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New discovery on infertility

In a study co-funded by FCT, a team of scientists from the Instituto Gulbenkian de Ciência (IGC), establishes 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 work was published in the latest edition of the prestigious journal Science.

At fertilization, the embryo inherits genetic information and essential cell structures from both the mother and the father. The centrioles are carried only by the sperm and thus inherited from the father, while the egg loses its centrioles upon formation. This difference had been known since the beginning of the last century, but its significance for fertility was an enigma until now, when the team of IGC scientists showed that when centrioles are not eliminated from the egg precursor cell, mothers are infertile.

 "The mechanism by which centrioles disappear in the oocytes (the egg precursor cells) of all animals was an 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 of the team, saw that the centrioles are eliminated in stages. First, they lose their coating and only then they disappear. They also saw that the loss of the centriole lining is triggered by the loss of an important regulator of these structures, a protein named Polo. "Surprisingly, it was enough to maintain Polo levels in the cells to maintain the lining of the centrioles and prevent their elimination in the oocyte. Something no one had been able to do before," says Ana Marques.

The embryo must have the correct number of centrioles to develop. "When we artificially kept the mother's centrioles, the resulting embryo had too many centrioles (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 happens in many animals, including humans.

This research has wider implications, as according to Mónica Bettencourt-Dias "it is likely that this mechanism of turning centrioles on/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 Science Institute 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: ©AnaMarques (IGC). Example of an ovum where the centrioles were artificially retained. The centrioles form filaments (microtubules) giving the impression of a starry sky.