title: Identity, developmental restriction and reactivity of extralaminar cells capping mammalian neuromuscular junctions.
abstract: Neuromuscular junctions (NMJs) are normally thought to comprise three major cell types: skeletal muscle fibres, motor neuron terminals and perisynaptic terminal Schwann cells. Here we studied a fourth population of junctional cells in mice and rats, revealed using a novel cytoskeletal antibody (2166). These cells lie outside the synaptic basal lamina but form caps over NMJs during postnatal development. NMJ-capping cells also bound rPH, HM-24, CD34 antibodies and cholera toxin B subunit. Bromodeoxyuridine incorporation indicated activation, proliferation and spread of NMJ-capping cells following denervation in adults, in advance of terminal Schwann cell sprouting. The NMJ-capping cell reaction coincided with expression of tenascin-C but was independent of this molecule because capping cells also dispersed after denervation in tenascin-C-null mutant mice. NMJ-capping cells also dispersed after local paralysis with botulinum toxin and in atrophic muscles of transgenic R6/2 mice. We conclude that NMJ-capping cells (proposed name 'kranocytes') represent a neglected, canonical cellular constituent of neuromuscular junctions where they could play a permissive role in synaptic regeneration.
authors.affiliation: Euan MacDonald Centre for Motor Neurone Disease Research, The University of Edinburgh, 1 George Square, Edinburgh EH8 9JZ, UK.
authors.forename: Felipe A
authors.initials: FA
authors.lastname: Court
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Gillingwater
authors.forename: Shona
authors.initials: S
authors.lastname: Melrose
authors.forename: Diane L
authors.initials: DL
authors.lastname: Sherman
authors.forename: Kay N
authors.initials: KN
authors.lastname: Greenshields
authors.forename: A Jennifer
authors.initials: AJ
authors.lastname: Morton
authors.forename: John B
authors.initials: JB
authors.lastname: Harris
authors.forename: Hugh J
authors.initials: HJ
authors.lastname: Willison
authors.forename: Richard R
authors.initials: RR
authors.lastname: Ribchester
mesh_terms: D000818:Animals; D001485:Basement Membrane / Q000166:cytology / Q000648:ultrastructure; D049109:Cell Proliferation; D002478:Cells, Cultured; D007150:Immunohistochemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D009046:Motor Neurons / Q000378:metabolism; D009469:Neuromuscular Junction / Q000166:cytology* / Q000378:metabolism / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012583:Schwann Cells / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure