Regulation and function of CLIP-170/CLASP2-dependent microtubule stabilization at the postsynaptic membrane of the neuromuscular junction. (a) Working model summarizing the role of neural agrin to capture MTs at the postsynaptic membrane of the NMJ. Agrin-induced MT capturing at AChR clusters is regulated through: (1) local GSK3β inactivation promoting the recruitment of unphosphorylated CLASP2 to MT plus-ends and lattice; (2) recruitment of CLIP-170 through CLIP/CLASP and CLIP/MT interactions; (3) local, PI3-K–dependent recruitment and immobilization of LL5β in the synaptic membrane. Molecules and their interactions inferred from work published in other systems rather than from present data in muscle cells are marked by broken symbols. (b) At developing NMJs, constitutively expressed synaptic AChRs are delivered to synaptic membrane by lateral diffusion in the plane of the cell membrane (arrows). At adult NMJs, MTs stabilized by mechanisms outlined in panel a ensure focal delivery of synaptic AChRs to the crests of synaptic folds. Cartoon in panel b is modified from Ruegg, 2005.