CELL-INTERACTION BETWEEN COMPARTMENTS ESTABLISHES THE PROXIMAL-DISTALAXIS OF DROSOPHILA LEGS

THE appendage primordia of Drosophila are subdivided into compartments (1-4) by the localized expression of transcription factors(5-7). Inter action between cells in adjacent compartments establishes organizing c entres responsible for generating spatial pattern and promoting cell p roliferation in the developing appendages(7-9). Localized expression o f hedgehog (hh) in the posterior compartment of the leg: imaginal disc directs expression of wingless (wg) in ventral-anterior cells and dec apentaplegic (dpp) in dorsal-anterior cells near the anterior-posterio r compartment boundary(8); wg then acts to specify ventral cell fate(1 0-12) and to organize the dorsal-ventral axis of the leg(13,14). Inter action between wg-expressing ventral cells and dorsal cells near the a nterior-posterior compartment boundary promotes axis formation in the leg(14,15). Here we show that the combined action of log-expressing ce lls in the ventral-anterior compartment and dpp-expressing cells in th e dorsal-anterior compartment activates expression of Distal-less, a g ene required for proximal-distal axis formation in the limbs. These re sults demonstrate that sequential interaction between anterior-posteri or and dorsal-ventral compartments establishes the proximal-distal axi s of the limbs.