Unstable spindle in an ESC dividing at the periphery of a colony. Time-lapse (spinning-disk confocal microscopy) of a H2B-RFP (red) expressing ESC colony labeled with CellMaskTM deep red (cyan) with one cell dividing at the periphery of the colony. One frame is shown every 2 min. One Z plane is shown. Scale bar: 10 μm.