The pathways leading to airway epithelial cell differentiation and renewal are undergoing intense study as these programs are essential for repair following lung injury, and may be dysregulated leading to epithelial cell metaplasia in asthma and chronic obstructive airway disease. This project addresses the mechanism of normal restoration of the airway epithelium after injury. The current paradigm for airway epithelial cell regeneration is a one-step process, whereby regulatory factors direct a self-renewing P63+ progenitor cell to a differentiated type. In this project, we establish a new model based on our finding that the transcription factor Myb defines an essential intermediate stage in the progression from progenitor to specialized cell. Our findings suggest that the Myb+P63- cell is obligatory for the differentiation of a ciliated and secretory airway cell types. Myb is transietly expressed during lung development and in our primary-culture models, and is absent in the healthy adult lung. Myb is increased in our mouse models of lung injury and in airways of individuals with chronic obstructive lung disease. Depleting Myb in primary-culture of mouse and human airway epithelial cells abrogates differentiation. Accordingly, we generated mice with airway epithelial cell-specific deletion of Myb, and likewise found a failure to develop ciliated ad secretory cells. Genome-wide gene expression comparison between Myb deficient and sufficient cells identified programs for ciliated and secretory cell differentiation, and a reductin of Sox2 levels. Validation data demonstrated Sox2 was decreased in P63- airway epithelial cells, suggesting a Myb dependent requirement for Sox2. Together, these findings lead us to hypothesize that Myb regulates a program essential for the maintenance, repair and regeneration of differentiated airway epithelial cells. Using Myb targeted deficient mice and primary culture models, we propose to investigate (1) Myb-dependent cellular determinants for repair and regeneration using mouse injury models, and (2) identify Myb-dependent molecular programs for airway epithelial differentiation. The studies will establish a new model for understanding the pathogenesis of airways disease and define key elements as targets for reparative therapies.