MKL2 gene expression and validation of conditional Mkl2 KO mice. (A) MKL1 and MKL2 mRNA levels were assessed in PreMegE cells from 3 WT mice differentiated in vitro using megakaryocyte differentiation medium. Shown is the fold increase in mRNA over freshly sorted PreMegE of megakaryocytes from 5-day cultured PreMegE cells after normalization to the 18S internal control. All 3 mice show an increase in both MKL1 and MKL2 during megakaryocyte differentiation. (B) Mkl2 expression was assessed in megakaryocytes differentiated in vitro from PreMegE of WT (n = 3) and Mkl1 KO (n = 3) mice. Shown is the fold increase in mRNA over HSC. Error bars represent SEM. (C) PCR of genomic DNA isolated from HSC, PreMegE, and MkP after 3 days of mTPO culture showed specific deletion of the Mkl2 locus in megakaryocytes of Pf4-Cre expressing Mkl2^F/F mice. Mkl2^F/F mice without Pf4-Cre were negative controls.