The effect of M40 on HSCs is mediated through Tpo/Mpl. (A) Peripheral blood platelet counts in Mpl^−/−, M40^−/−, and Mpl^−/−M40^−/− mice. (B) Phenotypic LT-HSC frequencies in Mpl^−/−, M40^−/−, and Mpl^−/−M40^−/− mice as determined by CD34⁻Flk2⁻CD150⁺LSK surface markers. Each symbol represents an individual mouse. The mean in each group is indicated by horizontal lines. P value is calculated by the Student t test.