(A) Individual EC cultures were transfected with control siRNA or with siRNAs directed to Cdc42, Rac1, Rac2, RhoA, k-Ras, and Rap1b, and then were suspended in 3D collagen matrices for 72 hr using the Factor-induced model. Data are reported as the mean total vessel area per high-power field (HPF) ± standard deviation (SD) (n = 15, p < 0.01). Asterisk indicates significance compared to control cultures. Fixed cultures were fixed, stained and photographed. Bar equals 25 μm (B). (B) Lysates generated from siRNA transfected cultures in (A) were used in Western blots to assess specific protein knockdown versus control. (C,D) Individual EC cultures were transfected with siRNA targeting Cdc42, combinations of Cdc42 with Rac1, Rac2, k-Ras, and Rap1B siRNAs, or a control siRNA. EC tubulogenesis assays were performed with the cells the Factor-induced model and after 72 hr, cultures were fixed, photographed (D) and quantitated (C). Data are reported as the mean vessel area ± SD (n = 15; p < 0.01). Asterisk indicates significance compared to control while the square indicates significance compared to Cdc42 siRNA treatment. Bar equals 25 μm.