Abstract

The extent of neurogenesis in Drosophila is under the control of the so‐called neurogenic genes, named for their mutant phenotype of causing neural hyperplasia. Their wild‐type products appear to be responsible for a signal chain that decides the fate of ectodermal cells in the embryo. Various kinds of data, from cell transplantation experiments as well as from genetic and molecular analyses, suggest that the proteins encoded by the genes Notch and Delta may act at the membrane of the signal‐transmitting cells to provide a ligand to a still unknown receptor molecule; in contrast, the locus of Enhancer of split codes for several functions related to the transduction and further processing of the signal.