Aging theories have changed over time due to the modification of qualities associated with health markers or drivers of aging, such as cellular senescence or genomic instability, which decrease pluripotency and regeneration potentials. While most living beings age, the hydrozoan Turritopsis dohrnii, a jellyfish, is the only organism that can regenerate following sexual reproduction and hence become physiologically immortal.
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Life Cycle Diagram of T. rubra and T. dohrnii. Credit: pnas.org
Turritopsis dohrnii is the only metazoan that can regenerate its medusae repeatedly after reproduction, implying biological immortality and challenging our concept of aging. A team of scientists from Spain has published discoveries that might show how the jellyfish Turritopsis dohrnii can exist forever, at least in principle.
The scientists recount analyzing the genomes of the immortal jellyfish and a close mortal relative species to see whether they could discover relevant changes in their research now available online.
Cloning is the reason for jellyfish immortality
T. dohrnii begins its life as a larva floating around in the sea. At certain times they form themselves on the seafloor and grow as polyps. The species then clone themselves frequently to build a colony. When the colony reaches maturity, it begins to produce mature medusas. Other organisms reproduce similarly but can die if the colonies are in danger. When T. dohrnii gets into situations leading to death, things change. One of the medusas can change into a cyst, identical to its original polyp, and attach itself to the seafloor in a new area, restarting the cycle.
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Because it forms by an ability to clone, the organism never truly dies—some form of itself lives on endlessly. The researchers sought to discover how the organism recycles itself in this new study. They collected samples and performed whole genome analysis to find out. They analyzed the same for a close relative of T. dohrnii, Turritopsis rubra, which does not have an immortal ability once they analyzed the entire genome. Then the scientists sought genetic distinctions that allowed one species to be immortal while the other died when problems occurred.
T. dohrnii had twice the gene numbers responsible for gene repair and protection as other species. It also contained mutations that allowed it to halt cell proliferation and keep telomeres from breaking down. The scientists also discovered that when the jelly was metamorphosing, some genes involved in development reverted to their pre-metamorphosis form.
Clinical significance
Jellyfish have certain biological features that permit their immortality which is not replicable in human models. However, the study gives an idea of the process of aging. The features that prevent aging are biological. The drivers of the aging process are absent in the jellyfish species that clones itself for immortality.
Conclusion
Scientists can now understand the unique features of the species of jellyfish that clones. With its ability to clone itself, severe conditions only allow it to reproduce again, giving it the ability to live forever. The feature of T. dohrnii that allow reproduction are missing in other species. These unique distinctions offer an explanation of why the T. dohrnii can live forever.
References
Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation
