Frizzled2 receives the WntA morphogen during butterfly wing pattern formation

Abstract

Butterfly color patterns provide visible and biodiverse phenotypic readouts of the patterning processes that occur in a developing epithelium. While the secreted ligand WntA was shown to instruct the color pattern formation in butterflies, its modes of reception and signal transduction remain elusive. Butterfly genomes encode four homologues of the Frizzled-family of Wnt receptors. Here we show that CRISPR mosaic knock-outs of frizzled2 (fz2) phenocopy the color pattern effects of WntA loss-of-function in multiple nymphalids. While WntA mosaic clones result in intermediate patterns of reduced size, consistently with a morphogen function, fz2 clones are cell-autonomous. Shifts in pupal expression in WntA crispants show that WntA and fz2 are under positive and negative feedback, respectively. Fz1 is required for Wnt-independent planar cell polarity (PCP) in the wing epithelium. Fz3 and Fz4 show phenotypes consistent with Wnt competitive-antagonist functions in vein formation (Fz3 and Fz4), wing margin specification (Fz3), and color patterning in the Discalis and Marginal Band Systems (Fz4). Overall, these data show that the WntA/Frizzled2 morphogen-receptor pair forms a signaling axis that instructs butterfly color patterning, and shed light on the functional diversity of insect Frizzled receptors.