In the eye imaginal disc BOSS is first detected in cells lying three rows posterior to the morphogenetic furrow. Its expression is restricted to the R8 cell, identifiable by its characteristic shape and position in the ommatidial cluster.
BOSS is localized to the apical regions of the monolayer epithelium.
In later stages of eye development boss is more widely expressed. The protein is found in all photoreceptor cells, even into adulthood. Mutation of roughex perturbs cell fate determination. Many rux mutant clusters contain multiple boss -expressing cells. In some of these clusters, R8 cells are missing.