MuSK: A Kinase Critical for the Formation and Maintenance of the Neuromuscular Junction

Muscle-specific kinase (MuSK) is a RTK that is specifically expressed in skeletal muscle fibers and critical for the formation and maintenance of the neuromuscular junction (NMJ), a peripheral synapse formed between motoneurons and muscle fibers (1, 2). The acetylcholine receptors (AChRs) are concentrated at the crest of junctional folds on muscle fibers, critical for muscle contraction. Impaired NMJ formation or function inflicts muscular dystrophy. Being large and accessible, this peripheral synapse has served as a classic model of synapse function and synaptogenesis and has contributed a great deal to the understanding of molecular mechanisms of synapse formation in the brain. In this chapter, we will review the structures of MuSK in various vertebrates, its role in NMJ formation and maintenance, possible pathways that have been suggested by recent studies, and how MuSK may be a target in muscular dystrophy.