Mkl1 deficiency leads to an increased percentage of committed CD41⁺c-kit⁺ megakaryocytic progenitors and a decreased percentage of mature high-ploidy megakaryocytes. (A) Comparison of percentages of CD41⁺ cells in WT, HET, and Mkl1 KO BM (n = 6 per genotype). (B) Comparison of serum TPO concentration (n = 3 per genotype). (C) Comparison of percentages of CD41⁺ c-kit⁺ cells in WT, HET, and Mkl1 KO BM (n = 6 per genotype). (D) Comparison of numbers of megakaryocytes per high-power field in the femurs of WT, HET, and Mkl1 KO mice (n = 2 per genotype). (E,F) In vivo ploidy analysis of CD41-positive BM cells taken from WT, HET, and Mkl1 KO mice (n = 6 in WT and HET; n = 8 in Mkl1 KO mice). *P < .05 from both WT versus KO and HET versus KO.