Sonic hedgehog (SHH) is a member of a small group of secreted Proteins that are essential for development in both verteb es and inverteb es. Three mammalian hedgehog genes (sonic, desert, Indian) share about 60% homology and all signal via the same receptors. Recombinant SHH is a non-glycosylated Protein, containing 175 amino acids, with a molecular weight of 19.7 kDa. The Cys at position 25 has been substituted with Ile.