Platelets expressing talin1(W359A) exhibit partially impaired αIIbβ3 activation. (A-B) αIIbβ3-integrin activation (JON/A-PE binding) was measured in washed platelets isolated from mice with the indicated genotypes. Platelets were stimulated for 10 minutes with increasing concentrations of Par4-AP (A) or convulxin (B), stained with JON/A-PE, and immediately analyzed by flow cytometry. Bar graphs represent MFI ± SEM (n = 6, 3 independent experiments). (C) Representative images of rhodamine-phalloidin–stained talin1 mutant platelets spread on fibrinogen-coated glass in the presence of 100 μM ADP for 45 minutes. (D) Quantitation of platelet area (μm²); n = 5 independent experiments; mean ± SEM. *P < .05, **P < .01, ***P < .001.