We have obtained clear images of the erythrocyte membrane skeleton from negatively stained preparations that originate directly from the intact cell but in which the spectrin meshwork is artificially spread to allow close inspection. Our procedure requires less than 2 min at 50C in phosphate buffers. We flnd 200-nm-long spectrin tetramers crosslinked by junctional complexes. Each junction contains a regular 37-nm rod, probably an actin oligomer of approximately 13 monomers. Densities appear at variable places in the meshwork but distinct globules occur with great frequency 78 nm from the spectrin tetramer's junctional insertion end, very close to the known binding site for ankyrin. Most frequently, five or six spectrin tetramers insert into each junction, producing a meshwork that displays remarkably regular long range order.head end of the spectrin molecules but preserve the associations with actin and band 4.1 at the tail end of spectrin have also been performed (11). The resultant electron micrographs showed fragments containing variable-length actin filaments and globules from which several convoluted filaments of spectrin projected.Although some of the earliest microscopic images of the intact erythrocyte membrane skeleton were obtained by negative staining (1, 2), in only one micrograph published by Pinder et al. (12) can one see individual spectrin tetramers and fragmentary hints of the band 4. 1-actin oligomer junctions. We have now obtained clear images of the spectrin meshwork from negatively stained preparations that originate directly from the intact cell but in which the spectrin filaments are artificially spread to allow close inspection.Electron micrographs of the isolated mammalian erythrocyte cytoskeleton have demonstrated the existence of a continuous reticulum underlying the membrane (1, 2) but have not provided high-resolution information about the details of the structure and connections within this membrane skeleton. Although aspects of the skeleton have been visualized in thin sections of the erythrocyte ghost (3, 4), a major problem when examining the intact erythrocyte membrane or its skeleton is that the high density of proteins makes it very difficult to visualize the individual macromolecules and their connections.The erythrocyte membrane skeleton is believed to consist of a cross-linked meshwork consisting of spectrin, actin, band 4.1, and other associated proteins. Two linkages are viewed as essential for the integrity of this meshwork: first, spectrin heterodimers must associate head to head to form tetramers and, second, tail ends of the tetramers must crosslink the meshwork by binding to junctions that include short actin oligomers and band 4.1 protein. This view of the membrane skeleton has come from studying individual purified molecules and their modes of association in vitro (5-9). While these studies have told us much about the shapes of the individual molecules and the affinities and positions of their binding sites, evidence that the assemblies that have been crea...

No abstract

Transcription of the 2.5 megabase dystrophin gene gives rise to multiple isoforms. We describe a 5.2 kilobase transcript, expressed specifically in peripheral nerve, that initiates at a previously unrecognized exon located approximately 850 basepairs upstream of dystrophin exon 56. The likely product of this transcript (Dp116) is detected by C-terminal dystrophin antibodies exclusively in peripheral nerve and cultured Schwann cells. Dp116 is located along the Schwann cell membrane but is not present in the compact myelin lamellae or in axons. Dp116 lacks actin-binding and spectrin-like rod domains, arguing that it functions differently in the Schwann cell than does the major dystrophin transcript in muscle.

Abstract. We use a highly specific and sensitive antibody to further characterize the distribution of dystrophin in skeletal, cardiac, and smooth muscle . No evidence for localization other than at the cell surface is apparent in skeletal muscle and no 427-kD dystrophin labeling was detected in sciatic nerve . An elevated concentration of dystrophin appears at the myotendinous junction and the neuromuscular junction, labeling in the latter being more intense specifically in the troughs of the synaptic folds. In cardiac muscle the distribution of dystrophin is limited to the surface plasma membrane but is notably absent from the membrane that overlays adherens junctions of the intercalated disks. In smooth muscle, the plasma membrane labeling is considerably less abundant than in cardiac or skeletal