Clusters of differentiated cells contributing to organ structures retain the potential to re-enter the cell cycle and replace cells lost during development or upon damage. To do so, they must be designated spatially and respond to proper activation cues. Here we show that in the case of Drosophila differentiated larval tracheal cells, progenitor potential is conferred by the spatially restricted activity of the Snoo transcription cofactor. Furthermore, Dpp signalling regulated by endocrine hormonal cues provides the temporal trigger for their activation. Finally, we elucidate the genetic network elicited by Snoo and Dpp activity. These results illustrate a regulatory mechanism that translates intrinsic potential and extrinsic cues into the facultative stem cell features of differentiated progenitors.
An important feature of organs is their ability to maintain their structure and function in spite of natural or accidental cell loss. This capacity is often sustained by so-called stem cells, which are able to provide new cells of the different types in the organ. In addition, some specialized cells, known as facultative stem cells, also retain the ability to re-enter the cell cycle and replace lost tissue. This process has to be very precisely regulated to provide for the maintenance of the tissues and organs while preventing uncontrolled cellular growth. We have analysed this mechanism in the Drosophila trachea; there, a group of Differentiated Adult Progenitor cells (or DAP cells) share the features of facultative stem cells as they remain quiescent during larval growth, reactivate their proliferation at the last larval stage and give rise to the different cell types of the adult tracheal network during metamorphosis. The DAP cells, conversely to the majority of the larval cells, do not enter endocycle and by doing so they acquire the features of adult progenitor cells. In this paper we identify the regulatory mechanism that integrates spatial and temporal cues to precisely activate the tracheal adult progenitor program.