IMiDs inhibit proplatelet formation of human megakaryocytes. (A) Representative phase-contrast microscopic images of megakaryocytes derived from CD34⁺ HSPCs with or without 10 µM of lenalidomide (Len) or pomalidomide (Pom). Arrows denote megakaryocytes with proplatelets. Lower panels show enlarged images. Images were captured by BZ-X700 (Keyence) with ×20 (upper; scale bars, 50 µm) and ×40 (lower; scale bars, 25 µm) objective lens. (B) Mean percentages of megakaryocytes with proplatelets in 500 cells analyzed per sample. Data are from 3 independent experiments and expressed as means ± standard errors of the mean. P values were determined by 2-tailed Student t test. (C) Transmission electron microscopic images of representative megakaryocytes for each treatment group are shown. Arrowheads denote demarcation membranes. Images were captured by Tecnai F20 electron microscope with ×5000 magnification (scale bar, 1 µm).