| Congenital Diaphragmatic Hernia (CDH) is a deadly birth defect. Diaphragm malformation is commonly believed to be the cause of CDH, as the characteristic symptom is an aberrant opening in the diaphragm through which abdominal organs protrude. My results demonstrate a role for Roundabout (Robo) receptor genes in a mouse model of CDH. Global inactivation of Robo1 and Robo2 (hereafter Robo1;2) led to diaphragm malformation and respiratory failure at birth, classical CDH phenotypes. We traced the primary defect to a failure in foregut organ positioning, a phenotype that precedes and likely underlies diaphragm malformation. These findings offer the first demonstration of a diaphragm-independent mechanism of CDH. Many CDH survivors suffer life-long breathing deficiencies. To uncover the causes for postnatal morbidity using the Robo mouse model of CDH, we conditionally inactivated Robo1;2. While Robo conditional mutants survived birth, their lungs exhibited an elevated lung immune response and simplified distal lung structures. Unexpectedly, I found that Robo1;2 are expressed in pulmonary neuroendocrine cells (PNECs), a rare and poorly understood population of innervated airway epithelial cells. While PNECs have been implicated in immune responses, the specific mechanism has not been elucidated. My results show that PNECs, which normally form groupings, fail to cluster in Robo mutants and as a result, PNEC neuropeptides are dysregulated. We show that one of the upregulated peptides promotes infiltration of immune cells, which then remodel and simplify distal lung structures. These findings demonstrate that PNEC clustering is a genetically controlled process which is essential for proper regulation of lung immune responses. The mammalian lung continues to develop and mature after birth through a process called alveologenesis. During this process the units of gas exchange, or alveoli, are formed. Despite the importance of alveologenesis to lung function, the process is poorly understood. Through a three dimensional imaging study, I uncovered new insights into key cellular events occurring during alveologenesis. My results highlight the dynamic role myofibroblasts and myofibroblast-produced factors play in normal alveologenesis and in mouse models of impaired alveologenesis. |
