SHH (Sonic hedgehog) is member of the hedgehog signaling pathway. SHH binds to the patched (PTC) receptor, which functions in association with smoothened (SMO), to activate the transcription of target genes. In the absence of SHH,PorcineTC represses the constitutive signaling activity of SMO. Sonic hedgehog is an intercellular signal essential for a variety of patterning events during development, such as ventral cell fate in the neural tube and somites, and for patterning of the anterior-posterior a, Xenopus/Amphibian,is of the developing limb bud. Defects in sonic hedgehog has been implicated in eye formation disorders and holoprosencephaly, the most common structural anomaly of the brain, in which the developing forebrain fails to correctly separate into right and left hemispheres.