Although the perfect biological age to have children is before thirty, in today’s society most women delay their pregnancy much longer. From the age of 35, fertility decreases exponentially, and complications during pregnancy also increase. Finding out how and why this occurs is the first step in developing more effective assisted reproductive therapies.
It is known, for example, that eggs deteriorate with age, and often contain an abnormal number of chromosomes, which are the containers for genetic material . Now, a work published in the journal Current Biology exposes new data on what happens inside those aged eggs that lose viability over time. And, thanks to new microscopy techniques, we can increasingly study processes that occur at the molecular level more closely. In this case, the scientists ‘spied’ on the cell division process in the ovules of adult female mice , and the results are revealing.
Cell choreography failures
“We have found that the microtubules that direct chromosome segregation during cell division behave abnormally in older eggs,” explains Greg FitzHarris, a researcher at the University of Montreal Hospital Research Center (Canada). Microtubules are small cylindrical structures that are arranged in the shape of a spindle that joins the chromosomes. In this way, a perfectly organized biological machinery is formed that is capable of gathering chromosomes and classifying them during cell division , and then sending them to the opposite poles of future daughter cells in a process called chromosome segregation .
This is a time when everything must work perfectly, in this way the daughter cells will have exactly the number and chromosomes that correspond to them. However, in the aged ovules studied by the authors of this work, “instead of mounting a shaft in a controlled symmetric way, the microtubules go in all directions. The apparent altered movement of the microtubules seems to contribute to errors in chromosome segregation , and therefore represents a new explanation for age-related infertility “, explains the researcher.
Until now, the most accepted explanation for the chromosomal abnormalities of the ovules was the theory of the ‘loss of cohesion’, which comes to say that the ‘glue’ that holds the chromosomes together does not work well in the older eggs.
“Our work does not contradict this idea, but it demonstrates another problem: microtubule defects, which cause defective spindles and in doing so appear to contribute to a specific type of chromosome segregation error, ” adds FitzHarris.
Furthermore, it was found that spindle defects are independent of the age of the chromosomes. To verify this, the researchers swapped the nuclei of young eggs with those of the old ones, and they observed the same problems in those old cells with young nuclei. “This shows that maternal age influences microtubule alignment regardless of the age of the chromosomes contained in the nuclei of each ovule,” says Shoma Nakagawa, another of the authors.
The discovery opens the door to the development of new fertility treatments to help older women become pregnant and minimize associated problems during pregnancy. In any case, experts warn that the best treatment is to prevent, and avoid as far as possible, delaying the search for pregnancy at such late ages that it is impossible or that its risks are greatly increased.
