The axolotl is a small amphibian native to Mexico, and it has fascinated researchers for years. Unlike most animals, it can stay in a young, tadpole-like state for its whole life, which is why some people call it the “Peter Pan” of the animal kingdom.
Still, it is not just that odd, almost ageless quality that interests experts. The axolotl can also regrow full limbs and parts of major organs after injuries caused by normal life, accidents, or predator attacks.
Zebrafish can regrow their tail fins again and again, as well as several internal tissues. Mice have a much more limited ability, but they can regrow the tips of their digits, and humans can sometimes do something similar when the nail bed is still intact.
In research published in the Proceedings of the National Academy of Sciences, scientists identified a shared genetic process that appears to help drive this kind of regrowth. They believe it could one day help them understand how to move closer to human limb regeneration.
Instead of looking at only one animal, the team compared several models of regeneration. That approach helped them see which parts of the healing process were unique to one species and which parts seemed to be shared.
For human medicine, that kind of comparison is important. Scientists are not saying people will regrow arms or legs soon, but they are trying to understand the basic instructions that allow some animals to rebuild complex tissue.
“It showed us that there are universal, unifying genetic programs that are driving regeneration in very different types of organisms, salamanders, zebrafish, and mice.”
More than one million people around the world have a limb amputated each year. Many lose limbs because of health problems such as diabetes, cancer, infection, or severe injury.
Prosthetic limbs have improved a lot in recent years, especially when it comes to comfort, fit, and function. Even so, they still cannot fully replace the complex feeling, control, and movement of a natural limb.
The team behind the research hopes these new findings may help scientists look for ways to repair or regrow tissue more like these animals do. That goal remains far off, but the study gives researchers a clearer place to start.
When skin began to regrow in the axolotl, zebrafish, and mice, two genes called SP6 and SP8 became active. That pushed scientists to look more closely at how those genes work during the rebuilding process.
Using gene-editing methods, the team removed SP8 from axolotls. When they did that, the animals could no longer regrow limb bones in the normal way. Researchers saw similar effects in mice that lacked SP6 and SP8.
The therapy delivered a molecule called FGF8, which helped stimulate bone regrowth in mice. It did not solve everything, but it partly helped compensate for the missing genes and gave the team another lead to study.
Humans do not naturally have this same level of regenerative ability. Still, with more research, scientists hope they may one day copy some parts of the process and use them to improve treatment for people with limb loss.
“The gene-therapy approach in this study is a new avenue that can complement and potentially augment what will surely be a multi-disciplinary solution to one day regenerate human limbs.”
“Many times, scientists work in their silos: we’re just working in axolotl, or we’re just working in mouse, or just working in fish,” he explained. “A real standout feature of this research is that we work across all these different organisms. That is really powerful, and it’s something that I hope we’ll see more of in the field.”
