Antlers are some of the fastest-growing bone in the animal kingdom: Deer, moose, elk, and reindeer sprout up to half a meter of new bone growth in a month prior to the mating season. Now, researchers studying their genomes have discovered how. Genes that both promote and suppress cancer are partially responsible, suggesting the bony tissue may reveal new ways to fight cancer.
The study started when scientists in China and their colleagues abroad sequenced the genomes of 44 ruminants, including cows, deer, giraffes, pronghorn sheep, and other mammals that have complex stomachs for digesting plants. Many of these ruminants sprout bony protrusions, including the skin- and hair-covered bony ossicles of giraffes; the horns of cattle, which have an additional hard sheath; pronghorns in which this sheath is shed every year; and the annually shed antlers of deer, elk, and moose.
The scientists then looked for the genes underlying the evolution and development of this headgear. Qiang Qiu, a geneticist from Northwestern Polytechnical University in Xi’an, China, and colleagues mapped out which genes were active in 16 live tissues from sheep, goats, and deer, including horns and antlers. They also assessed which genes were active in the developing embryos of some animals.
Horns and antlers evolved once in an ancestor to all these animals, they found. What’s more, these new structures emerged when genes that help build nerve, bone, and skin tissue altered and became active in forming these bony protrusions, Qiu and colleagues report today in Science. In particular, changes to genes involved in bone formation and the development of an embryonic tissue called the neural crest likely helped lead to headgear in the first place. As further evidence of a single origin for bony headgear, Chinese water deer and two species of musk deer, both of which lack antlers, have a mutation in one of the genes linked to bone formation.
In regular deer, the researchers found eight active genes that are normally involved in promoting tumor formation and growth. That suggests, Qiu says, that antler growth is more like that of bone cancer than that of typical bones. However, in contrast to bone cancer, where tumors grow unchecked, antler growth is tightly regulated by the activity of tumor-suppressing and tumor-growth-inhibiting genes, the team reports.
“Deer antlers [are] using essentially a controlled form of bone cancer growth,” says Edward Davis, an evolutionary paleobiologist at the University of Oregon in Eugene who was not involved with the work. The involvement of the tumor-promoting genes isn’t surprising, he says; what’s surprising is the involvement of the cancer-controlling genes.
But that surprise may have done more than just turbocharge deer antler growth. The cancer-suppressing genes that keep growth in check also protect against cancer in general, Qiu says. Zoos, for example, have documented cancer rates in deer that are five times lower than rates in other mammals—perhaps, Davis says, a “happy accident” of antler evolution.