Project Summary Whole-body regeneration (the ability to regenerate all body parts) is one of the greatest mysteries in biology. Harnessing this process would be a medical moonshot triumph, as it would provide therapeutic strategies to enable regrowth of any type of missing tissues in human patients. In order to understand and control regeneration, we need to uncover the full regulatory network of the regeneration program, and identify critical mechanisms that may lead to the dysfunction of this network. Here, we propose to use new functional genomic analysis tools (Spatial Transcriptomics, ATAC-seq, and single-cell transcriptomics) coupled with high- throughput gene perturbation experiments to study two unique experimental paradigms. In the first paradigm, we will compare two evolutionary cousins: the freshwater planarian, which is an immortal flatworm with unparalleled regenerative ability throughout the animal kingdom, and the pathogenic flatworm schistosome, which only has limited regenerative ability. We will reveal the critical regulatory components of the short-term wound-induced response that are essential for launching and sustaining regeneration. In the second paradigm, we will study surgically constructed planarian chimeras to unravel the immunological pathways that regulate regeneration in order to manage the long-term risks of uncontrolled cell proliferation that is associated with repeated regeneration. Collectively, our study will advance the understanding of the fundamental biological basis of regenerative medicine and provide useful targets for activating regeneration.