Math5 does not induce ommatidial precluster formation. Confocal micrographs of Rough (green) and Elav (red) expression in developing Drosophila eye discs. In all panels, horizontal arrows mark the position of the morphogenetic furrow (MF) and anterior is down. (A) w-; gal4-7, ato1/TM6Tb control. In the MF, Rough is expressed within R8, R2, and R5 cells of ommatidial preclusters (green nuclei). After differentiation these cells coexpress Rough and Elav (cells with green nuclei and red cytoplasm). (B) atonal-rescued eyes initiate precluster formation within the MF. Some ommatidia have extra Rough-positive nuclei. (C) Xath5-rescued discs initiate precluster formation, marked by Rough expression (green nuclei alone) in the MF. (D) In UAS-Math5 eye discs, cells expressing only Rough were never observed. However, many differentiated photoreceptors (labeled in red) also express Rough. (E) Scute-rescued eye disc also fail to initiate Rough precluster expression. Similar to Math5, many differentiated photoreceptors coexpress Rough and Elav. (F) Rough MF precluster expression in NeuroD-rescued eyes. Scale bar, 25 μm.