Distinct pathways for autocrine and paracrine Wingless signalling inDrosophila embryos

Abstract

TWO secreted proteins, Wingless1,2 and Hedgehog3,4, instruct cell fates within the segmented epidermis of Drosophila embryos (reviewed in ref. 5). Wingless (Wg) is expressed by the most pos-terior 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 dependent6,7. Local Wg signalling stabilizes Hh expression8–10 and local Hh signalling stabilizes Wg expression11,12. Direct Wg autoregulation (autocrine signalling) is masked by its paracrine role in maintaining hh, which in turn maintains wg. I have usedzeste-white3 (zM3)13 and patched(ptc)11,14 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) andcubitus interruptus (ci) relative to zw3 andarmadillo (arm). I also find that Wg autoregulation during this early hh-dependent phase differs from later Wg autoregulation15 by lack of gooseberry (gsb) participation.