Fig. 3. Horizontal and vertical divisions of GFP⁺ RNECs. (A) Snapshots from a time-lapse video recording showing two cells in the same field, one of which divided horizontally (cell 1) and one of which divided vertically (cell 2). The dashed line indicates the apical surface of the neuroepithelium and arrowheads the plane of cell division (which is perpendicular to the orientation of the mitotic spindle). See also Movie 1 at http://dev.biologists.org/supplemental/. Scale bar: 40µm. (B) Higher magnification view of cell 1 dividing horizontally in time frame 12h08. (C) Higher magnification view of cell 2 dividing vertically in time frame 13h18. (D) Quantitative analysis of the distribution of mitotic spindle orientations relative to the plane of the neuroepithelium in live retinal explants, as determined by time-lapse video microscopy of GFP⁺ RNECs.