Patterning of the Drosophila nervous system: the achaete-scute gene complex

The genes of the achaete-scute complex (AS-C) confer on cells the ability to become neural precursors. Their expression is restricted to groups of cells, the proneural clusters, which occupy specific positions within the embryo neural anlagen and the larva imaginal discs. Neuroblasts or sensory organ mother cells are born within these clusters. Thus, the patterns of expression of the AS-C genes help to define the topology of the nervous system.