The spectrin-based skeleton at the postsynaptic membrane of the neuromuscular junction

Membrane skeletons, in particular the spectrin-based skeleton, are thought to participate in the organization of specialized membrane domains by restr icting integral proteins to specific membrane sites. In the neuromuscular j unction, discrete isoforms of spectrin and ankyrin, the peripheral protein that links spectrin to the membrane, colocalize with voltage-dependent sodi um channels and N-CAM at the troughs of the postsynaptic membrane folds. Mo reover, beta-spectrin, N-CAM, and sodium channels become clustered at the e ndplate during a period of time coincident with postsynaptic fold formation and synapse maturation. These observations suggest a role of the spectrin skeleton in directing and maintaining postsynaptic accumulations of sodium channels and N-CAM. In addition, the coexistence of spectrin and dystrophin at the troughs of the junctional folds raises the question of their respec tive functions in this membrane domain, where both cytoskeletal proteins ha ve the potential to associate with sodium channels via ankyrin and syntroph in, respectively. Possible scenarios are discussed here with respect to acc umulating evidence from studies of assembly of similar membrane domains in neurons. Microsc. Res. Tech. 49: 101-107, 2000. (C) 2000 Wiley-Liss, Inc.