Many animal tissues maintain populations of slowly proliferating stem cells that contribute to tissue homeostasis and repair. In Drosophila, for example, stem cells reside throughout the midgut and within the hindgut and renal tubules. But how and when do these cells arise? Volker Hartenstein and colleagues now show that Drosophila gut progenitors migrate across tissue boundaries and adopt the fate of the organ in which they come to reside (). Using lineage tracing, the researchers demonstrate that a subset of adult midgut progenitors, which are initially located in the larval midgut, migrate posteriorly during development and contribute to the adult ureter and, subsequently, the renal stem cell population. In addition, they report, a population of hindgut progenitors migrates anteriorly into the midgut territory to differentiate and give rise to midgut enterocytes. These findings suggest that a stable boundary between the midgut (an endodermal tissue) and the hindgut/renal tubules (ectodermal tissues) does not exist and instead multipotent progenitors are able to cross the boundaries between these domains.
