wingless expression mediates determination of peripheral nervous system elements in late stages of Drosophila wing disc development.

We have used conditional wingless genotypes to dissect the role of this gene in late stages of wing disc development. One of these genotypes (wgIL/wg-lacZ) is simultaneously a reporter of wingless transcription and temperature-sensitive for wingless function, and has allowed us to define its pattern of transcription in the absence of wingless activity. The primordia of a subset of the bristles of the notum, which develop in or immediately adjacent to wingless-expressing cells, depend upon wingless activity. The time-course of this contribution and the effect on proneural gene expression together suggest that wingless may regulate the activity of products of the achaete-scute complex in proneural clusters. wingless activity is also required at the presumptive wing margin and is a necessary precondition for the change in proliferation pattern in this region. The involvement of wingless in transducing or mediating positional signals for spatial patterning in imaginal disc development is discussed.