Inactivation of the ERK pathway impaired vacuole formation in human orthochromatic erythroblasts. (A) Representative cytospin images showing morphology of orthochromatic erythroblasts treated with DMSO or U0126. Black arrows indicate large vacuoles in cytoplasm. Scale bar, 5 μm. (B) Quantification of erythroblasts that harbored vacuoles with a size >100 pixels. A total of 100 cells of each group from 3 independent experiments were used for quantification. (C) Representative EM images (a and b) of orthochromatic erythroblasts treated with DMSO or U0126. White arrows indicate vacuoles. Scale bar, 5 μm. (D) Quantification of erythroblasts harboring vacuoles with a size >1 μm². A total of 100 cells of each group from 3 independent experiments were used for the quantification. (E) Quantitative analysis of the average area of intracellular vacuoles in erythroblasts, and 100 cells of each group from 3 independent experiments were used for quantification. Data are expressed as mean ± standard deviation. *P < .05, **P < .01.