DISTALLESS EXPRESSION IN CRUSTACEANS AND THE PATTERNING OF BRANCHED LIMBS

In Drosophila, Distalless (Dll) is critical in establishing the proxim al/distal axis of the leg. Lack of proper Dll expression causes distal limb structures to be truncated or lost. Dll expression was examined through the course of development in the limbs of two crustaceans, Tri ops and Nebalia. Because the limbs of these two species are branched, they provide a comparison to the uniramous (unbranched) leg of Drosoph ila. In Triops and Nebalia, development of limb branches is not tightl y coupled with Dll expression: in some cases, branches can arise prior to Dll expression and in others, certain branches never express Dll. These data suggest that, while Dll may indeed initiate overall limb ou tgrowth, limb branches are unlikely to be patterned by a simple iterat ion of the mechanism patterning the unbranched leg of Drosophila.