Leg patterning driven by proximal-distal interactions and EGFR signaling.

wingless and decapentaplegic signaling establishes the proximal-distal axis of Drosophila legs by activating the expression of genes such as Distalless and dachshund in broad proximal-distal domains during early leg development. However, here we show that wingless and decapentaplegic are not required throughout all of proximal-distal development. The tarsus, which has been proposed to be an ancestral structure, is instead defined by the activity of Distalless, dachshund, and a distal gradient of epidermal growth factor receptor (EGFR)-Ras signaling. Our results uncover a mechanism for appendage patterning directed by genes expressed in proximal-distal domains and possibly conserved in other arthropods and vertebrates.