Most of the cells in the expansion culture divide once daily and maintain their large size and Kit^high phenotype. (A) Staining characteristics of ex vivo extensively expanding erythroid cultures indicate that most of the cells divide once daily. There is also a minor population of cells that divide 2 or 3 times in 24 hours. Results from 1 of 3 experiments are shown. (B) The major cell population that divides only once daily is composed of large (FSC^high), nucleated (DNA^high), Kit^high cells that retain these characteristics from day to day (blue lines), shown for 24 and 48 hours of culture after CFSE staining. In contrast, the minor, rapidly dividing population is composed of smaller (FSC^low), Kit^low cells, many of which are enucleated (DNA^low/−; red lines). These results suggest that the minor population consists of terminally maturing erythroid cells.