A new method was devised to visualize actin polymerization induced by postsynaptic differentiation signals in cultured muscle cells. This entails masking myofibrillar filamentous (F)-actin with jasplakinolide, a cell-permeant F-actin-binding toxin, before synaptogenic stimulation, and then probing new actin assembly with fluorescent phalloidin. With this procedure, actin polymerization associat...

Congenital myasthenic syndromes (CMS) can arise from presynaptic, synaptic, or postsynaptic defects. Mutations of the acetylcholine receptor (AChR) that increase or decrease the synaptic response to acetylcholine (ACh) are a common cause of the postsynaptic CMS. An increased response occurs in the slow-channel syndromes. Here, dominant mutations in different AChR subunits and in different domai...

Aggregation of the nicotinic acetylcholine receptor (AChR) at sites of nerve-muscle contact is one of the earliest events to occur during the development of the neuromuscular junction. The stimulus presented to the muscle by nerve and the mechanisms underlying postsynaptic differentiation are not known. The purpose of this study was to examine the distribution of phosphotyrosine (PY)-containing...

We have examined the properties and intracellular localization of acetylcholine receptors in the C2 muscle cell line and in a variant (T-) that accumulates AChR intracellularly. On immunoblots, the subunit structures of the AChR from wild-type and T- cells were similar except that the gamma and delta subunits of the variant AChR had altered mobilities. Digestion with endoglycosidases H and F de...

In a majority of patients with myasthenia gravis (MG), anti-acetylcholine receptor (AChR) antibodies target postsynaptic AChR clusters and thus compromise the membrane integrity of neuromuscular junctions (NMJs) and lead to muscle weakness. Antibody-induced endocytosis of AChRs in the postsynaptic membrane represents the initial step in the pathogenesis of MG; however, the molecular mechanisms ...

PURPOSE To establish a novel model of autoimmune ocular myasthenia gravis (oMG) in mice and study the pathogenic mechanisms of oMG. METHODS oMG was induced in HLA-DQ8 transgenic, HLA-DR3 transgenic, major histocompatibility complex (MHC) class II-deficient, C57BL/6, and C57BL/10 mice by immunization with an Escherichia coli plasmid expressing the recombinant human acetylcholine receptor (AChR...

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 a...

Agrin activates an intracellular signaling pathway to induce the formation of postsynaptic specializations on muscle fibers. In myotubes in culture, this pathway has been shown to include autophosphorylation of the muscle-specific kinase MuSK, activation of Src-family kinases, tyrosine phosphorylation of the acetylcholine receptor (AChR) beta subunit, a decrease in receptor detergent extractabi...

Immunization of animals with acetylcholine receptor (AChR) protein from the electric organs of Electrophorus electricus and Torpedo californica induces an autoimmune response to the AChR of mammalian skeletal muscle. Rats and guinea pigs develop experimental autoimmune myasthenia gravis (EAMG) after a single inoculation with small quantities of AChR and adjuvant. The indicence and severity of d...

The effects of prostaglandin E2 (PGE2), an important metabolite of arachidonic acid, were studied on the activity of nicotinic AChR channels in cultured chick sympathetic ganglion neurons. In whole cell recordings, PGE2 (25 nM) inhibited significantly the ACh-evoked macroscopic current. In cell-attached patch recordings, PGE2 significantly inhibited single AChR channel currents as a result of a...