scholarly journals Mechanism of disease and therapeutic rescue of Dok7 congenital myasthenia

Nature ◽  
2021 ◽  
Author(s):  
Julien Oury ◽  
Wei Zhang ◽  
Nadia Leloup ◽  
Akiko Koide ◽  
Alexis D. Corrado ◽  
...  
Keyword(s):  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Late Onset ◽  
Point Mutations ◽  
Neuromuscular Synapse ◽  
Adaptor Protein ◽  
Common Disease ◽  
Tyrosine Residues ◽  
Neonatal Lethality ◽  
Congenital Myasthenia

AbstractCongenital myasthenia (CM) is a devastating neuromuscular disease, and mutations in DOK7, an adaptor protein that is crucial for forming and maintaining neuromuscular synapses, are a major cause of CM1,2. The most common disease-causing mutation (DOK71124_1127 dup) truncates DOK7 and leads to the loss of two tyrosine residues that are phosphorylated and recruit CRK proteins, which are important for anchoring acetylcholine receptors at synapses. Here we describe a mouse model of this common form of CM (Dok7CM mice) and a mouse with point mutations in the two tyrosine residues (Dok72YF). We show that Dok7CM mice had severe deficits in neuromuscular synapse formation that caused neonatal lethality. Unexpectedly, these deficits were due to a severe deficiency in phosphorylation and activation of muscle-specific kinase (MUSK) rather than a deficiency in DOK7 tyrosine phosphorylation. We developed agonist antibodies against MUSK and show that these antibodies restored neuromuscular synapse formation and prevented neonatal lethality and late-onset disease in Dok7CM mice. These findings identify an unexpected cause for disease and a potential therapy for both DOK7 CM and other forms of CM caused by mutations in AGRIN, LRP4 or MUSK, and illustrate the potential of targeted therapy to rescue congenital lethality.

scholarly journals Laminin-1 redistributes postsynaptic proteins and requires rapsyn, tyrosine phosphorylation, and Src and Fyn to stably cluster acetylcholine receptors

2002 ◽  
Vol 157 (5) ◽  
pp. 883-895 ◽  
Author(s):  
P. Angelo Marangi ◽  
Simon T. Wieland ◽  
Christian Fuhrer
Keyword(s):  
Tyrosine Phosphorylation ◽  
Tyrosine Kinases ◽  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Cluster Formation ◽  
Neuromuscular Synapse ◽  
Achr Cluster ◽  
Signaling Mechanisms ◽  
Neuromuscular Synaptogenesis ◽  
Laminin 1

Clustering of acetylcholine receptors (AChRs) is a critical step in neuromuscular synaptogenesis, and is induced by agrin and laminin which are thought to act through different signaling mechanisms. We addressed whether laminin redistributes postsynaptic proteins and requires key elements of the agrin signaling pathway to cause AChR aggregation. In myotubes, laminin-1 rearranged dystroglycans and syntrophins into a laminin-like network, whereas inducing AChR-containing clusters of dystrobrevin, utrophin, and, to a marginal degree, MuSK. Laminin-1 also caused extensive coclustering of rapsyn and phosphotyrosine with AChRs, but none of these clusters were observed in rapsyn −/− myotubes. In parallel with clustering, laminin-1 induced tyrosine phosphorylation of AChR β and δ subunits. Staurosporine and herbimycin, inhibitors of tyrosine kinases, prevented laminin-induced AChR phosphorylation and AChR and phosphotyrosine clustering, and caused rapid dispersal of clusters previously induced by laminin-1. Finally, laminin-1 caused normal aggregation of AChRs and phosphotyrosine in myotubes lacking both Src and Fyn kinases, but these clusters dispersed rapidly after laminin withdrawal. Thus, laminin-1 redistributes postsynaptic proteins and, like agrin, requires tyrosine kinases for AChR phosphorylation and clustering, and rapsyn for AChR cluster formation, whereas cluster stabilization depends on Src and Fyn. Therefore, the laminin and agrin signaling pathways overlap intracellularly, which may be important for neuromuscular synapse formation.

43K Protein and Acetylcholine Receptors Colocalize during the Initial Stages of Neuromuscular Synapse Formation in Vivo

1993 ◽  
Vol 155 (1) ◽  
pp. 275-280 ◽  
Author(s):  
Peter G. Noakes ◽  
William D. Phillips ◽  
Theresa A. Hanley ◽  
Joshua R. Sanes ◽  
John P. Merlie
Keyword(s):  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Neuromuscular Synapse

scholarly journals Neuregulin/ErbB regulate neuromuscular junction development by phosphorylation of α-dystrobrevin

2011 ◽  
Vol 195 (7) ◽  
pp. 1171-1184 ◽  
Author(s):  
Nadine Schmidt ◽  
Mohammed Akaaboune ◽  
Nadesan Gajendran ◽  
Isabel Martinez-Pena y Valenzuela ◽  
Sarah Wakefield ◽  
...  
Keyword(s):  
Nervous System ◽  
Synaptic Transmission ◽  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Neuromuscular Synapse ◽  
Muscle Membrane ◽  
Erbb Signaling ◽  
Cultured Myotubes ◽  
The Stability ◽  
And Function

Neuregulin (NRG)/ErbB signaling is involved in numerous developmental processes in the nervous system, including synapse formation and function in the central nervous system. Although intensively investigated, its role at the neuromuscular synapse has remained elusive. Here, we demonstrate that loss of neuromuscular NRG/ErbB signaling destabilized anchoring of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane and that this effect was caused by dephosphorylation of α-dystrobrevin1, a component of the postsynaptic scaffold. Specifically, in mice in which NRG signaling to muscle was genetically or pharmacologically abolished, postsynaptic AChRs moved rapidly from the synaptic to the perisynaptic membrane, and the subsynaptic scaffold that anchors the AChRs was impaired. These defects combined compromised synaptic transmission. We further show that blockade of NRG/ErbB signaling abolished tyrosine phosphorylation of α-dystrobrevin1, which reduced the stability of receptors in agrin-induced AChR clusters in cultured myotubes. Our data indicate that NRG/ErbB signaling maintains high efficacy of synaptic transmission by stabilizing the postsynaptic apparatus via phosphorylation of α-dystrobrevin1.

scholarly journals Src, Fyn, and Yes Are Not Required for Neuromuscular Synapse Formation But Are Necessary for Stabilization of Agrin-Induced Clusters of Acetylcholine Receptors

2001 ◽  
Vol 21 (9) ◽  
pp. 3151-3160 ◽  
Author(s):  
Cynthia L. Smith ◽  
Peggy Mittaud ◽  
Elizabeth D. Prescott ◽  
Christian Fuhrer ◽  
Steven J. Burden
Keyword(s):  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Neuromuscular Synapse

scholarly journals Absence of α-Syntrophin Leads to Structurally Aberrant Neuromuscular Synapses Deficient in Utrophin

2000 ◽  
Vol 150 (6) ◽  
pp. 1385-1398 ◽  
Author(s):  
Marvin E. Adams ◽  
Neal Kramarcy ◽  
Stuart P. Krall ◽  
Susana G. Rossi ◽  
Richard L. Rotundo ◽  
...  
Keyword(s):  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Synapse Formation ◽  
Neuromuscular Junctions ◽  
Neuromuscular Synapse ◽  
Synaptic Cleft ◽  
Multiple Protein ◽  
Oxide Synthase ◽  
Related Proteins ◽  
Dystrophin Protein

The syntrophins are a family of structurally related proteins that contain multiple protein interaction motifs. Syntrophins associate directly with dystrophin, the product of the Duchenne muscular dystrophy locus, and its homologues. We have generated α-syntrophin null mice by targeted gene disruption to test the function of this association. The α-Syn−/− mice show no evidence of myopathy, despite reduced levels of α-dystrobrevin–2. Neuronal nitric oxide synthase, a component of the dystrophin protein complex, is absent from the sarcolemma of the α-Syn−/− mice, even where other syntrophin isoforms are present. α-Syn−/− neuromuscular junctions have undetectable levels of postsynaptic utrophin and reduced levels of acetylcholine receptor and acetylcholinesterase. The mutant junctions have shallow nerve gutters, abnormal distributions of acetylcholine receptors, and postjunctional folds that are generally less organized and have fewer openings to the synaptic cleft than controls. Thus, α-syntrophin has an important role in synapse formation and in the organization of utrophin, acetylcholine receptor, and acetylcholinesterase at the neuromuscular synapse.

scholarly journals GA-Binding Protein Is Dispensable for Neuromuscular Synapse Formation and Synapse-Specific Gene Expression

2007 ◽  
Vol 27 (13) ◽  
pp. 5040-5046 ◽  
Author(s):  
Alexander Jaworski ◽  
Cynthia L. Smith ◽  
Steven J. Burden
Keyword(s):  
Gene Expression ◽  
Synapse Formation ◽  
Binding Protein ◽  
Neuromuscular Synapse ◽  
Specific Gene ◽  
Promoter Regions ◽  
Specific Gene Expression ◽  
Muscle Gene Expression ◽  
Synaptic Region ◽  
Ga Binding Protein

ABSTRACT The mRNAs encoding postsynaptic components at the neuromuscular junction are concentrated in the synaptic region of muscle fibers. Accumulation of these RNAs in the synaptic region is mediated, at least in part, by selective transcription of the corresponding genes in synaptic myofiber nuclei. The transcriptional mechanisms that are responsible for synapse-specific gene expression are largely unknown, but an Ets site in the promoter regions of acetylcholine receptor (AChR) subunit genes and other “synaptic” genes is required for synapse-specific transcription. The Ets domain transcription factor GA-binding protein (GABP) has been implicated to mediate synapse-specific gene expression. Inactivation of GABPα, the DNA-binding subunit of GABP, leads to early embryonic lethality, preventing analysis of synapse formation in gabpα mutant mice. To study the role of GABP at neuromuscular synapses, we conditionally inactivated gabpα in skeletal muscle and studied synaptic differentiation and muscle gene expression. Although expression of rb, a target of GABP, is elevated in muscle tissue deficient in GABPα, clustering of synaptic AChRs at synapses and synapse-specific gene expression are normal in these mice. These data indicate that GABP is dispensable for synapse-specific transcription and maintenance of normal AChR expression at synapses.

scholarly journals Activation of the Epidermal Growth Factor (EGF) Receptor Induces Formation of EGF Receptor- and Grb2-Containing Clathrin-Coated Pits

2006 ◽  
Vol 26 (2) ◽  
pp. 389-401 ◽  
Author(s):  
Lene E. Johannessen ◽  
Nina Marie Pedersen ◽  
Ketil Winther Pedersen ◽  
Inger Helene Madshus ◽  
Espen Stang
Keyword(s):  
Growth Factor ◽  
Epidermal Growth Factor ◽  
Egf Receptor ◽  
Point Mutations ◽  
Adaptor Protein ◽  
Mitogen Activated Protein Kinase ◽  
Coated Pits ◽  
Α Subunit ◽  
Sh3 Domains ◽  
Epidermal Growth

ABSTRACT In HeLa cells depleted of adaptor protein 2 complex (AP2) by small interfering RNA (siRNA) to the μ2 or α subunit or by transient overexpression of an AP2 sequestering mutant of Eps15, endocytosis of the transferrin receptor (TfR) was strongly inhibited. However, epidermal growth factor (EGF)-induced endocytosis of the EGF receptor (EGFR) was inhibited only in cells where the α subunit had been knocked down. By immunoelectron microscopy, we found that in AP2-depleted cells, the number of clathrin-coated pits was strongly reduced. When such cells were incubated with EGF, new coated pits were formed. These contained EGF, EGFR, clathrin, and Grb2 but not the TfR. The induced coated pits contained the α subunit, but labeling density was reduced compared to control cells. Induction of clathrin-coated pits required EGFR kinase activity. Overexpression of Grb2 with inactivating point mutations in N- or C-terminal SH3 domains or in both SH3 domains inhibited EGF-induced formation of coated pits efficiently, even though Grb2 SH3 mutations did not block activation of mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3-kinase (PI3K). Our data demonstrate that EGFR-induced signaling and Grb2 are essential for formation of clathrin-coated pits accommodating the EGFR, while activation of MAPK and PI3K is not required.

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