Fig. 1. Developing Drosophila visual system. (A) Horizontal view of wild-type third instar visual system (anterior to left) of animal expressing CD8:GFP under the control of Sca-Gal4 (Sca:GFP). GFP is expressed in the OPC, IPC, medulla cortex and portions of the lobula cortex. Sca:GFP (green). Neuronal nuclei are visualized using anti-Elav (blue); photoreceptor axons, lamina monopolar axons and axons from neurons of the lobula cortex (a subset of which contact the medulla neuropil) are visualized using anti-Fasciclin 2 (Fas2) (red). Dotted line indicates anterior edge of lobula cortex. (B) Lateral view (anterior at bottom) of Sca:GFP animal in which neuronal nuclei have been visualized using anti-Elav (blue) and glial nuclei using anti-Repo (red). Schematics of (C) horizontal view and (D) lateral view, indicating cell populations and axons described in the text. ep, epithelial glia; IPC, inner proliferation center; lamc, lamina cortex; lamn, lamina neuropil; lobc, lobula cortex; ma, marginal glia; medc, medulla cortex; mg, medulla glia; medn, medulla neuropil; OPC, outer proliferation center; os, optic stalk.