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Chomphoo S, Kondo H, Hipkaeo W. Electron-translucency and partial defects of synaptic basal lamina in the electrocyte synapse of an electric ray (Narke japonica) in 3D embedment-free section electron microscopy. Microsc Res Tech 2024; 87:1647-1653. [PMID: 38461470 DOI: 10.1002/jemt.24534] [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: 11/13/2023] [Revised: 01/31/2024] [Accepted: 02/14/2024] [Indexed: 03/12/2024]
Abstract
The synaptic basal lamina of the electrocytes was disclosed to be electron-translucent to some extent when viewed in an en-face direction in embedment-free section transmission electron microscopy (EFS-TEM), and synaptic vesicles located close to the presynaptic membrane were seen through the synaptic basal lamina together with the presynaptic and postsynaptic membranes. This feature of translucency has the potential to analyze possible spatial interrelations in situ between bioactive molecules in the synaptic basal lamina and the synaptic vesicles in further studies. The synaptic basal lamina, appearing as an electron-dense line sandwiched by two parallel lines representing the presynaptic and postsynaptic membranes in ultrathin sections cut right to the synaptic junctional plane in conventional TEM, was not fully continuous but randomly intermittent along its trajectory. Compatible with the intermittent line appearance, the en-face 3D view in embedment-free section TEM revealed for the first time partial irregular defects of the synaptic basal lamina. Considering the known functional significance of several molecules contained in the synaptic basal lamina in the maintenance and exertion of the synapse, its partial defects may not represent its rigid structural features, but its immature structure under remodeling or its dynamic changes in consistency such as the sol/gel transition, whose validity needs further examination. RESEARCH HIGHLIGHTS: In embedment-free section TEM, a 3D en-face view of synaptic basal lamina in situ is reliably possible. The basal lamina en-face is electron-translucent, which makes it possible to analyze spatial interrelation between pre- and post-synaptic components. Partial irregular defects in the basal lamina are revealed in Torpedo electrocytes, suggesting its remodeling or dynamic changes in consistency.
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Affiliation(s)
- Surang Chomphoo
- Electron Microscopy Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
| | - Hisatake Kondo
- Electron Microscopy Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
- Department of Anatomy, Graduate School of Medicine, Tohoku University, Sendai, Japan
| | - Wiphawi Hipkaeo
- Electron Microscopy Unit, Department of Anatomy, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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2
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Mis K, Grubic Z, Lorenzon P, Sciancalepore M, Mars T, Pirkmajer S. In Vitro Innervation as an Experimental Model to Study the Expression and Functions of Acetylcholinesterase and Agrin in Human Skeletal Muscle. Molecules 2017; 22:molecules22091418. [PMID: 28846617 PMCID: PMC6151842 DOI: 10.3390/molecules22091418] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 08/18/2017] [Accepted: 08/23/2017] [Indexed: 12/19/2022] Open
Abstract
Acetylcholinesterase (AChE) and agrin, a heparan-sulfate proteoglycan, reside in the basal lamina of the neuromuscular junction (NMJ) and play key roles in cholinergic transmission and synaptogenesis. Unlike most NMJ components, AChE and agrin are expressed in skeletal muscle and α-motor neurons. AChE and agrin are also expressed in various other types of cells, where they have important alternative functions that are not related to their classical roles in NMJ. In this review, we first focus on co-cultures of embryonic rat spinal cord explants with human skeletal muscle cells as an experimental model to study functional innervation in vitro. We describe how this heterologous rat-human model, which enables experimentation on highly developed contracting human myotubes, offers unique opportunities for AChE and agrin research. We then highlight innovative approaches that were used to address salient questions regarding expression and alternative functions of AChE and agrin in developing human skeletal muscle. Results obtained in co-cultures are compared with those obtained in other models in the context of general advances in the field of AChE and agrin neurobiology.
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Affiliation(s)
- Katarina Mis
- Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia.
| | - Zoran Grubic
- Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia.
| | - Paola Lorenzon
- Department of Life Sciences, University of Trieste, via A. Fleming 22, I-34127 Trieste, Italy.
| | - Marina Sciancalepore
- Department of Life Sciences, University of Trieste, via A. Fleming 22, I-34127 Trieste, Italy.
| | - Tomaz Mars
- Department of Life Sciences, University of Trieste, via A. Fleming 22, I-34127 Trieste, Italy.
| | - Sergej Pirkmajer
- Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Zaloška 4, SI-1000 Ljubljana, Slovenia.
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3
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Jumbo-Lucioni P, Parkinson W, Broadie K. Overelaborated synaptic architecture and reduced synaptomatrix glycosylation in a Drosophila classic galactosemia disease model. Dis Model Mech 2014; 7:1365-78. [PMID: 25326312 PMCID: PMC4257005 DOI: 10.1242/dmm.017137] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Classic galactosemia (CG) is an autosomal recessive disorder resulting from loss of galactose-1-phosphate uridyltransferase (GALT), which catalyzes conversion of galactose-1-phosphate and uridine diphosphate (UDP)-glucose to glucose-1-phosphate and UDP-galactose, immediately upstream of UDP-N-acetylgalactosamine and UDP-N-acetylglucosamine synthesis. These four UDP-sugars are essential donors for driving the synthesis of glycoproteins and glycolipids, which heavily decorate cell surfaces and extracellular spaces. In addition to acute, potentially lethal neonatal symptoms, maturing individuals with CG develop striking neurodevelopmental, motor and cognitive impairments. Previous studies suggest that neurological symptoms are associated with glycosylation defects, with CG recently being described as a congenital disorder of glycosylation (CDG), showing defects in both N- and O-linked glycans. Here, we characterize behavioral traits, synaptic development and glycosylated synaptomatrix formation in a GALT-deficient Drosophila disease model. Loss of Drosophila GALT (dGALT) greatly impairs coordinated movement and results in structural overelaboration and architectural abnormalities at the neuromuscular junction (NMJ). Dietary galactose and mutation of galactokinase (dGALK) or UDP-glucose dehydrogenase (sugarless) genes are identified, respectively, as critical environmental and genetic modifiers of behavioral and cellular defects. Assaying the NMJ extracellular synaptomatrix with a broad panel of lectin probes reveals profound alterations in dGALT mutants, including depletion of galactosyl, N-acetylgalactosamine and fucosylated horseradish peroxidase (HRP) moieties, which are differentially corrected by dGALK co-removal and sugarless overexpression. Synaptogenesis relies on trans-synaptic signals modulated by this synaptomatrix carbohydrate environment, and dGALT-null NMJs display striking changes in heparan sulfate proteoglycan (HSPG) co-receptor and Wnt ligand levels, which are also corrected by dGALK co-removal and sugarless overexpression. These results reveal synaptomatrix glycosylation losses, altered trans-synaptic signaling pathway components, defective synaptogenesis and impaired coordinated movement in a CG neurological disease model.
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Affiliation(s)
- Patricia Jumbo-Lucioni
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37232, USA
| | - William Parkinson
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37232, USA
| | - Kendal Broadie
- Department of Biological Sciences, Kennedy Center for Research on Human Development, Vanderbilt University, Nashville, TN 37232, USA.
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4
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Wang Y, Dai Y, Li X, Chen CY, Li W, Yu Z. Inhibition of Smad signaling is implicated in cleft palate induced by all-trans retinoic acid. ACTA BIOLOGICA HUNGARICA 2011; 62:142-50. [PMID: 21555266 DOI: 10.1556/abiol.62.2011.2.4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The effect of all-trans retinoic acid (atRA) on palatal fusion and the underlying mechanisms were investigated using organ culture. Compared with control group, the atRA-treated group (1 μM and 5 μM) had more medial edge epithelium (ME) remaining within the midline epithelial seam (MES). At 10 μM atRA, the opposing shelves were not in contact at the culture end (72 h). Cell death detection by TUNEL and laminin immunohistochemistry demonstrated that atRA (5 μM) induced apoptosis in mesenchyme and inhibited degradation of basal lamina within MES. Notably, migration and apoptosis of ME cells and degradation of basal lamina within MES markedly represented vehicle control palatal shelves in culture. Additionally, apoptosis was not detected in mesenchyme of control palatal shelves. Immunoblotting analysis revealed that Smad2 and Smad3 were endogenously activated and expression of Smad7 was inhibited during the fusion process. In contrast, atRA treatment abrogated phosphorylation of Smad2 and Smad3 and inducible expression of Smad7 in ME. From these data, it is assumed that inhibition of Smad pathway by atRA in ME may play a critical role in abrogation of the ME cell apoptosis and degradation of the basal laminin, which might contribute to failure of palatal fusion.
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Affiliation(s)
- Yuming Wang
- Henan Academy of Medical Sciences, Zhengzhou, China
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5
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Olofsson B, Page DT. Condensation of the central nervous system in embryonic Drosophila is inhibited by blocking hemocyte migration or neural activity. Dev Biol 2005; 279:233-43. [PMID: 15708571 DOI: 10.1016/j.ydbio.2004.12.020] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2004] [Revised: 12/09/2004] [Accepted: 12/09/2004] [Indexed: 01/24/2023]
Abstract
Condensation is a process whereby a tissue undergoes a coordinated decrease in size and increase in cellular density during development. Although it occurs in many developmental contexts, the mechanisms underlying this process are largely unknown. Here, we investigate condensation in the embryonic Drosophila ventral nerve cord (VNC). Two major events coincide with condensation during embryogenesis: the deposition of extracellular matrix by hemocytes, and the onset of central nervous system activity. We find that preventing hemocyte migration by removing the function of the Drosophila VEGF receptor homologue, Pvr, or by disrupting Rac1 function in these cells, inhibits condensation. In the absence of hemocytes migrating adjacent to the developing VNC, the extracellular matrix components Collagen IV, Viking and Peroxidasin are not deposited around this tissue. Blocking neural activity by targeted expression of tetanus toxin light chain or an inwardly rectifying potassium channel also inhibits condensation. We find that disrupting Rac1 function in either glia or neurons, including those located in the nerve cord, causes a similar phenotype. Our data suggest that condensation of the VNC during Drosophila embryogenesis depends on both hemocyte-deposited extracellular matrix and neural activity, and allow us to propose a mechanism whereby these processes work together to shape the developing central nervous system.
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Affiliation(s)
- Birgitta Olofsson
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK
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6
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Jevsek M, Mars T, Mis K, Grubic Z. Origin of acetylcholinesterase in the neuromuscular junction formed in the in vitro innervated human muscle. Eur J Neurosci 2004; 20:2865-71. [PMID: 15579140 DOI: 10.1111/j.1460-9568.2004.03752.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Synaptic basal lamina is interposed between the pre- and postsynaptic membrane of the neuromuscular junction (NMJ). This position permits deposition of basal lamina-bound NMJ components of both neuronal and muscle fibre origin. One such molecule is acetylcholinesterase (AChE). The origin of NMJ AChE has been investigated previously as the answer would elucidate the relative contributions of muscle fibers and motor neurons to NMJ formation. However, in the experimental models used in prior investigations either the neuronal or muscular components of the NMJs were removed, or the NMJs were poorly differentiated. Therefore, the question of AChE origin in the intact and functional NMJ remains open. Here, we have approached this question using an in vitro model in which motor neurons, growing from embryonic rat spinal cord explants, form well differentiated NMJs with cultured human myotubes. By immunocytochemical staining with species-specific anti-AChE antibodies, we are able to differentiate between human (muscular) and rat (neuronal) AChE at the NMJ. We observed strong signal at the NMJ after staining with human AChE antibodies, which suggests a significant muscular AChE contribution. However, a weaker, but still clearly recognizable signal is observed after staining with rat AChE antibodies, suggesting a smaller fraction of AChE was derived from motor neurons. This is the first report demonstrating that both motor neuron and myotube contribute synaptic AChE under conditions where they interact with each other in the formation of an intact and functional NMJ.
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Affiliation(s)
- Marko Jevsek
- Laboratory for Molecular Neurobiology, Institute of Pathophysiology, Medical School, University of Ljubljana, Zaloska 4, 1000 Ljubljana, Slovenia
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7
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Abstract
The postsynaptic density (PSD) at excitatory dendritic synapses comprises a protein complex of glutamate receptors, scaffolding elements, and signaling enzymes. For example, NMDA receptors (NMDARs) are linked to several proteins in the PSD, such as PSD-95, and are also tethered via binding proteins such as alpha-actinin directly to filamentous actin of the cytoskeleton. Depolymerization of the cytoskeleton modulates the activity of NMDARs, and, in turn, strong activation of NMDARs can trigger depolymerization of actin. Myosin, the motor protein of muscular contraction and nonmuscle motility, is also associated with NMDARs and the PSD. We show here that constitutively active myosin light chain kinase (MLCK) enhances NMDAR-mediated whole-cell and synaptic currents in acutely isolated CA1 pyramidal and cultured hippocampal neurons, whereas inhibitors of MLCK depress these currents. This MLCK-dependent regulation was observed in cell-attached patches but was lost after excision to inside-out patches. Furthermore, the enhancement induced by constitutively active MLCK and the depression of MLCK inhibitors were eliminated after depolymerization of the cytoskeleton. NMDARs and MLCK did not colocalize in clusters on the dendrites of cultured hippocampal neurons, further indicating that the effects of MLCK are mediated indirectly via actomyosin. Our results suggest that MLCK enhances actomyosin contractility to either increase the membrane tension on NMDARs or to alter physical relationships between the actin cytoskeleton and the linker proteins of NMDARs.
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8
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Rodgers KD, Barritt L, Miner JH, Cosgrove D. The laminins in the murine inner ear: developmental transitions and expression in cochlear basement membranes. Hear Res 2001; 158:39-50. [PMID: 11506935 DOI: 10.1016/s0378-5955(01)00283-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The laminins are a family of heterotrimeric extracellular matrix molecules that form suprastructural networks in basement membranes and elsewhere. They interact with integrin receptors, playing key roles in modulating programs of cytodifferentiation and maintaining tissue homeostasis in animals. Earlier studies have demonstrated an extensive laminin network in both the developing and adult cochlea, primarily associated with the basement membranes. These studies, however, did not address the laminin chain composition of these networks. In this study, we used antibodies specific for the known laminin chains to examine the composition of laminins in both the developing and adult murine cochlea. The results illustrate a complex and dynamic postnatal developmental regulation pattern for most of these chains, and suggest that an unusually large number of laminin heterotrimers are present in both the developing and adult cochlea. The laminin composition at postnatal day 2 is relatively simple. By postnatal day 7, however, activation of several laminin chains results in a very complex laminin composition. In the basement membrane underlying the region of the basilar membrane under the developing organ of Corti, eight of the 11 known basement membrane laminins are possible by co-localization inference. Dynamic changes in expression continue through day 14, but simplify by adulthood. Thus, the most dynamic period for laminin expression in the mouse cochlea coincides with terminal cytodifferentiation of the cochlear epithelial structures. Considering the well established role of laminins in regulating both embryonic and organ development in other systems, these data suggest a closer look at the role of the laminins in cochlear development and function may be warranted.
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Affiliation(s)
- K D Rodgers
- Department of Genetics, Boys Town National Research Hospital, Omaha, NE 68131, USA
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9
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Jacobson C, Côté PD, Rossi SG, Rotundo RL, Carbonetto S. The dystroglycan complex is necessary for stabilization of acetylcholine receptor clusters at neuromuscular junctions and formation of the synaptic basement membrane. J Cell Biol 2001; 152:435-50. [PMID: 11157973 PMCID: PMC2195998 DOI: 10.1083/jcb.152.3.435] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The dystrophin-associated protein (DAP) complex spans the sarcolemmal membrane linking the cytoskeleton to the basement membrane surrounding each myofiber. Defects in the DAP complex have been linked previously to a variety of muscular dystrophies. Other evidence points to a role for the DAP complex in formation of nerve-muscle synapses. We show that myotubes differentiated from dystroglycan-/- embryonic stem cells are responsive to agrin, but produce acetylcholine receptor (AChR) clusters which are two to three times larger in area, about half as dense, and significantly less stable than those on dystroglycan+/+ myotubes. AChRs at neuromuscular junctions are similarly affected in dystroglycan-deficient chimeric mice and there is a coordinate increase in nerve terminal size at these junctions. In culture and in vivo the absence of dystroglycan disrupts the localization to AChR clusters of laminin, perlecan, and acetylcholinesterase (AChE), but not rapsyn or agrin. Treatment of myotubes in culture with laminin induces AChR clusters on dystroglycan+/+, but not -/- myotubes. These results suggest that dystroglycan is essential for the assembly of a synaptic basement membrane, most notably by localizing AChE through its binding to perlecan. In addition, they suggest that dystroglycan functions in the organization and stabilization of AChR clusters, which appear to be mediated through its binding of laminin.
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Affiliation(s)
- C Jacobson
- Department of Biology, McGill University/Center for Neuroscience Research, Montréal General Hospital Research Institute, Montréal, Québec H3G 1A4, Canada
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10
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Tandai-Hiruma M, Mori-Okamoto J, Kotani M, Miura K, Takishima K, Nishida Y. Expression and electrophysiological function of actin in chick cerebellar neurons. Neurochem Res 2000; 25:1095-106. [PMID: 11055747 DOI: 10.1023/a:1007670012531] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Among several monoclonal antibodies obtained by immunizing Balb/c mice with cerebellar synaptic membrane fractions from E20 chick embryos, the antibody, named M35, suppressed Ca-spikes in immature cultured chick cerebellar neurons. M35 immunoprecipitated 43 kDa protein from a 125I-labeled embryonic crude cerebellar membrane fraction. Immunohistochemically, the M35 antigen was expressed most intensively in Purkinje cells, but its expression was limited to highly motile structures at developmental neuronal remodeling. Electrophysiologically, M35 facilitated current responses to AMPA and inhibited the responses to GABA in cultured cerebellar Purkinje neurons. The several peptides derived from the affinity-purified 43 kDa protein were found to have homologous amino acid sequences to non-muscle actins. These results suggest that the antigen recognized by M35 may play an essential role probably as membrane ion channels modulating synaptic functions in not only the development and growth but also the neuronal activity of chick cerebellar Purkinje cells.
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Affiliation(s)
- M Tandai-Hiruma
- Department of Physiology, National Defense Medical College, Tokorozawa, Saitama, Japan.
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11
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Abstract
alpha-Dystroglycan (alpha -DG) is a laminin/agrin receptor expressed in skeletal muscle as well as in nervous system and other tissues. Glycosylation of the core protein of alpha-DG is extensive, variable from tissue to tissue, and functionally relevant. To address differential glycosylation of alpha-DG in the retina, we have investigated the distribution of this protein using two different antibodies: 1B7 directed against the core protein of alpha-dystroglycan, and IIH6 directed against a carbohydrate moiety (Ervasti and Campbell [1993] J Cell Biol 122:809-823). Monoclonal antibody 1B7 recognizes a broader band than IIH6, which seems to recognize only a subset of alpha-DG forms in retina. These data reflect the existence of differentially glycosylated isoforms of alpha-DG. Monoclonal antibody 1B7 shows an extensive staining for alpha-DG in the inner limiting membrane as well as in the ganglion cell and inner plexiform layers labeling Müller cell processes, whereas monoclonal antibody IIH6 staining is restricted to the inner limiting membrane and blood vessels. Our data indicate that there are distinct isoforms of alpha-DG that are localized in apposition to basal lamina in the inner limiting membrane and blood vessels or within the parenchyma of the retina along Müller glia. Both isoforms are expressed in a Müller cell line in culture and coimmunoprecipitate with beta-dystroglycan. These data suggest that DGs may participate in organizing synapses and basement membrane assembly in the retina.
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Affiliation(s)
- H Moukhles
- Centre for Research in Neuroscience, McGill University and Montreal General Hospital Research Institute, Montreal, Quebec H3G 1A4, Canada
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12
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Li M, Bermak JC, Wang ZW, Zhou QY. Modulation of dopamine D(2) receptor signaling by actin-binding protein (ABP-280). Mol Pharmacol 2000; 57:446-52. [PMID: 10692483 DOI: 10.1124/mol.57.3.446] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Proteins that bind to G protein-coupled receptors have recently been identified as regulators of receptor anchoring and signaling. In this study, actin-binding protein 280 (ABP-280), a widely expressed cytoskeleton-associated protein that plays an important role in regulating cell morphology and motility, was found to associate with the third cytoplasmic loop of dopamine D(2) receptors. The specificity of this interaction was originally identified in a yeast two-hybrid screen and confirmed by protein binding. The functional significance of the D(2) receptor-ABP-280 association was evaluated in human melanoma cells lacking ABP-280. D(2) receptor agonists were less potent in inhibiting forskolin-stimulated cAMP production in these cells. Maximal inhibitory responses of D(2) receptor activation were also reduced. Further yeast two-hybrid experiments showed that ABP-280 association is critically dependent on the carboxyl domain of the D(2) receptor third cytoplasmic loop, where there is a potential serine phosphorylation site (S358). Serine 358 was replaced with aspartic acid to mimic the effects of receptor phosphorylation. This mutant (D(2)S358D) displayed compromised binding to ABP-280 and coupling to adenylate cyclase. PKC activation also generated D(2) receptor signaling attenuation, but only in ABP-containing cells, suggesting a PKC regulatory role in D(2)-ABP association. A mechanism for these results may be derived from a role of ABP-280 in the clustering of D(2) receptors, as determined by immunocytochemical analysis in ABP-deficient and replete cells. Our results suggest a new molecular mechanism of modulating D(2) receptor signaling by cytoskeletal protein interaction.
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Affiliation(s)
- M Li
- Department of Pharmacology, University of California, Irvine, California, USA
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Montanaro F, Lindenbaum M, Carbonetto S. alpha-Dystroglycan is a laminin receptor involved in extracellular matrix assembly on myotubes and muscle cell viability. J Biophys Biochem Cytol 1999; 145:1325-40. [PMID: 10366602 PMCID: PMC2133146 DOI: 10.1083/jcb.145.6.1325] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
alpha-Dystroglycan (alpha-DG) is a laminin-binding protein and member of a glycoprotein complex associated with dystrophin that has been implicated in the etiology of several muscular dystrophies. To study the function of DG, C2 myoblasts were transfected stably with an antisense DG expression construct. Myotubes from two resulting clones (11F and 11E) had at least a 40-50% and 80-90% reduction, respectively, in alpha-DG but normal or near normal levels of alpha-sarcoglycan, integrin beta1 subunit, acetylcholine receptors (AChRs), and muscle-specific kinase (MuSK) when compared with parental C2 cells or three clones (11A, 9B, and 10C) which went through the same transfection and selection procedures but expressed normal levels of alpha-DG. Antisense DG-expressing myoblasts proliferate at the same rate as parental C2 cells and differentiate into myotubes, however, a gradual loss of cells was observed in these cultures. This loss correlates with increased apoptosis as indicated by greater numbers of nuclei with condensed chromatin and more nuclei labeled by the TUNEL method. Moreover, there was no sign of increased membrane permeability to Trypan blue as would be expected with necrosis. Unlike parental C2 myotubes, 11F and 11E myotubes had very little laminin (LN) on their surfaces; LN instead tended to accumulate on the substratum between myotubes. Exogenous LN bound to C2 myotubes and was redistributed into plaques along with alpha-DG on their surfaces but far fewer LN/alpha-DG plaques were seen after LN addition to 11F or 11E myotubes. These results suggest that alpha-DG is a functional LN receptor in situ which is required for deposition of LN on the cell and, further, implicate alpha-DG in the maintenance of myotube viability.
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Affiliation(s)
- F Montanaro
- Center for Research in Neuroscience, McGill University, Montreal General Hospital Research Institute, Montreal, Quebec H3G 1A4, Canada
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14
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alpha-Dystroglycan functions in acetylcholine receptor aggregation but is not a coreceptor for agrin-MuSK signaling. J Neurosci 1998. [PMID: 9698325 DOI: 10.1523/jneurosci.18-16-06340.1998] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
alpha-dystroglycan (alpha-DG) is an agrin-binding protein that has been implicated in acetylcholine receptor (AChR) clustering, but it is unclear whether it acts as a coreceptor involved in initial agrin signaling or as a component involved in later events. To investigate its role, we have generated antisense derivatives of the C2 mouse muscle cell line, which have reduced alpha-DG expression. When compared with wild-type cells, the alpha-DG-deficient myotubes have a dramatic reduction in the number of spontaneous and agrin-induced AChR clusters. Several findings suggest that this decrease in AChR clustering is likely not because of a defect in agrin signaling through the MuSK receptor tyrosine kinase. Compared with wild-type cells, the alpha-DG-deficient cell lines showed only a transient reduction in the level of agrin-induced MuSK tyrosine phosphorylation and no reduction in AChR beta-subunit tyrosine phosphorylation. Additionally, agrin-induced phosphorylation of MuSK in wild-type myotubes was not decreased using agrin fragments that lack the domain primarily responsible for binding to alpha-DG. Finally, neural agrin-induced phosphorylation of MuSK was unaffected by treatments such as excess muscle agrin or anti-alpha-DG antibodies, both of which block agrin-alpha-DG binding. Together, these results suggest that alpha-DG is not required for agrin-MuSK signaling but rather that it may play a role elsewhere in the clustering pathway, such as in the downstream consolidation or maintenance of AChR clusters.
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Meier T, Masciulli F, Moore C, Schoumacher F, Eppenberger U, Denzer AJ, Jones G, Brenner HR. Agrin can mediate acetylcholine receptor gene expression in muscle by aggregation of muscle-derived neuregulins. J Cell Biol 1998; 141:715-26. [PMID: 9566971 PMCID: PMC2132745 DOI: 10.1083/jcb.141.3.715] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The neural isoforms of agrin can stimulate transcription of the acetylcholine receptor (AChR) epsilon subunit gene in electrically active muscle fibers, as does the motor neuron upon the formation of a neuromuscular junction. It is not clear, however, whether this induction involves neuregulins (NRGs), which stimulate AChR subunit gene transcription in vitro by activating ErbB receptors. In this study, we show that agrin- induced induction of AChR epsilon subunit gene transcription is inhibited in cultured myotubes overexpressing an inactive mutant of the ErbB2 receptor, demonstrating involvement of the NRG/ErbB pathway in agrin- induced AChR expression. Furthermore, salt extracts from the surface of cultured myotubes induce tyrosine phosphorylation of ErbB2 receptors, indicating that muscle cells express biological NRG-like activity on their surface. We further demonstrate by RT-PCR analysis that muscle NRGs have Ig-like domains required for their immobilization at heparan sulfate proteoglycans (HSPGs) of the extracellular matrix. In extrasynaptic regions of innervated muscle fibers in vivo, ectopically expressed neural agrin induces the colocalized accumulation of AChRs, muscle-derived NRGs, and HSPGs. By using overlay and radioligand-binding assays we show that the Ig domain of NRGs bind to the HSPGs agrin and perlecan. These findings show that neural agrin can induce AChR subunit gene transcription by aggregating muscle HSPGs on the muscle fiber surface that then serve as a local sink for focal binding of muscle-derived NRGs to regulate AChR gene expression at the neuromuscular junction.
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Affiliation(s)
- T Meier
- Department of Physiology, University of Basel, Vesalgasse 1, CH-4051 Basel, Switzerland
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16
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Andres C, Seidman S, Beeri R, Timberg R, Soreq H. Transgenic acetylcholinesterase induces enlargement of murine neuromuscular junctions but leaves spinal cord synapses intact. Neurochem Int 1998; 32:449-56. [PMID: 9676744 DOI: 10.1016/s0197-0186(97)00121-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Acetylcholinesterase (AChE) produced by spinal cord motoneurons accumulates within axo-dendritic spinal cord synapses. It is also secreted from motoneuron cell bodies, through their axons, into the region of neuromuscular junctions, where it terminates cholinergic neurotransmission. Here we show that transgenic mice expressing human AChE in their spinal cord motoneurons display primarily normal axo-dendritic spinal cord cholinergic synapses in spite of the clear excess of transgenic over host AChE within these synapses. This is in contrast to our recent observation that a modest excess of AChE drastically affects the structure and long-term functioning of neuromuscular junctions in these mice although they express human AChE in their spinal cord, but not muscle. Enlarged muscle endplates with either exaggerated or drastically shortened post-synaptic folds then lead to a progressive neuromotor decline and massive amyotrophy (Andres et al., 1997). These findings demonstrate that excess neuronal AChE may cause distinct effects on spinal cord and neuromuscular synapses and attribute the late-onset neuromotor deterioration observed in AChE transgenic mice to neuromuscular junction abnormalities.
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Affiliation(s)
- C Andres
- Department of Biological Chemistry, The Hebrew University of Jerusalem, Israel
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17
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Cartaud A, Coutant S, Petrucci TC, Cartaud J. Evidence for in situ and in vitro association between beta-dystroglycan and the subsynaptic 43K rapsyn protein. Consequence for acetylcholine receptor clustering at the synapse. J Biol Chem 1998; 273:11321-6. [PMID: 9556625 DOI: 10.1074/jbc.273.18.11321] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The accumulation of dystrophin and associated proteins at the postsynaptic membrane of the neuromuscular junction and their co-distribution with nicotinic acetylcholine receptor (AChR) clusters in vitro suggested a role for the dystrophin complex in synaptogenesis. Co-transfection experiments in which alpha- and beta-dystroglycan form a complex with AChR and rapsyn, a peripheral protein required for AChR clustering (Apel, D. A., Roberds, S. L., Campbell, K. P., and Merlie, J. P. (1995) Neuron 15, 115-126), suggested that rapsyn functions as a link between AChR and the dystrophin complex. We have investigated the interaction between rapsyn and beta-dystroglycan in Torpedo AChR-rich membranes using in situ and in vitro approaches. Cross-linking experiments were carried out to study the topography of postsynaptic membrane polypeptides. A cross-linked product of 90 kDa was labeled by antibodies to rapsyn and beta-dystroglycan; this demonstrates that these polypeptides are in close proximity to one another. Affinity chromatography experiments and ligand blot assays using rapsyn solubilized from Torpedo AChR-rich membranes and constructs containing beta-dystroglycan C-terminal fragments show that a rapsyn-binding site is present in the juxtamembranous region of the cytoplasmic tail of beta-dystroglycan. These data point out that rapsyn and dystroglycan interact in the postsynaptic membrane and thus reinforce the notion that dystroglycan could be involved in synaptogenesis.
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Affiliation(s)
- A Cartaud
- Biologie Cellulaire des Membranes, Département de Biologie Supramoléculaire et Cellulaire, Institut Jacques Monod, UMR 9922, CNRS et Université Paris VII, 2 Place Jussieu, 75251 Paris Cédex 05, France
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18
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Role of actin in anchoring postsynaptic receptors in cultured hippocampal neurons: differential attachment of NMDA versus AMPA receptors. J Neurosci 1998. [PMID: 9502803 DOI: 10.1523/jneurosci.18-07-02423.1998] [Citation(s) in RCA: 393] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We used actin-perturbing agents and detergent extraction of primary hippocampal cultures to test directly the role of the actin cytoskeleton in localizing GABAA receptors, AMPA- and NMDA-type glutamate receptors, and potential anchoring proteins at postsynaptic sites. Excitatory postsynaptic sites on dendritic spines contained a high concentration of F-actin that was resistant to cytochalasin D but could be depolymerized using the novel compound latrunculin A. Depolymerization of F-actin led to a 40% decrease in both the number of synaptic NMDA receptor (NMDAR1) clusters and the number of AMPA receptor (GluR1)-labeled spines. The nonsynaptic NMDA receptors appeared to remain clustered and to coalesce in cell bodies. alpha-Actinin-2, which binds both actin and NMDA receptors, dissociated from the receptor clusters, but PSD-95 remained associated with both the synaptic and nonsynaptic receptor clusters, consistent with a proposed cross-linking function. AMPA receptors behaved differently; on GABAergic neurons, the clusters redistributed to nonsynaptic sites, whereas on pyramidal neurons, many of the clusters appeared to disperse. Furthermore, in control neurons, AMPA receptors were detergent extractable from pyramidal cell spines, whereas AMPA receptors on GABAergic neurons and NMDA receptors were unextractable. GABAA receptors were not dependent on F-actin for the maintenance or synaptic localization of clusters. These results indicate fundamental differences in the mechanisms of receptor anchoring at postsynaptic sites, both regarding the anchoring of a single receptor (the AMPA receptor) in pyramidal cells versus GABAergic interneurons and regarding the anchoring of different receptors (AMPA vs NMDA receptors) at a single class of postsynaptic sites on pyramidal cell dendritic spines.
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19
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Edwards JP, Hatton PA, Wareham AC. Electrophysiology of the neuromuscular junction of the laminin-2 (merosin) deficient C57 BL/6J dy2J/dy2J dystrophic mouse. Brain Res 1998; 788:262-8. [PMID: 9555049 DOI: 10.1016/s0006-8993(98)00010-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The C57 BL/6J dy2J/dy2J dystrophic mouse expresses an abnormal truncated form of the alpha2 subunit of the protein laminin-2 (or merosin), which is unable to form a stable link between the extracellular matrix and the dystrophin-associated proteins, resulting in muscular dystrophy. Morphological abnormalities of the peripheral nervous system and neuromuscular junction have also been reported. The electrophysiological properties of the neuromuscular junctions of diaphragm, extensor digitorum longus (EDL), and soleus from C57 BL/6J dy2J/dy2J mice and controls are described. No evidence for the presence of denervated fibres were found. Mean MEPP amplitudes were significantly increased in EDL and soleus but reduced in the diaphragm from affected mice. Mean MEPP frequencies were raised in all the dy2J/dy2J muscles studied. dy2J/dy2J muscles were paralysed by low concentrations of mu-conotoxin suggesting that embryonic (tetrodotoxin and mu-conotoxin resistant) sodium channels are not widespread on dy2J/dy2J muscle as has previously been reported. EPP latencies were significantly prolonged in the diaphragm and EDL but not soleus from dy2J/dy2J mice. Quantal contents were higher in all dy2J/dy2J muscles. In the dy2J/dy2J diaphragm failures in neurotransmission occurred and a faster rate of rundown of EPPs were apparent. Some changes appear from a direct effect of dystrophy, whilst increased MEPP frequency and quantal content, and failures in neurotransmission indicate neuronal abnormalities.
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Affiliation(s)
- J P Edwards
- Division of Neuroscience, School of Biological Sciences, 1.124 Stopford Building, University of Manchester, Oxford Road, Manchester M13 9PT, UK
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20
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Laminin and alpha-dystroglycan mediate acetylcholine receptor aggregation via a MuSK-independent pathway. J Neurosci 1998. [PMID: 9454835 DOI: 10.1523/jneurosci.18-04-01250.1998] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Specific isoforms of laminin (LN) are concentrated at neuromuscular junctions (NMJs) where they may participate in synaptic organization or function. In myotubes from C2 cells, LN is concentrated within the majority of spontaneous acetylcholine receptor (AChR) aggregates. Neural agrin substantially increases this colocalization, suggesting that agrin can recruit LN into AChR aggregates. Addition of LN to C2 myotubes induces a more than twofold increase in the number of AChR aggregates. These aggregates have a larger size and are more dense than are those induced by agrin, suggesting that LN is involved in the growth and/or stabilization of AChR aggregates. Consistent with this hypothesis, an antiserum to LN reduces the size of individual AChR aggregates but increases their number. In C2 myotubes, extracellular matrix receptors containing the integrin beta1 subunit are poorly colocalized with AChR aggregates, suggesting that integrins may not be involved in LN-induced aggregation. In contrast, almost all AChR aggregates are associated with dystroglycan immunoreactivity, and monoclonal antibody (mAb) IIH6 against alpha-dystroglycan (alpha-DG), a LN and agrin receptor, causes a concentration-dependent inhibition of LN-induced aggregation. Moreover, S27 cells, which lack a functional alpha-DG, and two C2-derived cell lines expressing antisense DG mRNA fail to aggregate AChRs in response to LN. Finally, LN-induced AChR aggregation does not involve the phosphorylation of the muscle-specific tyrosine kinase receptor (MuSK) or the AChR beta subunit. We hypothesize that the interaction of LN with alpha-DG contributes to the growth and/or stabilization of AChR microaggregates into macroaggregates at the developing NMJ via a MuSK-independent mechanism.
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21
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Chapter 10 Development of the neuromuscular junction. Dev Biol 1998. [DOI: 10.1016/s1569-2582(98)80025-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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22
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Zhou H, Muramatsu T, Halfter W, Tsim KW, Peng HB. A role of midkine in the development of the neuromuscular junction. Mol Cell Neurosci 1997; 10:56-70. [PMID: 9361288 DOI: 10.1006/mcne.1997.0638] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Midkine (MK) is a member of a family of developmentally regulated neurotrophic and heparin-binding growth factors. It is expressed during the midgestation period in a retinoid-acid dependent manner during embryogenesis in the mouse. In vitro, it promotes neurite outgrowth from spinal cord neurons and cell migration. It expression is strongest in the central nervous system, thus suggesting a function for this protein in neural development. In this study, the role of MK in synaptogenesis was examined in the Xenopus system. A Xenopus MK cDNA was cloned from an embryonic library encompassing neurulation and synaptogenesis stages. By Northern blot analysis, MK mRNA was detected from the onset of neurulation and throughout the stages of synaptogenesis in the Xenopus embryo. This suggests that MK is also an important growth regulator in Xenopus embryogenesis. To study the function of MK in the development of the neuromuscular junction (NMJ), fusion proteins were made and their ability to induce the formation of acetylcholine receptor (AChR) clusters in cultured muscle cells was studied. Beads coated with MK strongly induce AChR clustering. When nerve-muscle cocultures were labeled with antibodies made against the MK fusion protein, MK immunoreactivity was detected at the NMJ. Unlike heparin-binding growth-associated molecule (HB-GAM), another member of this growth factor family, MK expression cannot be detected in the muscle but is present in spinal cord neurites. Consistent with these in vitro data is the observation that MK mRNA is only localized in the central nervous system but the protein is deposited at the intersomitic junction where the NMJ is located in vivo. Exogenously applied MK does bind to the heparan sulfate proteoglycan on the surface of Xenopus muscle cells. Agrin, a heparan-sulfate proteoglycan that induces the formation of AChR clusters in cultured muscle cells, binds strongly to MK. Bath application of MK in conjunction with agrin results in a change in the pattern of AChR clustering induced by agrin alone. These data suggest that MK is a neuron-derived factor that participates in the signal transduction process during NMJ development.
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Affiliation(s)
- H Zhou
- Department of Cell Biology and Anatomy, University of North Carolina, Chapel Hill 27599-7090, USA
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23
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Abstract
Neural agrin, in the absence of a nerve terminal, can induce the activity-resistant expression of acetylcholine receptor (AChR) subunit genes and the clustering of synapse-specific adult-type AChR channels in nonsynaptic regions of adult skeletal muscle fibers. Here we show that, when expression plasmids for neural agrin are injected into the extrasynaptic region of innervated muscle fibers, the following components of the postsynaptic apparatus are aggregated and colocalized with ectopic agrin-induced AChR clusters: laminin-beta2, MuSK, phosphotyrosine-containing proteins, beta-dystroglycan, utrophin, and rapsyn. These components have been implicated to play a role in the differentiation of neuromuscular junctions. Furthermore, ErbB2 and ErbB3, which are thought to be involved in the regulation of neurally induced AChR subunit gene expression, were colocalized with agrin-induced AChR aggregates at ectopic nerve-free sites. The postsynaptic muscle membrane also contained a high concentration of voltage-gated Na+ channels as well as deep, basal lamina-containing invaginations comparable to the secondary synaptic folds of normal endplates. The ability to induce AChR aggregation in vivo was not observed in experiments with a muscle-specific agrin isoform. Thus, a motor neuron-specific agrin isoform is sufficient to induce a full ectopic postsynaptic apparatus in muscle fibers kept electrically active at their original endplate sites.
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24
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Matsumura K, Chiba A, Yamada H, Fukuta-Ohi H, Fujita S, Endo T, Kobata A, Anderson LV, Kanazawa I, Campbell KP, Shimizu T. A role of dystroglycan in schwannoma cell adhesion to laminin. J Biol Chem 1997; 272:13904-10. [PMID: 9153251 DOI: 10.1074/jbc.272.21.13904] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Dystroglycan is encoded by a single gene and cleaved into two proteins alpha- and beta-dystroglycan by posttranslational processing. Recently, alpha-dystroglycan was demonstrated to be an extracellular laminin-binding protein anchored to the cell membrane by a transmembrane protein beta-dystroglycan in striated muscle and Schwann cells. However, the biological functions of the dystroglycan-laminin interaction remain obscure, and in particular, it is still unclear if dystroglycan plays a role in cell adhesion. In the present study, we characterized the role of dystroglycan in the adhesion of schwannoma cells to laminin-1. Immunochemical analysis demonstrated that the dystroglycan complex, comprised of alpha- and beta-dystroglycan, was a major laminin-binding protein complex in the surface membrane of rat schwannoma cell line RT4. It also demonstrated the presence of alpha-dystroglycan, but not beta-dystroglycan, in the culture medium, suggesting secretion of alpha-dystroglycan by RT4 cells. RT4 cells cultured on dishes coated with laminin-1 became spindle in shape and adhered to the bottom surface tightly. Monoclonal antibody IIH6 against alpha-dystroglycan was shown previously to inhibit the binding of laminin-1 to alpha-dystroglycan. In the presence of IIH6, but not several other control antibodies in the culture medium, RT4 cells remained round in shape and did not adhere to the bottom surface. The adhesion of RT4 cells to dishes coated with fibronectin was not affected by IIH6. The known inhibitors of the interaction of alpha-dystroglycan with laminin-1, including EDTA, sulfatide, fucoidan, dextran sulfate, heparin, and sialic acid, also perturbed the adhesion of RT4 cells to laminin-1, whereas the reagents which do not inhibit the interaction, including dextran, chondroitin sulfate, dermatan sulfate, and GlcNAc, did not. Altogether, these results support a role for dystroglycan as a major cell adhesion molecule in the surface membrane of RT4 cells.
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Affiliation(s)
- K Matsumura
- Department of Neurology and Neuroscience, Teikyo University School of Medicine, Tokyo 173, Japan.
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25
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Cohen MW, Jacobson C, Yurchenco PD, Morris GE, Carbonetto S. Laminin-induced clustering of dystroglycan on embryonic muscle cells: comparison with agrin-induced clustering. J Cell Biol 1997; 136:1047-58. [PMID: 9060469 PMCID: PMC2132475 DOI: 10.1083/jcb.136.5.1047] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/1996] [Revised: 11/15/1996] [Indexed: 02/03/2023] Open
Abstract
The effect of laminin on the distribution of dystroglycan (DG) and other surface proteins was examined by fluorescent staining in cultures of muscle cells derived from Xenopus embryos. Western blotting confirmed that previously characterized antibodies are reactive in Xenopus. In control cultures, alphaDG, betaDG, and laminin binding sites were distributed as microclusters (<1 microm2 in area) over the entire dorsal surface of the muscle cells. Treatment with laminin induced the formation of macroclusters (1-20 microm2), accompanied by a corresponding decline in the density of the microclusters. With 6 nM laminin, clustering was apparent within 150 min and near maximal within 1 d. Laminin was effective at 30 pM, the lowest concentration tested. The laminin fragment E3, which competes with laminin for binding to alphaDG, inhibited laminin-induced clustering but did not itself cluster DG, thereby indicating that other portions of the laminin molecule in addition to its alphaDG binding domain are required for its clustering activity. Laminin-induced clusters also contained dystrophin, but unlike agrin-induced clusters, they did not contain acetylcholine receptors, utrophin, or phosphotyrosine, and their formation was not inhibited by a tyrosine kinase inhibitor. The results reinforce the notion that unclustered DG is mobile on the surface of embryonic muscle cells and suggest that this mobile DG can be trapped by at least two different sets of molecular interactions. Laminin self binding may be the basis for the laminin-induced clustering.
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Affiliation(s)
- M W Cohen
- Department of Physiology, McGill University, Montreal, Quebec, Canada
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26
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Matsumura K, Yamada H, Saito F, Sunada Y, Shimizu T. Peripheral nerve involvement in merosin-deficient congenital muscular dystrophy and dy mouse. Neuromuscul Disord 1997; 7:7-12. [PMID: 9132144 DOI: 10.1016/s0960-8966(96)00402-6] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Merosin, also called laminin-2, is an isoform of laminin comprised of the alpha 2, beta 1 and gamma 1 chains. Deficiency of merosin alpha 2 chain was recently identified as the primary cause of the classical form of congenital muscular dystrophy (CMD), an autosomal recessive neuromuscular disorder characterised by muscular dystrophy and brain white matter abnormalities. Interestingly, merosin-deficient CMD and its animal model dy mouse are also accompanied by dysmyelination of peripheral motor nerves. In peripheral nerve, merosin is expressed in the endoneurium surrounding the Schwann cell/myelin sheath, while the putative merosin receptors dystroglycan and alpha 6 beta 4 integrin are expressed in the outer membrane of Schwann cell/myelin sheath. Together with the well known fact that the deposition of laminin in the basement membrane is essential for Schwann cell myelination, these findings indicate that the interaction of merosin with dystroglycan and/or alpha 6 beta 4 integrin plays an important role in peripheral myelinogenesis and that the disturbance of this interaction leads to peripheral dysmyelination in merosin deficiency. The clinical significance of peripheral dysmyelination in merosin deficiency is also discussed.
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Affiliation(s)
- K Matsumura
- Department of Neurology and Neuroscience, Teikyo University School of Medicine, Tokyo, Japan.
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27
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Schmidt RE. Synaptic dysplasia in sympathetic autonomic ganglia. JOURNAL OF NEUROCYTOLOGY 1996; 25:777-91. [PMID: 9023724 DOI: 10.1007/bf02284841] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- R E Schmidt
- Department of Pathology, Washington University School of Medicine, Saint Louis MO 63110, USA
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28
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Abstract
Although glial cells ensheath synapses throughout the nervous system, the functional consequences of this relationship are uncertain. Recent studies suggest that glial cells may promote the formation of synapses and help to maintain their function by providing nerve terminals with energy substrates and glutamate precursors.
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Affiliation(s)
- F W Pfrieger
- Department of Neurobiology, Stanford University School of Medicine, California 94305-5401, USA. pfrieger@leland,stanford.edu
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29
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Müller BM, Kistner U, Kindler S, Chung WJ, Kuhlendahl S, Fenster SD, Lau LF, Veh RW, Huganir RL, Gundelfinger ED, Garner CC. SAP102, a novel postsynaptic protein that interacts with NMDA receptor complexes in vivo. Neuron 1996; 17:255-65. [PMID: 8780649 DOI: 10.1016/s0896-6273(00)80157-9] [Citation(s) in RCA: 343] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Synapse-associated proteins (SAPs) are constituents of the pre- and postsynaptic submembraneous cytomatrix. Here, we present SAP102, a novel 102kDa SAP detected in dendritic shafts and spines of asymmetric type 1 synapses. SAP102 is enriched in preparations of synaptic junctions, where it biochemically behaves as a component of the cortical cytoskeleton. Antibodies directed against NMDA receptors coimmunoprecipitate SAP102 from rat brain synaptosomes. Recombinant proteins containing the carboxy-terminal tail of NMDA receptor subunit NR2B interact with SAP102 from rat brain homogenates. All three PDZ domains in SAP102 bind the cytoplasmic tail of NR2B in vitro. These data represent direct evidence that in vivo SAP102 is involved in linking NMDA receptors to the submembraneous cytomatrix associated with postsynaptic densities at excitatory synapses.
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Affiliation(s)
- B M Müller
- Center for Molecular Neurobiology, University of Hamburg, Federal Republic of Germany
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30
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Son YJ, Trachtenberg JT, Thompson WJ. Schwann cells induce and guide sprouting and reinnervation of neuromuscular junctions. Trends Neurosci 1996; 19:280-5. [PMID: 8799973 DOI: 10.1016/s0166-2236(96)10032-1] [Citation(s) in RCA: 175] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The "terminal' Schwann cells that sit atop the neuromuscular junction sense neuromuscular transmission and respond to perturbations of this transmission by extending long processes. These processes have the ability to induce nerve growth and serve as substrates to guide this growth. These processes thus play major roles in muscle reinnervation and in sprouting. An absence of nerve sprouting is correlated with the apoptotic death of terminal Schwann cells at denervated endplates in neonatal muscles. Thus, Schwann cells appear to participate actively in the maintenance and repair of neuromuscular synapses.
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Affiliation(s)
- Y J Son
- Dept of Neurobiology and Anatomy, Washington University School of Medicine, St Louis, MO 63110, USA
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