PROJECT SUMMARY The mammalian lung has the capacity to repair itself following various injuries. Alveolar repair is a dynamic and coordinated process whereby stem/progenitor cells in the lung undergo differentiation into specialized cells to repair the damaged epithelium. Recent studies have uncovered a distinct intermediate progenitor cell state that exists during the transition between stem/progenitor cells and these specialized cells; however, the dynamic cellular behaviors and molecular regulatory landscape that drives intermediate progenitor cell transitions toward repair is poorly understood. Here, we propose two aims to dissect the cellular and molecular mechanisms that control alveolar repair in vivo in the regenerating mammalian lung. First, we investigate IPC transitions in the context of homeostasis instead of in acute injury models (virus and bleo) as in the parent grant. We use single cell laser ablation to model the death of a single cell, as occurs occasionally over a lifespan, and then investigate whether and how IPCs form in response using fluorescent cell lineage-reporter mice. In the second aim, we turn to bleomycin- induced lung injury – the most common mouse model for pulmonary fibrosis – but instead of using single cell ‘omics approaches as in the parent grant, we take a spatial transcriptomics approach that preserves the spatial architecture and cell-cell neighborhoods in alveoli. We apply spatial transcriptomics at a time point that matches the parent grant and will allow integration of both datasets. This project will generate extensive, high quality imaging and ‘omics datasets that together with the parent grant enable quantitative and predictive models of the key regulatory mechanisms that mammalian drive alveolar repair in vivo. Given that many of the cellular and molecular mechanisms of lung biology are conserved between mouse and human, our findings have the potential to uncover putative targets for modulating alveolar repair in the context of human disease.