Signaling by the Drosophila epidermal growth factor receptor (Egfr) plays an important role in many aspects of development, including oogenesis, embryogenesis and proper development of both the eye and the wing. In the ovary, the Egfr pathway is known to play a key role in the establishment of the body axes during oogenesis. In the wing, Egfr signaling plays an important role in vein tissue specification, and in the eye it has been found to be important for photoreceptor cell differentiation. Microarray screens by our lab and others have been used to identify potential downstream transcriptional targets of the Egf receptor using the Drosophila ovary as a model system. Our initial work compared gene expression using fly ovaries in which the activity of the Egfr-pathway was reduced (grk mutant), normal (OreR), or constitutively active (CY2/λTop). We have employed a number of approaches to further investigate the expression, biological function, and mechanism of action of an initial set of putative genes of interest, focusing primarily on genes of previously unknown function. Several of these targets exhibit developmentally regulated expression in the ovary. UAS-RNAi was used to knock down expression of various target genes in either specific tissues or ubiquitously via a tubulin driver. Gene knockdown phenotypes include abnormal wing morphology, decreased eggshell integrity, and, in at least one case, lethality. We are currently extending our studies by utilizing the UAS/Gal4 system to perform a functional screen of previously identified, but untested, target genes whose expression is highly upregulated in response to constitutive Egf receptor activity. In particular, the available libraries of UAS-RNAi transgenic flies are being used in concert with ovarian and wing disc Gal4 driver lines to identify additional genes with roles in Drosophila developmental events. We have identified several additional genes which may have roles in normal eggshell formation. RT-PCR has confirmed the up-regulation of some of our newly identified targets, and we are further investigating gene expression patterns via in situ hybridization.