THE DYNAMICS OF NEUROGENIC SIGNALING UNDERLYING BRISTLE DEVELOPMENT IN DROSOPHILA-MELANOGASTER

We have examined expression of the neurogenic gene, Delta (Dl), and th e regulatory relationships between the Delta-Notch signalling pathway and the proneural gene, achaete, during microchaeta development in Dro sophila. Delta is expressed in all microchaeta proneural cells and mic rochaeta sensory organ precursors (SOPs) and is expressed dynamically in SOP progeny. We find that Delta expression in microchaeta proneural cells is detected prior to the onset of achaete expression and arises normally in the absence of achaete/scute function, indicating that in itial Delta expression in the notum is not dependent on proneural gene function. Activation of the Delta-Notch pathway results in loss of De lta protein accumulation, suggesting that Delta expression is regulate d, in part, by Delta-Notch signalling activity. We find that Delta sig nalling is required for correct delineation of early proneural gene ex pression in developing nora. Within microchaeta proneural stripes, we demonstrate that Delta-Notch signalling prohibits adoption of the SOP fate by repressing expression of proneural genes. (C) 1997 Elsevier Sc ience ireland Ltd.