MuSK binds to BMPs and the BMP receptors ALK3 and ALK6 and regulates the transcriptional output of BMP signaling in muscle cells. MuSK regulation of BMP signaling is cell type-specific because BMP induced the expression of different sets of genes in myoblasts and myotubes in a manner that depended on MuSK. The kinase activity of MuSK, which is required for proper NMJ formation, is dispensable for MuSK-mediated regulation of BMP signaling. JM, juxta-membrane; TK, tyrosine kinase; CRD/Fz, CRD/frizzled-like domain.