Reproduction: Some sperm cells ENCOURAGE each other in the race to be the first to lay eggs

To win the race to fertilize an egg, some sperm cells do not play properly and, in fact, poison their opposition, a study found.

Experts in Germany have found in studies in mice that sperm carrying a genetic factor called a “haplotype t” are able to move faster towards their target.

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

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

In white blood cells and cancer cells, RAC1 is known to play a role in directing 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 underlying causes of certain forms of male infertility, increasing the possibility of future treatments.

“Haplotype sperm can inactivate sperm without it,” said Bernhard Herrmann, author of the Max Planck Institute for Molecular Genetics in Berlin.

“The trick is that the t-haplotype” poisons “all sperm, but at the same time produces an antidote, which acts only in t-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 genetic variants that are distributed to all sperm and distort the regulation signals, so that, by itself, to 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 are evenly divided between them – are able to produce another factor that counteracts this signal disturbance, allowing them to swim straight.

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

However, when 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 the progressive movement.

In fact, the researchers said, 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 chromosomes 17, have high levels of RAC1 and are almost unable to move.

On the other hand, sperm from mice that do not have the t-haplotype at all also lose their ability to swim properly when given the RAC1 inhibitor – indicating that low levels of RAC1 are also detrimental to fertility. male.

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

“Both reduced or excessive RAC1 activity interferes with efficient forward movement,” she added.

The aberrant RAC1 activity could, the team speculated, also explain some forms of male fertility in humans – which means that the results could pave the way for new forms of fertility treatment.

“Our data show that sperm cells are ruthless competitors,” said Professor Herrmann, adding that the t-haplotype also provides a demonstration of how some genes use “dirty tricks” to pass on.

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

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