Fig. 7. β1 integrins regulate EC growth through effects on survival rather than proliferation. In vivo (A,B) and in vitro (C-E) effects of β1 deletion on EC growth. The ratios of BrdU/CD31 (A) and TUNEL/CD31 (B) double-positive ECs relative to total ECs were calculated from multiple immunostained cryosections prepared from three (A) or four (B) pairs of control and Tie2-Cre mutant mouse embryos at e9.0, prior to the onset of overt morbidity. Bars in A and B are means + s.e.m., and differences are not statistically significant by Student's t-test (A, n=1200 control and n=965 Tie2-Cre mutant ECs, P=0.625; B, n=1299 control and n=1116 mutant ECs, P=0.36). (C) Growth rate of embryonic Itgb1^flox/flox ECs cultured on gelatin (Gel) or vitronectin (VN). (D) Incorporation of BrdU into DNA after 6 hours of culture. (E) Entry of the apoptotic-cell-permeant dye, YO-PRO-1, into proliferating EC cultures. In C-E, data are means + s.d. of replicate measurements, and each experiment was repeated with similar results. ^**P<0.01 and ^*P<0.05 by Student's t-test.