In the 1970s, a gene related to how our brain grows our limbs was given the name “hedgehog” in relation to the spiky appearance of fruit flies with a defective version of the gene. In 1995, three strains of the “hedgehog” gene were found and named “Desert-Hedgehog”, “Indian-Hedgehog”, and amusingly, “Sonic-Hedgehog”. In recent years the “Sonic-Hedgehog” gene has become the subject of much focus, due to its relation to stem-cell division and the development of certain cancers.
Sonic Hedgehog Homolog (SHH) is one of three proteins in the mammalian hedgehog family, the others being desert hedgehog (DHH) and Indian hedgehog (IHH). SHH is the best studied ligand of the hedgehog signaling pathway. It plays a key role in regulating vertebrate organogenesis, such as in the growth of digits on limbs and organization of the brain. Sonic Hedgehog is the best established example of a morphogen as defined by Lewis Wolpert's French flag model—a molecule that diffuses to form a concentration gradient and has different effects on the cells of the developing embryo depending on its concentration. SHH remains important in the adult. It controls cell division of adult stem cells and has been implicated in development of some cancers.
The Hedgehog Gene (hh) was first identified in the classic Heidelberg screens of Eric Wieschaus and Christiane Nusslein-Volhard, as published in 1978. These screens, which led to their winning the Nobel Prize in 1995 along with developmental geneticist Edward B. Lewis, identified genes that control the segmentation pattern of Drosophila melanogaster (fruit fly) embryos. The hh loss of function mutant phenotype causes the embryos to be covered with denticles (small pointy projections), resembling a hedgehog.
Investigations aimed at finding a hedgehog equivalent in mammals revealed three homologous genes. The first two discovered, desert hedgehog and Indian hedgehog, were named for species of hedgehogs, while Sonic Hedgehog was named after Sega's video game character Sonic the Hedgehog. In zebrafish, the orthologues of the three mammalian hh genes are: shh a, shh b (formerly described as tiggywinkle hedgehog named for Mrs. Tiggy-Winkle, a character from Beatrix Potter's books for children), and Indian hedgehog b (formerly described as echidna hedgehog, named for the spiny anteater. It should be noted that this may have also been a playful reference to Knuckles the Echidna, another character from the Sonic the Hedgehog (series) of video games).