A mouse embryo can slow the growth of some body parts and accelerate that of others, helping to sculpt an animal with the proper proportions.
When a developing fly larva is injured, its uninjured sections grow more sluggishly, allowing the damaged section to catch up. To learn whether more-complex animals rely on the same strategy, Alberto Roselló-Díez and Alexandra Joyner at the Sloan Kettering Institute in New York City and their colleagues used genetic techniques to halt the proliferation of some of the bone-forming cells in the left hind leg of mouse embryos.
After this intervention, normal bone-forming cells in this leg multiplied at a higher rate than normal. As a result, the mouse pups were born with right and left limbs of roughly the same length. The rest of the embryos’ bodies also grew more slowly after the intervention, perhaps as a result of stress signals sent out by bone-forming cells.