Abnormal MK maturation in Nbeal2^−/− mice. (A) CD41 labeling and hematoxylin and eosin staining of bone sections (×60) in control and Nbeal2^−/− mice. Arrows point at MKs. Two representative large polyploid MKs are shown in the bottom panels at high magnification (×100). Note the presence of leukocytes (L) within MKs (emperipolesis) at high magnification (×100) in the Nbeal2^−/− samples. (B) Quantitation of MKs in bone sections from (A) (5 different fields in 5 mice). Similar total MK numbers in control and Nbeal2^−/− mice (top panel), but the numbers of large MKs with more than 2 nuclear lobes (middle panel) and the numbers of small MKs with 2 or less nuclear lobes (bottom panel) are significantly different in Nbeal2^−/− mice. (C) Percentage of CD41⁺ cells in bone marrow cultures in the presence of thrombopoietin (TPO) (1 and 5 ng/mL) at different time points (1, 3, and 5 days) (n = 4). (D) Ploidy profile of CD41⁺ cells at day 3 (n = 4). (E) Percentage of proplatelet-forming MKs upon adhesion to fibrinogen of cultured MKs purified by bovine serum albumin gradient (n = 4). For all graphs, bars represent mean ± standard error of the mean. *P < .05. NS, nonsignificant.