Identification of adult midgut precursors in Drosophila

The adult Drosophila is thought to arise from an endodermal rudiment specified during embryogenesis. Previous studies have reported the presence of individual cells termed adult precursors (AMPs) as well as midgut islands or islets in embryonic and larval tissue. Yet the precise relationship between progenitor cell populations and the cells of the adult has not been characterized. Using a combination of molecular markers and directed cell lineage tracing, we provide evidence that the adult arises from a molecularly distinct population of single cells present by the embryonic/larval transition. AMPs reside in a distinct basal position in the larval where they remain through all subsequent larval and pupal stages and into adulthood. At least five phases of AMP activity are associated with the stepwise process of formation. Our data shows that during larval stages AMPs give rise to the presumptive adult epithelium; during pupal stages AMPs contribute to the final size, cell number and form. Finally, a genetic screen has led to the identification of the Ecdysone receptor as a regulator of AMP expansion.