Increased bleeding and defective thrombus formation in Csk KO and DKO mice. (A) Hemostatic response was measured in tail bleeding assays by an excision of a 5-mm portion of the tail tip followed by the determination of lost blood/body weight (normalized blood loss) (n = 11-57 mice per genotype). Tail bleeding assays were conducted in a double-blinded manner. (B) Laser injury–induced thrombus formation in vivo. Composite bright-field and fluorescence images of (Bi) platelet accumulation (green) or (Bii) fibrin generation (red) in cremaster muscle arterioles monitored by DyLight488-labaled anti-GPIbβ antibody (0.1 μg/g body weight) or Alexa Fluor 647–labeled anti-fibrin antibody (0.2 μg/g body weight) signal, respectively by confocal intravital microscopy (scale bar, 10 μm). Each curve represents the median integrated fluorescence intensity of (Biii) platelets or (Biv) fibrin in relative fluorescence units (RFUs) (n = 25-37; 5 mice per genotype). See also supplemental Videos 1 and 2. (C) FeCl₃ injury-induced thrombus formation in vivo. Filter paper soaked in 10% FeCl₃ was applied to carotid artery for 3 minutes. (Ci) Representative fluorescence images of platelet accumulation (green) monitored by DyLight488-labeled anti-GPIbβ antibody (0.1 μg/g body weight) by confocal intravital microscopy (scale bar, 200 μm). (Cii) Each curve represents the median integrated thrombus fluorescence intensity in RFU. (Ciii) Area under the curve (AUC) was measured (n = 8-11 mice per genotype). See also supplemental Video 3. *P < .05, **P < .01, ***P < .001; 1-way ANOVA with Tukey’s test; data represent mean ± SEM.