Conservation and variation in pair-rule gene expression and function in the intermediate-germ beetle .

A set of pair-rule (PR) segmentation genes (PRGs) promotes the formation of alternate body segments in Whereas embryos are long-germ, with segments specified more or less simultaneously, most insects add segments sequentially as the germband elongates. The hide beetle represents an intermediate between short- and long-germ development, ideal for comparative study of PRGs. We show that eight of nine PRG orthologs are expressed in stripes in Functional results parse these genes into three groups: -, - and - play roles in both germband elongation and PR patterning; - and - function exclusively as complementary, classic PRGs, supporting functional decoupling of elongation and segment formation; and orthologs of , , and show more variable function in and other species. While extensive cell death generally prefigured PRG RNAi-mediated cuticle defects, an organized region with high mitotic activity near the margin of the segment addition zone is likely to have contributed to truncation of embryos. Our results suggest general conservation of clock-like regulation of PR stripe addition in sequentially segmenting species while highlighting regulatory rewiring involving a subset of PRG orthologs.