Rag GTPases and mTORC1 regulate intestinal stem cell activity in response to nutrient availability

The intestinal epithelium, predominantly composed of enterocytes (ECs), integrates dietary cues to regulate intestinal stem cell (ISC) activity and maintain intestinal homeostasis. However, the underlying mechanisms remain incompletely understood. Here, we demonstrate the functions of essential nutrient-sensing mediators Rag GTPases and mTORC1 on Drosophila ISC activity. Inhibition of Rag GTPases in ECs triggers Mitf activation, which subsequently induces Upd3 expression to non-cell autonomously increase the ISC proliferation and differentiation through stimulating the JAK-STAT pathway. Inactivation of mTORC1 in ECs also activates the Upd3-JAK-STAT axis and increases ISC activity, but through a Mitf-independent mechanism. Moreover, in contrast to mTORC1 inactivation blocking ISC proliferation and differentiation, depletion of Rag GTPases in ISCs shows no obvious cell autonomous effect on ISC activity. Consistent with inhibition of the nutrient-responsive pathway in ECs promoting ISC proliferation, long-term nutrient starvation enhances ISC activity and Upd3 expression. Together, our findings reveal a nutrient-sensing regulatory network that controls ISC proliferation involving the Rag GTPases-Mitf axis and mTORC1 activity.