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Blocking apoptotic signaling rescues axon guidance in Netrin mutants. Cell Rep 2013; 3:595-606. [PMID: 23499445 DOI: 10.1016/j.celrep.2013.02.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2012] [Revised: 01/14/2013] [Accepted: 02/14/2013] [Indexed: 11/21/2022] Open
Abstract
Netrins are guidance cues that form gradients to guide growing axons. We uncover a mechanism for axon guidance by demonstrating that axons can accurately navigate in the absence of a Netrin gradient if apoptotic signaling is blocked. Deletion of the two Drosophila NetA and NetB genes leads to guidance defects and increased apoptosis, and expression of either gene at the midline is sufficient to rescue the connectivity defects and cell death. Surprisingly, pan-neuronal expression of NetB rescues equally well, even though no Netrin gradient has been established. Furthermore, NetB expression blocks apoptosis, suggesting that NetB acts as a neurotrophic factor. In contrast, neuronal expression of NetA increases axon defects. Simply blocking apoptosis in NetAB mutants is sufficient to rescue connectivity, and inhibition of caspase activity in subsets of neurons rescues guidance independently of survival. In contrast to the traditional role of Netrin as simply a guidance cue, our results demonstrate that guidance and survival activities may be functionally related.
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Abstract
Glial cells have diverse functions that are necessary for the proper development and function of complex nervous systems. Various insects, primarily the fruit fly Drosophila melanogaster and the moth Manduca sexta, have provided useful models of glial function during development. The present review will outline evidence of glial contributions to embryonic, visual, olfactory and wing development. We will also outline evidence for non-developmental functions of insect glia including blood-brain-barrier formation, homeostatic functions and potential contributions to synaptic function. Where relevant, we will also point out similarities between the functions of insect glia and their vertebrate counterparts.
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Affiliation(s)
- Robert J Parker
- Department of Zoology, University of British Columbia, 6270 University Blvd. Vancouver, BC, Canada V6T 1Z4
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Parker RJ, Auld VJ. Signaling in glial development: differentiation migration and axon guidance. Biochem Cell Biol 2004; 82:694-707. [PMID: 15674437 DOI: 10.1139/o04-119] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Glial cells have diverse functions that are necessary for the proper development and function of complex nervous systems. During development, a variety of reciprocal signaling interactions between glia and neurons dictate all parts of nervous system development. Glia may provide attractive, repulsive, or contact-mediated cues to steer neuronal growth cones and ensure that neurons find their appropriate synaptic targets. In fact, both neurons and glia may act as migrational substrates for one another at different times during development. Also, the exchange of trophic signals between glia and neurons is essential for the proper bundling, fasciculation, and ensheathement of axons as well as the differentiation and survival of both cell types. The growing number of links between glial malfunction and human disease has generated great interest in glial biology. Because of its relative simplicity and the many molecular genetic tools available, Drosophila is an excellent model organism for studying glial development. This review will outline the roles of glia and their interactions with neurons in the embryonic nervous system of the fly.Key words: glia, axon guidance, migration, EGF receptor.
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Affiliation(s)
- Robert J Parker
- Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, BC V6T 1Z4, Canada
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Affiliation(s)
- Matthew Freeman
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
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Settle M, Gordon MD, Nadella M, Dankort D, Muller W, Jacobs JR. Genetic identification of effectors downstream of Neu (ErbB-2) autophosphorylation sites in a Drosophila model. Oncogene 2003; 22:1916-26. [PMID: 12673197 DOI: 10.1038/sj.onc.1206240] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The ErbB-2/Neu receptor tyrosine kinase plays a causal role in tumorigenesis in mammals. Neu's carboxyl terminus contains five phosphorylated tyrosines that mediate transformation through interaction with cytoplasmic SH2 or PTB containing adaptor proteins. We show that Drosophila adaptors signal from individual phosphotyrosine sites of rat Neu. Activated Neu expression in the midline glia suppressed apoptosis, similar to that seen with activated Drosophila EGF-R expression. Expression in eye and wing tissues generated graded phenotypes suitable for dosage-sensitive modifier genetics. Suppression of ErbB-2/Neu-induced phenotypes in tissues haplosufficient for genes encoding adaptor protein or second messengers suggests that pTyr 1227(YD) signals require Shc, and that pTyr 1253 (YE) signalling does not employ Ras, but does require Raf function. Signalling from pTyr (YB) was affected by a haplosufficiency in drk (Grb-2), and in genes thought to function downstream of Grb-2: dab, sos, csw (Shp-2), and dos (Gab-1). These data demonstrate the power of Drosophila genetics to unmask the molecules that signal from oncogenic ErbB-2/Neu.
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MESH Headings
- Adaptor Proteins, Vesicular Transport
- Animals
- Animals, Genetically Modified
- Apoptosis/genetics
- Apoptosis/physiology
- Drosophila Proteins/genetics
- Drosophila Proteins/physiology
- Drosophila melanogaster/embryology
- Drosophila melanogaster/genetics
- Drosophila melanogaster/growth & development
- Drosophila melanogaster/metabolism
- ErbB Receptors/physiology
- Eye/growth & development
- Eye Proteins/genetics
- Eye Proteins/physiology
- Gene Dosage
- Gene Expression Regulation, Developmental
- Morphogenesis/genetics
- Morphogenesis/physiology
- Nerve Tissue Proteins/genetics
- Nerve Tissue Proteins/physiology
- Phenotype
- Phosphorylation
- Phosphotyrosine/chemistry
- Protein Kinases
- Protein Processing, Post-Translational
- Protein Structure, Tertiary
- Protein Tyrosine Phosphatases/genetics
- Protein Tyrosine Phosphatases/physiology
- Protein Tyrosine Phosphatases, Non-Receptor
- Proteins/genetics
- Proteins/physiology
- Proto-Oncogene Proteins c-raf/genetics
- Proto-Oncogene Proteins c-raf/physiology
- Rats
- Receptor, ErbB-2/chemistry
- Receptor, ErbB-2/physiology
- Receptors, Invertebrate Peptide/physiology
- Recombinant Fusion Proteins/physiology
- Shc Signaling Adaptor Proteins
- Signal Transduction/genetics
- Signal Transduction/physiology
- Son of Sevenless Protein, Drosophila/genetics
- Son of Sevenless Protein, Drosophila/physiology
- Structure-Activity Relationship
- Wings, Animal/growth & development
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Affiliation(s)
- Mark Settle
- Department of Biology, McMaster University, Hamilton, ON, Canada
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Besse F, Pret AM. Apoptosis-mediated cell death within the ovarian polar cell lineage of Drosophila melanogaster. Development 2003; 130:1017-27. [PMID: 12538526 DOI: 10.1242/dev.00313] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Polar cells have been described as pairs of specific follicular cells present at each pole of Drosophila egg chambers. They are required at different stages of oogenesis for egg chamber formation and establishment of both the anteroposterior and planar polarities of the follicular epithelium. We show that definition of polar cell pairs is a progressive process since early stage egg chambers contain a cluster of several polar cell marker-expressing cells at each pole, while as of stage 5, they contain invariantly two pairs of such cells. Using cell lineage analysis, we demonstrate that these pre-polar cell clusters have a polyclonal origin and derive specifically from the polar cell lineage, rather than from that giving rise to follicular cells. In addition, selection of two polar cells from groups of pre-polar cells occurs via an apoptosis-dependent mechanism and is required for correct patterning of the anterior follicular epithelium of vitellogenic egg chambers.
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Affiliation(s)
- Florence Besse
- Institut Jacques Monod, UMR 7592-CNRS/Université Pierre et Marie Curie/Université Denis Diderot, Laboratoire de Génétique du Développement et Evolution, 2-4, place Jussieu, 75251 Paris Cedex 05, France
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Oland LA, Tolbert LP. Key interactions between neurons and glial cells during neural development in insects. ANNUAL REVIEW OF ENTOMOLOGY 2002; 48:89-110. [PMID: 12194908 DOI: 10.1146/annurev.ento.48.091801.112654] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Nervous system function is entirely dependent on the intricate and precise pattern of connections made by individual neurons. Much of the insightful research into mechanisms underlying the development of this pattern of connections has been done in insect nervous systems. Studies of developmental mechanisms have revealed critical interactions between neurons and glia, the non-neuronal cells of the nervous system. Glial cells provide trophic support for neurons, act as struts for migrating neurons and growing axons, form boundaries that restrict neuritic growth, and have reciprocal interactions with neurons that govern specification of cell fate and axonal pathfinding. The molecular mechanisms underlying these interactions are beginning to be understood. Because many of the cellular and molecular mechanisms underlying neural development appear to be common across disparate insect species, and even between insects and vertebrates, studies in developing insect nervous systems are elucidating mechanisms likely to be of broad significance.
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Affiliation(s)
- Lynne A Oland
- Arizona Research Laboratories Division of Neurobiology, University of Arizona, Tucson, Arizona 85721, USA.
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Bergmann A, Tugentman M, Shilo BZ, Steller H. Regulation of cell number by MAPK-dependent control of apoptosis: a mechanism for trophic survival signaling. Dev Cell 2002; 2:159-70. [PMID: 11832242 DOI: 10.1016/s1534-5807(02)00116-8] [Citation(s) in RCA: 167] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Trophic mechanisms in which neighboring cells mutually control their survival by secreting extracellular factors play an important role in determining cell number. However, how trophic signaling suppresses cell death is still poorly understood. We now show that the survival of a subset of midline glia cells in Drosophila depends upon direct suppression of the proapoptotic protein HID via the EGF receptor/RAS/MAPK pathway. The TGFalpha-like ligand SPITZ is activated in the neurons, and glial cells compete for limited amounts of secreted SPITZ to survive. In midline glia that fail to activate the EGFR pathway, HID induces apoptosis by blocking a caspase inhibitor, Diap1. Therefore, a direct pathway linking a specific extracellular survival factor with a caspase-based death program has been established.
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Affiliation(s)
- Andreas Bergmann
- Department of Biology, Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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Jacobs JR. The midline glia of Drosophila: a molecular genetic model for the developmental functions of glia. Prog Neurobiol 2000; 62:475-508. [PMID: 10869780 DOI: 10.1016/s0301-0082(00)00016-2] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The Midline Glia of Drosophila are required for nervous system morphogenesis and midline axon guidance during embryogenesis. In origin, gene expression and function, this lineage is analogous to the floorplate of the vertebrate neural tube. The expression or function of over 50 genes, summarised here, has been linked to the Midline Glia. Like the floorplate, the cells which generate the Midline Glia lineage, the mesectoderm, are determined by the interaction of ectoderm and mesoderm during gastrulation. Determination and differentiation of the Midline Glia involves the Drosophila EGF, Notch and segment polarity signaling pathways, as well as twelve identified transcription factors. The Midline Glia lineage has two phases of cell proliferation and of programmed cell death. During embryogenesis, the EGF receptor pathway signaling and Wrapper protein both function to suppress apoptosis only in those MG which are appropriately positioned to separate and ensheath midline axonal commissures. Apoptosis during metamorphosis is regulated by the insect steroid, Ecdysone. The Midline Glia participate in both the attraction of axonal growth cones towards the midline, as well as repulsion of growth cones from the midline. Midline axon guidance requires the Drosophila orthologs of vertebrate genes expressed in the floorplate, which perform the same function. Genetic and molecular evidence of the interaction of attractive (Netrin) and repellent (Slit) signaling is reviewed and summarised in a model. The Midline Glia participate also in the generation of extracellular matrix and in trophic interactions with axons. Genetic evidence for these functions is reviewed.
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Affiliation(s)
- J R Jacobs
- Department of Biology, McMaster University, 1280 Main Street W., L8S 4K1, Hamilton, Canada.
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Abstract
Selective cell death provides developing tissues with the means to precisely sculpt emerging structures. By imposing patterned cell death across a tissue, boundaries can be created and tightened. As such, programmed cell death is becoming recognized as a major mechanism for patterning of a variety of complex structures. Typically, cell types are initially organized into a fairly loose pattern; selective death then removes cells between pattern elements to create correct structures. In this review, we examine the role of selective cell death across the course of Drosophila development, including the tightening of embryonic segmental boundaries, head maturation, refining adult structures such as the eye and the wing, and the ability of cell death to correct for pattern defects introduced by gene mutation. We also review what is currently known of the relationship between signals at the cell surface that are responsible for tissue patterning and the basal cell death machinery, an issue that remains poorly understood.
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Affiliation(s)
- J C Rusconi
- Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri, MO 63110, USA
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Lanoue BR, Gordon MD, Battye R, Jacobs JR. Genetic analysis of vein function in the Drosophila embryonic nervous system. Genome 2000. [DOI: 10.1139/g00-014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Drosophila epidermal growth factor receptor (EGFR) may be activated by two ligands expressed in the embryonic nervous system, Spitz and Vein. Previous studies have established Spitz as an essential activator of EGFR signaling in nervous system development. Here, we report the pattern of expression of vein mRNA in the nervous system and characterize the contribution of vein to cell lineage and axonogenesis. The number of midline glia (MG) precursors is reduced in vein mutants before the onset of embryonic apoptosis. In contrast to spitz, mis-expression of vein does not suppress apoptosis in the MG. These data indicate that early midline EGFR signaling, requiring vein and spitz, establishes MG precursor number, whereas later EGFR signals, requiring spitz, suppress apoptosis in the MG. vein mutants show early irregularities during axon tract establishment, which resolve later to variable defasciculation and thinner intersegmental axon tracts. vein and spitz phenotypes act additively in the regulation of MG cell number, but show synergism in a midline neuronal cell number phenotype and in axon tract architecture. vein appears to act downstream of spitz to briefly amplify local EGFR activation.Key words: Drosophila, vein, midline, axonogenesis, EGF receptor, lineage, neuregulin, spitz, CNS.
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