Fig. 3. Fate of Wg-expressing neurons in the mature optic lobe. Specimens harboring the transgene wg-lacZ were examined during the late pupal stage [about 200 hours AEL (after egg laying)] for the location and axonal projection pattern of the Wg-positive neurons. (A) Most Wg-positive neurons are located at dorsal and ventral positions in the medulla and lobula cortices. In this image, a dorsal cluster of neurons is visible in the upper right corner of the yellow box (anti-ß-gal staining; blue). MNG and Xi glia (anti-Repo staining; red) are indicated in their distinct positions relative to the medulla and lobula neuropiles (med n'pil, lob n'pil; anti-HRP staining; green). The medulla cortex (med ctx) is also indicated. (A') A higher-magnification view of the yellow-boxed region in A. Clusters of wg-lacZ-positive neurons (anti-ß-gal staining; grayscale) extend axons (yellow arrowheads) towards the edge of the medulla neuropile and into the proximal medulla layer (green arrowhead). (B) A late pupal stage specimen with wg-lacZ-positive neurons visible (blue) along the dorsal edge of the cortices. In this image, glial layers of the lamina (lam) are visible. (B') The image in B with anti-HRP staining omitted and wg-lacZ expression shown in grayscale. wg-lacZ-positive neurons elaborate long axons that project tangentially into the medulla and lobula neuropiles (yellow and green arrowheads). Glia (red; yellow arrows) are associated with the wg-lacZ-positive axons In this specimen, the lamina marginal (Ma) and epithelial (Ep) glial layers are indicated, but wg-lacZ-positive axon tracts are not found extending toward these layers at this stage. Scale bars: in A, 15 µm for A,B,B'; in A', 10 µm.