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Vemula S, Muvavarirwa T, Doornbos F, Whitman MC. Neuromuscular Junction Development Differs Between Extraocular and Skeletal Muscles and Between Different Extraocular Muscles. Invest Ophthalmol Vis Sci 2024; 65:28. [PMID: 38767908 PMCID: PMC11114620 DOI: 10.1167/iovs.65.5.28] [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: 12/22/2023] [Accepted: 04/23/2024] [Indexed: 05/22/2024] Open
Abstract
Purpose To determine whether development of neuromuscular junctions (NMJs) differs between extraocular muscles (EOMs) and other skeletal muscles. Methods Mouse EOMs, diaphragm, and tibialis anterior (TA) were collected at postnatal day (P)0, P3, P7, P10, P14, and P21, and 12 weeks. Whole muscles were stained with α-bungarotoxin, anti-neurofilament antibody, and slow or fast myosin heavy chain antibody, and imaged with a confocal microscope. Images were quantified using Imaris software. Results NMJs in the EOMs show a unique pattern of morphological development compared to diaphragm and TA. At P0, diaphragm and TA NMJs were oval plaques; EOM single NMJs were long, thin rods. NMJs in the three muscle types progress to mature morphology at different rates. At all ages, EOM single NMJs were larger, especially relative to myofiber size. The inferior oblique and inferior rectus muscles show delayed single NMJ development compared to other EOMs. NMJs on multiply-innervated fibers in the EOMs vary widely in size, and there were no consistent differences between muscles or over time. Incoming motor nerves formed complex branching patterns, dividing first into superficial and deep branches, each of which branched extensively over the full width of the muscle. Motor axons that innervate multiply-innervated fibers entered the muscle with the axons that innervate singly-innervated fibers, then extended both proximally and distally. EOM NMJs had more subsynaptic nuclei than skeletal muscle NMJs throughout development. Conclusions EOMs show a unique pattern of NMJ development and have more subsynaptic nuclei than other muscles, which may contribute to the exquisite control of eye movements.
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Affiliation(s)
- Sampath Vemula
- Department of Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
- Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts, United States
| | - Tapiwa Muvavarirwa
- Department of Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
- Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts, United States
| | - Fleur Doornbos
- Department of Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
- Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts, United States
| | - Mary C. Whitman
- Department of Ophthalmology, Boston Children's Hospital, Boston, Massachusetts, United States
- Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States
- F.M. Kirby Neurobiology Center, Boston Children's Hospital, Boston, Massachusetts, United States
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Guangming G, Mei C, Qinfeng Y, Xiang G, Chenchen Z, Qingyuan S, Wei X, Junhua G. Neurexin and neuroligins jointly regulate synaptic degeneration at the Drosophila neuromuscular junction based on TEM studies. Front Cell Neurosci 2023; 17:1257347. [PMID: 38026694 PMCID: PMC10646337 DOI: 10.3389/fncel.2023.1257347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 09/12/2023] [Indexed: 12/01/2023] Open
Abstract
The Drosophila larval neuromuscular junction (NMJ) is a well-known model system and is often used to study synapse development. Here, we show synaptic degeneration at NMJ boutons, primarily based on transmission electron microscopy (TEM) studies. When degeneration starts, the subsynaptic reticulum (SSR) swells, retracts and folds inward, and the residual SSR then degenerates into a disordered, thin or linear membrane. The axon terminal begins to degenerate from the central region, and the T-bar detaches from the presynaptic membrane with clustered synaptic vesicles to accelerate large-scale degeneration. There are two degeneration modes for clear synaptic vesicles. In the first mode, synaptic vesicles without actin filaments degenerate on the membrane with ultrafine spots and collapse and disperse to form an irregular profile with dark ultrafine particles. In the second mode, clear synaptic vesicles with actin filaments degenerate into dense synaptic vesicles, form irregular dark clumps without a membrane, and collapse and disperse to form an irregular profile with dark ultrafine particles. Last, all residual membranes in NMJ boutons degenerate into a linear shape, and all the residual elements in axon terminals degenerate and eventually form a cluster of dark ultrafine particles. Swelling and retraction of the SSR occurs prior to degradation of the axon terminal, which degenerates faster and with more intensity than the SSR. NMJ bouton degeneration occurs under normal physiological conditions but is accelerated in Drosophila neurexin (dnrx) dnrx273, Drosophila neuroligin (dnlg) dnlg1 and dnlg4 mutants and dnrx83;dnlg3 and dnlg2;dnlg3 double mutants, which suggests that both neurexin and neuroligins play a vital role in preventing synaptic degeneration.
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Affiliation(s)
- Gan Guangming
- School of Medicine, Southeast University, Nanjing, Jiangsu, China
- School of Life Science and Technology, The Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu, China
| | - Chen Mei
- School of Life Science and Technology, The Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu, China
| | - Yu Qinfeng
- School of Medicine, Southeast University, Nanjing, Jiangsu, China
| | - Gao Xiang
- School of Medicine, Southeast University, Nanjing, Jiangsu, China
| | - Zhang Chenchen
- School of Medicine, Southeast University, Nanjing, Jiangsu, China
| | - Sheng Qingyuan
- School of Life Science and Technology, The Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu, China
| | - Xie Wei
- School of Life Science and Technology, The Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu, China
- The Collaborative Innovation Center for Brain Science, Southeast University, Nanjing, Jiangsu, China
| | - Geng Junhua
- School of Life Science and Technology, The Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing, Jiangsu, China
- Shenzhen Research Institute of Southeast University, Shenzhen, Guangdong, China
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Muscarinic Receptors in Developmental Axonal Competition at the Neuromuscular Junction. Mol Neurobiol 2023; 60:1580-1593. [PMID: 36526930 PMCID: PMC9899176 DOI: 10.1007/s12035-022-03154-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Accepted: 11/29/2022] [Indexed: 12/23/2022]
Abstract
In recent years, we have studied by immunohistochemistry, intracellular recording, and western blotting the role of the muscarinic acetylcholine receptors (mAChRs; M1, M2, and M4 subtypes) in the mammalian neuromuscular junction (NMJ) during development and in the adult. Here, we evaluate our published data to emphasize the mAChRs' relevance in developmental synaptic elimination and their crosstalk with other metabotropic receptors, downstream kinases, and voltage-gated calcium channels (VGCCs). The presence of mAChRs in the presynaptic membrane of motor nerve terminals allows an autocrine mechanism in which the secreted acetylcholine influences the cell itself in feedback. mAChR subtypes are coupled to different downstream pathways, so their feedback can move in a broad range between positive and negative. Moreover, mAChRs allow direct activity-dependent interaction through ACh release between the multiple competing axons during development. Additional regulation from pre- and postsynaptic sites (including neurotrophic retrograde control), the agonistic and antagonistic contributions of adenosine receptors (AR; A1 and A2A), and the tropomyosin-related kinase B receptor (TrkB) cooperate with mAChRs in the axonal competitive interactions which lead to supernumerary synapse elimination that achieves the optimized monoinnervation of musculoskeletal cells. The metabotropic receptor-driven balance between downstream PKA and PKC activities, coupled to developmentally regulated VGCC, explains much of how nerve terminals with different activities finally progress to their withdrawal or strengthening.
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Trigeminal Sensory Supply Is Essential for Motor Recovery after Facial Nerve Injury. Int J Mol Sci 2022; 23:ijms232315101. [PMID: 36499425 PMCID: PMC9740813 DOI: 10.3390/ijms232315101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 11/27/2022] [Accepted: 11/29/2022] [Indexed: 12/03/2022] Open
Abstract
Recovery of mimic function after facial nerve transection is poor. The successful regrowth of regenerating motor nerve fibers to reinnervate their targets is compromised by (i) poor axonal navigation and excessive collateral branching, (ii) abnormal exchange of nerve impulses between adjacent regrowing axons, namely axonal crosstalk, and (iii) insufficient synaptic input to the axotomized facial motoneurons. As a result, axotomized motoneurons become hyperexcitable but unable to discharge. We review our findings, which have addressed the poor return of mimic function after facial nerve injuries, by testing the hypothesized detrimental component, and we propose that intensifying the trigeminal sensory input to axotomized and electrophysiologically silent facial motoneurons improves the specificity of the reinnervation of appropriate targets. We compared behavioral, functional, and morphological parameters after single reconstructive surgery of the facial nerve (or its buccal branch) with those obtained after identical facial nerve surgery, but combined with direct or indirect stimulation of the ipsilateral infraorbital nerve. We found that both methods of trigeminal sensory stimulation, i.e., stimulation of the vibrissal hairs and manual stimulation of the whisker pad, were beneficial for the outcome through improvement of the quality of target reinnervation and recovery of vibrissal motor performance.
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Raffa P, Easler M, Urciuolo A. Three-dimensional in vitro models of neuromuscular tissue. Neural Regen Res 2022; 17:759-766. [PMID: 34472462 PMCID: PMC8530117 DOI: 10.4103/1673-5374.322447] [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: 01/31/2021] [Revised: 03/08/2021] [Accepted: 05/18/2021] [Indexed: 12/13/2022] Open
Abstract
Skeletal muscle is a dynamic tissue in which homeostasis and function are guaranteed by a very defined three-dimensional organization of myofibers in respect to other non-muscular components, including the extracellular matrix and the nervous network. In particular, communication between myofibers and the nervous system is essential for the overall correct development and function of the skeletal muscle. A wide range of chronic, acute and genetic-based human pathologies that lead to the alteration of muscle function are associated with modified preservation of the fine interaction between motor neurons and myofibers at the neuromuscular junction. Recent advancements in the development of in vitro models for human skeletal muscle have shown that three-dimensionality and integration of multiple cell types are both key parameters required to unveil pathophysiological relevant phenotypes. Here, we describe recent achievement reached in skeletal muscle modeling which used biomaterials for the generation of three-dimensional constructs of myotubes integrated with motor neurons.
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Affiliation(s)
- Paolo Raffa
- Institute of Pediatric Research IRP, Padova, Italy
| | - Maria Easler
- Institute of Pediatric Research IRP, Padova, Italy
| | - Anna Urciuolo
- Institute of Pediatric Research IRP, Padova, Italy
- Molecular Medicine Department, University of Padova, Padova, Italy
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Hörner SJ, Couturier N, Bruch R, Koch P, Hafner M, Rudolf R. hiPSC-Derived Schwann Cells Influence Myogenic Differentiation in Neuromuscular Cocultures. Cells 2021; 10:cells10123292. [PMID: 34943800 PMCID: PMC8699767 DOI: 10.3390/cells10123292] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 11/20/2021] [Accepted: 11/21/2021] [Indexed: 12/13/2022] Open
Abstract
Motoneurons, skeletal muscle fibers, and Schwann cells form synapses, termed neuromuscular junctions (NMJs). These control voluntary body movement and are affected in numerous neuromuscular diseases. Therefore, a variety of NMJ in vitro models have been explored to enable mechanistic and pharmacological studies. So far, selective integration of Schwann cells in these models has been hampered, due to technical limitations. Here we present robust protocols for derivation of Schwann cells from human induced pluripotent stem cells (hiPSC) and their coculture with hiPSC-derived motoneurons and C2C12 muscle cells. Upon differentiation with tuned BMP signaling, Schwann cells expressed marker proteins, S100b, Gap43, vimentin, and myelin protein zero. Furthermore, they displayed typical spindle-shaped morphologies with long processes, which often aligned with motoneuron axons. Inclusion of Schwann cells in coculture experiments with hiPSC-derived motoneurons and C2C12 myoblasts enhanced myotube growth and affected size and number of acetylcholine receptor plaques on myotubes. Altogether, these data argue for the availability of a consistent differentiation protocol for Schwann cells and their amenability for functional integration into neuromuscular in vitro models, fostering future studies of neuromuscular mechanisms and disease.
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Affiliation(s)
- Sarah Janice Hörner
- Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, 68163 Mannheim, Germany; (S.J.H.); (N.C.); (R.B.); (M.H.)
- Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany
| | - Nathalie Couturier
- Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, 68163 Mannheim, Germany; (S.J.H.); (N.C.); (R.B.); (M.H.)
| | - Roman Bruch
- Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, 68163 Mannheim, Germany; (S.J.H.); (N.C.); (R.B.); (M.H.)
| | - Philipp Koch
- Central Institute of Mental Health, Medical Faculty Mannheim of Heidelberg University, 68159 Mannheim, Germany;
- Hector Institute for Translational Brain Research (HITBR gGmbH), 68159 Mannheim, Germany
- German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Mathias Hafner
- Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, 68163 Mannheim, Germany; (S.J.H.); (N.C.); (R.B.); (M.H.)
- Institute of Medical Technology, Mannheim University of Applied Sciences and Heidelberg University, 68163 Mannheim, Germany
| | - Rüdiger Rudolf
- Institute of Molecular and Cell Biology, Mannheim University of Applied Sciences, 68163 Mannheim, Germany; (S.J.H.); (N.C.); (R.B.); (M.H.)
- Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany
- Institute of Medical Technology, Mannheim University of Applied Sciences and Heidelberg University, 68163 Mannheim, Germany
- Correspondence:
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Lago-Baldaia I, Fernandes VM, Ackerman SD. More Than Mortar: Glia as Architects of Nervous System Development and Disease. Front Cell Dev Biol 2020; 8:611269. [PMID: 33381506 PMCID: PMC7767919 DOI: 10.3389/fcell.2020.611269] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 11/17/2020] [Indexed: 12/12/2022] Open
Abstract
Glial cells are an essential component of the nervous system of vertebrates and invertebrates. In the human brain, glia are as numerous as neurons, yet the importance of glia to nearly every aspect of nervous system development has only been expounded over the last several decades. Glia are now known to regulate neural specification, synaptogenesis, synapse function, and even broad circuit function. Given their ubiquity, it is not surprising that the contribution of glia to neuronal disease pathogenesis is a growing area of research. In this review, we will summarize the accumulated evidence of glial participation in several distinct phases of nervous system development and organization-neural specification, circuit wiring, and circuit function. Finally, we will highlight how these early developmental roles of glia contribute to nervous system dysfunction in neurodevelopmental and neurodegenerative disorders.
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Affiliation(s)
- Inês Lago-Baldaia
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Vilaiwan M. Fernandes
- Department of Cell and Developmental Biology, University College London, London, United Kingdom
| | - Sarah D. Ackerman
- Institute of Neuroscience, Howard Hughes Medical Institute, University of Oregon, Eugene, OR, United States
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Morphological remodeling during recovery of the neuromuscular junction from terminal Schwann cell ablation in adult mice. Sci Rep 2020; 10:11132. [PMID: 32636481 PMCID: PMC7341867 DOI: 10.1038/s41598-020-67630-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2020] [Accepted: 06/09/2020] [Indexed: 12/22/2022] Open
Abstract
Schwann cells (SCs) are integral to the formation and function of the peripheral nervous system (PNS). Exemplifying their importance, the loss or dysfunction of SCs is a feature of a myriad of diseases and conditions that compromise the PNS. Thus, it remains essential to understand the rules that govern the proliferation, differentiation and reconnection of Schwann cells with peripheral axons. Here, we examined the consequences of locally and acutely ablating terminal Schwann cells (tSCs) at the adult mouse neuromuscular junction (NMJ) by using mice expressing diphtheria toxin receptor (DTR) preferentially in tSCs compared to myelinating SCs followed by local application of diphtheria toxin (DTX). After DTX application, tSCs died but, importantly and contrary to expectations, their associated motor axons did not fully degenerate. Within 3 weeks, tSCs returned and reestablished coverage of the synapse with increased numbers. Furthermore, the post-synaptic muscle fibers displayed increased distinct clusters of acetylcholine receptors and axon terminals exhibited numerous terminal varicosities. The lack of degeneration of bare motor axon terminals and the morphological remodeling that occurs upon the return of tSCs to the NMJ may have wider implications for the mechanisms governing tSC occupancy of the adult NMJ and for conditions that adversely affect tSCs.
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