Hedgehog regulation of epithelial cell state and morphogenesis in the larynx

The larynx enables speech while regulating swallowing and respiration. Larynx function hinges on the laryngeal epithelium which originates as part of the anterior foregut and undergoes extensive remodeling to separate from the esophagus and form vocal folds that interface with the adjacent trachea. Here we find that Sonic hedgehog (SHH) is essential for epithelial integrity in the larynx as well as the anterior foregut. During larynx-esophageal separation, lowShhexpression marks specific domains of actively remodeling epithelium that undergo an epithelial to mesenchymal transition (EMT) characterized by the induction of N-Cadherin and movement of cells out of the epithelial layer. Consistent with a role for SHH signaling in regulating this process,Shhmutants undergo an abnormal EMT throughout the anterior foregut and larynx, marked by a cadherin switch, movement out of the epithelial layer and cell death. Unexpectedly,Shhmutant epithelial cells are replaced by a new population ofPax-1expressing cells that form a rudimentary epithelium. These findings have important implications for interpreting the etiology of HH- dependent birth defects within the foregut. We propose that SHH signaling has a default role in maintaining epithelial identity throughout the anterior foregut and that regionalized reductions in SHH trigger epithelial remodeling.