DKO mice have macrothrombocytopenia and dysfunctional platelets. Peripheral blood was taken from mice with the indicated genotypes and (A) platelet counts and (B) platelet volume analyzed. (C) Representative peripheral blood smears stained with Wright Giemsa are consistent with low platelet count and high MPV in DKO mice. Images were taken using an oil-immersion 100× lens. Black arrows indicate platelets. (D) Bleeding times from mice with different genotypes (WT, n = 31; Mkl1 KO, n = 6; Mkl2 cKO, n = 10; DKO, n = 13). (E) Flow cytometry of peripheral blood platelets showing FSC vs SSC in the absence (top) and presence (bottom) of ADP. Note change in shape of platelet gate (circled in red) in response to ADP stimulation. Red blood cells (RBCs) are indicated. (F) Representative data showing total CD41/61 (x-axis) versus the activated JON/A conformation (y-axis) of CD41/CD61 in resting (blue) and ADP treated (red) platelets of 4- to 6-week-old mice. (n.s. indiates not significant; ****P < .0001; ***P < .001; **P < .01). All error bars represent SEM. Data from 4 independent experiments are summarized in Table 1.