MuSK, a muscle-specific receptor tyrosine kinase that is activated by agrin, has a critical role
in neuromuscular synapse formation. In cultured myotubes, agrin stimulates the rapid
phosphorylation of MuSK, leading to MuSK activation and tyrosine phosphorylation and
clustering of acetylcholine receptors. Agrin, however, fails to stimulate tyrosine
phosphorylation of MuSK that is force-expressed in myoblasts and fibroblasts, indicating that
myotubes contain an additional activity that is required for agrin to stimulate MuSK. Certain …