1
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Brown RI, Barber HM, Kucenas S. Satellite glial cell manipulation prior to axotomy enhances developing dorsal root ganglion central branch regrowth into the spinal cord. Glia 2024; 72:1766-1784. [PMID: 39141572 PMCID: PMC11325082 DOI: 10.1002/glia.24581] [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: 12/05/2023] [Revised: 05/30/2024] [Accepted: 06/02/2024] [Indexed: 08/16/2024]
Abstract
The central and peripheral nervous systems (CNS and PNS, respectively) exhibit remarkable diversity in the capacity to regenerate following neuronal injury with PNS injuries being much more likely to regenerate than those that occur in the CNS. Glial responses to damage greatly influence the likelihood of regeneration by either promoting or inhibiting axonal regrowth over time. However, despite our understanding of how some glial lineages participate in nerve degeneration and regeneration, less is known about the contributions of peripheral satellite glial cells (SGC) to regeneration failure following central axon branch injury of dorsal root ganglia (DRG) sensory neurons. Here, using in vivo, time-lapse imaging in larval zebrafish coupled with laser axotomy, we investigate the role of SGCs in axonal regeneration. In our studies we show that SGCs respond to injury by relocating their nuclei to the injury site during the same period that DRG neurons produce new central branch neurites. Laser ablation of SGCs prior to axon injury results in more neurite growth attempts and ultimately a higher rate of successful central axon regrowth, implicating SGCs as inhibitors of regeneration. We also demonstrate that this SGC response is mediated in part by ErbB signaling, as chemical inhibition of this receptor results in reduced SGC motility and enhanced central axon regrowth. These findings provide new insights into SGC-neuron interactions under injury conditions and how these interactions influence nervous system repair.
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Affiliation(s)
- Robin I Brown
- Department of Biology, University of Virginia, Charlottesville, Virginia, USA
- Program in Fundamental Neuroscience, University of Virginia, Charlottesville, Virginia, USA
| | - Heather M Barber
- Program in Fundamental Neuroscience, University of Virginia, Charlottesville, Virginia, USA
- Cell & Developmental Biology Graduate Program, University of Virginia, Charlottesville, Virginia, USA
| | - Sarah Kucenas
- Department of Biology, University of Virginia, Charlottesville, Virginia, USA
- Program in Fundamental Neuroscience, University of Virginia, Charlottesville, Virginia, USA
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2
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Antagonistic Activities of Fmn2 and ADF Regulate Axonal F-Actin Patch Dynamics and the Initiation of Collateral Branching. J Neurosci 2022; 42:7355-7369. [PMID: 36481742 PMCID: PMC9525169 DOI: 10.1523/jneurosci.3107-20.2022] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Revised: 08/17/2022] [Accepted: 08/22/2022] [Indexed: 12/15/2022] Open
Abstract
Interstitial collateral branching of axons is a critical component in the development of functional neural circuits. Axon collateral branches are established through a series of cellular processes initiated by the development of a specialized, focal F-actin network in axons. The formation, maintenance and remodeling of this F-actin patch is critical for the initiation of axonal protrusions that are subsequently consolidated to form a collateral branch. However, the mechanisms regulating F-actin patch dynamics are poorly understood. Fmn2 is a formin family member implicated in multiple neurodevelopmental disorders. We find that Fmn2 regulates the initiation of axon collateral protrusions in chick spinal neurons and in zebrafish motor neurons. Fmn2 localizes to the protrusion-initiating axonal F-actin patches and regulates the lifetime and size of these F-actin networks. The F-actin nucleation activity of Fmn2 is necessary for F-actin patch stability but not for initiating patch formation. We show that Fmn2 insulates the F-actin patches from disassembly by the actin-depolymerizing factor, ADF, and promotes long-lived, larger patches that are competent to initiate axonal protrusions. The regulation of axonal branching can contribute to the neurodevelopmental pathologies associated with Fmn2 and the dynamic antagonism between Fmn2 and ADF may represent a general mechanism of formin-dependent protection of Arp2/3-initiated F-actin networks from disassembly.SIGNIFICANCE STATEMENT Axonal branching is a key process in the development of functional circuits and neural plasticity. Axon collateral branching is initiated by the elaboration of F-actin filaments from discrete axonal F-actin networks. We show that the neurodevelopmental disorder-associated formin, Fmn2, is a critical regulator of axon collateral branching. Fmn2 localizes to the collateral branch-inducing F-actin patches in axons and regulates the stability of these actin networks. The F-actin nucleation activity of Fmn2 protects the patches from ADF-mediated disassembly. Opposing activities of Fmn2 and ADF exert a dynamic regulatory control on axon collateral branch initiation and may underly the neurodevelopmental defects associated with Fmn2.
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3
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Haynes EM, Burnett KH, He J, Jean-Pierre MW, Jarzyna M, Eliceiri KW, Huisken J, Halloran MC. KLC4 shapes axon arbors during development and mediates adult behavior. eLife 2022; 11:74270. [PMID: 36222498 PMCID: PMC9596160 DOI: 10.7554/elife.74270] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 10/11/2022] [Indexed: 11/13/2022] Open
Abstract
Development of elaborate and polarized neuronal morphology requires precisely regulated transport of cellular cargos by motor proteins such as kinesin-1. Kinesin-1 has numerous cellular cargos which must be delivered to unique neuronal compartments. The process by which this motor selectively transports and delivers cargo to regulate neuronal morphogenesis is poorly understood, although the cargo-binding kinesin light chain (KLC) subunits contribute to specificity. Our work implicates one such subunit, KLC4, as an essential regulator of axon branching and arborization pattern of sensory neurons during development. Using live imaging approaches in klc4 mutant zebrafish, we show that KLC4 is required for stabilization of nascent axon branches, proper microtubule (MT) dynamics, and endosomal transport. Furthermore, KLC4 is required for proper tiling of peripheral axon arbors: in klc4 mutants, peripheral axons showed abnormal fasciculation, a behavior characteristic of central axons. This result suggests that KLC4 patterns axonal compartments and helps establish molecular differences between central and peripheral axons. Finally, we find that klc4 mutant larva are hypersensitive to touch and adults show anxiety-like behavior in a novel tank test, implicating klc4 as a new gene involved in stress response circuits.
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Affiliation(s)
- Elizabeth M Haynes
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Center for Quantitative Cell Imaging, University of Wisconsin-MadisonMadisonUnited States,Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States,Morgridge Institute for ResearchMadisonUnited States
| | - Korri H Burnett
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
| | - Jiaye He
- Morgridge Institute for ResearchMadisonUnited States,National Innovation Center for Advanced Medical DevicesShenzenChina
| | - Marcel W Jean-Pierre
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
| | - Martin Jarzyna
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
| | - Kevin W Eliceiri
- Center for Quantitative Cell Imaging, University of Wisconsin-MadisonMadisonUnited States,Morgridge Institute for ResearchMadisonUnited States
| | - Jan Huisken
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Morgridge Institute for ResearchMadisonUnited States,Department of Biology and Psychology, Georg-August-UniversityGöttingenGermany
| | - Mary C Halloran
- Department of Integrative Biology, University of Wisconsin-MadisonMadisonUnited States,Department of Neuroscience, University of Wisconsin-MadisonMadisonUnited States
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4
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Lee AJ, Yoon D, Han S, Hugonnet H, Park W, Park JK, Nam Y, Park Y. Label-free monitoring of 3D cortical neuronal growth in vitro using optical diffraction tomography. BIOMEDICAL OPTICS EXPRESS 2021; 12:6928-6939. [PMID: 34858689 PMCID: PMC8606138 DOI: 10.1364/boe.439404] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 09/17/2021] [Accepted: 09/18/2021] [Indexed: 05/10/2023]
Abstract
The highly complex central nervous systems of mammals are often studied using three-dimensional (3D) in vitro primary neuronal cultures. A coupled confocal microscopy and immunofluorescence labeling are widely utilized for visualizing the 3D structures of neurons. However, this requires fixation of the neurons and is not suitable for monitoring an identical sample at multiple time points. Thus, we propose a label-free monitoring method for 3D neuronal growth based on refractive index tomograms obtained by optical diffraction tomography. The 3D morphology of the neurons was clearly visualized, and the developmental processes of neurite outgrowth in 3D spaces were analyzed for individual neurons.
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Affiliation(s)
- Ariel J Lee
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- KAIST Institute for Health Science and Technology, KAIST, Daejeon 34141, Republic of Korea
- Current Affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Contributed equally
| | - DongJo Yoon
- Department of Bio and Brain Engineering, KAIST, Daejeon 34141, Republic of Korea
- Contributed equally
| | - SeungYun Han
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- KAIST Institute for Health Science and Technology, KAIST, Daejeon 34141, Republic of Korea
- Current Affiliation: Department of Applied Physics, Yale University, New Haven, CT 06520, USA
- Contributed equally
| | - Herve Hugonnet
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- KAIST Institute for Health Science and Technology, KAIST, Daejeon 34141, Republic of Korea
| | - WeiSun Park
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- KAIST Institute for Health Science and Technology, KAIST, Daejeon 34141, Republic of Korea
| | - Je-Kyun Park
- Department of Bio and Brain Engineering, KAIST, Daejeon 34141, Republic of Korea
| | - YoonKey Nam
- Department of Bio and Brain Engineering, KAIST, Daejeon 34141, Republic of Korea
| | - YongKeun Park
- Department of Physics, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
- KAIST Institute for Health Science and Technology, KAIST, Daejeon 34141, Republic of Korea
- Tomocube Inc., Daejeon, Republic of Korea
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5
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Motahari Z, Maynard TM, Popratiloff A, Moody SA, LaMantia AS. Aberrant early growth of individual trigeminal sensory and motor axons in a series of mouse genetic models of 22q11.2 deletion syndrome. Hum Mol Genet 2021; 29:3081-3093. [PMID: 32901287 PMCID: PMC7645708 DOI: 10.1093/hmg/ddaa199] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Revised: 07/29/2020] [Accepted: 09/01/2020] [Indexed: 02/06/2023] Open
Abstract
We identified divergent modes of initial axon growth that prefigure disrupted differentiation of the trigeminal nerve (CN V), a cranial nerve essential for suckling, feeding and swallowing (S/F/S), a key innate behavior compromised in multiple genetic developmental disorders including DiGeorge/22q11.2 Deletion Syndrome (22q11.2 DS). We combined rapid in vivo labeling of single CN V axons in LgDel+/− mouse embryos, a genomically accurate 22q11.2DS model, and 3D imaging to identify and quantify phenotypes that could not be resolved using existing methods. We assessed these phenotypes in three 22q11.2-related genotypes to determine whether individual CN V motor and sensory axons wander, branch and sprout aberrantly in register with altered anterior–posterior hindbrain patterning and gross morphological disruption of CN V seen in LgDel+/−. In the additional 22q11.2-related genotypes: Tbx1+/−, Ranbp1−/−, Ranbp1+/− and LgDel+/−:Raldh2+/−; axon phenotypes are seen when hindbrain patterning and CN V gross morphology is altered, but not when it is normal or restored toward WT. This disordered growth of CN V sensory and motor axons, whose appropriate targeting is critical for optimal S/F/S, may be an early, critical determinant of imprecise innervation leading to inefficient oropharyngeal function associated with 22q11.2 deletion from birth onward.
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Affiliation(s)
- Zahra Motahari
- Institute for Neuroscience, Washington, DC 20037, USA.,Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC 20037, USA
| | - Thomas M Maynard
- The Fralin Biomedical Research Institute at Virginia Tech-Carilion School of Medicine, Roanoke, VA 24016, USA
| | - Anastas Popratiloff
- Institute for Neuroscience, Washington, DC 20037, USA.,Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC 20037, USA
| | - Sally A Moody
- Institute for Neuroscience, Washington, DC 20037, USA.,Department of Anatomy and Cell Biology, The George Washington University School of Medicine and Health Sciences, Washington, DC 20037, USA
| | - Anthony-S LaMantia
- The Fralin Biomedical Research Institute at Virginia Tech-Carilion School of Medicine, Roanoke, VA 24016, USA.,Department of Biological Sciences, Virginia Tech, Blacksburg, VA 24060, USA
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6
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Shorey M, Rao K, Stone MC, Mattie FJ, Sagasti A, Rolls MM. Microtubule organization of vertebrate sensory neurons in vivo. Dev Biol 2021; 478:1-12. [PMID: 34147472 DOI: 10.1016/j.ydbio.2021.06.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/11/2021] [Accepted: 06/12/2021] [Indexed: 01/30/2023]
Abstract
Dorsal root ganglion (DRG) neurons are the predominant cell type that innervates the vertebrate skin. They are typically described as pseudounipolar cells that have central and peripheral axons branching from a single root exiting the cell body. The peripheral axon travels within a nerve to the skin, where free sensory endings can emerge and branch into an arbor that receives and integrates information. In some immature vertebrates, DRG neurons are preceded by Rohon-Beard (RB) neurons. While the sensory endings of RB and DRG neurons function like dendrites, we use live imaging in zebrafish to show that they have axonal plus-end-out microtubule polarity at all stages of maturity. Moreover, we show both cell types have central and peripheral axons with plus-end-out polarity. Surprisingly, in DRG neurons these emerge separately from the cell body, and most cells never acquire the signature pseudounipolar morphology. Like another recently characterized cell type that has multiple plus-end-out neurites, ganglion cells in Nematostella, RB and DRG neurons maintain a somatic microtubule organizing center even when mature. In summary, we characterize key cellular and subcellular features of vertebrate sensory neurons as a foundation for understanding their function and maintenance.
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Affiliation(s)
- Matthew Shorey
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Kavitha Rao
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Michelle C Stone
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Floyd J Mattie
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA
| | - Alvaro Sagasti
- Molecular, Cell and Developmental Biology Department and Molecular Biology Institute, University of California, Los Angeles, CA, 90095, USA
| | - Melissa M Rolls
- Department of Biochemistry and Molecular Biology and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, PA, 16802, USA.
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7
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Holt E, Stanton-Turcotte D, Iulianella A. Development of the Vertebrate Trunk Sensory System: Origins, Specification, Axon Guidance, and Central Connectivity. Neuroscience 2021; 458:229-243. [PMID: 33460728 DOI: 10.1016/j.neuroscience.2020.12.037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 12/09/2020] [Accepted: 12/31/2020] [Indexed: 12/26/2022]
Abstract
Crucial to an animal's movement through their environment and to the maintenance of their homeostatic physiology is the integration of sensory information. This is achieved by axons communicating from organs, muscle spindles and skin that connect to the sensory ganglia composing the peripheral nervous system (PNS), enabling organisms to collect an ever-constant flow of sensations and relay it to the spinal cord. The sensory system carries a wide spectrum of sensory modalities - from sharp pain to cool refreshing touch - traveling from the periphery to the spinal cord via the dorsal root ganglia (DRG). This review covers the origins and development of the DRG and the cells that populate it, and focuses on how sensory connectivity to the spinal cord is achieved by the diverse developmental and molecular processes that control axon guidance in the trunk sensory system. We also describe convergences and differences in sensory neuron formation among different vertebrate species to gain insight into underlying developmental mechanisms.
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Affiliation(s)
- Emily Holt
- Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, and Brain Repair Centre, Life Science Research Institute, 1348 Summer Street, Halifax, Nova Scotia B3H-4R2, Canada
| | - Danielle Stanton-Turcotte
- Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, and Brain Repair Centre, Life Science Research Institute, 1348 Summer Street, Halifax, Nova Scotia B3H-4R2, Canada
| | - Angelo Iulianella
- Department of Medical Neuroscience, Faculty of Medicine, Dalhousie University, and Brain Repair Centre, Life Science Research Institute, 1348 Summer Street, Halifax, Nova Scotia B3H-4R2, Canada.
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8
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Anbalagan S, Blechman J, Gliksberg M, Gordon L, Rotkopf R, Dadosh T, Shimoni E, Levkowitz G. Robo2 regulates synaptic oxytocin content by affecting actin dynamics. eLife 2019; 8:45650. [PMID: 31180321 PMCID: PMC6590984 DOI: 10.7554/elife.45650] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Accepted: 06/08/2019] [Indexed: 12/28/2022] Open
Abstract
The regulation of neuropeptide level at the site of release is essential for proper neurophysiological functions. We focused on a prominent neuropeptide, oxytocin (OXT) in the zebrafish as an in vivo model to visualize and quantify OXT content at the resolution of a single synapse. We found that OXT-loaded synapses were enriched with polymerized actin. Perturbation of actin filaments by either cytochalasin-D or conditional Cofilin expression resulted in decreased synaptic OXT levels. Genetic loss of robo2 or slit3 displayed decreased synaptic OXT content and robo2 mutants displayed reduced mobility of the actin probe Lifeact-EGFP in OXT synapses. Using a novel transgenic reporter allowing real-time monitoring of OXT-loaded vesicles, we show that robo2 mutants display slower rate of vesicles accumulation. OXT-specific expression of dominant-negative Cdc42, which is a key regulator of actin dynamics and a downstream effector of Robo2, led to a dose-dependent increase in OXT content in WT, and a dampened effect in robo2 mutants. Our results link Slit3-Robo2-Cdc42, which controls local actin dynamics, with the maintenance of synaptic neuropeptide levels.
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Affiliation(s)
- Savani Anbalagan
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Janna Blechman
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Michael Gliksberg
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Ludmila Gordon
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
| | - Ron Rotkopf
- Bioinformatics Unit, LSCF, Weizmann Institute of Science, Rehovot, Israel.,Electron Microscopy Unit, Weizmann Institute of Science, Rehovot, Israel
| | - Tali Dadosh
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel
| | - Eyal Shimoni
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel
| | - Gil Levkowitz
- Department of Molecular Cell Biology, Weizmann Institute of Science, Rehovot, Israel
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9
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Pioneer axons employ Cajal's battering ram to enter the spinal cord. Nat Commun 2019; 10:562. [PMID: 30718484 PMCID: PMC6362287 DOI: 10.1038/s41467-019-08421-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2018] [Accepted: 01/09/2019] [Indexed: 01/17/2023] Open
Abstract
Sensory axons must traverse a spinal cord glia limitans to connect the brain with the periphery. The fundamental mechanism of how these axons enter the spinal cord is still debatable; both Ramon y Cajal’s battering ram hypothesis and a boundary cap model have been proposed. To distinguish between these hypotheses, we visualized the entry of pioneer axons into the dorsal root entry zone (DREZ) with time-lapse imaging in zebrafish. Here, we identify that DRG pioneer axons enter the DREZ before the arrival of neural crest cells at the DREZ. Instead, actin-rich invadopodia in the pioneer axon are necessary and sufficient for DREZ entry. Using photoactivable Rac1, we demonstrate cell-autonomous functioning of invasive structures in pioneer axon spinal entry. Together these data support the model that actin-rich invasion structures dynamically drive pioneer axon entry into the spinal cord, indicating that distinct pioneer and secondary events occur at the DREZ. The fundamental mechanism of how sensory axons traverse a spinal cord glia limitans remains debatable, with some suggesting a role for boundary cap cells at the dorsal root entry zone (DREZ). Here, authors use time-lapse imaging of DRG axons at the DREZ to show that pioneer axons enter the DREZ before the presence of boundary cap cells, and that this entry is critically dependent on the development of actin-rich invasion structures reminiscent of invadopodia.
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10
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Gurung S, Asante E, Hummel D, Williams A, Feldman-Schultz O, Halloran MC, Sittaramane V, Chandrasekhar A. Distinct roles for the cell adhesion molecule Contactin2 in the development and function of neural circuits in zebrafish. Mech Dev 2018; 152:1-12. [PMID: 29777776 DOI: 10.1016/j.mod.2018.05.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 04/02/2018] [Accepted: 05/09/2018] [Indexed: 01/17/2023]
Abstract
Contactin2 (Cntn2)/Transient Axonal Glycoprotein 1 (Tag1), a neural cell adhesion molecule, has established roles in neuronal migration and axon fasciculation in chick and mouse. In zebrafish, antisense morpholino-based studies have indicated roles for cntn2 in the migration of facial branchiomotor (FBM) neurons, the guidance of the axons of the nucleus of the medial longitudinal fascicle (nucMLF), and the outgrowth of Rohon-Beard (RB) central axons. To study functions of Cntn2 in later stages of neuronal development, we generated cntn2 mutant zebrafish using CRISPR-Cas9. Using a null mutant allele, we detected genetic interactions between cntn2 and the planar cell polarity gene vangl2, as shown previously with cntn2 morphants, demonstrating a function for cntn2 during FBM neuron migration in a sensitized background of reduced planar cell polarity signaling. In addition, maternal-zygotic (MZ) cntn2 mutant larvae exhibited aberrant touch responses and swimming, suggestive of defects in sensorimotor circuits, consistent with studies in mice. However, the nucMLF axon convergence, FBM neuron migration, and RB outgrowth defects seen in morphants were not seen in the mutants, and we show here that they are likely off-target effects of morpholinos. However, MLF axons exhibited local defasciculation in MZcntn2 mutants, consistent with a role for Cntn2 in axon fasciculation. These data demonstrate distinct roles for zebrafish cntn2 in neuronal migration and axon fasciculation, and in the function of sensorimotor circuits.
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Affiliation(s)
- Suman Gurung
- Division of Biological Sciences and Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
| | - Emilia Asante
- Division of Biological Sciences and Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
| | - Devynn Hummel
- Division of Biological Sciences and Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA
| | - Ashley Williams
- Department of Biology, Georgia Southern University, Statesboro, GA 30458, USA
| | - Oren Feldman-Schultz
- Department of Integrative Biology, Department of Neuroscience, University of Wisconsin, Madison, WI 53706, USA
| | - Mary C Halloran
- Department of Integrative Biology, Department of Neuroscience, University of Wisconsin, Madison, WI 53706, USA
| | - Vinoth Sittaramane
- Department of Biology, Georgia Southern University, Statesboro, GA 30458, USA
| | - Anand Chandrasekhar
- Division of Biological Sciences and Bond Life Sciences Center, University of Missouri, Columbia, MO 65211, USA.
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11
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Papandréou MJ, Leterrier C. The functional architecture of axonal actin. Mol Cell Neurosci 2018; 91:151-159. [PMID: 29758267 DOI: 10.1016/j.mcn.2018.05.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Revised: 05/10/2018] [Accepted: 05/11/2018] [Indexed: 11/17/2022] Open
Abstract
The cytoskeleton builds and supports the complex architecture of neurons. It orchestrates the specification, growth, and compartmentation of the axon: axon initial segment, axonal shaft, presynapses. The cytoskeleton must then maintain this intricate architecture for the whole life of its host, but also drive its adaptation to new network demands and changing physiological conditions. Microtubules are readily visible inside axon shafts by electron microscopy, whereas axonal actin study has long been focused on dynamic structures of the axon such as growth cones. Super-resolution microscopy and live-cell imaging have recently revealed new actin-based structures in mature axons: rings, hotspots and trails. This has caused renewed interest for axonal actin, with efforts underway to understand the precise organization and cellular functions of these assemblies. Actin is also present in presynapses, where its arrangement is still poorly defined, and its functions vigorously debated. Here we review the organization of axonal actin, focusing on recent advances and current questions in this rejuvenated field.
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12
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Lam PY, Mendu SK, Mills RW, Zheng B, Padilla H, Milan DJ, Desai BN, Peterson RT. A high-conductance chemo-optogenetic system based on the vertebrate channel Trpa1b. Sci Rep 2017; 7:11839. [PMID: 28928472 PMCID: PMC5605526 DOI: 10.1038/s41598-017-11791-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 08/30/2017] [Indexed: 01/04/2023] Open
Abstract
Optogenetics is a powerful research approach that allows localized optical modulation of selected cells within an animal via the expression of genetically encoded photo-excitable ion channels. Commonly used optogenetic techniques rely on the expression of microbial opsin variants, which have many excellent features but suffer from various degrees of blue spectral overlap and limited channel conductance. Here, we expand the optogenetics toolbox in the form of a tunable, high-conductance vertebrate cation channel, zTrpa1b, coupled with photo-activated channel ligands, such as optovin and 4g6. Our results demonstrate that zTrpa1b/ligand pairing offers high light sensitivity, millisecond-scale response latency in vivo, as well as adjustable channel off latency. Exogenous in vivo expression of zTrpa1b in sensory neurons allowed subcellular photo-activation, enabling light-dependent motor control. zTrpa1b/ligand was also suitable for cardiomyocyte pacing, as shown in experiments performed on zebrafish hearts in vivo as well as in human stem cell-derived cardiomyocytes in vitro. Therefore, zTrpa1b/optovin represents a novel tool for flexible, high-conductance optogenetics.
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Affiliation(s)
- Pui-Ying Lam
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA. .,Department of Systems Biology, Harvard Medical School, Boston, MA, 02115, USA. .,Broad Institute, Cambridge, MA, 02142, USA. .,Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City, UT, 84112, USA.
| | - Suresh K Mendu
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
| | - Robert W Mills
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA
| | - Baohui Zheng
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA
| | - Hugo Padilla
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA.,Department of Systems Biology, Harvard Medical School, Boston, MA, 02115, USA.,Broad Institute, Cambridge, MA, 02142, USA.,Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City, UT, 84112, USA
| | - David J Milan
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA
| | - Bimal N Desai
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, VA, 22908, USA
| | - Randall T Peterson
- Cardiovascular Research Center, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, 02129, USA. .,Department of Systems Biology, Harvard Medical School, Boston, MA, 02115, USA. .,Broad Institute, Cambridge, MA, 02142, USA. .,Department of Pharmacology and Toxicology, College of Pharmacy, University of Utah, Salt Lake City, UT, 84112, USA.
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13
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Lee TJ, Lee JW, Haynes EM, Eliceiri KW, Halloran MC. The Kinesin Adaptor Calsyntenin-1 Organizes Microtubule Polarity and Regulates Dynamics during Sensory Axon Arbor Development. Front Cell Neurosci 2017; 11:107. [PMID: 28473757 PMCID: PMC5397401 DOI: 10.3389/fncel.2017.00107] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Accepted: 03/29/2017] [Indexed: 11/30/2022] Open
Abstract
Axon growth and branching, and development of neuronal polarity are critically dependent on proper organization and dynamics of the microtubule (MT) cytoskeleton. MTs must organize with correct polarity for delivery of diverse cargos to appropriate subcellular locations, yet the molecular mechanisms regulating MT polarity remain poorly understood. Moreover, how an actively branching axon reorganizes MTs to direct their plus ends distally at branch points is unknown. We used high-speed, in vivo imaging of polymerizing MT plus ends to characterize MT dynamics in developing sensory axon arbors in zebrafish embryos. We find that axonal MTs are highly dynamic throughout development, and that the peripheral and central axons of sensory neurons show differences in MT behaviors. Furthermore, we show that Calsyntenin-1 (Clstn-1), a kinesin adaptor required for sensory axon branching, also regulates MT polarity in developing axon arbors. In wild type neurons the vast majority of MTs are directed in the correct plus-end-distal orientation from early stages of development. Loss of Clstn-1 causes an increase in MTs polymerizing in the retrograde direction. These misoriented MTs most often are found near growth cones and branch points, suggesting Clstn-1 is particularly important for organizing MT polarity at these locations. Together, our results suggest that Clstn-1, in addition to regulating kinesin-mediated cargo transport, also organizes the underlying MT highway during axon arbor development.
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Affiliation(s)
- Tristan J Lee
- Department of Zoology, University of Wisconsin-MadisonMadison, WI, USA.,Department of Neuroscience, University of Wisconsin-MadisonMadison, WI, USA.,Neuroscience Training Program, University of Wisconsin-MadisonMadison, WI, USA
| | - Jacob W Lee
- Department of Zoology, University of Wisconsin-MadisonMadison, WI, USA.,Department of Neuroscience, University of Wisconsin-MadisonMadison, WI, USA
| | - Elizabeth M Haynes
- Department of Zoology, University of Wisconsin-MadisonMadison, WI, USA.,Department of Neuroscience, University of Wisconsin-MadisonMadison, WI, USA.,Laboratory for Optical and Computational Instrumentation, University of Wisconsin-MadisonMadison, WI, USA
| | - Kevin W Eliceiri
- Laboratory for Optical and Computational Instrumentation, University of Wisconsin-MadisonMadison, WI, USA
| | - Mary C Halloran
- Department of Zoology, University of Wisconsin-MadisonMadison, WI, USA.,Department of Neuroscience, University of Wisconsin-MadisonMadison, WI, USA.,Neuroscience Training Program, University of Wisconsin-MadisonMadison, WI, USA
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14
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Armijo-Weingart L, Gallo G. It takes a village to raise a branch: Cellular mechanisms of the initiation of axon collateral branches. Mol Cell Neurosci 2017; 84:36-47. [PMID: 28359843 DOI: 10.1016/j.mcn.2017.03.007] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Revised: 01/03/2017] [Accepted: 03/01/2017] [Indexed: 12/14/2022] Open
Abstract
The formation of axon collateral branches from the pre-existing shafts of axons is an important aspect of neurodevelopment and the response of the nervous system to injury. This article provides an overview of the role of the cytoskeleton and signaling mechanisms in the formation of axon collateral branches. Both the actin filament and microtubule components of the cytoskeleton are required for the formation of axon branches. Recent work has begun to shed light on how these two elements of the cytoskeleton are integrated by proteins that functionally or physically link the cytoskeleton. While a number of signaling pathways have been determined as having a role in the formation of axon branches, the complexity of the downstream mechanisms and links to specific signaling pathways remain to be fully determined. The regulation of intra-axonal protein synthesis and organelle function are also emerging as components of signal-induced axon branching. Although much has been learned in the last couple of decades about the mechanistic basis of axon branching we can look forward to continue elucidating this complex biological phenomenon with the aim of understanding how multiple signaling pathways, cytoskeletal regulators and organelles are coordinated locally along the axon to give rise to a branch.
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Affiliation(s)
- Lorena Armijo-Weingart
- Shriners Pediatric Research Center, Temple University, Department of Anatomy and Cell Biology, 3500 North Broad St, Philadelphia, PA 19140, United States
| | - Gianluca Gallo
- Shriners Pediatric Research Center, Temple University, Department of Anatomy and Cell Biology, 3500 North Broad St, Philadelphia, PA 19140, United States.
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15
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Huemer K, Squirrell JM, Swader R, LeBert DC, Huttenlocher A, Eliceiri KW. zWEDGI: Wounding and Entrapment Device for Imaging Live Zebrafish Larvae. Zebrafish 2016; 14:42-50. [PMID: 27676647 DOI: 10.1089/zeb.2016.1323] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Zebrafish, an established model organism in developmental biology, is also a valuable tool for imaging wound healing in space and time with cellular resolution. However, long-term imaging of wound healing poses technical challenges as wound healing occurs over multiple temporal scales. The traditional strategy of larval encapsulation in agarose successfully limits sample movement but impedes larval development and tissue regrowth and is therefore not amenable to long-term imaging of wound healing. To overcome this challenge, we engineered a functionally compartmentalized device, the zebrafish Wounding and Entrapment Device for Growth and Imaging (zWEDGI), to orient larvae for high-resolution microscopy, including confocal and second harmonic generation (SHG), while allowing unrestrained tail development and regrowth. In this device, larval viability was maintained and tail regrowth was improved over embedding in agarose. The quality of tail fiber SHG images collected from larvae in the device was similar to fixed samples but provided the benefit of time lapse data collection. Furthermore, we show that this device was amenable to long-term (>24 h) confocal microscopy of the caudal fin. Finally, the zWEDGI was designed and fabricated using readily available techniques so that it can be easily modified for diverse experimental imaging protocols.
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Affiliation(s)
- Kayla Huemer
- 1 Morgridge Institute for Research , Madison, Wisconsin.,2 Department of Biomedical Engineering, UW-Madison , Madison, Wisconsin.,3 Laboratory for Optical and Computational Instrumentation, UW-Madison , Madison, Wisconsin
| | - Jayne M Squirrell
- 3 Laboratory for Optical and Computational Instrumentation, UW-Madison , Madison, Wisconsin
| | - Robert Swader
- 1 Morgridge Institute for Research , Madison, Wisconsin
| | - Danny C LeBert
- 4 Cellular and Molecular Pathology Graduate Program, UW-Madison , Madison, Wisconsin
| | - Anna Huttenlocher
- 5 Department of Medical Microbiology and Immunology.,6 Department of Pediatrics, UW-Madison , Madison, Wisconsin
| | - Kevin W Eliceiri
- 1 Morgridge Institute for Research , Madison, Wisconsin.,2 Department of Biomedical Engineering, UW-Madison , Madison, Wisconsin.,3 Laboratory for Optical and Computational Instrumentation, UW-Madison , Madison, Wisconsin
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16
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Charcot-Marie-Tooth 2b associated Rab7 mutations cause axon growth and guidance defects during vertebrate sensory neuron development. Neural Dev 2016; 11:2. [PMID: 26791407 PMCID: PMC4721196 DOI: 10.1186/s13064-016-0058-x] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2015] [Accepted: 01/11/2016] [Indexed: 12/02/2022] Open
Abstract
Background Charcot-Marie-Tooth2b (CMT2b) is an axonal form of a human neurodegenerative disease that preferentially affects sensory neurons. CMT2b is dominantly inherited and is characterized by unusually early onset, presenting in the second or third decade of life. Five missense mutations in the gene encoding Rab7 GTPase have been identified as causative in human CMT2b disease. Although several studies have modeled CMT2b disease in cultured neurons and in Drosophila, the mechanisms by which defective Rab7 leads to disease remain poorly understood. Results We used zebrafish to investigate the effects of CMT2b-associated Rab7 mutations in a vertebrate model. We generated transgenic animals expressing the CMT2b-associated mutant forms of Rab7 in sensory neurons, and show that these Rab7 variants cause neurodevelopmental defects, including defects in sensory axon growth, branching and pathfinding at early developmental stages. We also find reduced axon growth and branching in neurons expressing a constitutively active form of Rab7, suggesting these defects may be caused by Rab7 gain-of-function. Further, we use high-speed, high-resolution imaging of endosome transport in vivo and find that CMT2b-associated Rab7 variants cause reduced vesicle speeds, suggesting altered transport may underlie axon development defects. Conclusions Our data provide new insight into how disease-associated alterations in Rab7 protein disrupt cellular function in vertebrate sensory neurons. Moreover, our findings suggest that defects in axon development may be a previously unrecognized component of CMT2b disease.
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17
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Bassi A, Schmid B, Huisken J. Optical tomography complements light sheet microscopy for in toto imaging of zebrafish development. Development 2015; 142:1016-20. [PMID: 25655702 PMCID: PMC4352980 DOI: 10.1242/dev.116970] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Fluorescently labeled structures can be spectrally isolated and imaged at high resolution in living embryos by light sheet microscopy. Multimodal imaging techniques are now needed to put these distinct structures back into the context of the surrounding tissue. We found that the bright-field contrast of unstained specimens in a selective plane illumination microscopy (SPIM) setup can be exploited for in vivo tomographic reconstructions of the three-dimensional anatomy of zebrafish, without causing phototoxicity. We report multimodal imaging of entire zebrafish embryos over several hours of development, as well as segmentation, tracking and automatic registration of individual organs. Summary: Bright-field imaging of unstained specimens during selective plane illumination microscopy can provide in vivo tomographic reconstruction of zebrafish anatomy.
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Affiliation(s)
- Andrea Bassi
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany Politecnico di Milano, Dipartimento di Fisica, Milano 20133, Italy
| | - Benjamin Schmid
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
| | - Jan Huisken
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden 01307, Germany
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18
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Calsyntenin-1 regulates axon branching and endosomal trafficking during sensory neuron development in vivo. J Neurosci 2014; 34:9235-48. [PMID: 25009257 DOI: 10.1523/jneurosci.0561-14.2014] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Precise regulation of axon branching is crucial for neuronal circuit formation, yet the mechanisms that control branch formation are not well understood. Moreover, the highly complex morphology of neurons makes them critically dependent on protein/membrane trafficking and transport systems, although the functions for membrane trafficking in neuronal morphogenesis are largely undefined. Here we identify a kinesin adaptor, Calsyntenin-1 (Clstn-1), as an essential regulator of axon branching and neuronal compartmentalization in vivo. We use morpholino knockdown and a Clstn-1 mutant to show that Clstn-1 is required for formation of peripheral but not central sensory axons, and for peripheral axon branching in zebrafish. We used live imaging of endosomal trafficking in vivo to show that Clstn-1 regulates transport of Rab5-containing endosomes from the cell body to specific locations of developing axons. Our results suggest a model in which Clstn-1 patterns separate axonal compartments and define their ability to branch by directing trafficking of specific endosomes.
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19
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Moreno RL, Ribera AB. Spinal neurons require Islet1 for subtype-specific differentiation of electrical excitability. Neural Dev 2014; 9:19. [PMID: 25149090 PMCID: PMC4153448 DOI: 10.1186/1749-8104-9-19] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2013] [Accepted: 07/16/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND In the spinal cord, stereotypic patterns of transcription factor expression uniquely identify neuronal subtypes. These transcription factors function combinatorially to regulate gene expression. Consequently, a single transcription factor may regulate divergent development programs by participation in different combinatorial codes. One such factor, the LIM-homeodomain transcription factor Islet1, is expressed in the vertebrate spinal cord. In mouse, chick and zebrafish, motor and sensory neurons require Islet1 for specification of biochemical and morphological signatures. Little is known, however, about the role that Islet1 might play for development of electrical membrane properties in vertebrates. Here we test for a role of Islet1 in differentiation of excitable membrane properties of zebrafish spinal neurons. RESULTS We focus our studies on the role of Islet1 in two populations of early born zebrafish spinal neurons: ventral caudal primary motor neurons (CaPs) and dorsal sensory Rohon-Beard cells (RBs). We take advantage of transgenic lines that express green fluorescent protein (GFP) to identify CaPs, RBs and several classes of interneurons for electrophysiological study. Upon knock-down of Islet1, cells occupying CaP-like and RB-like positions continue to express GFP. With respect to voltage-dependent currents, CaP-like and RB-like neurons have novel repertoires that distinguish them from control CaPs and RBs, and, in some respects, resemble those of neighboring interneurons. The action potentials fired by CaP-like and RB-like neurons also have significantly different properties compared to those elicited from control CaPs and RBs. CONCLUSIONS Overall, our findings suggest that, for both ventral motor and dorsal sensory neurons, Islet1 directs differentiation programs that ultimately specify electrical membrane as well as morphological properties that act together to sculpt neuron identity.
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Affiliation(s)
- Rosa L Moreno
- Department of Physiology, University of Colorado Anschutz Medical Campus, RC-1 North, 7403A, Mailstop 8307, 12800 E 19th Ave,, 80045 Aurora, CO, USA.
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20
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Wagner E, Stolfi A, Gi Choi Y, Levine M. Islet is a key determinant of ascidian palp morphogenesis. Development 2014; 141:3084-92. [PMID: 24993943 DOI: 10.1242/dev.110684] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The anterior-most ectoderm of ascidian larvae contains the adhesive papillae, or palps, which play an important role in triggering the metamorphosis of swimming tadpoles. In Ciona intestinalis, the palps consist of three conical protrusions within a field of thickened epithelium that form late in embryogenesis, as tailbuds mature into larvae. The palp protrusions express the LIM-homeodomain transcription factor Islet. Protrusion occurs through differential cell elongation, probably mediated by Islet, as we find that ectopic expression of Islet is sufficient to promote cell lengthening. FGF signaling is required for both Islet expression and palp morphogenesis. Importantly, we show that Islet expression can rescue the palp-deficient phenotype that results from inhibition of FGF signaling. We conclude that Islet is a key regulatory factor governing morphogenesis of the palps. It is conceivable that Islet is also essential for the cellular morphogenesis of placode-derived sensory neurons in vertebrates.
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Affiliation(s)
- Eileen Wagner
- Center for Integrative Genomics, Division of Genetics, Genomics, and Development, Department of Molecular and Cell Biology, University of California-Berkeley, Berkeley, CA 94720, USA
| | - Alberto Stolfi
- New York University, Center for Developmental Genetics, Department of Biology, 1009 Silver Center, 100 Washington Square East, New York, NY 10003-6688, USA
| | - Yoon Gi Choi
- Functional Genomics Laboratory, Department of Molecular and Cell Biology, University of California-Berkeley, 255 Life Sciences Addition #3200, Berkeley, CA 94720-3200, USA
| | - Mike Levine
- Center for Integrative Genomics, Division of Genetics, Genomics, and Development, Department of Molecular and Cell Biology, University of California-Berkeley, Berkeley, CA 94720, USA
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21
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Abstract
Development of the nervous system requires efficient extension and guidance of axons and dendrites culminating in synapse formation. Axonal growth and navigation during embryogenesis are controlled by extracellular cues. Many of the same extracellular signals also regulate axonal branching. The emergence of collateral branches from the axon augments the complexity of nervous system innervation and provides an additional mechanism for target selection. Rho-family GTPases play an important role in regulating intracellular cytoskeletal and signaling pathways that facilitate axonal morphological changes. RhoA/G and Rac1 GTPase functions are complex and they can induce or inhibit branch formation, depending on neuronal type, cell context or signaling mechanisms. Evidence of a role of Cdc42 in axon branching is mostly lacking. In contrast, Rac3 has thus far been implicated in the regulation of axon branching. Future analysis of the upstream regulators and downstream effectors mediating the effects of Rho-family GTPase will provide insights into the cellular processes effected, and shed light on the sometimes opposing roles of these GTPases in the regulation of axon branching.
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Affiliation(s)
- Mirela Spillane
- Shriners Hospitals Pediatric Research Center; Center for Neural Repair and Rehabilitation; Temple University; Department of Anatomy and Cell Biology; Philadelphia, PA USA
| | - Gianluca Gallo
- Shriners Hospitals Pediatric Research Center; Center for Neural Repair and Rehabilitation; Temple University; Department of Anatomy and Cell Biology; Philadelphia, PA USA
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22
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Arnold DB, Gallo G. Structure meets function: actin filaments and myosin motors in the axon. J Neurochem 2013; 129:213-220. [PMID: 24147838 DOI: 10.1111/jnc.12503] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2013] [Revised: 10/16/2013] [Accepted: 10/17/2013] [Indexed: 12/14/2022]
Abstract
This review focuses on recent advances in the understanding of the organization and roles of actin filaments, and associated myosin motor proteins, in regulating the structure and function of the axon shaft. 'Patches' of actin filaments have emerged as a major type of actin filament organization in axons. In the distal axon, patches function as precursors to the formation of filopodia and branches. At the axon initial segment, patches locally capture membranous organelles and contribute to polarized trafficking. The trapping function of patches at the initial segment can be ascribed to interactions with myosin motors, and likely also applies to patches in the more distal axon. Finally, submembranous rings of actin filaments were recently described in axons, which form an actin-spectrin cytoskeleton, likely contributing to the maintenance of axon integrity. Continued investigation into the roles of axonal actin filaments and myosins will shed light on fundamental aspects of the development, adult function and the repair of axons in the nervous system.
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Affiliation(s)
- Don B Arnold
- University of Southern California Department of Biology 1050 Childs Way RRI 204b Los Angeles, CA 90089-2910 ph: 213-821-1266
| | - Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Temple University, Department of Anatomy and Cell Biology, 2500 North Broad St, Philadelphia, PA 19140, ph: 215-926-9362
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23
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Nerve growth factor-induced formation of axonal filopodia and collateral branches involves the intra-axonal synthesis of regulators of the actin-nucleating Arp2/3 complex. J Neurosci 2013; 32:17671-89. [PMID: 23223289 DOI: 10.1523/jneurosci.1079-12.2012] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Nerve growth factor (NGF) induces collateral branching along sensory axons by promoting the formation of axonal filopodia dependent on the actin-nucleating Arp2/3 complex. This study shows that chicken embryonic sensory axons contain mRNAs for the actin-nucleating Arp2/3 complex activator WAVE1 and the complex stabilizer cortactin. NGF increases the axonal levels of WAVE1 and cortactin through localized protein synthesis even in axons isolated from the cell body. Inhibition of protein synthesis in severed axons impairs NGF-induced branching, the formation of axonal filopodia, and the initiation of Arp2/3-dependent axonal actin patches, which serve as precursors to the emergence of filopodia. Overexpression of WAVE1 or cortactin in axons not treated with NGF increased the rate of actin patch formation and the frequency of the emergence of filopodia from actin patches, respectively. Antisense inhibition of cortactin mRNA translation in isolated axons blocked NGF-induced filopodia. NGF also activated the Rac1 GTPase, which drives WAVE1 activity, in a protein synthesis-independent manner. Similarly, inhibition of protein synthesis did not impair the effects of NGF on the axonal microtubule cytoskeleton during branching. The effects of NGF on Rac1 activity and increases in axonal levels of WAVE1 and cortactin were both dependent on phosphoinositide 3-kinase (PI3K) signaling. Collectively, the data indicate that NGF promotes sensory axon branching through regulation of the actin cytoskeleton using both canonical signaling mechanisms and intra-axonal protein synthesis downstream of PI3K signaling. Finally, we present experimental evidence of axonal mRNA translation in sensory axons in the living embryonic spinal cord.
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24
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Chen Z, Lee H, Henle SJ, Cheever TR, Ekker SC, Henley JR. Primary neuron culture for nerve growth and axon guidance studies in zebrafish (Danio rerio). PLoS One 2013; 8:e57539. [PMID: 23469201 PMCID: PMC3587632 DOI: 10.1371/journal.pone.0057539] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 01/25/2013] [Indexed: 12/21/2022] Open
Abstract
Zebrafish (Danio rerio) is a widely used model organism in genetics and developmental biology research. Genetic screens have proven useful for studying embryonic development of the nervous system in vivo, but in vitro studies utilizing zebrafish have been limited. Here, we introduce a robust zebrafish primary neuron culture system for functional nerve growth and guidance assays. Distinct classes of central nervous system neurons from the spinal cord, hindbrain, forebrain, and retina from wild type zebrafish, and fluorescent motor neurons from transgenic reporter zebrafish lines, were dissociated and plated onto various biological and synthetic substrates to optimize conditions for axon outgrowth. Time-lapse microscopy revealed dynamically moving growth cones at the tips of extending axons. The mean rate of axon extension in vitro was 21.4±1.2 µm hr−1 s.e.m. for spinal cord neurons, which corresponds to the typical ∼0.5 mm day−1 growth rate of nerves in vivo. Fluorescence labeling and confocal microscopy demonstrated that bundled microtubules project along axons to the growth cone central domain, with filamentous actin enriched in the growth cone peripheral domain. Importantly, the growth cone surface membrane expresses receptors for chemotropic factors, as detected by immunofluorescence microscopy. Live-cell functional assays of axon extension and directional guidance demonstrated mammalian brain-derived neurotrophic factor (BDNF)-dependent stimulation of outgrowth and growth cone chemoattraction, whereas mammalian myelin-associated glycoprotein inhibited outgrowth. High-resolution live-cell Ca2+-imaging revealed local elevation of cytoplasmic Ca2+ concentration in the growth cone induced by BDNF application. Moreover, BDNF-induced axon outgrowth, but not basal outgrowth, was blocked by treatments to suppress cytoplasmic Ca2+ signals. Thus, this primary neuron culture model system may be useful for studies of neuronal development, chemotropic axon guidance, and mechanisms underlying inhibition of neural regeneration in vitro, and complement observations made in vivo.
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Affiliation(s)
- Zheyan Chen
- Mayo Graduate School, College of Medicine, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Han Lee
- Mayo Graduate School, College of Medicine, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Steven J. Henle
- Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Thomas R. Cheever
- Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Stephen C. Ekker
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - John R. Henley
- Mayo Graduate School, College of Medicine, Mayo Clinic, Rochester, Minnesota, United States of America
- Department of Neurologic Surgery, Mayo Clinic, Rochester, Minnesota, United States of America
- Department of Physiology and Biomedical Engineering, Mayo Clinic, Rochester, Minnesota, United States of America
- * E-mail:
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25
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Gallo G. Mechanisms underlying the initiation and dynamics of neuronal filopodia: from neurite formation to synaptogenesis. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2013; 301:95-156. [PMID: 23317818 DOI: 10.1016/b978-0-12-407704-1.00003-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Filopodia are finger-like cellular protrusions found throughout the metazoan kingdom and perform fundamental cellular functions during development and cell migration. Neurons exhibit a wide variety of extremely complex morphologies. In the nervous system, filopodia underlie many major morphogenetic events. Filopodia have roles spanning the initiation and guidance of neuronal processes, axons and dendrites to the formation of synaptic connections. This chapter addresses the mechanisms of the formation and dynamics of neuronal filopodia. Some of the major lessons learned from the study of neuronal filopodia are (1) there are multiple mechanisms that can regulate filopodia in a context-dependent manner, (2) that filopodia are specialized subcellular domains, (3) that filopodia exhibit dynamic membrane recycling which also controls aspects of filopodial dynamics, (4) that neuronal filopodia contain machinery for the orchestration of the actin and microtubule cytoskeleton, and (5) localized protein synthesis contributes to neuronal filopodial dynamics.
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Affiliation(s)
- Gianluca Gallo
- Shriners Hospitals Pediatric Research Center, Center for Neural Repair and Rehabilitation, Department of Anatomy and Cell Biology, Temple University, Philadelphia, PA, USA.
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26
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Focal increases of axoplasmic Ca2+, aggregation of sodium-calcium exchanger, N-type Ca2+ channel, and actin define the sites of spheroids in axons undergoing oxidative stress. J Neurosci 2012; 32:12028-37. [PMID: 22933787 DOI: 10.1523/jneurosci.0408-12.2012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Axonal spheroids occur as part of the pathology of a variety of neurologic diseases. Reactive oxygen species (ROS) trigger formation of spheroids, axonal severing, and Ca(2+) overload. The mechanisms by which ROS lead to the spheroid formation at specific axonal sites remain elusive. Here, using adult mouse primary neurons, we investigate the role of Ca(2+), its regulating systems, and cytoskeletal changes in formation of axonal spheroids triggered by ROS. The results reveal that dramatically higher axoplasmic Ca(2+) levels occur at the sites of axonal spheroids than in the rest of the axon. High focal axoplasmic Ca(2+) levels correlate with focal aggregation of the reverse Na(+)/Ca(2+) exchanger 1, voltage-gated N-type Ca(2+) channel α1B subunit, and actin at the sites of spheroids in individual axons. This study provides new insights into the mechanism of a spheroid formation at specific sites along axons undergoing oxidative stress and a basis for new neuroprotective strategies.
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27
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St John JA, Key B. HuC-eGFP mosaic labelling of neurons in zebrafish enables in vivo live cell imaging of growth cones. J Mol Histol 2012; 43:615-23. [PMID: 23104578 DOI: 10.1007/s10735-012-9462-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 10/19/2012] [Indexed: 11/29/2022]
Abstract
The field of axon guidance is taking advantage of the powerful genetic and imaging tools that are now available to visualise growth behaviour in living cells, both in vivo and in real time. We have developed a method to visualise individual neurons within the living zebrafish embryo which provides exceptional cellular resolution of growth cones and their filopodia. We generated a DNA construct in which the HuC promoter drives expression of eGFP. Injection of the plasmid into single cell fertilised zebrafish egg resulted in mosaic expression of eGFP in neurons throughout the developing embryo. By manipulating the concentration of injected plasmid, it was possible to optimise the numbers of neurons that expressed the construct so that individual growth cones could be easily visualised. We then used time-lapse high magnification widefield epifluorescence microscopy to visualise the growth cones as they were exploring their environment. Growth cones both near the surface of the embryo as well as deep within the developing brain of embryos at 20 h post fertilisation were clearly imaged. With time-lapse sequence imaging with intervals between frames as frequent as 1 s there was minimal loss of fluorescence intensity and the dynamic nature of the growth cones became evident. This method therefore provides high magnification, high resolution time-lapse imaging of living neurons in vivo and by use of widefield epifluorescence rather than confocal it is a relatively inexpensive microscopy method.
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Affiliation(s)
- James A St John
- Eskitis Institute for Cell and Molecular Therapies, Griffith University, 170 Kessels Rd, Nathan, Brisbane, 4111, Australia.
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Andersen EF, Halloran MC. Centrosome movements in vivo correlate with specific neurite formation downstream of LIM homeodomain transcription factor activity. Development 2012; 139:3590-9. [PMID: 22899847 DOI: 10.1242/dev.081513] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Neurons must develop complex structure to form proper connections in the nervous system. The initiation of axons in defined locations on the cell body and their extension to synaptic targets are critical steps in neuronal morphogenesis, yet the mechanisms controlling axon formation in vivo are poorly understood. The centrosome has been implicated in multiple aspects of neuronal morphogenesis; however, its function in axon development is under debate. Conflicting results from studies of centrosome function in axonogenesis suggest that its role is context dependent and underscore the importance of studying centrosome function as neurons develop in their natural environment. Using live imaging of zebrafish Rohon-Beard (RB) sensory neurons in vivo, we discovered a spatiotemporal relationship between centrosome position and the formation of RB peripheral, but not central, axons. We tested centrosome function by laser ablation and found that centrosome disruption inhibited peripheral axon outgrowth. In addition, we show that centrosome position and motility are regulated by LIM homeodomain transcription factor activity, which is specifically required for the development of RB peripheral axons. Furthermore, we show a correlation between centrosome mislocalization and ectopic axon formation in bashful (laminin alpha 1) mutants. Thus, both intrinsic transcription factor activity and extracellular cues can influence centrosome position and axon formation in vivo. This study presents the first positive association between the centrosome and axon formation in vivo and suggests that the centrosome is important for differential neurite formation in neurons with complex axonal morphologies.
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Affiliation(s)
- Erica F Andersen
- Genetics Training Program, Department of Zoology, Department of Neuroscience, University of Wisconsin, 1117 W. Johnson Street, Madison, WI 53706, USA
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Wang F, Wolfson SN, Gharib A, Sagasti A. LAR receptor tyrosine phosphatases and HSPGs guide peripheral sensory axons to the skin. Curr Biol 2012; 22:373-82. [PMID: 22326027 PMCID: PMC3298620 DOI: 10.1016/j.cub.2012.01.040] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Revised: 01/06/2012] [Accepted: 01/20/2012] [Indexed: 11/20/2022]
Abstract
BACKGROUND Peripheral axons of somatosensory neurons innervate the skin early in development to detect touch stimuli. Embryological experiments had suggested that the skin produces guidance cues that attract sensory axons, but neither the attractants nor their neuronal receptors had previously been identified. RESULTS To investigate peripheral axon navigation to the skin, we combined live imaging of developing zebrafish Rohon-Beard (RB) neurons with molecular loss-of-function manipulations. Simultaneously knocking down two members of the leukocyte antigen-related (LAR) family of receptor tyrosine phosphatases expressed in RB neurons, or inhibiting their function with dominant-negative proteins, misrouted peripheral axons to internal tissues. Time-lapse imaging indicated that peripheral axon guidance, rather than outgrowth or maintenance, was defective in LAR-deficient neurons. Peripheral axons displayed a similar misrouting phenotype in mutants defective in heparan sulfate proteoglycan (HSPG) production and avoided regions in which HSPGs were locally degraded. CONCLUSIONS HSPGs and LAR family receptors are required for sensory axon guidance to the skin. Together, our results support a model in which peripheral HSPGs are attractive ligands for LAR receptors on RB neurons.
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Affiliation(s)
- Fang Wang
- Department of Molecular, Cell and Developmental Biology, University of California Los Angeles, Los Angeles, CA 90095, USA.
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