In a famous segment from Walt Disney’s 1940 film “Fantasia,” Mickey Mouse is a sorcerer’s apprentice tormented by a broom that he brings to life to help with his chores. At one point, Mickey completely loses it, grabs an ax and savagely chops the cheery, bouncing broom into splinters.
But the story doesn’t end there. As Mickey walks away, the splinters begin to wiggle and regrow, until each one become a new broom.
Researcher Alejandro Sánchez Alvarado specializes in studying a real-life organism that can actually do this – at least the regeneration part. It’s a flatworm called Schmidtea mediterranea that can be repeatedly sliced and diced and nearly every piece will grow into a new worm.
“They are masters of regeneration. They are incredibly good at this. In fact, many, many people thought it was essentially just witchcraft,” Sánchez Alvarado says.
For decades, researchers have been trying to understand how certain worms or lizards are able to regenerate severed body parts in the hope they might offer lessons for the treatment of humans.
It turns out flatworm regeneration isn’t magical or limitless, but new research from Sánchez Alvarado’s lab at the Stowers Institute in Kansas City shows something nearly as incredible: this ability is contained in a single cell.
At Sánchez Alvarado’s lab, flatworms grow in big aquarium tanks. Swimming around, they look like squirming specks, but the researcher says he’s got a soft spot for them.
“Once you put them under the microscope and you see their photoreceptors, they look like little manga characters,” Sánchez Alvarado says. “They’re actually quite cute.”
Using a combination of new DNA testing methods, post-doctoral researcher An Zeng narrowed down the flatworm cells that seemed to have the most potential as engines for regeneration.
He then took these single cells and injected them into flatworms that had been irradiated so they could no longer regenerate.
Amazingly, these essentially dead flatworms regrew completely. In fact, they’re still alive and well.
“They were injected maybe six months ago. There’s still alive,” Sánchez Alvarado says. “They recovered their capacity to regenerate.”
The researchers think they’ve isolated what are known as pluripotent stem cells. These are cells that can create any other type of cell that the body might need.
Pluripotent stem cells are the starting point for fetal development in all animals, including humans, but Schmidtea mediterranea are one of the few that continue making them in adulthood.
Big step forward
Peter Reddien, a biology professor at MIT, says the Stowers research marks a big step forward.
“If we want to understand regeneration, then we definitely want to have our hands on the cells that give the animals that ability,” says Reddien, who did post-doctoral work in Sanchez Alvarado’s lab but was not involved in his latest research.
A few years ago, Reddien and other researchers at MIT discovered that the flatworm’s ability to regenerate is contained in pluripotent cells.
Now the Stowers researchers have identified which cells those actually are, Reddien says, scientists can take the next step in figuring out how they work.
“Zeroing in on the molecular features of a cell that is acting as an adult pluripotent stem cell is an exciting direction,” he says.
Excitement over stem cell medicine hasn’t always lived up to the hype, although scientists have had some success using stem cells to regrow bones and skin.
But some experts say stem cell medicine has the potential to go much further, to the point of growing entire organs, repairing brain damage or even counteracting aging.
Sanchez Alvarado says he doesn’t let himself get carried away thinking about such things.
“Could we be able to activate regenerative processes in humans in the future? Sure, why not? But how far in the future? No idea,” Sánchez Alvarado says.
Instead, he says the big payoff for him is taking part of the larger scientific process and being one of the first people ever to watch something like a flatworm regrow from a single cell.
“It’s one of those things that’s why you do science,” Sánchez Alvarado says. “You live for these moments, right?”
Because no matter how much he learns about regeneration, he says, it never seems any less magical.
Alex Smith is a health reporter for KCUR. You can reach him on Twitter @AlexSmithKCUR