How a small set of cells go on to become tissues and organs is one of the fundamental questions in the field of developmental biology. The eye-antennal imaginal discs give rise to the compound eye, ocelli, antennae, maxillary palps and the head capsule. Fourteen genes that form the retinal determination(RD) network are responsible for the proper specification of the compound eye and for many aspects of its development. Among them are the zinc finger proteins, Teashirt(Tsh) and its paralog,Tiptop(Tio). Understanding the specific functions of Tsh/Tio in the early eye-antennal imaginal disc development is the primary focus of my work. Tsh/Tio have redundant expression patterns in the larval third instar imaginal discs and are suggested to be functionally equivalent. Knockdown of each gene individually has very mild,if any, phenotype in the eye, while knocking down both genes simultaneously results in flies with small or missing eyes. We have evidence suggesting that tsh, functions with another RD gene twin of eyeless(toy),to maintain cells in a proliferative state. We determined that Tsh and Toy are required together during the embryonic and first larval instar stages. Simultaneous removal of both tsh and toy during these stages results in headless flies. We are examining how the loss of Tsh and Toy affects the expression of other RD network genes and whether the headless phenotype is due to increased cell death or a loss of cell proliferation. Also,I have evidence that Tsh/Tio play a part in antagonizing non-ocular fates.My results reveal that Tsh/Tio are capable of repressing cut, a key specification gene of the antenna and head epidermis when misexpressed in the antennal disc.Work from several labs has shown that the Sine Oculis(So) and Eyes Absent(Eya) proteins, which are also members of the RD network, function to repress the expression of gene regulatory networks that control surrounding non-ocular fates. My results suggest that the Tsh/Tio repress cut independent of the So-Eya complex. Finally,I have evidence that this Tsh/Tio require the co-repressor C-terminal Binding Protein(CtBP).