CORNICHON AND THE EGF RECEPTOR SIGNALING PROCESS ARE NECESSARY FOR BOTH ANTERIOR-POSTERIOR AND DORSAL-VENTRAL PATTERN-FORMATION IN DROSOPHILA

In Drosophila, the dorsal-ventral polarity of the egg chamber depends on the localization of the oocyte nucleus and the gurken RNA to the do rsal-anterior corner of the oocyte. Gurken protein presumably acts as a ligand for the Drosophila EGF receptor (torpedo/DER) expressed in th e somatic follicle cells surrounding the oocyte. cornichon is a gene r equired in the germline for dorsal-ventral signaling, cornichon, gurke n, and torpedo also function in an earlier signaling event that establ ishes posterior follicle cell fates and specifies the anterior-posteri or polarity of the egg chamber. Mutations in all three genes prevent t he formation of a correctly polarized microtubule cytoskeleton require d for proper localization of the anterior and posterior determinants b icoid and oskar and for the asymmetric positioning of the oocyte nucle us.