Putting the Brakes on Bone Growth

Bone growth is a tightly controlled process, in which cartilage cells slowly differentiate into a scaffold for bone cells. If the differentiation happens too fast, growth is cut short and stubby limbs result. New results on pages 613 and 663 of this issue, from three independent teams of researchers, help unravel the cycle of protein interactions that control this bone growth. The signaling molecule Indian hedgehog interacts with another protein in a negative feedback loop that slows the differentiation process and allows bones to reach their full length.