Agrin elicits membrane lipid condensation at sites of acetylcholine receptor clusters in C2C12 myotubes

Stetzkowski‐Marden, Françoise; Gaus, Katharina; Recouvreur, Michel; Cartaud, Annie; Cartaud, Jean

doi:10.1194/jlr.m600182-jlr200

Cited by 49 publications

(62 citation statements)

References 71 publications

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“…Cartaud et al suggested that raft lipid domains were involved in the sorting and subsequent delivery of AChR and rapsyn to the plasma membrane ( 16 ) and that AChR was constitutively associated with raft lipid domains together with syntrophin, rapsyn, and other postsynaptic components, independently of agrin stimulation ( 17 ). Agrin activation of MuSK was necessary, however, for inducing the coalescence of rafts and for AChR clustering.…”

Section: Preparation Of Achr Membranes Crude Achr-membranesmentioning

confidence: 99%

Partition profile of the nicotinic acetylcholine receptor in lipid domains upon reconstitution

Bermúdez

Antollini

Nievas

et al. 2010

Journal of Lipid Research

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tains a relatively large extracellular domain and four hydrophobic membrane-spanning segments referred to as M1-M4, ending in a short extracellular carboxyl terminal domain. Three concentric rings can be distinguished in the AChR transmembrane (TM) region ( 1, 2 ): the M2 TM segments of all subunits outline the inner ring and form the walls of the ion channel proper; M1 and M3 constitute the middle ring; and the M4 segments form the outer ring, which is in closest contact with the AChR lipid microenvironment.One outstanding characteristic of the mature neuromuscular junction (NMJ) is the high density of AChR clusters at the postsynaptic membrane ( 3 ). Neural agrin, an extracellular proteoglycan, initiates the cascade of events in the AChR clustering process in the myotubes by fi rst activating MuSK (muscle-specifi c receptor tyrosine kinase), which subsequently induces the activation of several other intracellular enzymes. Finally, association of AChR with rapsyn, a cytoplasmic peripheral membrane protein colocalized with AChR in vivo, mediates binding to the cytoskeleton ( 3, 4 ), leading in turn to effi cient receptor clustering ( 5 ). Lipids have been postulated to be involved in AChR nanodomain organization and clustering, presumably at early, preinnervation stages of development ( 6 ). The plasma membrane organization of living cells is currently considered to be a mosaic of macroscopic and stable or transient and short-scale segregated domains (reviewed by Ref. 7 ). Lipid domains termed lipid "rafts" are highly enriched in both cholesterol (Chol) and sphingolipids.Abstract The nicotinic acetylcholine receptor (AChR) is in intimate contact with the lipids in its native membrane. Here we analyze the possibility that it is the intrinsic properties of the AChR that determine its partition into a given lipid domain. Torpedo AChR or a synthetic peptide corresponding to the AChR ␥ M4 segment (the one in closer contact with lipids) was reconstituted into "raft "-containing model membranes. The distribution of the AChR was assessed by Triton X-100 extraction in combination with fl uorescence studies, and lipid analyses were performed on each sample. The infl uence of rapsyn, a peripheral protein involved in AChR aggregation, was studied. Raft -like domain aggregation was also studied using membranes containing the ganglioside GM1 followed by GM1 crosslinking. The ␥ M4 peptide displays a marked preference for raft -like domains. In contrast, AChR alone or in the presence of rapsyn or ganglioside aggregation exhibits no such preference for raft-like domains, but it does cause a signifi cant reduction in the total amount of these domains. The results indicate that the distribution of the AChR in lipid domains cannot be due exclusively to the intrinsic physicochemical properties of the protein and that there must be an external signal in native cell membranes that directs the AChR to a specifi c membrane domain. The nicotinic acetylcholine receptor (AChR) is a pentameric transmembrane glycoprotein composed of four dif...

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Section: Preparation Of Achr Membranes Crude Achr-membranesmentioning

confidence: 99%

Partition profile of the nicotinic acetylcholine receptor in lipid domains upon reconstitution

Bermúdez

Antollini

Nievas

et al. 2010

Journal of Lipid Research

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“…Rapsyn stability is increased at the synapse by the chaperone Hsp90b, and rapsyn interacts with and inhibits calpain, and thus antagonizes the AChR cluster-dispersing effect of ACh. Agrin signaling is regulated by Musk endocytosis, the E3 ubiquitin ligase Pdzrn3, lipid microdomains (Kishi et al, 2005;Stetzkowski-Marden et al, 2006;Willmann et al, 2006;Zhu et al, 2006) and intracellular calcium (Megeath and Fallon 1998). Many pathways illustrated here have been identified in cultured muscle and non-muscle cells, and their role in vivo remains to be studied.…”

Section: Lrp4 As An Agrin Co-receptormentioning

confidence: 99%

To build a synapse: signaling pathways in neuromuscular junction assembly

2010

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SummarySynapses, as fundamental units of the neural circuitry, enable complex behaviors. The neuromuscular junction (NMJ) is a synapse type that forms between motoneurons and skeletal muscle fibers and that exhibits a high degree of subcellular specialization. Aided by genetic techniques and suitable animal models, studies in the past decade have brought significant progress in identifying NMJ components and assembly mechanisms. This review highlights recent advances in the study of NMJ development, focusing on signaling pathways that are activated by diffusible cues, which shed light on synaptogenesis in the brain and contribute to a better understanding of muscular dystrophy. Key words: Neural development, Neuromuscular junction, Retrograde signaling, Synapse formation IntroductionThe brain contains billions of nerve cells, or neurons, which receive and integrate signals from the environment, and which govern the body's responses. Nervous system activity is made possible by synapses, contacts formed either between neurons or between a neuron and a target cell. Synapses are asymmetric structures in which neurotransmitter molecules are released from the presynaptic membrane and activate receptors on the postsynaptic membrane, thus establishing neuronal communication. As such, synapses are fundamental units of neural circuitry and enable complex behaviors. The neuromuscular junction (NMJ) is a type of synapse formed between motoneurons and skeletal muscle fibers. Large and easily accessed experimentally, this peripheral synapse has contributed greatly to the understanding of the general principles of synaptogenesis and to the development of potential therapeutic strategies for muscular disorders. The NMJ uses different neurotransmitters in different species; for example, acetylcholine (ACh) in vertebrates and glutamate in Drosophila, both of which are excitatory and cause muscle contraction. In Caenorhabditis elegans, there are two types of NMJs: at excitatory NMJs, ACh causes muscle contraction, whereas inhibitory NMJs release g-aminobutyric acid (GABA) to cause muscle relaxation. Motor nerve terminals differentiate to form presynaptic active zones, where synaptic vesicles dock and release neurotransmitters. On the apposed postsynaptic membranes, neurotransmitter receptors are packed at high densities. Aided by genetic techniques and by the use of suitable animal models, including rodents, zebrafish, Drosophila and C. elegans, studies in the past decade have brought significant progress, not only in identifying components present in pre-and postsynaptic membranes, but also in understanding the mechanisms that underpin NMJ assembly. This review highlights recent advances in the study of NMJ development, focusing on signaling pathways that are activated by diffusible cues from motor nerves and muscle fibers. Readers are referred to other outstanding reviews for a broad view of NMJ development (see Froehner, 1993;Hall and Sanes, 1993;Kummer et al., 2006;Salpeter and Loring, 1985;Schaeffer et al., 2001). NMJ formati...

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“…However, several receptors and transmembrane proteins of the postsynaptic density (PSD) purify with detergent-resistant membrane (DRM) fractions, indicating a possible association with lipid rafts. Examples of this are acetylcholine receptors (Stetzkowski-Marden et al, 2006; references in Allen et al, 2007), K ϩ channels (Wong and Schlichter, 2004), and glutamatergic receptors (Hering et al, 2003). Extrinsic membrane scaffolding proteins associated with excitatory synapses (GRIP, PSD-95) (Hering et al, 2003) are also purified in DRM fractions.…”

Section: Introductionmentioning

confidence: 99%

Control of the Postsynaptic Membrane Viscosity

Renner

Choquet²,

Triller³

2009

J. Neurosci.

139

154

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The physical properties of the postsynaptic membrane (PSM), including its viscosity, determine its capacity to regulate the net flux of synaptic membrane proteins such as neurotransmitter receptors. To address these properties, we studied the lateral diffusion of glycophosphatidylinositol-anchored green fluorescent protein and cholera toxin bound to the external leaflet of the plasma membrane. Relative to extrasynaptic regions, their mobility was reduced at synapses and even more at inhibitory than at excitatory ones. This indicates a higher density of obstacles and/or higher membrane viscosity at inhibitory contacts. Actin depolymerization reduced the confinement and accelerated a population of fast, mobile molecules. The compaction of obstacles thus depends on actin cytoskeleton integrity. Cholesterol depletion increased the mobility of the slow diffusing molecules, allowing them to diffuse more rapidly through the crowded PSM. Thus, the PSM has lipid-raft properties, and the density of obstacles to diffusion depends on filamentous actin. Therefore, lipid composition and actin-dependent protein compaction regulate viscosity of the PSM and, consequently, the molecular flow in and out of synapses.

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Agrin elicits membrane lipid condensation at sites of acetylcholine receptor clusters in C2C12 myotubes

Cited by 49 publications

References 71 publications

Partition profile of the nicotinic acetylcholine receptor in lipid domains upon reconstitution

Partition profile of the nicotinic acetylcholine receptor in lipid domains upon reconstitution

To build a synapse: signaling pathways in neuromuscular junction assembly

Control of the Postsynaptic Membrane Viscosity

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