However, the inactivation of Yap1 by itself in AT2 cells resulted in increased AT2 to AT1 cell differentiation and decreased pulmonary fibrosis based on hydroxyproline content and significantly less Col1a1 and Col3a1 RNA expression (Figure 4A–D and K–N & Figure 4—figure supplement 1). Here, COL1A1 is linked to pulmonary fibrosis.