EGF RECEPTOR SIGNALING INDUCES POINTED P1 TRANSCRIPTION AND INACTIVATES YAN PROTEIN IN THE DROSOPHILA EMBRYONIC VENTRAL ECTODERM

The induction of different cell fates along the dorsoventral axis of t he Drosophila embryo requires a graded activity of the EGF receptor ty rosine kinase (DER). Were we have identified primary and secondary tar get genes of DER, which mediate the determination of discrete ventral cell fates. High levels of DER activation in the ventralmost cells tri gger expression of the transcription factors encoded by ventral nervou s system defective (vnd) and pointed P1 (pntP1). Concomitant with the induction of pntP1, high levels of DER activity lead to inactivation o f the Yan protein, a transcriptional repressor of Pointed-target genes . These two antagonizing transcription factors subsequently control th e expression of secondary target genes such as otd, argos and tartan. The simultaneous effects of the DER pathway on pntP1 induction and Yan inactivation may contribute to the definition of the border of the ve ntralmost cell fates.