Fig. 3. Ligand binding to the extracellular domain of β1 integrin is required for RhoA activation and fibronectin fibrillogenesis. (A) GE11 cells expressing indicated β1 integrin subunits stained for paxillin (green), F-actin (red). Nuclei are stained blue with Topro-3. Scale bar: 10 µm. (B) Western blot analysis of RhoA activity assay on lysates of GE11 cells expressing indicated β1 integrin subunits. Quantification shows relative RhoA activation ± s.d. compared with GEβ1 cells from two experiments. (C) Assembled fibronectin-biotin on GE11 cells expressing indicated β1 integrin subunits; fibronectin is red and nuclei are blue. Scale bar: 50 µm. (D) Mean fluorescence analyzed by flow cytometry, demonstrating binding of indicated integrins to different concentrations of soluble FITC-fibronectin.