1
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Chen X, Perry S, Fan Z, Wang B, Loxterkamp E, Wang S, Hu J, Dickman D, Han C. Tissue-specific knockout in the Drosophila neuromuscular system reveals ESCRT's role in formation of synapse-derived extracellular vesicles. PLoS Genet 2024; 20:e1011438. [PMID: 39388480 DOI: 10.1371/journal.pgen.1011438] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2024] [Accepted: 09/25/2024] [Indexed: 10/12/2024] Open
Abstract
Tissue-specific gene knockout by CRISPR/Cas9 is a powerful approach for characterizing gene functions during development. However, this approach has not been successfully applied to most Drosophila tissues, including the Drosophila neuromuscular junction (NMJ). To expand tissue-specific CRISPR to this powerful model system, here we present a CRISPR-mediated tissue-restricted mutagenesis (CRISPR-TRiM) toolkit for knocking out genes in motoneurons, muscles, and glial cells. We validated the efficacy of CRISPR-TRiM by knocking out multiple genes in each tissue, demonstrated its orthogonal use with the Gal4/UAS binary expression system, and showed simultaneous knockout of multiple redundant genes. We used CRISPR-TRiM to discover an essential role for SNARE components in NMJ maintenance. Furthermore, we demonstrate that the canonical ESCRT pathway suppresses NMJ bouton growth by downregulating retrograde Gbb signaling. Lastly, we found that axon termini of motoneurons rely on ESCRT-mediated intra-axonal membrane trafficking to release extracellular vesicles at the NMJ. Thus, we have successfully developed an NMJ CRISPR mutagenesis approach which we used to reveal genes important for NMJ structural plasticity.
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Affiliation(s)
- Xinchen Chen
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Sarah Perry
- Department of Neurobiology, University of Southern California, Los Angeles, California, United States of America
| | - Ziwei Fan
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Bei Wang
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Elizabeth Loxterkamp
- Department of Neurobiology, University of Southern California, Los Angeles, California, United States of America
| | - Shuran Wang
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Jiayi Hu
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Dion Dickman
- Department of Neurobiology, University of Southern California, Los Angeles, California, United States of America
| | - Chun Han
- Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
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2
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Kaneko T, Li R, He Q, Yang L, Ye B. Transsynaptic BMP Signaling Regulates Fine-Scale Topography between Adjacent Sensory Neurons. eNeuro 2024; 11:ENEURO.0322-24.2024. [PMID: 39137988 PMCID: PMC11360983 DOI: 10.1523/eneuro.0322-24.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2024] [Revised: 07/25/2024] [Accepted: 07/30/2024] [Indexed: 08/15/2024] Open
Abstract
Sensory axons projecting to the central nervous system are organized into topographic maps that represent the locations of sensory stimuli. In some sensory systems, even adjacent sensory axons are arranged topographically, forming "fine-scale" topographic maps. Although several broad molecular gradients are known to instruct coarse topography, we know little about the molecular signaling that regulates fine-scale topography at the level of two adjacent axons. Here, we provide evidence that transsynaptic bone morphogenetic protein (BMP) signaling mediates local interneuronal communication to regulate fine-scale topography in the nociceptive system of Drosophila larvae. We first show that the topographic separation of the axon terminals of adjacent nociceptors requires their common postsynaptic target, the A08n neurons. This phenotype is recapitulated by knockdown of the BMP ligand, Decapentaplegic (Dpp), in these neurons. In addition, removing the Type 2 BMP receptors or their effector (Mad transcription factor) in single nociceptors impairs the fine-scale topography, suggesting the contribution of BMP signaling originated from A08n. This signaling is likely mediated by phospho-Mad in the presynaptic terminals of nociceptors to ensure local interneuronal communication. Finally, reducing Dpp levels in A08n reduces the nociceptor-A08n synaptic contacts. Our data support that transsynaptic BMP signaling establishes the fine-scale topography by facilitating the formation of topographically correct synapses. Local BMP signaling for synapse formation may be a developmental strategy that independently regulates neighboring axon terminals for fine-scale topography.
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Affiliation(s)
- Takuya Kaneko
- Life Sciences Institute and Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109
| | - Ruonan Li
- Life Sciences Institute and Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109
- School of Medicine, Dalian University, Dalian 116622, China
| | - Qun He
- School of Medicine, Dalian University, Dalian 116622, China
| | - Limin Yang
- School of Medicine, Dalian University, Dalian 116622, China
| | - Bing Ye
- Life Sciences Institute and Department of Cell and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109
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3
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Biswas DD, Shi Y, El Haddad L, Sethi R, Huston M, Kehoe S, Scarrow ER, Strickland LM, Pucci LA, Dhindsa JS, Hunanyan A, La Spada AR, ElMallah MK. Respiratory neuropathology in spinocerebellar ataxia type 7. JCI Insight 2024; 9:e170444. [PMID: 39053472 PMCID: PMC11457860 DOI: 10.1172/jci.insight.170444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2023] [Accepted: 07/12/2024] [Indexed: 07/27/2024] Open
Abstract
Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant neurological disorder caused by deleterious CAG repeat expansion in the coding region of the ataxin 7 gene (polyQ-ataxin-7). Infantile-onset SCA7 leads to severe clinical manifestation of respiratory distress, but the exact cause of respiratory impairment remains unclear. Using the infantile-SCA7 mouse model, the SCA7266Q/5Q mouse, we examined the impact of pathological polyQ-ataxin-7 on hypoglossal (XII) and phrenic motor units. We identified the transcript profile of the medulla and cervical spinal cord and investigated the XII and phrenic nerves and the neuromuscular junctions in the diaphragm and tongue. SCA7266Q/5Q astrocytes showed significant intranuclear inclusions of ataxin-7 in the XII and putative phrenic motor nuclei. Transcriptomic analysis revealed dysregulation of genes involved in amino acid and neurotransmitter transport and myelination. Additionally, SCA7266Q/5Q mice demonstrated blunted efferent output of the XII nerve and demyelination in both XII and phrenic nerves. Finally, there was an increased number of neuromuscular junction clusters with higher expression of synaptic markers in SCA7266Q/5Q mice compared with WT controls. These preclinical findings elucidate the underlying pathophysiology responsible for impaired glial cell function and death leading to dysphagia, aspiration, and respiratory failure in infantile SCA7.
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Affiliation(s)
- Debolina D Biswas
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Yihan Shi
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Léa El Haddad
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Ronit Sethi
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Meredith Huston
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Sean Kehoe
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Evelyn R Scarrow
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Laura M Strickland
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Logan A Pucci
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Justin S Dhindsa
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Ani Hunanyan
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
| | - Albert R La Spada
- Departments of Pathology and Laboratory Medicine, Neurology, Biological Chemistry, and Neurobiology and Behavior, and
- UCI Center for Neurotherapeutics, University of California Irvine, Irvine, California, USA
| | - Mai K ElMallah
- Division of Pulmonary and Sleep Medicine, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina, USA
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4
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Nguyen TH, Vicidomini R, Choudhury SD, Han TH, Maric D, Brody T, Serpe M. scRNA-seq data from the larval Drosophila ventral cord provides a resource for studying motor systems function and development. Dev Cell 2024; 59:1210-1230.e9. [PMID: 38569548 PMCID: PMC11078614 DOI: 10.1016/j.devcel.2024.03.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 12/05/2023] [Accepted: 03/06/2024] [Indexed: 04/05/2024]
Abstract
The Drosophila larval ventral nerve cord (VNC) shares many similarities with the spinal cord of vertebrates and has emerged as a major model for understanding the development and function of motor systems. Here, we use high-quality scRNA-seq, validated by anatomical identification, to create a comprehensive census of larval VNC cell types. We show that the neural lineages that comprise the adult VNC are already defined, but quiescent, at the larval stage. Using fluorescence-activated cell sorting (FACS)-enriched populations, we separate all motor neuron bundles and link individual neuron clusters to morphologically characterized known subtypes. We discovered a glutamate receptor subunit required for basal neurotransmission and homeostasis at the larval neuromuscular junction. We describe larval glia and endorse the general view that glia perform consistent activities throughout development. This census represents an extensive resource and a powerful platform for future discoveries of cellular and molecular mechanisms in repair, regeneration, plasticity, homeostasis, and behavioral coordination.
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Affiliation(s)
| | | | | | | | - Dragan Maric
- Flow and Imaging Cytometry Core, NINDS, NIH, Bethesda, MD 20892, USA
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5
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Akiyama T, Raftery LA, Wharton KA. Bone morphogenetic protein signaling: the pathway and its regulation. Genetics 2024; 226:iyad200. [PMID: 38124338 PMCID: PMC10847725 DOI: 10.1093/genetics/iyad200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 10/27/2023] [Indexed: 12/23/2023] Open
Abstract
In the mid-1960s, bone morphogenetic proteins (BMPs) were first identified in the extracts of bone to have the remarkable ability to induce heterotopic bone. When the Drosophila gene decapentaplegic (dpp) was first identified to share sequence similarity with mammalian BMP2/BMP4 in the late-1980s, it became clear that secreted BMP ligands can mediate processes other than bone formation. Following this discovery, collaborative efforts between Drosophila geneticists and mammalian biochemists made use of the strengths of their respective model systems to identify BMP signaling components and delineate the pathway. The ability to conduct genetic modifier screens in Drosophila with relative ease was critical in identifying the intracellular signal transducers for BMP signaling and the related transforming growth factor-beta/activin signaling pathway. Such screens also revealed a host of genes that encode other core signaling components and regulators of the pathway. In this review, we provide a historical account of this exciting time of gene discovery and discuss how the field has advanced over the past 30 years. We have learned that while the core BMP pathway is quite simple, composed of 3 components (ligand, receptor, and signal transducer), behind the versatility of this pathway lies multiple layers of regulation that ensures precise tissue-specific signaling output. We provide a sampling of these discoveries and highlight many questions that remain to be answered to fully understand the complexity of BMP signaling.
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Affiliation(s)
- Takuya Akiyama
- Department of Biology, Rich and Robin Porter Cancer Research Center, The Center for Genomic Advocacy, Indiana State University, Terre Haute, IN 47809, USA
| | - Laurel A Raftery
- School of Life Sciences, University of Nevada, 4505 S. Maryland Parkway, Las Vegas, NV 89154, USA
| | - Kristi A Wharton
- Department of Molecular Biology, Cell Biology, and Biochemistry, Carney Institute for Brain Science, Brown University, Providence, RI 02912, USA
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6
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Vicidomini R, Serpe M. Local BMP signaling: A sensor for synaptic activity that balances synapse growth and function. Curr Top Dev Biol 2022; 150:211-254. [PMID: 35817503 PMCID: PMC11102767 DOI: 10.1016/bs.ctdb.2022.04.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Synapse development is coordinated by intercellular communication between the pre- and postsynaptic compartments, and by neuronal activity itself. In flies as in vertebrates, neuronal activity induces input-specific changes in the synaptic strength so that the entire circuit maintains stable function in the face of many challenges, including changes in synapse number and strength. But how do neurons sense synapse activity? In several studies carried out using the Drosophila neuromuscular junction (NMJ), we demonstrated that local BMP signaling provides an exquisite sensor for synapse activity. Here we review the main features of this exquisite sensor and discuss its functioning beyond monitoring the synapse activity but rather as a key controller that operates in coordination with other BMP signaling pathways to balance synapse growth, maturation and function.
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Affiliation(s)
- Rosario Vicidomini
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States
| | - Mihaela Serpe
- Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States.
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7
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Nguyen TH, Han TH, Newfeld SJ, Serpe M. Selective Disruption of Synaptic BMP Signaling by a Smad Mutation Adjacent to the Highly Conserved H2 Helix. Genetics 2020; 216:159-175. [PMID: 32737119 PMCID: PMC7463279 DOI: 10.1534/genetics.120.303484] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Accepted: 07/16/2020] [Indexed: 01/08/2023] Open
Abstract
Bone morphogenetic proteins (BMPs) shape normal development and function via canonical and noncanonical signaling pathways. BMPs initiate canonical signaling by binding to transmembrane receptors that phosphorylate Smad proteins and induce their translocation into the nucleus and regulation of target genes. Phosphorylated Smads also accumulate at cellular junctions, but this noncanonical, local BMP signaling modality remains less defined. We have recently reported that phosphorylated Smad (pMad in Drosophila) accumulates at synaptic junctions in protein complexes with genetically distinct composition and regulation. Here, we examined a wide collection of DrosophilaMad alleles and searched for molecular features relevant to pMad accumulation at synaptic junctions. We found that strong Mad alleles generally disrupt both synaptic and nuclear pMad, whereas moderate Mad alleles have a wider range of phenotypes and can selectively impact different BMP signaling pathways. Interestingly, regulatory Mad mutations reveal that synaptic pMad appears to be more sensitive to a net reduction in Mad levels than nuclear pMad. Importantly, a previously uncharacterized allele, Mad8 , showed markedly reduced synaptic pMad but only moderately diminished nuclear pMad. The postsynaptic composition and electrophysiological properties of Mad8 neuromuscular junctions (NMJs) were also altered. Using biochemical approaches, we examined how a single point mutation in Mad8 could influence the Mad-receptor interface and identified a key motif, the H2 helix. Our study highlights the biological relevance of Smad-dependent, synaptic BMP signaling and uncovers a highly conserved structural feature of Smads, critical for normal development and function.
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Affiliation(s)
- Tho Huu Nguyen
- Section on Cellular Communication, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892
| | - Tae Hee Han
- Section on Cellular Communication, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892
| | - Stuart J Newfeld
- School of Life Sciences, Arizona State University, Tempe, Arizona 85287-4501
| | - Mihaela Serpe
- Section on Cellular Communication, Eunice Kennedy Shiver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892
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8
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BMP-dependent synaptic development requires Abi-Abl-Rac signaling of BMP receptor macropinocytosis. Nat Commun 2019; 10:684. [PMID: 30737382 PMCID: PMC6368546 DOI: 10.1038/s41467-019-08533-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 01/09/2019] [Indexed: 12/01/2022] Open
Abstract
Retrograde BMP trans-synaptic signaling is essential for synaptic development. Despite the importance of endocytosis-regulated BMP receptor (BMPR) control of this developmental signaling, the mechanism remains unknown. Here, we provide evidence that Abelson interactor (Abi), a substrate for Abl kinase and component of the SCAR/WAVE complex, links Abl and Rac1 GTPase signaling to BMPR macropinocytosis to restrain BMP-mediated synaptic development. We find that Abi acts downstream of Abl and Rac1, and that BMP ligand Glass bottom boat (Gbb) induces macropinocytosis dependent on Rac1/SCAR signaling, Abl-mediated Abi phosphorylation, and BMPR activation. Macropinocytosis acts as the major internalization route for BMPRs at the synapse in a process driven by Gbb activation and resulting in receptor degradation. Key regulators of macropinocytosis (Rabankyrin and CtBP) control BMPR trafficking to limit BMP trans-synaptic signaling. We conclude that BMP-induced macropinocytosis acts as a BMPR homeostatic mechanism to regulate BMP-mediated synaptic development. BMP ligands act as retrograde signalling molecules to regulate presynaptic development, and regulation of BMP receptors by endocytosis may be an important component of this signalling pathway. Here, the authors show that Abi-mediated macropinocytosis of BMP receptors in Drosophila larva and contributes to neuromuscular development.
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9
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Heo K, Nahm M, Lee MJ, Kim YE, Ki CS, Kim SH, Lee S. The Rap activator Gef26 regulates synaptic growth and neuronal survival via inhibition of BMP signaling. Mol Brain 2017; 10:62. [PMID: 29282074 PMCID: PMC5745669 DOI: 10.1186/s13041-017-0342-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 12/12/2017] [Indexed: 12/24/2022] Open
Abstract
In Drosophila, precise regulation of BMP signaling is essential for normal synaptic growth at the larval neuromuscular junction (NMJ) and neuronal survival in the adult brain. However, the molecular mechanisms underlying fine-tuning of BMP signaling in neurons remain poorly understood. We show that loss of the Drosophila PDZ guanine nucleotide exchange factor Gef26 significantly increases synaptic growth at the NMJ and enhances BMP signaling in motor neurons. We further show that Gef26 functions upstream of Rap1 in motor neurons to restrain synaptic growth. Synaptic overgrowth in gef26 or rap1 mutants requires BMP signaling, indicating that Gef26 and Rap1 regulate synaptic growth via inhibition of BMP signaling. We also show that Gef26 is involved in the endocytic downregulation of surface expression of the BMP receptors thickveins (Tkv) and wishful thinking (Wit). Finally, we demonstrate that loss of Gef26 also induces progressive brain neurodegeneration through Rap1- and BMP signaling-dependent mechanisms. Taken together, these results suggest that the Gef26-Rap1 signaling pathway regulates both synaptic growth and neuronal survival by controlling BMP signaling.
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Affiliation(s)
- Keunjung Heo
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, 08826, South Korea.,Department of Cell & Developmental Biology, Dental Research Institute, Seoul National University, Seoul, 03080, South Korea
| | - Minyeop Nahm
- Department of Neurology, Hanyang University College of Medicine, Seoul, 04763, South Korea
| | - Min-Jung Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, 08826, South Korea.,Department of Cell & Developmental Biology, Dental Research Institute, Seoul National University, Seoul, 03080, South Korea
| | - Young-Eun Kim
- Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, 06351, South Korea
| | - Chang-Seok Ki
- Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, 06351, South Korea
| | - Seung Hyun Kim
- Department of Neurology, Hanyang University College of Medicine, Seoul, 04763, South Korea
| | - Seungbok Lee
- Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, 08826, South Korea.
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10
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Shilts J, Broadie K. Secreted tissue inhibitor of matrix metalloproteinase restricts trans-synaptic signaling to coordinate synaptogenesis. J Cell Sci 2017; 130:2344-2358. [PMID: 28576972 DOI: 10.1242/jcs.200808] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 05/29/2017] [Indexed: 12/20/2022] Open
Abstract
Synaptogenesis is coordinated by trans-synaptic signals that traverse the specialized synaptomatrix between presynaptic and postsynaptic cells. Matrix metalloproteinase (Mmp) activity sculpts this environment, balanced by secreted tissue inhibitors of Mmp (Timp). Here, we use the simplified Drosophila melanogaster matrix metalloproteome to test the consequences of eliminating all Timp regulatory control of Mmp activity at the neuromuscular junction (NMJ). Using in situ zymography, we find Timp limits Mmp activity at the NMJ terminal and shapes extracellular proteolytic dynamics surrounding individual synaptic boutons. In newly generated timp null mutants, NMJs exhibit architectural overelaboration with supernumerary synaptic boutons. With cell-targeted RNAi and rescue studies, we find that postsynaptic Timp limits presynaptic architecture. Functionally, timp null mutants exhibit compromised synaptic vesicle cycling, with activity that is lower in amplitude and fidelity. NMJ defects manifest in impaired locomotor function. Mechanistically, we find that Timp limits BMP trans-synaptic signaling and the downstream synapse-to-nucleus signal transduction. Pharmacologically restoring Mmp inhibition in timp null mutants corrects bone morphogenetic protein (BMP) signaling and synaptic properties. Genetically restoring BMP signaling in timp null mutants corrects NMJ structure and motor function. Thus, Timp inhibition of Mmp proteolytic activity restricts BMP trans-synaptic signaling to coordinate synaptogenesis.
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Affiliation(s)
- Jarrod Shilts
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA
| | - Kendal Broadie
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37235, USA
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11
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Deshpande M, Feiger Z, Shilton AK, Luo CC, Silverman E, Rodal AA. Role of BMP receptor traffic in synaptic growth defects in an ALS model. Mol Biol Cell 2016; 27:2898-910. [PMID: 27535427 PMCID: PMC5042577 DOI: 10.1091/mbc.e16-07-0519] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Accepted: 08/03/2016] [Indexed: 12/12/2022] Open
Abstract
In a Drosophila model of ALS, neuronal defects are associated with altered endosomal traffic of growth factor receptors and loss of growth-promoting signals. Manipulation of an endosomal recycling pathway suppresses these neuronal defects. The findings suggest that rerouting membrane traffic could be therapeutic in ALS. TAR DNA-binding protein 43 (TDP-43) is genetically and functionally linked to amyotrophic lateral sclerosis (ALS) and regulates transcription, splicing, and transport of thousands of RNA targets that function in diverse cellular pathways. In ALS, pathologically altered TDP-43 is believed to lead to disease by toxic gain-of-function effects on RNA metabolism, as well as by sequestering endogenous TDP-43 and causing its loss of function. However, it is unclear which of the numerous cellular processes disrupted downstream of TDP-43 dysfunction lead to neurodegeneration. Here we found that both loss and gain of function of TDP-43 in Drosophila cause a reduction of synaptic growth–promoting bone morphogenic protein (BMP) signaling at the neuromuscular junction (NMJ). Further, we observed a shift of BMP receptors from early to recycling endosomes and increased mobility of BMP receptor–containing compartments at the NMJ. Inhibition of the recycling endosome GTPase Rab11 partially rescued TDP-43–induced defects in BMP receptor dynamics and distribution and suppressed BMP signaling, synaptic growth, and larval crawling defects. Our results indicate that defects in receptor traffic lead to neuronal dysfunction downstream of TDP-43 misregulation and that rerouting receptor traffic may be a viable strategy for rescuing neurological impairment.
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Affiliation(s)
| | - Zachary Feiger
- Department of Biology, Brandeis University, Waltham, MA 02453
| | | | - Christina C Luo
- Department of Biology, Brandeis University, Waltham, MA 02453
| | - Ethan Silverman
- Department of Biology, Brandeis University, Waltham, MA 02453
| | - Avital A Rodal
- Department of Biology, Brandeis University, Waltham, MA 02453
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12
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Beckwith EJ, Ceriani MF. Communication between circadian clusters: The key to a plastic network. FEBS Lett 2015; 589:3336-42. [PMID: 26297822 DOI: 10.1016/j.febslet.2015.08.017] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 08/10/2015] [Accepted: 08/11/2015] [Indexed: 10/23/2022]
Abstract
Drosophila melanogaster is a model organism that has been instrumental in understanding the circadian clock at different levels. A range of studies on the anatomical and neurochemical properties of clock neurons in the fly led to a model of interacting neural circuits that control circadian behavior. Here we focus on recent research on the dynamics of the multiple communication pathways between clock neurons, and, particularly, on how the circadian timekeeping system responds to changes in environmental conditions. It is increasingly clear that the fly clock employs multiple signalling cues, such as neuropeptides, fast neurotransmitters, and other signalling molecules, in the dynamic interplay between neuronal clusters. These neuronal groups seem to interact in a plastic fashion, e.g., rearranging their hierarchy in response to changing environmental conditions. A picture is emerging supporting that these dynamic mechanisms are in place to provide an optimal balance between flexibility and an extraordinary accuracy.
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Affiliation(s)
- Esteban J Beckwith
- Department of Life Sciences, Imperial College, London SW7 2AZ, United Kingdom.
| | - M Fernanda Ceriani
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires 1405 BWE, Argentina.
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13
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The translational regulator Cup controls NMJ presynaptic terminal morphology. Mol Cell Neurosci 2015; 67:126-36. [PMID: 26102195 DOI: 10.1016/j.mcn.2015.06.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2014] [Revised: 06/14/2015] [Accepted: 06/18/2015] [Indexed: 02/02/2023] Open
Abstract
During oogenesis and early embryonic development in Drosophila, translation of proteins from maternally deposited mRNAs is tightly controlled. We and others have previously shown that translational regulatory proteins that function during oogenesis also have essential roles in the nervous system. Here we examine the role of Cup in neuromuscular system development. Maternal Cup controls translation of localized mRNAs encoding the Oskar and Nanos proteins and binds to the general translation initiation factor eIF4E. In this paper, we show that zygotic Cup protein is localized to presynaptic terminals at larval neuromuscular junctions (NMJs). cup mutant NMJs have strong phenotypes characterized by the presence of small clustered boutons called satellite boutons. They also exhibit an increase in the frequency of spontaneous glutamate release events (mEPSPs). Reduction of eIF4E expression synergizes with partial loss of Cup expression to produce satellite bouton phenotypes. The presence of satellite boutons is often associated with increases in retrograde bone morphogenetic protein (BMP) signaling, and we show that synaptic BMP signaling is elevated in cup mutants. cup genetically interacts with two genes, EndoA and Dap160, that encode proteins involved in endocytosis that are also neuronal modulators of the BMP pathway. Endophilin protein, encoded by the EndoA gene, is downregulated in a cup mutant. Our results are consistent with a model in which Cup and eIF4E work together to ensure efficient localization and translation of endocytosis proteins in motor neurons and control the strength of the retrograde BMP signal.
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14
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Suvarna Y, Maity N, Shivamurthy MC. Emerging Trends in Retrograde Signaling. Mol Neurobiol 2015; 53:2572-8. [PMID: 26081150 DOI: 10.1007/s12035-015-9280-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Accepted: 06/02/2015] [Indexed: 01/09/2023]
Abstract
Retrograde signaling is defined as the signaling events leading from the plastids to the nucleus in plants and across the chemical synapse, from the postsynaptic neuron to the presynaptic neuron in animals. The discovery of various retrograde messengers has opened many avenues and clouds of thoughts as to the role of retrograde signaling. They have been implicated particularly in long-term potentiation (LTP) and synaptic plasticity. But the basic assumptions about retrograde signaling have not been studied upon for many years. This review focuses on established facts and hypothesis put forward in retrograde signaling.
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Affiliation(s)
- Yashasvi Suvarna
- Department of Pharmacology, M. S. Ramaiah Medical College, Bangalore, Karnataka, India.
| | - Nivedita Maity
- Department of Pharmacology, M. S. Ramaiah Medical College, Bangalore, Karnataka, India
| | - M C Shivamurthy
- Department of Pharmacology, M. S. Ramaiah Medical College, Bangalore, Karnataka, India
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15
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Kim YJ, Igiesuorobo O, Ramos CI, Bao H, Zhang B, Serpe M. Prodomain removal enables neto to stabilize glutamate receptors at the Drosophila neuromuscular junction. PLoS Genet 2015; 11:e1004988. [PMID: 25723514 PMCID: PMC4344203 DOI: 10.1371/journal.pgen.1004988] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Accepted: 01/06/2015] [Indexed: 11/24/2022] Open
Abstract
Stabilization of neurotransmitter receptors at postsynaptic specializations is a key step in the assembly of functional synapses. Drosophila Neto (Neuropillin and Tolloid-like protein) is an essential auxiliary subunit of ionotropic glutamate receptor (iGluR) complexes required for the iGluRs clustering at the neuromuscular junction (NMJ). Here we show that optimal levels of Neto are crucial for stabilization of iGluRs at synaptic sites and proper NMJ development. Genetic manipulations of Neto levels shifted iGluRs distribution to extrajunctional locations. Perturbations in Neto levels also produced small NMJs with reduced synaptic transmission, but only Neto-depleted NMJs showed diminished postsynaptic components. Drosophila Neto contains an inhibitory prodomain that is processed by Furin1-mediated limited proteolysis. neto null mutants rescued with a Neto variant that cannot be processed have severely impaired NMJs and reduced iGluRs synaptic clusters. Unprocessed Neto retains the ability to engage iGluRs in vivo and to form complexes with normal synaptic transmission. However, Neto prodomain must be removed to enable iGluRs synaptic stabilization and proper postsynaptic differentiation. Synapse development is initiated by genetic programs, but is coordinated by neuronal activity, by communication between the pre- and postsynaptic compartments, and by cellular signals that integrate the status of the whole organisms and its developmental progression. The molecular mechanisms underlining these processes are poorly understood. In particular, how neurotransmitter receptors are recruited and stabilized at central synapses remain the subject of intense research. The Drosophila NMJ is a glutamatergic synapse similar in composition and physiology with mammalian central excitatory synapses. Like mammals, Drosophila utilizes auxiliary subunit(s) to modulate the formation and function of glutamatergic synapses. We have previously reported that Neto is an auxiliary protein essential for functional glutamate receptors and for organization of postsynaptic specializations. Here we report that synapse assembly and NMJ development are exquisitely sensitive to postsynaptic Neto levels. Furthermore, we show that Neto activity is controlled by Furin-type proteases, which regulate the processing and maturation of many developmentally important proteins, from growth factors and neuropeptides to extracellular matrix components. Such concerted control may serve to coordinate synapse assembly with synapse growth and developmental progression.
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Affiliation(s)
- Young-Jun Kim
- Program in Cellular Regulation and Metabolism, NICHD, NIH, Bethesda, Maryland, United States of America
| | - Oghomwen Igiesuorobo
- Program in Cellular Regulation and Metabolism, NICHD, NIH, Bethesda, Maryland, United States of America
| | - Cathy I. Ramos
- Program in Cellular Regulation and Metabolism, NICHD, NIH, Bethesda, Maryland, United States of America
| | - Hong Bao
- Division of Biological Sciences, University of Missouri, Columbia, Missouri, United States of America
| | - Bing Zhang
- Division of Biological Sciences, University of Missouri, Columbia, Missouri, United States of America
| | - Mihaela Serpe
- Program in Cellular Regulation and Metabolism, NICHD, NIH, Bethesda, Maryland, United States of America
- * E-mail:
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16
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Homma M, Nagashima S, Fukuda T, Yanagi S, Miyakawa H, Suzuki E, Morimoto T. Downregulation of Centaurin gamma1A increases synaptic transmission at Drosophila larval neuromuscular junctions. Eur J Neurosci 2014; 40:3158-70. [PMID: 25074496 DOI: 10.1111/ejn.12681] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 06/24/2014] [Accepted: 06/25/2014] [Indexed: 12/22/2022]
Abstract
Adequate regulation of synaptic transmission is critical for appropriate neural circuit functioning. Although a number of molecules involved in synaptic neurotransmission have been identified, the molecular mechanisms regulating neurotransmission are not fully understood. Here, we focused on Centaurin gamma1A (CenG1A) and examined its role in synaptic transmission regulation using Drosophila larval neuromuscular junctions. CenG1A is a member of the Centaurin family, which contains Pleckstrin homology, ADP ribosylation factor GTPase-activating protein, and ankyrin repeat domains. Due to the existence of these functional domains, CenG1A is proposed to be involved in the process of synaptic release; however, no evidence for this has been found to date. In this study, we investigated the potential role for CenG1A in the process of synaptic release by performing intracellular recordings in larval muscle cells. We found that neurotransmitter release from presynaptic cells was enhanced in cenG1A mutants. This effect was also observed in larvae with reduced CenG1A function in either presynaptic or postsynaptic cells. In addition, we revealed that suppressing CenG1A function in postsynaptic muscle cells led to an increase in the probability of neurotransmitter release, whereas its suppression in presynaptic neurons led to an increase in neurotransmitter release probability and an increase in the number of synaptic vesicles. These results suggested that CenG1A functions at both presynaptic and postsynaptic sites as a negative regulator of neurotransmitter release. Our study provided evidence for a key role of CenG1A in proper synaptic transmission at neuromuscular junctions.
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Affiliation(s)
- Mizuho Homma
- Laboratory of Cellular Neurobiology, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachiouji, Tokyo, Japan
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17
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Etherington SJ, Johnstone VPA, Everett AW. Modulation of synaptic vesicle exocytosis in muscle-dependent long-term depression at the amphibian neuromuscular junction. PLoS One 2014; 9:e87174. [PMID: 24489862 PMCID: PMC3904971 DOI: 10.1371/journal.pone.0087174] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Accepted: 12/20/2013] [Indexed: 11/24/2022] Open
Abstract
We have labeled recycling synaptic vesicles at the somatic Bufo marinus neuromuscular junction with the styryl dye FM2-10 and provide direct evidence for refractoriness of exocytosis associated with a muscle activity-dependent form of long-term depression (LTD) at this synapse. FM2-10 dye unloading experiments demonstrated that the rate of vesicle exocytosis from the release ready pool (RRP) of vesicles was more than halved in the LTD (induced by 20 min of low frequency stimulation). Recovery from LTD, observed as a partial recovery of nerve-evoked muscle twitch amplitude, was accompanied by partial recovery of the refractoriness of RRP exocytosis. Unexpectedly, paired pulse plasticity, another routinely used indicator of presynaptic forms of synaptic plasticity, was unchanged in the LTD. We conclude that the LTD induces refractoriness of the neuromuscular vesicle release machinery downstream of presynaptic calcium entry.
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Affiliation(s)
- Sarah J. Etherington
- School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Perth, Western Australia, Australia
- School of Veterinary and Life Sciences, Murdoch University, Perth, Western Australia, Australia
- * E-mail:
| | - Victoria P. A. Johnstone
- School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Perth, Western Australia, Australia
- Department of Physiology, Monash University, Clayton, Victoria, Australia
| | - Alan W. Everett
- School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Perth, Western Australia, Australia
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18
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New approaches for studying synaptic development, function, and plasticity using Drosophila as a model system. J Neurosci 2013; 33:17560-8. [PMID: 24198346 DOI: 10.1523/jneurosci.3261-13.2013] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The fruit fly Drosophila melanogaster has been established as a premier experimental model system for neuroscience research. These organisms are genetically tractable, yet their nervous systems are sufficiently complex to study diverse processes that are conserved across metazoans, including neural cell fate determination and migration, axon guidance, synaptogenesis and function, behavioral neurogenetics, and responses to neuronal injury. For several decades, Drosophila neuroscientists have taken advantage of a vast toolkit of genetic and molecular techniques to reveal fundamental principles of neuroscience illuminating to all systems, including the first behavioral mutants from Seymour Benzer's pioneering work in the 1960s and 1970s, the cloning of the first potassium channel in the 1980s, and the identification of the core genes that orchestrate axon guidance and circadian rhythms in the 1990s. Over the past decade, new tools and innovations in genetic, imaging, and electrophysiological technologies have enabled the visualization, in vivo, of dynamic processes in synapses with unprecedented resolution. We will review some of the fresh insights into synaptic development, function, and plasticity that have recently emerged in Drosophila with an emphasis on the unique advantages of this model system.
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Sulkowski M, Kim YJ, Serpe M. Postsynaptic glutamate receptors regulate local BMP signaling at the Drosophila neuromuscular junction. Development 2013; 141:436-47. [PMID: 24353060 DOI: 10.1242/dev.097758] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Effective communication between pre- and postsynaptic compartments is required for proper synapse development and function. At the Drosophila neuromuscular junction (NMJ), a retrograde BMP signal functions to promote synapse growth, stability and homeostasis and coordinates the growth of synaptic structures. Retrograde BMP signaling triggers accumulation of the pathway effector pMad in motoneuron nuclei and at synaptic termini. Nuclear pMad, in conjunction with transcription factors, modulates the expression of target genes and instructs synaptic growth; a role for synaptic pMad remains to be determined. Here, we report that pMad signals are selectively lost at NMJ synapses with reduced postsynaptic sensitivities. Despite this loss of synaptic pMad, nuclear pMad persisted in motoneuron nuclei, and expression of BMP target genes was unaffected, indicating a specific impairment in pMad production/maintenance at synaptic termini. During development, synaptic pMad accumulation followed the arrival and clustering of ionotropic glutamate receptors (iGluRs) at NMJ synapses. Synaptic pMad was lost at NMJ synapses developing at suboptimal levels of iGluRs and Neto, an auxiliary subunit required for functional iGluRs. Genetic manipulations of non-essential iGluR subunits revealed that synaptic pMad signals specifically correlated with the postsynaptic type-A glutamate receptors. Altering type-A receptor activities via protein kinase A (PKA) revealed that synaptic pMad depends on the activity and not the net levels of postsynaptic type-A receptors. Thus, synaptic pMad functions as a local sensor for NMJ synapse activity and has the potential to coordinate synaptic activity with a BMP retrograde signal required for synapse growth and homeostasis.
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Affiliation(s)
- Mikolaj Sulkowski
- Program in Cellular Regulation and Metabolism, NICHD, NIH, Bethesda, MD 20892, USA
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20
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Beckwith EJ, Gorostiza EA, Berni J, Rezával C, Pérez-Santángelo A, Nadra AD, Ceriani MF. Circadian period integrates network information through activation of the BMP signaling pathway. PLoS Biol 2013; 11:e1001733. [PMID: 24339749 PMCID: PMC3858370 DOI: 10.1371/journal.pbio.1001733] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 10/30/2013] [Indexed: 11/18/2022] Open
Abstract
Circadian pacemaker neurons in the Drosophila brain gather network information through the highly conserved BMP signaling pathway to establish the daily period of locomotor behavior. Living organisms use biological clocks to maintain their internal temporal order and anticipate daily environmental changes. In Drosophila, circadian regulation of locomotor behavior is controlled by ∼150 neurons; among them, neurons expressing the PIGMENT DISPERSING FACTOR (PDF) set the period of locomotor behavior under free-running conditions. To date, it remains unclear how individual circadian clusters integrate their activity to assemble a distinctive behavioral output. Here we show that the BONE MORPHOGENETIC PROTEIN (BMP) signaling pathway plays a crucial role in setting the circadian period in PDF neurons in the adult brain. Acute deregulation of BMP signaling causes period lengthening through regulation of dClock transcription, providing evidence for a novel function of this pathway in the adult brain. We propose that coherence in the circadian network arises from integration in PDF neurons of both the pace of the cell-autonomous molecular clock and information derived from circadian-relevant neurons through release of BMP ligands. The circadian clock controls rhythms in behavior, physiology, and metabolism in all living organisms. The molecular components as well as the neuronal network required to keep this clock running have been identified in several species. In the Drosophila brain this neuronal network is represented by an ensemble of 150 neurons, and among them, those expressing the Pigment Dispersing Factor (PDF) neuropeptide encompass the “central oscillator”—also called master clock as it ensures 24-hour periods—of the fly brain. In this study we show that the widely conserved Bone Morphogenetic Protein (BMP) signaling pathway is present in PDF neurons, and upon adult-specific activation it lengthens the endogenous period of locomotor behavior. We find that period lengthening correlates with delayed accumulation of nuclear PERIOD, a core component of the molecular clock. We also identified a putative DNA binding motif for the BMP pathway nuclear components within the regulatory region of the Clock (Clk) promoter, another core component of the circadian machinery. Interestingly, upon BMP pathway activation endogenous CLK levels are downregulated, thus accounting for the lengthening of the endogenous period. We propose that the endogenous period is a network property commanded by PDF neurons that results from integration of information from both the autonomous molecular clock and the nonautonomous BMP signaling pathway.
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Affiliation(s)
- Esteban J. Beckwith
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
| | - E. Axel Gorostiza
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
| | - Jimena Berni
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
| | - Carolina Rezával
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
| | - Agustín Pérez-Santángelo
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
| | - Alejandro D. Nadra
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, UBA. IQUIBICEN-CONICET, Buenos Aires, Argentina
| | - María Fernanda Ceriani
- Laboratorio de Genética del Comportamiento, Fundación Instituto Leloir, IIB-BA-CONICET, Buenos Aires, Argentina
- * E-mail:
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21
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p21-Activated kinase (PAK) is required for Bone Morphogenetic Protein (BMP)-induced dendritogenesis in cortical neurons. Mol Cell Neurosci 2013; 57:83-92. [PMID: 24141051 DOI: 10.1016/j.mcn.2013.10.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 10/01/2013] [Accepted: 10/08/2013] [Indexed: 01/21/2023] Open
Abstract
Bone Morphogenetic Proteins (BMPs) are crucial for many aspects of the development and differentiation of the nervous system and are important in controlling cytoskeletal remodeling during neuronal morphogenesis. BMPs are TGFβ superfamily members that signal through a heteromeric complex of type I and type II BMP receptors. The BMPRII receptor is particularly important in mediating remodeling of the neuronal cytoskeleton through the activation of BMPRII-bound cytoskeletal regulators, such as LIM Kinase (LIMK). Here, we show that PAK1, a key regulator of diverse neuronal processes and an upstream activator of LIMK, binds to the BMP type I receptor, ALK2. Although, PAK1 is dispensable for activation of the Smad transcriptional mediators, abrogation of PAK1 expression or inhibition of PAK1 activity prevents BMP-induced neurite outgrowth in cultured neuroblastoma cell lines. Moreover, in primary murine embryonic cortical neurons, inhibition of PAK activity blocks BMP7-induced cofilin phosphorylation, prevents remodeling of the actin cytoskeleton and thereby blocks BMP7-induced dendrite formation. Thus, we propose a model in which BMP7 signaling leads to the recruitment of ALK2-bound PAK1 to BMPRII, which binds a downstream regulator of the actin cytoskeleton, LIMK1, and that the BMP receptor complex thereby acts as a scaffold to localize and coordinate actin cytoskeletal remodeling. We propose that this scaffold plays a key role in mediating BMP7-dependent dendritogenesis in primary cortical neurons.
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22
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Teodoro RO, Pekkurnaz G, Nasser A, Higashi-Kovtun ME, Balakireva M, McLachlan IG, Camonis J, Schwarz TL. Ral mediates activity-dependent growth of postsynaptic membranes via recruitment of the exocyst. EMBO J 2013; 32:2039-55. [PMID: 23812009 DOI: 10.1038/emboj.2013.147] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Accepted: 05/28/2013] [Indexed: 11/09/2022] Open
Abstract
Remodelling neuronal connections by synaptic activity requires membrane trafficking. We present evidence for a signalling pathway by which synaptic activity and its consequent Ca(2+) influx activate the small GTPase Ral and thereby recruit exocyst proteins to postsynaptic zones. In accord with the ability of the exocyst to direct delivery of post-Golgi vesicles, constitutively active Ral expressed in Drosophila muscle causes the exocyst to be concentrated in the region surrounding synaptic boutons and consequently enlarges the membrane folds of the postsynaptic plasma membrane (the subsynaptic reticulum, SSR). SSR growth requires Ral and the exocyst component Sec5 and Ral-induced enlargement of these membrane folds does not occur in sec5(-/-) muscles. Chronic changes in synaptic activity influence the plastic growth of this membrane in a manner consistent with activity-dependent activation of Ral. Thus, Ral regulation of the exocyst represents a control point for postsynaptic plasticity. This pathway may also function in mammals as expression of activated RalA in hippocampal neurons increases dendritic spine density in an exocyst-dependent manner and increases Sec5 in spines.
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Affiliation(s)
- Rita O Teodoro
- The F.M. Kirby Neurobiology Center, Department of Neurology, Boston Children's Hospital, Boston, MA, USA.
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Rapid feedback regulation of synaptic efficacy during high-frequency activity at the Drosophila larval neuromuscular junction. Proc Natl Acad Sci U S A 2013; 110:9142-7. [PMID: 23674684 DOI: 10.1073/pnas.1221314110] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
High-frequency firing of neurons depresses transmitter release at many synapses. At the glutamatergic synapse of the Drosophila larval neuromuscular junction, we find that presynaptic depression is modulated by postsynaptic ionotropic glutamate receptor (iGluR) activity. Although basal release at low frequency was insensitive to postsynaptic iGluR activity, recovery from depression elicited by high-frequency presynaptic trains decreased with partial block of native iGluRs. Moreover, recovery from depression increased with optical activation of the light-gated mammalian iGluR6 (LiGluR) expressed postsynaptically. The enhancement of recovery from depression occurred within 2 min of optical activation of LiGluR and persisted for minutes after optical deactivation. This effect depended on cAMP-dependent presynaptic recruitment of vesicles from the reserve pool. Our findings reveal a unique dimension to postsynaptic iGluR activity: fast retrograde signaling that preserves transmission efficacy during high-frequency presynaptic firing.
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Menon KP, Carrillo RA, Zinn K. Development and plasticity of the Drosophila larval neuromuscular junction. WILEY INTERDISCIPLINARY REVIEWS-DEVELOPMENTAL BIOLOGY 2013; 2:647-70. [PMID: 24014452 DOI: 10.1002/wdev.108] [Citation(s) in RCA: 163] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The Drosophila larval neuromuscular system is relatively simple, containing only 32 motor neurons in each abdominal hemisegment, and its neuromuscular junctions (NMJs) have been studied extensively. NMJ synapses exhibit developmental and functional plasticity while displaying stereotyped connectivity. Drosophila Type I NMJ synapses are glutamatergic, while the vertebrate NMJ uses acetylcholine as its primary neurotransmitter. The larval NMJ synapses use ionotropic glutamate receptors (GluRs) that are homologous to AMPA-type GluRs in the mammalian brain, and they have postsynaptic scaffolds that resemble those found in mammalian postsynaptic densities. These features make the Drosophila neuromuscular system an excellent genetic model for the study of excitatory synapses in the mammalian central nervous system. The first section of the review presents an overview of NMJ development. The second section describes genes that regulate NMJ development, including: (1) genes that positively and negatively regulate growth of the NMJ, (2) genes required for maintenance of NMJ bouton structure, (3) genes that modulate neuronal activity and alter NMJ growth, (4) genes involved in transsynaptic signaling at the NMJ. The third section describes genes that regulate acute plasticity, focusing on translational regulatory mechanisms. As this review is intended for a developmental biology audience, it does not cover NMJ electrophysiology in detail, and does not review genes for which mutations produce only electrophysiological but no structural phenotypes.
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Affiliation(s)
- Kaushiki P Menon
- Broad Center, Division of Biology, California Institute of Technology, Pasadena, CA, USA
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25
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Benavente F, Pinto C, Parada M, Henríquez JP, Osses N. Bone morphogenetic protein 2 inhibits neurite outgrowth of motor neuron-like NSC-34 cells and up-regulates its type II receptor. J Neurochem 2012; 122:594-604. [PMID: 22612292 DOI: 10.1111/j.1471-4159.2012.07795.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bone morphogenetic proteins (BMPs) regulate several aspects of neuronal behavior. For instance, BMP-2 has the ability to modulate, either positively or negatively, the outgrowth of neuronal processes in diverse cell types. In Drosophila motor neurons, the BMP type II receptor (BMPRII) homolog wishful thinking plays crucial roles on neuromuscular synaptogenesis signaling through Smad-dependent and Smad-independent pathways. However, a role for BMP signaling at the vertebrate neuromuscular junction has not been addressed. Herein, we have analyzed the expression of BMPRII and the effect of BMP-2 during the morphological differentiation of motor neuron-like NSC-34 cells. Our data indicate that BMPRII is up-regulated and becomes accumulated in somas and growth cones upon motor neuronal differentiation. BMP-2 inhibits the differentiation of NSC-34 cells, an effect that correlates with activation of a Smad-dependent pathway, induction of the inhibitory Id1 transcription factor, and down-regulation of the neurogenic factor Mash1. BMP-2 also activates effectors of Smad-independent pathways. Remarkably, BMP-2 treatment significantly increases the expression of BMPRII. Our findings provide the first evidence to suggest a role for BMP pathways on the differentiation of motor neurons leading to successful assembly and/or regeneration of the vertebrate neuromuscular synapse.
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Affiliation(s)
- Francisca Benavente
- Instituto de Química, Facultad de Ciencias, Pontificia Universidad Católica de Valparaíso, Chile
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26
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Glutamate receptors in synaptic assembly and plasticity: case studies on fly NMJs. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 970:3-28. [PMID: 22351049 DOI: 10.1007/978-3-7091-0932-8_1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The molecular and cellular mechanisms that control the composition and functionality of ionotropic glutamate receptors may be considered as most important "set screws" for adjusting excitatory transmission in the course of developmental and experience-dependent changes within neural networks. The Drosophila larval neuromuscular junction has emerged as one important invertebrate model system to study the formation, maintenance, and plasticity-related remodeling of glutamatergic synapses in vivo. By exploiting the unique genetic accessibility of this organism combined with diverse tools for manipulation and analysis including electrophysiology and state of the art imaging, considerable progress has been made to characterize the role of glutamate receptors during the orchestration of junctional development, synaptic activity, and synaptogenesis. Following an introduction to basic features of this model system, we will mainly focus on conceptually important findings such as the selective impact of glutamate receptor subtypes on the formation of new synapses, the coordination of presynaptic maturation and receptor subtype composition, the role of nonvesicularly released glutamate on the synaptic localization of receptors, or the homeostatic feedback of receptor functionality on presynaptic transmitter release.
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27
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Postsynaptic TRPC1 function contributes to BDNF-induced synaptic potentiation at the developing neuromuscular junction. J Neurosci 2011; 31:14754-62. [PMID: 21994391 DOI: 10.1523/jneurosci.3599-11.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Brain-derived neurotrophic factor (BDNF) induces synaptic potentiation at both neuromuscular junctions (NMJs) and synapses of the CNS through a Ca2+ -dependent pathway. The molecular mechanism underlying BDNF-induced synaptic potentiation, especially the regulation of Ca2+ dynamics, is not well understood. Using the Xenopus NMJ in culture as a model system, we show that pharmacological inhibition or morpholino-mediated knockdown of Xenopus TRPC1 (XTRPC1) significantly attenuated the BDNF-induced potentiation of the frequency of spontaneous synaptic responses at the NMJ. Functionally, XTRPC1 was required specifically in postsynaptic myocytes for BDNF-induced Ca2+ elevation and full synaptic potentiation at the NMJ, suggesting a previously underappreciated postsynaptic function of Ca2+ signaling in neurotrophin-induced synaptic plasticity, in addition to its well established role at presynaptic sites. Mechanistically, blockade of the p75 neurotrophin receptor abolished BDNF-induced postsynaptic Ca2+ elevation and restricted BDNF-induced synaptic potentiation, while knockdown of the TrkB receptor in postsynaptic myocytes had no effect. Our study suggests that BDNF-induced synaptic potentiation involves coordinated presynaptic and postsynaptic responses and identifies TRPC1 as a molecular mediator for postsynaptic Ca2+ elevation required for BDNF-induced synaptic plasticity.
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28
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Henríquez JP, Krull CE, Osses N. The Wnt and BMP families of signaling morphogens at the vertebrate neuromuscular junction. Int J Mol Sci 2011; 12:8924-46. [PMID: 22272112 PMCID: PMC3257109 DOI: 10.3390/ijms12128924] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2011] [Revised: 11/18/2011] [Accepted: 11/22/2011] [Indexed: 11/16/2022] Open
Abstract
The neuromuscular junction has been extensively employed in order to identify crucial determinants of synaptogenesis. At the vertebrate neuromuscular synapse, extracellular matrix and signaling proteins play stimulatory and inhibitory roles on the assembly of functional synapses. Studies in invertebrate species have revealed crucial functions of early morphogens during the assembly and maturation of the neuromuscular junction. Here, we discuss growing evidence addressing the function of Wnt and Bone morphogenetic protein (BMP) signaling pathways at the vertebrate neuromuscular synapse. We focus on the emerging role of Wnt proteins as positive and negative regulators of postsynaptic differentiation. We also address the possible involvement of BMP pathways on motor neuron behavior for the assembly and/or regeneration of the neuromuscular junction.
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Affiliation(s)
- Juan P. Henríquez
- Laboratory of Developmental Neurobiology (LDNB), Department of Cell Biology, Faculty of Biological Sciences, University of Concepcion, and CMA Bio-Bio, Concepcion 4089100, Chile
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +56-41-220-4531; Fax: +56-41-224-5975
| | - Catherine E. Krull
- University of Michigan, 5211 Dental, Ann Arbor, Michigan, MI 48109, USA; E-Mail:
| | - Nelson Osses
- Institute of Chemistry, Faculty of Sciences, Pontificia Universidad Católica de Valparaíso, Valparaiso 2340025, Chile; E-Mail:
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29
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Veverytsa L, Allan DW. Retrograde BMP signaling controls Drosophila behavior through regulation of a peptide hormone battery. Development 2011; 138:3147-57. [PMID: 21750027 DOI: 10.1242/dev.064105] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Retrograde BMP signaling in neurons plays conserved roles in synaptic efficacy and subtype-specific gene expression. However, a role for retrograde BMP signaling in the behavioral output of neuronal networks has not been established. Insect development proceeds through a series of stages punctuated by ecdysis, a complex patterned behavior coordinated by a dedicated neuronal network. In Drosophila, larval ecdysis sheds the old cuticle between larval stages, and pupal ecdysis everts the head and appendages to their adult external position during metamorphosis. Here, we found that mutants of the type II BMP receptor wit exhibited a defect in the timing of larval ecdysis and in the completion of pupal ecdysis. These phenotypes largely recapitulate those previously observed upon ablation of CCAP neurons, an integral subset of the ecdysis neuronal network. Here, we establish that retrograde BMP signaling in only the efferent subset of CCAP neurons (CCAP-ENs) is required to cell-autonomously upregulate expression of the peptide hormones CCAP, Mip and Bursicon β. In wit mutants, restoration of wit exclusively in CCAP neurons significantly rescued peptide hormone expression and ecdysis phenotypes. Moreover, combinatorial restoration of peptide hormone expression in CCAP neurons in wit mutants also significantly rescued wit ecdysis phenotypes. Collectively, our data demonstrate a novel role for retrograde BMP signaling in maintaining the behavioral output of a neuronal network and uncover the underlying cellular and gene regulatory substrates.
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Affiliation(s)
- Lyubov Veverytsa
- Department of Cellular and Physiological Sciences, Room 2420 Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC V6T 1Z3, Canada
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Rodal AA, Blunk AD, Akbergenova Y, Jorquera RA, Buhl LK, Littleton JT. A presynaptic endosomal trafficking pathway controls synaptic growth signaling. ACTA ACUST UNITED AC 2011; 193:201-17. [PMID: 21464232 PMCID: PMC3082179 DOI: 10.1083/jcb.201009052] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Association of Nwk with SNX16 promotes down-regulation of synaptic growth signaling at the interface between early and recycling endosomes. Structural remodeling of synapses in response to growth signals leads to long-lasting alterations in neuronal function in many systems. Synaptic growth factor receptors alter their signaling properties during transit through the endocytic pathway, but the mechanisms controlling cargo traffic between endocytic compartments remain unclear. Nwk (Nervous Wreck) is a presynaptic F-BAR/SH3 protein that regulates synaptic growth signaling in Drosophila melanogaster. In this paper, we show that Nwk acts through a physical interaction with sorting nexin 16 (SNX16). SNX16 promotes synaptic growth signaling by activated bone morphogenic protein receptors, and live imaging in neurons reveals that SNX16-positive early endosomes undergo transient interactions with Nwk-containing recycling endosomes. We identify an alternative signal termination pathway in the absence of Snx16 that is controlled by endosomal sorting complex required for transport (ESCRT)–mediated internalization of receptors into the endosomal lumen. Our results define a presynaptic trafficking pathway mediated by SNX16, NWK, and the ESCRT complex that functions to control synaptic growth signaling at the interface between endosomal compartments.
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Affiliation(s)
- Avital A Rodal
- Department of Biology, The Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
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The RhoGAP crossveinless-c interacts with Dystrophin and is required for synaptic homeostasis at the Drosophila neuromuscular junction. J Neurosci 2011; 31:492-500. [PMID: 21228159 DOI: 10.1523/jneurosci.4732-10.2011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Duchenne muscular dystrophy is caused by mutations in the Dystrophin gene and is characterized by muscle degeneration and the occurrence of mental deficits in a significant number of patients. Although Dystrophin and its closely related ortholog Utrophin are present at a variety of synapses, little is known about their roles in the nervous system. Previously, we reported that absence of postsynaptic Dystrophin from the Drosophila neuromuscular junction (NMJ) disrupts synaptic homeostasis, resulting in increased stimulus-evoked neurotransmitter release. Here, we show that RhoGAP crossveinless-c (cv-c), a negative regulator of Rho GTPase signaling pathways, genetically interacts with Dystrophin. Electrophysiological characterization of the cv-c-deficient NMJ and the use of presynaptic- and postsynaptic-specific transgenic rescue versus RNA interference reveal that the absence of postsynaptic cv-c results in elevated evoked neurotransmitter release. The cv-c mutant NMJ exhibits an increased number of presynaptic neurotransmitter release sites and higher probability of vesicle release without apparent changes in postsynaptic glutamate receptor numbers or function. Moreover, we find that decreasing expression of the Rho GTPase Cdc42 suppresses the high neurotransmitter release in the cv-c and Dystrophin mutants, suggesting that Cdc42 is a substrate of Cv-c. These results indicate that Dystrophin and the Rho GTPase signaling pathway likely interact at the postsynaptic side of the NMJ to maintain synaptic homeostasis. The absence of this postsynaptic pathway results in presynaptic structural and functional alterations, suggesting that retrograde signaling mechanisms are affected.
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Kim NC, Marqués G. Identification of downstream targets of the bone morphogenetic protein pathway in the Drosophila nervous system. Dev Dyn 2011; 239:2413-25. [PMID: 20652954 DOI: 10.1002/dvdy.22368] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Bone Morphogenetic Protein (BMP) signaling mediated by the receptor Wishful thinking (Wit) is essential for nervous system development in Drosophila. Mutants lacking wit function show defects in neuromuscular junction development and function, specification of neurosecretory phenotypes, and eclosion behavior that result in lethality. The ligand is Glass bottom boat, the Drosophila ortholog of mammalian BMP-7, which acts as a retrograde signal through the Wit receptor. In order to identify transcriptional targets of the BMP pathway in the Drosophila nervous system, we have analyzed the gene expression profile of wit mutant larval central nervous system. Genes differentially expressed identified by microarray analysis have been verified by quantitative PCR and studied by in situ hybridization. Among the genes thus identified, we find solute transporters, neuropeptides, mitochondrial proteins, and novel genes. In addition, several genes are regulated by wit in an isoform-specific manner that suggest regulation of alternative splicing by BMP signaling.
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Affiliation(s)
- Nam Chul Kim
- Department of Cell Biology, The University of Alabama at Birmingham, Birmingham, Alabama, USA
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Frenkel L, Fernanda Ceriani M. Circadian Plasticity: From Structure to Behavior. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2011; 99:107-38. [DOI: 10.1016/b978-0-12-387003-2.00005-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
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Autoregulatory and paracrine control of synaptic and behavioral plasticity by octopaminergic signaling. Nat Neurosci 2010; 14:190-9. [PMID: 21186359 DOI: 10.1038/nn.2716] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2010] [Accepted: 11/10/2010] [Indexed: 01/08/2023]
Abstract
Adrenergic signaling has important roles in synaptic plasticity and metaplasticity. However, the underlying mechanisms of these functions remain poorly understood. We investigated the role of octopamine, the invertebrate counterpart of adrenaline and noradrenaline, in synaptic and behavioral plasticity in Drosophila. We found that an increase in locomotor speed induced by food deprivation was accompanied by an activity- and octopamine-dependent extension of octopaminergic arbors and that the formation and maintenance of these arbors required electrical activity. Growth of octopaminergic arbors was controlled by a cAMP- and CREB-dependent positive-feedback mechanism that required Octβ2R octopamine autoreceptors. Notably, this autoregulation was necessary for the locomotor response. In addition, octopamine neurons regulated the expansion of excitatory glutamatergic neuromuscular arbors through Octβ2Rs on glutamatergic motor neurons. Our results provide a mechanism for global regulation of excitatory synapses, presumably to maintain synaptic and behavioral plasticity in a dynamic range.
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Nahm M, Long AA, Paik SK, Kim S, Bae YC, Broadie K, Lee S. The Cdc42-selective GAP rich regulates postsynaptic development and retrograde BMP transsynaptic signaling. ACTA ACUST UNITED AC 2010; 191:661-75. [PMID: 21041451 PMCID: PMC3003324 DOI: 10.1083/jcb.201007086] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Inhibition of Cdc42 by dRich induces postsynaptic release of the BMP ligand Glass bottom boat. Retrograde bone morphogenetic protein signaling mediated by the Glass bottom boat (Gbb) ligand modulates structural and functional synaptogenesis at the Drosophila melanogaster neuromuscular junction. However, the molecular mechanisms regulating postsynaptic Gbb release are poorly understood. In this study, we show that Drosophila Rich (dRich), a conserved Cdc42-selective guanosine triphosphatase–activating protein (GAP), inhibits the Cdc42–Wsp pathway to stimulate postsynaptic Gbb release. Loss of dRich causes synaptic undergrowth and strongly impairs neurotransmitter release. These presynaptic defects are rescued by targeted postsynaptic expression of wild-type dRich but not a GAP-deficient mutant. dRich inhibits the postsynaptic localization of the Cdc42 effector Wsp (Drosophila orthologue of mammalian Wiskott-Aldrich syndrome protein, WASp), and manifestation of synaptogenesis defects in drich mutants requires Wsp signaling. In addition, dRich regulates postsynaptic organization independently of Cdc42. Importantly, dRich increases Gbb release and elevates presynaptic phosphorylated Mad levels. We propose that dRich coordinates the Gbb-dependent modulation of synaptic growth and function with postsynaptic development.
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Affiliation(s)
- Minyeop Nahm
- Interdisplinary Program in Brain Science, Seoul National University, Seoul, Republic of Korea
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36
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Xiong X, Wang X, Ewanek R, Bhat P, Diantonio A, Collins CA. Protein turnover of the Wallenda/DLK kinase regulates a retrograde response to axonal injury. ACTA ACUST UNITED AC 2010; 191:211-23. [PMID: 20921142 PMCID: PMC2953441 DOI: 10.1083/jcb.201006039] [Citation(s) in RCA: 215] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Regenerative responses to axonal injury involve changes in gene expression; however, little is known about how such changes can be induced from a distant site of injury. In this study, we describe a nerve crush assay in Drosophila melanogaster to study injury signaling and regeneration mechanisms. We find that Wallenda (Wnd), a conserved mitogen-activated protein kinase (MAPK) kinase kinase homologous to dual leucine zipper kinase, functions as an upstream mediator of a cell-autonomous injury signaling cascade that involves the c-Jun NH(2)-terminal kinase MAPK and Fos transcription factor. Wnd is physically transported in axons, and axonal transport is required for the injury signaling mechanism. Wnd is regulated by a conserved E3 ubiquitin ligase, named Highwire (Hiw) in Drosophila. Injury induces a rapid increase in Wnd protein concomitantly with a decrease in Hiw protein. In hiw mutants, injury signaling is constitutively active, and neurons initiate a faster regenerative response. Our data suggest that the regulation of Wnd protein turnover by Hiw can function as a damage surveillance mechanism for responding to axonal injury.
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Affiliation(s)
- Xin Xiong
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
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37
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Defects in mitochondrial axonal transport and membrane potential without increased reactive oxygen species production in a Drosophila model of Friedreich ataxia. J Neurosci 2010; 30:11369-78. [PMID: 20739558 DOI: 10.1523/jneurosci.0529-10.2010] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Friedreich ataxia, a neurodegenerative disorder resulting from frataxin deficiency, is thought to involve progressive cellular damage from oxidative stress. In Drosophila larvae with reduced frataxin expression (DfhIR), we evaluated possible mechanisms of cellular neuropathology by quantifying mitochondrial axonal transport, membrane potential (MMP), and reactive oxygen species (ROS) production in the DfhIR versus wild-type nervous system throughout development. Although dying-back neuropathy in DfhIR larvae did not occur until late third instar, reduced MMP was already apparent at second instar in the cell bodies, axons and neuromuscular junctions (NMJs) of segmental nerves. Defects in axonal transport of mitochondria appeared late in development in distal nerve of DfhIR larvae, with retrograde movement preferentially affected. As a result, by late third instar the neuromuscular junctions (NMJs) of DfhIR larvae accumulated a higher density of mitochondria, many of which were depolarized. Notably, increased ROS production was not detected in any neuronal region or developmental stage in DfhIR larvae. However, when challenged with antimycin A, neurons did respond with a larger increase in ROS. We propose that pathology in the frataxin-deficient nervous system involves decreased MMP and ATP production followed by failures of mitochondrial transport and NMJ function.
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dCIP4 (Drosophila Cdc42-interacting protein 4) restrains synaptic growth by inhibiting the secretion of the retrograde Glass bottom boat signal. J Neurosci 2010; 30:8138-50. [PMID: 20554864 DOI: 10.1523/jneurosci.0256-10.2010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The bone morphogenetic protein (BMP) ligand Glass bottom boat (Gbb) acts as a retrograde growth signal at the Drosophila neuromuscular junction (NMJ). Endocytic regulation of presynaptic BMP receptors has been proposed to attenuate retrograde BMP signaling. However, it remains unknown whether the Gbb signal is also regulated by postsynaptic mechanisms. Here, we provide evidence that Drosophila Cdc42-interacting protein 4 (dCIP4) functions postsynaptically to inhibit synaptic growth. dCIP4 is localized postsynaptically at NMJs. dcip4 mutations lead to synaptic overgrowth and increased presynaptic phosphorylated mothers against decapentaplegic (Mad) levels, and these defects are rescued by muscle-specific expression of dCIP4. Biochemical and genetic analyses demonstrate that dCIP4 acts downstream of Cdc42 to activate the postsynaptic Wsp-Arp2/3 pathway. We also show that BMP signaling is necessary for synaptic overgrowth in larvae lacking postsynaptic dcip4 or wsp. Finally, dCIP4 and Wsp inhibit Gbb secretion. Thus, we propose that dCIP4 restrains synaptic growth by inhibiting postsynaptic Gbb secretion through the Wsp-Arp2/3 pathway.
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Ellis JE, Parker L, Cho J, Arora K. Activin signaling functions upstream of Gbb to regulate synaptic growth at the Drosophila neuromuscular junction. Dev Biol 2010; 342:121-33. [PMID: 20346940 DOI: 10.1016/j.ydbio.2010.03.012] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 03/16/2010] [Accepted: 03/16/2010] [Indexed: 11/20/2022]
Abstract
Activins are members of the TGF-ss superfamily of secreted growth factors that control a diverse array of processes in vertebrates including endocrine function, cell proliferation, differentiation, immune response and wound repair. In Drosophila, the Activin ligand Dawdle (Daw) has been shown to regulate several aspects of neuronal development such as embryonic axonal pathfinding, neuroblast proliferation in the larval brain and growth cone motility in the visual system. Here we identify a novel role for Activin signaling in regulating synaptic growth at the larval neuromuscular junction (NMJ). Mutants for Daw, the Activin type I receptor Baboon (Babo), and the signal transducer dSmad2, display reduced NMJ size suggesting that Daw utilizes a canonical Activin signal-transduction pathway in this context. Additionally, loss of Daw/Babo activity affects microtubule stability, axonal transport and distribution of Futsch, the Drosophila microtubule associated protein 1B (MAP1B) homolog. We find that Babo signaling is required postsynaptically in the muscle, in contrast to the well-characterized retrograde BMP/Gbb signal that is required for synaptic growth and function in presynaptic cells. Finally, we show that the Daw/Babo pathway acts upstream of gbb, and is involved in maintenance of muscle gbb expression, suggesting that Activins regulate NMJ growth by modulating BMP activity through transcriptional regulation of ligand expression.
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Affiliation(s)
- J E Ellis
- Department of Developmental and Cell Biology, University of California Irvine, Irvine, CA 92697, USA
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40
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Groh C, Meinertzhagen IA. Brain plasticity in Diptera and Hymenoptera. Front Biosci (Schol Ed) 2010; 2:268-88. [PMID: 20036946 DOI: 10.2741/s63] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
To mediate different types of behaviour, nervous systems need to coordinate the proper operation of their neural circuits as well as short- and long-term alterations that occur within those circuits. The latter ultimately devolve upon specific changes in neuronal structures, membrane properties and synaptic connections that are all examples of plasticity. This reorganization of the adult nervous system is shaped by internal and external influences both during development and adult maturation. In adults, behavioural experience is a major driving force of neuronal plasticity studied particularly in sensory systems. The range of adaptation depends on features that are important to a particular species, and is therefore specific, so that learning is essential for foraging in honeybees, while regenerative capacities are important in hemimetabolous insects with long appendages. Experience is usually effective during a critical period in early adult life, when neural function becomes tuned to future conditions in an insect's life. Tuning occur at all levels, in synaptic circuits, neuropile volumes, and behaviour. There are many examples, and this review incorporates only a select few, mainly those from Diptera and Hymenoptera.
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Affiliation(s)
- Claudia Groh
- Life Sciences Centre, Dalhousie University, Halifax, NS, Canada B3H 4J1
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Abstract
Although WNTs have been long thought of as regulators of cell fate, recent studies highlight their involvement in crucial aspects of synaptic development in the nervous system. Particularly compelling are recent studies of the neuromuscular junction in nematodes, insects, fish and mammals. These studies place WNTs as major determinants of synapse differentiation and neurotransmitter receptor clustering.
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42
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Impaired synaptic vesicle release and immaturity of neuromuscular junctions in spinal muscular atrophy mice. J Neurosci 2009; 29:842-51. [PMID: 19158308 DOI: 10.1523/jneurosci.4434-08.2009] [Citation(s) in RCA: 303] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The motor neuron disease spinal muscular atrophy (SMA) causes profound muscle weakness that most often leads to early death. At autopsy, SMA is characterized by loss of motor neurons and muscle atrophy, but the initial cellular events that precipitate motor unit dysfunction and loss remain poorly characterized. Here, we examined the function and corresponding structure of neuromuscular junction (NMJ) synapses in a mouse model of severe SMA (hSMN2/delta7SMN/mSmn-/-). Surprisingly, most SMA NMJs remained innervated even late in the disease course; however they showed abnormal synaptic transmission. There was a two-fold reduction in the amplitudes of the evoked endplate currents (EPCs), but normal spontaneous miniature EPC (MEPC) amplitudes. These features in combination indicate reduced quantal content. SMA NMJs also demonstrated increased facilitation suggesting a reduced probability of vesicle release. By electron microscopy, we found a decreased density of synaptic vesicles that is likely to contribute to the reduced release probability. In addition to presynaptic defects, there were postsynaptic abnormalities. EPC and MEPC decay time constants were prolonged because of a slowed switch from the fetal acetylcholine receptor (AChR) gamma-subunit to the adult epsilon-subunit. There was also reduced size of AChR clusters and small myofibers, which expressed an immature pattern of myosin heavy chains. Together these results indicate that impaired synaptic vesicle release at NMJs in severe SMA is likely to contribute to failed postnatal maturation of motor units and muscle weakness.
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Nervous wreck and Cdc42 cooperate to regulate endocytic actin assembly during synaptic growth. J Neurosci 2008; 28:8316-25. [PMID: 18701694 DOI: 10.1523/jneurosci.2304-08.2008] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Regulation of synaptic morphology depends on endocytosis of activated growth signal receptors, but the mechanisms regulating this membrane-trafficking event are unclear. Actin polymerization mediated by Wiskott-Aldrich syndrome protein (WASp) and the actin-related protein 2/3 complex generates forces at multiple stages of endocytosis. FCH-BIN amphiphysin RVS (F-BAR)/SH3 domain proteins play key roles in this process by coordinating membrane deformation with WASp-dependent actin polymerization. However, it is not known how other WASp ligands, such as the small GTPase Cdc42, coordinate with F-BAR/SH3 proteins to regulate actin polymerization at membranes. Nervous Wreck (Nwk) is a conserved neuronal F-BAR/SH3 protein that localizes to periactive zones at the Drosophila larval neuromuscular junction (NMJ) and is required for regulation of synaptic growth via bone morphogenic protein signaling. Here, we show that Nwk interacts with the endocytic proteins dynamin and Dap160 and functions together with Cdc42 to promote WASp-mediated actin polymerization in vitro and to regulate synaptic growth in vivo. Cdc42 function is associated with Rab11-dependent recycling endosomes, and we show that Rab11 colocalizes with Nwk at the NMJ. Together, our results suggest that synaptic growth activated by growth factor signaling is controlled at an endosomal compartment via coordinated Nwk and Cdc42-dependent actin assembly.
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Caygill EE, Johnston LA. Temporal regulation of metamorphic processes in Drosophila by the let-7 and miR-125 heterochronic microRNAs. Curr Biol 2008; 18:943-50. [PMID: 18571409 DOI: 10.1016/j.cub.2008.06.020] [Citation(s) in RCA: 216] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 06/03/2008] [Accepted: 06/04/2008] [Indexed: 10/21/2022]
Abstract
BACKGROUND The let-7 and lin-4 microRNAs belong to a class of temporally expressed, noncoding regulatory RNAs that function as heterochronic switch genes in the nematode C. elegans. Heterochronic genes control the relative timing of events during development and are considered a major force in the rapid evolution of new morphologies. let-7 is highly conserved and in Drosophila is temporally coregulated with the lin-4 homolog, miR-125. Little is known, however, about their requirement outside the nematode or whether they universally control the timing of developmental processes. RESULTS We report the generation of a Drosophila mutant that lacks let-7 and miR-125 activities and that leads to a pleiotropic phenotype arising during metamorphosis. We focus on two defects and demonstrate that loss of let-7 and miR-125 results in temporal delays in two distinct metamorphic processes: the terminal cell-cycle exit in the wing and maturation of neuromuscular junctions (NMJs) at adult abdominal muscles. We identify the abrupt (ab) gene, encoding a nuclear protein, as a bona fide let-7 target and provide evidence that let-7 governs the maturation rate of abdominal NMJs during metamorphosis by regulating ab expression. CONCLUSIONS Drosophila Iet-7 and miR-125 mutants exhibit temporal misregulation of specific metamorphic processes. As in C. elegans, Drosophila let-7 is both necessary and sufficient for the appropriate timing of a specific cell-cycle exit, indicating that its function as a heterochronic microRNA is conserved. The ab gene is a target of let-7, and its repression in muscle is essential for the timing of NMJ maturation during metamorphosis. Our results suggest that let-7 and miR-125 serve as conserved regulators of events necessary for the transition from juvenile to adult life stages.
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Affiliation(s)
- Elizabeth E Caygill
- Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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Koch I, Schwarz H, Beuchle D, Goellner B, Langegger M, Aberle H. Drosophila ankyrin 2 is required for synaptic stability. Neuron 2008; 58:210-22. [PMID: 18439406 DOI: 10.1016/j.neuron.2008.03.019] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Revised: 12/10/2007] [Accepted: 03/20/2008] [Indexed: 10/22/2022]
Abstract
Synaptic connections are stabilized through transsynaptic adhesion complexes that are anchored in the underlying cytoskeleton. The Drosophila neuromuscular junction (NMJs) serves as a model system to unravel genes required for the structural remodeling of synapses. In a mutagenesis screen for regulators of synaptic stability, we recovered mutations in Drosophila ankyrin 2 (ank2) affecting two giant Ank2 isoforms that are specifically expressed in the nervous system and associate with the presynaptic membrane cytoskeleton. ank2 mutant larvae show severe deficits in the stability of NMJs, resulting in a reduction in overall terminal size, withdrawal of synaptic boutons, and disassembly of presynaptic active zones. In addition, lack of Ank2 leads to disintegration of the synaptic microtubule cytoskeleton. Microtubules and microtubule-associated proteins fail to extend into distant boutons. Interestingly, Ank2 functions downstream of spectrin in the anchorage of synaptic microtubules, providing the cytoskeletal scaffold that is essential for synaptic stability.
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Affiliation(s)
- Iris Koch
- Max-Planck-Institute for Developmental Biology, Department III/Genetics, Spemannstrasse 35, 72076 Tübingen, Germany
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Pack-Chung E, Kurshan PT, Dickman DK, Schwarz TL. A Drosophila kinesin required for synaptic bouton formation and synaptic vesicle transport. Nat Neurosci 2007; 10:980-9. [PMID: 17643120 DOI: 10.1038/nn1936] [Citation(s) in RCA: 126] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2007] [Accepted: 06/07/2007] [Indexed: 12/12/2022]
Abstract
The morphological transition of growth cones to synaptic boutons characterizes synaptogenesis. Here we have isolated mutations in immaculate connections (imac; CG8566), a previously uncharacterized Drosophila gene encoding a member of the Kinesin-3 family. Whereas earlier studies in Drosophila implicated Kinesin-1 in transporting synaptic vesicle precursors, we find that Imac is essential for this transport. An unexpected feature of imac mutants is the failure of synaptic boutons to form. Motor neurons lacking imac properly target to muscles but remain within target fields as thin processes, a structure that is distinct from either growth cones or mature terminals. Few active zones form at these endings. We show that the arrest of synaptogenesis is not a secondary consequence of the absence of transmission. Our data thus indicate that Imac transports components required for synaptic maturation and provide insight into presynaptic maturation as a process that can be differentiated from axon outgrowth and targeting.
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Affiliation(s)
- Eunju Pack-Chung
- Program in Neurobiology, Children's Hospital, 300 Longwood Avenue, Boston, Massachusetts 02115, USA
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