Project Summary Despite the enormous regenerative capacity of skeletal tissues, failed bone repair affects up to 10% of long- bone fracture patients. Issues of skeletal healing also affect bones of the craniofacial region, where over 12 million people experience craniofacial skeletal injury in the United States annually. Options for prevention and treatment of these healing issues are severely limited in clinical practice, and a comprehensive mechanism of most regenerative processes remains poorly defined. The periosteum and bone marrow stroma are required for efficient fracture healing as sources of osteochondral progenitor cells during new bone formation. We aim to advance the understanding of bone-specific progenitor cell populations for applications in skeletal regeneration. Leucine-rich repeat-containing G-protein coupled receptor 6 (Lgr6) is an adult stem/progenitor cell marker that additionally functions as an auxiliary receptor in the Wnt/β-catenin pathway. While Lgr family members are often expendable for normal function when stem cell populations are static, they can become important for cell expansion and regeneration following injury. Our preliminary data suggest Lgr6 marks a population of osteochondral-lineage cells, and Lgr6 is expressed in progenitors following skeletal injury; this indicates a subset of adult stem cells associated with regenerative processes of the skeleton. However, a specific role for Lgr6 in the context of fracture healing has not been explored, to our knowledge. In Aim 1, I will use a reporter mouse model to trace the contribution of novel Lgr6+ adult osteoprogenitor cells to the fracture healing process. In Aim 2, I complement the analysis of progenitor fate in Aim 1 by investigating signaling pathways that may involve Lgr6 expression in bone-specific progenitor cells. Overall, the proposed aims combined are designed to reveal potential therapeutic targets to aid in skeletal regeneration. This will provide novel tools for fracture healing studies. The conclusions from this project will have broad future applications, particularly in skeletal healing of the craniofacial region.