The evolution and expression of panarthropod frizzled genes

Wnt signaling regulates many important processes during metazoan development. It has been shown that Wnt ligands represent an ancient diverse family of proteins that likely function in complex signaling landscapes to induce target cells and tissues via receptors including those of the Frizzled family. The four subfamilies of Fz receptors also evolved early in metazoan evolution. To compare with other metazoans and arthropods such as insects, we explored the repertoire of fz genes in three panarthropod species: Parasteatoda tepidariorum, Glomeris marginata and Euperipatoides kanangensis, representing the Chelicerata, Myriapoda and Onychophora respectively. We found that these three diverse panarthropods each have four fz genes with representatives of all four metazoan fz subfamilies found in Glomeris and Euperipatoides while Parasteatoda does not have a fz3 gene but has two fz4 paralogues. Furthermore we characterized the expression patterns of all fz genes in Parasteatoda, Glomeris and Euperipatoides and found both conserved and divergent expression of these genes among these animals and in comparison to insects. Our study provides new insights into the evolution and developmental functions of fz receptors and Wnt signaling more generally.Ralf Janssen and Anna Schönauer contributed equally to this work.