Further studies showed that when the gene that codes for insulin-like growth factor 1 (a hormone known to influence growth and metabolism) is disabled specifically in mouse hind legs, chondrocyte growth stops after phase two. That result suggests, Cooper says, that the gene might play a key role in determining how long different bones grow-and might provide clues to drugs that could help treat bone growth defects.
"It's a very interesting new twist to a very old question of how bones grow," says Cornelia Farnum, an anatomist and professor emeritus at Cornell University. Identifying the three phases of chondrocyte growth will make it easier for scientists to figure out exactly what drives the changes that happen during each phase, she says. That, in turn, could help explain how genetic changes have driven the different shapes that skeletons have evolved.