PROJECT SUMMARY The generation of neuronal diversity in the nervous system requires the specification and differentiation of a multitude of cellular lineages. Successive developmental programs control the generation of individual neuronal types, cell migration, axon extension, and ultimately the formation of functional synaptic connections. The specific genetic programs underlying the differentiation of mature neurons from their progenitors remain incompletely characterized, in part because of the difficulty in studying neuronal progenitor cells in their native environments. Similarly, mechanisms enabling tissue regeneration following injury in the adult nervous sysem are incompletely understood. In the vertebrate olfactory system, primary sensory neurons and other cell types are continuously regenerated throughout adult life via the proliferation and differentiation of multipotent neural progenitor cells. This feature makes the olfactory system particularly amenable for studies on the properties of adult neural stem cells. Following injury that results in destruction of all mature neurons and support cells in the olfactory epithelium, adult stem cells are activated to reconstitute all cell types in this structure. Of particular interest are the mechanisms that support regeneration of the olfactory epithelium following injury and whether and how they differ from mechanisms subserving tissue homeostasis under normal conditions. Elucidation of these regulatory networks is critical for understanding how mature neuronal and non-neuronal cell types are generated from the adult tissue stem cell of the olfactory epithelium. In this application we propose to investigate the cellular mechanisms and genetic pathways subserving the reconstitution of the olfactory epithelium following injury. Specifically, we propose a unique suite of approaches including single cell transcriptome profiling combined with rigorous statistical analysis, in vivo lineage tracing, and genetic pertubations to (1) elucidate the mechanisms underlying injury-induced regeneration in the olfactory epithelium stem cell niche and (2) establish the roles of canonical Wnt signaling and Sox2 in early olfactory neurogenesis. Together these investigations will provide a model for understanding the mechanisms regulating other neural stem cell types and lay the groundwork for the future development of treatments and therapeutics to ameliorate neural tissue damage and degeneration.