Abnormal morphology of mature MYH9Δ megakaryocytes. (A) TEM images illustrating a typical mature WT megakaryocyte (left) and an irregularly shaped MYH9Δ megakaryocyte (right) containing a dilated DMS that results in rare and enlarged platelet territories (PTs). Bars represent 5 μm. (B) Representative fields and threshold areas (red) of the DMS of WT and MYH9Δ megakaryocytes. (C) Quantification of the DMS by measurement of the perimeter per field of the threshold area. Data are expressed in pixels and are the mean plus or minus sem for 3 mice, with a total of 23 megakaryocytes analyzed. **P < .01 using Student unpaired t test.