Fig. 3. Distal cell neurons invade the lamina in slit mutants. (A-D) Third instar visual systems in which IPC neuroblasts and distal cell neurons are visualized using anti-Fasciclin 3 (Fas3, red), photoreceptor axons using GMR:GFP (green), and neuronal nuclei using anti-Elav (blue). (A,B) Horizontal view (anterior to left). (A) In wild type, IPC neuroblasts (which express Fas3) and their distal cell neuron progeny (which express Fas3 and Elav) are adjacent to the posterior edge of the lamina (arrowhead). (B) In slit^dui/slit² mutants, distal cell neurons enter the base of the lamina (arrow) and reach the lamina's anterior edge (arrowhead). Distal cell neurons also enter the neuropil of the lamina (asterisk) and photoreceptor innervation is disrupted. (C,D) Lateral view (anterior at bottom). (C) In wild type, distal cell neurons are immediately adjacent to the posterior face of the lamina. (D) In slit^dui/slit² mutants, distal cell neurons enter the posterior face of the lamina (arrow) and reach its anterior edge (arrowhead). dcn, distal cell neuron progeny; IPC, inner proliferation center; lamc, lamina cortex; lamn, lamina neuropil; lobc, lobula cortex; medc, medulla cortex; medn, medulla neuropil.