Interestingly, two genes defining the AEC2 cell fate, ETV5 and SOX9, are also expressed in the IPF Lysopos population, but while SOX9 is expressed at levels exceeding that of bona fide AEC2s, ETV5 expression is much lower, suggesting that they regulate different aspects of the IPF alveolar epithelial fate. The gene discussed is SOX9; the disease is idiopathic pulmonary fibrosis.