A role for the ecdysone response gene E93 in imaginal patterning during metamorphosis

Drosophila melanogaster E93 is an early ecdysone response gene that encodes a pipsqueak domain transcription factor. E93 is induced by ecdysone at the end of larval development, and directs the death and elimination of several larval tissues during metamorphosis. Although E93 has been considered a dedicated regulator of larval cell death, I have found that E93 is also widely expressed in imaginal tissues during metamorphosis, where it is required for the proper patterning of many adult structures. Our working hypothesis is that E93 functions in imaginal tissues as a metamorphosis-specific cofactor that determines the pupa-specific action of numerous other transcription factors involved in imaginal patterning. For my thesis work, I focused on a single E93-dependent patterning process, the induction of bracts by bristle cells in the pupal leg. This induction is known to be mediated by EGFR signaling. My studies position E93 downstream of the transcription factor Pointed in the EGFR pathway, and upstream of the bract target gene Distal-less, consistent with the view that E93 functions to control target gene specificity of EGFR signaling during metamorphosis. I also present the results of experiments to dissect functional domains within the E93 protein and to determine whether alternate products of E93 execute the cell death and imaginal patterning functions of E93.;Chapter II--V will present these works in detail and Chapter VI will discuss future directions of this interesting project.