Fig. 1.

Shh pathway activation. The Shh pathway consists of the Sonic hedgehog ligand (Shh), Patched receptor (Ptch), Smoothened receptor (Smo), Suppressor of fused (SuFu) and transcription factors (Gli). The illustration shows the canonical activation of the Shh signaling pathway. a In the absence of the Shh ligand, Ptch binds to a constitutively active Smo, suppressing its activity. In the absence of activated Smo, SuFu forms SuFu–Gli complexes and restrains Gli activity. b In the presence of the Shh ligand, its binding with Ptch results in endocytic degradation of Ptch in the lysosome. Activated Smo induces the dissociation of SuFu–Gli complexes and translocation of Gli proteins into the nucleus