THE REGULATION AND FUNCTION OF THE HELIX-LOOP-HELIX GENE, ASENSE, IN DROSOPHILA NEURAL PRECURSORS

asense is a member of the achaete-scute complex (AS-C) of helix-loop-h elix genes involved in Drosophila neurogenesis. Unlike the other AS-C members, which are expressed in subsets of the ectodermal areas (prone ural clusters) that give rise to neural precursors, asense is one of a number of genes that are specifically expressed in the neural precurs ors themselves (the neural precursor genes). We have identified a muta nt asense phenotype that may reflect this later expression pattern. As a step in understanding the determination of neural precursors from t he proneural clusters, we have investigated the potential role of the AS-C products as direct transcriptional activators of neural precursor genes by analysing the regulation of asense. Using genomic rescues an d asense-lacZ fusion genes, the neural precursor regulatory element ha s been identified. We show that this element contains binding sites fo r AS-C/daughterless heterodimers. Deletion of these sites reduces the expression from the fusion gene, but significant expression is still a chieved, pointing to the existence of other regulators of asense in ad dition to the AS-C. asense differs from the other AS-C members in its expression pattern, regulation, mutant phenotype and some DNA-binding properties.