Fig. 1. Production of lipid-modified Wnt and Hedgehog (Hh) proteins. (A) Porcupine (Porc), or MOM-1 in C. elegans, is an endoplasmic reticulum (ER) protein that is required in Wnt producing cells, and which is thought to attach a palmitate to Wnt. In C. elegans, the MOM-3 gene product (not yet identified molecularly) may assist in the production or release of active Wnt. (B) In Hh-producing cells, Rasp is necessary for the acylation of the Hh protein. The C terminus of Hh is cholesterol-modified. Release of lipid-modified Hh requires the transmembrane protein Dispatched (Disp). (C,D) The Wnt (C) and Hh (D) proteins, showing the approximate positions of cysteine residues (blue vertical lines) and lipid modifications.