Abnormal MK distribution upon maturation of Myh9^−/−MKs. (A) TEM images showing the in situ ultrastructure of WT (top panels) and Myh9^−/− (bottom panels) MKs. Higher magnifications (right images) show the normal granule distribution in the WT cytoplasm and clusters of α (α) and dense (δ) granules in Myh9^−/− MKs. (B) TEM observations of in situ bone marrow showing the presence of granule clusters (g) located near the nucleus (n) and the developing pre-DMS in immature stage I WT (top panels) and Myh9^−/− (bottom panels) MKs. Right images are magnification of left images. (C) Detail showing the abnormal organelle positioning in platelets from Myh9^−/− mice. (Left) Dense granules aligned around membrane complex. (Right) Mitochondria aligned along the RER.