A wingless-dependent polar coordinate system in Drosophila imaginal discs.

The patterning of the imaginal discs in Drosophila melanogaster is a progressive process that, like the patterning of the larval epidermis during embryogenesis, requires the activity of segment polarity genes. One segment polarity gene, wingless, encodes a homolog of the mouse proto-oncogene Wnt-1 and plays a prominent role in the patterning of the larval epidermis and the imaginal discs. However, whereas the function of wingless in the embryo is initially associated with a pattern of stripes along the anteroposterior axis that are part of a Cartesian coordinate system, it is shown here that during imaginal development wingless is associated with a pattern of sectors that provide references for a polar coordinate system homologous to that postulated in a well-known model for the regeneration of insect and vertebrate limbs.