Shape instabilities during ESC divisions at the periphery of a colony. Time-lapse (spinning-disk confocal microscopy) of a colony of ESCs expressing H2B-RFP (red) and labeled with CellMaskTM deep red (cyan) showing shape instabilities in cells dividing at the periphery of the colony. One frame is shown every 5 min. One Z plane is shown. Scale bar: 10 μm.