Optic lobe neuroepithelial cells and neuroblasts are arranged in distinct medio-lateral zones. (a) The developing optic lobe generates a lateral epithelial region (to the right of the arrowheads). Epithelial cells express three proteins that localize to cellular junctions: Scrib (green) localizes to the basolateral septate junctions in epithelial cells; DE-Cad (red) localizes to the basolateral zonula adherens; and PatJ (blue) localizes to apical and subapical regions in epithelial cells. Medial neuroblasts (to the left of the arrowheads) are more round and lack the clear subcellular localization of these junctional proteins. (b) sc-lacZ (red) is expressed in the lateral epithelium of the optic lobe (to the right of the arrowheads). Expression is diminished in medial optic lobe neuroblasts (to the left of the arrowheads). Medial neuroblasts express the bHLH transcription factor Dpn (blue), which is not expressed by neuroepithelial cells. Dlg (green) outlines all cell cortices but is enriched at adherens junctions. (c) Asense (red) shows weak cytoplasmic expression in medial Dpn (blue) positive neuroblasts (to the left of the open arrowheads). Asense is nuclear in the progeny of neuroblasts (filled arrowheads). (d) Pros protein (red) forms a basal crescent (inset) in mitotic medial optic lobe neuroblasts (filled arrowhead). Dpn (blue) is restricted to the neuroblasts but Pros (red) is inherited by the basal progeny cells where it localizes to the nucleus. (e) Mira (red) forms a basal crescent in mitotic neuroblasts (filled arrowhead) (metaphase; n = 9 and telophase n = 9). Note that neither Pros nor Mira are present in neuroepithelial cells (to the right of the arrowheads). (f) Insc protein (red) forms an apical crescent in mitotic medial optic lobe neuroblasts (filled arrowhead and inset). These neuroblasts reveal weak cytoplasmic Dpn (blue). Dlg (green) is enriched apically, where it co-localizes with the Insc crescent at the apical cortex (inset). Some progeny cells in the medulla cortex also express insc (arrow). All images are single confocal sections from third instar brains, with anterior to the top and lateral to the right. Open arrowheads mark the boundary between the neuroepithelium (to the right) and the neuroblast zone (to the left).