The secret of cyclic immortality
The gene of the "immortal" jellyfish has been sequenced
Polina Loseva, N+1
Spanish scientists have compiled a list of genes that are probably responsible for the "immortality" of the jellyfish Turritopsis dohrnii. To do this, they sequenced its genome and compared it with the genome of the jellyfish Turritopsis rubra. It turned out that the "immortal" jellyfish, unlike its relative, acquired additional copies — up to eight pieces — of genes that are associated with the processes of cell rejuvenation. The work was published in the journal Proceedings of the National Academy of Sciences (Pascual-Torner et al., Comparative genomics of mortal and immortal cnidarians unveils novel keys behind rejuvenation).
The jellyfish Turritopsis dohrnii is often called the only "immortal" animal. But her immortality is not like what, for example, is described in myths for the ancient Greek gods. T. dohrnii can be killed — but by itself, that is, "from old age", she seems to almost never die.
The life cycle of many jellyfish is arranged according to the principle of "polyp — jellyfish — larva": that is, the jellyfish releases germ cells that meet each other and produce a larva. The larva settles to the bottom and grows into a polyp, from which a new jellyfish then bud off. Such a cycle is similar to the reproduction of most animals, since there is fertilization and generational change in it.
Cycle T. dohrnii is arranged in a similar way. But there is one detail: after reproduction, the jellyfish itself can, after undergoing some transformations, settle to the bottom and turn back into a polyp. It can again turn out to be a jellyfish that is able to reproduce — and there is no evidence yet that this process ever stops. This is what biologists mean when they call T. dohrnii is biologically immortal.
The life cycle of two jellyfish: "mortal" (left) and "immortal" (right)
To find out what mechanisms prevent the jellyfish from aging after reproduction, Maria Pascual-Torner from University of Oviedo and her colleagues sequenced the T genome. dohrnii, and at the same time its relatives T. rubra, which does not know how to turn from a jellyfish back into a polyp. In total, they found 17468 genes in T. dohrnii and 9324 genes in T. rubra. The researchers then compared these genomes with each other and with the genomes of other animals. They looked for genes associated with key aging processes (hallmakrs of aging), which one of the co-authors of the work, Carlos Lopez-Otín, identified in 2013.
Scientists have found that T. dohrnii genes associated with aging are often found in several copies — compared to T. rubra, other shooting, vertebrates and even humans. T. rubra also found genes with additional copies of genes, but much less than their "immortal" relative.
The researchers believe that the presence of several copies indicates that these genes were particularly strongly influenced by selection — which means that they could play a role in gaining "immortality". Among these genes, many were associated with copying and repairing DNA — that is, eliminating genetic instability, one of the important causes of aging. There were also those that encode antioxidants — substances that neutralize free radicals in the cell. There were also differences in proteins associated with telomerase and telomeric loops — perhaps they somehow help the jellyfish to lengthen the ends of their chromosomes and thereby avoid cellular aging.
Finally, the scientists tested whether these genes and their additional copies work during the life cycle of T. dohrnii. It turned out that many of them actually participate in the transformation of a jellyfish into a polyp, but in different ways. For example, the genes responsible for repairing DNA and maintaining telomere length came into play after the polyp was formed — and before it turned into a jellyfish. And the genes associated with the work of stem cells and intracellular signaling, on the contrary, were expressed at the early stages of transformation into a polyp.
Thus, the authors of the work once again confirmed that even in such exceptional cases as the only known "immortal" animal, the same mechanisms of anti-aging are involved as in all other animals, including humans. But it will take a long time to figure out exactly how these mechanisms work, and whether it is possible to reproduce them in some other living system.
Scientists from time to time sequence the genomes of different centenarians — and everywhere they find about the same thing: differences in a large set of genes responsible for several mechanisms of maintaining youth at once.
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