Experimental Cell Research 163 (1986) 143-150 Talin Is a Post-synaptic Component of the Rat Neuromuscular Junction ROBERT SEALOCK,‘, * BRYCE PASCHAL,2’ ** MARY BECKERLE2 and KEITH BURRIDGE2 ‘Department of Physiology and ‘Department of Anatomy, University of North Carolina, Chapel Hill, NC 27514, USA Talin is a protein, recently discovered in chicken gizzard, which occurs at sites of actin-plasma membrane interaction in several cell types. Vinculin also occurs at many of these sites, possibly in association with talin. In this study, three antisera against talin were used to probe the neuromuscular junction of rat skeletal muscle, which is also a site of vinculin accumulation. By immunofluorescence, all three sera stained the junction strongly in frozen sections of rat diaphragm. The extrajunctional periphery was lightly and irregu- larly stained in some muscle cells; others seemed not to be stained outside the junction. Staining remained at junctions and increased in extrajunctional regions of muscle denervat- ed 6 weeks before sacrifice. The staining in all cases was abolished by competition with purified talin. One serum tested by immunoblotting recognized one protein at M, 215000 (identical with the value for chicken gizzard talin) and traces of a second at M, 190000 (corresponding to a known proteolytic fragment of talin). We conclude that rat muscle talin is similar in its general protein structure to chicken gizzard talin, and is a post-synaptic Component of the neuromuscular junction. @ 1986 Academic Press, IX. The neuromuscular junction in skeletal muscle is a site of cell-cell contact involving remarkably specialized regions of the two participating cells. On the post-synaptic (muscle) side, the specializations include extensive infoldings of the plasma membrane (junctional folds) (e.g., [l]), large aggregates or plaques of acetylcholine receptors at the tops of the folds (i.e., nearest the nerve terminal) [2], and concentrations of several cytoskeletal proteins. The latter include a non- sarcomeric form of actin [3] and vinculin, a-actinin, and filamin [4]. In other cells, vinculin is concentrated at sites of interaction of actin filaments (stress fibers) with the plasma membrane [5-71. Since it lies particularly close to the cytoplas- mic surface of the membrane [8], vinculin is believed to be a key component in the attachment of the filaments to the membrane and in their organization, and, hence, in the organization of the plasma membrane itself (reviewed in [9-l 11). Its role at the neuromuscular junction is presumably similar, although no role for any of the cytoskeletal proteins at the junction has been established. Talin is a large intracellular protein (M, 215 000) recently isolated fromchicken gizzard [12, 131. Its functions are largely unknown. It is, however, distributed coextensively with vinculin (as determined by immunofluorescence) at focal * To whom offprint requests should be sent. ** Present address: Department of Cell Biology, Uni- versity of Massachusetts Medical School, Worcester, MA 01604, USA. lo-868333 Copyright @ 1986 by Academic Ress, Inc. All rights of reproduction in any form reserved 0014-4827/86 $03.00