EGF domain swap converts a drosophila EGF receptor activator into an inhibitor

In Drosophila the function of the epidermal growth factor (EGF) receptor is modulated zygotically by three EGF-like proteins: Spitz (Spi), which is a potent activator; Vein (Vn), which is a moderate activator; and Argos (Aos), which is an inhibitor. Chimeric molecules were constructed in which the EGF domain of Vn was swapped with the EGF domain from each factor. The modified Vn proteins behaved both in vitro and in vivo with properties characteristic of the factor from which the EGF domain was derived. These results demonstrate that the EGF domain is the key determinant that gives DER inhibitors and activators their distinct properties.