WntA instructs colour pattern formation in butterfly wings, but the mechanism of WntA reception is not well studied, as WntA has been lost in classical model systems such as Drosophila. Here, Joe Hanly, Ling Sheng Loh and colleagues investigate the relationship between WntA and Frizzled receptors in butterfly wing patterning. First, the authors generate mosaic knockouts of Frizzled2 (Fz2) in six species and observe that these knockouts phenocopy the patterns of WntA loss-of-function mutants. fz2 clones have cell-autonomous effects and can dislocate patterns, while WntA clones result in cell non-autonomous pattern contractions, suggesting that WntA acts as a morphogen. Although the findings show that WntA signals only through Fz2, Fz2 signalling is not exclusive to WntA. Then, using in situ hybridization to examine WntA and fz2 mRNA expression in early pupal wings, the authors observe that WntA signalling represses fz2 expression, and a positive WntA signalling feedback refines WntA expression. Furthermore, the authors assay other Frizzled receptors and find that Fz1 is required for planar cell polarity in the wing epithelium, as in Drosophila, whereas Fz3 and Fz4 have roles in colour patterning and wing margin specification. Overall, this study shows that WntA signals through Fz2 to instruct wing colour patterning and provides insight into the diverse functions of Frizzled receptors in tissue patterning.
