Fig. 5. roe expression is under the control of N activity. Panels show third instar eye disc regions around the MF; anterior is upwards. (A) In situ hybridization staining: roe is expressed in the MF (yellow arrowhead) and posterior to it. (B,B') -Roe staining (turquoise, monochrome in B'). Roe is a nuclear protein detected at high levels in the MF and at lower levels posterior to it. Roe is higher in interommatidial (progenitor) cells and shows only low levels in photoreceptors (Elav, red). (C) Third instar eye disc posterior to the MF showing -Roe (turquoise) and -Elav (red) staining. Note higher levels of Roe in R1/R6 precursors (examples marked with asterisks). (D,D') High magnification of an ommatidial precluster showing -Elav (red), -Roe (blue) and sev^GAL4 UAS-GFP (green) staining (D) and schematic cartoon (D'). Note that sev^GAL4 and Roe are co-expressed in R1/R6 precursors prior to Elav detection. (E,E') N loss-of-function clones (marked by absence of Ubi-GFP, green) cause reduction in Roe expression levels (blue, monochrome in E'), both within the MF (compare to B') and posterior to it. Photoreceptors are marked with -Elav (red in E). (F-F'') Clones expressing N^ECD (marked by co-expression of GFP, green, outlined in F') cause ectopic MF initiation in cells anterior to endogenous MF and ectopic cell-autonomous upregulation of Roe (blue, monochrome in F') posterior to MF. Clones are as expected associated with loss of photoreceptors (note reduction in -Elav, red and monochrome in F''). Close to and within the MF, N^ECD-expressing clones cause a precocious initiation of the MF state with associated non-autonomous Roe activation (see also Results).