Fig. 3. Sens is required for inner photoreceptor differentiation. Adult retinas from wild-type (A-C,G,I,K,M) or sens^E2.1 late LOF (D-F,H,J,L,N) Drosophila. (A-J) Cryosections (10 µm); dorsal left, distal up. (K,L) Plastic sections (1 µm). (M,N) Optical sections from retinal whole-mounts. Samples were stained for Rh3 (purple, A,B,D,E,H-J; red, M,N), Rh4 (green, A,D,G,H,M,N), Rh5 (green, B,E), Rh6 (green, C,F; purple, G), Elav (purple, C,F; green, I,J), or the actin/rhabdomere marker, phalloidin (blue, M,N). R7 and R8 layers of WT rhabdomeres are clearly separated within the retina (A-C,G,I), but are ambiguously positioned in sens late LOF eyes (D,E,H,J). Wild-type control R8 nuclei (I, Elav, green) lie along the base of the retina (dotted white line), whereas sens late LOF R8 nuclei (F,J) are often located midway in the retina (purple, F or green, J). Wild-type control plastic sections (K) show a single small IPR rhabdomere (arrow); OPR rhabdomeres are circled in black; single ommatidia are outlined with a dotted blue line. In sens late LOF eyes (L), two small rhabdomeres are observed in the R7 and R8 positions (arrows). Rh3 and Rh4 staining reveals a single opsin-expressing cell (the R7) in wild-type ommatidia (M), whereas two opsin-positive cells (R7 and sens-negative `R8') are observed in sens late LOF ommatidia (N). Phalloidin marks OPR rhabdomeres. Inset in N is higher magnification of a single ommatidium with Rh4 expression in R7, and Rh3 expression in R8. (O) Summary of control, full sens LOF, or late sens LOF phenotypes. `R2' represents the pre-R8 cell that transforms into an R2/R5 OPR; `R8' represents sens-negative R8s. See Fig. 1 for color code.