In the absence of the Hh ligand, the receptor PTCH (Patched) acts to prevent high expression and activity of SMO (Smoothened). When Hh is bound, the repression of SMO is relieved which leads to activation of the GLI transcription factors: activators Gli1 and Gli2 and repressor Gli3. Activated GLI then controls the transcription of hedgehog target genes.
Pathway adapted from [KEGG](http://www.genome.jp/kegg-bin/show_pathway?hsa04340).