•Distinct branches of Wnt signaling regulate NMJ formation.•Genetic experiments support the functional role of Wnt/MuSK interaction in vivo.•A role for Wnt signaling in neuromuscular junction ...maintenance is proposed.
The development and maintenance of the neuromuscular connectivity relies on a temporally fine-tuned balance of distinct bi-directional communication between motor neurons and their muscle targets. Disruption of this communication leads to functional and structural defects that affect the motor function and causes severe neuromuscular pathologies. A limited number of secreted molecules exchanged across the synaptic cleft are critical for the development and maintenance of the nerve/muscle contact. Among those factors, members of the large family of Wnt molecules, best known for their role in numerous developmental processes have emerged as complex key players at the neuromuscular junction (NMJ), being possibly involved in multiple aspects of synapse positioning, differentiation and maintenance. Yet, their specific mode of action and downstream signaling in vivo remain controversial in mammals creating a certain degree of confusion as to the mechanistic frame of Wnt-elicited function at the NMJ. Recent advances in understanding the role of the Wnt signaling network during mammalian NMJ formation and maintenance is reviewed here.
Magi-1c Strochlic, Laure; Cartaud, Annie; Labas, Valérie ...
The Journal of cell biology,
05/2001, Letnik:
153, Številka:
5
Journal Article
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The muscle-specific receptor tyrosine kinase (MuSK) forms part of a receptor complex, activated by nerve-derived agrin, that orchestrates the differentiation of the neuromuscular junction (NMJ). The ...molecular events linking MuSK activation with postsynaptic differentiation are not fully understood. In an attempt to identify partners and/or effectors of MuSK, cross-linking and immunopurification experiments were performed in purified postsynaptic membranes from the Torpedo electrocyte, a model system for the NMJ. Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) analysis was conducted on both cross-link products, and on the major peptide coimmunopurified with MuSK; this analysis identified a polypeptide corresponding to the COOH-terminal fragment of membrane-associated guanylate kinase (MAGUK) with inverted domain organization (MAGI)-1c. A bona fide MAGI-1c (150 kD) was detected by Western blotting in the postsynaptic membrane of Torpedo electrocytes, and in a high molecular mass cross-link product of MuSK. Immunofluorescence experiments showed that MAGI-1c is localized specifically at the adult rat NMJ, but is absent from agrin-induced acetylcholine receptor clusters in myotubes in vitro. In the central nervous system, MAGUKs play a primary role as scaffolding proteins that organize cytoskeletal signaling complexes at excitatory synapses. Our data suggest that a protein from the MAGUK family is involved in the MuSK signaling pathway at the vertebrate NMJ.
To report the identification of 2 new homozygous recessive mutations in the synaptotagmin 2 (
) gene as the genetic cause of severe and early presynaptic forms of congenital myasthenic syndromes ...(CMSs).
Next-generation sequencing identified new homozygous intronic and frameshift mutations in the
gene as a likely cause of presynaptic CMS. We describe the clinical and electromyographic patient phenotypes, perform ex vivo splicing analyses to characterize the effect of the intronic mutation on exon splicing, and analyze the functional impact of this variation at the neuromuscular junction (NMJ).
The 2 infants presented a similar clinical phenotype evoking first a congenital myopathy characterized by muscle weakness and hypotonia. Next-generation sequencing allowed to the identification of 1 homozygous intronic mutation c.465+1G>A in patient 1 and another homozygous frameshift mutation c.328_331dup in patient 2, located respectively in the 5' splice donor site of
intron 4 and in exon 3. Functional studies of the intronic mutation validated the abolition of the splice donor site of exon 4 leading to its skipping. In-frame skipping of exon 4 that encodes part of the C2A calcium-binding domain of SYT2 is associated with a loss-of-function effect resulting in a decrease of neurotransmitter release and severe pre- and postsynaptic NMJ defects.
This study identifies new homozygous recessive
mutations as the underlying cause of severe and early presynaptic form of CMS expanding the genetic spectrum of recessive
-related CMS associated with defects in neurotransmitter release.
The muscle-specific receptor tyrosine kinase (MuSK) forms part of a receptor complex, activated by nerve-derived agrin, that orchestrates the differentiation of the neuromuscular junction (NMJ). The ...molecular events linking MuSK activation with postsynaptic differentiation are not fully understood. In an attempt to identify partners and/or effectors of MuSK, cross-linking and immunopurification experiments were performed in purified postsynaptic membranes from the Torpedo electrocyte, a model system for the NMJ. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) analysis was conducted on both cross-link products, and on the major peptide coimmunopurified with MuSK; this analysis identified a polypeptide corresponding to the COOH-terminal fragment of membrane-associated guanylate kinase (MAGUK) with inverted domain organization (MAGI)-1c. A bona fide MAGI-1c (150 kD) was detected by Western blotting in the postsynaptic membrane of Torpedo electrocytes, and in a high molecular mass cross-link product of MuSK. Immunofluorescence experiments showed that MAGI-1c is localized specifically at the adult rat NMJ, but is absent from agrin-induced acetylcholine receptor clusters in myotubes in vitro. In the central nervous system, MAGUKs play a primary role as scaffolding proteins that organize cytoskeletal signaling complexes at excitatory synapses. Our data suggest that a protein from the MAGUK family is involved in the MuSK signaling pathway at the vertebrate NMJ.
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