PT - JOURNAL ARTICLE AU - Varun Chaudhary AU - Michael Boutros TI - Evidence of functional long-range Wnt/Wg in the developing <em>Drosophila</em> wing epithelium AID - 10.1101/412627 DP - 2018 Jan 01 TA - bioRxiv PG - 412627 4099 - http://biorxiv.org/content/early/2018/09/09/412627.short 4100 - http://biorxiv.org/content/early/2018/09/09/412627.full AB - Wnts are secreted proteins that regulate cell fate specification during development of all metazoans. Wnt proteins were proposed to spread over several cell diameters to activate signalling directly at a distance. In the Drosophila wing epithelium, an extracellular gradient of Wingless (Wg, the homolog of Wnt1) was observed extending over several cells away from producing cells. However, it was also recently shown that a membrane-tethered Neurotactin-Wg fusion protein (NRT-Wg) can rescue the loss-of endogenous Wg, leading to proper patterning of the wing. Therefore, whether Wg spreading is required for correct tissue patterning during development remains controversial and the functional range of wild-type Wg is unclear. Here, by capturing secreted Wg on distally located cells we show that Wg can act directly up to eleven cell distances. Cells located outside the reach of extracellular Wg depend on the Frizzled2 receptor to maintain target gene expression. We find that NRT-Wg is not restricted to the producing cells and propose that it can rescue signalling defects by perdurance in the receiving cells. These results provide insight into the mechanisms by which Wnt proteins mediate patterning of a rapidly growing tissue.