Sonic Hedgehog (SHH) is one of three proteins in the hedgehog (HH) family, the others being Desert Hedgehog (DHH) and Indian Hedgehog (IHH).

The hedgehog gene (hh) was first identifed in the classic Heidelberg screens of Eric Wiechaus and Christiane Nusslein-Volhard, as published in 1978. These screens, which led to their both winning the Nobel Prize in 1995, 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), much like a hedgehog. On cloning the homologous gene in vertebrates, there were found to be three versions. The first two discovered, Desert and Indian Hedgehog, were named for species of hedgehogs, while Sonic Hedgehog was named for the Sega Genesis character Sonic the Hedgehog. Of the three HH homologues, SHH has been found to have the most critical roles in development, acting as a morphgen responsible for patterning many systems, including the limb and midline structures in the brain and spinal cord.

Mutations in the human sonic hedgehog gene (shh) cause holoprosencephaly (HPE) as a result of the loss of the ventral midline.

External link

• An introductory article on shh