Sonic Hedgehog Leads Nerves Around

Dr Jonathan Clarke

Just after a young limb buds out from a developing body, nerves follow. Eventually, they’ll fill the arm or leg — all the way down to the digits — with fibers to let it feel and move. But the nerves don’t go it alone. Like other elements of the growing limb, they rely on molecules called morphogens to find their way.

One such molecule, a protein called Sonic hedgehog, helps the otherwise blind nerves tell the thumb side of the limb from the pinky side. Genes pump out Sonic in one place, and then it naturally spreads out, thinning along the way as seen in these glowing tendrils in this image. Areas with more Sonic repel nerve tendrils, while areas with less call to them — letting nerves know which way is “up,” so to speak.

About the Author

Charlie Wood

Charlie Wood is a science writer with a bachelor’s degree in physics from Brown University and a master’s degree in science journalism from New York University. In previous lives he taught physics in Mozambique and English in Japan, but these days he freelances from his home in New York.