Modulating the levels and activity of the retinal determination network is sufficient to induce the specification of distinct tissue fates in <i>Drosophila</i>

A pair of eye-antennal discs give rise to most tissues that form the adult head of the fruit fly Drosophila melanogaster, including a pair of compound eyes and a trio of simple eyes called ocelli. These two visual organs are anatomically distinct, innervate different regions of the brain, and control some distinct visual and circadian behaviors. Several members of the retinal determination gene regulatory network are differentially expressed within the compound eyes and ocelli. We have manipulated the network as well as the transcriptional repressor Groucho (Gro) within the area of the eye-antennal disc that gives rise to the ocelli, interocellar head epidermis, and several classes of mechanosensory bristles. We observe several changes in tissue identity, including a dramatic transformation of the ocelli into compound eyes. Our findings suggest that modulation of transcription factor levels and/or activity is sufficient to induce the specification of distinct tissue fates. This could potentially give the same transcriptional networks the ability to generate an array of cell, tissue and organ types.