The Arp2/3 complex is essential for the actin cluster formation and revolving movement. (A) Arp3 siRNAs efficiently down-regulate the Arp2/3 complex. (B) Time-lapse images of HeLa cells expressing GFP-UtrCH and DsRed-histone H1. Top, control (Luc siRNA); bottom, Arp3 siRNA. Images were taken every 3 s and images are shown at 30-s intervals. Spatiotemporal representation is also shown. (C) Time-lapse images of HeLa cells expressing GFP-UtrCH and DsRed-histone H1. Top, control (Luc siRNA); middle, Arp3 siRNA1; bottom, Arp3 siRNA1 + myc-Arp3res. Arrowheads indicate the actin cluster. (D) Percentages of cells showing the revolving movement of the actin cluster. Control (Luc siRNA), 100% (n = 22); Arp3 siRNA1, 26.3% (n = 19); Arp3 siRNA1 + myc-Arp3res, 73.3% (n = 15); Arp3 siRNA1 + HA-Arp3res, 70.6% (n = 17). (E) Staining with phalloidin of HeLa cells transfected with luciferase siRNA (left), Arp3 siRNA1 (middle), and Arp3 siRNA2 (right). The bottom sections show the retraction fibers, and the middle sections show the cortical actin structures and the actin cluster, which is indicated by a white circle with a yellow arrowhead. (F) Double staining with anti-Arp3 (green) and anti-Arp1α (red) antibodies of HeLa cells transfected with luciferase siRNA (left) and Arp3 siRNA1 (right). Arrowheads, the patchy staining of endogenous Arp3. (G) Staining with anti-Arp3 antibody (red) of HeLa cells expressing GFP-UtrCH. Arrowheads, the actin cluster. Bars, 10 µm.