Engrailed gene expression in the abdominal segment of Oncopeltus: gradients and cell states in the insect segment.

A monoclonal antibody that recognizes the product of the segmental gene, engrailed (en), of Drosophila has been used to analyse expression of the homologous gene of Oncopeltus. engrailed expression in the abdominal segment of larval Oncopeltus is confined to a narrow band of epidermal cells localized immediately anterior to the segment border. Expression varies in intensity during postembryonic development: no gene product is detectable in newly moulted larvae, but reappears soon after initiation of intermoult activities. One possible function of en in this system is revealed by a series of operations confronting cells from different anteroposterior levels in the segment. New segment borders are generated only when en-expressing cells confront cells from the anteriormost region of the segment. All other combinations result in intercalation of intermediate intrasegmental levels. It is therefore suggested that the most important function of en is the establishment of new, and presumably the maintenance of existing, segment borders.