Immortal jellyfish: the secret to cheating death

(Natural History Museum, London) Link to article

Virtually every day we can see advertisements for things to do to slow the aging process. These include eating healthy, exercising more, stimulating our brains, etc. But slowing it down does not mean to stop it forever. Everything dies, right? Maybe not. 

Life multiplies. That's one of its definitions. But what if it produces offspring and continues to grow itself? Is that possible? Talk to Christian Sommer (Germany) and Giorgio Bavestrello (Italy), because they are the researchers who discovered something amazing about a tiny jellyfish Turritopsis dohrnii. It doesn't die. They published their work in Scientia Marina (cool name!), a journal from Spain. (Don't be confused by the species name in the article; Turritopsis nutricula was later changed to T. dohrnii.)

Jellyfish are a type of animal called a hydrozoan (Greek for "water animal"). These usually live in 2 stages called a polyp and a medusa, and most hydrozoans are found in saltwater. The polyp form grows in groups called colonies and look like tree trunks with a narrow base and many tentacles waving out the top. The medusa (named after the female beast in Roman mythology with snakes for hair) is a free-swimming sexual form of hydrozoan. It's the familiar floppy umbrella-shaped creature we know as the jellyfish. The jellyfish releases male or female cells which merge to form an egg, and when it sticks to a surface, it begins to grow into a polyp. As long as conditions are good, it will continue to mature into another form that stops eating. It uses its energy reserves to change shape which looks like upside down stacked cups that break free and grow into the medusa.

Drawing from learnaboutnature.com

So, what's this about being immortal? This sounds like a regular cycle of life. The parent dies as its offspring continue on. Well, Sommer and Bavestrello discovered a type of jellyfish that sometimes goes directly from medusa form to polyp and then back to medusa again. No male or female cells are needed to combine. The tentacles of the medusa shrink and are absorbed into the body (resorbed is the scientific term) before it settles on the floor and becomes a polyp. This happens when there isn't enough food around or environmental conditions aren't favorable.

Here are the drawings from the paper by Sommer and Bavestrello. The medusa contracts (A to B), then after it settles, more tentacles reach out like mold structures or strawberry plants (C and D), and from them the new polyp appears (E). It's not as grand as the picture above, but these Turritopsis dohrnii are only 1-4 millimeters wide!

Drawings from the 1992 paper by Sommer and Bavestrello

They discovered this rejuvenation process by accident. After collecting medusa samples, they fed them for a few days and got new medusa. But then they stopped eating, and that's when the researchers noticed the curled up balls of medusa on the bottom of their Petri dishes. So, something stressed them into that transformation.

The link from the Natural History Museum at the top of the page goes on to describe another researcher, Shin Kubota from the Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Japan. From 2009 to 2011, he kept the same species of jellyfish alive going through its normal life cycle in his laboratory. This happened for 10 cycles! The really amazing thing, aside from culturing them in a lab with careful attention to temperature and a supply of fresh water, is that Kubota actually fed these miniscule creatures by hand (well, ok with needles serving as chopsticks)!

Professor Shin Kubota

All of this research suggests that when ballast water is sucked into cargo or cruise ships in an area where Turritopsis dohrnii are, they may survive as these rejuvenated polyps until they are released in other locations. Then, their normal life cycle may resume. Fortunately, they are not harmful to the environment, but they can still be labeled as a potential invasive species.

Finally, aside from the novelty of being an eternal creature (as long as it's not eaten), why is this tiny jellyfish the least bit important? Think about it. Turritopsis dohrnii changes from a medusa to a polyp which means its cells have had to do what only stem cells have been known to do. That is, stem cells are like the earliest form of cells in the body, and from them we get blood, liver, brain, stomach, bone, and all other types of cells. But Turritopsis dohrnii changes its fully formed adult medusa cells! How? That's what researchers are looking into, so that any ethical issues of using human stem cells for medical research can be overcome. Life may not go on eternally, but science can continue.

Watch this video (7:04) for more details, plus a fun part of Shin Kubota's work.

Here's another video (3:33) with some of the same and some new information.