Impaired megakaryocyte maturation in hepatocyte Notch1-deficient mice. Femurs were isolated from Notch1^fl/fl mice or HC Notch1^−/− mice treated with vehicle or exogenous TPO (1 μg/kg) for consecutive 5 days and then fixed followed by H&E staining to evaluate megakaryocyte maturation and differentiation (A). Blue arrows indicate the mature megakaryocytes (defined as megakaryocytes having 4-16 nuclear lobes), and red arrows indicate the immature megakaryocytes (defined as megakaryocytes lacking lobulation of the nucleus or <4 nuclear lobes). The number of mature (B) or immature (C) megakaryocytes was quantified (mean ± SE; n = 6; 1-way ANOVA). (D) The number of circulating platelets was measured after supplementation of exogenous TPO (1 μg/kg) for consecutive 5 days (paired student t test). ∗∗∗P < .001.