Identification of a Palmitic Acid-modified Form of Human Sonic hedgehog

The zone of polarizing activity (ZPA) is a region at the posterior margin of the limb bud that induces mirror-image duplications when grafted to the anterior of a second limb. We have isolated a vertebrate gene, Sonic hedgehog, related to the Drosophila segment polarity gene hedgehog, which is expressed specifically in the ZPA and in other regions of the embryo, that is capable of polarizing limbs in grafting experiments. Retinoic acid, which can convert anterior limb bud tissue into tissue with polarizing activity, concomitantly induces Sonic hedgehog expression in the anterior limb bud. Implanting cells that express Sonic hedgehog into anterior limb buds is sufficient to cause ZPA-like limb duplications. Like the ZPA, Sonic hedgehog expression leads to the activation of Hox genes. Sonic hedgehog thus appears to function as the signal for antero-posterior patterning in the limb.

The protein Sonic hedgehog (Shh) is essential for a variety of patterning events during development. It is the signal from the notochord that induces ventral cell fate in the neural tube and somites, and is the polarizing signal for patterning of the anterior-posterior axis of the developing limb bud. Because of these and other inductive functions of Shh, it is important to understand how the Hedgehog (Hh) signal is received by the target cells. Here we describe binding studies using labelled Shh that strongly suggest that the Hh receptor is encoded by patched (ptc), a gene first identified in genetic screens in Drosophila.

Hedgehog (Hh) proteins comprise a family of secreted signaling molecules essential for patterning a variety of structures in animal embryogenesis. During biosynthesis, Hh undergoes an autocleavage reaction, mediated by its carboxyl-terminal domain, that produces a lipid-modified amino-terminal fragment responsible for all known Hh signaling activity. Here it is reported that cholesterol is the lipophilic moiety covalently attached to the amino-terminal signaling domain during autoprocessing and that the carboxyl-terminal domain acts as an intramolecular cholesterol transferase. This use of cholesterol to modify embryonic signaling proteins may account for some of the effects of perturbed cholesterol biosynthesis on animal development.