Mitomycin C–sensitive expansion of β-galactosidase–expressing cells in flt-1^−/− ES cell cultures at earlier times.

(A) Quantitative image analysis of the β-galactosidase⁺areas of flt-1^+/− (light blue bars) andflt-1^−/− (dark blue bars) ES cell cultures on days 2 to 5 of in vitro differentiation. For days 2 and 3, the bars represent the average β-galactosidase⁺ area for 9 individual attached ES cell clumps. For days 4 and 5, the bars represent the average β-galactosidase⁺ area for 2 culture wells. The asterisk (*) indicates significance atP < .001. (B-F) Days 4 to 6flt-1^−/− ES cell cultures untreated (B,D,F) or treated with mitomycin C (C,E) and stained for β-galactosidase activity. (B) Day 4 flt-1^+/− culture. (C) Day 5flt-1^−/− culture treated on day 4 with mitomycin C. Note decrease in stained area relative to (D) untreated day 5 flt-1^−/− culture. (E) Day 6flt-1^−/− culture treated on day 5 with mitomycin C. Note decrease in stained area relative to (F) untreated day 6 flt-1^−/− culture. Original magnification, ×20.