By comparing the DNA of two jellyfish species, researchers have found genes that can stop and reverse aging in immortal jellyfish.
An immortal jellyfish species has double copies of genes that protect and repair DNA. This discovery sheds light on aging and age-related disorders in humans.
Jellyfish begin their life as floating larvae. They attach to the seabed and develop into sprout-shaped polyps. These bottom dwellers clone themselves, forming stacked colonies that then grow into free-swimming, umbrella-shaped medusa.
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That stage is a one-way street for most jellyfish, but the immortal jellyfish Turritopsis dohrniic can reverse the cycle. When their lives get tough, for example in a rough environment or after an injury, they melt their bodies into an amorphous cyst, reattach to the seabed and turn back into polyps. They can repeat this cycle indefinitely to avoid the death of old age.
To find out how this immortal jellyfish counteracts aging, molecular biologist Maria Pascual-Torner of the University of Oviedo in Spain and her colleagues mapped the complete genome of the jellyfish and compared it with that of the related but mortal crimson jellyfish. Turritopsis rubra.
They found that the immortal jellyfish had twice as many copies of genes involved in DNA repair and protection. These duplicates were able to produce greater amounts of protective and repair proteins. The jellyfish also had unique mutations that inhibited cell division and prevented the telomeres, the protective caps on the ends of chromosomes, from dying.
Ravages of time
To determine how the immortal jellyfish changes into the polyp shape, the scientists looked at which genes were active during this reverse metamorphosis. They found that the jellyfish turned off developmental genes to transform the cells back to a primordial state, and activated other genes that allow the budding cells to re-specialize once a new medusa begins to grow. According to Pascual-Torner, these genetic changes together protect the animal against the ravages of time.
But marine biologist Maria Pia Miglietta of Texas A&M University in Galveston, USA, points out that the crimson jellyfish can also rejuvenate, just not as often as the immortal jellyfish. The comparison between these jellyfish reveals differences in the degree of immortality rather than the key to immortality itself, she says.
Pascual-Torner expects the genes to be relevant to human aging. They can inspire regenerative medicine or provide insight into age-related diseases such as cancer and neurodegeneration. “The next step is to investigate these gene variants in mice or in humans,” she says.