Pdk1^−/−mice display increased localization of MKs in the BM hematopoietic compartment with less sinusoidal contact, a substantial BM MK hyperplasia, and an upregulation of extramedullary thrombopoiesis. (A) Representative images of GPIb immunostaining of BM sections from 2-month-old Pdk1^fl/fl and Pdk1^−/− mice (left). Quantification of Pdk1^fl/fl and Pdk1^−/− BM MKs per visual field. Arithmetic means ± SEM (n = 6, unpaired 2-tailed Student t test; right) are shown. Scale bar equals 50 μm. (B) Representative images of hematoxylin and eosin stainings as well as GPIb immunostaining of spleen sections from 6-month-old Pdk1^fl/fl and Pdk1^−/− mice (left). Quantification of Pdk1^fl/fl and Pdk1^−/− spleen MKs per visual field. Arithmetic means ± SEM (n = 6, unpaired 2-tailed Student t test; right) are shown. Scale bar equals 50 μm. (C) Representative confocal microscopy images of immunostained BM sections (n = 5). Green, MKs (GPIb); red, sinusoids (endoglin, CD105); gray, nuclei (4′,6-diamidino-2-phenylindole [DAPI]). Scale bar equals 20 μm. Boxes in the left panels mark the section in the illustrations which are highlighted in a higher magnification in the right panels. (D) Arithmetic means ± SEM (n = 6, unpaired 2-tailed Student t test) of MKs per visual field in immunostained BM sections of Pdk1^fl/fl and Pdk1^−/− mice. (E) Quantification of MK distance from sinusoids in BM sections of Pdk1^fl/fl and Pdk1^−/− mice (means ± SEM, n = 6, 750 MKs, Wilcoxon-Mann-Whitney test). (F) Quantification of MK localization in the BM of Pdk1^fl/fl and Pdk1^−/− mice (arithmetic means ± SEM, n = 6, 2-way ANOVA with Bonferroni correction for multiple comparisons). BMHC, bone marrow hematopoietic compartment; Intrasin., intrasinusoidal; SC, sinusoidal contact. **P < .01 indicates statistically significant difference.