Sonic Hedgehog (Shh) is one of three highly conserved proteins that share the same signaling pathway and make up the Hedgehog family. Sonic Hedgehog is expressed in key embryonic tissues, is involved in regulating the patterning of the developing nervous system, somite and limb, and also plays an important role in the development of certain tissues like hair, tooth and bone. It interacts with the Patched and Smoothened transmembrane receptors.