A thousand and one roles for the Drosophila EGF receptor.

In the Drosophila genome there is a single member of the EGF receptor tyrosine kinase family. This receptor fulfills multiple roles during development, as reflected by the many designations given to mutant alleles in the locus (Egfr, DER, faint little ball, torpedo and Ellipse). The full scope of EGFR functions became apparent only in recent years: receptor activation was shown to have an instructive role in successive cell fate determination events during oogenesis, embryogenesis, and the proliferation and differentiation of imaginal discs. To ensure the fidelity of these processes, the precise place and time of receptor activation are tightly regulated by the localized presentation of activating ligands, in conjunction with a negative-feedback loop generated by an inhibitory secreted factor. The cellular mechanisms that translate EGFR activation to discrete cell fates are now the focus of intense studies.