Fibrin clot retraction is impaired in talin1-deficient and talin1(L325R) mutant platelets. (A) Clot retraction of PRP from Tln1^(wt/fl),Cre⁺ or Tln1^(L325R/fl),Cre⁺, or Tln1^(fl/fl),Cre⁺ mice was initiated by 1.0 U/mL thrombin and photographed after 2 hours. As indicated, 0.5mM MnCl₂, 10μM cytochalasin D, or 50μM eptifibatide was added to PRP 5 minutes before the addition of thrombin. Efficient clot retraction, visible as a consolidated clot and transparent clot liquor, was observed in PRP from Tln1^(wt/fl),Cre⁺ mice and Tln1^(L325R/fl),Cre⁺ mice in the presence of manganese. (B) Fibrin clot retraction was quantified by calculating the weight of the serum extruded from the clot relative to the initial clot weight and expressed as a percentage. n = 3. *P < .005.