Spatial expression of Sonic hedgehog in the lung epithelium during branching morphogenesis.

Sonic hedgehog (Shh), a homologue of Drosophila hedgehog, was specifically expressed in lung epithelium during branching morphogenesis, but was not uniformly expressed in lung epithelium. Shh was intensely expressed in the distal tips of the bronchial tubes during branching morphogenesis, and Shh was localized on the apical side of the epithelium. On the other hand, Bmp-4, one of the target genes of Shh, was also specifically expressed in the epithelium at the branching point. These results suggest that Shh and Bmp-4 are involved in the branching morphogenesis of lung epithelium.