Defects in cell-cycle progression and increased apoptosis caused by Dot1L KO during erythropoiesis. (A) Representative histograms showing cell-cycle progression of cultured WT and KO yolk sac cells. Dissociated yolk sac cells of WT and Dot1L KO embryos were plated in methylcellulose growth medium, which supports erythroid lineage growth, and were cultured for 4 days. The cells were harvested, and cell cycle was analyzed by propidium iodide staining and flow cytometry. Differences in percentages of cells in all stages of the cell cycle were significantly different (P < .02, t test). (B) Analysis of apoptosis was examined in yolk sac cells cultured in erythropoietin-containing growth medium by annexin V staining and flow cytometry.