Researchers have discovered a unique strain of mouse that can regrow body parts without any scarring. They hope this could lead to new therapies for people. This ScienCentral News video explains.
Furry, little mice may not be your favorite things in the world, but they don't generally have the fear factor of horror films… unless, perhaps, they start regrowing their body parts.
While studying an autoimmune disease in a specially bred species of mouse, immunologist Ellen Heber-Katz and her research team at Philadelphia's Wistar Institute discovered the animals' natural ability to regenerate. "It's interesting and exciting that mammals may not have lost the ability to regenerate, the way amphibians or starfish do," Heber-Katz says.
Researchers routinely keep track of lab mice using unique ear piercings. But the Wistar team saw that the strain of mouse they were working with completely re-grew this tissue after only four weeks.
image: The Wistar Institute
"When we went back to look at the mice, to look at the different groups of mice, there were no earholes, so we couldn't distinguish one mouse from another," she explains. "It was quite amazing and we repeated the experiment and it repeated and we knew that there was something really phenomenal going on here."
The strain, called the Murphy Roth's Large (MRL), is commonly used as a model to study autoimmune disease. "This mouse was generated approximately 40 yrs ago and this ability to regenerate happens to be a property of that strain of mouse," says Heber-Katz. She speculates that the capability could have emerged by chance after generations of breeding and inbreeding.
In further experiments, these so-called "healer mice" also regrew tissue in the tail, the optic nerve of the eye, the toes, and even the heart. "After an injury to the heart in the healer mouse, the heart, after sixty days, recovers completely," she explains. "Whereas our control mouse shows severe scar formation and very little healing."
The healer mice also don't form scar tissue, which can prevent replacement of damaged cells with new ones. Heber-Katz observed two mechanisms for healing. One is a breakdown after injury of the so-called basement membrane, a layer between the epidermis and the dermis that normally keeps tissues separate. When that layer disappears, proteins in the epidermis and the dermis interact and stimulate cell division, a process that also occurs in salamanders when they regenerate their limbs and tails. The second mechanism involves collagen, a tissue associated with scarring. In these mice, collagen made after an injury does not crosslink into a mass, so no scar tissue forms to halt cell migration and division.
However, she points out that even in amphibians there are parts that don't regenerate. "Each organ is different, so you see different kinds of responses," Heber-Katz says. "But we also believe that there's a molecular correlate with this, so if certain molecules are present they heal better, and if those molecules are not present or are reduced then they don't heal as well."
While she cautions that research in mice doesn't always translate to people, Heber-Katz hopes that studying how these mice repair themselves might one day lead to ways to enhance our own healing abilities.
"We basically saw that it was identical to what was going on in limb regeneration in amphibians… so that makes it quite unusual in terms of being a mammal and healing this way," she says. "What we're hoping is that our own tissue will be able to direct itself, will be able to heal itself, and form a normal tissue."
So, the researchers are mapping the genes involved in the mouse regeneration, and hope they may one day come up with a therapy that would actually allow regeneration to occur. "One might imagine that this could be applied locally and one could get growth. It may be something that you have to administer systemically… after an injury you could potentially administer something and shut it off after a month," she explains. Since old cells are being replaced in these mice, Heber-Katz wants to study whether they might also live longer than normal.