Hedgehog pathway
Sonic Hedgehog (SHh), Indian Hedgehog (IHh) and Desert Hedgehog (DHh)
are the ligands and Patched 1 (PTCH) is the cognate receptor involved in
this pathway. When the receptor is unoccupied by the ligand, it
functions as a constitutive inhibitor of a transmembrane protein
Smoothened (Smo) and the target gene transcription is repressed by Gli
repressor. On binding of ligand to Patched 1, the repression on
Smoothened is released, allowing the Gli transcriptional activators to
promote transcription of target genes (Kumar et al., 2018) .