Mice lacking PIP5KIγ form unstable thrombi in vivo. Ferric chloride was applied to an exposed carotid artery of anesthetized mice, and the formation of thrombi was monitored using a Doppler flowmeter. Mice lacking (A) p90 PIP5KIγ or (B) both PIP5KIγ isoforms form thrombi as rapidly as control mice. (C) However, mice lacking both p87 and p90 PIP5KIγ form thrombi that are frequently unstable.