Ablation of Jam-A results in enhanced integrin outside-in signaling. (A) Photographs of clot retraction using washed Jam-A^wt/wt and Jam-A^gt/gt platelets. Quantitation of the percentage of clot retraction from 3 independent experiments. (B) Western blots of protein lysates from Jam-A^wt/wt and Jam-A^gt/gt platelets exposed for 1 hour to immobilized Fg or BSA and probed with anti-phospho-specific p38 or anti-p38, or anti-phospho-specific Erk2 or anti-Erk2, or anti-phospho–specific myosin light chain or anti–myosin light chain. Quantitation of normalized optical density of 3 independent experiments. (C) Western blots of protein lysates from panel A probed using anti-phospho–specific β₃Y⁷⁷³ or anti-β₃. Quantitation of normalized optical density of 3 independent experiments.