title: The carboxyl-terminal region of Dok-7 plays a key, but not essential, role in activation of muscle-specific receptor kinase MuSK and neuromuscular synapse formation.
abstract: As the synapse between a motor neuron and skeletal muscle, the neuromuscular junction (NMJ) is required for muscle contraction. The formation and maintenance of NMJs are controlled by the muscle-specific receptor kinase MuSK. Dok-7 is the essential cytoplasmic activator of MuSK, and indeed mice lacking Dok-7 form no NMJs. Moreover, DOK7 gene mutations underlie DOK7 myasthenia, an NMJ synaptopathy. Previously, we failed to detect MuSK activation in myotubes by Dok-7 mutated in the N-terminal pleckstrin homology (PH) or phosphotyrosine binding (PTB) domain or that lacked the C-terminal region (Dok-7-ΔC). Here, we found by quantitative analysis that Dok-7-ΔC marginally, but significantly, activated MuSK in myotubes, unlike the PH- or PTB-mutant. Purified, recombinant Dok-7-ΔC, but not other mutants, also showed marginal ability to activate MuSK's cytoplasmic portion, carrying the kinase domain. Consistently, forced expression of Dok-7-ΔC rescued Dok-7-deficient mice from neonatal lethality caused by the lack of NMJs, indicating restored MuSK activation and NMJ formation. However, these mice showed only marginal activation of MuSK and died by 3 weeks of age apparently due to an abnormally small number and size of NMJs. Thus, Dok-7's C-terminal region plays a key, but not fully essential, role in MuSK activation and NMJ formation.
authors.affiliation: Division of Genetics, Department of Cancer Biology.
authors.forename: Ryo
authors.initials: R
authors.lastname: Ueta
authors.affiliation: Division of Genetics, Department of Cancer Biology.
authors.forename: Tohru
authors.initials: T
authors.lastname: Tezuka
authors.affiliation: Division of Genetics, Department of Cancer Biology.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Izawa
authors.affiliation: Division of Genetics, Department of Cancer Biology.
authors.forename: Sadanori
authors.initials: S
authors.lastname: Miyoshi
authors.affiliation: Department of Bioengineering, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.|Drug Discovery Initiative, The University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Satoru
authors.initials: S
authors.lastname: Nagatoishi
authors.affiliation: Department of Bioengineering, School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan.|Drug Discovery Initiative, The University of Tokyo, Tokyo 113-0033, Japan.|Laboratory of Medical Proteomics, The Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tsumoto
authors.affiliation: Division of Genetics, Department of Cancer Biology.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Yamanashi
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051379:Mice; D009124:Muscle Proteins / Q000737:chemistry* / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000201:enzymology* / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*
chemical_list: C511694:Dok-7 protein, mouse; D009124:Muscle Proteins; C511695:MuSK protein, mouse; D020794:Receptor Protein-Tyrosine Kinases
keywords: Dok-; MuSK; myasthenia; neuromuscular junction; skeletal muscle