Horizontal and vertical divisions of GFP-labeled retinal progenitor cells. Timelapse video recording of two retinal progenitor cells in the same field of view. The cell on the right divides horizontally and the cell on the left divides vertically. The white line indicates the apical surface of the neuroepithelium. The arrowheads indicate the plane of cell division (which is perpendicular to the orientation of the mitotic spindle). Time (in hours) is shown in the bottom left-hand corner of the screen.