scholarly journals Postsynaptic Abnormalities at the Neuromuscular Junctions of Utrophin-deficient Mice

1997 ◽  
Vol 136 (4) ◽  
pp. 883-894 ◽  
Author(s):  
Anne E. Deconinck ◽  
Allyson C. Potter ◽  
Jonathon M. Tinsley ◽  
Sarah J. Wood ◽  
Ruth Vater ◽  
...  
Keyword(s):  
Protein Complex ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Transmembrane Protein ◽  
Cluster Formation ◽  
Congenital Myasthenic Syndrome ◽  
Achr Cluster ◽  
Myasthenic Syndrome ◽  
Dystrophin Protein ◽  
Deficient Mice

Utrophin is a dystrophin-related cytoskeletal protein expressed in many tissues. It is thought to link F-actin in the internal cytoskeleton to a transmembrane protein complex similar to the dystrophin protein complex (DPC). At the adult neuromuscular junction (NMJ), utrophin is precisely colocalized with acetylcholine receptors (AChRs) and recent studies have suggested a role for utrophin in AChR cluster formation or maintenance during NMJ differentiation. We have disrupted utrophin expression by gene targeting in the mouse. Such mice have no utrophin detectable by Western blotting or immunocytochemistry. Utrophindeficient mice are healthy and show no signs of weakness. However, their NMJs have reduced numbers of AChRs (α-bungarotoxin [α-BgTx] binding reduced to ∼60% normal) and decreased postsynaptic folding, though only minimal electrophysiological changes. Utrophin is thus not essential for AChR clustering at the NMJ but may act as a component of the postsynaptic cytoskeleton, contributing to the development or maintenance of the postsynaptic folds. Defects of utrophin could underlie some forms of congenital myasthenic syndrome in which a reduction of postsynaptic folds is observed.

An improved method for culturing myotubes on laminins for the robust clustering of postsynaptic machinery

2019 ◽  
Author(s):  
Marcin Pęziński ◽  
Patrycja Daszczuk ◽  
Bhola Shankar Pradhan ◽  
Hanns Lochmüller ◽  
Tomasz J. Prószyński
Keyword(s):  
Motor Neurons ◽  
High Throughput Screening ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Neuromuscular Disorders ◽  
Cluster Assembly ◽  
Achr Cluster ◽  
Robust Clustering ◽  
Coated Surfaces

AbstractMotor neurons form specialized synapses with skeletal muscle fibers, called neuromuscular junctions (NMJs). Cultured myotubes are used as a simplified in vitro system to study the postsynaptic specialization of muscles. The stimulation of myotubes with the glycoprotein agrin or laminin-111 induces the clustering of postsynaptic machinery that contains acetylcholine receptors (AChRs). When myotubes are grown on laminin-coated surfaces, AChR clusters undergo developmental remodeling to form topologically complex structures that resemble mature NMJs. Needing further exploration are the molecular processes that govern AChR cluster assembly and its developmental maturation. Here, we describe an improved protocol for culturing muscle cells to promote the formation of complex AChR clusters. We screened various laminin isoforms and showed that laminin-221 was the most potent for inducing AChR clusters, whereas laminin-121, laminin-211, and laminin-221 afforded the highest percentages of topologically complex assemblies. Human primary myotubes that were formed by myoblasts obtained from patient biopsies also assembled AChR clusters that underwent remodeling in vitro. Collectively, these results demonstrate an advancement of culturing myotubes that can facilitate high-throughput screening for potential therapeutic targets for neuromuscular disorders.

scholarly journals The Extracellular Linker of Muscle Acetylcholine Receptor Channels Is a Gating Control Element

2000 ◽  
Vol 116 (3) ◽  
pp. 327-340 ◽  
Author(s):  
Claudio Grosman ◽  
Frank N. Salamone ◽  
Steven M. Sine ◽  
Anthony Auerbach
Keyword(s):  
Acetylcholine Receptors ◽  
Single Channel ◽  
Channel Gating ◽  
Congenital Myasthenic Syndrome ◽  
Control Element ◽  
Dependent Manner ◽  
Α Subunit ◽  
Transmembrane Segments ◽  
Channel Opening ◽  
Myasthenic Syndrome

We describe the functional consequences of mutations in the linker between the second and third transmembrane segments (M2–M3L) of muscle acetylcholine receptors at the single-channel level. Hydrophobic mutations (Ile, Cys, and Phe) placed near the middle of the linker of the α subunit (αS269) prolong apparent openings elicited by low concentrations of acetylcholine (ACh), whereas hydrophilic mutations (Asp, Lys, and Gln) are without effect. Because the gating kinetics of the αS269I receptor (a congenital myasthenic syndrome mutant) in the presence of ACh are too fast, choline was used as the agonist. This revealed an ∼92-fold increased gating equilibrium constant, which is consistent with an ∼10-fold decreased EC50 in the presence of ACh. With choline, this mutation accelerates channel opening ∼28-fold, slows channel closing ∼3-fold, but does not affect agonist binding to the closed state. These ratios suggest that, with ACh, αS269I acetylcholine receptors open at a rate of ∼1.4 × 106 s−1 and close at a rate of ∼760 s−1. These gating rate constants, together with the measured duration of apparent openings at low ACh concentrations, further suggest that ACh dissociates from the diliganded open receptor at a rate of ∼140 s−1. Ile mutations at positions flanking αS269 impair, rather than enhance, channel gating. Inserting or deleting one residue from this linker in the α subunit increased and decreased, respectively, the apparent open time approximately twofold. Contrary to the αS269I mutation, Ile mutations at equivalent positions of the β, ε, and δ subunits do not affect apparent open-channel lifetimes. However, in β and ε, shifting the mutation one residue to the NH2-terminal end enhances channel gating. The overall results indicate that this linker is a control element whose hydrophobicity determines channel gating in a position- and subunit-dependent manner. Characterization of the transition state of the gating reaction suggests that during channel opening the M2–M3L of the α subunit moves before the corresponding linkers of the β and ε subunits.

scholarly journals Regulation of the Rapsyn Promoter by Kaiso and δ-Catenin

2004 ◽  
Vol 24 (16) ◽  
pp. 7188-7196 ◽  
Author(s):  
Marianna Rodova ◽  
Kevin F. Kelly ◽  
Michael VanSaun ◽  
Juliet M. Daniel ◽  
Michael J. Werle
Keyword(s):  
Transcription Factor ◽  
Neuromuscular Junction ◽  
Acetylcholine Receptors ◽  
Consensus Sequence ◽  
Specific Protein ◽  
C2c12 Cells ◽  
Congenital Myasthenic Syndrome ◽  
P120 Catenin ◽  
Myasthenic Syndrome

ABSTRACT Rapsyn is a synapse-specific protein that is required for clustering acetylcholine receptors at the neuromuscular junction. Analysis of the rapsyn promoter revealed a consensus site for the transcription factor Kaiso within a region that is mutated in a subset of patients with congenital myasthenic syndrome. Kaiso is a POZ-zinc finger family transcription factor which recognizes the specific core consensus sequence CTGCNA (where N is any nucleotide). Previously, the only known binding partner for Kaiso was the cell adhesion cofactor, p120 catenin. Here we show that δ-catenin, a brain-specific member of the p120 catenin subfamily, forms a complex with Kaiso. Antibodies against Kaiso and δ-catenin recognize proteins in the nuclei of C2C12 myocytes and at the postsynaptic domain of the mouse neuromuscular junction. Endogenous Kaiso in C2C12 cells coprecipitates with the rapsyn promoter in vivo as shown by chromatin immunoprecipitation assay. Minimal promoter assays demonstrated that the rapsyn promoter can be activated by Kaiso and δ-catenin; this activation is apparently muscle specific. These results provide the first experimental evidence that rapsyn is a direct sequence-specific target of Kaiso and δ-catenin. We propose a new model of synapse-specific transcription that involves the interaction of Kaiso, δ-catenin, and myogenic transcription factors at the neuromuscular junction.

scholarly journals Transmembrane Collagens in Neuromuscular Development and Disorders

2021 ◽  
Vol 13 ◽  
Author(s):  
Tomoko Wakabayashi
Keyword(s):  
Molecular Mechanisms ◽  
Neuromuscular Junctions ◽  
Transmembrane Protein ◽  
Axon Growth ◽  
Congenital Myasthenic Syndrome ◽  
Loss Of Function ◽  
C Elegans ◽  
Ocular Motor Disorders ◽  
Multistep Process ◽  
Neuromuscular Development

Neuromuscular development is a multistep process and involves interactions among various extracellular and transmembrane molecules that facilitate the precise targeting of motor axons to synaptogenic regions of the target muscle. Collagenous proteins with transmembrane domains have recently emerged as molecules that play essential roles in multiple aspects of neuromuscular formation. Membrane-associated collagens with interrupted triple helices (MACITs) are classified as an unconventional subtype of the collagen superfamily and have been implicated in cell adhesion in a variety of tissues, including the neuromuscular system. Collagen XXV, the latest member of the MACITs, plays an essential role in motor axon growth within the developing muscle. In humans, loss-of-function mutations of collagen XXV result in developmental ocular motor disorders. In contrast, collagen XIII contributes to the formation and maintenance of neuromuscular junctions (NMJs), and disruption of its function leads to the congenital myasthenic syndrome. Transmembrane collagens are conserved not only in mammals but also in organisms such as C. elegans, where a single MACIT, COL-99, has been documented to function in motor innervation. Furthermore, in C. elegans, a collagen-like transmembrane protein, UNC-122, is implicated in the structural and functional integrity of the NMJ. This review article summarizes recent advances in understanding the roles of transmembrane collagens and underlying molecular mechanisms in multiple aspects of neuromuscular development and disorders.

First Characterization of Congenital Myasthenic Syndrome Type 5 in North Africa

2021 ◽  
Author(s):  
khaoula rochdi ◽  
Mathieu Cerino ◽  
Nathalie Da Silva ◽  
Valerie Delague ◽  
Halima Nahili ◽  
...  
Keyword(s):  
Neuromuscular Junctions ◽  
Clinical Findings ◽  
Congenital Myasthenic Syndrome ◽  
Homozygous Mutation ◽  
North African ◽  
The North ◽  
African Populations ◽  
North African Population ◽  
Myasthenic Syndrome

Abstract Congenital myasthenic syndromes (CMS) are associated with defects in the structure and the function of neuromuscular junctions. These rare disorders can result from mutations in the collagenic tail of endplate acetylcholinesterase (COLQ) essentially associated with autosomal recessive inheritance.With the lowered cost of genetic testing and increased access to next-generation sequencing, many mutations have been reported to date. In this study we identified the first COLQ homozygous mutation c.1193T>A in the North African population. This study outlines the genetic and phenotypic features of a CMS patient in a Moroccan family. It also describes a novel COLQ missense mutation associated with CMS-5. COLQ mutations are probably underdiagnosed in these North African populations, this is an issue as CMS-5 may be treated with ephedrine, and albuterol. Indeed, patients can seriously benefit and even recover after the treatment that should be planned according to genetic tests and clinical findings.

Laminin and alpha7beta1 integrin regulate agrin-induced clustering of acetylcholine receptors

2000 ◽  
Vol 113 (16) ◽  
pp. 2877-2886 ◽  
Author(s):  
D.J. Burkin ◽  
J.E. Kim ◽  
M. Gu ◽  
S.J. Kaufman
Keyword(s):  
Motor Neurons ◽  
Acetylcholine Receptors ◽  
Neuromuscular Junctions ◽  
Cluster Formation ◽  
Site Directed Mutagenesis ◽  
Synaptic Membrane ◽  
Before And After ◽  
Stable Association ◽  
Achr Clustering ◽  
Alpha7beta1 Integrin

The clustering of acetylcholine receptors (AChRs) in the post-synaptic membrane of skeletal muscle is an early developmental event in the formation of the neuromuscular junction. Several studies show that laminin, as well as neural agrin, can induce AChR clustering in C2C12 myofibers. We recently showed that specific isoforms of the alpha7beta1 integrin (a receptor normally found at neuromuscular junctions) colocalize and physically interact with AChR clusters in a laminin-dependent fashion. In contrast, induction with agrin alone fails to promote localization of the integrin with AChR clusters. Together both agrin and laminin enhance the interaction of the integrin with AChRs and their aggregation into clusters. To further understand this mechanism we investigated cluster formation and the association of the alpha7beta1 integrin and AChR over time following induction with laminin and/or agrin. Our results show that the alpha7beta1 integrin associates with AChRs early during the formation of the post-synaptic membrane and that laminin modulates this recruitment. Laminin induces a rapid stable association of the integrin and AChRs and this association is independent of clustering. In addition to laminin-1, merosin (laminin-2/4) is present both before and after formation of neuromuscular junctions and also promotes AChR clustering and colocalization with the integrin as well as synergism with agrin. Using site directed mutagenesis we demonstrate that a tyrosine residue in the cytoplasmic domain of both (α)7A and (α)7B chains regulates the localization of the integrin with AChR clusters. We also provide evidence that laminin, through its association with the alpha7beta1 integrin, reduces by 20-fold the concentration of agrin required to promote AChR clustering and accelerates the formation of clusters. Thus laminin, agrin and the alpha7beta1 integrin act in a concerted manner early in the development of the post-synaptic membrane, with laminin priming newly formed myofibers to rapidly and vigorously respond to low concentrations of neural agrin produced by innervating motor neurons.

Congenital myasthenic syndrome with acetylcholinesterase deficiency and calcium deposits at neuromuscular junctions

1994 ◽  
Vol 4 (5-6) ◽  
pp. S27
Author(s):  
P Confalonieri ◽  
M Mora ◽  
L Morandi ◽  
C Ciano ◽  
R Mantegazza ◽  
...  
Keyword(s):  
Neuromuscular Junctions ◽  
Congenital Myasthenic Syndrome ◽  
Myasthenic Syndrome ◽  
Calcium Deposits

scholarly journals A novel c.973G>T mutation in the ε-subunit of the acetylcholine receptor causing congenital myasthenic syndrome in an iranian family

2019 ◽  
Vol 22 (1) ◽  
pp. 95-98
Author(s):  
P Karimzadeh ◽  
S Parvizi Omran ◽  
H Ghaedi ◽  
MD Omrani
Keyword(s):  
Neuromuscular Junctions ◽  
Molecular Genetic ◽  
Molecular Genetic Analysis ◽  
Congenital Myasthenic Syndrome ◽  
Inherited Disorders ◽  
Direct Dna Sequencing ◽  
Gene Segregation ◽  
Electrophysiological Studies ◽  
Novel Variant ◽  
Myasthenic Syndrome

AbstractCongenital myasthenic syndrome (CMS) constitutes a group of inherited disorders of neuromuscular junctions. The majority of postsynaptic syndromes result from mutations in the CHRNE gene that causes muscle nicotine acetylcholine deficiency. In this study, we report on a 2 and a half-year-old boy with normal developmental milestones and bilateral ptosis. Clinical courses, electrophysiological studies and molecular genetic analysis were assessed. Polymerase chain reaction (PCR) and direct DNA sequencing of the CHRNE gene were performed for the proband and all the family members. A novel homozygous missense mutation of c.973G>T was found in the CHRNE gene. Segregation studies were suggested to be the genetic cause of the disease. Using three in silico tools and the American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) variant classification guidelines indicated that the novel variant c.973G>T was likely pathogenic. Our results recommended first screening of the CHRNE gene for pathogenic mutations in Iranian origin.

Sign in / Sign up

Export Citation Format

Share Document