Patterns in evolution: veins of the Drosophila wing.

The development of the Drosophila wing is a classical model for studying the genetic control of tissue size, shape and patterning. A detailed picture of how positional information is interpreted by cells in the imaginal disc and translated into the adult wing vein pattern has recently emerged. It highlights the central role of dose-dependent activation of distinct cell transcription programs in response to the Hedgehog (Hh) and Decapentaplegic (Dpp) morphogens, as well as an early role of Notch signalling, in connecting the positioning of vein primordia and vein differentiation proper. The biochemical basis of the cross-talk that operates between these different signalling pathways is less well understood. New strategies made possible by the genome sequencing of several insect models should provide an important complement to the knowledge obtained from >60 years of genetic studies.