The role of Yap in lung development
Mahoney, John Edmund
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The mechanisms by which epithelial progenitor cells integrate local signals to balance proliferation with differentiation and regulate patterning during lung organogenesis are still poorly understood. The Hippo pathway and its transcription co-activator Yap have recently emerged as major regulators of progenitor cell expansion and differentiation in development and cancer. Here we investigated the role of Yap signaling in the cellular and molecular events associated with lung epithelial morphogenesis and differentiation. We provide evidence that when airway epithelial tubules are forming and branching, a nuclear to cytoplasmic shift of Yap marks the boundary between the progenitors of the distal lung and the airway compartment. At this transition zone, Yap specifies a transcriptional program that controls the expression of Sox2, restricting distal gene expression and initiating an airway progenitor cell program key to generate the airway epithelium and its branched tubular structures. In Yap deficient mice, epithelial progenitors are unable to properly respond to local Tgf beta-induced cues to control levels and distribution of Sox2, resulting in expansion of the distal epithelial compartment and inability to form airways. Moreover, we show that Yap levels and phosphorylation status play a major role in regulating differentiation of airway progenitors later in development and in adult life. Analysis of YAP-interacting partners in adult airway progenitors by Mass Spectroscopy suggests phosphorylated Yap interactions with ciliome proteins. Our study reveals a crucial role for Yap in specification and differentiation of airway progenitors likely to be also relevant in regeneration-repair of the adult airway epithelium.