The up side of a gas shortage

The key to building strong bones and healthy joints is oxygen scarcity in the developing embryo. As Provot et al. show on page 451, a protein activated by low oxygen levels orchestrates the formation of limb bones and joints. The work demonstrates that one function of the protein is spurring differentiation of cartilage-constructing chondrocytes.

An embryo acquires all of its oxygen via diffusion, and some parts of the body can run short. But instead of suffocating tender young cells, an oxygen shortage galvanizes them to differentiate. Low oxygen levels switch on a transcription factor called hypoxia-inducible-factor-1 (Hif-1). The researchers had previously shown that Hif-1 promotes growth and survival of chondrocytes, which sculpt a cartilage template that later fills with bone. Provot et al. wanted to determine whether the transcription factor spurs...