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Julien Oury, Yun Liu, Ana Töpf, Slobodanka Todorovic, Esthelle Hoedt, Veeramani Preethish-Kumar, Thomas A Neubert, Weichun Lin, Hanns Lochmüller, Steven J Burden
Complex mechanisms are required to form neuromuscular synapses, direct their subsequent maturation, and maintain the synapse throughout life. Transcriptional and post-translational pathways play important roles in synaptic differentiation and direct the accumulation of the neurotransmitter receptors, acetylcholine receptors (AChRs), to the postsynaptic membrane, ensuring for reliable synaptic transmission. Rapsyn, an intracellular peripheral membrane protein that binds AChRs, is essential for synaptic differentiation, but how Rapsyn acts is poorly understood...
March 6, 2019: Journal of Cell Biology
Edith Bonnin, Pauline Cabochette, Alessandro Filosa, Ramona Jühlen, Shoko Komatsuzaki, Mohammed Hezwani, Achim Dickmanns, Valérie Martinelli, Marjorie Vermeersch, Lynn Supply, Nuno Martins, Laurence Pirenne, Gianina Ravenscroft, Marcus Lombard, Sarah Port, Christiane Spillner, Sandra Janssens, Ellen Roets, Jo Van Dorpe, Martin Lammens, Ralph H Kehlenbach, Ralf Ficner, Nigel G Laing, Katrin Hoffmann, Benoit Vanhollebeke, Birthe Fahrenkrog
Nucleoporins build the nuclear pore complex (NPC), which, as sole gate for nuclear-cytoplasmic exchange, is of outmost importance for normal cell function. Defects in the process of nucleocytoplasmic transport or in its machinery have been frequently described in human diseases, such as cancer and neurodegenerative disorders, but only in a few cases of developmental disorders. Here we report biallelic mutations in the nucleoporin NUP88 as a novel cause of lethal fetal akinesia deformation sequence (FADS) in two families...
December 13, 2018: PLoS Genetics
Shruthi Shanmukha, Gayathri Narayanappa, Atchayaram Nalini, Phalguni Anand Alladi, Trichur R Raju
Skeletal muscle atrophy is the most prominent feature of amyotrophic lateral sclerosis (ALS), an adult-onset neurodegenerative disease of motor neurons. However, the contribution of skeletal muscle to disease progression remains elusive. Our previous studies have shown that intrathecal injection of cerebrospinal fluid from sporadic ALS patients (ALS-CSF) induces several degenerative changes in motor neurons and glia of neonatal rats. Here, we describe various pathologic events in the rat extensor digitorum longus muscle following intrathecal injection of ALS-CSF...
April 16, 2018: Disease Models & Mechanisms
Hiroshi Nishimune, Kazuhiro Shigemoto
Neuromuscular junctions (NMJs) form between nerve terminals of spinal cord motor neurons and skeletal muscles, and perisynaptic Schwann cells and kranocytes cap NMJs. One muscle fiber has one NMJ, which is innervated by one motor nerve terminal. NMJs are excitatory synapses that use P/Q-type voltage-gated calcium channels to release the neurotransmitter acetylcholine. Acetylcholine receptors accumulate at the postsynaptic specialization called the end plate on the muscle fiber membrane, the sarcolemma. Proteins essential for the organization of end plates include agrin secreted from nerve terminals, Lrp4 and MuSK receptors for agrin, and Dok-7 and rapsyn cytosolic proteins in the muscle...
May 2018: Neurologic Clinics
Claire Legay, Lin Mei
The neuromuscular junction (NMJ) is indispensable for survival. This synapse between motoneurons and skeletal muscle fibers allows posture, movement and respiration. Therefore, its dysfunction creates pathologies than can be lethal. The molecular mechanisms of NMJ development and maintenance are the subject of intensive studies. This mini-review focuses on some of the most recent discoveries. An unexpected role for a protein, rapsyn, which has been known for 40 years to aggregate acetylcholine receptors has emerged...
August 2017: Journal of Neurochemistry
Masaharu Takamori
In the neuromuscular junction, postsynaptic nicotinic acetylcholine receptor (nAChR) clustering, trans-synaptic communication and synaptic stabilization are modulated by the molecular mechanisms underlying synaptic plasticity. The synaptic functions are based presynaptically on the active zone architecture, synaptic vesicle proteins, Ca2+ channels and synaptic vesicle recycling. Postsynaptically, they are based on rapsyn-anchored nAChR clusters, localized sensitivity to ACh, and synaptic stabilization via linkage to the extracellular matrix so as to be precisely opposed to the nerve terminal...
April 24, 2017: International Journal of Molecular Sciences
Mohamed Aittaleb, Isabel Martinez-Pena Y Valenzuela, Mohammed Akaaboune
A bimolecular fluorescence complementation (BiFC) approach was used to study the molecular interactions between different components of the postsynaptic protein complex at the neuromuscular junction of living mice. We show that rapsyn forms complex with both α-dystrobrevin and α-syntrophin at the crests of junctional folds. The linkage of rapsyn to α-syntrophin and/or α-dystrobrevin is mediated by utrophin, a protein localized at acetylcholine receptor (AChR)-rich domains. In mice deficient in α-syntrophin, in which utrophin is no longer present at the synapse, rapsyn interaction with α-dystrobrevin was completely abolished...
May 15, 2017: Journal of Cell Science
Raphael Vezina-Audette, Mathieu Tremblay, Salvatore Carbonetto
Previous work has shown that myotubes cultured on laminin-coated substrates form complex aggregates of synaptic proteins that are similar in shape and composition to neuromuscular junctions (NMJs). Here we show that laminin instructs the location of complex aggregates which form only on the lower surface when laminin is coated onto culture dishes but over the entire cell when laminin is added in solution. Silencing of myotubes by agents that block electrical activity (tetrodotoxin, verapamil) or by inhibitors of calmodulin dependent kinase (CaMKII) render the myotube permissive for the formation of complex aggregates...
January 2017: Matrix Biology: Journal of the International Society for Matrix Biology
Lei Li, Yu Cao, Haitao Wu, Xinchun Ye, Zhihui Zhu, Guanglin Xing, Chengyong Shen, Arnab Barik, Bin Zhang, Xiaoling Xie, Wenbo Zhi, Lin Gan, Huabo Su, Wen-Cheng Xiong, Lin Mei
Neurotransmission is ensured by a high concentration of neurotransmitter receptors at the postsynaptic membrane. This is mediated by scaffold proteins that bridge the receptors with cytoskeleton. One such protein is rapsyn (receptor-associated protein at synapse), which is essential for acetylcholine receptor (AChR) clustering and NMJ (neuromuscular junction) formation. We show that the RING domain of rapsyn contains E3 ligase activity. Mutation of the RING domain that abolishes the enzyme activity inhibits rapsyn- as well as agrin-induced AChR clustering in heterologous and muscle cells...
December 7, 2016: Neuron
Hua Wen, Jeffrey Michael Hubbard, Wei-Chun Wang, Paul Brehm
Rapsyn-deficient myasthenic syndrome is characterized by a weakness in voluntary muscle contraction, a direct consequence of greatly reduced synaptic responses that result from poorly clustered acetylcholine receptors. As with other myasthenic syndromes, the general muscle weakness is also accompanied by use-dependent fatigue. Here, we used paired motor neuron target muscle patch-clamp recordings from a rapsyn-deficient mutant line of zebrafish to explore for the first time the mechanisms causal to fatigue...
October 19, 2016: Journal of Neuroscience
Sudhakar Aare, Sally Spendiff, Madhusudanarao Vuda, Daren Elkrief, Anna Perez, Qinghua Wu, Dominique Mayaki, Sabah N A Hussain, Stefan Hettwer, Russell T Hepple
BACKGROUND: Skeletal muscle displays a marked accumulation of denervated myofibers at advanced age, which coincides with an acceleration of muscle atrophy. METHODS: In this study, we evaluated the hypothesis that the accumulation of denervated myofibers in advanced age is due to failed reinnervation by examining muscle from young adult (YA) and very old (VO) rats and from a murine model of sporadic denervation secondary to neurotrypsin over-expression (Sarco mouse)...
2016: Skeletal Muscle
Amy C Visser, Ruple S Laughlin, William J Litchy, Eduardo E Benarroch, Margherita Milone
INTRODUCTION: Fluoxetine is a selective serotonin reuptake inhibitor and long-lived open channel blocker of the acetylcholine receptor, often used in the treatment of slow-channel congenital myasthenic syndromes (CMS). METHODS: We report a 42-year-old woman who had a history of episodic limb weakness that worsened after initiation of fluoxetine for treatment of depression. Genetic testing for CMS revealed a homozygous pathogenic mutation in the rapsyn (RAPSN) gene (p...
January 2017: Muscle & Nerve
Valérie Vilmont, Bruno Cadot, Elsa Vezin, Fabien Le Grand, Edgar R Gomes
The neuromuscular junction (NMJ) allows the transformation of a neuronal message into a mechanical force by muscle contraction and is the target of several neuromuscular disorders. While the neuronal side is under extensive research, the muscle appeared recently to have a growing role in the formation and integrity of the neuromuscular junction. We used an in vitro model of mature myofibers to study the role of dynein on major postsynaptic proteins. We found that dynein affects the expression and the clustering of acetylcholine receptors (AChRs), muscle specific tyrosine kinase (MuSK) and Rapsyn...
June 10, 2016: Scientific Reports
Po-Ju Chen, Isabel Martinez-Pena Y Valenzuela, Mohamed Aittaleb, Mohammed Akaaboune
UNLABELLED: Rapsyn, a 43 kDa scaffold protein, is required for the clustering of acetylcholine receptors (AChRs) at synaptic sites between mammalian motor neurons and muscle cells. However, the mechanism by which rapsyn is inserted and retained at postsynaptic sites at the neuromuscular junction (NMJ) in vivo remains largely unknown. We found that neither the N-terminal myristoylation nor the cysteine-rich RING H2 domain of rapsyn is required for its stable association with the postsynaptic membrane of NMJs...
May 25, 2016: Journal of Neuroscience
Jayden A Clark, Katherine A Southam, Catherine A Blizzard, Anna E King, Tracey C Dickson
Degeneration of the distal axon and neuromuscular junction (NMJ) is considered a key and early feature of the pathology that accompanies motor neuron loss in people with amyotrophic lateral sclerosis (ALS). The mutant SOD1(G93A) mouse replicates many features of the disease, however the sequence of events resulting in degeneration of the neuromuscular circuitry remains unknown. Furthermore, despite widespread degenerative neuronal pathology throughout the spinal cord in this model, hindlimb motor function is lost before forelimb function...
October 2016: Journal of Chemical Neuroanatomy
D Natera-de Benito, M Bestué, J J Vilchez, T Evangelista, A Töpf, A García-Ribes, M J Trujillo-Tiebas, M García-Hoyos, C Ortez, A Camacho, E Jiménez, M Dusl, A Abicht, H Lochmüller, J Colomer, A Nascimento
Rapsyn (RAPSN) mutations are a common cause of postsynaptic congenital myasthenic syndromes. We present a comprehensive description of the clinical and molecular findings of ten patients with CMS due to mutations in RAPSN, mostly with a long-term follow-up. Two patients were homozygous and eight were heterozygous for the common p.Asn88Lys mutation. In three of the heterozygous patients we have identified three novel mutations (c.869T > C; p.Leu290Pro, c.1185delG; p.Thr396Profs*12, and c.358delC; p.Gln120Serfs*8)...
February 2016: Neuromuscular Disorders: NMD
Nazanin Ghazanfari, Erna L T B Linsao, Sofie Trajanovska, Marco Morsch, Paul Gregorevic, Simon X Liang, Stephen W Reddel, William D Phillips
We investigated the influence of postsynaptic tyrosine kinase signaling in a mouse model of muscle-specific kinase (MuSK) myasthenia gravis (MG). Mice administered repeated daily injections of IgG from MuSK MG patients developed impaired neuromuscular transmission due to progressive loss of acetylcholine receptor (AChR) from the postsynaptic membrane of the neuromuscular junction. In this model, anti-MuSK-positive IgG caused a reduction in motor endplate immunolabeling for phosphorylated Src-Y418 and AChR β-subunit-Y390 before any detectable loss of MuSK or AChR from the endplate...
December 2015: Physiological Reports
Mohamed Aittaleb, Po-Ju Chen, Mohammed Akaaboune
Rapsyn, a scaffold protein, is required for the clustering of acetylcholine receptors (AChRs) at contacts between motor neurons and differentiating muscle cells. Rapsyn is also expressed in cells that do not express AChRs. However, its function in these cells remains unknown. Here, we show that rapsyn plays an AChR-independent role in organizing the distribution and mobility of lysosomes. In cells devoid of AChRs, rapsyn selectively induces the clustering of lysosomes at high density in the juxtanuclear region without affecting the distribution of other intracellular organelles...
October 15, 2015: Journal of Cell Science
Joel Oger, Hans Frykman
This review describes the state of the art for the use of laboratory testing in myasthenia gravis. The review brings a detailed description of the different clinical forms of auto-immune myasthenia and of the Lambert Eaton Myasthenic Syndrome (LEMS). They stress the differences between the different forms of acquired (auto-immune) myasthenia. Then they present a summary of the different antibodies found in the disease. They insist on the advantage of the RIPA assay to measure antibodies to the acetylcholine receptor...
September 20, 2015: Clinica Chimica Acta; International Journal of Clinical Chemistry
Dustin Herrmann, Marion Straubinger, Said Hashemolhosseini
Previously, we demonstrated that the protein kinase CK2 associates with and phosphorylates the receptor tyrosine kinase MuSK (muscle specific receptor tyrosine kinase) at the neuromuscular junction (NMJ), thereby preventing fragmentation of the NMJs (Cheusova, T., Khan, M. A., Schubert, S. W., Gavin, A. C., Buchou, T., Jacob, G., Sticht, H., Allende, J., Boldyreff, B., Brenner, H. R., and Hashemolhosseini, S. (2006) Genes Dev. 20, 1800-1816). Here, we asked whether CK2 interacts with other proteins involved in processes at the NMJ, which would be consistent with the previous observation that CK2 appears enriched at the NMJ...
September 11, 2015: Journal of Biological Chemistry
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