Figure 1

The Hedgehog signaling pathway. (a) In the absence of Hedgehog ligands, Patched protein inhibits the activity of Smoothened, which resembles G-protein-coupled receptors. (b) On activation by a ligand of the Hedgehog family, the inhibition of Smoothened by Patched is relieved and Smoothened is freed to trigger an intracellular signaling cascade; this ultimately leads to transcriptional regulation by transcription factors of the Gli family.