Sonic hedgehog

Are there related proteins? Lots. In mammals, Sonic is related to two other hedgehogs: Indian and Desert. When expressed appropriately, the three proteins can substitute for one another but they do have unique functions: Desert hedgehog is needed for spermatogenesis and Indian hedgehog regulates cartilage differentiation. In the zebrafish, Sonic is related to Tiggywinkle hedgehog — which is thought to be involved in eye and brain development — and Echidna hedgehog is needed for formation of muscle pioneer cells. In the nematode, two protein families with some sequence similarity to Hedgehogs have been proposed: groundhog and warthog. It can only be a matter of time before someone coins hogwash, hogshead, etc...