Expressed most strongly in R7, within the mature ommatidial cluster.
In the eye disc of third instar larva, high level of β-gal expression in presumptive R7 photoreceptor cells, first detected 12 to 13 columns posterior to the morphogenetic furrow; much lower level of expression detected in other photoreceptor cells. During pupal development, continued expression in R7 photoreceptor; apparent increase in level of expression in R8. In the adult retina, detected in R7 and at lower levels in R8.