Russian biologists, together with foreign colleagues, have studied the mitochondrial genomes of Japanese centenarians and found out what their features affect the long life of carriers. Scientists have come to the conclusion that biologically, life expectancy is not rigidly fixed and varies markedly depending on the set of genes of a particular organism.
For a long time, scientists believed that all multicellular organisms are subject to aging and death. In the 20th century, it turned out that the situation is not so simple: a number of species show the so-called negligible senescence. Certain species, such as the creeping species Turritopsis nutricula, are potentially biologically immortal. Of course, this thesis must be taken with caution, since in order to be convinced of the "immortality" of an organism, one must observe such a creature for an infinite number of years that science cannot do. Now we can only say that scientists have not recorded deaths from old age in representatives of this species.
After scientists discovered negligible aging in naked mole rats, it became clear that the aging situation could be ambiguous for mammals as well. This potentially indicates that for certain combinations of genes, a person's lifespan may differ from the standard. There are hypotheses that the death and aging of multicellular organisms are not their original features. It was as if multicellular organisms acquired all this in the course of evolution, since the death of older individuals allowed the species to change faster in a rapidly changing environment.
The authors of the new work turned to data on the Japanese famous for their long-livers. They studied the carriers of the mitochondrial haplogroup D4a, which are unusually numerous among those Japanese who are over 105 years old. The mitochondrial genome is inherited only in the female line, and in particular, D4a is distributed mainly in Japan, Thailand and Laos.
The researchers focused on how the mitochondrial genome of carriers of this haplogroup affects the accumulation of mutations in somatic (non-sex) cells. The accumulation of such mutations after cell division is one of the main factors of aging. The frequency of such mutations is the higher, the more direct repeats of individual segments are in the DNA, therefore, researchers consider such repeats as alleles (an allele is called different forms of the same gene), potentially harmful in old age.
Scientists searched for such alleles in the mitochondrial genome of carriers of the D4a haplogroup. The researchers found that the common forward repeats of these alleles - the longest repeats in the mitochondrial genome - are dotted "breaks." They are mutations in the form of genes, the appearance of which is changed by random processes. These genes are not repeated from one common direct repeat to another.
From this, the researchers conclude that such breaks in DNA at least partially explain the extraordinary longevity among the Japanese - carriers of the haplogroup D4a. At the same time, the authors could not find any signs that such a feature of mitochondrial DNA somehow helps its carriers to transfer their genes within the framework of selection. When they tried to find in 700 mammalian species a similar relationship between the low number of direct shared repeats in mitochondrial DNA and success in sexual selection, they also found no such relationship.
Apparently, this feature manifests itself only at such an old age that reproduction is almost not going on (it does not go completely for women because of menopause and is unlikely for men because of the age and reproductive status of their sexual partners). If the chances of reproduction from a particular DNA feature do not increase, then such a feature of the genome does not experience any positive selection.
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However, this trait does not prevent its carriers from going through natural selection, that is, reproducing or thriving at a young and middle age. The absence of "minuses" in this feature of mitochondrial DNA makes it a positive feature. Scientists note that finding such a selection-neutral trait that promotes healthy and long-term aging is important both for the development of future gerontological drugs and in order to better understand the evolutionary processes that led to aging.
