Reproduction: some sperm cells SELL each other in the race to be the first in the egg

To win the race to fertilize an egg, some sperm cells do not play cleanly and poison their opposition, a study has revealed.

Experts in Germany found, in studies on mice, that sperm carrying a genetic factor called a “t-haplotype” can move faster toward their goal.

Meanwhile, their competition without this group of genes is less effective in progressing and they are more likely to end up meandering without circles in circles.

The researchers related the difference in motility (the ability to move) to a protein called RAC1, which transfers signals from outside sperm cells inward.

In white blood cells and cancer cells, RAC1 is known to play a role in directing its host cells to others that emit chemical signals.

Given this and the findings of the new study, it is possible that the protein plays a similar role in sperm cells, helping them find their way to their egg target.

The findings may even shed new light on the reasons for certain forms of male infertility, which increases the possibility of future treatments.

“T haplotype sperm manage to inactivate sperm without it,” said the author of the paper Bernhard Herrmann, who is the director of the Max Planck Institute for Molecular Genetics in Berlin.

“The trick is that the haplotype” poisons “all sperm, but at the same time produces an antidote, which only acts on the sperm and protects them.”

“Imagine a marathon in which all participants receive poisoned drinking water, but some runners also take an antidote.”

The team explained that the t haplotype contains certain gene variants that are distributed to all sperm and distort the regulatory signals, so that, by themselves, they would prevent the so-called “progressive” moment.

However, half of the sperm (those that also end up with the t haplotype when the animal’s chromosomes divide evenly among each other) are able to produce another factor that counteracts this signal disruption and allows them to swim straight.

In their study, the researchers first examined the sperm of male mice that had the t-haplotype on only one of their two “17 chromosomes” and found that some of the cells (with the haplotype t) they were able to swim straight, while the others did not.

However, by treating all sperm with a substance that inhibits RAC1, the team noted that cells without the haplotype t regained the ability to swim properly.

This, they explained, confirms that the t haplotype interferes with RAC1 activity, which in turn stops progressive movement.

In fact, according to the researchers, any aberrant level of RAC1 activity is bad for sperm. Mice with two copies of the haplotype t, for example, with one on each of their 17 chromosomes, have high levels of RAC1 and are almost unable to move.

On the other hand, sperm from mice that have no t haplotype also lose their ability to swim properly when given the RAC1 inhibitor, indicating that low RAC1 levels are also bad for male fertility. .

“The competitiveness of individual sperm depends on an optimal level of active RAC1,” said the author of the paper and molecular geneticist Alexandra Amaral.

“Both reduced and excessive RAC1 activity interferes with effective forward movement,” he added.

The aberrant activity of RAC1 could, according to the team, speculate, also explain some forms of male fertility in humans, meaning that the findings could pave the way for new forms of fertility treatment.

“Our data highlights the fact that sperm cells are ruthless competitors,” said Professor Herrmann, who added that the t haplotype also provides a demonstration of how some genes use “dirty tricks” to transmit themselves.

“Genetic differences can give sperm an advantage in the race for life, thus promoting the transmission of particular genetic variants to the next generation.”

The full findings of the study were published in the journal PLOS Genetics.