Hedgehog (Hh) signaling molecule is a localized protein ligand secreted by signaling cells with a small range of action, usually no more than 20 cells. The Hedgehog signaling pathway controls cell fate, proliferation, and differentiation during many developmental processes in vertebrates and invertebrates, and when abnormally activated, it is responsible for the development and progression of tumors. The signaling protein induces different cell fates depending on the concentration of Hh signaling molecules. Like other morphogen, its production is tightly controlled in time and space. Hedgehog is synthesized and secreted as precursor in the cell, and then self-catalyzed to degrade outside the cell, and then undergo cholesterol and palmitoylation at different n-terminal amino acid residues, thereby limiting its diffusion and increasing its affinity to the plasma membrane.
