Insect legs all look pretty similar, consisting of proximal, medial and distal regions. Nevertheless, report Herke and co-workers, the regulatory mechanisms that govern leg specification and segmentation in the milkweed bug Oncopeltus fasciatus are more different from those acting in Drosophila melanogaster than expected from simple morphological and molecular comparisons (see ). The researchers use RNAi to show that in O. fasciatus,tiptop is required for the segmentation of the distal leg and to switch appendage identity from antenna to leg. In contrast to D. melanogaster leg specification, Antennapedia (Antp) is not required to specify leg identity in O. fasciatus. However, in both insects Antp controls medial leg segmentation. Based on their results, Herke et al. propose that a tiptop-like activity is a likely component of an ancestral leg specification mechanism and speculate about how insect legs may have evolved from a ground-state appendage.
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