Protecting and supporting the chest’s delicate organs, the closed rib cage of terrestrial vertebrates was a key adaptation for the transition from water onto land. The sturdy rib cage must also remain flexible, to allow the expansion of the lungs during breathing. This dual function relies on the structure of the ribs, composed of sections of bone (shown above in red, in a mouse rib cage) and softer cartilage (in blue). Scientists studying how these two types of tissue arise suggest that a gradient of a protein known as Hedgehog, decreasing from the midline of the back to the front of an animal, could be responsible for patterning the ribs early in development: high levels of Hedgehog would cause embryonic cells to give rise to bone, and low levels to cartilage. Their approach, based on genetic tools and computational modelling, could also be used more generally to explore other features of human development.
Written by Emmanuelle Briolat