WINGLESS SIGNALING IN THE DROSOPHILA EYE AND EMBRYONIC EPIDERMIS

After the onset of pupation, sensory organ precursors, the progenitors of the interommatidial bristles, are selected in the developing Droso phila eye. We have found that wingless, when expressed ectopically in the eye via the sevenless promoter, blocks this process, Transgenic ey es have reduced expression of acheate, suggesting that wingless acts a t the level of the proneural genes to block bristle development, This is in contrast to the wing, where wingless positively regulates acheat e to promote bristle formation, The sevenless promoter is not active i n the acheate-positive cells, indicating that the wingless is acting i n a paracrine manner, Clonal analysis revealed a requirement for the g enes porcupine, dishevelled and armadillo in mediating the wingless ef fect, Overexpression of zeste white-3 partially blocks the ability of wingless to inhibit bristle formation, consistent with the notion that wingless acts in opposition to zeste white-3. Thus the wingless signa ling pathway in the eye appears to be very similar to that described i n the embryo and wing, The Notch gene product has also been suggested to play a role in wingless signaling (J. P. Couso and A. M. Martinet A rias (1994) Cell 79, 259-72), Because Notch has many functions during eye development, including its role in inhibiting bristle formation th rough the neurogenic pathway, it is difficult to assess the relationsh ip of Notch to wingless in the eye. However, we present evidence that wingless signaling still occurs normally in the complete absence of No tch protein in the embryonic epidermis, Thus, in the simplest model fo r wingless signalling, a direct role for Notch is unlikely.