FIGURE 9.

A hypothetical model for TGF-β∼Shh cross-talk in the developing lung. Shh is made in the lung epithelium. The Shh receptor complex, Ptc/smoothened is expressed on the cell surface of lung mesenchymal cells. Activation of Shh pathway leads to increased Gli-3 activity, which in turn stimulates Gli-1 and Ptc transcription. TGF-β ligand acts through TβRII and as yet unknown intracellular mediators (e.g. Smads) to interfere with Shh signal transduction in mesenchymal cells, evidenced by reductions in both Ptc and Gli-1 observed in this study.