Dok-7 regulates neuromuscular synapse formation by recruiting Crk and Crk-L.
Agrin, released by motor neurons, promotes neuromuscular synapse formation by stimulating MuSK, a receptor tyrosine kinase expressed in skeletal muscle. Phosphorylated MuSK recruits docking protein-7 (Dok-7), an adaptor protein that is expressed selectively in muscle. In the absence of Dok-7, neuromuscular synapses fail to form, and mutations that impair Dok-7 are a major cause of congenital myasthenia in humans. How Dok-7 stimulates synaptic differentiation is poorly understood. Once recruited to MuSK, Dok-7 directly stimulates MuSK kinase activity. This unusual activity of an adapter protein is mediated by the N-terminal region of Dok-7, whereas most mutations that cause congenital myasthenia truncate the C-terminal domain. Here, we demonstrate that Dok-7 also functions downstream from MuSK, and we identify the proteins that are recruited to the C-terminal domain of Dok-7. We show that Agrin stimulates phosphorylation of two tyrosine residues in the C-terminal domain of Dok-7, which leads to recruitment of two adapter proteins: Crk and Crk-L. Furthermore, we show that selective inactivation of Crk and Crk-L in skeletal muscle leads to severe defects in neuromuscular synapses in vivo, revealing a critical role for Crk and Crk-L downstream from Dok-7 in presynaptic and postsynaptic differentiation.
Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA.
Peter T
PT
Hallock
Chong-Feng
CF
Xu
Tae-Ju
TJ
Park
Thomas A
TA
Neubert
Tom
T
Curran
Steven J
SJ
Burden
D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D018171:Agrin / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism; D009154:Mutation; D009469:Neuromuscular Junction / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D050737:Proto-Oncogene Proteins c-crk / Q000235:genetics / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism; D013569:Synapses / Q000378:metabolism*; D013997:Time Factors; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; D018171:Agrin; C082869:CRKL protein; C476798:Crk protein, mouse; C511694:Dok-7 protein, mouse; D009124:Muscle Proteins; D009687:Nuclear Proteins; D050737:Proto-Oncogene Proteins c-crk; D011950:Receptors, Cholinergic; D049452:Green Fluorescent Proteins; D014443:Tyrosine; C511695:MuSK protein, mouse; D020794:Receptor Protein-Tyrosine Kinases