title: Mechanism of acetylcholine receptor cluster formation induced by DC electric field.
abstract: BACKGROUND
  The formation of acetylcholine receptor (AChR) cluster is a key event during the development of the neuromuscular junction. It is induced through the activation of muscle-specific kinase (MuSK) by the heparan-sulfate proteoglycan agrin released from the motor axon. On the other hand, DC electric field, a non-neuronal stimulus, is also highly effective in causing AChRs to cluster along the cathode-facing edge of muscle cells.
  
  
  RESULTS
  To understand its molecular mechanism, quantum dots (QDs) were used to follow the movement of AChRs as they became clustered under the influence of electric field. From analyses of trajectories of AChR movement in the membrane, it was concluded that diffuse receptors underwent Brownian motion until they were immobilized at sites of cluster formation. This supports the diffusion-mediated trapping model in explaining AChR clustering under the influence of this stimulus. Disrupting F-actin cytoskeleton assembly and interfering with rapsyn-AChR interaction suppressed this phenomenon, suggesting that these are integral components of the trapping mechanism induced by the electric field. Consistent with the idea that signaling pathways are activated by this stimulus, the localization of tyrosine-phosphorylated forms of AChR β-subunit and Src was observed at cathodal AChR clusters. Furthermore, disrupting MuSK activity through the expression of a kinase-dead form of this enzyme abolished electric field-induced AChR clustering.
  
  
  CONCLUSIONS
  These results suggest that DC electric field as a physical stimulus elicits molecular reactions in muscle cells in the form of cathodal MuSK activation in a ligand-free manner to trigger a signaling pathway that leads to cytoskeletal assembly and AChR clustering.
authors: Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
authors: Hailong Luke
authors: HL
authors: Zhang
authors: H Benjamin
authors: HB
authors: Peng
mesh_terms: D018171:Agrin; D000818:Animals; D002478:Cells, Cultured; D004558:Electric Stimulation; D032342:Muscle Cells / Q000737:chemistry* / Q000166:cytology; D009469:Neuromuscular Junction / Q000737:chemistry*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D015398:Signal Transduction; D055672:Static Electricity; D014981:Xenopus; D029867:Xenopus Proteins / Q000378:metabolism*
chemical_list: D018171:Agrin; D011950:Receptors, Cholinergic; D029867:Xenopus Proteins; C570712:MuSK protein, Xenopus; D020794:Receptor Protein-Tyrosine Kinases