Inhibitors of vesicle trafficking block enucleation of primary erythroblasts. (A) Representative transmission electron microscopic image of mouse fetal liver erythroblasts cultured in vitro for 42 hours is shown. V indicates vacuoles; Mi, mitochondria; Nu, nucleus; R, incipient reticulocyte; and arrowheads, vesicles. Scale bar, 1 μm. (B-C) Enucleation assays of primary mouse fetal liver erythroblasts were performed in the presence of MiTMAB, monensin, or their respective solvents. MiTMAB or monensin was added to culture at 38 hours, and flow cytometric analysis was performed after 48 hours of total culture time. Measured percentages of reticulocytes are shown as mean ± standard deviation for 3 independent experiments. (D-E) Effect of MiTMAB (D) and monensin (E) on enucleation, cell cycle, viability, and differentiation when added to erythroblast cultures at 38 hours. Representative flow plots are shown.