Why do eggs age so quickly?
Female germ cells live by their own biological clockKirill Stasevich, Compulenta
The lifetime of oocytes is determined by genes that have almost nothing in common with the "aging genes" of the rest of the body's cells. All the efforts of eggs are spent on protecting DNA, and due to the fact that they do not particularly monitor their own condition, oocytes age much faster than other cells.
All cells of the body age, obeying the course of the biological clock, but the eggs prefer to do it separately from the rest. Colin Murphy and colleagues from Princeton University (USA) have been studying aging processes for a long time using the example of the roundworm Caenorhabditis elegans. This worm lives an average of 21 days, but its fertility drops sharply after a week, and after nine days the nematode generally loses the ability to reproduce. And this is despite the fact that the female may still have a stock of oocytes – they just suddenly lose their quality and cannot form an embryo.
As a matter of fact, a similar picture can be seen throughout the animal kingdom. As for a person, women's ability to get pregnant begins to decline by the age of 40, and this is considered one of the signs of general aging of the body. However, not everything is so simple: previous studies have shown that at least in nematodes it is possible to prolong fertility without increasing the total life time. Changes in cellular processes controlled by the TGF-b protein gave the worms three extra days for successful reproduction.
Signaling pathway of TGF-b (transforming growth factor-beta –VM)
At the next stage of the work, the researchers tried to find out which genetic mechanisms control fertility and longevity. It turned out that nematodes have completely different groups of genes doing this. The shelf life of oocytes did not depend on the aging of other cells. The scientists reported on the results of their experiments at the annual congress of the American Society of Cell Biology.
The cells of the body, or somatic cells, have with them a whole arsenal of tools that allow them to resist aging. They have special genes designed to protect cellular biochemistry from stress and related aging.
But oocytes, unlike somatic cells, do not care about personal safety at all, and they do not have any protective mechanisms for their own proteins. Instead, they spend all their energy protecting DNA and synthesizing a large number of proteins that monitor the accuracy of the distribution of chromosomes during the maturation of germ cells. Observing the health of chromosomes, oocytes do not take care of themselves at all, and therefore fail quite early. If it were possible to somehow activate their dormant protection systems, then this would raise the age bar, after which it is no longer possible for a woman to have children.
Prepared based on the materials of ScienceNews: Eggs have their own biological clock.
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08.12.2011