Notch signals lead to an enhanced cellular expansion of CD45RA⁻cells and delay the cellular expansion of CD45RA^intand CD45RA^hiprogenitors. Cocultures were initiated with CD90^low cells (HSCs) placed on OP9-Ctrl, -DL4^hi, and -DL4^low cells and analyzed by flow cytometry at days 7, 14, and 21 of culture. The cellular fold expansion based on the absolute numbers of cells recovered (from day 0 5-10 000 HSC plated) is shown for CD45RA^int and CD45RA^hi cells. (A) Bar graphs show mean and SE of at least 10 independent experiments. (B) Precursor-product relationship between CD45RA^int and CD45RA^hi cells. Cocultures were initiated with CD90^low cells (HSCs) placed on OP9-Ctrl, -DL4^hi, and -DL4^low cells. After 21 days of culture, OP9-Ctrl, -DL4^hi, and -DL4^low cultures were harvested separately and CD45RA^−/int cells were sorted by flow cytometry and recultured under the same conditions in stem media. This defines a new day 0 (purity analysis for this day 0 shown). Two and 3 days later, cells were analyzed for the expression of CD34 and CD45RA on gated CD34⁺CD38⁻CD7⁻ cells. Numbers within each plot indicate the percentage of cells in the indicated gates. Representative plots of 3 independent experiments are shown.