scholarly journals Agrin regulates CLASP2-mediated capture of microtubules at the neuromuscular junction synaptic membrane

2012 ◽  
Vol 198 (3) ◽  
pp. 421-437 ◽  
Author(s):  
Nadine Schmidt ◽  
Sreya Basu ◽  
Stefan Sladecek ◽  
Sabrina Gatti ◽  
Jeffrey van Haren ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Acetylcholine Receptor ◽  
Three Dimensional ◽  
Postsynaptic Membrane ◽  
Dimensional Structure ◽  
Muscle Membrane ◽  
Synaptic Membrane ◽  
Dense Network ◽  
Phosphatidylinositol 3 Kinase ◽  
Neuronal Regulation

Agrin is the major factor mediating the neuronal regulation of postsynaptic structures at the vertebrate neuromuscular junction, but the details of how it orchestrates this unique three-dimensional structure remain unknown. Here, we show that agrin induces the formation of the dense network of microtubules in the subsynaptic cytoplasm and that this, in turn, regulates acetylcholine receptor insertion into the postsynaptic membrane. Agrin acted in part by locally activating phosphatidylinositol 3-kinase and inactivating GSK3β, which led to the local capturing of dynamic microtubules at agrin-induced acetylcholine receptor (AChR) clusters, mediated to a large extent by the microtubule plus-end tracking proteins CLASP2 and CLIP-170. Indeed, in the absence of CLASP2, microtubule plus ends at the subsynaptic muscle membrane, the density of synaptic AChRs, the size of AChR clusters, and the numbers of subsynaptic muscle nuclei with their selective gene expression programs were all reduced. Thus, the cascade linking agrin to CLASP2-mediated microtubule capturing at the synaptic membrane is essential for the maintenance of a normal neuromuscular phenotype.

scholarly journals CLASP2-dependent microtubule capture at the neuromuscular junction membrane requires LL5β and actin for focal delivery of acetylcholine receptor vesicles

2015 ◽  
Vol 26 (5) ◽  
pp. 938-951 ◽  
Author(s):  
Sreya Basu ◽  
Stefan Sladecek ◽  
Isabel Martinez de la Peña y Valenzuela ◽  
Mohammed Akaaboune ◽  
Ihor Smal ◽  
...  
Keyword(s):  
Neuromuscular Junction ◽  
Actin Cytoskeleton ◽  
Acetylcholine Receptor ◽  
Acetylcholine Receptors ◽  
Postsynaptic Membrane ◽  
Interaction Partner ◽  
Synaptic Membrane ◽  
Microtubule Capture

A novel mechanism is described for the agrin-mediated focal delivery of acetylcholine receptors (AChRs) to the postsynaptic membrane of the neuromuscular junction. Microtubule capture mediated by CLASP2 and its interaction partner, LL5β, and an intact subsynaptic actin cytoskeleton are both required for focal AChR transport to the synaptic membrane.

scholarly journals 300-kD subsynaptic protein copurifies with acetylcholine receptor-rich membranes and is concentrated at neuromuscular synapses

1987 ◽  
Vol 104 (4) ◽  
pp. 939-946 ◽  
Author(s):  
ML Woodruff ◽  
J Theriot ◽  
SJ Burden
Keyword(s):  
Acetylcholine Receptor ◽  
Electric Organ ◽  
Postsynaptic Membrane ◽  
Synaptic Membrane ◽  
Binding Assays ◽  
Western Blots ◽  
Neuromuscular Synapses ◽  
Peripheral Membrane Proteins ◽  
Torpedo Electric Organ ◽  
Skeletal Muscle Antibodies

Acetylcholine receptor-rich membranes from the electric organ of Torpedo californica are enriched in the four different subunits of the acetylcholine receptor and in two peripheral membrane proteins at 43 and 300 kD. We produced monoclonal antibodies against the 300-kD protein and have used these antibodies to determine the location of the protein, both in the electric organ and in skeletal muscle. Antibodies to the 300-kD protein were characterized by Western blots, binding assays to isolated membranes, and immunofluorescence on tissue. In Torpedo electric organ, antibodies to the 300-kD protein stain only the innervated face of the electrocytes. The 300-kD protein is on the intracellular surface of the postsynaptic membrane, since antibodies to the 300-kD protein bind more efficiently to saponin-permeabilized, right side out membranes than to intact membranes. Some antibodies against the Torpedo 300-kD protein cross-react with amphibian and mammalian neuromuscular synapses, and the cross-reacting protein is also highly concentrated on the intracellular surface of the post-synaptic membrane.

Rituximab in AChR subtype of myasthenia gravis: systematic review

2020 ◽  
Vol 91 (4) ◽  
pp. 392-395 ◽  
Author(s):  
Vincenzo Di Stefano ◽  
Antonino Lupica ◽  
Marianna Gabriella Rispoli ◽  
Antonio Di Muzio ◽  
Filippo Brighina ◽  
...  
Keyword(s):  
Systematic Review ◽  
Neuromuscular Junction ◽  
Myasthenia Gravis ◽  
Acetylcholine Receptor ◽  
Autoimmune Disorder ◽  
Postsynaptic Membrane ◽  
Receptor Subtype ◽  
Registration Number ◽  
Randomised Controlled ◽  
Time To Relapse

Myasthenia gravis (MG) is a chronic autoimmune disorder of the neuromuscular junction characterised by an autoantibody against acetylcholine receptor (AChR-Ab), autoantibody against muscle-specific kinase (MuSK-Ab), lipoprotein-related protein 4 or agrin in the postsynaptic membrane at the neuromuscular junction. Many patients are resistant to conventional treatment and effective therapies are needed. Rituximab (RTX) is a monoclonal antibody directed against CD20 antigen on B cells which has been successfully employed in anti-MuSK-Ab+MG, but the efficacy in anti-AChR-Ab+MG is still debated. The purpose of this systematic review was to describe the best evidence for RTX in the acetylcholine receptor subtype. The authors undertook a literature search during the period of 1999–2019 according to the Preferred Reporting Items for Systematic Reviews and Meta-Analys methodology, employing (myasthenia)+(gravis)+(RTX) as search terms. The analysis was confined to studies that include at least five patients with confirmed anti-AChR-Ab+MG. Thirteen studies have been selected, showing a good safety. The data obtained were heterogeneous in terms of posology, administration scheme and patients’ evaluation, ranging from a minimum of two to a maximum of three cycles. RTX led to a sustained clinical improvement with prolonged time to relapse, in parallel to a reduction or discontinuation of other immunosuppressive therapies. Treatment with RTX appears to work in some but not all patients with anti-AChR-Ab+MG, but randomised controlled trials are needed. Future studies should take into account the subtype of MG and employ reliable measures of outcome and severity focusing on how to identify patients who may benefit from the treatment. Trial registration number: NCT02110706.

scholarly journals Asynchronous assembly of the acetylcholine receptor and of the 43-kD nu1 protein in the postsynaptic membrane of developing Torpedo marmorata electrocyte.

1989 ◽  
Vol 108 (1) ◽  
pp. 127-139 ◽  
Author(s):  
E Kordeli ◽  
J Cartaud ◽  
H O Nghiêm ◽  
A Devillers-Thiéry ◽  
J P Changeux
Keyword(s):  
Plasma Membrane ◽  
Acetylcholine Receptor ◽  
Postsynaptic Membrane ◽  
Synaptic Membrane ◽  
Asymmetric Distribution ◽  
Subsequent Stage ◽  
Torpedo Marmorata ◽  
Intracellular Compartments ◽  
Membrane Compartments

The assembly of the nicotinic acetylcholine receptor (AchR) and the 43-kD protein (v1), the two major components of the post synaptic membrane of the electromotor synapse, was followed in Torpedo marmorata electrocyte during embryonic development by immunocytochemical methods. At the first developmental stage investigated (45-mm embryos), accumulation of AchR at the ventral pole of the newly formed electrocyte was observed within columns before innervation could be detected. No concomitant accumulation of 43-kD immunoreactivity in AchR-rich membrane domains was observed at this stage, but a transient asymmetric distribution of the extracellular protein, laminin, which paralleled that of the AchR, was noticed. At the subsequent stage studied (80-mm embryos), codistribution of the two proteins was noticed on the ventral face of the cell. Intracellular pools of AchR and 43-kD protein were followed at the EM level in 80-mm electrocytes. AchR immunoreactivity was detected within membrane compartments, which include the perinuclear cisternae of the endoplasmic reticulum and the plasma membrane. On the other hand, 43-kD immunoreactivity was not found associated with the AchR in the intracellular compartments of the cell, but codistributed with the AchR at the level of the plasma membrane. The data reported in this study suggest that AchR clustering in vivo is not initially determined by the association of the AchR with the 43-kD protein, but rather relies on AchR interaction with extracellular components, for instance from the basement membrane, laid down in the tissue before the entry of the electromotor nerve endings.

scholarly journals The structural dynamics of macropinosome formation and PI3-kinase-mediated sealing revealed by lattice lightsheet microscopy

2020 ◽  
Author(s):  
Shayne Quinn ◽  
Lu Huang ◽  
Jason Kerkvliet ◽  
Joel Swanson ◽  
Steve Smith ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Phosphatidylinositol 3 Kinase ◽  
Membrane Ruffling ◽  
Pi3k Activity ◽  
Intracellular Organelles ◽  
Early Production ◽  
A Minor ◽  
Pharmacologic Inhibition

Abstract Macropinosomes are formed by shaping actin-rich plasma membrane ruffles into large intracellular organelles in a phosphatidylinositol 3-kinase (PI3K)-coordinated manner. Here, we utilize lattice lightsheet microscopy and image visualization methods to map the three-dimensional structure and dynamics of macropinosome formation relative to PI3K activity. We show that multiple ruffling morphologies produce macropinosomes and that the majority form through non-specific collisions of adjacent PI3K-rich ruffles. By combining multiple volumetric representations of the plasma membrane structure and PI3K products, we show that PI3K activity begins early throughout the entire ruffle volume and continues to increase until peak activity concentrates at the base of the ruffle after the macropinosome closes. Additionally, areas of the plasma membrane rich in ruffling had increased PI3K activity and produced many macropinosomes of various sizes. Pharmacologic inhibition of PI3K activity had little effect on the rate and morphology of membrane ruffling, demonstrating that early production of 3'-phosphoinositides within ruffles plays a minor in regulating their morphology. However, 3'-phosphoinositides are critical for the fusogenic activity that seals ruffles into macropinosomes. Taken together these data indicate that local PI3K activity is amplified in ruffles and serves as a priming mechanism for closure and sealing of ruffles into macropinosomes.

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