Neuromuscular junction is a synapse between motoneurons and skeletal muscles, where acetylcholine receptors (AChRs) are concentrated to control muscle contraction. Studies of this synapse have contributed to our understanding of synapse assembly and pathological mechanisms of neuromuscular disorders. Nevertheless, underlying mechanisms of NMJ formation was not well understood. To this end, we took a novel approach - studying mutant genes implicated in congenital myasthenic syndrome (CMS). We showed that knock-in mice carrying N88K, a prevalent CMS mutation of Rapsyn (Rapsn), died soon after birth with profound NMJ deficits. Rapsn is an adapter protein that bridges AChRs to the cytoskeleton and possesses E3 ligase activity. In investigating how N88K impairs the NMJ, we uncovered a novel signaling pathway by which Agrin-LRP4-MuSK induces tyrosine phosphorylation of Rapsn, which is required for its self-association and E3 ligase activity. Our results also provide insight into pathological mechanisms of CMS.
All data generated or analysed during this study are included in the manuscript and supporting files. Source data about statistical results are provided in excel files, including Figures 1E-J, 2E-H, 2M, 2N, 3A, 3B, 3D, 3E, 4B, 4F, 5D, 5F, 5H, 6D, 6G, 6I, 7B, 7F, 7H, 7J, 7L, 7N, 8B, 8C, 8D, ; Figure 1-figure supplement 1C, 1E, 1H, Figure 4-figure supplement 1B, Figure 4-figure supplement 2B and 2D, Figure 5-figure supplement 1D, Figure 7-figure supplement 1C and E.
- Lin Mei
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Animal experimentation: This study was performed in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All of the animals were handled according to approved institutional animal care and use committee (IACUC) protocols (2017-0115) of the University of Case Western Reserve University. Animal protocols have been approved by the Institutional Animal Care and Use Committee of Case Western Reserve University.
- Gary L Westbrook, Oregon Health and Science University, United States
© 2019, Xing et al.
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