FIG. 4.
Cell cycle progression of wild-type ES cells upon serum withdrawal. Wild-type ES cells were labeled with BrdU for 30 min and harvested prior to or following 8, 16, or 24 h of serum starvation as indicated. Cell cycle distribution (left panels) was determined by staining cells for DNA content with PI, and the rates of DNA synthesis (right panels) were determined by immunostaining cells for BrdU incorporation (y axis) and plotting against DNA content (x axis). The percentages of cells in the G1, S, and G2 phases are indicated.