Albert McKeon

Nov 20th 2020

Scientists Are Cracking the Mysteries Behind Limb Regeneration


Humans tend to forget they are animals. As Homo sapiens, we are — along with chimps and gorillas — members of the hominid family, a branch of the animal kingdom.

It makes sense, then, that advances in the regrowth of animal limbs are spurring talk of limb regeneration in humans. That’s right. An adult frog growing new legs could improve the chances of successful human regeneration.

Several regeneration studies with frogs, worms and other animals have some scientists believing they’re in the early stages of creating a DNA roadmap that could give human amputees real hope of again having a limb that’s not prosthetic or computerized but naturally grown. No one’s rushing to suggest the regrowth of human limbs is around the corner, but science can sometimes lead to wonderfully unexpected places.

A Control Gene Might Dictate Regeneration

A flurry of separate studies on various organisms have ignited speculation that what works for frogs and fish could similarly work for humans.

Consider a 2018 study by the genetics and cell biology department of the University of Minnesota that looked at why animals regenerate neurons while humans instead form scar tissue, preventing the rebuilding of damaged spinal cord nerves. The researchers studied an amphibian known as the Mexican salamander, native to lakes near Mexico City. They found that a molecular protein in the frog directs cells to regenerate spinal cord nerves, whereas that same protein in humans does less directing and instead causes scar formation.

Another study last year made a big leap in limb regeneration. A Tufts University biology research team triggered the regrowth of legs that were amputated on adult African clawed frogs. They applied a female sex hormone to the frogs’ amputated back legs and within six months the regenerated limbs had bone volume, organized nerve fiber and blood vessels. The limbs were strong enough to move and swim.

Harvard University biologists this year announced they had pinpointed a master control gene that powers the re-growth of worms. The EGR gene (EGR stands for early growth response) plays a role in the regeneration. That study turned heads because the EGR gene is also present in humans.

Pace of Research Could Help Humans

What do these experiments and studies on animals mean for human regeneration? Many biologists believe it could be the start of something big.

Humans already regenerate some organs, including skin when cuts aren’t deep and fingertips if the cells remain intact, David Gardiner, a University of California-Irvine cell biologist, told Live Science. Gardiner studies regeneration in salamanders. He believes limb regeneration is possible in humans, but it depends on cells being in the right place to build the right structures in the right order.

Jumping from salamanders to worms, Harvard assistant professor Mansi Srivastava also holds out hope that human regeneration might be possible. Srivastava, who specializes in organismic and evolutionary biology and led the study on three-banded panther worm, said the pace of biomedical research could lead to human limb regrowth in only 10 years.

“It’s a very natural question to look at the natural world and think, if a gecko can do this, why can’t I?” Srivastava told The New York Times. “There are many species that can regenerate, and others that can’t, but it turns out if you compare genomes across all animals, most of the genes that we have are also in the three-banded panther worm … so we think that some of these answers are probably not going to come from whether or not certain genes are present, but from how they are wired or networked together.”