Segmentation gene expression and function in Vanessa cardui, an emerging model for Lepidoptera

Although all insects are segmented, the genes that control this process vary across species. Many of the pair-rule (PR) genes that direct segment formation in Drosophila are similarly utilized in other holometabolous insects, but more distantly related species use different genes for PR-patterning. Previously, we showed that Lepidoptera lack a highly conserved PR-gene, paired. Here, we used the painted lady butterfly Vanessa cardui as a lepidopteran model to explore the expression and function of PR-genes in this large clade of moths and butterflies. Orthologs of four Drosophila PR-genes are expressed in PR-like stripes and at least one displays PR-like function. Neither of the two genes that have PR-function in Hemiptera but not in Drosophila have PR-roles in Vanessa. Rather, the hemipteran PR-gene Blimp1 functions in a novel fashion in abdominal segmentation in Vanessa. Thus, while butterflies appear to share PR-patterning mechanisms with other insects, they utilize only a subset of the Drosophila PR-gene orthologs and have not taken on hemipteran PR-orthologs for this process. These findings suggest extensive rewiring of the segmentation gene regulatory network in Lepidoptera.