dKO megakaryocytes display an aberrant DMS and are incapacitated to form proplatelets. (A) Electron microscope images of bone marrow–derived cultured megakaryocytes. Representative pictures are shown. WT^lox megakaryocytes display a normal compact DMS, whereas dKO megakaryocytes present with an abnormal less compact DMS or even larger vacuolar cytoplasmic structures. See supplemental Figure 3 for additional pictures. (B) Micrograph of the periphery of a bone marrow explant (left) (contour indicated by dashed line). A megakaryocyte (MK) in the center of the image has formed proplatelets (ProPLTs, arrowheads). Such MKs with ProPLTs are counted as one unit, and the percentage of units with proplatelets of total counted megakaryocytes is depicted (bar graph on the right). See supplemental Videos 1-3 showing WT megakaryocytes forming proplatelets and supplemental Figure 4 for explant still images.