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Learning from regenerators · Turritopsis dohrnii

The “immortal” jellyfish.

The “immortal jellyfish” (Turritopsis dohrnii) can reverse its life cycle, reverting from its adult medusa stage through an intermediate cyst-like stage to an earlier polyp stage. During this process, cellular transdifferentiation and tissue reorganisation help the organism return to an earlier developmental stage. This remarkable ability gives it the potential for biological immortality, although it remains vulnerable to predation, disease and other causes of death.

Established: supported by the published scientific literatureTurritopsis dohrnii
Illustration of the jellyfish Turritopsis dohrnii with callouts for the bell, the stomach and the tentacles, and a magnified view of tentacles carrying stinging cells.
Turritopsis dohrnii, adult medusa form, with the bell, stomach and tentacles highlighted. Illustration, not to scale.

At a glance

Scientific name
Turritopsis dohrnii
Group
Hydrozoan jellyfish (cnidarian)
Known for
Reversing its life cycle
Why it is studied
A window on rejuvenation and cell plasticity

Up close

Region by region, magnified.

What each highlighted part of the jellyfish can do, how it does it and what the research shows.

Magnified illustration of the jellyfish's bell

01 Life cycle

A life cycle that runs backwards.

Like many hydrozoans, Turritopsis lives as a colony of polyps attached to a surface, which bud off free-swimming jellyfish (medusae) that reproduce. Unusually, the medusa can turn back into a polyp.

What happens
Medusae at any stage, even after sexual maturity, can transform back into a colony of polyps, either directly or after a resting period.
Why it is remarkable
It was the first animal known to revert to a colonial, juvenile form after reaching sexual maturity in a solitary stage.
The caveat
“Immortal” describes this potential to restart its life cycle, not an inability to die.

Source: Piraino et al., 1996

Magnified illustration of the jellyfish's stomach inside its bell

02 Bell and stomach

The cells that make it possible.

The bell gives the jellyfish its shape and lets it swim. The stomach, part of its digestive (gastrovascular) system, hangs inside it. Both turn out to matter for life-cycle reversal.

What was shown
In experiments where parts of the medusa were removed, the transformation into a polyp happened only if cells from the outer surface of the bell and part of the gastrovascular system were present.
Transdifferentiation
During reversal, specialised cells change into different cell types. This process, transdifferentiation, is how the adult body is rebuilt into a juvenile one.
Why it matters
It shows a transformation potential unparalleled in the animal kingdom, achieved from differentiated adult cells.

Source: Piraino et al., 1996

Magnified illustration of the jellyfish's tentacles and stinging cells

03 Tentacles

Tentacles armed with stinging cells.

Like all cnidarians, Turritopsis captures food with tentacles carrying specialised stinging cells called nematocysts.

What they do
Tentacles capture prey and sense the surrounding environment.
Stinging cells
Nematocysts fire a tiny harpoon-like thread that helps the jellyfish catch its prey.
Why they are interesting here
They are some of the most specialised cells in the animal, yet the body they belong to can still be rebuilt into a juvenile form.
Magnified illustration of the jellyfish's tentacles

04 The genome

Clues in its genes.

Comparing the genome of Turritopsis dohrnii with that of a close relative that cannot rejuvenate has pointed to possible explanations.

Gene differences
Variants and expansions in genes linked to DNA replication and repair, telomere maintenance, the redox environment, stem cells and communication between cells.
During reversal
Targets of a gene-silencing complex (polycomb repressive complex 2) are silenced and pluripotency targets are activated.
What it suggests
These factors may act as inducers of pluripotency, helping the jellyfish rejuvenate.

Source: Pascual-Torner et al., 2022

Unvalidated: hypothetical, requires experimental validation

Why it matters to us.

Turritopsis shows that specialised adult cells can, in the right conditions, be turned back into a younger state. Whether lessons from such a distant animal apply to human tissue is an open question.

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Sources

Where this comes from.

  1. Piraino S, Boero F, Aeschbach B, Schmid V. Reversing the life cycle: medusae transforming into polyps and cell transdifferentiation in Turritopsis nutricula (Cnidaria, Hydrozoa). Biological Bulletin. 1996;190(3):302–312. (The species studied is now classified as T. dohrnii.) doi.org/10.2307/1543022
  2. Pascual-Torner M, Carrero D, Pérez-Silva JG, et al. Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation. PNAS. 2022;119(36):e2118763119. doi.org/10.1073/pnas.2118763119

Summaries are simplified for a general audience. Illustrations are artistic, not anatomical drawings.

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