: 249] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The NF-kappaB-like transcription factor Relish plays a central role in the innate immune response of Drosophila. Unlike other NF-kappaB proteins, Relish is activated by endoproteolytic cleavage to generate a DNA-binding Rel homology domain and a stable IkappaB-like fragment. This signal-induced endoproteolysis requires the activity of several gene products, including the IkappaB kinase complex and the caspase Dredd. Here we used mutational analysis and protein microsequencing to demonstrate that a caspase target site, located in the linker region between the Rel and the IkappaB-like domain, is the site of signal-dependent cleavage. We also show physical interaction between Relish and Dredd, suggesting that Dredd indeed is the Relish endoprotease. In addition to the caspase target site, the C-terminal 107 aa of Relish are required for endoproteolysis and signal-dependent phosphorylation by the Drosophila IkappaB kinase beta. Finally, an N-terminal serine-rich region in Relish and the PEST domain were found to negatively regulate Relish activation.
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Affiliation(s)
- Svenja Stoven
- Umeå Centre for Molecular Pathogenesis, Umeå University, S-901 87 Umeå, Sweden.
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119
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Affiliation(s)
- Dan Hultmark
- Umeå Centre for Molecular Pathogenesis, Umeå University, S-901 87 Umeå, Sweden.
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120
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Imler JL, Hoffmann JA. Toll receptors in Drosophila: a family of molecules regulating development and immunity. Curr Top Microbiol Immunol 2003; 270:63-79. [PMID: 12467244 DOI: 10.1007/978-3-642-59430-4_4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In recent years, Toll-like receptors (TLRs) have emerged as key receptors which detect microbes and initiate an inflammatory response. The Toll receptor was originally identified and characterized 14 years ago for its role in the embryonic development of the fruit-fly Drosophila melanogaster. Subsequently, it was also shown to be an essential component of the signaling pathway mediating the anti-fungal host defense in this model organism. New factors involved in the activation of the Toll receptor or in intracytoplasmic signaling during the immune response in Drosophila have recently been identified. The existence of significant functional differences between mammalian TLRs and Drosophila Toll receptors is also becoming apparent.
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Affiliation(s)
- J L Imler
- UPR9022 du CNRS, Institut de Biologie Moléculaire et Cellulaire, 15 rue Descartes, 67000 Strasbourg, France.
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121
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Foley E, O'Farrell PH. Nitric oxide contributes to induction of innate immune responses to gram-negative bacteria in Drosophila. Genes Dev 2003; 17:115-25. [PMID: 12514104 PMCID: PMC195964 DOI: 10.1101/gad.1018503] [Citation(s) in RCA: 188] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Studies in mammals uncovered important signaling roles of nitric oxide (NO), and contributions to innate immunity. Suggestions of conservation led us to explore the involvement of NO in Drosophila innate immunity. Inhibition of nitric oxide synthase (NOS) increased larval sensitivity to gram-negative bacterial infection, and abrogated induction of the antimicrobial peptide Diptericin. NOS was up-regulated after infection. Antimicrobial peptide reporters revealed that NO triggered an immune response in uninfected larvae. NO induction of Diptericin reporters in the fat body required immune deficiency (imd) and domino. These findings show that NOS activity is required for a robust innate immune response to gram-negative bacteria, NOS is induced by infection, and NO is sufficient to trigger response in the absence of infection. We propose that NO mediates an early step of the signal transduction pathway, inducing the innate immune response upon natural infection with gram-negative bacteria.
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Affiliation(s)
- Edan Foley
- Department of Biochemistry and Biophysics, University of California San Francisco, San Francisco, California 94143, USA
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122
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Naitza S, Rossé C, Kappler C, Georgel P, Belvin M, Gubb D, Camonis J, Hoffmann JA, Reichhart JM. The Drosophila immune defense against gram-negative infection requires the death protein dFADD. Immunity 2002; 17:575-81. [PMID: 12433364 DOI: 10.1016/s1074-7613(02)00454-5] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Drosophila responds to Gram-negative infections by mounting an immune response that depends on components of the IMD pathway. We recently showed that imd encodes a protein with a death domain with high similarity to that of mammalian RIP. Using a two-hybrid screen in yeast, we have isolated the death protein dFADD as a molecule that associates with IMD. Our data show that loss of dFADD function renders flies highly susceptible to Gram-negative infections without affecting resistance to Gram-positive bacteria. By genetic analysis we show that dFADD acts downstream of IMD in the pathway that controls inducibility of the antibacterial peptide genes.
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Affiliation(s)
- Silvia Naitza
- Institut de Biologie Moleculaire et Cellulaire, UPR 9022 du CNRS, 15 Rue René Descartes, 67084 Cedex, Strasbourg, France.
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123
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Boutros M, Agaisse H, Perrimon N. Sequential activation of signaling pathways during innate immune responses in Drosophila. Dev Cell 2002; 3:711-22. [PMID: 12431377 DOI: 10.1016/s1534-5807(02)00325-8] [Citation(s) in RCA: 369] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Innate immunity is essential for metazoans to fight microbial infections. Genome-wide expression profiling was used to analyze the outcome of impairing specific signaling pathways after microbial challenge. We found that these transcriptional patterns can be dissected into distinct groups. We demonstrate that, in addition to signaling through the Toll and Imd pathways, signaling through the JNK and JAK/STAT pathways controls distinct subsets of targets induced by microbial agents. Each pathway shows a specific temporal pattern of activation and targets different functional groups, suggesting that innate immune responses are modular and recruit distinct physiological programs. In particular, our results may imply a close link between the control of tissue repair and antimicrobial processes.
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Affiliation(s)
- Michael Boutros
- Department of Genetics, Harvard Medical School, 200 Longwood Avenue, Boston, MA 02115, USA
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124
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Khush RS, Cornwell WD, Uram JN, Lemaitre B. A ubiquitin-proteasome pathway represses the Drosophila immune deficiency signaling cascade. Curr Biol 2002; 12:1728-37. [PMID: 12401167 DOI: 10.1016/s0960-9822(02)01214-9] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
BACKGROUND The inducible production of antimicrobial peptides is a major immune response in Drosophila. The genes encoding these peptides are activated by NF-kappaB transcription factors that are controlled by two independent signaling cascades: the Toll pathway that regulates the NF-kappaB homologs, Dorsal and DIF; and the IMD pathway that regulates the compound NF-kappaB-like protein, Relish. Although numerous components of each pathway that are required to induce antimicrobial gene expression have been identified, less is known about the mechanisms that either repress antimicrobial genes in the absence of infection or that downregulate these genes after infection. RESULTS In a screen for factors that negatively regulate the IMD pathway, we isolated two partial loss-of-function mutations in the SkpA gene that constitutively induce the antibacterial peptide gene, Diptericin, a target of the IMD pathway. These mutations do not affect the systemic expression of the antifungal peptide gene, Drosomycin, a target of the Toll pathway. SkpA encodes a homolog of the yeast and human Skp1 proteins. Skp1 proteins function as subunits of SCF-E3 ubiquitin ligases that target substrates to the 26S proteasome, and mutations affecting either the Drosophila SCF components, Slimb and dCullin1, or the proteasome also induce Diptericin expression. In cultured cells, inhibition of SkpA and Slimb via RNAi increases levels of both the full-length Relish protein and the processed Rel-homology domain. CONCLUSIONS In contrast to other NF-kappaB activation pathways, the Drosophila IMD pathway is repressed by the ubiquitin-proteasome system. A possible target of this proteolytic activity is the Relish transcription factor, suggesting a mechanism for NF-kappaB downregulation in Drosophila.
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Affiliation(s)
- Ranjiv S Khush
- Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette, France.
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125
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Sun H, Bristow BN, Qu G, Wasserman SA. A heterotrimeric death domain complex in Toll signaling. Proc Natl Acad Sci U S A 2002; 99:12871-6. [PMID: 12351681 PMCID: PMC130552 DOI: 10.1073/pnas.202396399] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2002] [Indexed: 12/27/2022] Open
Abstract
Signaling from the transmembrane receptor Toll to Rel-related transcription factors regulates dorsoventral patterning of the Drosophila embryo, as well as larval and adult immunity. To identify additional pathway components, we have used double-stranded RNA interference to investigate Drosophila counterparts of genes that regulate the mammalian Rel family member NF-kappaB. Experiments in cultured cells reveal that the fly orthologue of the adaptor protein MyD88 is essential for signal transduction from Toll to a second adaptor protein, Tube. By using coimmunoprecipitation studies, we find a heterotrimeric association of the death domains of MyD88, Tube, and the protein kinase Pelle. Site-directed mutational analyses of interaction sites defined by crystallographic studies demonstrate that Tube recruits MyD88 and Pelle into the heterotrimer by two distinct binding surfaces on the Tube death domain. Furthermore, functional assays confirm that the formation of this heterotrimer is critical for signal transduction by the Toll pathway.
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Affiliation(s)
- Huaiyu Sun
- Center for Molecular Genetics, Section of Cell and Developmental Biology, Division of Biology, University of California at San Diego, La Jolla, CA 92093, USA
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126
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Luna C, Wang X, Huang Y, Zhang J, Zheng L. Characterization of four Toll related genes during development and immune responses in Anopheles gambiae. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2002; 32:1171-1179. [PMID: 12213252 DOI: 10.1016/s0965-1748(02)00053-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Toll-like receptors (TLRs) are a group of evolutionary conserved proteins with diverse biological functions. In Drosophila melanogaster, Toll protein plays an important role in pattern formation in embryogenesis and in antimicrobial immunity in larvae and adults. In insects, Toll and two other related proteins, Tehao and 18-wheeler have been shown to participate in the activation of the innate immune responses to fungal and bacterial pathogens. In this paper we report the cloning and characterization of four TLR gene from malaria vector mosquito Anopheles gambiae, AgToll, AgToll6, AgTrex, and AgToll9, orthologues of DmToll, DmToll6, DmTollo (Toll8) and DmToll9 (CG5528) in Drosophila melanogaster. The expression profiles of these genes during development, in different adult tissues and after immune challenge were examined. As expected for the orthologue of Drosophila Toll, AgToll was found to be expressed highly in the ovary and may play a role in pattern formation during embryogenesis. AgToll9, surprisingly, was found to be highly expressed in the adult gut. The potential roles of these genes in development and immunity were discussed.
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Affiliation(s)
- Coralia Luna
- Department of Epidemiology and Public Health, Yale University School of Medicine, New Haven, CT 06520, USA
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127
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Stathopoulos A, Levine M. Linear signaling in the Toll-Dorsal pathway of Drosophila: activated Pelle kinase specifies all threshold outputs of gene expression while the bHLH protein Twist specifies a subset. Development 2002; 129:3411-9. [PMID: 12091311 DOI: 10.1242/dev.129.14.3411] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Differential activation of the Toll receptor leads to the formation of a broad Dorsal nuclear gradient that specifies at least three patterning thresholds of gene activity along the dorsoventral axis of precellular embryos. We investigate the activities of the Pelle kinase and Twist basic helix-loop-helix (bHLH) transcription factor in transducing Toll signaling. Pelle functions downstream of Toll to release Dorsal from the Cactus inhibitor. Twist is an immediate-early gene that is activated upon entry of Dorsal into nuclei. Transgenes misexpressing Pelle and Twist were introduced into different mutant backgrounds and the patterning activities were visualized using various target genes that respond to different thresholds of Toll-Dorsal signaling. These studies suggest that an anteroposterior gradient of Pelle kinase activity is sufficient to generate all known Toll-Dorsal patterning thresholds and that Twist can function as a gradient morphogen to establish at least two distinct dorsoventral patterning thresholds. We discuss how the Dorsal gradient system can be modified during metazoan evolution and conclude that Dorsal-Twist interactions are distinct from the interplay between Bicoid and Hunchback, which pattern the anteroposterior axis.
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Affiliation(s)
- Angelike Stathopoulos
- Department of Molecular and Cell Biology, Division of Genetics and Development, 401 Barker Hall, University of California, Berkeley, CA 94720, USA
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128
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Leulier F, Vidal S, Saigo K, Ueda R, Lemaitre B. Inducible expression of double-stranded RNA reveals a role for dFADD in the regulation of the antibacterial response in Drosophila adults. Curr Biol 2002; 12:996-1000. [PMID: 12123572 DOI: 10.1016/s0960-9822(02)00873-4] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In Drosophila, the immune deficiency (Imd) pathway controls antibacterial peptide gene expression in the fat body in response to Gram-negative bacterial infection. The ultimate target of the Imd pathway is Relish, a transactivator related to mammalian P105 and P100 NF-kappaB precursors. Relish is processed in order to translocate to the nucleus, and this cleavage is dependent on both Dredd, an apical caspase related to caspase-8 of mammals, and the fly Ikappa-B kinase complex (dmIKK). dTAK1, a MAPKKK, functions upstream of the dmIKK complex and downstream of Imd, a protein with a death domain similar to that of mammalian receptor interacting protein (RIP). Finally, the peptidoglycan recognition protein-LC (PGRP-LC) acts upstream of Imd and probably functions as a receptor for the Imd pathway. Using inducible expression of dFADD double-stranded RNA, we demonstrate that dFADD is a novel component of the Imd pathway: dFADD double-stranded RNA expression reduces the induction of antibacterial peptide-encoding genes after infection and renders the fly susceptible to Gram-negative bacterial infection. Epistatic studies indicate that dFADD acts between Imd and Dredd. Our results reinforce the parallels between the Imd and the TNF-R1 pathways.
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Affiliation(s)
- François Leulier
- Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette, France
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129
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Abstract
The innate immune system is a universal and ancient form of host defense against infection. Innate immune recognition relies on a limited number of germline-encoded receptors. These receptors evolved to recognize conserved products of microbial metabolism produced by microbial pathogens, but not by the host. Recognition of these molecular structures allows the immune system to distinguish infectious nonself from noninfectious self. Toll-like receptors play a major role in pathogen recognition and initiation of inflammatory and immune responses. Stimulation of Toll-like receptors by microbial products leads to the activation of signaling pathways that result in the induction of antimicrobial genes and inflammatory cytokines. In addition, stimulation of Toll-like receptors triggers dendritic cell maturation and results in the induction of costimulatory molecules and increased antigen-presenting capacity. Thus, microbial recognition by Toll-like receptors helps to direct adaptive immune responses to antigens derived from microbial pathogens.
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Affiliation(s)
- Charles A Janeway
- Section of Immunobiology and Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA.
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130
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De Gregorio E, Spellman PT, Tzou P, Rubin GM, Lemaitre B. The Toll and Imd pathways are the major regulators of the immune response in Drosophila. EMBO J 2002; 21:2568-79. [PMID: 12032070 PMCID: PMC126042 DOI: 10.1093/emboj/21.11.2568] [Citation(s) in RCA: 629] [Impact Index Per Article: 28.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Microarray studies have shown recently that microbial infection leads to extensive changes in the Drosophila gene expression programme. However, little is known about the control of most of the fly immune-responsive genes, except for the antimicrobial peptide (AMP)-encoding genes, which are regulated by the Toll and Imd pathways. Here, we used oligonucleotide microarrays to monitor the effect of mutations affecting the Toll and Imd pathways on the expression programme induced by septic injury in Drosophila adults. We found that the Toll and Imd cascades control the majority of the genes regulated by microbial infection in addition to AMP genes and are involved in nearly all known Drosophila innate immune reactions. However, we identified some genes controlled by septic injury that are not affected in double mutant flies where both Toll and Imd pathways are defective, suggesting that other unidentified signalling cascades are activated by infection. Interestingly, we observed that some Drosophila immune-responsive genes are located in gene clusters, which often are transcriptionally co-regulated.
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Affiliation(s)
| | - Paul T. Spellman
- Centre de Génétique Moléculaire, CNRS, F-91198 Gif-sur-Yvette, France and
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720-3200, USA Corresponding author e-mail:
| | | | - Gerald M. Rubin
- Centre de Génétique Moléculaire, CNRS, F-91198 Gif-sur-Yvette, France and
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720-3200, USA Corresponding author e-mail:
| | - Bruno Lemaitre
- Centre de Génétique Moléculaire, CNRS, F-91198 Gif-sur-Yvette, France and
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, CA 94720-3200, USA Corresponding author e-mail:
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131
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Abstract
Insects have been very successful in adapting to their environment, and the ability of the insect immune system to detect and elicit the appropriate response against various invading pathogens has helped in this success. Unlike the vertebrate immune system, which consists of both innate and adaptive components, insect immunity probably consists entirely of an innate immune response, as no evidence of an adaptive response has been found. The innate immune response is described as either a reaction against "lack of self," or the interaction between host germline-encoded receptors and molecules unique to a particular class of invading organisms. Once the invading organism is recognized, the host immune response can be activated via signaling pathways that lead to the appropriate reaction. This review endeavors to put forth how through genetic, molecular, and biochemical studies of the fruit fly Drosophila melanogaster, as well as other insects, it is now understood that aspects of the insect and vertebrate innate immune system are very similar.
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Affiliation(s)
- M J Williams
- Umeå Centre for Molecular Pathogenesis, Umeå University, S-901 87 Umeå, Sweden
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132
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Choe KM, Werner T, Stöven S, Hultmark D, Anderson KV. Requirement for a peptidoglycan recognition protein (PGRP) in Relish activation and antibacterial immune responses in Drosophila. Science 2002; 296:359-62. [PMID: 11872802 DOI: 10.1126/science.1070216] [Citation(s) in RCA: 445] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Components of microbial cell walls are potent activators of innate immune responses in animals. For example, the mammalian TLR4 signaling pathway is activated by bacterial lipopolysaccharide and is required for resistance to infection by Gram-negative bacteria. Other components of microbial surfaces, such as peptidoglycan, are also potent activators of innate immune responses, but less is known about how those components activate host defense. Here we show that a peptidoglycan recognition protein, PGRP-LC, is absolutely required for the induction of antibacterial peptide genes in response to infection in Drosophila and acts by controlling activation of the NF-kappaB family transcription factor Relish.
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Affiliation(s)
- Kwang-Min Choe
- Molecular Biology Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA
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133
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Gottar M, Gobert V, Michel T, Belvin M, Duyk G, Hoffmann JA, Ferrandon D, Royet J. The Drosophila immune response against Gram-negative bacteria is mediated by a peptidoglycan recognition protein. Nature 2002; 416:640-4. [PMID: 11912488 DOI: 10.1038/nature734] [Citation(s) in RCA: 488] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The antimicrobial defence of Drosophila relies largely on the challenge-induced synthesis of an array of potent antimicrobial peptides by the fat body. The defence against Gram-positive bacteria and natural fungal infections is mediated by the Toll signalling pathway, whereas defence against Gram-negative bacteria is dependent on the Immune deficiency (IMD) pathway. Loss-of-function mutations in either pathway reduce the resistance to corresponding infections. The link between microbial infections and activation of these two pathways has remained elusive. The Toll pathway is activated by Gram-positive bacteria through a circulating Peptidoglycan recognition protein (PGRP-SA). PGRPs appear to be highly conserved from insects to mammals, and the Drosophila genome contains 13 members. Here we report a mutation in a gene coding for a putative transmembrane protein, PGRP-LC, which reduces survival to Gram-negative sepsis but has no effect on the response to Gram-positive bacteria or natural fungal infections. By genetic epistasis, we demonstrate that PGRP-LC acts upstream of the imd gene. The data on PGRP-SA with respect to the response to Gram-positive infections, together with the present report, indicate that the PGRP family has a principal role in sensing microbial infections in Drosophila.
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Affiliation(s)
- Marie Gottar
- UPR 9022 du Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 15 rue René Descartes, F67084 Strasbourg, Cedex, France
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134
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Abstract
Immune systems are, increasingly, being studied from comparative perspectives. The analysis of the immune-defense systems of invertebrates, such as fruit flies and earthworms, is an important part of this effort. These systems are innate, natural non-specific, non-anticipatory and non-clonal. This is in contrast to the macrophage T and B systems that characterize vertebrate adaptive immunity whose properties can be categorized as adaptive, induced, specific, anticipatory, and clonal. In this review, we will focus on the earthworm system. Earthworms, like other complex invertebrates, possess several leukocyte types and synthesize and secrete a variety of immunoprotective molecules. The system as a whole effects phagocytosis, encapsulation, agglutination, opsonization, clotting and lysis of foreign components. At least two major leukocytes, small coelomocytes, and large coelomocytes mediate lytic reactions against several targets. Destruction of tumor cells in vitro shows that phagocytosis and natural killer cell responses are distinct properties of coelomocytes. A third type, the chlorogogen cell, synthesizes and sheds effector lytic molecules. Among the lytic molecules, three have been identified and sequenced (fetidins, CCF-1, lysenin) and another has been discovered (eiseniapore), while three other molecules, H(1) H(2) H(3), share agglutinating and lysing functions. In contrast to these, Lumbricin I is the only known molecule of the earthworm system that is antimicrobial but non-lytic. Altogether the cellular and humoral components of the earthworm system function to distinguish between self and not self, dispose of internal (cancer?), damaged components and external antigens (microbes). The evolutionary context of the earthworm innate immune system is discussed at the end of this article.
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Affiliation(s)
- Edwin L Cooper
- Laboratory of Comparative Immunology, UCLA, Los Angeles 90095-1763, USA.
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135
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Skriwan C, Fajardo M, Hägele S, Horn M, Wagner M, Michel R, Krohne G, Schleicher M, Hacker J, Steinert M. Various bacterial pathogens and symbionts infect the amoeba Dictyostelium discoideum. Int J Med Microbiol 2002; 291:615-24. [PMID: 12008915 DOI: 10.1078/1438-4221-00177] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The haploid soil amoeba Dictyostelium discoideum is a suitable model organism to study host-pathogen interactions with Legionella pneumophila. In this study we show that D. discoideum AX2 is also susceptible to infection with other important human pathogens and obligate intracellular symbionts. Infection assays demonstrated that Legionella-like amoebal pathogens (LLAP K62), Mycobacterium avium and the obligate intracellular endosymbionts of Acanthamoeba sp. strains TUME1, UWE25 and UWC6 were able to multiply within Dictyostelium. Salmonella typhimurium and Pseudomonas aeruginosa also invaded Dictyostelium, however were degraded shortly after uptake. Comitin-minus host cells were more permissive to infections with L. pneumophila and LLAP K62. Furthermore, this mutation significantly delayed the degradation of S. typhimurium. Accompanying electron and fluorescence microscopy of infected AX2 cells revealed that L. pneumophila and M. avium replicate within vacuoles, while LLAP K62, TUME1 and UWE25 were tightly enclosed by membranous structures within the cytoplasm. The beta-proteobacterium UWC6 was found to persist in the cytoplasm. The observed subcellular locations which correspond to the locations within the respective natural hosts suggest that D. discoideum is a representative model system for these pathogens and symbionts.
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Affiliation(s)
- Carina Skriwan
- Institut für Molekulare Infektionsbiologie, Universität Würzburg, Germany
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136
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Rutschmann S, Kilinc A, Ferrandon D. Cutting edge: the toll pathway is required for resistance to gram-positive bacterial infections in Drosophila. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 168:1542-6. [PMID: 11823479 DOI: 10.4049/jimmunol.168.4.1542] [Citation(s) in RCA: 158] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In Drosophila, the response against various microorganisms involves different recognition and signaling pathways, as well as distinct antimicrobial effectors. On the one hand, the immune deficiency pathway regulates the expression of antimicrobial peptides that are active against Gram-negative bacteria. On the other hand, the Toll pathway is involved in the defense against filamentous fungi and controls the expression of antifungal peptide genes. The gene coding for the only known peptide with high activity against Gram-positive bacteria, Defensin, is regulated by both pathways. So far, survival experiments to Gram-positive bacteria have been performed with Micrococcus luteus and have failed to reveal the involvement of one or the other pathway in host defense against such infections. In this study, we report that the Toll pathway, but not that of immune deficiency, is required for resistance to other Gram-positive bacteria and that this response does not involve Defensin.
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Affiliation(s)
- Sophie Rutschmann
- Institut de Biologie Moléculaire et Cellulaire, Unité Propre de Recherche 9022 du Centre National de la Recherche Scientifique, Strasbourg, France
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137
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Abstract
In response to microbial infections, Drosophila mounts a multifaceted immune response involving humoral reactions that culminate in the destruction of invading organisms by lytic peptides. These defense mechanisms are activated via two distinct signaling pathways. One of these, the Toll pathway, controls resistance to fungal and Gram-positive bacterial infections, whereas the Imd pathway is responsible for defense against Gram-negative bacterial infections. Current evidence indicates that recognition of infectious nonself agents results from interactions between microbial wall components and extracellular pattern recognition proteins. We discuss here evolutionary perspectives on our present understanding of the antimicrobial defenses of Drosophila.
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Affiliation(s)
- Jules A Hoffmann
- CNRS, Institute of Molecular and Cellular Biology, 15 rue Descartes, 67000 Strasbourg, France.
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138
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Tauszig-Delamasure S, Bilak H, Capovilla M, Hoffmann JA, Imler JL. Drosophila MyD88 is required for the response to fungal and Gram-positive bacterial infections. Nat Immunol 2002; 3:91-7. [PMID: 11743586 DOI: 10.1038/ni747] [Citation(s) in RCA: 231] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
We report here the identification and functional characterization of DmMyD88, a gene encoding the Drosophila homolog of mammalian MyD88. DmMyD88 combines a Toll-IL-1R homology (TIR) domain and a death domain. Overexpression of DmMyD88 was sufficient to induce expression of the antifungal peptide Drosomycin, and induction of Drosomycin was markedly reduced in DmMyD88-mutant flies. DmMyD88 interacted with Toll through its TIR domain and required the death domain proteins Tube and Pelle to activate expression of Drs, which encodes Drosomycin. DmMyD88-mutant flies were highly susceptible to infection by fungi and Gram-positive bacteria, but resisted Gram-negative bacterial infection much as did wild-type flies. Phenotypic comparison of DmMyD88-mutant flies and MyD88-deficient mice showed essential differences in the control of Gram-negative infection in insects and mammals.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Amino Acid Sequence
- Animals
- Animals, Genetically Modified
- Antigens, Differentiation/genetics
- Antigens, Differentiation/physiology
- Antimicrobial Cationic Peptides/biosynthesis
- Antimicrobial Cationic Peptides/genetics
- Antimicrobial Cationic Peptides/physiology
- Chromosome Mapping
- Disease Susceptibility
- Drosophila Proteins/genetics
- Drosophila Proteins/physiology
- Drosophila melanogaster/genetics
- Drosophila melanogaster/immunology
- Drosophila melanogaster/microbiology
- Enterococcus faecalis/physiology
- Epistasis, Genetic
- Escherichia coli/physiology
- Female
- Gene Expression Regulation/physiology
- Genes, Insect
- Gram-Negative Bacteria/physiology
- Hypocreales/physiology
- Insect Proteins/biosynthesis
- Insect Proteins/genetics
- Insect Proteins/physiology
- Membrane Glycoproteins/physiology
- Micrococcus luteus/physiology
- Molecular Sequence Data
- Myeloid Differentiation Factor 88
- Protein Serine-Threonine Kinases/physiology
- Protein Structure, Tertiary
- Receptors, Cell Surface
- Receptors, Immunologic/genetics
- Receptors, Immunologic/physiology
- Recombinant Fusion Proteins
- Sequence Alignment
- Sequence Homology, Amino Acid
- Toll-Like Receptors
- Transfection
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Affiliation(s)
- Servane Tauszig-Delamasure
- UPR9022 du Centre National de la Recherche Scientifique, Institut de Biologie Moléculaire et Cellulaire, 15, rue René Descartes, 67000 Strasbourg, France
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139
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Michel T, Reichhart JM, Hoffmann JA, Royet J. Drosophila Toll is activated by Gram-positive bacteria through a circulating peptidoglycan recognition protein. Nature 2001; 414:756-9. [PMID: 11742401 DOI: 10.1038/414756a] [Citation(s) in RCA: 564] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Microbial infection activates two distinct intracellular signalling cascades in the immune-responsive fat body of Drosophila. Gram-positive bacteria and fungi predominantly induce the Toll signalling pathway, whereas Gram-negative bacteria activate the Imd pathway. Loss-of-function mutants in either pathway reduce the resistance to corresponding infections. Genetic screens have identified a range of genes involved in these intracellular signalling cascades, but how they are activated by microbial infection is largely unknown. Activation of the transmembrane receptor Toll requires a proteolytically cleaved form of an extracellular cytokine-like polypeptide, Spätzle, suggesting that Toll does not itself function as a bona fide recognition receptor of microbial patterns. This is in apparent contrast with the mammalian Toll-like receptors and raises the question of which host molecules actually recognize microbial patterns to activate Toll through Spätzle. Here we present a mutation that blocks Toll activation by Gram-positive bacteria and significantly decreases resistance to this type of infection. The mutation semmelweis (seml) inactivates the gene encoding a peptidoglycan recognition protein (PGRP-SA). Interestingly, seml does not affect Toll activation by fungal infection, indicating the existence of a distinct recognition system for fungi to activate the Toll pathway.
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Affiliation(s)
- T Michel
- Institut de Biologie Moleculaire et Cellulaire, UPR 9022 du CNRS, 15 rue Rene Descartes, 67084 Strasbourg Cedex, France
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140
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Abstract
Toll-like receptors have a crucial role in the detection of microbial infection in mammals and insects. In mammals, these receptors have evolved to recognize conserved products unique to microbial metabolism. This specificity allows the Toll proteins to detect the presence of infection and to induce activation of inflammatory and antimicrobial innate immune responses. Recognition of microbial products by Toll-like receptors expressed on dendritic cells triggers functional maturation of dendritic cells and leads to initiation of antigen-specific adaptive immune responses.
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Affiliation(s)
- R Medzhitov
- Section of Immunobiology, Yale University School Medicine, and Howard Hughes Medical Institute, New Haven, Connecticut 06520, USA.
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141
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Georgel P, Naitza S, Kappler C, Ferrandon D, Zachary D, Swimmer C, Kopczynski C, Duyk G, Reichhart JM, Hoffmann JA. Drosophila immune deficiency (IMD) is a death domain protein that activates antibacterial defense and can promote apoptosis. Dev Cell 2001; 1:503-14. [PMID: 11703941 DOI: 10.1016/s1534-5807(01)00059-4] [Citation(s) in RCA: 328] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
We report the molecular characterization of the immune deficiency (imd) gene, which controls antibacterial defense in Drosophila. imd encodes a protein with a death domain similar to that of mammalian RIP (receptor interacting protein), a protein that plays a role in both NF-kappaB activation and apoptosis. We show that imd functions upstream of the DmIKK signalosome and the caspase DREDD in the control of antibacterial peptide genes. Strikingly, overexpression of imd leads to constitutive transcription of these genes and to apoptosis, and both effects are blocked by coexpression of the caspase inhibitor P35. We also show that imd is involved in the apoptotic response to UV irradiation. These data raise the possibility that antibacterial response and apoptosis share common control elements in Drosophila.
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Affiliation(s)
- P Georgel
- Institut de Biologie Moleculaire et Cellulaire, UPR 9022 du CNRS, Strasbourg, France
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142
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Silverman N, Maniatis T. NF-kappaB signaling pathways in mammalian and insect innate immunity. Genes Dev 2001; 15:2321-42. [PMID: 11562344 DOI: 10.1101/gad.909001] [Citation(s) in RCA: 695] [Impact Index Per Article: 30.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Affiliation(s)
- N Silverman
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
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143
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Wu LP, Choe KM, Lu Y, Anderson KV. Drosophila immunity: genes on the third chromosome required for the response to bacterial infection. Genetics 2001; 159:189-99. [PMID: 11560896 PMCID: PMC1461779 DOI: 10.1093/genetics/159.1.189] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We have screened the third chromosome of Drosophila melanogaster for mutations that prevent the normal immune response. We identified mutant lines on the basis of their failure to induce transcription of an antibacterial peptide gene in response to infection or their failure to form melanized clots at the site of wounding. These mutations define 14 genes [immune response deficient (ird) genes] that have distinct roles in the immune response. We have identified the molecular basis of several ird phenotypes. Two genes, scribble and kurtz/modulo, affect the cellular organization of the fat body, the tissue responsible for antimicrobial peptide production. Two ird genes encode components of the signaling pathways that mediate responses to bacterial infection, a Drosophila gene encoding a homolog of I kappa B kinase (DmIkk beta) and Relish, a Rel-family transcription factor. These genetic studies should provide a basis for a comprehensive understanding of the genetic control of immune responses in Drosophila.
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Affiliation(s)
- L P Wu
- Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA
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144
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DiDonato JA. IKK alpha on center stage. SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2001; 2001:pe1. [PMID: 11698579 DOI: 10.1126/stke.2001.97.pe1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Inhibitor of kappaB kinase alpha (IKK alpha) was originally identified as a component of a multiprotein kinase complex that regulates the activity of the transcription factor nuclear factor-kappaB (NF-kappaB) through phosphorylation of its inhibitor proteins, the IkappaBs. DiDonato discusses new roles that have been discovered for IKK alpha, focusing especially on its role in epidermal differentiation and on a new function of IKK alpha in B cell maturation. In epidermal differentiation, IKK alpha regulates the production of a secreted differentiation factor through a pathway that is independent of its role in activation of NF-kappaB. In B cell maturation, conventional NF-kappaB signal-induced activation of IKK alpha results in phosphorylation of p100 precursor proteins and increased proteolytic processing and constitutive NF-kappaB activation.
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Affiliation(s)
- J A DiDonato
- Department of Cancer Biology, The Lerner Research Institute at The Cleveland Clinic, Cleveland, OH 44195, USA.
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145
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Senftleben U, Cao Y, Xiao G, Greten FR, Krähn G, Bonizzi G, Chen Y, Hu Y, Fong A, Sun SC, Karin M. Activation by IKKalpha of a second, evolutionary conserved, NF-kappa B signaling pathway. Science 2001; 293:1495-9. [PMID: 11520989 DOI: 10.1126/science.1062677] [Citation(s) in RCA: 1060] [Impact Index Per Article: 46.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
In mammals, the canonical nuclear factor kappaB (NF-kappaB) signaling pathway activated in response to infections is based on degradation of IkappaB inhibitors. This pathway depends on the IkappaB kinase (IKK), which contains two catalytic subunits, IKKalpha and IKKbeta. IKKbeta is essential for inducible IkappaB phosphorylation and degradation, whereas IKKalpha is not. Here we show that IKKalpha is required for B cell maturation, formation of secondary lymphoid organs, increased expression of certain NF-kappaB target genes, and processing of the NF-kappaB2 (p100) precursor. IKKalpha preferentially phosphorylates NF-kappaB2, and this activity requires its phosphorylation by upstream kinases, one of which may be NF-kappaB-inducing kinase (NIK). IKKalpha is therefore a pivotal component of a second NF-kappaB activation pathway based on regulated NF-kappaB2 processing rather than IkappaB degradation.
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Affiliation(s)
- U Senftleben
- Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
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146
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Vidal S, Khush RS, Leulier F, Tzou P, Nakamura M, Lemaitre B. Mutations in the Drosophila dTAK1 gene reveal a conserved function for MAPKKKs in the control of rel/NF-kappaB-dependent innate immune responses. Genes Dev 2001; 15:1900-12. [PMID: 11485985 PMCID: PMC524699 DOI: 10.1101/gad.203301] [Citation(s) in RCA: 239] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In mammals, TAK1, a MAPKKK kinase, is implicated in multiple signaling processes, including the regulation of NF-kappaB activity via the IL1-R/TLR pathways. TAK1 function has largely been studied in cultured cells, and its in vivo function is not fully understood. We have isolated null mutations in the Drosophila dTAK1 gene that encodes dTAK1, a homolog of TAK1. dTAK1 mutant flies are viable and fertile, but they do not produce antibacterial peptides and are highly susceptible to Gram-negative bacterial infection. This phenotype is similar to the phenotypes generated by mutations in components of the Drosophila Imd pathway. Our genetic studies also indicate that dTAK1 functions downstream of the Imd protein and upstream of the IKK complex in the Imd pathway that controls the Rel/NF-kappaB like transactivator Relish. In addition, our epistatic analysis places the caspase, Dredd, downstream of the IKK complex, which supports the idea that Relish is processed and activated by a caspase activity. Our genetic demonstration of dTAK1's role in the regulation of Drosophila antimicrobial peptide gene expression suggests an evolutionary conserved role for TAK1 in the activation of Rel/NF-kappaB-mediated host defense reactions.
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Affiliation(s)
- S Vidal
- Centre de Génétique Moléculaire, CNRS, 91198 Gif-sur-Yvette, France
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147
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Fernandez NQ, Grosshans J, Goltz JS, Stein D. Separable and redundant regulatory determinants in Cactus mediate its dorsal group dependent degradation. Development 2001; 128:2963-74. [PMID: 11532919 DOI: 10.1242/dev.128.15.2963] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Dorsal-ventral polarity within the Drosophila syncytial blastoderm embryo is determined by the maternally encoded dorsal group signal transduction pathway that regulates nuclear localization of the transcription factor Dorsal. Nuclear uptake of Dorsal, a Rel/NFκB homolog, is controlled by the interaction with its cognate IκB inhibitor protein Cactus, which is degraded on the ventral side of the embryo in response to dorsal group signaling. Previous studies have suggested that an N-terminally located kinase target motif similar to that found in IκB proteins is involved in the spatially controlled degradation of Cactus. We report studies of the in vivo function and distribution of fusion proteins comprising segments of Cactus attached to Escherichia coli β-galactosidase (lacZ). Full-length Cactus-lacZ expressed in vivo normalizes the ventralized phenotype of embryos that lack Cactus and faithfully reconstitutes dorsal group-regulated degradation, while fusion protein constructs that lack the first 125 amino acids of Cactus escape dorsal group-dependent degradation. Furthermore, Cactus-lacZ constructs that lack only the putative IκB-dependent kinase target-like motif can nevertheless undergo spatially regulated dorsal group-dependent degradation and we have identified the regulatory determinant responsible for dorsal group-dependent degradation of Cactus in the absence of this motif. Taken together, our studies indicate the presence of two distinct redundantly acting determinants in the N terminus of Cactus that direct dorsal group-dependent degradation. Strikingly, the regulatory domain of human IκBα can also direct polarized degradation of Cactus-lacZ fusion protein.
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Affiliation(s)
- N Q Fernandez
- Department of Molecular Genetics, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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148
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Abstract
Innate immunity is the first-line host defense of multicellular organisms that rapidly operates to limit infection upon exposure to infectious agents. In addition, the cells and molecules operating during this early stage of the immune response in vertebrates have a decisive impact on the shaping of the subsequent adaptive response. Genetic studies initially performed in the fruitfly Drosophila and later in mice have revealed the importance of proteins of the Toll family in the innate immune response. We present here our current understanding of the role of this evolutionary ancient family of proteins that are thought to function as cytokine receptors (Toll in Drosophila) or pattern-recognition receptors (TLRs in mammals) and activate similar, albeit non-identical, signal-transduction pathways in flies and mammals.
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Affiliation(s)
- J L Imler
- Institute of Molecular and Cellular Biology, CNRS, 15 rue René Descartes, 67084 Cedex, Strasbourg, France
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149
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Salmerón A, Janzen J, Soneji Y, Bump N, Kamens J, Allen H, Ley SC. Direct phosphorylation of NF-kappaB1 p105 by the IkappaB kinase complex on serine 927 is essential for signal-induced p105 proteolysis. J Biol Chem 2001; 276:22215-22. [PMID: 11297557 DOI: 10.1074/jbc.m101754200] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The p105 precursor protein of NF-kappaB1 acts as an NF-kappaB inhibitory protein, retaining associated Rel subunits in the cytoplasm of unstimulated cells. Tumor necrosis factor alpha (TNFalpha) and interleukin-1alpha (IL-1alpha) stimulate p105 degradation, releasing associated Rel subunits to translocate into the nucleus. By using knockout embryonic fibroblasts, it was first established that the IkappaB kinase (IKK) complex is essential for these pro-inflammatory cytokines to trigger efficiently p105 degradation. The p105 PEST domain contains a motif (Asp-Ser(927)-Gly-Val-Glu-Thr), related to the IKK target sequence in IkappaBalpha, which is conserved between human, mouse, rat, and chicken p105. Analysis of a panel of human p105 mutants in which serine/threonine residues within and adjacent to this motif were individually changed to alanine established that only serine 927 is essential for p105 proteolysis triggered by IKK2 overexpression. This residue is also required for TNFalpha and IL-1alpha to stimulate p105 degradation. By using a specific anti-phosphopeptide antibody, it was confirmed that IKK2 overexpression induces serine 927 phosphorylation of co-transfected p105 and that endogenous p105 is also rapidly phosphorylated on this residue after TNFalpha or IL-1alpha stimulation. In vitro kinase assays with purified proteins demonstrated that both IKK1 and IKK2 can directly phosphorylate p105 on serine 927. Together these experiments indicate that the IKK complex regulates the signal-induced proteolysis of NF-kappaB1 p105 by direct phosphorylation of serine 927 in its PEST domain.
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Affiliation(s)
- A Salmerón
- Division of Cellular Immunology, the National Institute for Medical Research, Mill Hill, London NW7 1AA, United Kingdom
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150
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Pujol N, Link EM, Liu LX, Kurz CL, Alloing G, Tan MW, Ray KP, Solari R, Johnson CD, Ewbank JJ. A reverse genetic analysis of components of the Toll signaling pathway in Caenorhabditis elegans. Curr Biol 2001; 11:809-21. [PMID: 11516642 DOI: 10.1016/s0960-9822(01)00241-x] [Citation(s) in RCA: 302] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Both animals and plants respond rapidly to pathogens by inducing the expression of defense-related genes. Whether such an inducible system of innate immunity is present in the model nematode Caenorhabditis elegans is currently an open question. Among conserved signaling pathways important for innate immunity, the Toll pathway is the best characterized. In Drosophila, this pathway also has an essential developmental role. C. elegans possesses structural homologs of components of this pathway, and this observation raises the possibility that a Toll pathway might also function in nematodes to trigger defense mechanisms or to control development. RESULTS We have generated and characterized deletion mutants for four genes supposed to function in a nematode Toll signaling pathway. These genes are tol-1, trf-1, pik-1, and ikb-1 and are homologous to the Drosophila melanogaster Toll, dTraf, pelle, and cactus genes, respectively. Of these four genes, only tol-1 is required for nematode development. None of them are important for the resistance of C. elegans to a number of pathogens. On the other hand, C. elegans is capable of distinguishing different bacterial species and has a tendency to avoid certain pathogens, including Serratia marcescens. The tol-1 mutants are defective in their avoidance of pathogenic S. marcescens, although other chemosensory behaviors are wild type. CONCLUSIONS In C. elegans, tol-1 is important for development and pathogen recognition, as is Toll in Drosophila, but remarkably for the latter rôle, it functions in the context of a behavioral mechanism that keeps worms away from potential danger.
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Affiliation(s)
- N Pujol
- Laboratoire de Génétique et Physiologie du Développement, Institut National de la Santé et de la Recherche Médicale/Centre National pour la Recherche Scientifique/Université de la Mediterranée, 13288, Marseille, France
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