Frizzled2 receives WntA signaling during butterfly wing pattern formation.
Butterfly color patterns provide visible and biodiverse phenotypic readouts of the patterning processes. Although the secreted ligand WntA has been shown to instruct the color pattern formation in butterflies, its mode of reception remains elusive. Butterfly genomes encode four homologs of the Frizzled-family of Wnt receptors. Here, we show that CRISPR mosaic knockouts of frizzled2 (fz2) phenocopy the color pattern effects of WntA loss of function in multiple nymphalids. Whereas WntA mosaic clones result in intermediate patterns of reduced size, fz2 clones are cell-autonomous, consistent with a morphogen function. Shifts in expression of WntA and fz2 in WntA crispant pupae show that they are under positive and negative feedback, respectively. Fz1 is required for Wnt-independent planar cell polarity 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.
Peer reviewed: True
Acknowledgements: We thank Rachel Canalichio and the staff of the Wilbur V. Harlan Greenhouse at the GWU for butterfly rearing and host plant resources; Bob Reed, Brian Counterman and Donya Shodja for stimulating discussions and comments on the manuscript; Chip Taylor and Ann Ryan for providing Passionvine Butterfly artificial diet; and Richard Merrill for facilitating H. melpomene experiments.
Funder: Smithsonian Institution; doi: http://dx.doi.org/10.13039/100000014
Funder: George Washington University; doi: http://dx.doi.org/10.13039/100007108
Deutsche Forschungsgemeinschaft (ME4845/1-1)