Recombinant Mouse Sonic Hedgehog is part of a small group of secreted proteins that are vital for development in both vertebrates and invertebrates. 3 mammalian hedgehog genes （sonic，desert，Indian） share about 60% homology. The Mouse Sonic Hedgehog is 99% homologous to the human gene. Sonic HedgeHog is a protein that is vital in guding the early embryo. It has been associated as the major inductive signal in patterning of the ventral neural tube，the anterior-posterior limb axis，and the ventral somites. Sonic HedgeHog binds to the patched receptor，which functions in association with smoothened，to activate the transcription of target genes. In the absence of sonic HedgeHog，patched receptor represses the constitutive signaling activity of smoothened. Sonic HedgeHog also regulates another factor，the gli oncogene. Sonic HedgeHog intercellular signal is essential for a various patterning events during development: signal produced by the notochord that induces ventral cell fate in the neural tube and somites，and the polarizing signal for patterning of the anterior-posterior axis of the developing limb bud. Sonic HedgeHog exhibits both floor plate- and motor neuron-inducing activity. Mutations in a long-range Sonic HedgeHog enhancer located in an intron of the limb region 1 gene result in preaxial polydactyly.
