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Kang Y, Saito M, Toyoda H. Molecular, Morphological and Electrophysiological Differences between Alpha and Gamma Motoneurons with Special Reference to the Trigeminal Motor Nucleus of Rat. Int J Mol Sci 2024; 25:5266. [PMID: 38791305 PMCID: PMC11121624 DOI: 10.3390/ijms25105266] [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: 04/15/2024] [Revised: 04/30/2024] [Accepted: 05/01/2024] [Indexed: 05/26/2024] Open
Abstract
The muscle contraction during voluntary movement is controlled by activities of alpha- and gamma-motoneurons (αMNs and γMNs, respectively). In spite of the recent advances in research on molecular markers that can distinguish between αMNs and γMNs, electrophysiological membrane properties and firing patterns of γMNs have remained unknown, while those of αMNs have been clarified in detail. Because of the larger size of αMNs compared to γMNs, blindly or even visually recorded MNs were mostly αMNs, as demonstrated with molecular markers recently. Subsequently, the research on αMNs has made great progress in classifying their subtypes based on the molecular markers and electrophysiological membrane properties, whereas only a few studies demonstrated the electrophysiological membrane properties of γMNs. In this review article, we provide an overview of the recent advances in research on the classification of αMNs and γMNs based on molecular markers and electrophysiological membrane properties, and discuss their functional implication and significance in motor control.
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Affiliation(s)
- Youngnam Kang
- Department of Behavioral Physiology, Graduate School of Human Sciences, Osaka University, Osaka 565-0871, Japan
| | - Mitsuru Saito
- Department of Oral Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, Sakuragaoka 8-35-1, Kagoshima 890-8544, Japan;
| | - Hiroki Toyoda
- Department of Oral Physiology, Graduate School of Dentistry, The University of Osaka, Osaka 565-0871, Japan
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2
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de Nooij JC, Zampieri N. The making of a proprioceptor: a tale of two identities. Trends Neurosci 2023; 46:1083-1094. [PMID: 37858440 DOI: 10.1016/j.tins.2023.09.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2023] [Revised: 09/26/2023] [Accepted: 09/27/2023] [Indexed: 10/21/2023]
Abstract
Proprioception, the sense of body position in space, has a critical role in the control of posture and movement. Aside from skin and joint receptors, the main sources of proprioceptive information in tetrapods are mechanoreceptive end organs in skeletal muscle: muscle spindles (MSs) and Golgi tendon organs (GTOs). The sensory neurons that innervate these receptors are divided into subtypes that detect discrete aspects of sensory information from muscles with different biomechanical functions. Despite the importance of proprioceptive neurons in motor control, the developmental mechanisms that control the acquisition of their distinct functional properties and positional identity are not yet clear. In this review, we discuss recent findings on the development of mouse proprioceptor subtypes and challenges in defining them at the molecular and functional level.
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Affiliation(s)
- Joriene C de Nooij
- Department of Neurology, Division of Translational Neurobiology, Vagelos College of Physicians and Surgeons, 650 West 168th Street, New York, NY 10032, USA; Columbia University Motor Neuron Center, Columbia University Medical Center, 630 West 168th Street, New York, NY 10032, USA.
| | - Niccolò Zampieri
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Robert-Rössle-Strasse 10, 13125 Berlin, Germany.
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3
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Andersen J, Thom N, Shadrach JL, Chen X, Onesto MM, Amin ND, Yoon SJ, Li L, Greenleaf WJ, Müller F, Pașca AM, Kaltschmidt JA, Pașca SP. Single-cell transcriptomic landscape of the developing human spinal cord. Nat Neurosci 2023; 26:902-914. [PMID: 37095394 DOI: 10.1038/s41593-023-01311-w] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 03/20/2023] [Indexed: 04/26/2023]
Abstract
Understanding spinal cord assembly is essential to elucidate how motor behavior is controlled and how disorders arise. The human spinal cord is exquisitely organized, and this complex organization contributes to the diversity and intricacy of motor behavior and sensory processing. But how this complexity arises at the cellular level in the human spinal cord remains unknown. Here we transcriptomically profiled the midgestation human spinal cord with single-cell resolution and discovered remarkable heterogeneity across and within cell types. Glia displayed diversity related to positional identity along the dorso-ventral and rostro-caudal axes, while astrocytes with specialized transcriptional programs mapped into white and gray matter subtypes. Motor neurons clustered at this stage into groups suggestive of alpha and gamma neurons. We also integrated our data with multiple existing datasets of the developing human spinal cord spanning 22 weeks of gestation to investigate the cell diversity over time. Together with mapping of disease-related genes, this transcriptomic mapping of the developing human spinal cord opens new avenues for interrogating the cellular basis of motor control in humans and guides human stem cell-based models of disease.
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Affiliation(s)
- Jimena Andersen
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
- Department of Human Genetics, Emory University, Atlanta, GA, USA
| | - Nicholas Thom
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
| | | | - Xiaoyu Chen
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
| | - Massimo Mario Onesto
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
- Neurosciences Graduate Program, Stanford University, Stanford, CA, USA
| | - Neal D Amin
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
| | - Se-Jin Yoon
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA
| | - Li Li
- Department of Human Genetics, Emory University, Atlanta, GA, USA
| | - William J Greenleaf
- Department of Genetics, Stanford University, Stanford, CA, USA
- Department of Applied Physics, Stanford University, Stanford, CA, USA
| | - Fabian Müller
- Department of Genetics, Stanford University, Stanford, CA, USA
- Center for Bioinformatics, Saarland University, Saarbrücken, Germany
| | - Anca M Pașca
- Department of Pediatrics, Division of Neonatology, Stanford University, Stanford, CA, USA
| | | | - Sergiu P Pașca
- Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA, USA.
- Stanford Brain Organogenesis, Wu Tsai Neurosciences Institute, Stanford, CA, USA.
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4
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Cao R, Chen P, Wang H, Jing H, Zhang H, Xing G, Luo B, Pan J, Yu Z, Xiong WC, Mei L. Intrafusal-fiber LRP4 for muscle spindle formation and maintenance in adult and aged animals. Nat Commun 2023; 14:744. [PMID: 36765071 PMCID: PMC9918736 DOI: 10.1038/s41467-023-36454-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2022] [Accepted: 01/30/2023] [Indexed: 02/12/2023] Open
Abstract
Proprioception is sensed by muscle spindles for precise locomotion and body posture. Unlike the neuromuscular junction (NMJ) for muscle contraction which has been well studied, mechanisms of spindle formation are not well understood. Here we show that sensory nerve terminals are disrupted by the mutation of Lrp4, a gene required for NMJ formation; inducible knockout of Lrp4 in adult mice impairs sensory synapses and movement coordination, suggesting that LRP4 is required for spindle formation and maintenance. LRP4 is critical to the expression of Egr3 during development; in adult mice, it interacts in trans with APP and APLP2 on sensory terminals. Finally, spindle sensory endings and function are impaired in aged mice, deficits that could be diminished by LRP4 expression. These observations uncovered LRP4 as an unexpected regulator of muscle spindle formation and maintenance in adult and aged animals and shed light on potential pathological mechanisms of abnormal muscle proprioception.
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Affiliation(s)
- Rangjuan Cao
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA.,Department of Hand and Foot Surgery, China-Japan Union Hospital of Jilin University, Changchun, China
| | - Peng Chen
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Hongsheng Wang
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Hongyang Jing
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Hongsheng Zhang
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Guanglin Xing
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Bin Luo
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Jinxiu Pan
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Zheng Yu
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA
| | - Wen-Cheng Xiong
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA. .,Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, 44106, USA.
| | - Lin Mei
- Department of Neurosciences, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA. .,Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, 44106, USA.
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5
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Khan MN, Cherukuri P, Negro F, Rajput A, Fabrowski P, Bansal V, Lancelin C, Lee TI, Bian Y, Mayer WP, Akay T, Müller D, Bonn S, Farina D, Marquardt T. ERR2 and ERR3 promote the development of gamma motor neuron functional properties required for proprioceptive movement control. PLoS Biol 2022; 20:e3001923. [PMID: 36542664 PMCID: PMC9815657 DOI: 10.1371/journal.pbio.3001923] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 01/05/2023] [Accepted: 11/16/2022] [Indexed: 12/24/2022] Open
Abstract
The ability of terrestrial vertebrates to effectively move on land is integrally linked to the diversification of motor neurons into types that generate muscle force (alpha motor neurons) and types that modulate muscle proprioception, a task that in mammals is chiefly mediated by gamma motor neurons. The diversification of motor neurons into alpha and gamma types and their respective contributions to movement control have been firmly established in the past 7 decades, while recent studies identified gene expression signatures linked to both motor neuron types. However, the mechanisms that promote the specification of gamma motor neurons and/or their unique properties remained unaddressed. Here, we found that upon selective loss of the orphan nuclear receptors ERR2 and ERR3 (also known as ERRβ, ERRγ or NR3B2, NR3B3, respectively) in motor neurons in mice, morphologically distinguishable gamma motor neurons are generated but do not acquire characteristic functional properties necessary for regulating muscle proprioception, thus disrupting gait and precision movements. Complementary gain-of-function experiments in chick suggest that ERR2 and ERR3 could operate via transcriptional activation of neural activity modulators to promote a gamma motor neuron biophysical signature of low firing thresholds and high firing rates. Our work identifies a mechanism specifying gamma motor neuron functional properties essential for the regulation of proprioceptive movement control.
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Affiliation(s)
- Mudassar N. Khan
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
- * E-mail: (MNK); (TM)
| | - Pitchaiah Cherukuri
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
- SRM University Andhra Pradesh, Mangalagiri-Mandal, Neeru Konda, Amaravati, Andhra Pradesh, India
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - Ashish Rajput
- University Medical Center Hamburg Eppendorf, Center for Molecular Neurobiology Hamburg (ZMNH), Institute of Medical Systems Biology, Hamburg, Germany
- Maximon AG, Zug, Switzerland
| | - Piotr Fabrowski
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
| | - Vikas Bansal
- University Medical Center Hamburg Eppendorf, Center for Molecular Neurobiology Hamburg (ZMNH), Institute of Medical Systems Biology, Hamburg, Germany
- Biomedical Data Science and Machine Learning Group, German Center for Neurodegenerative Diseases, Tübingen, Germany
| | - Camille Lancelin
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
| | - Tsung-I Lee
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
| | - Yehan Bian
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
| | - William P. Mayer
- Atlantic Mobility Action Project, Brain Repair Centre, Department of Medical Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Turgay Akay
- Atlantic Mobility Action Project, Brain Repair Centre, Department of Medical Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada
| | - Daniel Müller
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
| | - Stefan Bonn
- University Medical Center Hamburg Eppendorf, Center for Molecular Neurobiology Hamburg (ZMNH), Institute of Medical Systems Biology, Hamburg, Germany
| | - Dario Farina
- Department of Bioengineering, Imperial College London, Royal School of Mines, London, United Kingdom
| | - Till Marquardt
- Interfaculty Chair for Neurobiological Research, RWTH Aachen University: Medical Faculty (UKA), Clinic for Neurology & Faculty for Mathematics, Computer and Natural Sciences, Institute for Biology 2, Aachen, Germany
- Developmental Neurobiology Laboratory, European Neuroscience Institute (ENI-G), Göttingen, Germany
- * E-mail: (MNK); (TM)
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6
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Enander JMD, Jones AM, Kirkland M, Hurless J, Jörntell H, Loeb GE. A model for self-organization of sensorimotor function: the spinal monosynaptic loop. J Neurophysiol 2022; 127:1460-1477. [PMID: 35264006 PMCID: PMC9208450 DOI: 10.1152/jn.00242.2021] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2021] [Revised: 02/11/2022] [Accepted: 03/02/2022] [Indexed: 01/05/2023] Open
Abstract
Recent spinal cord literature abounds with descriptions of genetic preprogramming and the molecular control of circuit formation. In this paper, we explore to what extent circuit formation based on learning rather than preprogramming could explain the selective formation of the monosynaptic projections between muscle spindle primary afferents and homonymous motoneurons. We adjusted the initially randomized gains in the neural network according to a Hebbian plasticity rule while exercising the model system with spontaneous muscle activity patterns similar to those observed during early fetal development. Normal connectivity patterns developed only when we modeled β motoneurons, which are known to innervate both intrafusal and extrafusal muscle fibers in vertebrate muscles but were not considered in previous literature regarding selective formation of these synapses in animals with paralyzed muscles. It was also helpful to correctly model the greatly reduced contractility of extrafusal muscle fibers during early development. Stronger and more coordinated muscle activity patterns such as observed later during neonatal locomotion impaired projection selectivity. These findings imply a generic functionality of a musculoskeletal system to imprint important aspects of its mechanical dynamics onto a neural network, without specific preprogramming other than setting a critical period for the formation and maturation of this general pattern of connectivity. Such functionality would facilitate the successful evolution of new species with altered musculoskeletal anatomy, and it may help to explain patterns of connectivity and associated reflexes that appear during abnormal development.NEW & NOTEWORTHY A novel model of self-organization of early spinal circuitry based on a biologically realistic plant, sensors, and neuronal plasticity in conjunction with empirical observations of fetal development. Without explicit need for guiding genetic rules, connection matrices emerge that support functional self-organization of the mature pattern of Ia to motoneuron connectivity in the spinal circuitry.
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Affiliation(s)
- Jonas M D Enander
- Department of Experimental Medical Science, Faculty of Medicine, Lund University, Lund, Sweden
| | - Adam M Jones
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California
| | - Matthieu Kirkland
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California
| | - Jordan Hurless
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California
| | - Henrik Jörntell
- Department of Experimental Medical Science, Faculty of Medicine, Lund University, Lund, Sweden
| | - Gerald E Loeb
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California
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7
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Dasen JS. Establishing the Molecular and Functional Diversity of Spinal Motoneurons. ADVANCES IN NEUROBIOLOGY 2022; 28:3-44. [PMID: 36066819 DOI: 10.1007/978-3-031-07167-6_1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Spinal motoneurons are a remarkably diverse class of neurons responsible for facilitating a broad range of motor behaviors and autonomic functions. Studies of motoneuron differentiation have provided fundamental insights into the developmental mechanisms of neuronal diversification, and have illuminated principles of neural fate specification that operate throughout the central nervous system. Because of their relative anatomical simplicity and accessibility, motoneurons have provided a tractable model system to address multiple facets of neural development, including early patterning, neuronal migration, axon guidance, and synaptic specificity. Beyond their roles in providing direct communication between central circuits and muscle, recent studies have revealed that motoneuron subtype-specific programs also play important roles in determining the central connectivity and function of motor circuits. Cross-species comparative analyses have provided novel insights into how evolutionary changes in subtype specification programs may have contributed to adaptive changes in locomotor behaviors. This chapter focusses on the gene regulatory networks governing spinal motoneuron specification, and how studies of spinal motoneurons have informed our understanding of the basic mechanisms of neuronal specification and spinal circuit assembly.
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Affiliation(s)
- Jeremy S Dasen
- NYU Neuroscience Institute, Department of Neuroscience and Physiology, NYU School of Medicine, New York, NY, USA.
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8
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Zuccaro E, Piol D, Basso M, Pennuto M. Motor Neuron Diseases and Neuroprotective Peptides: A Closer Look to Neurons. Front Aging Neurosci 2021; 13:723871. [PMID: 34603008 PMCID: PMC8484953 DOI: 10.3389/fnagi.2021.723871] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 08/26/2021] [Indexed: 12/02/2022] Open
Abstract
Motor neurons (MNs) are specialized neurons responsible for muscle contraction that specifically degenerate in motor neuron diseases (MNDs), such as amyotrophic lateral sclerosis (ALS), spinal and bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Distinct classes of MNs degenerate at different rates in disease, with a particular class named fast-fatigable MNs (FF-MNs) degenerating first. The etiology behind the selective vulnerability of FF-MNs is still largely under investigation. Among the different strategies to target MNs, the administration of protective neuropeptides is one of the potential therapeutic interventions. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with beneficial effects in many neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and more recently SBMA. Another neuropeptide that has a neurotrophic effect on MNs is insulin-like growth factor 1 (IGF-1), also known as somatomedin C. These two peptides are implicated in the activation of neuroprotective pathways exploitable in the amelioration of pathological outcomes related to MNDs.
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Affiliation(s)
- Emanuela Zuccaro
- Department of Biomedical Sciences, University of Padua, Padua, Italy
- Veneto Institute of Molecular Medicine, Padua, Italy
- Padova Neuroscience Center, Padua, Italy
| | - Diana Piol
- Department of Biomedical Sciences, University of Padua, Padua, Italy
| | - Manuela Basso
- Department of Cellular, Computational and Integrative Biology – CIBIO, University of Trento, Trento, Italy
| | - Maria Pennuto
- Department of Biomedical Sciences, University of Padua, Padua, Italy
- Veneto Institute of Molecular Medicine, Padua, Italy
- Padova Neuroscience Center, Padua, Italy
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9
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Alkaslasi MR, Piccus ZE, Hareendran S, Silberberg H, Chen L, Zhang Y, Petros TJ, Le Pichon CE. Single nucleus RNA-sequencing defines unexpected diversity of cholinergic neuron types in the adult mouse spinal cord. Nat Commun 2021; 12:2471. [PMID: 33931636 PMCID: PMC8087807 DOI: 10.1038/s41467-021-22691-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 03/25/2021] [Indexed: 02/05/2023] Open
Abstract
In vertebrates, motor control relies on cholinergic neurons in the spinal cord that have been extensively studied over the past hundred years, yet the full heterogeneity of these neurons and their different functional roles in the adult remain to be defined. Here, we develop a targeted single nuclear RNA sequencing approach and use it to identify an array of cholinergic interneurons, visceral and skeletal motor neurons. Our data expose markers for distinguishing these classes of cholinergic neurons and their rich diversity. Specifically, visceral motor neurons, which provide autonomic control, can be divided into more than a dozen transcriptomic classes with anatomically restricted localization along the spinal cord. The complexity of the skeletal motor neurons is also reflected in our analysis with alpha, gamma, and a third subtype, possibly corresponding to the elusive beta motor neurons, clearly distinguished. In combination, our data provide a comprehensive transcriptomic description of this important population of neurons that control many aspects of physiology and movement and encompass the cellular substrates for debilitating degenerative disorders.
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Affiliation(s)
- Mor R Alkaslasi
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- Department of Neuroscience, Brown University, Providence, RI, USA
| | - Zoe E Piccus
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- Department of Neuroscience, Brown University, Providence, RI, USA
| | - Sangeetha Hareendran
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Hanna Silberberg
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Li Chen
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Yajun Zhang
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Timothy J Petros
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Claire E Le Pichon
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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10
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Abstract
The muscle spindle is an important sense organ for motor control and proprioception. Specialized intrafusal fibers are innervated by both stretch sensitive afferents and γ motor neurons that control the length of the spindle and tune the sensitivity of the muscle spindle afferents to both dynamic movement and static length. γ motor neurons share many similarities with other skeletal motor neurons, making it challenging to identify and specifically record or stimulate them. This short review will discuss recent advances in genetic and molecular biology techniques, electrophysiological recording, optical imaging, computer modelling, and stem cell culture techniques that have the potential to help answer important questions about fusimotor function in motor control and disease.
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11
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An Atoh1 CRE Knock-In Mouse Labels Motor Neurons Involved in Fine Motor Control. eNeuro 2021; 8:ENEURO.0221-20.2021. [PMID: 33468540 PMCID: PMC7901153 DOI: 10.1523/eneuro.0221-20.2021] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Revised: 01/05/2021] [Accepted: 01/08/2021] [Indexed: 11/21/2022] Open
Abstract
Motor neurons (MNs) innervating the digit muscles of the intrinsic hand (IH) and intrinsic foot (IF) control fine motor movements. The ability to reproducibly label specifically IH and IF MNs in mice would be a beneficial tool for studies focused on fine motor control. To this end, we find that a CRE knock-in mouse line of Atoh1, a developmentally expressed basic helix-loop-helix (bHLH) transcription factor, reliably expresses CRE-dependent reporter genes in ∼60% of the IH and IF MNs. We determine that CRE-dependent expression in IH and IF MNs is ectopic because an Atoh1 mouse line driving FLPo recombinase does not label these MNs although other Atoh1-lineage neurons in the intermediate spinal cord are reliably identified. Furthermore, the CRE-dependent reporter expression is enriched in the IH and IF MN pools with much sparser labeling of other limb-innervating MN pools such as the tibialis anterior (TA), gastrocnemius (GS), quadricep (Q), and adductor (Ad). Lastly, we find that ectopic reporter expression begins postnatally and labels a mixture of α and γ-MNs. Altogether, the Atoh1 CRE knock-in mouse strain might be a useful tool to explore the function and connectivity of MNs involved in fine motor control when combined with other genetic or viral strategies that can restrict labeling specifically to the IH and IF MNs. Accordingly, we provide an example of sparse labeling of IH and IF MNs using an intersectional genetic approach.
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12
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Ragagnin AMG, Shadfar S, Vidal M, Jamali MS, Atkin JD. Motor Neuron Susceptibility in ALS/FTD. Front Neurosci 2019; 13:532. [PMID: 31316328 PMCID: PMC6610326 DOI: 10.3389/fnins.2019.00532] [Citation(s) in RCA: 120] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Accepted: 05/08/2019] [Indexed: 12/11/2022] Open
Abstract
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the death of both upper and lower motor neurons (MNs) in the brain, brainstem and spinal cord. The neurodegenerative mechanisms leading to MN loss in ALS are not fully understood. Importantly, the reasons why MNs are specifically targeted in this disorder are unclear, when the proteins associated genetically or pathologically with ALS are expressed ubiquitously. Furthermore, MNs themselves are not affected equally; specific MNs subpopulations are more susceptible than others in both animal models and human patients. Corticospinal MNs and lower somatic MNs, which innervate voluntary muscles, degenerate more readily than specific subgroups of lower MNs, which remain resistant to degeneration, reflecting the clinical manifestations of ALS. In this review, we discuss the possible factors intrinsic to MNs that render them uniquely susceptible to neurodegeneration in ALS. We also speculate why some MN subpopulations are more vulnerable than others, focusing on both their molecular and physiological properties. Finally, we review the anatomical network and neuronal microenvironment as determinants of MN subtype vulnerability and hence the progression of ALS.
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Affiliation(s)
- Audrey M G Ragagnin
- Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Sina Shadfar
- Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Marta Vidal
- Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Md Shafi Jamali
- Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia
| | - Julie D Atkin
- Centre for Motor Neuron Disease Research, Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, NSW, Australia.,Department of Biochemistry and Genetics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, VIC, Australia
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13
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A Role for Sensory end Organ-Derived Signals in Regulating Muscle Spindle Proprioceptor Phenotype. J Neurosci 2019; 39:4252-4267. [PMID: 30926747 DOI: 10.1523/jneurosci.2671-18.2019] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 02/21/2019] [Accepted: 03/21/2019] [Indexed: 01/09/2023] Open
Abstract
Proprioceptive feedback from Group Ia/II muscle spindle afferents and Group Ib Golgi tendon afferents is critical for the normal execution of most motor tasks, yet how these distinct proprioceptor subtypes emerge during development remains poorly understood. Using molecular genetic approaches in mice of either sex, we identified 24 transcripts that have not previously been associated with a proprioceptor identity. Combinatorial expression analyses of these markers reveal at least three molecularly distinct proprioceptor subtypes. In addition, we find that 12 of these transcripts are expressed well after proprioceptors innervate their respective sensory receptors, and expression of three of these markers, including the heart development molecule Heg1, is significantly reduced in mice that lack muscle spindles. These data reveal Heg1 as a putative marker for proprioceptive muscle spindle afferents. Moreover, they suggest that the phenotypic specialization of functionally distinct proprioceptor subtypes depends, in part, on extrinsic sensory receptor organ-derived signals.SIGNIFICANCE STATEMENT Sensory feedback from muscle spindle (MS) and Golgi tendon organ (GTO) sensory end organs is critical for normal motor control, but how distinct MS and GTO afferent sensory neurons emerge during development remains poorly understood. Using (bulk) transcriptome analysis of genetically identified proprioceptors, this work reveals molecular markers for distinct proprioceptor subsets, including some that appear selectively expressed in MS afferents. Detailed analysis of the expression of these transcripts provides evidence that MS/GTO afferent subtype phenotypes may, at least in part, emerge through extrinsic, sensory end organ-derived signals.
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14
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Miao N, Bian S, Lee T, Mubarak T, Huang S, Wen Z, Hussain G, Sun T. Opposite Roles of Wnt7a and Sfrp1 in Modulating Proper Development of Neural Progenitors in the Mouse Cerebral Cortex. Front Mol Neurosci 2018; 11:247. [PMID: 30065628 PMCID: PMC6056652 DOI: 10.3389/fnmol.2018.00247] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Accepted: 06/28/2018] [Indexed: 12/22/2022] Open
Abstract
The Wingless (Wnt)-mediated signals are involved in many important aspects of development of the mammalian cerebral cortex. How Wnts interact with their modulators in cortical development is still unclear. Here, we show that Wnt7a and secreted frizzled-related protein 1 (Sfrp1), a soluble modulator of Wnts, are co-expressed in mouse embryonic cortical neural progenitors (NPs). Knockout of Wnt7a in mice causes microcephaly due to reduced NP population and neurogenesis, and Sfrp1 has an opposing effect compared to Wnt7a. Similar to Dkk1, Sfrp1 decreases the Wnt1 and Wnt7a activity in vitro. Our results suggest that Wnt7a and Sfrp1 play opposite roles to ensure proper NP progeny in the developing cortex.
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Affiliation(s)
- Nan Miao
- Center for Precision Medicine, School of Medicine and School of Biomedical Sciences, Huaqiao University, Xiamen, China
| | - Shan Bian
- Department of Cell and Developmental Biology, Weill Cornell Medicine, Cornell University, New York, NY, United States
| | - Trevor Lee
- Department of Cell and Developmental Biology, Weill Cornell Medicine, Cornell University, New York, NY, United States
| | - Taufif Mubarak
- Department of Cell and Developmental Biology, Weill Cornell Medicine, Cornell University, New York, NY, United States
| | - Shiying Huang
- College of Oceanology and Food Science, Quanzhou Normal University, Quanzhou, China
| | - Zhihong Wen
- Marine Biomedical Laboratory and Center for Translational Biopharmaceuticals, Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan
| | - Ghulam Hussain
- Department of Physiology, Government College University, Faisalabad, Pakistan
| | - Tao Sun
- Center for Precision Medicine, School of Medicine and School of Biomedical Sciences, Huaqiao University, Xiamen, China
- Department of Cell and Developmental Biology, Weill Cornell Medicine, Cornell University, New York, NY, United States
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15
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Nishimura K, Ohta M, Saito M, Morita-Isogai Y, Sato H, Kuramoto E, Yin DX, Maeda Y, Kaneko T, Yamashiro T, Takada K, Oh SB, Toyoda H, Kang Y. Electrophysiological and Morphological Properties of α and γ Motoneurons in the Rat Trigeminal Motor Nucleus. Front Cell Neurosci 2018; 12:9. [PMID: 29416504 PMCID: PMC5787551 DOI: 10.3389/fncel.2018.00009] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 01/08/2018] [Indexed: 11/18/2022] Open
Abstract
The muscle contraction during voluntary movement is regulated by activities of α- and γ-motoneurons (αMNs and γMNs, respectively). The tension of jaw-closing muscles can be finely tuned over a wide range. This excellent function is likely to be achieved by the specific populations of αMNs innervating jaw-closing muscles. Indeed, we have recently demonstrated that in the rat dorsolateral trigeminal motor nucleus (dl-TMN), the size distribution of αMNs was bimodal and the population of smaller αMNs showed a size distribution similar to that of γMNs, by immunohistochemically identifying αMNs and γMNs based on the expressions of estrogen-related receptor gamma (Err3) and neuronal DNA binding protein NeuN together with ChAT. This finding suggests the presence of αMNs as small as γMNs. However, differences in the electrophysiological membrane properties between αMNs and γMNs remain unknown also in the dl-TMN. Therefore, in the present study, we studied the electrophysiological membrane properties of MNs in the dl-TMN of infant rats at postnatal days 7–12 together with their morphological properties using whole-cell current-clamp recordings followed by immunohistochemical staining with an anti-NeuN and anti-ChAT antibodies. We found that the ChAT-positive and NeuN-positive αMNs were divided into two subclasses: the first one had a larger cell body and displayed a 4-aminopyridine (4-AP)-sensitive current while the second one had a smaller cell body and displayed a less prominent 4-AP-sensitive current and a low-threshold spike, suitable for their orderly recruitment. We finally found that γMNs showing ChAT-positive and NeuN-negative immunoreactivities had smaller cell bodies and displayed an afterdepolarization mediated by flufenamate-sensitive cation current. It is suggested that these electrophysiological and morphological features of MNs in the dl-TMN are well correlated with the precise control of occlusion.
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Affiliation(s)
- Kayo Nishimura
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan.,Department of Orthodontics and Dentofacial Orthopedics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Masahiro Ohta
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan.,Department of Removable Prosthodontics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Mitsuru Saito
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan.,Department of Oral Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan
| | - Yukako Morita-Isogai
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan.,Department of Orthodontics and Dentofacial Orthopedics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Hajime Sato
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Eriko Kuramoto
- Department of Oral Anatomy and Cell Biology, Graduate School of Medical and Dental Sciences, Kagoshima University, Kagoshima, Japan.,Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Dong Xu Yin
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Yoshinobu Maeda
- Department of Removable Prosthodontics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Takeshi Kaneko
- Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Takashi Yamashiro
- Department of Orthodontics and Dentofacial Orthopedics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Kenji Takada
- Department of Orthodontics and Dentofacial Orthopedics, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Seog Bae Oh
- Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul, South Korea
| | - Hiroki Toyoda
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan
| | - Youngnam Kang
- Department of Neuroscience and Oral Physiology, Osaka University Graduate School of Dentistry, Suita, Japan.,Department of Neurobiology and Physiology, School of Dentistry, Seoul National University, Seoul, South Korea
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16
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Colón A, Guo X, Akanda N, Cai Y, Hickman JJ. Functional analysis of human intrafusal fiber innervation by human γ-motoneurons. Sci Rep 2017; 7:17202. [PMID: 29222416 PMCID: PMC5722897 DOI: 10.1038/s41598-017-17382-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Accepted: 11/21/2017] [Indexed: 11/09/2022] Open
Abstract
Investigation of neuromuscular deficits and diseases such as SMA, as well as for next generation prosthetics, utilizing in vitro phenotypic models would benefit from the development of a functional neuromuscular reflex arc. The neuromuscular reflex arc is the system that integrates the proprioceptive information for muscle length and activity (sensory afferent), to modify motoneuron output to achieve graded muscle contraction (actuation efferent). The sensory portion of the arc is composed of proprioceptive sensory neurons and the muscle spindle, which is embedded in the muscle tissue and composed of intrafusal fibers. The gamma motoneurons (γ-MNs) that innervate these fibers regulate the intrafusal fiber's stretch so that they retain proper tension and sensitivity during muscle contraction or relaxation. This mechanism is in place to maintain the sensitivity of proprioception during dynamic muscle activity and to prevent muscular damage. In this study, a co-culture system was developed for innervation of intrafusal fibers by human γ-MNs and demonstrated by morphological and immunocytochemical analysis, then validated by functional electrophysiological evaluation. This human-based fusimotor model and its incorporation into the reflex arc allows for a more accurate recapitulation of neuromuscular function for applications in disease investigations, drug discovery, prosthetic design and neuropathic pain investigations.
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Affiliation(s)
- A Colón
- Hybrid Systems Lab, NanoScience Technology Center, University of Central Florida, 12424 Research Parkway, Suite 400, Orlando, FL, 32826, USA
| | - X Guo
- Hybrid Systems Lab, NanoScience Technology Center, University of Central Florida, 12424 Research Parkway, Suite 400, Orlando, FL, 32826, USA
| | - N Akanda
- Hybrid Systems Lab, NanoScience Technology Center, University of Central Florida, 12424 Research Parkway, Suite 400, Orlando, FL, 32826, USA
| | - Y Cai
- Hybrid Systems Lab, NanoScience Technology Center, University of Central Florida, 12424 Research Parkway, Suite 400, Orlando, FL, 32826, USA
| | - J J Hickman
- Hybrid Systems Lab, NanoScience Technology Center, University of Central Florida, 12424 Research Parkway, Suite 400, Orlando, FL, 32826, USA.
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17
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Walsh P, Truong V, Hill C, Stoflet ND, Baden J, Low WC, Keirstead SA, Dutton JR, Parr AM. Defined Culture Conditions Accelerate Small-molecule-assisted Neural Induction for the Production of Neural Progenitors from Human-induced Pluripotent Stem Cells. Cell Transplant 2017; 26:1890-1902. [PMID: 29390875 PMCID: PMC5802631 DOI: 10.1177/0963689717737074] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2017] [Revised: 09/20/2017] [Accepted: 09/25/2017] [Indexed: 12/13/2022] Open
Abstract
The use of defined conditions for derivation, maintenance, and differentiation of human-induced pluripotent stem cells (hiPSCs) provides a superior experimental platform to discover culture responses to differentiation cues and elucidate the basic requirements for cell differentiation and fate restriction. Adoption of defined systems for reprogramming, undifferentiated growth, and differentiation of hiPSCs was found to significantly influence early stage differentiation signaling requirements and temporal kinetics for the production of primitive neuroectoderm. The bone morphogenic protein receptor agonist LDN-193189 was found to be necessary and sufficient for neural induction in a monolayer system with landmark antigens paired box 6 and sex-determining region Y-box 1 appearing within 72 h. Preliminary evidence suggests this neuroepithelium was further differentiated to generate ventral spinal neural progenitors that produced electrophysiologically active neurons in vitro, maintaining viability posttransplantation in an immunocompromised host. Our findings support current developments in the field, demonstrating that adoption of defined reagents for the culture and manipulation of pluripotent stem cells is advantages in terms of simplification and acceleration of differentiation protocols, which will be critical for future clinical translation.
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Affiliation(s)
- Patrick Walsh
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
| | - Vincent Truong
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
| | - Caitlin Hill
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Nicolas D. Stoflet
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
| | - Jessica Baden
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
| | - Walter C. Low
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN, USA
| | - Susan A. Keirstead
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
- Department of Integrative Biology and Physiology, University of Minnesota, Minneapolis, MN, USA
| | - James R. Dutton
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | - Ann M. Parr
- Department of Neurosurgery, University of Minnesota, Minneapolis, MN, USA
- Stem Cell Institute, University of Minnesota, Minneapolis, MN, USA
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18
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Gamma motor neurons survive and exacerbate alpha motor neuron degeneration in ALS. Proc Natl Acad Sci U S A 2016; 113:E8316-E8325. [PMID: 27930290 DOI: 10.1073/pnas.1605210113] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The molecular and cellular basis of selective motor neuron (MN) vulnerability in amyotrophic lateral sclerosis (ALS) is not known. In genetically distinct mouse models of familial ALS expressing mutant superoxide dismutase-1 (SOD1), TAR DNA-binding protein 43 (TDP-43), and fused in sarcoma (FUS), we demonstrate selective degeneration of alpha MNs (α-MNs) and complete sparing of gamma MNs (γ-MNs), which selectively innervate muscle spindles. Resistant γ-MNs are distinct from vulnerable α-MNs in that they lack synaptic contacts from primary afferent (IA) fibers. Elimination of these synapses protects α-MNs in the SOD1 mutant, implicating this excitatory input in MN degeneration. Moreover, reduced IA activation by targeted reduction of γ-MNs in SOD1G93A mutants delays symptom onset and prolongs lifespan, demonstrating a pathogenic role of surviving γ-MNs in ALS. This study establishes the resistance of γ-MNs as a general feature of ALS mouse models and demonstrates that synaptic excitation of MNs within a complex circuit is an important determinant of relative vulnerability in ALS.
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19
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Emerging Roles of Filopodia and Dendritic Spines in Motoneuron Plasticity during Development and Disease. Neural Plast 2015; 2016:3423267. [PMID: 26843990 PMCID: PMC4710938 DOI: 10.1155/2016/3423267] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 09/10/2015] [Accepted: 09/21/2015] [Indexed: 01/16/2023] Open
Abstract
Motoneurons develop extensive dendritic trees for receiving excitatory and inhibitory synaptic inputs to perform a variety of complex motor tasks. At birth, the somatodendritic domains of mouse hypoglossal and lumbar motoneurons have dense filopodia and spines. Consistent with Vaughn's synaptotropic hypothesis, we propose a developmental unified-hybrid model implicating filopodia in motoneuron spinogenesis/synaptogenesis and dendritic growth and branching critical for circuit formation and synaptic plasticity at embryonic/prenatal/neonatal period. Filopodia density decreases and spine density initially increases until postnatal day 15 (P15) and then decreases by P30. Spine distribution shifts towards the distal dendrites, and spines become shorter (stubby), coinciding with decreases in frequency and increases in amplitude of excitatory postsynaptic currents with maturation. In transgenic mice, either overexpressing the mutated human Cu/Zn-superoxide dismutase (hSOD1G93A) gene or deficient in GABAergic/glycinergic synaptic transmission (gephyrin, GAD-67, or VGAT gene knockout), hypoglossal motoneurons develop excitatory glutamatergic synaptic hyperactivity. Functional synaptic hyperactivity is associated with increased dendritic growth, branching, and increased spine and filopodia density, involving actin-based cytoskeletal and structural remodelling. Energy-dependent ionic pumps that maintain intracellular sodium/calcium homeostasis are chronically challenged by activity and selectively overwhelmed by hyperactivity which eventually causes sustained membrane depolarization leading to excitotoxicity, activating microglia to phagocytose degenerating neurons under neuropathological conditions.
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20
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Powis RA, Gillingwater TH. Selective loss of alpha motor neurons with sparing of gamma motor neurons and spinal cord cholinergic neurons in a mouse model of spinal muscular atrophy. J Anat 2015; 228:443-51. [PMID: 26576026 DOI: 10.1111/joa.12419] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2015] [Indexed: 02/04/2023] Open
Abstract
Spinal muscular atrophy (SMA) is a neuromuscular disease characterised primarily by loss of lower motor neurons from the ventral grey horn of the spinal cord and proximal muscle atrophy. Recent experiments utilising mouse models of SMA have demonstrated that not all motor neurons are equally susceptible to the disease, revealing that other populations of neurons can also be affected. Here, we have extended investigations of selective vulnerability of neuronal populations in the spinal cord of SMA mice to include comparative assessments of alpha motor neuron (α-MN) and gamma motor neuron (γ-MN) pools, as well as other populations of cholinergic neurons. Immunohistochemical analyses of late-symptomatic SMA mouse spinal cord revealed that numbers of α-MNs were significantly reduced at all levels of the spinal cord compared with controls, whereas numbers of γ-MNs remained stable. Likewise, the average size of α-MN cell somata was decreased in SMA mice with no change occurring in γ-MNs. Evaluation of other pools of spinal cord cholinergic neurons revealed that pre-ganglionic sympathetic neurons, central canal cluster interneurons, partition interneurons and preganglionic autonomic dorsal commissural nucleus neuron numbers all remained unaffected in SMA mice. Taken together, these findings indicate that α-MNs are uniquely vulnerable among cholinergic neuron populations in the SMA mouse spinal cord, with γ-MNs and other cholinergic neuronal populations being largely spared.
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Affiliation(s)
- Rachael A Powis
- Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK.,Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Edinburgh, UK
| | - Thomas H Gillingwater
- Euan MacDonald Centre for Motor Neurone Disease Research, University of Edinburgh, Edinburgh, UK.,Centre for Integrative Physiology, School of Biomedical Sciences, University of Edinburgh, Edinburgh, UK
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21
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Lu DC, Niu T, Alaynick WA. Molecular and cellular development of spinal cord locomotor circuitry. Front Mol Neurosci 2015; 8:25. [PMID: 26136656 PMCID: PMC4468382 DOI: 10.3389/fnmol.2015.00025] [Citation(s) in RCA: 131] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 05/30/2015] [Indexed: 01/20/2023] Open
Abstract
The spinal cord of vertebrate animals is comprised of intrinsic circuits that are capable of sensing the environment and generating complex motor behaviors. There are two major perspectives for understanding the biology of this complicated structure. The first approaches the spinal cord from the point of view of function and is based on classic and ongoing research in electrophysiology, adult behavior, and spinal cord injury. The second view considers the spinal cord from a developmental perspective and is founded mostly on gene expression and gain-of-function and loss-of-function genetic experiments. Together these studies have uncovered functional classes of neurons and their lineage relationships. In this review, we summarize our knowledge of developmental classes, with an eye toward understanding the functional roles of each group.
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Affiliation(s)
- Daniel C Lu
- Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA USA
| | - Tianyi Niu
- Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA USA
| | - William A Alaynick
- Department of Neurosurgery, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA USA
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22
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Zhang Y, Lin S, Karakatsani A, Rüegg MA, Kröger S. Differential regulation of AChR clustering in the polar and equatorial region of murine muscle spindles. Eur J Neurosci 2014; 41:69-78. [PMID: 25377642 DOI: 10.1111/ejn.12768] [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] [Received: 03/13/2014] [Revised: 09/29/2014] [Accepted: 10/02/2014] [Indexed: 12/16/2022]
Abstract
Intrafusal fibers of muscle spindles are innervated in the central region by afferent sensory axons and at both polar regions by efferent γ-motoneurons. We previously demonstrated that both neuron-muscle contact sites contain cholinergic synapse-like specialisation, including aggregates of the nicotinic acetylcholine receptor (AChR). In this study we tested the hypothesis that agrin and its receptor complex (consisting of LRP4 and the tyrosine kinase MuSK) are involved in the aggregation of AChRs in muscle spindles, similar to their role at the neuromuscular junction. We show that agrin, MuSK and LRP4 are concentrated at the contact site between the intrafusal fibers and the sensory- and γ-motoneuron, respectively, and that they are expressed in the cell bodies of proprioceptive neurons in dorsal root ganglia. Moreover, agrin and LRP4, but not MuSK, are expressed in γ-motoneuron cell bodies in the ventral horn of the spinal cord. In agrin- and in MuSK-deficient mice, AChR aggregates are absent from the polar regions. In contrast, the subcellular concentration of AChRs in the central region where the sensory neuron contacts the intrafusal muscle fiber is apparently unaffected. Skeletal muscle-specific expression of miniagrin in agrin(-/-) mice in vivo is sufficient to restore the formation of γ-motoneuron endplates. These results show that agrin and MuSK are major determinants during the formation of γ-motoneuron endplates but appear dispensable for the aggregation of AChRs at the central region. Our results therefore suggest different molecular mechanisms for AChR clustering within two domains of intrafusal fibers.
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Affiliation(s)
- Yina Zhang
- Department of Physiological Genomics, Ludwig-Maximilians-University, Pettenkoferstrasse 12, D-80336, Munich, Germany; Helmholtz Center Munich, Neuherberg, Germany
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23
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Stifani N. Motor neurons and the generation of spinal motor neuron diversity. Front Cell Neurosci 2014; 8:293. [PMID: 25346659 PMCID: PMC4191298 DOI: 10.3389/fncel.2014.00293] [Citation(s) in RCA: 178] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2013] [Accepted: 09/02/2014] [Indexed: 11/13/2022] Open
Abstract
Motor neurons (MNs) are neuronal cells located in the central nervous system (CNS) controlling a variety of downstream targets. This function infers the existence of MN subtypes matching the identity of the targets they innervate. To illustrate the mechanism involved in the generation of cellular diversity and the acquisition of specific identity, this review will focus on spinal MNs (SpMNs) that have been the core of significant work and discoveries during the last decades. SpMNs are responsible for the contraction of effector muscles in the periphery. Humans possess more than 500 different skeletal muscles capable to work in a precise time and space coordination to generate complex movements such as walking or grasping. To ensure such refined coordination, SpMNs must retain the identity of the muscle they innervate. Within the last two decades, scientists around the world have produced considerable efforts to elucidate several critical steps of SpMNs differentiation. During development, SpMNs emerge from dividing progenitor cells located in the medial portion of the ventral neural tube. MN identities are established by patterning cues working in cooperation with intrinsic sets of transcription factors. As the embryo develop, MNs further differentiate in a stepwise manner to form compact anatomical groups termed pools connecting to a unique muscle target. MN pools are not homogeneous and comprise subtypes according to the muscle fibers they innervate. This article aims to provide a global view of MN classification as well as an up-to-date review of the molecular mechanisms involved in the generation of SpMN diversity. Remaining conundrums will be discussed since a complete understanding of those mechanisms constitutes the foundation required for the elaboration of prospective MN regeneration therapies.
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Affiliation(s)
- Nicolas Stifani
- Medical Neuroscience, Dalhousie University Halifax, NS, Canada
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24
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Formation of cholinergic synapse-like specializations at developing murine muscle spindles. Dev Biol 2014; 393:227-235. [DOI: 10.1016/j.ydbio.2014.07.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Revised: 07/14/2014] [Accepted: 07/15/2014] [Indexed: 12/30/2022]
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25
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Astrocyte-encoded positional cues maintain sensorimotor circuit integrity. Nature 2014; 509:189-94. [PMID: 24776795 PMCID: PMC4057936 DOI: 10.1038/nature13161] [Citation(s) in RCA: 219] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2013] [Accepted: 02/18/2014] [Indexed: 01/03/2023]
Abstract
Astrocytes, the most abundant cells in the central nervous system, promote synapse formation and help refine neural connectivity. Although they are allocated to spatially distinct regional domains during development, it is unknown whether region-restricted astrocytes are functionally heterogeneous. Here we show that postnatal spinal cord astrocytes express several region-specific genes, and that ventral astrocyte-encoded Semaphorin3a (Sema3a) is required for proper motor neuron and sensory neuron circuit organization. Loss of astrocyte-encoded Sema3a led to dysregulated α–motor neuron axon initial segment orientation, markedly abnormal synaptic inputs, and selective death of α–but not of adjacent γ–motor neurons. Additionally, a subset of TrkA+ sensory afferents projected to ectopic ventral positions. These findings demonstrate that stable maintenance of a positional cue by developing astrocytes influences multiple aspects of sensorimotor circuit formation. More generally, they suggest that regional astrocyte heterogeneity may help to coordinate postnatal neural circuit refinement.
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26
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Ashrafi S, Betley JN, Comer JD, Brenner-Morton S, Bar V, Shimoda Y, Watanabe K, Peles E, Jessell TM, Kaltschmidt JA. Neuronal Ig/Caspr recognition promotes the formation of axoaxonic synapses in mouse spinal cord. Neuron 2014; 81:120-9. [PMID: 24411736 PMCID: PMC3898991 DOI: 10.1016/j.neuron.2013.10.060] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/16/2013] [Indexed: 01/06/2023]
Abstract
Inhibitory microcircuits are wired with a precision that underlies their complex regulatory roles in neural information processing. In the spinal cord, one specialized class of GABAergic interneurons (GABApre) mediates presynaptic inhibitory control of sensory-motor synapses. The synaptic targeting of these GABAergic neurons exhibits an absolute dependence on proprioceptive sensory terminals, yet the molecular underpinnings of this specialized axoaxonic organization remain unclear. Here, we show that sensory expression of an NB2 (Contactin5)/Caspr4 coreceptor complex, together with spinal interneuron expression of NrCAM/CHL1, directs the high-density accumulation of GABAergic boutons on sensory terminals. Moreover, genetic elimination of NB2 results in a disproportionate stripping of inhibitory boutons from high-density GABApre-sensory synapses, suggesting that the preterminal axons of GABApre neurons compete for access to individual sensory terminals. Our findings define a recognition complex that contributes to the assembly and organization of a specialized GABAergic microcircuit. Sensory Ig/Caspr4 complex directs inhibitory synapse formation in mouse spinal cord Eliminating NB2 results in a reduced number of GABApre-sensory synapses Quantitative modeling suggests competition for formation of axoaxonic synapses Role for a contactin/Caspr complex in central synapse formation
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Affiliation(s)
- Soha Ashrafi
- Neuroscience Program, Weill Cornell Graduate School of Medical Sciences, New York, NY 10065, USA; Developmental Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
| | - J Nicholas Betley
- Howard Hughes Medical Institute, Kavli Institute of Brain Science, Departments of Neuroscience, Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - John D Comer
- Neuroscience Program, Weill Cornell Graduate School of Medical Sciences, New York, NY 10065, USA; Developmental Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA; Weill Cornell/Rockefeller/Sloan-Kettering Tri-Institutional MD-PhD Program, New York, NY 10065, USA
| | - Susan Brenner-Morton
- Howard Hughes Medical Institute, Kavli Institute of Brain Science, Departments of Neuroscience, Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Vered Bar
- Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yasushi Shimoda
- Department of Bioengineering, Nagaoka University of Technology, 1603-1, Kamitomiokamachi, Nagaoka, Niigata 940-2188, Japan
| | - Kazutada Watanabe
- Department of Bioengineering, Nagaoka University of Technology, 1603-1, Kamitomiokamachi, Nagaoka, Niigata 940-2188, Japan; Nagaoka National College of Technology, 888, Nishikatakaimachi, Nagaoka, Niigata 940-8532, Japan
| | - Elior Peles
- Department of Molecular Cell Biology, The Weizmann Institute of Science, Rehovot 76100, Israel
| | - Thomas M Jessell
- Howard Hughes Medical Institute, Kavli Institute of Brain Science, Departments of Neuroscience, Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.
| | - Julia A Kaltschmidt
- Neuroscience Program, Weill Cornell Graduate School of Medical Sciences, New York, NY 10065, USA; Developmental Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA.
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Zampieri N, Jessell TM, Murray AJ. Mapping sensory circuits by anterograde transsynaptic transfer of recombinant rabies virus. Neuron 2014; 81:766-78. [PMID: 24486087 DOI: 10.1016/j.neuron.2013.12.033] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2013] [Indexed: 01/14/2023]
Abstract
Primary sensory neurons convey information from the external world to relay circuits within the CNS, but the identity and organization of the neurons that process incoming sensory information remains sketchy. Within the CNS, viral tracing techniques that rely on retrograde transsynaptic transfer provide a powerful tool for delineating circuit organization. Viral tracing of the circuits engaged by primary sensory neurons has, however, been hampered by the absence of a genetically tractable anterograde transfer system. In this study, we demonstrate that rabies virus can infect sensory neurons in the somatosensory system, is subject to anterograde transsynaptic transfer from primary sensory to spinal target neurons, and can delineate output connectivity with third-order neurons. Anterograde transsynaptic transfer is a feature shared by other classes of primary sensory neurons, permitting the identification and potentially the manipulation of neural circuits processing sensory feedback within the mammalian CNS.
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Affiliation(s)
- Niccolò Zampieri
- Departments of Neuroscience and Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Kavli Institute for Brain Science, Columbia University, New York, NY 10032 USA
| | - Thomas M Jessell
- Departments of Neuroscience and Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Kavli Institute for Brain Science, Columbia University, New York, NY 10032 USA.
| | - Andrew J Murray
- Departments of Neuroscience and Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Kavli Institute for Brain Science, Columbia University, New York, NY 10032 USA
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