THE NUCLEAR-PROTEIN ENCODED BY THE DROSOPHILA NEUROGENIC GENE MASTERMIND IS WIDELY EXPRESSED AND ASSOCIATES WITH SPECIFIC CHROMOSOMAL REGIONS

The Drosophila neurogenic loci encode a diverse group of proteins that comprise an inhibitory signal transduction pathway. The pathway is us ed throughout development in numerous contexts. We have examined the d istribution of the neurogenic locus master mind protein (Mam). Mam is expressed through all germlayers during early embryogenesis, including ectodermal precursors to both neuroblasts and epidermoblasts. Mam is subsequently down-regulated within the nervous system and then reexpre ssed. It persists in the nervous system through late embryogenesis and postembryonically. Mam is ubiquitously expressed in wing and leg imag inal discs and is not down-regulated in sensory organ precursor cells of the wing margin or notum. In the eye disc, Mam shows most prominent expression posterior to the morphogenetic furrow. Expression of the p rotein during oogenesis appears limited to follicle cells. Immunohisto chemical detection of Mam on polytene chromosomes revealed binding at >100 sites. Chromosome colocalization studies with RNA polymerase and the groucho corepressor protein implicate Mam in transcriptional regul ation.