CyPA deficiency leads to reduced thrombus formation in vivo without affecting bleeding time. After injury of mesenteric arterioles with FeCl₃, platelet adhesion and thrombus formation were monitored in vivo by fluorescence microscopy. (A-B) Time to first thrombus formation after injury (A) and time to full occlusion of the injured vessel (blood flow stopped for > 1 minute; B). Each symbol represents one animal. (C) Representative images showing the level of thrombus formation at the indicated time points. Asterisk indicates occlusion of the vessel. Scale bar indicates 50 μm. (D) Tail bleeding times for Cypa^+/+ and Cypa^−/− mice. Each symbol represents 1 animal.