Dok-7 regulates neuromuscular synapse formation by recruiting Crk and Crk-L

• Published in: Genes & development 2010-11, Vol.24 (21), p.2451-2461
• Main Authors: Hallock, Peter T, Xu, Chong-Feng, Park, Tae-Ju, Neubert, Thomas A, Curran, Tom, Burden, Steven J
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Agrin - pharmacology; Animals; Blotting, Western; Cell Line; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; HEK293 Cells; Humans; Mice; Mice, Knockout; Microscopy, Confocal; Muscle Fibers, Skeletal - cytology; Muscle Fibers, Skeletal - drug effects; Muscle Fibers, Skeletal - metabolism; Muscle Proteins - genetics; Muscle Proteins - metabolism; Muscle, Skeletal - embryology; Muscle, Skeletal - metabolism; Mutation; Neuromuscular Junction - metabolism; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Phosphorylation - drug effects; Proto-Oncogene Proteins c-crk - genetics; Proto-Oncogene Proteins c-crk - metabolism; Receptor Protein-Tyrosine Kinases - genetics; Receptor Protein-Tyrosine Kinases - metabolism; Receptors, Cholinergic - genetics; Receptors, Cholinergic - metabolism; Research Paper; Synapses - metabolism; Time Factors; Tyrosine - genetics; Tyrosine - metabolism
• ISSN: 0890-9369; 1549-5477
• DOI: 10.1101/gad.1977710

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.