In humans and some other species that distinguish their sexes by XY chromosomes, females or females generally live longer than males or males. A recent study reveals that the large number of repetitive DNA sequences within the Y chromosome may be one of the reasons for the difference in lifespan. As an organism ages, these duplicates are prone to have detrimental effects on the body.
Although both the X and Y chromosomes carry some repetitive DNA sequences, the Y chromosome contains more repetitive sequences than the X chromosome. Scientists speculate that the large number of repetitive sequences will produce a toxic Y effect when the organism ages, thereby shortening the lifespan of both male and female organisms.
Y chromosome toxicity effect
Deoxyribonucleic acid (DNA) is a molecule located in human cells, part of which is a gene that gives instructions to the cell to make a specific protein. The rest, called Heterochromatin, is located in the nucleus in a tightly compressed form and has specific functions: some are responsible for controlling genes and others for protecting the integrity of chromosomes. This new study explores exactly how the Y chromosome becomes toxic as the organism ages.
The researchers examined a class of DNA sequences called transposable elements. These are repetitive DNA sequences that are inactive when the heterochromatin is in a compact, compressed state. But when the heterochromatin structure becomes loose, they start to move, from one position to another within the genome.
In this study, Drosophila was used as the subject. Male fruit flies have twice as many duplicated gene sequences in their chromosomes as females and have shorter life spans than females.
The researchers found that when male fruit flies are young, these repetitive sequences hover compactly inside the male fruit fly cells in an inactive state. However, as the flies age, the repeating sequences become less tightly bound and may begin to move.
Lead researcher Doris Bachtrog, a biologist at the University of California, Berkeley, says that these transposons “cut themselves out of a specific region of the genome (causing DNA damage) and insert themselves into a new region (potentially causing the inserted gene to become inactive).
This study suggests that this is why DNA repetitive sequences may become toxic as the organism ages.
Large amounts of repetitive DNA exist in both Drosophila and humans
Previous studies have shown that activation of repetitive DNA in Drosophila is associated with memory loss and DNA damage. This study proves that there is indeed a link between the two.
The researchers say it’s clear that fruit flies are not fully representative of humans, as their DNA sequences are more repetitive than those of humans, but in that sense, there are meaningful similarities.
“Humans contain a lot of repetitive DNA, and variations in heterochromatin have been identified as a driving factor in human aging,” Bartelog says, “and like fruit flies, males generally have shorter lifespans than females, suggesting that differences in the contents inside heterochromatin may be one of the reasons for the difference in lifespan between the two sexes. “
The study was published April 22 in the journal Public Library of Science – Genetics (PLOS Genetics).
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