Fig. 4. Horizontal divisions producing two daughter cells that acquire a similar morphology and cell body size. (A-E) Five examples of daughter cells produced by horizontal divisions of newborn RNECs, seen 60-90 hours after the division. Note the similarity in size and morphology of the two daughter cells in each case. In the example shown in E, it was possible to fix the explant after the recording, stain the nuclei with propidium iodide and find the two GFP⁺ daughter cells again in a confocal microscope. Both daughter cells have a similar body size and morphology and are located in the photoreceptor layer. (F) A two-photoreceptor clone in a frozen section of a newborn retinal explant, 10 days after infection with a retrovirus encoding GFP. (G) Quantification of cell body size of GFP-infected photoreceptor cells (PR) and interneuron layer cells (INL), measured in cryosections of retinal explants 10 days after infection with a GFP-encoding retrovirus. Results are mean±s.d. of 35 PR and 28 INL cells. (H) Cell-body sizes of pairs of daughter cells produced by horizontal divisions of GFP-infected RNECs, followed by video recording. The daughters of all 12 horizontal divisions followed are shown. Note that in 11 out of 12 cases the daughter cells are similar in size to photoreceptors. Scale bars: 20 µm in A-E; 10 µm in F.