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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.

Using the technique of time-of-flight mode impact-collision ion-scattering-spectroscopy, we have studied the structure of two kinds of Ag thin films deposited onto Si(111)7×7 substrates. We have shown that (1) the RT deposited Ag thin film of 10 ML thickness consists of type-A and type-B domains of Ag(111), with type-B being rotated 180° about the surface normal, (2) the experimental ICISS angle scans for the Si(111)√3×√3R30°-Ag surface cannot be explained by the embedded-Ag model proposed so far, (3) the Ag honeycomb structure residing on top of Si is unlikely for the √3 × √3-Ag surface, and (4) both the Ag-trimer and the HCT model, residing on top of Si are more likely, though a clear preference between these two models has not been obtained as yet.