DISSMANN E, Hinssen H. IMMUNOCYTOCHEMICAL LOCALIZATION OF GELSOLIN IN FIBROBLASTS, MYOGENIC CELLS, AND ISOLATED MYOFIBRILS. EUROPEAN JOURNAL OF CELL BIOLOGY. 1994;63(2):336-344.Gelsolin was localized by immunofluorescence in fibroblasts and skeletal muscle cells using antibodies which eliminated the risk of detecting xenogenic plasma gelsolin. Gelsolin was consistently found to be closely associated with the elements of the microfilament system: In fibroblasts, a preferential labeling of the stress fibers was observed, whereas with myogenic cells and myofibrils isolated from skeletal muscle, a specific staining of the I-Z-I region in the sarcomeres was found. From double labeling of gelsolin and actin it became evident that the staining patterns for both proteins were practically coincident: The width and location of the fluorescent bands varied with the degree of contraction of the myofibrils. The region of cross-bridges in the A-zone, where thick and thin filaments overlap, remained unstained. The gelsolin staining of myofibrils was EGTA-resistant; it persisted after glycerol extraction and extensive washing. The presence of gelsolin in myofibrils after this treatment was also confirmed by immunoblotting. From these observations it was concluded that a significant part of the total gelsolin in skeletal muscle cells is tightly associated with the thin filaments, and is an integral part of the myofibrils even at low Ca++-concentrations. Fmom the coincidence of actin and gelsolin staining in myofibrils it was concluded that gelsolin is localized along the whole length of the thin filaments in the sarcomere. Such a mode of association with filamentous actin is not fully explained by the current models of interaction of gelsolin with F-actin which involve either a filament severing or a capping of the ends of actin filaments rather than a stable lateral binding to the filaments without severing. It is assumed that, in myofibrils, actin-binding proteins like tropomyosin and nebulin inhibit the severing process but not the binding of gelsolin
