Amputated sea cucumber parts show signs of ‘immortality,’ researchers say - CNN

- Severed body parts from a sea cucumber survived for over three years in a lab, healing themselves and absorbing nutrients without a mouth.

- Researchers call the tissue fragments zombies because they maintain cellular function indefinitely without growing into new organisms.

- The discovery could provide a new model for medical research with immortal cells that thrive in natural conditions without ethical constraints.

What does it mean to be alive? A new study on an astonishing sea creature suggests the answer may be more complicated than it seems.

Some amputated fragments of Psolus fabricii — a type of sea cucumber native to the North Atlantic Ocean — puzzled researchers when they noticed that the severed parts did not simply decay and die but instead appeared to grow.

To find out more, the researchers humanely excised additional fragments from the feet, main body and tentacles of the marine animals and ran a number of lab experiments in untreated seawater. Indeed, the fragments refused to die. The various parts unexpectedly healed themselves and even managed to absorb nutrients despite lacking a mouth.

“This is the first case of tissue immortality in natural conditions,” said Sara Jobson, lead author of a study describing the finding that published Wednesday in the journal Science Advances. “These sea cucumbers are known for their high-regenerative capacity, so when they lose a tentacle or a tube foot they’re able to regrow it very well, but nobody’s ever looked at what happens to the tissues that are torn off, because we just assumed that they would die.”

The severed tissues, however, didn’t develop into whole new individuals — a process that can occur under certain conditions in some species of sea cucumber — bringing up some philosophical questions. “We lovingly call these tissue explants ‘our zombies,’ because they seem to ride the line between dead and alive,” said Jobson, a doctoral student of ocean sciences at Memorial University in Newfoundland and Labrador.

“They’re not regrowing into a whole new organism — as far as we can tell, they seem to be their own entity that’s maintaining cellular function, but not a reproducing individual. Why would these small tissue chunks maintain the ability to heal and survive without any reproductive purpose? What’s the evolutionary driver that allows that to happen?”

Many animals are able to amputate tissue voluntarily and regrow it, most famously lizards that sacrifice their tails to escape predators. But the lost tail itself doesn’t do anything, Jobson noted. To draw a parallel with the sea cucumber, it’s as if a lizard tail healed itself and then wiggled around in the woods, gaining its own nutrients and surviving for years.

What’s even more surprising is that the severed tissue has been going strong for more than three years. “As far as we can tell, there weren’t any signs of death, degradation or necrosis,” Jobson added, referring to cell death. “It seemed to be able to go on forever. We just had to cut ourselves off at some point and put the study out there.”

In the long term, such work could help researchers better understand regeneration, wound healing, tissue maintenance and aging, said Veronica Hinman, director of the Whitney Laboratory for Marine Bioscience at the University of Florida, via email. She did not participate in the study. “I think the bigger finding, though, is that this work tests assumptions about what it means to be ‘alive’ and how this depends on the whole organism, rather than on the local self-organizing properties of tissues themselves.”

The discovery that prompted the study was accidental, according to Jobson. “We work right on the coast, and we’re able to keep live animals in our lab,” she said. When a sea creature is needed for research, it’s usually pulled from its tank, she added, but some of the animals strongly attach themselves to their rock habitat or the aquarium itself. In this case, when a researcher removed the sea cucumber, some of its tube feet were left behind and stuck to the glass. This is normal, as the animal can detach them in the wild when under duress or attack from a predator and easily regrow them.

“We noticed that they were still there after a couple of days, and then weeks, and then months, and they were still stuck on,” Jobson said. “They were healing, and they even grew a little bit. They were surviving in their natural environment.”