Different ultrastructures of mature MKs differentiated in situ or in vitro. Electron microscopy images of WT murine MKs differentiated in the BM (in situ, upper panel) or in liquid culture in vitro (lower panel). The images of whole cells (left) and close-up views (right) are representative of at least 4 different mouse BM samples (in situ) and 10 different liquid cultures.