Our long-term goal is to explicate the molecular and cellular basis for the recently recognized physiologic programmed turnover (loss and regeneration) of alveoli present in lungs of adult mammals; and, use this information to induce alveolus formation in disease. In adult mice, calorie restriction (CR) increases the volume of individual alveoli and diminishes alveolar number and surface area without altering lung volume. CR causes, within 72 h, a 20 percent decrease in lung DNA due, at least partly, to apoptosis. Refeeding (RF) reverses these architectural and cellular changes. Thus, adult mammals have endogenous programs to a) eliminate alveoli and alveolar wall cells and b) cause replication of alveolar wall cells and regeneration of alveoli. Our hypothesis is that an analysis of gene expression during calorie restriction-refeeding (CR-RF) induced cell replication and alveolar regeneration will identify genes and signal pathways responsible for alveolus formation. To test our hypothesis, our Specific Aims, using adult mice subjected to CR-RF, are: 1) Use morphometric procedures to detect the onset of alveolar regeneration and replication of alveolar wall cells, identify the replicating alveolar wall cells, and determine if there are differences among cell types in the onset of replication. 2) Assess lung gene expression during alveolar wall cell replication and alveolar regeneration using microarray technology. 3) Use Northern analysis (N), Rnase protection assay (RPA), and Western blotting (W), to confirm microarray results in the lung. For selected genes and signal pathways, use N, RPA, or W to determine if the same CR-RF induced gene expression occurs a) in other organs of the same mice (less important genes), or b) in a lung specific manner in three other models of alveolus formation. Those genes whose lung expression during alveolus formation is shared among four different models of alveolus formation will be considered most important. 4) Manipulate selected genes and signal pathways pharmacologically when possible, or by knockout, and determine the effect on a) CR-RF-induced alveolar regeneration in mice or b) on alveolus formation in adult otherwise untreated wild-type mice fed ad libitum using morphometric procedures.