Proliferative symmetric and differentiative asymmetric division depends on the medio-lateral location within the optic lobe. (a, b) mCD8-GFP MARCM clones (green) are shown in mid third instar brains. Dlg is in red and DNA in blue. (a) A lateral clone contains columnar shaped epithelial cells that presumably were generated by proliferative symmetric divisions (the single confocal section shows three epithelial cells). The clone located at the medial edge of the optic lobe contains neuroblasts with attached strings of progeny cells (the single confocal section shows one neuroblast and three progeny cells). (b) A clone at the medial edge of the optic lobe comprises four progenitor cells and one progeny cell (the single confocal section shows two progenitor cells and one progeny cell). (c-e) GAL4c855adriven UAS-pon-gfp (green) reveals the division mode of optic lobe neuroepithelial cells and neuroblasts. Dlg is in red and DNA in blue. Brains at mid-third (c, d) and early third (e) instar. (c) Neuroepithelial cells undergoing mitosis round up at the apical surface of the epithelium and show basolateral Pon-GFP (metaphase: filled arrowheads). Upon cytokinesis Pon-GFP is partitioned equally to both daughter cells (telophase: open arrowhead). At the medial edge of the epithelium optic lobe neuroblasts reveal a basal crescent of Pon-GFP at metaphase (arrow; enlarged in (c')). (d) At the medial edge of the epithelium a neuroblast in anaphase segregates Pon-GFP asymmetrically to the basal daughter cell (arrow; enlarged in (d')). (e) A more dorsal confocal section reveals a neuroepithelial cell in anaphase segregating Pon-GFP symmetrically to both daughter cells (arrowhead) and a neuroblast (arrow; enlarged in (e')) in anaphase segregating Pon-GFP to the basal daughter cell. All images are single confocal sections, with anterior on top and lateral to the right.