DIRECT INVOLVEMENT OF A LAMIN-B-RELATED (54-KDA) PROTEIN IN THE ASSOCIATION OF INTERMEDIATE FILAMENTS WITH THE POSTSYNAPTIC MEMBRANE OF THETORPEDO-MARMORATA ELECTROCYTE

Mechanisms by which motor innervation induces postsynaptic membrane di fferentiation and functional compartmentalization of the subneural sar coplasm in skeletal muscle fibres are still poorly understood. However , transmembrane control of cytoskeletal activities by the nerve termin al may be considered. Here, we examine several properties of a 54 kDa protein, previously identified in the postsynaptic membrane of the Tor pedo marmorata electrocyte with anti-lamin B antibodies, in order to s tudy its role in the assembly of the subneural intermediate filament m eshwork. Using a ligand blot assay, we show that this protein binds de smin, a type III intermediate filaments protein, at micromolar concent rations. Moreover, purified acetylcholine receptor-rich membrane fragm ents are able to generate arrays of desmin filaments in vitro. Immuno- fluorescence experiments indicate that the 54 kDa protein becomes asso ciated with the acetylcholine receptor-rich membrane at an early stage of development of the electrocyte, and that a polarized desmin networ k develops concomitantly from the postsynaptic membrane. Taken togethe r, these data show that, like karyoskeletal iamin B, the 54 MDa protei n is involved in the organization of the subneural intermediate filame nt meshwork. Control of the assembly of the subneural cytoskeleton by components of the postsynaptic membrane may thus be a prerequisite for the functional compartmentalization of the muscle fibre triggered by motor innervation.