A HUVECs were transduced with adenoviral vector expressing RFP-conjugated F-actin binding peptide (LifeAct). Time-lapse imaging of F-actin in HUVEC spheroids was obtained at 20× magnification (Supplementary Movies S3 and S4). Representative images are shown at 0 and 2 h. Arrowheads indicate detached cells after Sema3C treatment. Scale bar, 100 μm. 