Could an aquarium pet that’s now embedded in modern pop culture be the answer to regrowing severed human limbs? Scientists are currently exploring that possibility with a new study published in the journal Natural Communications on Tuesday, June 10.
Salamanders and regrowth
The salamander used in the experiment is known as the axolotl. The amphibian is a pro when it comes to limb regeneration. If it loses a leg or an arm, it simply grows a new one. However, scientists are still investigating how exactly the axolotl activates this regeneration.
To find the answer, researchers used “genetically engineered glow in the dark” axolotls to better understand the biology that spurs this regrowth.
“This species is special,” James Monaghan, a Northeastern University biologist, told The Washington Post. He says axolotls have “really become the champion of some extreme abilities that animals have.”
Not your typical amphibians
Axolotls have long been kept in labs for research. They do not undergo a full metamorphosis like frogs or other amphibians. Scientists say the axolotl instead maintains features such as gills and webbed feet. The species is also capable of not only growing back limbs but heart, brain and lung tissues as well.
Through experimentation, scientists have discovered that these amphibians are capable of regrowing any part of their arm or leg. Now, biologists are trying to understand the cells responsible for this regeneration.
“Salamanders have been famous for their ability to regenerate arms for centuries,” said Monaghan. “One of the outstanding questions that has really plagued the field is how a salamander knows what to grow back.”
Retinoic acid
In their research, Monaghan and his fellow scientists investigated the use of a small molecule known as retinoic acid, which appears to be responsible for instructing the limb on which part to regrow. Retinoic acid derived from vitamin A, has been shown to possess regenerative properties. It’s related to retinol, which is often used in skin-care products.
Monaghan said, “Anyone that watches TV for 30 minutes watches a skin commercial with retinol.”
His team worked with the genetically engineered amphibians whose tissues glow in the dark. Biologists use the fluorescent tissue to monitor the presence of retinoic acid and track its presence after they have severed arms from the axolotls.
As painless as possible
Scientists reassured those concerned that they used anesthesia and closely tracked the animals’ health. They also noticed the animals didn’t “show signs of pain or distress after limb amputation the way mammals might; they regenerate fully within weeks,” Monaghan said.
However, when dosed with drugs that block an enzyme meant to break down the acid, the axolotls regenerated missing limbs improperly. For instance, some saw an upper arm growing where a forearm should be. The control group in the study, which didn’t receive the drug, regrew limbs normally.
Researchers said the findings indicate that retinoic acid performs as a “GPS device,” directing cells to the proper location to regrow limbs. Scientists said the chemical then seems to activate and regulate limb regeneration.
A long way to go
“While we are still far from regenerating human limbs, this study is a step in that direction,” Prayag Murawala, an assistant professor at MDI Biological Laboratory in Maine, told The Washington Post. Murawala’s lab assisted in producing the genetically modified amphibians used in Mohaghan’s research but did not conduct the study itself.
“Better understanding the gene regulatory circuit is essential if we have to recreate this in humans,” said Murawala.
As for human limb regrowth, Monaghan said that every human cell contains DNA with the information needed to regenerate body parts.
“We all have the same genes,” said Monaghan. We made these limbs when we were embryos.”
Monaghan said the key is now determining the correct chemical signals to send to those genes to induce them to regrow limbs after a human is born, thereby stimulating limb regeneration, similar to axolotls.
