Shorts: The immortal jellyfish with a reversible life-cycle

Immortality is discussed avidly as much as a science fiction concept as it is a scientific goal, but for this jellyfish immortality isn’t just a concept but a reality.

Immortality is seen by most as science fiction, and by others an elusive idea that is worth heavy investment. While human bodies age and die (through senescence), Turritopsis dohrnii recycles itself over and over again, rendering itself – for want of a better word – immortal. T. dohrnii is the only known metazoan with this amazing ability of reversing its life cycle, theoretically continually.

Source: Australian Academy of Science

The jellyfish’ life begins like most other hydrozoans as a fertilised egg, which then grows into a planula. The free-swimming planula larvae then swims for a short period of time before dropping to the sea floor and attaching itself to a surface. The planula develops into a tube-shaped polyp which then grows into a colony, and after a few days the polyps buds off and tiny jellyfish break away to form ephyra (immature jellyfish). Ephyra then mature into the fully formed medusae adults, ready to sexually reproduce and begin the next generation
This is when T. dohrnii splits from the pack of other hydrozoans – when it becomes stressed or starves it recycles itself. The bell reabsorbs the tentacles and settles on the sea floor to become a blob of cells. The blob then forms an outer shell and extends little roots called stolon’s, then growing the upright branches of the polyp structures from which the new Ephyra bud.

The process form which a cell starts to become a more specialised cell is called transdifferentiation. A cell that can develop into any type of cell is called totipotent, while cells that can only follow a certain route are called pluripotent. In 2012 researchers received the Nobel prize for taking mouse skin cells, reversing them back to pluripotent cells using transcription factors, and then growing heart, blood, and nerve cells. This amazing process is all part of the life cycle of T. dohrnii, but the process is unknown.
Researchers found two areas which could be critical sites for this transdifferentiation – the exumbrella epidermis (the outer layer of skin on the bell of the jellyfish) and portions of the digestive tract. These areas were found to have high replication frequency and the transformation could only occur if these tissues were present, implying they are vital to this unique process.

immortal-jellyfish-black-backgroundEvery cell contains the information needed to build a brand-new organism, but this molecular mechanism of T. dohrnii’ “immortality switch” remains to be elucidated. This transformative process offers tantalising possibilities for medical research, and could open doors for treating a multitude of diseases. Parkinson’s is a neurogenerative disease in which a loss of neurons in an advanced stage and loss of connections, transdifferentiation could be used to replace and renew these cells.
Another disease that could benefit from studying transdifferentiation is Cancer – Cancer is cell differentiation without rules, but it seems the rules we were not even aware of, if understood, could be leveraged to turn an uncontrolled pathway into a controlled one.

The secret to “immortality” may remain a mystery, but we now have the improbable opportunity to study this not so fictitious phenomenon.



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