Figure 4.

Analysis of the spreading and assembly of focal adhesions and actin stress fibers by FN−/− fibroblasts. The degree of spreading is seen from the Nomarski micrographs. Focal adhesions are visualized with the vinculin staining and actin stress fibers by means of tetramethyl rhodamine isothiocyanate–phalloidin staining. (A) FN−/− fibroblasts plated on fibronectin. The cells are fully spread. They have assembled focal adhesions and actin stress fibers. (B–E) FN−/− fibroblasts plated on the 120-kDa cell-binding domain of fibronectin. Cell spreading and assembly of focal adhesions and actin stress fibers are present in cells supplemented with the 40-kDa heparin-binding domain of fibronectin (C) or supplemented with antibodies directed against the ectodomain of mouse syndecan-4 (D) but absent in unsupplemented cells (B) or in cells supplemented with IgG (E). (F and G) FN−/− fibroblasts plated on rat monoclonal antibody directed against mouse β1 integrin chains. Cell spreading and assembly of focal adhesions and actin stress fibers are present in cells supplemented with antibodies directed against the ectodomain of mouse syndecan-4 (F) but not in those supplemented with IgG (G). (H and I) FN−/− fibroblasts plated on polylysine. No assembly of focal adhesions and actin stress fibers is evident in cells supplemented either with antibodies directed against the ectodomain of mouse syndecan-4 (H) or with IgG (I).