Required to establish the unique cell identity of photoreceptors R2 and R5 and consequently for ommatidial assembly in the developing eye imaginal disk. Repression of expression in R8 photoreceptor by senseless (sens) is an essential mechanism of R8 cell fate determination. Restricted to nuclei in the developing retina. Expressed in cells within, and posterior to, the morphogenetic furrow of the eye imaginal disk, expression is rapidly restricted to the R2, R3, R4, and R5 precursor cells. R2 and R5 fail to be correctly determined and appear to be transformed into cells of the R3/4/1/6 subtype.