Increased MK numbers in BM of Cdc42^−/− and Rac1/Cdc42^−/− mice. (A) Determination of MK numbers in hematoxylin and eosin–stained BM sections from wt (black), Rac1^−/− (dark gray), Cdc42^−/− (light gray), and Rac1/Cdc42^−/− (patterned) mice. (Left) Representative images. (Right) Statistical analysis. (B) Determination of MK number and morphology within the BM of anti–CD41-stained (green) cryosections. Endothelial cells are stained with anti-CD105 (red) and nuclei with 4,6 diamidino-2-phenylindole (DAPI) (blue). Results are expressed as mean MK number per visual field ± SD of 3 mice per group. (C) Functional endomitosis in Rac1^−/−, Cdc42^−/−, and Rac1/Cdc42^−/− MKs. Determination of the mean ploidy of BM-derived MKs from wt (black), Rac1^−/− (dark gray), Cdc42^−/− (light gray), and Rac1/Cdc42^−/− (patterned) mice. Results are expressed as mean ploidy ± SD (n = 4 per group; ***P < .001).