Stanford researchers use single cell genomics analysis (left) to reverse engineer the development of alveolar sacs in the lung (right). Alveoli are small balloon-like structures at the tips of the airways, where the gas exchange between our blood and the outside air occurs: blood vessels receive oxygen and deliver carbon dioxide. Alveoli are composed of two functionally very different cell types: Alveolar type I cells, the flattest cells in our body, facilitate gas exchange, whereas alveolar type II cells protect alveoli by secreting surfactants. The scientists found that both cell types arise from a single precursor, or 'progenitor,' cell during alveolar development. On the left, the experimental process is laid out: the scientists digested lung tissue to obtain single lung cells in suspension. They then captured individual cells in different chambers on a microfluidic chip. Finally, they measured which genes were active in each single cell at that moment using single cell mRNA sequencing.