Screening for breath: identifying Aurkb as a novel regulator of lung development

Abstract

The development of the lung is a highly regulated and complex process that is not fully characterised. Although there have been many studies into the development of the lung many of the mechanisms regulating lung organogenesis are still unclear. In recent years, the importance of epigenetic regulators in embryogenesis has been established but epigenetic control of lung morphogenesis is largely underexplored. I have developed a novel in vitro assay to grow embryonic lung stem cells. These cells, called pneumospheres express the early lung progenitor factor Sox9 and recapitulate the E11.5 lung throughout their time in culture. Pneumospheres can be genetically and chemically manipulated to assess the role of signalling pathways and genes-of-interest on lung progenitor cell self-renewal or differentiation. Using pneumospheres I performed a shRNA knockdown screen, targeting 130 genes involved in epigenetic regulation. Nineteen genes were identified in the screen and validated using in vitro and ex vivo culture systems to determine their role lung stem cells and branching morphogenesis. These experiments identified Aurora kinase B (Aurkb) as an interesting candidate gene. Aurkb exerts a dual role as a regulator of cell cycle and epigenetic control through phosphorylation of histones. Disruption of Aurkb either by short-hairpin RNA or by chemical inhibition in vitro abrogates growth of lung epithelial progenitor cells and causes defects in cell cycle, leading to an accumulation of cells in G2/M of the cell cycle. Conditional deletion of Aurkb in the embryonic lung, leads to a complete lack of lung tissue at birth and severe epithelial growth retardation can be seen as early as midgestation. Understanding the regulation of lung development will provide a better understanding of the lung organogenesis and how disruptions in normal biology can cause early lung diseases such as bronchopulmonary dysplasia or can have an impact on lung disorders later in life such as COPD or lung cancer.