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On average, every woman is born with a million immature eggsthat degenerate with age. They will not form again in their lifetime. By puberty, there are only about 300,000 left in your ovaries. And only 400 eggs are released during the reproductive phase, usually one each menstrual cycle. The vast majority of other cell types don’t live that long: they age and die. For example, red blood cells are eliminated at four months. However, neurons that are conserved for decades accumulate many problems, such as mutations and agglomerations of toxic proteins. Instead, some of the egg’s progenitor cells — called oocytes — will live for about half a century, keeping the woman’s DNA intact and the ability to produce healthy children. Until now, this amazing shielding of future eggs has been a mystery to science. This Wednesday, a team from the Center for Genomic Regulation in Barcelona announces that it has discovered its unique defense strategy.

Human cells usually have inside Hundreds or thousands of mitochondria, a kind of power plant of about a thousandth of a millimeter. In the mitochondria, energy is formed by the movement of electrons between five protein complexes and stored in the form of ATP, a molecule composed of 10 carbon atoms, 16 hydrogen atoms, five nitrogen atoms, 13 oxygen atoms, and three phosphorus atoms. Without this constant production there would be no human life.

In this essential process, however, unstable molecules, so-called reactive oxygen species, the accumulation of which can cause mutations in the DNA and kill the cell. The Barcelona researchers, led by the Turkish biologist Elvan Boke, have observed that the oocytes skip the step that produces the most harmful byproducts – the first of the five protein complexes – which explains why they can remain dormant for almost half a century without losing their ability to reproduce. “My mother had me when she was 26, so the cell I was born in was already 26 years old. Oocytes cannot afford to accumulate damage,” says Böke.

There is so much we don’t know about human reproduction that one in four cases of female infertility is unexplained.

Elvan Böke, biologist

The finding, published in the magazine Nature, could help understand why many women are unable to have children. “There are so many things we don’t know about human reproduction that one in four cases of female infertility is unexplained,” laments the Turkish biologist. His team has analyzed human oocytes as well as those of the African clawed frog, a classic laboratory animal that has starred in several studies whose authors have been awarded Nobel prizes. This Batrachian was the first vertebrate to be cloned in 1962, more than three decades before the sheep Puppet. The British biologist is responsible for this first cloning John GurdonHalf a century later he received the Nobel Prize in Medicine.

The authors of the new study say their results are “very surprising” because no animal cell has ever been observed that could live without this first mitochondrial protein complex. In the realm of eukaryotic organisms—those composed of cells that have their textbook, DNA, in a differentiated cell nucleus, such as animals, plants, and fungi—only one similar case was known: the one with the mistletoe cells. “It’s a parasitic plant that just wants to survive. And to survive long, it reduces harmful processes in your system. We also see the same mistletoe strategy in the egg cells,” emphasizes Böke.

The Turkish scientist arrived in Barcelona in 2017, from Harvard University (USA). His work, funded by 1.4 million euros from the European Research Council, is now focused on finding the alternative energy source that immature oocytes use during their decade-long latency. the biotechnologist Aida RodriguezCo-author of the new study, draws a vivid comparison: “As a long-term maintenance strategy, it’s like idling the engine.”

In rich countries, mothers are having their first child later and later. The average age at birth of Spanish women turned 33 years old according to the National Statistics Institute, for the first time in 2021. Last year nearly 11% of births were to women aged 40 and over, up from 5.5% a decade earlier. biologists deepak adhikari Y John Carollfrom Monash University (Australia), point out in an independent comment in the journal Nature that in these mothers the fertility of the egg cells decreases, probably caused by reactions in the mitochondria. The new study could help understand why eggs stop being a safe haven for the mother’s DNA over the years.

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Source elpais.com

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