By performing a DNA comparison of two similar jellyfish species, researchers
have found the genes that could stop and reverse ageing in immortal jellyfish.
An immortal species of jellyfish has double copies of genes that protect and
repair DNA. The finding could provide clues to human ageing and age-related
conditions.
Jellyfish start their lives as drifting larvae. They eventually attach to
the seafloor and develop into sprout-like polyps. The bottom-dwellers clone
themselves, forming stacked, sedentary colonies that bud off into
free-swimming umbrella-shaped medusas.
That stage is a dead end for most jellyfish – but the immortal jellyfish
(Turritopsis dohrnii) can reverse the cycle. When times get tough, like in
harsh environments or after injury, they melt their bodies into amorphous
cysts, reattach to the seafloor and regress into polyps. They can restart
the cycle indefinitely to skirt death by old age.
To find out how the immortal jellyfish staves off aging, Maria
Pascual-Torner at the University of Oviedo in Spain and her colleagues
sequenced its genome – its full set of genetic instructions – and compared
it to that of the related but mortal crimson jellyfish (Turritopsis rubra).
They found the immortal jellyfish had twice as many copies of genes
associated with DNA repair and protection. These duplicates could produce
greater amounts of protective and restorative proteins. The jellyfish also
had unique mutations that stunted cell division and prevented telomeres –
chromosomes’ protective caps – from deteriorating.
Then, to pinpoint how T. dohrnii reverts into polyp form, the scientists
looked at which genes were active during this reverse metamorphosis. They
found the jellies silenced developmental genes to return cells to a
primordial state and activated other genes that allow the nascent cells to
re-specialise once a new medusa buds off. Together, Pascual-Torner says,
these genetic alterations shield the animal from the weathering of time.
But Maria Pia Miglietta at Texas A&M University at Galveston points out
that the crimson jellyfish can also rejuvenate, just not as commonly as T.
dohrnii. Using them for comparison might reveal differences in the degree of
immortality rather than the key to immortality itself, she says.
Still, Pascual-Torner says the genes they identified could be relevant to
human ageing. They could inspire regenerative medicine or provide insights
into age-related diseases like cancer and neurodegeneration. “The next step
is to explore these gene variants in mice or in humans,” she says.
Reference:
López-Otín, C. et al. “Comparative genomics of mortal and immortal cnidarians
reveals new keys behind rejuvenation.” Proceedings of the National Academy of
Sciences. DOI: 10.1073/pnas.2118763119