(B) Quantification of vessel sprouts (mean values ± S.E.M.) upon VEGF treatment (30ng/mL) of embryoid bodies (EB) derived from murine ES cells (mESCs) with sense integrations in the Apelin gene (Apln STOP) of the splice acceptor described in Appendix Figure S1B or Cre-reverted antisense (Apln GO) sister cells. Apln GO (Day 2 n=6; Day 4 n=40, Day 6 n=54, Day 8 n= 32, Day 10 n=35, Day 11 n=31), Apln STOP (Day 2 n=4; Day 4 n=15, Day 6 n=31, Day 8 n= 28, Day 10 n=32, Day 11 n=37); ** P<0.01, *** P<0.001, two-way ANOVA. Representative brightfield images and automated analysis of vessel sprouts by Definiens software are shown in the bottom panels. Scale bars = 200 μm 