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Brown E, Kuszynski S, Akoachere F, Feduccia J, Malatinszky L, Luth ES. Generation of an endogenous auxin inducible degron-tagged SPAS-1/spastin to investigate its targeted depletion in C. elegans neurons. MICROPUBLICATION BIOLOGY 2024; 2024:10.17912/micropub.biology.001328. [PMID: 39583582 PMCID: PMC11582882 DOI: 10.17912/micropub.biology.001328] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Figures] [Subscribe] [Scholar Register] [Received: 08/20/2024] [Revised: 11/01/2024] [Accepted: 11/05/2024] [Indexed: 11/26/2024]
Abstract
To facilitate investigations of the microtubule severing protein spastin and its specific role in neurons, we aimed to create a C. elegans strain in which the spastin homolog SPAS-1 is visible and can be degraded with spatial and temporal precision. We used CRISPR-Cas9 to fuse an auxin-inducible degron and mScarlet to the endogenous SPAS-1 protein, enabling degradation of SPAS-1 in neurons during desired life stages. DNA sequencing confirmed in-frame insertion with the SPAS-1 N-terminus and fluorescence microscopy revealed endogenous SPAS-1 throughout the CRISPR-edited worms. Auxin treatment in rgef-1::TIR1; mScarlet::AID*::3xFLAG::spas-1 animals reduced mScarlet::SPAS-1 fluorescence in neuronal ganglia.
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Affiliation(s)
- Emily Brown
- Department of Biology, Simmons University, Boston, Massachusetts, United States
| | - Samantha Kuszynski
- Department of Biology, Simmons University, Boston, Massachusetts, United States
| | - Faith Akoachere
- Department of Biology, Simmons University, Boston, Massachusetts, United States
| | - James Feduccia
- Department of Biology, Simmons University, Boston, Massachusetts, United States
| | - Lili Malatinszky
- Department of Biology, Simmons University, Boston, Massachusetts, United States
| | - Eric S. Luth
- Department of Biology, Simmons University, Boston, Massachusetts, United States
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2
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Liu S, Alexander KD, Francis MM. Neural Circuit Remodeling: Mechanistic Insights from Invertebrates. J Dev Biol 2024; 12:27. [PMID: 39449319 PMCID: PMC11503349 DOI: 10.3390/jdb12040027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2024] [Revised: 10/07/2024] [Accepted: 10/10/2024] [Indexed: 10/26/2024] Open
Abstract
As nervous systems mature, neural circuit connections are reorganized to optimize the performance of specific functions in adults. This reorganization of connections is achieved through a remarkably conserved phase of developmental circuit remodeling that engages neuron-intrinsic and neuron-extrinsic molecular mechanisms to establish mature circuitry. Abnormalities in circuit remodeling and maturation are broadly linked with a variety of neurodevelopmental disorders, including autism spectrum disorders and schizophrenia. Here, we aim to provide an overview of recent advances in our understanding of the molecular processes that govern neural circuit remodeling and maturation. In particular, we focus on intriguing mechanistic insights gained from invertebrate systems, such as the nematode Caenorhabditis elegans and the fruit fly Drosophila melanogaster. We discuss how transcriptional control mechanisms, synaptic activity, and glial engulfment shape specific aspects of circuit remodeling in worms and flies. Finally, we highlight mechanistic parallels across invertebrate and mammalian systems, and prospects for further advances in each.
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Affiliation(s)
- Samuel Liu
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
- Program in Neuroscience, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
| | - Kellianne D. Alexander
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
- Program in Neuroscience, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
| | - Michael M. Francis
- Department of Neurobiology, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
- Program in Neuroscience, University of Massachusetts Chan Medical School, Worcester, MA 01605, USA
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3
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Chiba K, Kita T, Anazawa Y, Niwa S. Insight into the regulation of axonal transport from the study of KIF1A-associated neurological disorder. J Cell Sci 2023; 136:286709. [PMID: 36655764 DOI: 10.1242/jcs.260742] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Neuronal function depends on axonal transport by kinesin superfamily proteins (KIFs). KIF1A is the molecular motor that transports synaptic vesicle precursors, synaptic vesicles, dense core vesicles and active zone precursors. KIF1A is regulated by an autoinhibitory mechanism; many studies, as well as the crystal structure of KIF1A paralogs, support a model whereby autoinhibited KIF1A is monomeric in solution, whereas activated KIF1A is dimeric on microtubules. KIF1A-associated neurological disorder (KAND) is a broad-spectrum neuropathy that is caused by mutations in KIF1A. More than 100 point mutations have been identified in KAND. In vitro assays show that most mutations are loss-of-function mutations that disrupt the motor activity of KIF1A, whereas some mutations disrupt its autoinhibition and abnormally hyperactivate KIF1A. Studies on disease model worms suggests that both loss-of-function and gain-of-function mutations cause KAND by affecting the axonal transport and localization of synaptic vesicles. In this Review, we discuss how the analysis of these mutations by molecular genetics, single-molecule assays and force measurements have helped to reveal the physiological significance of KIF1A function and regulation, and what physical parameters of KIF1A are fundamental to axonal transport.
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Affiliation(s)
- Kyoko Chiba
- Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-0845, Japan
| | - Tomoki Kita
- Department of Applied Physics, Graduate School of Engineering, Tohoku University, 2-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8578, Japan
| | - Yuzu Anazawa
- Graduate School of Life Sciences, Tohoku University, 2-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8578, Japan
| | - Shinsuke Niwa
- Frontier Research Institute for Interdisciplinary Sciences (FRIS), Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-0845, Japan.,Department of Applied Physics, Graduate School of Engineering, Tohoku University, 2-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8578, Japan.,Graduate School of Life Sciences, Tohoku University, 2-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8578, Japan
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4
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Mizumoto K, Jin Y, Bessereau JL. Synaptogenesis: unmasking molecular mechanisms using Caenorhabditis elegans. Genetics 2023; 223:iyac176. [PMID: 36630525 PMCID: PMC9910414 DOI: 10.1093/genetics/iyac176] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 10/22/2022] [Indexed: 01/13/2023] Open
Abstract
The nematode Caenorhabditis elegans is a research model organism particularly suited to the mechanistic understanding of synapse genesis in the nervous system. Armed with powerful genetics, knowledge of complete connectomics, and modern genomics, studies using C. elegans have unveiled multiple key regulators in the formation of a functional synapse. Importantly, many signaling networks display remarkable conservation throughout animals, underscoring the contributions of C. elegans research to advance the understanding of our brain. In this chapter, we will review up-to-date information of the contribution of C. elegans to the understanding of chemical synapses, from structure to molecules and to synaptic remodeling.
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Affiliation(s)
- Kota Mizumoto
- Department of Zoology, University of British Columbia, Vancouver V6T 1Z3, Canada
| | - Yishi Jin
- Department of Neurobiology, University of California San Diego, La Jolla, CA 92093, USA
| | - Jean-Louis Bessereau
- Univ Lyon, University Claude Bernard Lyon 1, CNRS UMR 5284, INSERM U 1314, Melis, 69008 Lyon, France
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5
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Tahraoui-Bories J, Mérien A, González-Barriga A, Lainé J, Leteur C, Polvèche H, Carteron A, De Lamotte JD, Nicoleau C, Polentes J, Jarrige M, Gomes-Pereira M, Ventre E, Poydenot P, Furling D, Schaeffer L, Legay C, Martinat C. MBNL-dependent impaired development within the neuromuscular system in myotonic dystrophy type 1. Neuropathol Appl Neurobiol 2023; 49:e12876. [PMID: 36575942 PMCID: PMC10107781 DOI: 10.1111/nan.12876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2021] [Revised: 10/27/2022] [Accepted: 12/12/2022] [Indexed: 12/29/2022]
Abstract
AIMS Myotonic dystrophy type I (DM1) is one of the most frequent muscular dystrophies in adults. Although DM1 has long been considered mainly a muscle disorder, growing evidence suggests the involvement of peripheral nerves in the pathogenicity of DM1 raising the question of whether motoneurons (MNs) actively contribute to neuromuscular defects in DM1. METHODS By using micropatterned 96-well plates as a coculture platform, we generated a functional neuromuscular model combining DM1 and muscleblind protein (MBNL) knock-out human-induced pluripotent stem cells-derived MNs and human healthy skeletal muscle cells. RESULTS This approach led to the identification of presynaptic defects which affect the formation or stability of the neuromuscular junction at an early developmental stage. These neuropathological defects could be reproduced by the loss of RNA-binding MBNL proteins, whose loss of function in vivo is associated with muscular defects associated with DM1. These experiments indicate that the functional defects associated with MNs can be directly attributed to MBNL family proteins. Comparative transcriptomic analyses also revealed specific neuronal-related processes regulated by these proteins that are commonly misregulated in DM1. CONCLUSIONS Beyond the application to DM1, our approach to generating a robust and reliable human neuromuscular system should facilitate disease modelling studies and drug screening assays.
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Affiliation(s)
| | - Antoine Mérien
- INSERM/UEVE UMR 861, Université Paris Saclay, I-STEM, Corbeil-Essonnes, France
| | - Anchel González-Barriga
- INSERM, Institut de Myologie, Centre de Recherche en Myologie, Sorbonne Université, Paris, France
| | - Jeanne Lainé
- INSERM, Institut de Myologie, Centre de Recherche en Myologie, Sorbonne Université, Paris, France
| | | | | | | | | | | | | | | | - Mário Gomes-Pereira
- INSERM, Institut de Myologie, Centre de Recherche en Myologie, Sorbonne Université, Paris, France
| | | | | | - Denis Furling
- INSERM, Institut de Myologie, Centre de Recherche en Myologie, Sorbonne Université, Paris, France
| | - Laurent Schaeffer
- INMG, INSERM U1217, CNRS UMR5310, Université Lyon 1, Université de Lyon, Hospices Civils de Lyon, Lyon, France
| | - Claire Legay
- CNRS, SPINN-Saint-Pères Paris Institute for the Neurosciences, Université Paris Cité, Paris, France
| | - Cécile Martinat
- INSERM/UEVE UMR 861, Université Paris Saclay, I-STEM, Corbeil-Essonnes, France
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6
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O'Hagan R, Avrutis A, Ramicevic E. Functions of the tubulin code in the C. elegans nervous system. Mol Cell Neurosci 2022; 123:103790. [PMID: 36368428 DOI: 10.1016/j.mcn.2022.103790] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 10/27/2022] [Accepted: 11/03/2022] [Indexed: 11/11/2022] Open
Abstract
Due to their elongated and polarized morphology, neurons rely on the microtubule (MT) cytoskeleton for their shape, as well as for efficient intracellular transport that maintains neuronal function, survival, and connectivity. Although all MTs are constructed from α- and β-tubulins that are highly conserved throughout eukaryotes, different MT networks within neurons exhibit different dynamics and functions. For example, molecular motors must be able to differentially recognize the axonal and dendritic MTs to deliver appropriate cargos to sensory endings and synaptic regions. The Tubulin Code hypothesis proposes that MTs can be specialized in form and function by chemical differences in their composition by inclusion of different α- and β-tubulins into the MT lattice, as well as differences in post-translational enzymatic modifications. The chemical differences encode information that allow MTs to regulate interactions with various microtubule-based molecular motors such as kinesins and dyneins as well as with structural microtubule-associated proteins (MAPs), which can, in turn, modify the function or stability of MTs. Here, we review studies involving C. elegans, a model organism with a relatively simple nervous system that is amenable to genetic analysis, that have contributed to our understanding of how the Tubulin Code can specialize neuronal MT networks to establish differences in neuronal morphology and function. Such studies have revealed molecules and mechanisms that are conserved in vertebrates and have the potential to inform our understanding of neurological diseases involving defects in the cytoskeleton and intracellular transport.
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Affiliation(s)
- Robert O'Hagan
- formerly at Biology Dept., Montclair State University, Montclair, NJ 07043, United States of America.
| | - Alexandra Avrutis
- formerly at Biology Dept., Montclair State University, Montclair, NJ 07043, United States of America
| | - Ema Ramicevic
- formerly at Biology Dept., Montclair State University, Montclair, NJ 07043, United States of America
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7
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Post-embryonic remodeling of the C. elegans motor circuit. Curr Biol 2022; 32:4645-4659.e3. [DOI: 10.1016/j.cub.2022.09.065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 07/28/2022] [Accepted: 09/26/2022] [Indexed: 11/06/2022]
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8
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Lu YM, Zheng C. The Expression and Function of Tubulin Isotypes in Caenorhabditis elegans. Front Cell Dev Biol 2022; 10:860065. [PMID: 35399537 PMCID: PMC8987236 DOI: 10.3389/fcell.2022.860065] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 02/28/2022] [Indexed: 11/13/2022] Open
Abstract
Microtubules, made from the polymerization of the highly conserved α/β-tubulin heterodimers, serve as important components of the cytoskeleton in all eukaryotic cells. The existence of multiple tubulin isotypes in metazoan genomes and a dazzling variety of tubulin posttranslational modifications (PTMs) prompted the “tubulin code” hypothesis, which proposed that microtubule structure and functions are determined by the tubulin composition and PTMs. Evidence for the tubulin code has emerged from studies in several organisms with the characterization of specific tubulins for their expression and functions. The studies of tubulin PTMs are accelerated by the discovery of the enzymes that add or remove the PTMs. In tubulin research, the use of simple organisms, such as Caenorhabditis elegans, has been instrumental for understanding the expression and functional specialization of tubulin isotypes and the effects of their PTMs. In this review, we summarize the current understanding of the expression patterns and cellular functions of the nine α-tubulin and six β-tubulin isotypes. Expression studies are greatly facilitated by the CRISPR/Cas9-mediated endogenous GFP knock-in reporters and the organism-wide single cell transcriptomic studies. Meanwhile, functional studies benefit from the ease of genetic manipulation and precise gene replacement in C. elegans. These studies identified both ubiquitously expressed tubulin isotypes and tissue-specific isotypes. The isotypes showed functional redundancy, as well as functional specificity, which is likely caused by the subtle differences in their amino acid sequences. Many of these differences concentrate at the C-terminal tails that are subjected to several PTMs. Indeed, tubulin PTM, such as polyglutamylation, is shown to modulate microtubule organization and properties in both ciliated and non-ciliated neurons. Overall, studies from C. elegans support the distinct expression and function patterns of tubulin isotypes and the importance of their PTMs and offer the promise of cracking the tubulin code at the whole-genome and the whole-organism level.
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9
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Vasudevan A, Koushika SP. Molecular mechanisms governing axonal transport: a C. elegans perspective. J Neurogenet 2020; 34:282-297. [PMID: 33030066 DOI: 10.1080/01677063.2020.1823385] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Axonal transport is integral for maintaining neuronal form and function, and defects in axonal transport have been correlated with several neurological diseases, making it a subject of extensive research over the past several years. The anterograde and retrograde transport machineries are crucial for the delivery and distribution of several cytoskeletal elements, growth factors, organelles and other synaptic cargo. Molecular motors and the neuronal cytoskeleton function as effectors for multiple neuronal processes such as axon outgrowth and synapse formation. This review examines the molecular mechanisms governing axonal transport, specifically highlighting the contribution of studies conducted in C. elegans, which has proved to be a tractable model system in which to identify both novel and conserved regulatory mechanisms of axonal transport.
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Affiliation(s)
- Amruta Vasudevan
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
| | - Sandhya P Koushika
- Department of Biological Sciences, Tata Institute of Fundamental Research, Mumbai, India
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10
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Cuentas-Condori A, Miller Rd DM. Synaptic remodeling, lessons from C. elegans. J Neurogenet 2020; 34:307-322. [PMID: 32808848 PMCID: PMC7855814 DOI: 10.1080/01677063.2020.1802725] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2020] [Accepted: 07/07/2020] [Indexed: 02/08/2023]
Abstract
Sydney Brenner's choice of Caenorhabditis elegans as a model organism for understanding the nervous system has accelerated discoveries of gene function in neural circuit development and behavior. In this review, we discuss a striking example of synaptic remodeling in the C. elegans motor circuit in which DD class motor neurons effectively reverse polarity as presynaptic and postsynaptic domains at opposite ends of the DD neurite switch locations. Originally revealed by EM reconstruction conducted over 40 years ago, DD remodeling has since been investigated by live cell imaging methods that exploit the power of C. elegans genetics to reveal key effectors of synaptic plasticity. Although synapses are also extensively rewired in developing mammalian circuits, the underlying remodeling mechanisms are largely unknown. Here, we highlight the possibility that studies in C. elegans can reveal pathways that orchestrate synaptic remodeling in more complex organisms. Specifically, we describe (1) transcription factors that regulate DD remodeling, (2) the cellular and molecular cascades that drive synaptic remodeling and (3) examples of circuit modifications in vertebrate neurons that share some similarities with synaptic remodeling in C. elegans DD neurons.
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11
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Jin Y, Zheng B. Multitasking: Dual Leucine Zipper-Bearing Kinases in Neuronal Development and Stress Management. Annu Rev Cell Dev Biol 2020; 35:501-521. [PMID: 31590586 DOI: 10.1146/annurev-cellbio-100617-062644] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The dual leucine zipper-bearing kinase (DLK) and leucine zipper-bearing kinase (LZK) are evolutionarily conserved MAPKKKs of the mixed-lineage kinase family. Acting upstream of stress-responsive JNK and p38 MAP kinases, DLK and LZK have emerged as central players in neuronal responses to a variety of acute and traumatic injuries. Recent studies also implicate their function in astrocytes, microglia, and other nonneuronal cells, reflecting their expanding roles in the multicellular response to injury and in disease. Of particular note is the potential link of these kinases to neurodegenerative diseases and cancer. It is thus critical to understand the physiological contexts under which these kinases are activated, as well as the signal transduction mechanisms that mediate specific functional outcomes. In this review we first provide a historical overview of the biochemical and functional dissection of these kinases. We then discuss recent findings on regulating their activity to enhance cellular protection following injury and in disease, focusing on but not limited to the nervous system.
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Affiliation(s)
- Yishi Jin
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, California 92093, USA; .,Department of Neurosciences, School of Medicine, University of California, San Diego, La Jolla, California 92093, USA;
| | - Binhai Zheng
- Department of Neurosciences, School of Medicine, University of California, San Diego, La Jolla, California 92093, USA; .,VA San Diego Healthcare System, San Diego, California 92161, USA
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12
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Prokop A. Cytoskeletal organization of axons in vertebrates and invertebrates. J Cell Biol 2020; 219:e201912081. [PMID: 32369543 PMCID: PMC7337489 DOI: 10.1083/jcb.201912081] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2019] [Revised: 04/13/2020] [Accepted: 04/14/2020] [Indexed: 12/11/2022] Open
Abstract
The maintenance of axons for the lifetime of an organism requires an axonal cytoskeleton that is robust but also flexible to adapt to mechanical challenges and to support plastic changes of axon morphology. Furthermore, cytoskeletal organization has to adapt to axons of dramatically different dimensions, and to their compartment-specific requirements in the axon initial segment, in the axon shaft, at synapses or in growth cones. To understand how the cytoskeleton caters to these different demands, this review summarizes five decades of electron microscopic studies. It focuses on the organization of microtubules and neurofilaments in axon shafts in both vertebrate and invertebrate neurons, as well as the axon initial segments of vertebrate motor- and interneurons. Findings from these ultrastructural studies are being interpreted here on the basis of our contemporary molecular understanding. They strongly suggest that axon architecture in animals as diverse as arthropods and vertebrates is dependent on loosely cross-linked bundles of microtubules running all along axons, with only minor roles played by neurofilaments.
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Affiliation(s)
- Andreas Prokop
- School of Biology, Faculty of Biology, Medicine and Health, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK
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13
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Freal A, Hoogenraad CC. Neuronal Cytoskeleton: Presynaptic Boutons as Hotspots for Activity-Dependent Microtubule Nucleation. Curr Biol 2019; 29:R1307-R1309. [PMID: 31846677 DOI: 10.1016/j.cub.2019.11.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Local microtubule remodeling plays a crucial role in controlling the transport of neuronal cargo. A new study reveals that excitatory en passant boutons in the axon are hotspots for activity-induced microtubule nucleation and provide tracks for interbouton vesicle trafficking.
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Affiliation(s)
- Amélie Freal
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands; Department of Axonal Signaling, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands
| | - Casper C Hoogenraad
- Cell Biology, Neurobiology and Biophysics, Department of Biology, Faculty of Science, Utrecht University, 3584 CH Utrecht, The Netherlands; Department of Neuroscience, Genentech, Inc., South San Francisco, CA 94080, USA.
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14
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Gilsoul M, Grisar T, Delgado-Escueta AV, de Nijs L, Lakaye B. Subtle Brain Developmental Abnormalities in the Pathogenesis of Juvenile Myoclonic Epilepsy. Front Cell Neurosci 2019; 13:433. [PMID: 31611775 PMCID: PMC6776584 DOI: 10.3389/fncel.2019.00433] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Accepted: 09/09/2019] [Indexed: 12/17/2022] Open
Abstract
Juvenile myoclonic epilepsy (JME), a lifelong disorder that starts during adolescence, is the most common of genetic generalized epilepsy syndromes. JME is characterized by awakening myoclonic jerks and myoclonic-tonic-clonic (m-t-c) grand mal convulsions. Unfortunately, one third of JME patients have drug refractory m-t-c convulsions and these recur in 70-80% who attempt to stop antiepileptic drugs (AEDs). Behavioral studies documented impulsivity, but also impairment of executive functions relying on organization and feedback, which points to prefrontal lobe dysfunction. Quantitative voxel-based morphometry (VBM) revealed abnormalities of gray matter (GM) volumes in cortical (frontal and parietal) and subcortical structures (thalamus, putamen, and hippocampus). Proton magnetic resonance spectroscopy (MRS) found evidence of dysfunction of thalamic neurons. White matter (WM) integrity was disrupted in corpus callosum and frontal WM tracts. Magnetic resonance imaging (MRI) further unveiled anomalies in both GM and WM structures that were already present at the time of seizure onset. Aberrant growth trajectories of brain development occurred during the first 2 years of JME diagnosis. Because of genetic origin, disease causing variants were sought, first by positional cloning, and most recently, by next generation sequencing. To date, only six genes harboring pathogenic variants (GABRA1, GABRD, EFHC1, BRD2, CASR, and ICK) with Mendelian and complex inheritance and covering a limited proportion of the world population, are considered as major susceptibility alleles for JME. Evidence on the cellular role, developmental and cell-type expression profiles of these six diverse JME genes, point to their pathogenic variants driving the first steps of brain development when cell division, expansion, axial, and tangential migration of progenitor cells (including interneuron cortical progenitors) sculpture subtle alterations in brain networks and microcircuits during development. These alterations may explain "microdysgenesis" neuropathology, impulsivity, executive dysfunctions, EEG polyspike waves, and awakening m-t-c convulsions observed in JME patients.
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Affiliation(s)
- Maxime Gilsoul
- GIGA-Stem Cells, University of Liège, Liège, Belgium
- GIGA-Neurosciences, University of Liège, Liège, Belgium
- GENESS International Consortium, Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Thierry Grisar
- GENESS International Consortium, Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
| | - Antonio V. Delgado-Escueta
- GENESS International Consortium, Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- Epilepsy Genetics/Genomics Lab, Neurology and Research Services, VA Greater Los Angeles Healthcare System, Los Angeles, CA, United States
| | - Laurence de Nijs
- GENESS International Consortium, Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
- School for Mental Health and Neuroscience, Department of Psychiatry and Neuropsychology, Maastricht University, Maastricht, Netherlands
| | - Bernard Lakaye
- GIGA-Stem Cells, University of Liège, Liège, Belgium
- GIGA-Neurosciences, University of Liège, Liège, Belgium
- GENESS International Consortium, Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA, United States
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15
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Hu Z, Du X, Yang Y, Botchway BOA, Fang M. Progesterone and fluoxetine treatments of postpartum depressive-like behavior in rat model. Cell Biol Int 2019; 43:539-552. [PMID: 30811083 DOI: 10.1002/cbin.11123] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2018] [Accepted: 02/23/2019] [Indexed: 12/19/2022]
Abstract
Research studies have indicated that alterations in plasma progesterone levels might be associated with the hippocampal synaptic plasticity of postpartum depressive-like behavior. Herein, we assess both progesterone and fluoxetine effects in adult female Sprague-Dawley rats with postpartum depressive-like behavior. Depressive-like behavior of postpartum rats was established using chronic ultra-mild stress (CUMS) method for 1 week from gestation day 15. Postpartum rats that showed depressive-like behavior were treated with either progesterone (subcutaneously, 0.5 mg/kg) from gestation day 17 to gestation day 22 or fluoxetine (by gavage, 10 mg/kg/day) for 4 weeks after birth. Open field and sucrose preference tests were conducted at the start, week 2 and week 4 postpartum. Golgi staining, immunofluorescence and Western blot analyses of rats' hippocampi were conducted on week 4 postpartum. Results showed CUMS increases depressive-like behavior, however, treatment with progesterone and fluoxetine improves this behavior. Both progesterone and fluoxetine treatments increase the numbers of dendritic spines pyramidal neurons in the CA3 region of the hippocampus as well as protein expression levels of microtubule-associated protein 2 (MAP-2) and synaptophysin (SYP). CUMS-induced decrement of MAP-2 and SYP protein expressions can be prevented by treatment with progesterone in advanced pregnant stage and fluoxetine in the postpartum period.
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Affiliation(s)
- Zhiying Hu
- Hangzhou Red Cross Hospital, Hangzhou, China
| | - Xiaoxue Du
- Institute of Neuroscience, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Yang Yang
- Institute of Neuroscience, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Benson O A Botchway
- Institute of Neuroscience, Zhejiang University School of Medicine, Hangzhou, 310058, China
| | - Marong Fang
- Institute of Neuroscience, Zhejiang University School of Medicine, Hangzhou, 310058, China
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16
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Kelliher MT, Saunders HA, Wildonger J. Microtubule control of functional architecture in neurons. Curr Opin Neurobiol 2019; 57:39-45. [PMID: 30738328 DOI: 10.1016/j.conb.2019.01.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 01/04/2019] [Accepted: 01/07/2019] [Indexed: 01/20/2023]
Abstract
Neurons are exquisitely polarized cells whose structure and function relies on microtubules. Microtubules in signal-receiving dendrites and signal-sending axons differ in their organization and microtubule-associated proteins. These differences, coupled with microtubule post-translational modifications, combine to locally regulate intracellular transport, morphology, and function. Recent discoveries provide new insight into the regulation of non-centrosomal microtubule arrays in neurons, the relationship between microtubule acetylation and mechanosensation, and the spatial patterning of microtubules that regulates motor activity and cargo delivery in axons and dendrites. Together, these new studies bring us closer to understanding how microtubule function is locally tuned to match the specialized tasks associated with signal reception and transmission.
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Affiliation(s)
- Michael T Kelliher
- Integrated Program in Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA; Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Harriet Aj Saunders
- Integrated Program in Biochemistry, University of Wisconsin-Madison, Madison, WI 53706, USA; Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jill Wildonger
- Biochemistry Department, University of Wisconsin-Madison, Madison, WI 53706, USA.
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17
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Harterink M, Edwards SL, de Haan B, Yau KW, van den Heuvel S, Kapitein LC, Miller KG, Hoogenraad CC. Local microtubule organization promotes cargo transport in C. elegans dendrites. J Cell Sci 2018; 131:jcs.223107. [PMID: 30254025 DOI: 10.1242/jcs.223107] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Accepted: 09/14/2018] [Indexed: 02/05/2023] Open
Abstract
The specific organization of the neuronal microtubule cytoskeleton in axons and dendrites is an evolutionarily conserved determinant of neuronal polarity that allows for selective cargo sorting. However, how dendritic microtubules are organized and whether local differences influence cargo transport remains largely unknown. Here, we use live-cell imaging to systematically probe the microtubule organization in Caenorhabditis elegans neurons, and demonstrate the contribution of distinct mechanisms in the organization of dendritic microtubules. We found that most non-ciliated neurons depend on unc-116 (kinesin-1), unc-33 (CRMP) and unc-44 (ankyrin) for correct microtubule organization and polarized cargo transport, as previously reported. Ciliated neurons and the URX neuron, however, use an additional pathway to nucleate microtubules at the tip of the dendrite, from the base of the cilium in ciliated neurons. Since inhibition of distal microtubule nucleation affects distal dendritic transport, we propose a model in which the presence of a microtubule-organizing center at the dendrite tip ensures correct dendritic cargo transport.
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Affiliation(s)
- Martin Harterink
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
| | - Stacey L Edwards
- Genetic Models of Disease Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, US
| | - Bart de Haan
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
| | - Kah Wai Yau
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
| | - Sander van den Heuvel
- Developmental Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
| | - Lukas C Kapitein
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
| | - Kenneth G Miller
- Genetic Models of Disease Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, US
| | - Casper C Hoogenraad
- Cell Biology, Department of Biology, Faculty of Science, Utrecht University, Padualaan 8, 3584 Utrecht, The Netherlands
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18
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Gujar MR, Sundararajan L, Stricker A, Lundquist EA. Control of Growth Cone Polarity, Microtubule Accumulation, and Protrusion by UNC-6/Netrin and Its Receptors in Caenorhabditis elegans. Genetics 2018; 210:235-255. [PMID: 30045855 PMCID: PMC6116952 DOI: 10.1534/genetics.118.301234] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 07/23/2018] [Indexed: 11/18/2022] Open
Abstract
UNC-6/Netrin has a conserved role in dorsal-ventral axon guidance, but the cellular events in the growth cone regulated by UNC-6/Netrin signaling during outgrowth are incompletely understood. Previous studies showed that, in growth cones migrating away from UNC-6/Netrin, the receptor UNC-5 regulates growth cone polarity, as observed by polarized F-actin, and limits the extent of growth cone protrusion. It is unclear how UNC-5 inhibits protrusion, and how UNC-40 acts in concert with UNC-5 to regulate polarity and protrusion. New results reported here indicate that UNC-5 normally restricts microtubule (MT) + end accumulation in the growth cone. Tubulin mutant analysis and colchicine treatment suggest that stable MTs are necessary for robust growth cone protrusion. Thus, UNC-5 might inhibit protrusion in part by restricting growth cone MT accumulation. Previous studies showed that the UNC-73/Trio Rac GEF and UNC-33/CRMP act downstream of UNC-5 in protrusion. Here, we show that UNC-33/CRMP regulates both growth cone dorsal asymmetric F-actin accumulation and MT accumulation, whereas UNC-73/Trio Rac GEF activity only affects F-actin accumulation. This suggests an MT-independent mechanism used by UNC-5 to inhibit protrusion, possibly by regulating lamellipodial and filopodial actin. Furthermore, we show that UNC-6/Netrin and the receptor UNC-40/DCC are required for excess protrusion in unc-5 mutants, but not for loss of F-actin asymmetry or MT + end accumulation, indicating that UNC-6/Netrin and UNC-40/DCC are required for protrusion downstream of, or in parallel to, F-actin asymmetry and MT + end entry. F-actin accumulation might represent a polarity mark in the growth cone where protrusion will occur, and not protrusive lamellipodial and filopodial actin per se Our data suggest a model in which UNC-6/Netrin first polarizes the growth cone via UNC-5, and then regulates protrusion based upon this polarity (the polarity/protrusion model). UNC-6/Netrin inhibits protrusion ventrally via UNC-5, and stimulates protrusion dorsally via UNC-40, resulting in dorsally-directed migration. The polarity/protrusion model represents a novel conceptual paradigm in which to understand axon guidance and growth cone migration away from UNC-6/Netrin.
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Affiliation(s)
- Mahekta R Gujar
- Program in Molecular, Cellular, and Developmental Biology, Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66046
| | - Lakshmi Sundararajan
- Program in Molecular, Cellular, and Developmental Biology, Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66046
| | - Aubrie Stricker
- Program in Molecular, Cellular, and Developmental Biology, Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66046
| | - Erik A Lundquist
- Program in Molecular, Cellular, and Developmental Biology, Department of Molecular Biosciences, University of Kansas, Lawrence, Kansas 66046
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19
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Tang NH, Jin Y. Shaping neurodevelopment: distinct contributions of cytoskeletal proteins. Curr Opin Neurobiol 2018; 51:111-118. [PMID: 29574219 PMCID: PMC6066413 DOI: 10.1016/j.conb.2018.02.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2018] [Revised: 02/20/2018] [Accepted: 02/27/2018] [Indexed: 12/28/2022]
Abstract
Development of a neuron critically depends on the organization of its cytoskeleton. Cytoskeletal components, such as tubulins and actins, have the remarkable ability to organize themselves into filaments and networks to support specialized and compartmentalized functions. Alterations in cytoskeletal proteins have long been associated with a variety of neurodevelopmental disorders. This review focuses on recent findings, primarily from forward genetic screens in Caenorhabditis elegans that illustrate how different tubulin protein isotypes can play distinct roles in neuronal development and function. Additionally, we discuss studies revealing new regulators of the actin cytoskeleton, and highlight recent technological advances in in vivo imaging and functional dissection of the neuronal cytoskeleton.
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Affiliation(s)
- Ngang Heok Tang
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA.
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA.
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20
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Asghari Adib E, Smithson LJ, Collins CA. An axonal stress response pathway: degenerative and regenerative signaling by DLK. Curr Opin Neurobiol 2018; 53:110-119. [PMID: 30053694 DOI: 10.1016/j.conb.2018.07.002] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/02/2018] [Indexed: 02/08/2023]
Abstract
Signaling through the dual leucine zipper-bearing kinase (DLK) is required for injured neurons to initiate new axonal growth; however, activation of this kinase also leads to neuronal degeneration and death in multiple models of injury and neurodegenerative diseases. This has spurred current consideration of DLK as a candidate therapeutic target, and raises a vital question: in what context is DLK a friend or foe to neurons? Here, we review our current understanding of DLK's function and mechanisms in regulating both regenerative and degenerative responses to axonal damage and stress in the nervous system.
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Affiliation(s)
- Elham Asghari Adib
- Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA
| | - Laura J Smithson
- Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA
| | - Catherine A Collins
- Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.
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21
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Thapliyal S, Vasudevan A, Dong Y, Bai J, Koushika SP, Babu K. The C-terminal of CASY-1/Calsyntenin regulates GABAergic synaptic transmission at the Caenorhabditis elegans neuromuscular junction. PLoS Genet 2018. [PMID: 29529030 PMCID: PMC5864096 DOI: 10.1371/journal.pgen.1007263] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The C. elegans ortholog of mammalian calsyntenins, CASY-1, is an evolutionarily conserved type-I transmembrane protein that is highly enriched in the nervous system. Mammalian calsyntenins are strongly expressed at inhibitory synapses, but their role in synapse development and function is still elusive. Here, we report a crucial role for CASY-1 in regulating GABAergic synaptic transmission at the C. elegans neuromuscular junction (NMJ). The shorter isoforms of CASY-1; CASY-1B and CASY-1C, express and function in GABA motor neurons where they regulate GABA neurotransmission. Using pharmacological, behavioral, electrophysiological, optogenetic and imaging approaches we establish that GABA release is compromised at the NMJ in casy-1 mutants. Further, we demonstrate that CASY-1 is required to modulate the transport of GABAergic synaptic vesicle (SV) precursors through a possible interaction with the SV motor protein, UNC-104/KIF1A. This study proposes a possible evolutionarily conserved model for the regulation of GABA synaptic functioning by calsyntenins. GABA acts as a major inhibitory neurotransmitter in both vertebrate and invertebrate nervous systems. Despite the potential deregulation of GABA signaling in several neurological disorders, our understanding of the genetic factors that regulate GABAergic synaptic transmission has just started to evolve. Here, we identify a role for a cell adhesion molecule, CASY-1, in regulating GABA signaling at the C. elegans NMJ. We show that the mutants in casy-1 have reduced number of GABA vesicles at the synapse resulting in less GABA release from the presynaptic GABAergic motor neurons. Further, we show that the shorter isoforms of the casy-1 gene; casy-1b and casy-1c that carry a potential kinesin-motor binding domain are responsible for maintaining GABAergic signaling at the synapse. We show a novel interaction of the CASY-1 isoforms with the C- terminal of the UNC-104/KIF1A motor protein that mediates the trafficking of GABAergic synaptic vesicle precursors to the synapse, thus maintaining normal inhibitory signaling at the NMJ.
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Affiliation(s)
- Shruti Thapliyal
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Manauli, Punjab, India
| | - Amruta Vasudevan
- Department of Biological Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Yongming Dong
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109 and Department of Biochemistry, University of Washington, Seattle, WA, United Sttaes of America
| | - Jihong Bai
- Basic Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109 and Department of Biochemistry, University of Washington, Seattle, WA, United Sttaes of America
| | - Sandhya P. Koushika
- Department of Biological Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Kavita Babu
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Mohali, Knowledge City, Sector 81, SAS Nagar, Manauli, Punjab, India
- * E-mail: ,
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22
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Intermediate filament accumulation can stabilize microtubules in Caenorhabditis elegans motor neurons. Proc Natl Acad Sci U S A 2018; 115:3114-3119. [PMID: 29511101 DOI: 10.1073/pnas.1721930115] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neural circuits utilize a coordinated cellular machinery to form and eliminate synaptic connections, with the neuronal cytoskeleton playing a prominent role. During larval development of Caenorhabditis elegans, synapses of motor neurons are stereotypically rewired through a process facilitated by dynamic microtubules (MTs). Through a genetic suppressor screen on mutant animals that fail to rewire synapses, and in combination with live imaging and ultrastructural studies, we find that intermediate filaments (IFs) stabilize MTs to prevent synapse rewiring. Genetic ablation of IFs or pharmacological disruption of IF networks restores MT growth and rescues synapse rewiring defects in the mutant animals, indicating that IF accumulation directly alters MT stability. Our work sheds light on the impact of IFs on MT dynamics and axonal transport, which is relevant to the mechanistic understanding of several human motor neuron diseases characterized by IF accumulation in axonal swellings.
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23
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Jin Y, Qi YB. Building stereotypic connectivity: mechanistic insights into structural plasticity from C. elegans. Curr Opin Neurobiol 2017; 48:97-105. [PMID: 29182952 DOI: 10.1016/j.conb.2017.11.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2017] [Revised: 11/07/2017] [Accepted: 11/14/2017] [Indexed: 01/10/2023]
Abstract
The ability of neurons to modify or remodel their synaptic connectivity is critical for the function of neural circuitry throughout the life of an animal. Understanding the mechanisms underlying neuronal structural changes is central to our knowledge of how the nervous system is shaped for complex behaviors and how it further adapts to developmental and environmental demands. Caenorhabditis elegans provides a powerful model for examining developmental processes and for discovering mechanisms controlling neural plasticity. Recent findings have identified conserved themes underlying neural plasticity in development and under environmental stress.
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Affiliation(s)
- Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA.
| | - Yingchuan B Qi
- Zhejiang Key Laboratory of Organ Development and Regeneration, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China.
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24
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Borgen MA, Wang D, Grill B. RPM-1 regulates axon termination by affecting growth cone collapse and microtubule stability. Development 2017; 144:4658-4672. [PMID: 29084805 DOI: 10.1242/dev.154187] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2017] [Accepted: 10/21/2017] [Indexed: 12/14/2022]
Abstract
Axon termination is essential for efficient and accurate nervous system construction. At present, relatively little is known about how growth cone collapse occurs prior to axon termination in vivo Using the mechanosensory neurons of C. elegans, we found collapse prior to axon termination is protracted, with the growth cone transitioning from a dynamic to a static state. Growth cone collapse prior to termination is facilitated by the signaling hub RPM-1. Given the prominence of the cytoskeleton in growth cone collapse, we assessed the relationship between RPM-1 and regulators of actin dynamics and microtubule stability. Our results reveal several important findings about how axon termination is orchestrated: (1) RPM-1 functions in parallel to RHO-1 and CRMP/UNC-33, but is suppressed by the Rac isoform MIG-2; (2) RPM-1 opposes the function of microtubule stabilizers, including tubulin acetyltransferases; and (3) genetic epistasis suggests the microtubule-stabilizing protein Tau/PTL-1 potentially inhibits RPM-1. These findings provide insight into how growth cone collapse is regulated during axon termination in vivo, and suggest that RPM-1 signaling destabilizes microtubules to facilitate growth cone collapse and axon termination.
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Affiliation(s)
- Melissa A Borgen
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, FL 33458, USA
| | - Dandan Wang
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, FL 33458, USA
| | - Brock Grill
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, FL 33458, USA
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25
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Yu B, Wang X, Wei S, Fu T, Dzakah EE, Waqas A, Walthall WW, Shan G. Convergent Transcriptional Programs Regulate cAMP Levels in C. elegans GABAergic Motor Neurons. Dev Cell 2017; 43:212-226.e7. [PMID: 29033363 DOI: 10.1016/j.devcel.2017.09.013] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 06/26/2017] [Accepted: 09/15/2017] [Indexed: 02/07/2023]
Abstract
Both transcriptional regulation and signaling pathways play crucial roles in neuronal differentiation and plasticity. Caenorhabditis elegans possesses 19 GABAergic motor neurons (MNs) called D MNs, which are divided into two subgroups: DD and VD. DD, but not VD, MNs reverse their cellular polarity in a developmental process called respecification. UNC-30 and UNC-55 are two critical transcription factors in D MNs. By using chromatin immunoprecipitation with CRISPR/Cas9 knockin of GFP fusion, we uncovered the global targets of UNC-30 and UNC-55. UNC-30 and UNC-55 are largely converged to regulate over 1,300 noncoding and coding genes, and genes in multiple biological processes, including cAMP metabolism, are co-regulated. Increase in cAMP levels may serve as a timing signal for respecification, whereas UNC-55 regulates genes such as pde-4 to keep the cAMP levels low in VD. Other genes modulating DD respecification such as lin-14, irx-1, and oig-1 are also found to affect cAMP levels.
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Affiliation(s)
- Bin Yu
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Xiaolin Wang
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Shuai Wei
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Tao Fu
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Emmanuel Enoch Dzakah
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Ahmed Waqas
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China
| | - Walter W Walthall
- Department of Biology, Georgia State University, Atlanta, GA 30303, USA
| | - Ge Shan
- CAS Key Laboratory of Innate Immunity and Chronic Disease, CAS Center for Excellence in Molecular Cell Science, School of Life Sciences, University of Science and Technology of China, Hefei, Anhui Province 230027, China.
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26
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Li J, Zhang YV, Asghari Adib E, Stanchev DT, Xiong X, Klinedinst S, Soppina P, Jahn TR, Hume RI, Rasse TM, Collins CA. Restraint of presynaptic protein levels by Wnd/DLK signaling mediates synaptic defects associated with the kinesin-3 motor Unc-104. eLife 2017; 6:e24271. [PMID: 28925357 PMCID: PMC5605197 DOI: 10.7554/elife.24271] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2016] [Accepted: 08/11/2017] [Indexed: 12/19/2022] Open
Abstract
The kinesin-3 family member Unc-104/KIF1A is required for axonal transport of many presynaptic components to synapses, and mutation of this gene results in synaptic dysfunction in mice, flies and worms. Our studies at the Drosophila neuromuscular junction indicate that many synaptic defects in unc-104-null mutants are mediated independently of Unc-104's transport function, via the Wallenda (Wnd)/DLK MAP kinase axonal damage signaling pathway. Wnd signaling becomes activated when Unc-104's function is disrupted, and leads to impairment of synaptic structure and function by restraining the expression level of active zone (AZ) and synaptic vesicle (SV) components. This action concomitantly suppresses the buildup of synaptic proteins in neuronal cell bodies, hence may play an adaptive role to stresses that impair axonal transport. Wnd signaling also becomes activated when pre-synaptic proteins are over-expressed, suggesting the existence of a feedback circuit to match synaptic protein levels to the transport capacity of the axon.
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Affiliation(s)
- Jiaxing Li
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Yao V Zhang
- Junior Research Group Synaptic PlasticityHertie-Institute for Clinical Brain Research, University of TübingenTübingenGermany
- Graduate School of Cellular and Molecular NeuroscienceUniversity of TübingenTübingenGermany
| | - Elham Asghari Adib
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Doychin T Stanchev
- Junior Research Group Synaptic PlasticityHertie-Institute for Clinical Brain Research, University of TübingenTübingenGermany
- Graduate School of Cellular and Molecular NeuroscienceUniversity of TübingenTübingenGermany
| | - Xin Xiong
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Susan Klinedinst
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Pushpanjali Soppina
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Thomas Robert Jahn
- CHS Research Group Proteostasis in Neurodegenerative DiseaseDKFZ Deutsches KrebsforschungszentrumHeidelbergGermany
| | - Richard I Hume
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
| | - Tobias M Rasse
- Junior Research Group Synaptic PlasticityHertie-Institute for Clinical Brain Research, University of TübingenTübingenGermany
- CHS Research Group Proteostasis in Neurodegenerative DiseaseDKFZ Deutsches KrebsforschungszentrumHeidelbergGermany
| | - Catherine A Collins
- Department of Molecular, Cellular, and Developmental BiologyUniversity of MichiganAnn ArborUnited States
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27
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Brown G, El Bejjani R. SPAS-1 expression in neurons and vulva during L4 stage. MICROPUBLICATION BIOLOGY 2017; 2017:10.17912/W2P94X. [PMID: 32550364 PMCID: PMC7255884 DOI: 10.17912/w2p94x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- George Brown
- Department of Biology, Davidson College, Box 7118, Davidson, NC 28035, USA
| | - Rachid El Bejjani
- Department of Biology, Davidson College, Box 7118, Davidson, NC 28035, USA.,
Correspondence to: Rachid El Bejjani ()
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28
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Abstract
Although much is known about the regenerative capacity of retinal ganglion cells, very significant barriers remain in our ability to restore visual function following traumatic injury or disease-induced degeneration. Here we summarize our current understanding of the factors regulating axon guidance and target engagement in regenerating axons, and review the state of the field of neural regeneration, focusing on the visual system and highlighting studies using other model systems that can inform analysis of visual system regeneration. This overview is motivated by a Society for Neuroscience Satellite meeting, "Reconnecting Neurons in the Visual System," held in October 2015 sponsored by the National Eye Institute as part of their "Audacious Goals Initiative" and co-organized by Carol Mason (Columbia University) and Michael Crair (Yale University). The collective wisdom of the conference participants pointed to important gaps in our knowledge and barriers to progress in promoting the restoration of visual system function. This article is thus a summary of our existing understanding of visual system regeneration and provides a blueprint for future progress in the field.
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29
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Microtubule Organization Determines Axonal Transport Dynamics. Neuron 2017; 92:449-460. [PMID: 27764672 DOI: 10.1016/j.neuron.2016.09.036] [Citation(s) in RCA: 99] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Revised: 08/02/2016] [Accepted: 09/15/2016] [Indexed: 12/31/2022]
Abstract
Axonal microtubule (MT) arrays are the major cytoskeleton substrate for cargo transport. How MT organization, i.e., polymer length, number, and minus-end spacing, is regulated and how it impinges on axonal transport are unclear. We describe a method for analyzing neuronal MT organization using light microscopy. This method circumvents the need for electron microscopy reconstructions and is compatible with live imaging of cargo transport and MT dynamics. Examination of a C. elegans motor neuron revealed how age, MT-associated proteins, and signaling pathways control MT length, minus-end spacing, and coverage. In turn, MT organization determines axonal transport progression: cargoes pause at polymer termini, suggesting that switching MT tracks is rate limiting for efficient transport. Cargo run length is set by MT length, and higher MT coverage correlates with shorter pauses. These results uncover the principles and mechanisms of neuronal MT organization and its regulation of axonal cargo transport.
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30
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Differential regulation of polarized synaptic vesicle trafficking and synapse stability in neural circuit rewiring in Caenorhabditis elegans. PLoS Genet 2017. [PMID: 28636662 PMCID: PMC5500376 DOI: 10.1371/journal.pgen.1006844] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Neural circuits are dynamic, with activity-dependent changes in synapse density and connectivity peaking during different phases of animal development. In C. elegans, young larvae form mature motor circuits through a dramatic switch in GABAergic neuron connectivity, by concomitant elimination of existing synapses and formation of new synapses that are maintained throughout adulthood. We have previously shown that an increase in microtubule dynamics during motor circuit rewiring facilitates new synapse formation. Here, we further investigate cellular control of circuit rewiring through the analysis of mutants obtained in a forward genetic screen. Using live imaging, we characterize novel mutations that alter cargo binding in the dynein motor complex and enhance anterograde synaptic vesicle movement during remodeling, providing in vivo evidence for the tug-of-war between kinesin and dynein in fast axonal transport. We also find that a casein kinase homolog, TTBK-3, inhibits stabilization of nascent synapses in their new locations, a previously unexplored facet of structural plasticity of synapses. Our study delineates temporally distinct signaling pathways that are required for effective neural circuit refinement. In this study, we identify pathways that regulate the formation and maintenance of synapses, the functional connections between neurons, in the nervous system of the nematode C. elegans. Our work characterizes the interaction between molecular motors kinesin and dynein, which carry cargo and move towards opposite ends of microtubules during synapse formation. We also address the role of a protein kinase gene TTBK-3 in maintaining synapse structure once synaptic components have reached the sites of new synapses. Our findings shed mechanistic insight into the coordination of molecular motors and the cytoskeleton in neural circuit function.
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Hao Y, Collins C. Intrinsic mechanisms for axon regeneration: insights from injured axons in Drosophila. Curr Opin Genet Dev 2017; 44:84-91. [PMID: 28232273 PMCID: PMC5447494 DOI: 10.1016/j.gde.2017.01.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Revised: 01/17/2017] [Accepted: 01/26/2017] [Indexed: 12/18/2022]
Abstract
Axonal damage and loss are common and negative consequences of neuronal injuries, and also occur in some neurodegenerative diseases. For neurons to have a chance to repair their connections, they need to survive the damage, initiate new axonal growth, and ultimately establish new synaptic connections. This review discusses how recent work in Drosophila models have informed our understanding of the cellular pathways used by neurons to respond to axonal injuries. Similarly to mammalian neurons, Drosophila neurons appear to be more limited in their capacity regrow (regenerate) damaged axons in the central nervous system, but can undergo axonal regeneration to varying extents in the peripheral nervous system. Conserved cellular pathways are activated by axonal injury via mechanisms that are specific to axons but not dendrites, and new unanticipated inhibitors of axon regeneration can be identified via genetic screening. These findings, made predominantly via genetic and live imaging methods in Drosophila, emphasize the utility of this model organism for the identification and study of basic cellular mechanisms used for neuronal repair.
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Affiliation(s)
- Yan Hao
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA
| | - Catherine Collins
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.
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McLaughlin CN, Broihier HT. MYRFs on the Move to Rewire Circuits. Dev Cell 2017; 41:123-124. [PMID: 28441525 DOI: 10.1016/j.devcel.2017.04.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Synaptic plasticity occurs in response to intrinsic and extrinsic cues and is a key step in the formation of mature neuronal circuits. In this issue of Developmental Cell, Meng et al. (2017) find that two conserved Myrf transcription factors coexist in the same complex to promote developmental circuit remodeling.
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Affiliation(s)
- Colleen N McLaughlin
- Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Heather T Broihier
- Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106, USA.
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Chisholm AD, Hutter H, Jin Y, Wadsworth WG. The Genetics of Axon Guidance and Axon Regeneration in Caenorhabditis elegans. Genetics 2016; 204:849-882. [PMID: 28114100 PMCID: PMC5105865 DOI: 10.1534/genetics.115.186262] [Citation(s) in RCA: 59] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 09/06/2016] [Indexed: 11/18/2022] Open
Abstract
The correct wiring of neuronal circuits depends on outgrowth and guidance of neuronal processes during development. In the past two decades, great progress has been made in understanding the molecular basis of axon outgrowth and guidance. Genetic analysis in Caenorhabditis elegans has played a key role in elucidating conserved pathways regulating axon guidance, including Netrin signaling, the slit Slit/Robo pathway, Wnt signaling, and others. Axon guidance factors were first identified by screens for mutations affecting animal behavior, and by direct visual screens for axon guidance defects. Genetic analysis of these pathways has revealed the complex and combinatorial nature of guidance cues, and has delineated how cues guide growth cones via receptor activity and cytoskeletal rearrangement. Several axon guidance pathways also affect directed migrations of non-neuronal cells in C. elegans, with implications for normal and pathological cell migrations in situations such as tumor metastasis. The small number of neurons and highly stereotyped axonal architecture of the C. elegans nervous system allow analysis of axon guidance at the level of single identified axons, and permit in vivo tests of prevailing models of axon guidance. C. elegans axons also have a robust capacity to undergo regenerative regrowth after precise laser injury (axotomy). Although such axon regrowth shares some similarities with developmental axon outgrowth, screens for regrowth mutants have revealed regeneration-specific pathways and factors that were not identified in developmental screens. Several areas remain poorly understood, including how major axon tracts are formed in the embryo, and the function of axon regeneration in the natural environment.
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Affiliation(s)
| | - Harald Hutter
- Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, V5A 1S6, Canada
| | - Yishi Jin
- Section of Neurobiology, Division of Biological Sciences, and
- Department of Cellular and Molecular Medicine, School of Medicine, University of California, San Diego, La Jolla, California 92093
- Department of Pathology and Laboratory Medicine, Howard Hughes Medical Institute, Chevy Chase, Maryland, and
| | - William G Wadsworth
- Department of Pathology, Rutgers Robert Wood Johnson Medical School, Piscataway, New Jersey 08854
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Brill MS, Kleele T, Ruschkies L, Wang M, Marahori NA, Reuter MS, Hausrat TJ, Weigand E, Fisher M, Ahles A, Engelhardt S, Bishop DL, Kneussel M, Misgeld T. Branch-Specific Microtubule Destabilization Mediates Axon Branch Loss during Neuromuscular Synapse Elimination. Neuron 2016; 92:845-856. [PMID: 27773584 PMCID: PMC5133389 DOI: 10.1016/j.neuron.2016.09.049] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2016] [Revised: 08/14/2016] [Accepted: 09/21/2016] [Indexed: 01/17/2023]
Abstract
Developmental axon remodeling is characterized by the selective removal of branches from axon arbors. The mechanisms that underlie such branch loss are largely unknown. Additionally, how neuronal resources are specifically assigned to the branches of remodeling arbors is not understood. Here we show that axon branch loss at the developing mouse neuromuscular junction is mediated by branch-specific microtubule severing, which results in local disassembly of the microtubule cytoskeleton and loss of axonal transport in branches that will subsequently dismantle. Accordingly, pharmacological microtubule stabilization delays neuromuscular synapse elimination. This branch-specific disassembly of the cytoskeleton appears to be mediated by the microtubule-severing enzyme spastin, which is dysfunctional in some forms of upper motor neuron disease. Our results demonstrate a physiological role for a neurodegeneration-associated modulator of the cytoskeleton, reveal unexpected cell biology of branch-specific axon plasticity and underscore the mechanistic similarities of axon loss in development and disease. During synapse elimination, retreating axon branches dismantle their microtubules Microtubules are destabilized due to branch-specific severing Microtubule stabilization delays axon branch removal during synapse elimination The disease-associated microtubule severing protein spastin mediates microtubule loss
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Affiliation(s)
- Monika S Brill
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany.
| | - Tatjana Kleele
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Laura Ruschkies
- University Medical Center Hamburg-Eppendorf, Center for Molecular Neurobiology (ZMNH), Institute for Molecular Neurogenetics, Falkenried 94, 20251 Hamburg, Germany
| | - Mengzhe Wang
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Natalia A Marahori
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Miriam S Reuter
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Torben J Hausrat
- University Medical Center Hamburg-Eppendorf, Center for Molecular Neurobiology (ZMNH), Institute for Molecular Neurogenetics, Falkenried 94, 20251 Hamburg, Germany
| | - Emily Weigand
- Ball State University, Department of Biology, 2000 West University, Muncie, IN 47306, USA
| | - Matthew Fisher
- Ball State University, Department of Biology, 2000 West University, Muncie, IN 47306, USA
| | - Andrea Ahles
- Institute of Pharmacology and Toxicology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany; German Center for Cardiovascular Research, DZHK, Partner site Munich Heart Alliance, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Stefan Engelhardt
- Institute of Pharmacology and Toxicology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany; German Center for Cardiovascular Research, DZHK, Partner site Munich Heart Alliance, Biedersteiner Straße 29, 80802 Munich, Germany
| | - Derron L Bishop
- Indiana University School of Medicine, Department of Cellular and Integrative Physiology, Medical Science Building 385, Indianapolis, IN 46202, USA; Stark Neurosciences Research Institute, Indiana University School of Medicine, 320 W. 15(th) Street, Indianapolis, IN 46202, USA
| | - Matthias Kneussel
- University Medical Center Hamburg-Eppendorf, Center for Molecular Neurobiology (ZMNH), Institute for Molecular Neurogenetics, Falkenried 94, 20251 Hamburg, Germany
| | - Thomas Misgeld
- Institute of Neuronal Cell Biology, Technische Universität München, Biedersteiner Straße 29, 80802 Munich, Germany; Center of Integrated Protein Science (CIPSM), Butenandtstraße 5-13, 81377 Munich, Germany; German Center for Neurodegenerative Diseases (DZNE), Feodor-Lynen-Straße 17, 81377 Munich, Germany; Munich Cluster of Systems Neurology (SyNergy), Feodor-Lynen-Straße 17, 81377 Munich, Germany.
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Grill B, Murphey RK, Borgen MA. The PHR proteins: intracellular signaling hubs in neuronal development and axon degeneration. Neural Dev 2016; 11:8. [PMID: 27008623 PMCID: PMC4806438 DOI: 10.1186/s13064-016-0063-0] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 03/15/2016] [Indexed: 11/10/2022] Open
Abstract
During development, a coordinated and integrated series of events must be accomplished in order to generate functional neural circuits. Axons must navigate toward target cells, build synaptic connections, and terminate outgrowth. The PHR proteins (consisting of mammalian Phr1/MYCBP2, Drosophila Highwire and C. elegans RPM-1) function in each of these events in development. Here, we review PHR function across species, as well as the myriad of signaling pathways PHR proteins regulate. These findings collectively suggest that the PHR proteins are intracellular signaling hubs, a concept we explore in depth. Consistent with prominent developmental functions, genetic links have begun to emerge between PHR signaling networks and neurodevelopmental disorders, such as autism, schizophrenia and intellectual disability. Finally, we discuss the recent and important finding that PHR proteins regulate axon degeneration, which has further heightened interest in this fascinating group of molecules.
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Affiliation(s)
- Brock Grill
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, FL, 33458, USA.
| | - Rodney K Murphey
- Department of Biological Sciences, Florida Atlantic University, Jupiter, FL, 33458, USA
| | - Melissa A Borgen
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, FL, 33458, USA
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36
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Kurup N, Jin Y. Neural circuit rewiring: insights from DD synapse remodeling. WORM 2015; 5:e1129486. [PMID: 27073734 DOI: 10.1080/21624054.2015.1129486] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 11/24/2015] [Accepted: 12/04/2015] [Indexed: 01/27/2023]
Abstract
Nervous systems exhibit many forms of neuronal plasticity during growth, learning and memory consolidation, as well as in response to injury. Such plasticity can occur across entire nervous systems as with the case of insect metamorphosis, in individual classes of neurons, or even at the level of a single neuron. A striking example of neuronal plasticity in C. elegans is the synaptic rewiring of the GABAergic Dorsal D-type motor neurons during larval development, termed DD remodeling. DD remodeling entails multi-step coordination to concurrently eliminate pre-existing synapses and form new synapses on different neurites, without changing the overall morphology of the neuron. This mini-review focuses on recent advances in understanding the cellular and molecular mechanisms driving DD remodeling.
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Affiliation(s)
- Naina Kurup
- Neurobiology Section, Division of Biological Sciences, University of California , San Diego, La Jolla, CA, USA
| | - Yishi Jin
- Neurobiology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, USA; Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA, USA; Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA, USA
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Gartz Hanson M, Aiken J, Sietsema DV, Sept D, Bates EA, Niswander L, Moore JK. Novel α-tubulin mutation disrupts neural development and tubulin proteostasis. Dev Biol 2015; 409:406-19. [PMID: 26658218 DOI: 10.1016/j.ydbio.2015.11.022] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 11/10/2015] [Accepted: 11/27/2015] [Indexed: 10/22/2022]
Abstract
Mutations in the microtubule cytoskeleton are linked to cognitive and locomotor defects during development, and neurodegeneration in adults. How these mutations impact microtubules, and how this alters function at the level of neurons is an important area of investigation. Using a forward genetic screen in mice, we identified a missense mutation in Tuba1a α-tubulin that disrupts cortical and motor neuron development. Homozygous mutant mice exhibit cortical dysgenesis reminiscent of human tubulinopathies. Motor neurons fail to innervate target muscles in the limbs and show synapse defects at proximal targets. To directly examine effects on tubulin function, we created analogous mutations in the α-tubulin isotypes in budding yeast. These mutations sensitize yeast cells to microtubule stresses including depolymerizing drugs and low temperatures. Furthermore, we find that mutant α-tubulin is depleted from the cell lysate and from microtubules, thereby altering ratios of α-tubulin isotypes. Tubulin-binding cofactors suppress the effects of the mutation, indicating an important role for these cofactors in regulating the quality of the α-tubulin pool. Together, our results give new insights into the functions of Tuba1a, mechanisms for regulating tubulin proteostasis, and how compromising these may lead to neural defects.
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Affiliation(s)
- M Gartz Hanson
- Department of Pediatrics, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA
| | - Jayne Aiken
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO, USA
| | - Daniel V Sietsema
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO, USA
| | - David Sept
- Department of Biomedical Engineering and Center for Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI, USA
| | - Emily A Bates
- Department of Pediatrics, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA
| | - Lee Niswander
- Department of Pediatrics, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA
| | - Jeffrey K Moore
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, CO, USA.
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Giles AC, Opperman KJ, Rankin CH, Grill B. Developmental Function of the PHR Protein RPM-1 Is Required for Learning in Caenorhabditis elegans. G3 (BETHESDA, MD.) 2015; 5:2745-57. [PMID: 26464359 PMCID: PMC4683646 DOI: 10.1534/g3.115.021410] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Accepted: 10/06/2015] [Indexed: 12/12/2022]
Abstract
The PAM/Highwire/RPM-1 (PHR) proteins are signaling hubs that function as important regulators of neural development. Loss of function in Caenorhabditis elegans rpm-1 and Drosophila Highwire results in failed axon termination, inappropriate axon targeting, and abnormal synapse formation. Despite broad expression in the nervous system and relatively dramatic defects in synapse formation and axon development, very mild abnormalities in behavior have been found in animals lacking PHR protein function. Therefore, we hypothesized that large defects in behavior might only be detected in scenarios in which evoked, prolonged circuit function is required, or in which behavioral plasticity occurs. Using quantitative approaches in C. elegans, we found that rpm-1 loss-of-function mutants have relatively mild abnormalities in exploratory locomotion, but have large defects in evoked responses to harsh touch and learning associated with tap habituation. We explored the nature of the severe habituation defects in rpm-1 mutants further. To address what part of the habituation circuit was impaired in rpm-1 mutants, we performed rescue analysis with promoters for different neurons. Our findings indicate that RPM-1 function in the mechanosensory neurons affects habituation. Transgenic expression of RPM-1 in adult animals failed to rescue habituation defects, consistent with developmental defects in rpm-1 mutants resulting in impaired habituation. Genetic analysis showed that other regulators of neuronal development that function in the rpm-1 pathway (including glo-4, fsn-1, and dlk-1) also affected habituation. Overall, our findings suggest that developmental defects in rpm-1 mutants manifest most prominently in behaviors that require protracted or plastic circuit function, such as learning.
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Affiliation(s)
- Andrew C Giles
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, Florida 33458
| | - Karla J Opperman
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, Florida 33458
| | - Catharine H Rankin
- Department of Psychology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada Brain Research Centre, University of British Columbia, Vancouver, British Columbia V6T 2B5, Canada
| | - Brock Grill
- Department of Neuroscience, The Scripps Research Institute, Scripps Florida, Jupiter, Florida 33458
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Kevenaar JT, Hoogenraad CC. The axonal cytoskeleton: from organization to function. Front Mol Neurosci 2015; 8:44. [PMID: 26321907 PMCID: PMC4536388 DOI: 10.3389/fnmol.2015.00044] [Citation(s) in RCA: 128] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Accepted: 07/31/2015] [Indexed: 01/20/2023] Open
Abstract
The axon is the single long fiber that extends from the neuron and transmits electrical signals away from the cell body. The neuronal cytoskeleton, composed of microtubules (MTs), actin filaments and neurofilaments, is not only required for axon formation and axonal transport but also provides the structural basis for several specialized axonal structures, such as the axon initial segment (AIS) and presynaptic boutons. Emerging evidence suggest that the unique cytoskeleton organization in the axon is essential for its structure and integrity. In addition, the increasing number of neurodevelopmental and neurodegenerative diseases linked to defect in actin- and microtubule-dependent processes emphasizes the importance of a properly regulated cytoskeleton for normal axonal functioning. Here, we provide an overview of the current understanding of actin and microtubule organization within the axon and discuss models for the functional role of the cytoskeleton at specialized axonal structures.
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Affiliation(s)
- Josta T. Kevenaar
- Cell Biology, Faculty of Science, Utrecht UniversityUtrecht, Netherlands
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