Fig. 2. Transient sens expression rescues inner photoreceptor specification. (A) Coronal section of 55% pupal and 70% pupal heads from sca^109.68-GAL4, UAS-nuclear GFP (sca>nGFP) Drosophila. All PRs are marked with Elav (purple). GFP (green) is present in R8 cells at 55% APF, but not after 70% APF. (B) Summary of sens expression in full LOF and late LOF experiments. (C-E) Adult retinal sections stained for Salm (green); dorsal left, distal up. (C) UAS-sens/+, sens^E1/TM6B: the R7 and R8 layers of Salm-positive nuclei are labeled. (D) sens^E1 full LOF eyes (see Materials and methods) rarely develop IPRs (arrowhead). (E) sens^E1 mutant eyes with sca^109.68>sens (sens late LOF) develop two Salm-positive layers of IPRs (arrows). (F-H'') Adult cryosections of control and sens^E2.1 late LOF retinas stained for Salm (green, F-H,F'-H'), Pros (purple, F'-H'), or Sens (white, F''-H''). F-F'', G-G'', and H-H'' represent eyes co-stained for all three factors. Pros stains distal Salm-positive cells in both control and sens^E2.1 late LOF retinas, and the majority of Salm-positive cells in sens^E2.1 full LOF retinas. Sens is expressed in R8 cells only in control retinas (F'').