title: Essential roles of the acetylcholine receptor gamma-subunit in neuromuscular synaptic patterning.
abstract: Formation of the vertebrate neuromuscular junction (NMJ) takes place in a stereotypic pattern in which nerves terminate at select sarcolemmal sites often localized to the central region of the muscle fibers. Several lines of evidence indicate that the muscle fibers may initiate postsynaptic differentiation independent of the ingrowing nerves. For example, nascent acetylcholine receptors (AChRs) are pre-patterned at select regions of the muscle during the initial stage of neuromuscular synaptogenesis. It is not clear how these pre-patterned AChR clusters are assembled, and to what extent they contribute to pre- and post-synaptic differentiation during development. Here, we show that genetic deletion of the AChR gamma-subunit gene in mice leads to an absence of pre-patterned AChR clusters during initial stages of neuromuscular synaptogenesis. The absence of pre-patterned AChR clusters was associated with excessive nerve branching, increased motoneuron survival, as well as aberrant distribution of acetylcholinesterase (AChE) and rapsyn. However, clustering of muscle specific kinase (MuSK) proceeded normally in the gamma-null muscles. AChR clusters emerged at later stages owing to the expression of the AChR epsilon-subunit, but these delayed AChR clusters were broadly distributed and appeared at lower level compared with the wild-type muscles. Interestingly, despite the abnormal pattern, synaptic vesicle proteins were progressively accumulated at individual nerve terminals, and neuromuscular synapses were ultimately established in gamma-null muscles. These results demonstrate that the gamma-subunit is required for the formation of pre-patterned AChR clusters, which in turn play an essential role in determining the subsequent pattern of neuromuscular synaptogenesis.
authors.affiliation: Department of Neuroscience, UT Southwestern Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75235-9111, USA.
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
authors.forename: Daniel
authors.initials: D
authors.lastname: Padgett
authors.forename: Masazumi
authors.initials: M
authors.lastname: Takahashi
authors.forename: Hongqiao
authors.initials: H
authors.lastname: Li
authors.forename: Ayaz
authors.initials: A
authors.lastname: Sayeed
authors.forename: Russell W
authors.initials: RW
authors.lastname: Teichert
authors.forename: Baldomero M
authors.initials: BM
authors.lastname: Olivera
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: McArdle
authors.forename: William N
authors.initials: WN
authors.lastname: Green
authors.forename: Weichun
authors.initials: W
authors.lastname: Lin
mesh_terms: D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D002470:Cell Survival / Q000235:genetics / Q000502:physiology; D004594:Electrophysiology; D007150:Immunohistochemistry; D051379:Mice; D008817:Mice, Mutant Strains; D009046:Motor Neurons / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000196:embryology / Q000378:metabolism; D009469:Neuromuscular Junction / Q000196:embryology / Q000235:genetics / Q000378:metabolism*; D038081:Organogenesis / Q000235:genetics / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D009124:Muscle Proteins; D011950:Receptors, Cholinergic; C051609:peripheral membrane protein 43K; C511695:MuSK protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D000110:Acetylcholinesterase