Spatial regulation of DELTA expression mediates NOTCH signalling for segmentation of Drosophila legs

The Notch (N) signalling pathway is recruited for segregation of cell fates in a number of Drosophila tissue types. We show here that N dependent segm entation of Drosophila legs is regulated by a dynamic pattern of expression of its ligand, DELTA (DL). During third larval instar and early stages of pupation, high levels of DL expression is seen in stripes of cells in the l eg imaginal discs which later form the proximal borders of leg joints. Thes e domains also displayed heightened Dl enhancer activity. During subsequent stages of pupation, following segmentation of the leg primordium, DL expre ssion becomes uniform throughout these segments barring the joints. We furt her show that regulatory Dl mutations or mis-expression of DL abolish leg s egmentation. Domains of N signalling for segmentation of legs of flies are thus set up by a stringent spatial regulation of expression of its ligand a t the segment border. Further, a comparable role of DL in antennal developm ent reveals a common paradigm of DL-N signalling for segmentation of append ages in flies. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.