Distinct pathways for autocrine and paracrine Wingless signalling in Drosophila embryos.

Two secreted proteins, Wingless and Hedgehog, instruct cell fates within the segmented epidermis of Drosophila embryos (reviewed in ref. 5). Wingless (Wg) is expressed by the most posterior cells in each parasegment; Hedgehog (Hh) is expressed in the most anterior cells of the next parasegment. Immediately after gastrulation, the two cell types are mutually dependent. Local Wg signalling stabilizes Hh expression and local Hh signalling stabilizes Wg expression. Direct Wg autoregulation (autocrine signalling) is masked by its paracrine role in maintaining hh, which in turn maintains wg. I have used zeste-white3 (zw3) and patched (ptc) mutant backgrounds to uncouple genetically this positive-feedback loop and to study autocrine Wg signalling. I report here that direct Wg autoregulation differs from Wg signalling to adjacent cells in the importance of fused (fu), smoothened (smo) and cubitus interruptus (ci) relative to zw3 and armadillo (arm). I also find that Wg autoregulation during this early hh-dependent phase differs from later Wg autoregulation by lack of gooseberry (gsb) participation.