GSd427 driven by GMR-GAL4 caused defects in R-cell localization. (A-D) Apical (A and B) and basal (C and D) view of third-instar larval eye discs stained with anti-Elav. In wild type (A), R-cell bodies and nuclei are located at the apical region of the eye disc, and are absent at the basal region (C). The distance between the sections shown in A and C is ~12 μm. In larvae carrying GSd427 under control of GMR-GAL4 (B and D), many R-cell nuclei were mis-localized to the basal region (D). The distance between the sections shown in B and D is ~13 μm. (E and F) Longitudinal plastic sections of eye discs stained with anti-Elav (1 μm thick). Apical is up and basal is down. (E) In wild type, R-cell nuclei tanslocate to the apical region in the region posterior to the morphogenetic furrow (arrow). (F) In GSd427 larvae, many R-cell nuclei (arrowheads) were mis-localized to the basal region (~27.1% of ommatidia, n = 8 eye discs). Note that the majority of R-cell nuclei were able to translocate to the apical region at earlier stage (i.e. R cells located close to the furrow). Scale bars: A-D, 50 μm; E and F, 10 μm.