Updated: Jul 20
You might have heard of the “immortal jellyfish” before. Given the universality of the aging process, it’s no wonder that an animal capable of subverting it is so interesting to us. However, the “immortality” that these jellyfish possess isn’t quite what we usually imagine when we think of living forever.
Turritopsis dohrnii is a tiny (around 4.5 millimeters long when fully grown) jellyfish found in temperate to tropical waters around the world. Like most jellyfish, it begins its life cycle as a larva that travels through water before attaching itself to form a polyp. Cells in the polyp divide rapidly, forming anemone-like structures. When conditions are right, a segment of the polyp separates to become an independent organism that will eventually develop into the medusa, or adult stage.
The strange part comes when the Turritopsis medusa experiences stressful conditions that threaten its survival. Instead of dying, the medusa transforms into a cyst, which drops to the ocean floor to become a polyp once more. From there, the life cycle repeats.
So how does the biology behind this aging “reversal” work? The key process is known as transdifferentiation, or the conversion of a mature cell to a stem cell and then back to a mature cell of a different type. While stem cells differentiate to gain specific functions during the development of many organisms, Turritopsis is one of the only natural examples of mature cells undergoing transdifferentiation.
As it reverts to the polyp stage, every cell in the medusa’s body transdifferentiates into cell types found in the polyp, essentially returning to an earlier stage in the jellyfish’s life cycle. The journey from polyp to medusa to polyp again is believed to be repeatable, meaning that the jellyfish might never die from age.
While the exact mechanisms behind transdifferentiation is unknown, scientists believe that the answer lies in the Turritopsis’ genes. All cells contain the genetic information necessary to create the entire organism, but only some of that information is needed after a cell has differentiated. This means that gene regulation factors that control the expression of genes are of particular interest, as turning genes “on and off” can determine how a cell develops.
Research into Turritopsis is ongoing, but experts warn that, despite the excitement that an “immortal” organism rightly causes, any practical application is a long way off. Still, investigating how they cheat death can help us better understand the processes behind biological functions relevant to our own bodies.