The number, but not the size, of MKs in BM correlates with the number of platelets. (A) Platelet numbers were counted in the EDTA-anticoagulated peripheral blood of PF4Cre;Tgfb1^flox/flox (PF4;Tgfb1) and WT C57Bl/6 or Tgfb1^flox/flox mice using an automated hemovet cell counter (n = 20-23). (B) The correlation between platelet count and MK number in PF4;Tgfb1 and WT C57Bl/6 (n = 12) mice. (C) Representative H&E-stained image showing cytoplasm areas and nuclei of MKs. (D) The cytoplasm area, nucleus area, and total (cytoplasm plus nucleus) area were calculated by demarcation using hand drawing in high-magnification images from an Aperio scanner, and the areas were measured using an ImageScope program (data supplement; supplemental Figures 1 and 4; n = 6).