Effect of RUNX1 degradation inhibitor treatment on platelet granule formation during in vitro megakaryocyte differentiation of primary RUNX1-FPD bone marrow MNCs. Primary cells from a patient with RUNX1-FPD were treated and harvested as shown in Figure 5A. (A) Thin-section TEM images of cells treated with bortezomib, terameprocol, or vehicle. Arrows indicate ultrastructural components: dense granules (D), α-granules (α), open canalicular system (OCS), nucleus (N), mitochondria (M), and vacuoles (V). (B) Proportion of cells scored at given ranking for presence of dense granules. (C) Proportion of cells scored at given ranking for presence of α-granules. Rankings were designated as the following number of granules per cell: −, 0; +, 1 to 10; ++, 10 to 20; +++, >20. Unidentifiable granules were not included in the ranking. *P < .025; **P < .01, using a Bonferroni-adjusted χ2 test of independence.