Cdk1 activity is required for the actin cluster formation and revolving movement. (A) Staining with phalloidin of HeLa cells at the indicated phases (G2 to post-mitosis phase). Arrowheads, the cluster of actin filaments. (B) Time-lapse images of HeLa cells expressing GFP-UtrCH and DsRed-histone H1 from G2 to post-mitosis phase. Images were taken every 3 min. Arrowheads, the cluster of actin filaments. (C) Red bars represent the percentages of cells containing the cluster of actin filaments stained with phalloidin (n = 50 at each phase). Blue bars represent the percentages of cells exhibiting a revolving actin cluster visualized by GFP-UtrCH (n = 50). (D) Close examination of time-lapse images of HeLa cells expressing GFP-UtrCH and DsRed-histone H1. Asterisks indicate the region of the cleavage furrow. Images were taken every 30 s and images are shown at 1.5-min intervals. Arrowheads indicate the actin cluster. (E) Nocodazole-treated, prometaphase-arrested HeLa cells expressing GFP-UtrCH and DsRed-histone H1 were treated with 20 µM Ro3306 immediately after time 0. Images were taken every 2 min. Arrowheads, the actin cluster. Bars: (A, D, and E) 10 µm; (B) 5 µm.