DESCRIPTION (provided by applicant): Alveoli mediate gas exchange and are thus the key functional structure of the lung, and they are also the site of many important and intractable lung diseases. While its complex grapelike structure is comprised of several cell types (e.g., epithelial, mesenchymal, endothelial, and hematopoietic), the alveolar epithelium itself is quite simple and contains only two alveolar cell types (AT); the exquisitely thin AT1 cells that form the site of gas exchange and the cuboidal AT2 cells which secrete the surfactant that prevents alveolar collapse. We recently described the cellular process by which these cell types arise: a bipotent progenitor (BP) gives rise to both AT1 and AT2 fates. We also recently conducted single cell gene expression profiling of the developing alveolar epithelium, and used the data to reconstruct the full gene expression program of the lineage hierarchy from BP to both AT1 and AT2 fate. However, the signals that control this program are unknown. I propose to gene expression program of the developing the alveolar epithelial lineage hierarchy with expression profiling of surrounding alveolar cells to identify a critical receptor and its cognate ligand combine the that induce alveolar epithelial development. Understanding how AT fate specification is determined during development will provide significant insight to how it is disrupted in diseases like bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and lung adenocarcinoma as well as help in devising regenerative strategies to repair or replace diseased tissue. The mentored phase of the proposal will be carried out at Stanford University in Dr. Mark Krasnow's laboratory, a leading lab for training developmental and stem cell biologists. The mentored phase of the proposal focuses on identifying a signaling pathway that controls alveolar development. Towards this goal, I will 1) Use single RNAseq expression profiling to identify all receptor genes selectively expressed in the developing AT1 and AT2 lineage and to identify expression in surrounding alveolar mesenchymal and endothelial cells of any genes that encode their cognate ligands. This will identify outstanding candidates for the signaling pathways that control alveolar epithelial fate specification. For the second aim, I will 2) Elucidate the role of one candidate signaling pathway, the Fgf7-Fgfr2 pathway identified by initial expression profiling results, in alveolar development, by determining if the pathway is necessary and sufficient for alveolar epithelial fate specification, and what alveolar cells the pathway is required in to exert its effet. Preliminary data show that purified Fgf7 is a powerful inducer of alveolar cell development and alveolar morphogenesis in a newly established cell culture assay, so it provides a promising test case for elucidating the role of an identified candidate signaling pathway in a...