Control of bract formation in Drosophila: poxn, kek1, and the EGF-R pathway.

In Drosophila, the sensory organs are formed by cells that derive from a precursor cell through a fixed lineage. One exception to this rule is the bract cell that accompanies some of the adult bristles. The bract cell is derived from the surrounding epidermis and is induced by the bristle cells. On the adult tibia, bracts are associated with all mechanosensory bristles, but not with chemosensory bristles. The differences between chemosensory and mechanosensory lineages are controlled by the selector gene pox-neuro (poxn). Here we show that poxn is also involved in suppressing bract formation near the chemosensory bristles. We have identified the gene kek1, described as an inhibitor of the EGF-R signaling pathway, in a screen for poxn downstream genes. We show that kek1 can suppress bract formation and can interfere with other steps of sensory development, including SMC determination and shaft differentiation.