Ancestral notch-mediated segmentation revealed in the cockroach Periplaneta americana

Through division into segments, animal bodies can reach higher degrees of complexity and functionality through development and evolution. The segmentation mechanism of insects and vertebrates has been seen as fundamentally different, both at the anatomical and the molecular level, and consequently, independently evolved. However, this conclusion was mostly based on observations of derived insects such as Drosophila. We have cloned the Delta, Notch and hairy genes in the cockroach Periplaneta americana, a basal insect with short-germ band development, and carried out functional assays of Notch activity during its segmentation. Our results show that in more basal insects, segmentation involves a similar developmental mechanism as in vertebrates, including induction of segment formation by cyclic segmental stripes of hairy and Delta expression. This result indicates that Notch-mediated segmentation is the ancestral segmentation mechanism of insects, and together with previous results in the literature (Stollewerk et al. 2003, Involvement of Notch and Delta genes in spider segmentation. Nature 423:863-865), of arthropods as well. The similarity with vertebrate segmentation might suggest that Notch-mediated segmentation is an ancient developmental mechanism inherited from a common ancestor of insects and vertebrates.