The African spiny mouse can regenerate its skin. Learning how this occurs… (Ashley W. Seifert / Nature )
A mouse species often kept as an exotic pet can regenerate lost skin, according to a new study. The discovery may provide insights into how to create new tissue-generating treatments for people.
It is well known among pet collectors and researchers alike that the skin on the tail of the African spiny mouse, or acomys, comes off if you tug on it. The trait is a handy way for the mouse to get away from predators that catch them by the tail.
But the new research, published Wednesday in the journal Nature, revealed something surprising: Not only does the tail skin rip off, but it also grows back, and looks as good as new. And when the researchers looked to see whether this regenerative ability -- called autotomy -- spread to the skin on the rest of the body, they found that it did.
So how does the mouse do it?
To find out, the researchers first wanted to know what was different about this mouse's skin. When they tested it, they found that it tears easily, almost like a sheet of paper. In fact, 77 times less energy was required to tear the mouse's skin than the common house mouse you might find in your kitchen snacking on some cheese.
Not only did the skin rip easily, but it could rip anywhere on the body: Unlike salamanders, whose tails break off and regenerate at predefined points, the skin of the spiny mouse was, like our skin, a continuous sheet.
This seemingly problematic trait actually helps the mice, but only because their skin grows back quickly. Amazingly, big tears in the skin repaired themselves in less than 30 days. And not only did the skin regrow, but the hair follicles on the skin came back in as well, and in the right color. It wasn't long before the injured mouse looked as good as new.
When the researchers looked closely at what biological processes were underlying the regeneration, they found a big difference between the acomys' healing process and that of most mammals, including humans.
When we get injured, our skin does go through a modest process of regeneration. But it is incomplete, and dominated by what's called "wound-bed tissue" -- the tissue that generally leads to scarring as a healing mechanism.
In the spiny mouse, the team found that the substance underlying healing was a molecule called collagen III, which was aiding in the generation of new, normal tissue. In humans, there is far more of a molecule called collagen I, which leads to scarring.
The key, it seems, is a process called re-epithelialization, the replacement of lost skin cells with new ones. When a wound occurs, skin cells called epidermal cells "crawl" over the wound, covering it and establishing interactions with important factors that exist below the skin that promote healing. This process, it turned out, occurred extremely quickly in the mice. In normal house mice, it occurred more slowly, interrupting the epidermal cells' ability to communicate with molecules under the wound that can aid in tissue generation and leading to less-than-ideal results: If a house mouse is able to grow new hair over a wound, for example, it is often uncolored.
The researchers put this process to a more stringent test with a strange procedure used to probe regeneration: They punched holes in mouse ears. When you punch a hole in a house mouse's ear -- or in a a human's for that matter -- the response is mostly scarring, and the ear tissue does not regenerate. But in the African spiny mouse the team found that the ear hole does close, which is quite a feat considering the complex blend of cartilage, skin, hair, and other tissues that make up ears.
Again, the key was the rapid crawling of epidermal cells, and the unique "cross-talk" between those cells and important factors under the skin that appeared to lead to successful regeneration-factors that appeared quite similar in the mouse and in previous studies of salamander tail regeneration.
The speed with which the mouse's skin grew back, along with the specific molecules the researchers believe are involved in healing, could lead to new treatments for skin loss in humans. An encouraging sign is that the key molecules appear to be consistent with those observed in other regenerating species, like salamanders, which suggests that a common mechanism is at work.
But, as regenerative biology expert Elly Tanaka points out in a commentary published alongside the new research, much still has to be learned before applications can be developed. One open question, she writes, is how the immune system of the mouse deals with infections, given that they often have open wounds.
An answer to that question might provide another breakthrough. Not bad for a tiny mouse.
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