Figure 4.

Electron microscopy reveals a separation of the lamina cortex from the basement membrane. A, Schematic of the lamina cortex (la c) region shown in B and where it is localized in the fly head (box in E). The retina (re) is separated from the lamina cortex (light gray) by the basement membrane (arrowheads). The layer directly beneath the basement membrane (from the basement membrane to the black line) is filled with pigment vesicles and contains trachea (t) and the fenestrated glia (not seen in this picture), but no neuronal cell bodies. The cell bodies of the neuronal monopolar cells (n) and the satellite glia (g) are found in the layer adjacent to the lamina neuropil (la n; darker gray). The lamina neuropil houses the cell bodies of the epithelial glia (g) as well as axons from photoreceptors (a) and neurites from monopolar cells. B, The comparable region in the lamina cortex of a 14-d-old GMR-GAL4 fly. The magnification (F) shows the basement membrane (arrowheads) and pigment vesicles (asterisks). C, The lamina cortex of a 24- to 36-h-old GMR-GAL4; UAS-dBACE^RNAi fly still appears quite normal at the lower magnification (C), with glia (g), photoreceptor axons (a), and monopolar cells (n) present and only small lesions (arrows) detectable close to the basement membrane (arrowhead). G, A higher magnification of this area reveals that these lesions seem to be due to a loosening of the lamina tissue from the basement membrane (arrowhead). In addition, finger-like extensions from the basement membrane (arrow) are detectable. D, H, In a 14-d-old GMR-GAL4; UAS-dBACE^RNAi fly the gaps at the basement membrane have widened (black arrows in D) and vacuoles have formed in more proximal layers (white arrows in D). H, A magnification shows that the finger-like structures persist but are more stunted (arrow; the arrowhead points to the basement membrane). Scale bar in B applies to B–D; scale bar in F applies to F–H. me, medulla.