Re-entry into mitosis and regeneration of intestinal stem cells through enteroblast dedifferentiation in Drosophila midguts

Many adult tissues and organs including the intestine rely on resident stem cells to maintain homeostasis. In mammalian intestines, upon ablation of resident stem cells, the progenies of intestinal stem cells (ISCs) such as secretory cells and tuft cells can dedifferentiate to generate ISCs to drive epithelial regeneration, but whether and how the ISC progenies dedifferentiate to generate ISCs under physiological conditions remains unknown. Here we show that infection of pathogenic bacteria induces enteroblasts (EBs) as one type of ISC progenies to re-enter the mitotic cycle in the Drosophila intestine. The re-entry into mitosis is dependent on epithermal growth factor receptor (EGFR)-Ras signaling and ectopic activation of EGFR-Ras signaling in EBs is sufficient to drive EBs cell-autonomously to re-enter into mitosis. In addition, we examined whether EBs gain ISC identity as a prerequisite to divide, but the immunostaining with stem cell marker Delta shows that these dividing EBs do not gain ISC identity. After employing lineage tracing experiments, we further demonstrate that EBs dedifferentiate to generate functional ISCs after symmetric divisions of EBs. Together, our study in Drosophila intestines uncovers a new role of EGFR-Ras signaling in regulating re-entry into mitosis and dedifferentiation during regeneration and reveals a novel mechanism by which ISC progenies undergo dedifferentiation through a mitotic division, which has important implication to mammalian tissue homeostasis and tumorigenesis.