A defect in the choreography of sharing chromosomes in eggs during cell division would be one of the causes of female infertility related to age, say researchers in Quebec.
Researcher Greg FitzHarris and his colleagues at the Center Hospitalier de l’Université de Montréal (CRCHUM) observed for the first time a particular defect in mouse oocytes using new microscopy techniques.
This defect is also found in the oocytes of older women.
Thus, microtubules that orchestrate the separation of chromosomes during cell division are abnormal in older oocytes. In short, instead of forming a structure that unfolds in a controlled and perfectly symmetrical manner, called the spindle, the microtubules go in all directions.
This altered alignment dynamics contributes to chromosome separation errors and represents a new explanation for age-related female infertility.
Greg FitzHarris, Researcher at CRCHUM
Humans and other mammalian females are born with a fixed number of oocytes that remain dormant in the ovaries until a single egg is expelled at each menstrual cycle. However, around age 35 in women, fertility decreases significantly.
Did you know?
91% of women can become pregnant at the age of 30
77% at age 35
53% at age 40
One of the known causes of female infertility is a defect in ovules (called aneuploids) that causes them to have an abnormal number of chromosomes. This reality is becoming more and more frequent as the woman ages. This is one of the main reasons why women have difficulty becoming pregnant and pregnant.
It is also known that these defective eggs increase the risk of miscarriage and can cause Down’s disease in a term child.
The work of Professor Greg FitzHarris and the Montreal team does not contradict this idea, but show that there is also another problem: defects in microtubules that cause defective spindles and also contribute to a particular type of aneuploidy.
Did you know?
Microtubules are tiny cylindrical elements that organize together to form a spindle. This complex biological machine collects and sorts the chromosomes at the time of cell division and sends them to both ends of the daughter cells in a process called chromosomal segregation.
“In mice, about 50% of eggs from older females have a spindle with chaotic microtubule architecture and dynamics,” says FitzHarris.
The present work shows that maternal age influences the alignment of microtubules independently of the age of the chromosomes contained in the nucleus of each ovule.
In sum, it is the cellular machinery in general that works less well in aging, no matter the age of the chromosomes.
This new knowledge could one day lead to new fertility treatments to help women become pregnant and carry a pregnancy to term.
The researchers are currently testing micro-intervention techniques, directly in eggs, that would counteract this problem to rejuvenate eggs.
A treatment solution that will certainly take a few years to develop.
The details of this work are published in Current Biology .
The following video explains the study.