Srsf3-null platelets are preactivated. (A) The mean fluorescence intensity (MFI) of CD41, GPIX, GPIbα, and GPVI cell surface receptors in control and Pf4-Srsf3^Δ/Δ platelets assessed in diluted whole blood. (B-C) The expression of activated Integrin-αIIb-β3 receptor (JON/A) and P-selectin on the surface of washed control and Pf4-Srsf3^Δ/Δ platelets following agonist stimulation. (D-E) The expression of activated Integrin-αIIb-β3 receptor (JON/A) and P-selectin on the surface of control and Pf4-Srsf3^Δ/Δ platelets from diluted whole blood. The data are presented as mean plus or minus SEM. Two-tailed unpaired Student t test. ***P ≤ .001; **P ≤ .01; *P ≤ .05.