Sometimes, to save your own skin, you have to lose it first. That's the unusual technique that the African spiny mouse has evolved to elude predators, a new study reports. Pieces of a spiny mouse's hide rip off in the clutches of an attacker, the rodent scoots free—and then the skin grows back, almost as good as new. The discovery may help biologists understand regeneration at the molecular level and promote it in other mammals, including humans.
The ability to lose a body part to avoid capture and then replace it is common in some lizards, salamanders, crustaceans, and arthropods. But it was unheard of in mammals.
However, developmental biologist Ashley Seifert of the University of Florida in Gainesville and his colleagues were curious about stories they'd heard about the African spiny mouse, a type of rodent with stiff hairs on its back like the spines of a hedgehog. The mouse is sometimes kept as a pet, and it's known to lose patches of skin when handled. After tracking down the mice in the wild in Kenya, the researchers discovered that, indeed, the spiny mouse's skin is 20 times weaker than the skin of lab mice, most likely because it has larger hair follicles. The spiny mouse's wounds heal more quickly as well. Instead of scar tissue, new skin, complete with hair follicles, forms after an injury, the researchers report online today in Nature.
The team found that the animals can survive the loss of 60% of the skin off their backs. "It seems remarkable that an animal can lose so much skin and heal the skin so well that it looks normal," says Elly Tanaka, a developmental biologist at the Technical University of Dresden in Germany who was not involved with the work. A few lizards are known to shed skin as an escape response, but in their case, just the top layer sloughs off. The mice lose the entire skin, baring muscles underneath, and so replacing it is a much bigger task. "It's a nice example that shows the maximum capacity of what the mammalian skin can do in terms of healing," Tanaka says.
Seifert's team investigated the mechanism of regeneration by punching holes in the ears of spiny mice. They found that regeneration in the rodents' ears proceeds similarly to regeneration of limbs in newts. The body produces a pool of embryonic-like cells that gather beneath the layer of cells that first cover the wound. Those embryonic-like cells then become the different cell types needed to re-form the complete limb or ear tissue.
"It is truly exciting to discover that these mammals are capable of losing and regrowing complex tissue in such an efficient manner," says Tara Maginnis, an evolutionary biologist at the University of Portland in Oregon who was not involved with the work. "It's another 'gripping' example of how organisms can evolve alternative, adaptive traits not by inventing new structures or pathways but by modifying existing structures" such as the skin, she says.
Rabbits also have the ability to replace missing parts of their ears. And deer regrow antlers, but "the regeneration of a large portion of lost skin is certainly a remarkable and surprising example of mammalian regeneration," says Shannon Odelberg, a molecular biologist at the University of Utah in Salt Lake City. "This discovery puts scientists one step closer to being able to unravel the molecular bases of regeneration in vertebrates and possibly translating these discoveries into therapies."