POINTED, AN ETS DOMAIN TRANSCRIPTION FACTOR, NEGATIVELY REGULATES THEEGF RECEPTOR PATHWAY IN DROSOPHILA OOGENESIS

Spatially regulated activation of the Drosophila epidermal growth fact or (EGF) receptor by its ligand, Gurken, is required for establishment of the dorsal/ventral axis of the oocyte and embryo. During mid-oogen esis, Gurken is concentrated at the dorsal-anterior of the oocyte and is thought to activate the EGF receptor pathway in adjacent follicle c ells. In response to this signal, dorsal follicle cell fate is determi ned. These cells further differentiate into either appendage-producing or midline cells, resulting in patterning in the dorsal follicle cell layer. We show here that Pointed, an ETS transcription factor, is req uired in dorsal follicle cells for this patterning. Loss of pointed re sults in the loss of midline cells and an excess of appendage-forming cells, a phenotype associated with overactivation of the EGF receptor pathway in the dorsal region. Overexpression of pointed leads to a phe notype similar to that generated by loss of the EGF receptor pathway, This suggests that Pointed normally down-regulates EGF receptor signal ing in the midline to generate patterning in the dorsal region, Intere stingly, pointed expression is induced by the EGF receptor pathway, Th ese data indicate a novel antagonistic function for Pointed in oogenes is; in response to activation of the EGF receptor, pointed is expresse d and negatively regulates the EGF receptor pathway, possibly by integ rating information from a second pathway.