New discovery about infertility

In a study co-funded by FCT, a team of scientists from the Gulbenkian Institute of Science (IGC) has established a correlation between the disappearance of centrioles—structures responsible for cell division—in female eggs and the correct development of the embryo after fertilization. Led by researcher Mónica Bettencourt-Dias, the study was published in the latest edition of the prestigious journal Science.

During fertilization, the embryo inherits genetic information and essential cellular structures from both the mother and father. Centrioles are carried only by sperm and are therefore inherited from the father, while the egg loses its centrioles during formation. This difference has been known since the beginning of the last century, but its importance for fertility has been a mystery until now, when the IGC team of scientists showed that when centrioles are not eliminated from the egg precursor cell, mothers are infertile.

 "The mechanism by which centrioles disappear in oocytes (the precursor cells of eggs) in all animals was unknown and at the same time paradoxical, since these structures were thought to be exceptionally stable," says Mónica Bettencourt-Dias. Using the fruit fly (Drosophila melanogaster) as an experimental tool to study this process, Ana Marques and Inês Bento, researchers on the team, saw that centrioles are eliminated in stages. First, they lose their coating and only then do they disappear. They also saw that the loss of the centriole coating is triggered by the loss of an important regulator of these structures, a protein called Polo. "Surprisingly, maintaining Polo levels in the cells was sufficient to maintain the coating of the centrioles and prevent their elimination in the oocyte. This is something that no one had been able to do before," says Ana Marques.

The embryo must have the correct number of centrioles in order to develop. "When we artificially retained the mother's centrioles, the resulting embryo had an excessive number of centrioles (both maternal and paternal), resulting in abnormal cell divisions and aborted development, thus demonstrating that the elimination of the mother's centrioles is essential for sexual reproduction," says Inês Bento. The loss of centrioles in the maturation process of the female egg occurs in many animals, including humans.

This research has broader implications, as according to Mónica Bettencourt-Dias, "it is likely that this mechanism of switching centrioles on and off may affect many of the functions of these structures, including the formation and regeneration of various tissues, and that it may be altered in diseases such as cancer."

The study was conducted at the Gulbenkian Institute of Science and funded by the European Molecular Biology Organization (EMBO), the European Research Council (ERC), and the Foundation for Science and Technology.

Source: Gulbenkian Institute of Science
Image credits:©Ana Marques (IGC).Example of an egg cell where the centrioles have been artificially retained. The centrioles form filaments (microtubules) giving the impression of a starry sky.