Fig. 1. Cdc42 and Rac1 are required for EC tubular morphogenesis and invasion in 3D collagen matrices. (A) ECs transfected with the indicated siRNAs were suspended within collagen matrices for 48 hours (vasculogenesis assay). The culture media contained vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF-2) and phorbol ester (TPA), as described previously (Davis and Camarillo, 1996). Arrows indicate EC tubular networks with a lumenal structure. (B) ECs transfected with the indicated siRNAs were seeded onto collagen matrices (angiogenesis assay) and stimulated to invade for 48 hours in response to 200 ng/ml SDF-1, as described previously (Saunders et al., 2006). Arrows indicate the invading EC sprouts and tube formation; arrowheads indicate ECs on the monolayer. Bars, 100 µm.