Increased EC apoptosis in Ets1/Ets2 double-mutant mice and in cultured cells deprived of growth factor. (A-B) Anti-PECAM (red) and TUNEL (green) double staining of thin frozen sections from E11.5 embryo of genotype Ets1^−/−;Ets^A72/A72 (A) or Tie2-Cre Ets1^−/−;Ets2^fl/fl (B). The third figure in each panel is the merged image, as indicated. The graphic panel shows the ratio of apoptotic endothelial cells (staining for both PECAM and TUNEL) to total PECAM-positive cells, expressed as percentage of apoptotic cells. At least 300 cells were counted in sections obtained from 2 different E11.5 embryos of genotype Ets1^−/−;Ets^A72/A72 (C) or Tie2-Cre Ets1^−/−;Ets2^fl/fl (D), and appropriate controls as indicated in the figure. Bars, 50 μm. (C) LIVE/DEAD staining of cultured aortic ECs of indicated genotype without Cre (top panels) or with Cre (bottom panels), that is, Ets1/Ets2-null condition. Graph at right is quantification of the results. Cells staining red indicate apoptotic/dead cells. Bars, 50 μm. For all panels, error bars indicate SD. * P < .05 (significant difference) between control and double mutant as determined by Student t test.