Marked microthrombocytopenia in Arpc2^fl/flPF4-Cre mice. (A) Schematic of gene targeting strategy. Exon 8 of the Arpc2 gene, flanked by LoxP sites, was excised by PF4 promoter-driven expression of Cre recombinase. (B) Representative immunoblot demonstrating knockdown of p34 and loss of Arp2 and Arp3. (C) Platelet count (Plts) (n = 6) and (D) size (n = 5) in peripheral blood of the indicated mice. (E) Representative scanning electron microscopy images of resting platelets. Arrows indicate abnormally small platelets in Arpc2^fl/flPF4-Cre sample. (F) Percentage of reticulated platelets (n = 6-7). Blue bars, control; red bars, Arpc2^fl/flPF4-Cre. Data presented as mean ± SEM, ***P < .001. ns, Not significant.