Developmental territories created by mutual antagonism between Wingless and Decapentaplegic.

Drosophila appendages develop from imaginal discs which become subdivided into distinct regions during normal patterning. At least 3 axes of asymmetry are required to produce a chiral appendage such as a leg. The A/P compartments provide one axis of asymmetry in all discs. In leg and antennal discs, the anterior compartment becomes asymmetric in the D/V axis with decapentaplegic (dpp) expression defining dorsal anterior leg, and wingless (wg) expression defining ventral anterior leg. However, unlike wing discs, no D/V compartment has been demonstrated in legs or antennae. How are the dorsal anterior and ventral anterior territories defined and maintained? Here we show that wg inhibits dpp expression and dpp inhibits wg expression in leg and eye/antennal discs. This mutual repression provides a mechanism for maintaining separate regions of wg and dpp expression in a developing field. We propose the term 'territory' to describe regions of cells that are under the domineering influence of a particular morphogen. Territories differ from compartments in that they are not defined by lineage but are dynamically maintained by continuous morphogen signaling. We propose that the anterior compartment of the leg disc is divided into dorsal and ventral territories by the mutual antagonism between WG and DPP signaling.