FEEDBACK-REGULATION IS CENTRAL TO DELTA-NOTCH SIGNALING REQUIRED FOR DROSOPHILA WING VEIN MORPHOGENESIS

Delta and Notch are required for partitioning of vein and intervein ce ll fates within the provein during Drosophila metamorphosis. We find t hat partitioning of these fates is dependent on Delta-mediated signall ing from 22 to 30 hours after puparium formation at 25 degrees C. With in the provein, Delta is expressed more highly in central provein cell s (presumptive vein cells) and Notch is expressed more highly in later al provein cells (presumptive intervein cells). Accumulation of Notch in presumptive intervein cells is dependent on Delta signalling activi ty in presumptive vein cells and constitutive Notch receptor activity represses Delta accumulation in presumptive vein cells. When Delta pro tein expression is elevated ectopically in presumptive intervein cells , complementary Delta and Notch expression patterns in provein cells a re reversed, and vein loss occurs because central provein cells are un able to stably adopt the vein cell fate. Our findings imply that Delta -Notch signalling exerts feedback regulation on Delta and Notch expres sion during metamorphic wing vein development, and that the resultant asymmetries in Delta and Notch expression underlie the proper specific ation of vein and intervein cell fates within the provein.