Impaired endocytic pathway and proplatelet formation in Dnm2-null MKs. (A) Representative clathrin heavy chain, EEA1, APPL1, and calreticulin immunofluorescence images of Dnm2^fl/fl and Dnm2^fl/flPf4-Cre bone marrow MKs. Bars represent 10 µm. (B) Dnm2^fl/fl (n = 10) and Dnm2^fl/flPf4-Cre (n = 16) fetal liver–derived MKs extending proplatelets were counted 18 hours after BSA gradient (day 4 of culture) and expressed as percentage of total MKs (mean ± SEM; ***P < .0001). Representative light microscopy images of fetal liver–derived Dnm2^fl/fl (C) and Dnm2^fl/flPf4-Cre (D) MK-forming proplatelets in vitro. Areas within boxes in panels C1 and D1 are shown at higher magnification in panels C2 and D2, respectively. Bars represent 50 µm. Representative α-tubulin immunofluorescence images of fetal liver–derived Dnm2^fl/fl (E) and Dnm2^fl/flPf4-Cre (F) MK-forming proplatelets in vitro. Bars represent 20 µm.