The poisonous chromosome
The short life of men was associated with the "toxic" effect of the Y chromosome
However, so far biologists have studied this only on the example of fruit flies
Molecular biologists have found out that female individuals live longer than male individuals because of the last repeating sites in the Y chromosome, which cause aging cells to produce substances dangerous to their lives. The findings of the scientists were published by the scientific journal PLOS Genetics.
"Male Y chromosomes usually consist almost entirely of repeating transposons – fragments of the genomes of ancient viruses. In young cells, these sections of DNA are blocked by the protein "wrapper" of chromosomes, but with age its structure weakens. As a result, such sites are activated, which negatively affects the cells," the researchers write.
All mammals, many species of birds and insects use special chromosomes to determine the sex of future offspring. For example, girls have two X chromosomes in their genome, while boys have one X and one Y chromosome. Where the "male" and "female" embryo growth programs are contained and what controls them, scientists do not yet know.
Recent studies show that in the course of mammalian evolution, the Y chromosome decreases quite rapidly. This means that it may disappear altogether. Experiments on mice show that a full-fledged male organism can be grown without the Y chromosome in the cells of the embryo: to do this, you need to take only two genes from it and transfer them to other areas of the genome.
American molecular biologists led by Doris Bakhtrog, a professor at the University of California at Berkeley, have found out the possible cause of the disappearance of the Y chromosome and its unusual role in the aging process of men and male animals.
Previous experiments on flies of the species Drosophila melanogaster showed that in the Y chromosomes of insects there were many repeating sites that got into the genome of their ancestors as a result of contacts with retroviruses - transposons. If they are activated, new copies of these DNA sections appear in the genome, as well as various disorders in the work of cells.
Scientists are interested in what role transposons can play in the vital activity of insects. To answer this question, biologists tried to find another kind of flies, in the sex chromosomes of which there would be significantly fewer or more repetitions.
For this role , the researchers chose the drosophila species Drosophila miranda. Their X- and Y-chromosomes appeared relatively recently by evolutionary standards, about 1.5 million years ago. They appeared as a result of the fusion of one of the pairs of chromosomes common to both sexes with their X and Y chromosomes. In the future, the number of transposons in the Y chromosome of flies increased dramatically, while in the X chromosome their number practically did not change.
Thanks to this feature, geneticists were able to trace the influence of these repeats on the life of two species of flies. They tracked how the activity of repeating sites in the Y chromosomes of Drosophila miranda and Drosophila melanogaster changed. In parallel, scientists conducted similar work for X-chromosomes and common sections of the genome of males and females.
It turned out that the activity of transposons in the Y chromosome of males was relatively high even in adolescence. In old age, it increased sharply due to the destabilization of the "wrapper" of the chromosome in the structure of proteins. If scientists "turned on" them, various "garbage" began to accumulate in the cells of the flies faster, and their vital functions began to be disrupted.
Such processes negatively affected the typical life expectancy of male fruit flies – on average they lived about 78 days, and females – more than 98 days. Something similar, according to Bakhtrog and her colleagues, is characteristic of humans and other animals whose Y chromosomes have many transposons.
Biologists hope that further experiments on flies will help to study in detail exactly how transposons affect the vital activity of aging cells and how their activity is associated with senile diseases, including dementia. Thanks to this, scientists will be able to understand how to protect older men from the "toxic effect" of their Y chromosomes on the health of their cells.
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