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Death is a universal fact of life, unless you're a jellyfish. As explained in a new study, the jellyfish Turritopsis dohrnii "is the only species able to rejuvenate repeatedly after sexual reproduction, becoming biologically immortal," and its DNA might hold the answer to the secret of eternal life. T. dohrnii pulls off an amazing biological feat to cheat death. Every member of the species is an identical clone, and starts life as a polyp that becomes a mature organism called a medusa. This isn't particularly unique, but what's amazing about T. dohrnii is that if the medusas get injured, sick, or old, they don't throw in the towel. Instead, they become a "cyst" that turns back into a polyp and restarts the whole process, churning out more clones. While it might be a bit different from the idea of living forever in a vampire story, it is, strictly speaking, biological immortality. You can also call it, as scientists do, "life cycle reversal." It would be like if a person got old and turned back into a fetus, or a chicken into an egg.
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In a study published on Monday in the journal PNAS by researchers at the University of Oveidas in Spain, the authors describe how they compared the DNA of T. dohrnii to another closely-related jellyfish species that is not immortal to determine what makes it special. Specifically, they compared "genes involved in aging and DNA repair, together with the transcriptome [mRNA] analysis of life cycle reversal (LCR) of T. dohrnii," which has now "provided new insights into the molecular mechanisms underlying Turritopsis plasticity, which may contribute to the immortal phenotype of T. dohrnii," they wrote in the study. Indeed, the researchers found several differences that they pinned as likely having an effect contributing to the jellyfish's immortality. Overall, these changes "suggest that T. dohrnii may have more efficient replicative mechanisms and repair systems" than other species, the authors write. For example, they found more copies of POLD1 and POLA2 genes—which encode different proteins—in T. dohrnii than in its mortal relatives, which "suggest enhanced replicative capabilities in this species," the study notes. The species also had more copies of genes governing DNA repair, and those that govern telomerase, which are enzymes that replenish the telomeres on DNA that shorten with age. This "may contribute to a reduced telomere attrition and as a consequence to an enhanced cellular plasticity," the authors write, and "may indicate that telomerase activity could be enhanced or more finely regulated in this species."While this knowledge isn't going to let humans become "biologically immortal" like T. dohrnii—and even if it could, would we want it?—it is an astounding jump forward in our understanding of age and how some species defeat it entirely.