In aging animals, the intestine suffers structural and functional impairments and undergoes epithelial dysplasia. During normal tissue homeostasis, the intestinal stem cells (ISCs) divide slowly to replace the damaged cells, but old intestines show increased ISC division rate and accumulation of misdifferentiated cells. The increased proliferation and accumulation of misdifferentiated cells have been used as one of the hallmarks for the intestinal dysplasia to shorten lifespan. The Drosophila midgut includes self-renewed ISCs which is the only cell type to undergo mitosis in Drosophila midguts, even in the aged midguts, but whether their progeny such as EB, EC or EE can dedifferentiate to become ISCs in aged midguts has remained unexplored. Considering that the conserved genetic pathways and regulatory mechanisms employed to regulate ISC homeostasis and regeneration in both Drosophila and mammalian systems, and that the wealth of genetic tools are available in Drosophila, there is a critical need to establish a Drosophila intestinal model to investigate the process of epithelial dysplasia in response to the aging. Our preliminary studies have shown that activation of EGFR-Ras signaling can induce autonomous enteroblast (EB) mitosis. The further lineage-tracing analysis in EBs revealed that new stem cells are generated from the progeny of EBs, indicating that EBs can dedifferentiate to produce ISCs. Furthermore, we found that EBs re-entered mitosis in 50-day-old intestines, suggesting that EB differentiation is compromised during aging. Interestingly, we found that EGFR-Ras signaling was upregulated in EBs in aged intestines. Based on these preliminary findings, we hypothesize that upregulated EGFR-Ras signaling in aged intestines is crucial for the re-entry of mitosis and dedifferentiation of EBs. To test this hypothesis, the following two specific aims will be pursued. In Aim 1 we will determine the process of dedifferentiation in EBs upon the activation of EGFR-Ras signaling. In Aim 2 we will determine how EBs contribute to ISC regeneration in response to aging. At the completion of this proposed research, our expected outcomes will determine how EBs re-enter mitotic cycle to divide asymmetrically to produce functional ISCs in response to aging in the Drosophila intestine model. Considering the conserved genetic pathways and regulatory mechanisms in both Drosophila and mammals, these results are expected to have an important positive impact on uncovering the critical mechanisms by which the aging related intestinal disorders are regulated, which could be applied to the regenerative medicine.