IT’S MORNING IN early March, and Wallace Marshall—a towering, plaided-out cell biologist—is kneeling over a pond in San Francisco’s Golden Gate Park, digging through the muck.
“What’s that smell?” I ask.
“Uh, it’s the rotting stuff, you know,” Marshall says, piling vegetation into a pitcher. “I think there’s a lot of bacteria down in the muck. Which is actually good for stentors.”
“Stentor” sounds like a dinosaur or a minor He-Man villain. But in fact the stentor is one of the strangest, most mysterious organisms on Earth, and it just might be swimming in a pond near you. It’s made up of a single cell so massive you can see it with the naked eye. It’s got a genome organized like nothing else, as Marshall, a researcher at the University of California San Francisco, and colleagues reported last month in Current Biology. And it might just help Marshall and other scientists figure out how to bestow humans with the power of regeneration.
Measuring in at between 1 and 2 millimeters, the stentor is a thousand times longer than most bacteria and a billion times the volume. On top of that, for a single cell, it’s extremely complex. Hair-like structures called cilia beat around its mouth—more of an opening, really, than like human puckers—sucking in food like algae, even spitting out bits the cell doesn’t care for. Again, a single cell without a brain of its own.
More remarkable still for something without a central nervous system, it can flee predators, but at the same time ignore repetitive yet harmless stimuli. “If you’re living near the train tracks, you don’t get scared when the train goes by,” says Marshall. “And so a stentor, if you bump it again and again at the same intensity it will just learn to ignore it. It’s learning without a brain.” Should a stentor detect a threat, it’ll fire out a cloud of blue pigment, perhaps as a distraction, like an octopus might ink.
Should that fail, and a predator bites off a chunk of a stentor, it’ll show off its most miraculous skill: regeneration. “If you cut off the head or the mouth structure it’ll rebuild the mouth structure,” says Marshall. “If you cut off the tail it’ll rebuild the tail. It seems to know what’s missing.” Again, a single cell without a brain or a nervous system is pulling this all off. And if scientists unravel the secrets of stentor regeneration, they might be able to apply the organism’s powers to human beings.
With modern regenerative medicine, the idea is to replace damaged cells by differentiating stem cells into things like skin or muscle cells. “Which is great but—at some level this is a provocative statement—I feel like it’s trying to fix a radio by dumping in a bunch of transistors,” says Marshall. “What you really want to do is get the damaged cells themselves to regenerate in situ, in their natural position, because then you might be able to rebuild the tissue exactly like it was before.” You know, just like the stentor.
The stentor’s weirdness even penetrates right down to its genome. Last month, Marshall and colleagues sequenced it for the first time, hoping it could give insight into the stentor’s regenerative powers, and revealed particular oddities with what are known as introns. These are spacers within strands of DNA. In human DNA, introns can stretch over a thousand letters. In stentor? It’s 15, the shortest of any known organism.
Why exactly? Add that to the long list of stentor secrets. “One possibility is the cell is just trying to make its genome as compact as it can,” says Marshall. “Now, why that would be in a gigantic cell, I don’t really know.” On top of all that, a stentor stores hundreds of thousands of copies of its genome in its oversized single-cell body. In humans, each cell stores a measly two copies. For the stentor, having so many copies spread throughout its giant body might mean instructions are available wherever an injury occurs. Understand the genome, and you can better understand regeneration.
So what began as sifting through the rank muck of San Francisco’s ponds, now becomes a matter of sifting through a strange new genome. But who knows, maybe somewhere in there is the key to human regeneration. He-Man would be so proud.