Highwire Regulates Guidance of Sister Axons in the Drosophila Mushroom Body

Department of Developmental Biology, Hope Center for Neurological Disorders, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 11/2011; 31(48):17689-700. DOI: 10.1523/JNEUROSCI.3902-11.2011
Source: PubMed


Axons often form synaptic contacts with multiple targets by extending branches along different paths. PHR (Pam/Highwire/RPM-1) family ubiquitin ligases are important regulators of axon development, with roles in axon outgrowth, target selection, and synapse formation. Here we report the function of Highwire, the Drosophila member of the PHR family, in promoting the segregation of sister axons during mushroom body (MB) formation. Loss of highwire results in abnormal development of the axonal lobes in the MB, leading to thinned and shortened lobes. The highwire defect is attributable to guidance errors after axon branching, in which sister axons that should target different lobes instead extend together into the same lobe. The highwire mutant MB displays elevation in the level of the MAPKKK Wallenda/DLK (dual leucine zipper kinase), a previously identified substrate of Highwire, and genetic suppression studies show that Wallenda/DLK is required for the highwire MB phenotype. The highwire lobe defect is limited to α/β lobe axons, but transgenic expression of highwire in the pioneering α'/β' neurons rescues the phenotype. Mosaic analysis further shows that α/β axons of highwire mutant clones develop normally, demonstrating a non-cell-autonomous role of Highwire for axon guidance. Genetic interaction studies suggest that Highwire and Plexin A signals may interact to regulate normal morphogenesis of α/β axons.

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    • "Different guidance cues are likely required for the a and b branches. For instance, mutations in the Eph and Hiw genes result in specific effects on a branch versus b branch guidance, respectively (Boyle et al., 2006; Shin and DiAntonio, 2011). The drl gene encodes a receptor tyrosine kinase-related protein, which plays roles with its ligand WNT5 in MB development and was first isolated on its role in olfactory memory (Dura et al., 1993; Grillenzoni et al., 2007). "
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    ABSTRACT: In vivo axon pathfinding mechanisms in the neuron-dense brain remain relatively poorly characterized. We study the Drosophila mushroom body (MB) axons, whose α and β branches connect to different brain areas. We show that the Ryk family WNT5 receptor, DRL (derailed), which is expressed in the dorsomedial lineages, brain structure precursors adjacent to the MBs, is required for MB α branch axon guidance. DRL acts to capture and present WNT5 to MB axons rather than transduce a WNT5 signal. DRL's ectodomain must be cleaved and shed to guide α axons. DRL-2, another Ryk, is expressed within MB axons and functions as a repulsive WNT5 signaling receptor. Finally, our biochemical data support the existence of a ternary complex composed of the cleaved DRL ectodomain, WNT5, and DRL-2. Thus, the interaction of MB-extrinsic and -intrinsic Ryks via their common ligand acts to guide MB α axons. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.
    Cell Reports 05/2015; 11(8). DOI:10.1016/j.celrep.2015.04.035 · 8.36 Impact Factor
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    • "In Caenorhabditis elegans, the regulator of presynaptic morphology 1 (RPM-1) regulates synapse formation in motor neurons [13], and both axon termination and synapse formation in the mechanosensory neurons [14]. Studies in worms and flies have found that Hiw and RPM-1 function in axon guidance [15,16]. "
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    ABSTRACT: Background The PAM/Highwire/RPM-1 (PHR) proteins are conserved signaling proteins that regulate axon length and synapse formation during development. Loss of function in Caenorhabditis elegans rpm-1 results in axon termination and synapse formation defects in the mechanosensory neurons. An explanation for why these two phenotypes are observed in a single neuronal cell has remained absent. Further, it is uncertain whether the axon termination phenotypes observed in the mechanosensory neurons of rpm-1 mutants are unique to this specific type of neuron, or more widespread defects that occur with loss of function in rpm-1. Results Here, we show that RPM-1 is localized to both the mature axon tip and the presynaptic terminals of individual motor neurons and individual mechanosensory neurons. Genetic analysis indicated that GABAergic motor neurons, like the mechanosensory neurons, have both synapse formation and axon termination defects in rpm-1 mutants. RPM-1 functions in parallel with the active zone component SYD-2 (Liprin) to regulate not only synapse formation, but also axon termination in motor neurons. Our analysis of rpm-1−/−; syd-2−/− double mutants also revealed a role for RPM-1 in axon extension. The MAP3K DLK-1 partly mediated RPM-1 function in both axon termination and axon extension, and the relative role of DLK-1 was dictated by the anatomical location of the neuron in question. Conclusions Our findings show that axon termination defects are a core phenotype caused by loss of function in rpm-1, and not unique to the mechanosensory neurons. We show in motor neurons and in mechanosensory neurons that RPM-1 is localized to multiple, distinct subcellular compartments in a single cell. Thus, RPM-1 might be differentially regulated or RPM-1 might differentially control signals in distinct subcellular compartments to regulate multiple developmental outcomes in a single neuron. Our findings provide further support for the previously proposed model that PHR proteins function to coordinate axon outgrowth and termination with synapse formation.
    Neural Development 05/2014; 9(1):10. DOI:10.1186/1749-8104-9-10 · 3.45 Impact Factor
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    • "At the adult stage, hiw mutants cause similar anatomical overgrowth and physiological dysfunction of the Giant Fibre-tergotrochanteral motoneuron synapse in the Drosophila CNS (Uthaman et al. 2008). More recent studies show that hiw also plays a positive role in the segregation of sister axons during mushroom body formation, in a non-cell autonomous fashion (Shin & DiAntonio, 2011). In Caenorhabditis elegans, rpm-1 mutants show altered distribution and density of GABAergic NMJs, and abnormal targeting and morphology of glutamatergic synapses (Schaefer et al. 2000; Zhen et al. 2000). "
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    ABSTRACT: The covalent attachment of the 76 aa peptide ubiquitin to target proteins is a rapid and reversible modification that regulates protein stability, activity and localization. As such, it is a potent mechanism for sculpting the synapse. Recent studies from two genetic model organisms, C. elegans and Drosophila, have provided mounting evidence that ubiquitin-mediated pathways play important roles in controlling the presynaptic size, synaptic elimination and stabilization, synaptic transmission, postsynaptic receptor abundance, axonal degeneration and regeneration. While the data supporting the requirement of ubiquitination/deubiquitination for normal synaptic development and repair are compelling, detailed analyses of signaling events up- and down-stream of these ubiquitin modification are often challenging. This article summarizes the related research conducted in worms and flies and provides insight into the fundamental questions faced in this field.
    The Journal of Physiology 04/2013; 591(13). DOI:10.1113/jphysiol.2012.247940 · 5.04 Impact Factor
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