DKO mice have an accumulation of immature megakaryocytes in the BM. Paraffin sections from femurs of 6-week-old mice were stained with (A) anti-VWF antibody or (B) H&E. (C) Representative ploidy histograms for CD41⁺ bone marrow cells are shown along with the mean ploidy (MP) ± SEM of 4 mice per genotype. (D) Consistent with the decreased mean ploidy, the percentages of megakaryocytes with each ploidy level for n = 4 mice per genotype show that Mkl1 KO and DKO megakaryocytes have a significant increase in 2N megakaryocytes. (E) Flow cytometry confirms the increase in total CD41⁺ cells in the bone marrow using 4 mice per genotype. (F) Analysis of BM progenitors revealed an increase in the PreMegE and MkP populations in DKO BM (n.s. indicates not significant; **P < .01; *P < .05; all error bars represent SEM).