Figure 2.—

The effects of GSd447 misexpression on the developing visual system. (A, B) R-cell axons can be specifically labeled with an antibody to Chaoptin (Chp). They project from the eye imaginal disc, through the optic stalk (os) and into the optic lobe where R1–R6 axons terminate in the lamina plexus (la), while R7 and R8 axons terminate in the medulla (me). GMR-GAL4 drives expression in all cells of the eye posterior to the morphogenetic furrow. Expression of GMR-GAL4 alone (genotype: GMR-GAL4/+) has no effect on the normal pattern of projections. Bars in A and C, 20 μm. (B) Misexpression of GSd447 results in severe axon guidance defects (GMR-GAL4/GSd447). The lamina is depleted and the axon bundles that project into the medulla are thickened (arrow), suggesting R1–R6 axons are bypassing normal targets in the lamina layer. (C, D) Axon targeting to the lamina can be assessed with the ro-tlacZ reporter, which labels the R2–R5 axons using α−β-galactosidase immunochemistry. No axon targeting defects of the R2–R5 axons are seen in GMR-GAL4/+ controls, but large bundles of R2–R5 axons project past the lamina in GMR-GAL4/GSd447 individuals. (E, F) Immunostaining for Boss, and R8-specific marker, is unaltered in GMR-GAL4/GSd447 individuals. (G, H) Lz-GAL4 expresses specifically in R1, R6, and R7. Control animals (Lz-GAL4/+) have no axon targeting defects, but in Lz-GAL4/+; GSd447/+ larvae the lamina is thin, and axon bundles in the medulla are thickened. (I, J) MT14-GAL4 is specific for R2, R5, and R8. MT14-GAL4/+ animals have normal targeting of the R2–R5 axons as revealed by ro-tlacZ (I), but misexpression of GSd447 results in severe mistargeting of the R2–R5 axons past the lamina (GSd447/+; Mt14-GAL4/+) (J). (K) An antibody to the glial specific protein, Reversed Polarity (Repo), reveals the normal positioning of the two layers of laminar glia, the epithelial glia (ep) and marginal (ma) glia, in GMR-GAL4/+ controls. These glia present incoming R-cell axons with a stop signal to which R1–R6 cells respond. (L) Misexpression of GSd447 does not affect the positioning of the epithelial (ep) or marginal (ma) glia, which remain in ordered rows within the optic lobe.