D. Wt and ∆LE HUVECs co-cultured on fibroblast monolayers. Endothelial cells were identified either with an antibody against the endothelial cell marker PECAM-1 (left) or through expression of a nucleofected plasmid encoding the cytoskeletal marker Lifeact-GFP (right). Arrowheads indicate filopodia 