Reproduction: Some sperm cells POISON each other in the race to be first at the egg

A study has revealed the winner of the race to fertilize an egg.

Experts from Germany have found in studies of mice that sperm carrying a genetic factor, ‘t-haplotype’, can move faster towards their target.

Meanwhile, their competition without this group of genes is less effective at advancing, and they are likely to twist aimlessly in circles.

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

In white blood cells and cancer cells, RAC1 is known to play a role in directing its host cells at 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 for future treatments.

“Sperm with the t-haplotype succeeds in eliminating sperm without it,” said author Bernhard Herrmann, director 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 that only works in t-sperm and protects it.”

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

The team explained that the t-haplotype contains certain gene variants that are spread to all the sperm and distort the regulatory signals, which on its own would prevent the so-called ‘progressive’ moment.

Half of the sperm – those that also end up with the t-haplotype if the animal’s chromosomes are evenly distributed – can produce another factor that counteracts this signal disturbance so that they can swim straight.

In their study, the researchers first looked at sperm from the mice that had the t-haplotype on only one of their two ‘chromosomes 17’, and found that some cells (with the t-haplotype) could swim straight. , while the others do not.

However, in treating all the sperm with a substance that inhibits RAC1, the team noted that the cells without the t-haplotype again have the ability to swim correctly.

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

The researchers said that any abnormal level of RAC1 activity is bad for sperm. Mice with two copies of the t-haplotype, for example, with one on each of their chromosomes 17, have a high level of RAC1 and are almost unable to move.

On the other hand, sperm from mice that do not have the t-haplotype at all lose their ability to swim properly when they get the RAC1 inhibitor, suggesting that low RAC1 levels are also bad for male fertility.

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

“Both reduced or excessive RAC1 activity impedes effective forward movement,” she added.

The deviant RAC1 activity, according to the team, can also be explained for some forms of male fertility in humans, which means that the findings could pave the way for new forms of fertility treatment.

“Our data highlights the fact that sperm cells are relentless competitors,” Professor Herrmann said, adding that the t-haplotype also provides a demonstration of how some genes use ‘dirty tricks’ to be transmitted.

“Genetic differences can give individual sperm an advantage in the race for life and thus promote the transmission of specific gene variants to the next generation.”

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