Project Abstract Regenerative abilities vary significantly both between different species and between distinct tissues of a given species. Despite recent advances, many fundamental questions persist regarding the cellular and molecular mechanisms that govern effective tissue regeneration. This research program strives to uncover the genes and gene regulatory networks (GRNs) that operate within individual cells during distinct phases of regeneration. For regeneration to occur, surviving cells need to launch a response that promotes localized cellular reprogramming, proliferation, and tissue repatterning to replace what was lost. This investigation will shed light on how tissue regeneration is orchestrated by determining the genes and GRNs that trigger a regenerative response, support regenerative growth, and ultimately reestablish proper cell fates in the newly generated tissue. The work focuses on tissue regeneration in the powerful genetic model organism Drosophila melanogaster in combination with state-of-the-art single-cell technologies. Many crucial processes during regeneration occur in small subpopulations of cells, the study of which has been revolutionized by single-cell technologies. Investigating regeneration in Drosophila provides many key advantages including the availability of powerful genetic tools that support dissection of gene function in vivo, large-scale screens for genetic interactions, and quantitative assessments of regenerative growth, and repatterning. The goals in the coming years are to: (i) investigate blastema formation and the establishment of the regenerative microenvironment. What are the cellular and molecular events that activate, sustain, and organize cell-cell coordination during the early phase of regeneration? (ii) elucidate the genes and GRNs that drive the distinct phases of regeneration by unraveling gene regulatory mechanisms of the transcriptional programs activated during the key phases of regeneration: blastema formation, regenerative growth, and regenerative repatterning; (iii) compare tumorigenesis versus regeneration to uncover critical regulatory mechanisms. Tumors have been shown to co-opt pro-regenerative GRNs to drive tumor growth. Therefore, we aim to discover the regulatory mechanisms that effectively terminate regenerative growth by contrasting tissues undergoing regeneration versus tumorigenesis. Together these areas of research will advance our understanding of cell-type specific gene regulatory networks that initiate blastema formation, promote effective regenerative growth, and regulate cellular repatterning during regeneration. These insights will address central questions in the fields of developmental and regenerative biology and ultimately contribute to the pioneering field of regenerative medicine.