Granule distribution in proplatelet buds. (A) Cultured MKs bearing proplatelets were imaged after immunolabeling with anti-GPIbβ (red, RAM1) and anti-VWF antibodies (green). (B) Quantification of the number of VWF-positive granules (green labeling) per proplatelet bud as a function of the bud size. n = 123 proplatelet buds for WT cells, n = 115 proplatelet buds for Myh9^−/− cells, in 3 separate cultures. The variances in the point distribution were not statistically different.