As in animals, human eggs choose among the spermatozoa presented to them through Chemical signals. These are not always those of the romantic partner. Ultimately, this discovery could lead to a better understanding of infertility and more effective treatments.
In mammals, the selection of a male whose genetic make-up ensures the best possible offspring is also carried out at the cellular level. It was already known that oocytes select the best sperm through chemical signals. However, in humans, this mechanism was still relatively unknown. A new study published on June 10 in Proceeding of The Royal Society B now shows that human ova also select spermatozoa that reach them through the same mechanism. Whether the most romantic people like it or not, the spermatozoa preferred by the ova are not necessarily those of the partner. Ultimately, this discovery could help to better identify the causes of infertility in the world.
To reach this conclusion, researchers at Stockholm University (Sweden) studied cases of couples who had undergone in vitro fertilization. They extracted the fluid surrounding the egg and then added the chemoattractants and the subjects’ sperm. They then observed the behavior of the sperm of various donors in relation to different follicular fluids.
Result of the observations: Sperm reacted differently to each follicular fluid. Thus, thanks to the molecules that secrete around them, the ova attract the sperm of a particular man: “The follicular fluid of a particular woman was more able to attract the sperm of a particular man, while the follicular fluid of another woman was more able to attract the sperm of another man,” explains Professor John Fitzpatrick of Stockholm University and first author of the study.
“The idea that eggs select sperm is really new.”
Unlike sperm, whose sole purpose is to fertilize the eggs, whatever they may be, the egg cell carefully selects the sperm it is going to fertilize, either because of its genetic characteristics or because of its affinity with the chemoattractants it secretes. And it is clear from this experience that the somatic cell’s preferred spermatozoa that are not necessarily from the woman’s partner. “This shows that the interactions between the egg and the sperm depend on the specific identity of the women and men involved,” adds John Fitzpatrick.
“Thus, despite the great freedom of choice of human beings before mating, chemosensory communication between gametes still plays a role in selective sperm recruitment,” researchers note in their work.
“The idea that eggs select sperm is really new in the field of human fertility,” says Professor Daniel Brison, Scientific Director of the Department of Reproductive Medicine at Saint-Marys Hospital (Montreal, Canada) and principal author of this study.
Improving fertility treatments
“The next essential step is to determine whether these interactive effects between women and men are a common feature of mammalian reproduction, including in people who do not undergo assisted fertility treatment (although this is logistically and ethically difficult), and to investigate the possibility that the choice of partner affects the quality of the embryo under biologically relevant conditions”, continue.
“Research into the interaction between eggs and sperm will advance fertility treatments and may eventually help us understand some of the currently ‘unexplained’ causes of infertility in some couples,” Brison concludes.