Conservation and variation in pair-rule gene expression and function in the intermediate-germ beetle, Dermestes maculatus

Abstract

A set of pair-rule segmentation genes (PRGs) promote the formation of alternate body segments in Drosophila melanogaster. While Drosophila embryos are long-germ, with segments specified more-or-less simultaneously, most insects add segments sequentially as the germband elongates. The hide beetle, Dermestes maculatus, represents an intermediate between short- and long-germ development, ideal for comparative study of PRGs. Here we show that eight of nine Drosophila PRG-orthologs are expressed in stripes in Dermestes. Functional results parse these genes into three groups: Dmac-eve, -odd, and -run play roles in both germband elongation and PR-patterning. Dmac-slp and -prd function exclusively as complementary, classic PRGs, supporting functional decoupling of elongation and segment formation. Orthologs of ftz, ftz-f1, h, and opa show more variable function in Dermestes and other species. While extensive cell death generally prefigured Dermestes PRG RNAi cuticle defects, an organized region with high mitotic activity near the margin of the segment addition zone likely contributes to truncation of eveRNAi embryos. Our results suggest general conservation of clock-like regulation of PR-stripe addition in sequentially-segmenting species while highlighting regulatory re-wiring involving a subset of PRG-orthologs.