InR and Pi3K maintain intestinal homeostasis through STAT/EGFR and Notch signaling in enteroblasts.

ABSTRACT

To maintain the integrity of the adult gut, the proliferation and differentiation of stem cells must be strictly controlled. Several signaling pathways control the proliferation and differentiation of Drosophila intestinal epithelial cells. Although the modulatory effects of insulin pathway components on cell proliferation have been characterized, their specific role in which cell type and how these components interact with other regulatory signaling pathways remain largely unclear. In this study, we found that InR/Pi3K has major functions in enteroblasts (EBs) that were not previously described. The absence of InR/Pi3K in progenitors leads to a decrease in the number of EBs, while it has no significant effect on intestinal stem cells (ISCs). In addition, we found that InR/Pi3K regulates Notch activity in ISCs and EBs in an opposite way. This is also the reason for the decrease in EB. On the one hand, aberrantly low levels of Notch signaling in ISCs inhibit their proper differentiation into EBs; on the other hand, the higher Notch levels in EBs promote their excessive differentiation into enterocytes (ECs), leading to marked increases in abnormal ECs and decreased proliferation. Moreover, we found that Upd/JAK/STAT signaling acts as an effector or modifier of InR/Pi3K function in the midgut and cooperates with EGFR signaling to regulate cell proliferation. Altogether, our results demonstrate that InR and Pi3K are essential for coordinating stem cell differentiation and proliferation to maintain intestinal homeostasis.