Fig. 6. β1 integrins are required for EC adhesion and migration in a matrix-specific manner. Analysis of immortalized embryonic Itgb1^flox/flox ECs (A,B) or primary embryonic ECs (C-J). (A) Adhesion of adenovirus (Ad)-infected embryonic Itgb1^flox/flox ECs in serum-free medium after 30 minutes. Microplate coating concentrations were: fibronectin (FN), 20 nM; laminin (LM), 25 nM; collagen I (Col I), 55 nM; collagen IV (Col IV), 40 nM; Matrigel (MG), 125 µg/ml; vitronectin (VN), 20 nM. (B) Haptotactic migration of embryonic Itgb1^flox/flox ECs in serum-free medium after 4 hours. The ECM that served as the stimulus for migration was coated to the underside of a filter at the following concentrations: FN, 40 nM; LM, 50 nM; MG, 500 µg/ml; VN, 20 nM. (C) Cell spreading after 20 hours of culture. (D) Migration speed measured over 24 hours (fibronectin) or 14 hours (laminin) by timelapse videomicroscopy. (E-H) Representative migration tracks along with a phase-contrast image overlaid with DiI-Ac-LDL uptake fluorescence. Units on migration tracks are pixels. Coating concentrations were: fibronectin, 40 nM; laminin, 15 nM. Focal adhesion formation in control (I) and mutant (J) embryonic ECs on fibronectin as assessed by anti-FAK^pY397 (green), anti-CD31 (red) and DAPI (blue) staining. Values in A and B are means + s.d., and in C and D are means + s.e.m. ^**P<0.01 and ^*P<0.05 by Student's t-test. All experiments were performed at least twice and representative results are shown. Scale bars: 20 µm.