SPECIFIC TRUNCATIONS OF DROSOPHILA NOTCH DEFINE DOMINANT ACTIVATED AND DOMINANT-NEGATIVE FORMS OF THE RECEPTOR

The Notch gene of Drosophila plays an important role in cell fate spec ification throughout development. To investigate the functions of spec ific structural domains of the Notch protein in vivo, a series of dele tion mutants have been ectopically expressed under the hsp70 heat shoc k promoter. Two classes of dominant phenotypes are observed, one sugge stive of Notch loss-of-function mutations and the other of Notch gain- of-function,mutations. Dominant activated phenotypes result from overe xpression of a protein lacking most extracellular sequences, while dom inant negative phenotypes result from overexpression of a protein lack ing most intracellular sequences. These results support the notion tha t Notch functions as a receptor whose extracellular domain mediates li gand binding, resulting in the transmission of developmental signals b y the cytoplasmic domain. Finally, the phenotypes observed suggest tha t the cdc10/ankyrin repeat region within the intracellular domain play s an essential role in the postulated signal transduction events.