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Gu Z, Matsuura K, Letelier A, Basista M, Craig C, Imai F, Yoshida Y. Axon Fasciculation, Mediated by Transmembrane Semaphorins, Is Critical for the Establishment of Segmental Specificity of Corticospinal Circuits. J Neurosci 2023; 43:5753-5768. [PMID: 37344234 PMCID: PMC10423052 DOI: 10.1523/jneurosci.0073-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Revised: 04/21/2023] [Accepted: 04/27/2023] [Indexed: 06/23/2023] Open
Abstract
Axon fasciculation is thought to be a critical step in neural circuit formation and function. Recent studies have revealed various molecular mechanisms that underlie axon fasciculation; however, the impacts of axon fasciculation, and its corollary, defasciculation, on neural circuit wiring remain unclear. Corticospinal (CS) neurons in the sensorimotor cortex project axons to the spinal cord to control skilled movements. In rodents, the axons remain tightly fasciculated in the brain and traverse the dorsal funiculus of the spinal cord. Here we show that plexinA1 (PlexA1) and plexinA3 (PlexA3) receptors are expressed by CS neurons, whereas their ligands, semaphorin-5A (Sema5A) and semaphorin-5B (Sema5B) are expressed in the medulla at the decussation site of CS axons to inhibit premature defasciculation of these axons. In the absence of Sema5A/5B-PlexA1/A3 signaling, some CS axons are prematurely defasciculated in the medulla of the brainstem, and those defasciculated CS axons aberrantly transverse in the spinal gray matter instead of the spinal dorsal funiculus. In the absence of Sema5A/Sema5B-PlexA1/A3 signaling, CS axons, which would normally innervate the lumbar spinal cord, are unbundled in the spinal gray matter, and prematurely innervate the cervical gray matter with reduced innervation of the lumbar gray matter. In both Sema5A/5B and PlexA1/A3 mutant mice (both sexes), stimulation of the hindlimb motor cortex aberrantly evokes robust forelimb muscle activation. Finally, Sema5A/5B and PlexA1/A3 mutant mice show deficits in skilled movements. These results suggest that proper fasciculation of CS axons is required for appropriate neural circuit wiring and ultimately affect the ability to perform skilled movements.SIGNIFICANCE STATEMENT Axon fasciculation is believed to be essential for neural circuit formation and function. However, whether and how defects in axon fasciculation affect the formation and function of neural circuits remain unclear. Here we examine whether the transmembrane proteins semaphorin-5A (Sema5A) and semaphorin-5B (Sema5B), and their receptors, plexinA1 (PlexA1) and plexinA3 (PlexA3) play roles in the development of corticospinal circuits. We find that Sema5A/Sema5B and PlexA1/A3 are required for proper axon fasciculation of corticospinal neurons. Furthermore, Sema5A/5B and PlexA1/A3 mutant mice show marked deficits in skilled motor behaviors. Therefore, these results strongly suggest that proper corticospinal axon fasciculation is required for the appropriate formation and functioning of corticospinal circuits in mice.
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Affiliation(s)
- Zirong Gu
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
| | - Ken Matsuura
- Neural Circuit Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, 904-0495, Japan
| | | | - Mark Basista
- Burke Neurological Institute, White Plains, New York 10605
- Brain and Mind Research Institute, Weill Cornell Medicine, New York, New York 10065
| | - Corey Craig
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
| | - Fumiyasu Imai
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
- Burke Neurological Institute, White Plains, New York 10605
- Brain and Mind Research Institute, Weill Cornell Medicine, New York, New York 10065
| | - Yutaka Yoshida
- Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229
- Burke Neurological Institute, White Plains, New York 10605
- Brain and Mind Research Institute, Weill Cornell Medicine, New York, New York 10065
- Neural Circuit Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, 904-0495, Japan
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Abstract
Decoding the molecular mechanisms underlying axon guidance is key to precise understanding of how complex neural circuits form during neural development. Although substantial progress has been made over the last three decades in identifying numerous axon guidance molecules and their functional roles, little is known about how these guidance molecules collaborate to steer growth cones to their correct targets. Recent studies in Drosophila point to the importance of the combinatorial action of guidance molecules, and further show that selective fasciculation and defasciculation at specific choice points serve as a fundamental strategy for motor axon guidance. Here, I discuss how attractive and repulsive guidance cues cooperate to ensure the recognition of specific choice points that are inextricably linked to selective fasciculation and defasciculation, and correct pathfinding decision-making.
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Affiliation(s)
- Sangyun Jeong
- Division of Life Sciences (Molecular Biology Major), Department of Bioactive Material Sciences, and Research Center of Bioactive Materials, Jeonbuk National University, Jeonju 54896, Korea
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Saller MM, Huettl RE, Hanuschick P, Amend AL, Alberton P, Aszodi A, Huber AB. The role of Sema3-Npn-1 signaling during diaphragm innervation and muscle development. J Cell Sci 2016; 129:3295-308. [PMID: 27466379 PMCID: PMC5047703 DOI: 10.1242/jcs.186015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Accepted: 07/20/2016] [Indexed: 11/20/2022] Open
Abstract
Correct innervation of the main respiratory muscle in mammals, namely the thoracic diaphragm, is a crucial pre-requisite for the functionality of this muscle and the viability of the entire organism. Systemic impairment of Sema3A-Npn-1 (Npn-1 is also known as NRP1) signaling causes excessive branching of phrenic nerves in the diaphragm and into the central tendon region, where the majority of misguided axons innervate ectopic musculature. To elucidate whether these ectopic muscles are a result of misguidance of myoblast precursors due to the loss of Sema3A-Npn-1 signaling, we conditionally ablated Npn-1 in somatic motor neurons, which led to a similar phenotype of phrenic nerve defasciculation and, intriguingly, also formation of innervated ectopic muscles. We therefore hypothesize that ectopic myocyte fusion is caused by additional factors released by misprojecting growth cones. Slit2 and its Robo receptors are expressed by phrenic motor axons and migrating myoblasts, respectively, during innervation of the diaphragm. In vitro analyses revealed a chemoattractant effect of Slit2 on primary diaphragm myoblasts. Thus, we postulate that factors released by motor neuron growth cones have an influence on the migration properties of myoblasts during establishment of the diaphragm.
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Affiliation(s)
- Maximilian Michael Saller
- Experimental Surgery and Regenerative Medicine, Department of Surgery, Ludwig-Maximilians-University (LMU), Nußbaumstraße 20, Munich 80336, Germany Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg 85764, Germany
| | - Rosa-Eva Huettl
- Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg 85764, Germany Institute of Physiology, Department of Physiological Genomics, Ludwig-Maximilians-University (LMU), Schillerstraße 46, Munich 80336, Germany
| | - Philipp Hanuschick
- Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg 85764, Germany
| | - Anna-Lena Amend
- Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg 85764, Germany
| | - Paolo Alberton
- Experimental Surgery and Regenerative Medicine, Department of Surgery, Ludwig-Maximilians-University (LMU), Nußbaumstraße 20, Munich 80336, Germany
| | - Attila Aszodi
- Experimental Surgery and Regenerative Medicine, Department of Surgery, Ludwig-Maximilians-University (LMU), Nußbaumstraße 20, Munich 80336, Germany
| | - Andrea B Huber
- Institute of Developmental Genetics, Helmholtz Zentrum München - German Research Center for Environmental Health (GmbH), Ingolstädter Landstraße 1, Neuherberg 85764, Germany Bernstein Network for Computational Neuroscience, Albert-Ludwigs-University, Freiburg, Germany
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