Function of platelet integrins is kindlin-3 dose-dependent. (A) Densitometric quantification of kindlin-3 levels in K3+/+, K3+/n, K3n/n, and K3n/− platelets (N = 5, 5, 4, 4). GAPDH served as loading control. (B) K3+/+, K3+/n, K3n/n, K3n/− E14.5 embryos are free of bleeding. (C) Tail bleeding times of K3+/+, K3+/n, K3n/n, and K3−/− chimeric mice. (D-E) Binding of fibrinogen to platelets after treatment with 0.1 U/mL (D) and 1 U/mL thrombin (E). Resting platelets were used as control (N = 9, 8, 8, 10, 6 [D] and N = 8, 3, 8, 8, 2 [E]). (F-G) Activation of αIIbβ3 integrin on platelets upon stimulation with 0.1 U/mL (F) and 1 U/mL (G) thrombin (N = 13, 8, 11, 16, 5 [F] and N = 15, 10, 16, 16, 4 [G]). (H) β1 integrin activation index of K3+/+, K3+/n, K3n/n, K3n/−, and K3−/− platelets upon activation with 1 U/mL thrombin (N = 10, 7, 10, 8, 3). (I) Activation of αIIbβ3 integrin on control, kindlin-3^−/−, talin-1^−/−, and integrin β3^−/− platelets upon stimulation with 0.1 U/mL and 1 U/mL thrombin (N = 6, 6, 6, 3). (J) Western blot analyses of talin-1 and kindlin-3 expression in lysates from wild-type (+/+), K3−/−, and talin-1^−/− platelets. GAPDH served as loading control. (K) Platelet aggregation assays with +/+, K3−/−, and talin-1^−/− platelets in response to 0.1 U/mL thrombin. Values are given as mean ± SD and data were statistically analyzed by Student t test. *P < .05; **P < .01; ***P < .001. n.s., not significant.