Development and Plasticity of Alveolar Type 1 Cells

The alveolar type 1 (AT1) cell covers >95% of the gas exchange surface and is extremely thin to facilitate passive gas diffusion. The development of this highly specialized cell is poorly understood including fundamental questions regarding cell number and morphology. Using new molecular stereology and single cell imaging methods, we show that AT1 cells develop via a non-proliferative two-step process while maintaining proliferative potential. In the flattening step, AT1 cells remodel cell junctions and undergo molecular specification. In the folding step, AT1 cells are sculptured to match secondary septa formation, resulting in a single AT1 cell spanning multiple alveoli. AT1 cells grow in size by >10-fold, fueling most of the postnatal lung growth. Strikingly AT1 cells proliferate upon ectopic SOX2 expression and undergo stage-dependent cell fate reprogramming. These results contradict the traditional view of AT1 cells being terminally differentiated and provide insights to alveolar maturation. In this experiment, we conducted next-generation sequencing on flow-sorter AT1 cells isolated from mouse lungs ectopically expressing Sox2 under the control of the AT1-specific promoter Scnn1a versus control AT1 cells. Overall design: Two samples of Sox2-expressing AT1 cells versus two control AT1 samples.