MOLECULAR AND MECHANICAL REGULATION OF EMBRYONIC LUNG DEVELOPMENT

Abstract

During embryonic development, cells organize into complex, three-dimensional organs, a process called morphogenesis. To execute these collective behaviors, cells communicate amongst themselves and with their microenvironment using biochemical signals and physical forces. These signals are integrated to dictate cell position and to drive the expression of genes required for specialized cell functions. Branching morphogenesis is the process whereby a simple tube of cells becomes a vast, tree-like network that maximizes surface area for the flow and exchange of fluids. Branched organs, like the lung, kidney, and mammary gland, each have unique final architecture, suggesting distinct mechanisms of branching morphogenesis. The biochemical drivers of lung development have been identified, but the role of physical forces remains unclear. For my dissertation, I have uncovered how physical forces are integrated with biochemical signals to drive branching morphogenesis of the mouse lung. Using experiments and simulations, I have shown that smooth muscle cells derived from the mesenchyme that surrounds the airways physically sculpt new branches as they emerge (Chapter 2). Next, I used single-cell bioinformatics and genetics to show that the mesenchyme of developing lungs contains two layers of cell types (Chapter 3). With timelapse imaging and biophysical measurements of embryonic lungs, I showed that these layers are mechanically distinct and that they can influence airway shape. Delving further into transcriptional regulation of mesenchymal differentiation, I then demonstrate phenotypic plasticity in airway smooth muscle cells (Chapter 4). I then focused on the cells of the airways themselves and, using genetics, bioinformatics, and mechanical perturbations, showed that their earliest fate decisions require the successful execution of branching morphogenesis (Chapter 5). Finally, I applied some of these methods to explore lung development from an evolutionary perspective (Chapter 6). Using the lungs from three species of terrestrial vertebrates, I uncover parallels and unique features in how the pulmonary mesenchyme sculpts diverse airway shapes. My work reveals essential roles for physical signals in morphogenesis of the embryonic lung and provides insight into how biological tissues can be mechanically influenced to generate complex architecture.