Immortal Jellyfish?

There’s a particular species of jellyfish named Turritopsis dohrnii I would like to draw your attention to today. This jellyfish does a pretty neat trick, to wildly understate the case.

Like other jellyfish, T. dohrnii begin life as larvae, develop into polyps on the seafloor, and then bud off into free-swimming medusae (the familiar jellyfish form).

Unlike other jellyfish, if a Turritopsis dohrnii medusa gets injured or faces imminent death, it can do something truly incredible. Instead of dying, it reverts back to the polyp stage. This allows the jellyfish to survive virtually any undersea conditions, and it can “heal” itself by simply re-forming every cell.

This is called transdifferentiation—taking a cell and transforming it into a different type of cell—and it’s a hot topic of research in human stem cells right now. For jellyfish, it means they theoretically have the ability to repeat this cycle indefinitely, just hitting the biological reset button on occasion, watching the eons pass.

In reality, jellyfish often die before their body gets a chance to hit reset.

Okay, so they’re not immortal per se, but they can live indefinitely.

Human cells typically can’t do this. They tend to be able to divide a limited number of times, typically between 50 and 70. This is called the Hayflick limit, and it’s all about how long our telomeres are. Telomeres are little caps on top of the chromosome that protect the integrity of the DNA.

Every time a cell divides, the telomere gets used up just a little bit more. Once they become too short, the cell’s programming causes it to stop dividing in order to prevent passing on damaged DNA.

So, human cells just stop dividing and go into senescence, which is kind of like retirement for cells: they’re still here, but they won’t make any more new cells.

There’s one line of human cells that doesn’t seem to die, though. These are cancer cells that were scraped from the cervix of Henrietta Lacks in 1951. These cells were scraped and used without her knowledge or permission, and the fact that she was a poor Black woman in Baltimore should surprise nobody.

These cells came to be referred to as HeLa cells, and they have undoubtedly saved millions of lives.

Cancer cells are characterized by uncontrolled division and a lack of normal cell death. HeLa cells have an added mutation called p53 that allows them to bypass the gene for uncontrolled growth, yet remain able to reproduce indefinitely.

Those 73 year old cells are still alive, still helping with research. Those telomeres are still being rebuilt every time.

Rebecca Skloot does an incredible job of telling this story, with lots of interviews with family members and other primary sources, and plenty of research.

Humans are far from jellyfish, and those HeLa cells only live outside of the human body. Nevertheless, we continue to learn by observing, and the tantalizing idea that we might be able to extend the lifespan of our internal organs or even our bodies is out there.

Had you heard about the “immortal” jellyfish before this? How about Henrietta Lacks or HeLa cells? Are there other good cases for “biological immortality” out there that you know about?