Protection against mutations
Spermatozoa were able to repair DNA damage
Scientists have found that the activity of genes in human spermatozoa allows them to repair DNA before passing it on to the next generation. The researchers' article was published in the journal Cell (Xia et al., Widespread Transcriptional Scanning in the Testis Modulates Gene Evolution Rates).
Earlier studies have shown that human spermatozoa activate up to 90% of the genes contained in them. This is typical for other animal species and even insects. In the cells of most organs, about 60% of the genes are usually active. This is enough for the cell to do its job. Such an unusual number of active genes in spermatozoa has long been of interest to scientists.
New work by researchers from New York, Texas and Columbia Universities shows the reasons for this difference. The authors found out that these genes together make it possible to restore DNA and protect the integrity of genetic information transmitted to the next generation.
"We also found that such repair in spermatozoa is less active in genes that are activated or transcribed less frequently," explains Itai Yanai, professor of the Department of Biochemistry and Molecular Pharmacology at the New York University School of Medicine. — This confirms the theory that evolution uses the frequency of transcription as a lever. Some genes are preserved in this case, while others are changed to ensure the survival of the organism."
An example of such genes may be sites associated with immunity. This is because it must constantly evolve, as the body must recognize and attack constantly changing bacteria and viruses.
To conduct a new study, the authors analyzed the patterns of gene expression during sperm maturation. First, they collected human testicular tissue samples taken from volunteers' biopsies. Using a microfluidic device, the scientists then passed all the cells through a special tube.
Inside the tube, each cell was placed in its own drop of water, which acted as a mini-tester. The enzymes inside each drop "opened" the cell and attached labels to each transcribed fragment of genetic material. The labeled transcripts were then used to create maps whose genes were switched on at each point of sperm maturation. The team then compared these results with known DNA variations in human population databases to estimate how often a given gene was "repaired".
The researchers found that genes activated even several times during sperm development contained 15-20% fewer DNA code errors than non-expressed genes. The authors attribute this effect to transcription-related repair. This process replaces defective sections of DNA just before transcription. The RNA transcripts are then read to build proteins.
The new work may shed light on the causes of many genetic diseases associated with changes in the sperm of aging fathers. Male reproductive cells are known to divide and multiply throughout a person's life, and errors occur in them every new cycle. According to the authors of the work, their research can help create sensors that scan male germ cells in real time for adverse genetic changes.
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