Porcupine (Porc) protein may be involved in secretion or ER transport, as Wingless is retained in the ER in porcupine mutant Drosophila embryos. In C. elegans, the porcupine homolog mom-1 has a similar function in promoting secretion of the Wnt protein Mom-2. Porcupine has some homology to a family of o-acyl transferases and may be involved in lipid modification of Wnt proteins. A special form of monounsaturated palmitoylation has been detected on a serine residue in the Wnt protein and could be mediated by porc as well. The human Porcupine gene is implicated in a genetic disease, Focal dermal hypoplasia. Porcupine, encodes a multipass transmembrane ER protein, which is required for normal distribution of Wg in embryos. Porc stimulates the processing of Wg when expressed in Drosophila cells in vitro and is also necessary for the localization of Drosophila Wnt-3 on the axon tracts of the embryonic central nervous system.