Dok-7 regulates neuromuscular synapse formation by recruiting Crk and Crk-L
- Peter T. Hallock1,
- Chong-Feng Xu2,
- Tae-Ju Park3,
- Thomas A. Neubert2,
- Tom Curran3 and
- Steven J. Burden1,4
- 1Molecular Neurobiology Program, Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA;
- 2Structural Biology Program, Skirball Institute of Biomolecular Medicine, New York University Medical School, New York, New York 10016, USA;
- 3Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia, Boulevard, Philadelphia, Pennsylvania 19104, USA
Abstract
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.
Keywords
- Neuromuscular synapse
- acetylcholine receptor
- congenital myasthenia
- receptor tyrosine kinase
- synapse formation
- mouse development
Footnotes
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↵4 Corresponding author.
E-MAIL burden{at}saturn.med.nyu.edu; FAX (212) 263-8214.
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Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.1977710.
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Supplemental material is available at http://www.genesdev.org.
- Received August 3, 2010.
- Accepted September 10, 2010.
- Copyright © 2010 by Cold Spring Harbor Laboratory Press