Reproduction: Some POISON sperm cells will mate in the race to be the first to the egg

To win the race to fertilize an egg, some sperm cells do not play fair, and in fact poison the face, a study has revealed.

German experts, in studies of mice, found that sperm that carry a genetic trait called the ‘haplotype’ are able to move more rapidly towards their target.

At the same time, their competition without this group of genes is less effective on progression, and they are more likely to wrap around aimlessly in circles.

The researchers linked the difference in motility (the ability to move) to a protein called RAC1, which transfers signals from the outside of 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 to others that suppress chemical signals.

With this, and the findings of the new study, it is possible that the protein has the same place in sperm cells, helping them find their way to their egg target.

The findings could even shed new light on the causes behind certain types of male infertility, increasing potential for future treatments.

‘Sperm with the haplotype regulates sperm excretion without it,’ said the paper’s author 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 works only in the sperm and protects them.’

‘Imagine a marathon, in which all participants get poisonous drinking water, but some runners take antidepressants.’

The team explained that there are some gene differences in the haplotype that are transmitted to the sperm and distort regulatory signals, thus preventing, by itself, the so-called ‘advanced’ moment. .

However, half of the sperm – the ones that also end up with the haplotype when the animal’s chromosomes are evenly spaced – are capable of producing another contradictory factor. distracting these signals, allowing them to swim directly.

In their study, the researchers first looked at sperm from those male mice that had the haplotype on just one of their two ’17 chromosomes’, and found that it was viable for some of the cells ( with the haplotype) swim directly, while the others did not.

By treating the entire sperm with a substance that inhibits RAC1, however, the team noted that the cells without the haplotype regained their ability to swim properly. .

This, they explained, confirms that the haplotype inhibits RAC1 activity, which in itself inhibits progressive movement.

In fact, the researchers said, any unstable level of RAC1 activity is bad for sperm. Mice with two copies of the haplotype, for example, have one on each of their 17 chromosomes, with high levels of RAC1 and almost immobility.

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

‘Individual sperm competitiveness appears to be dependent on the optimal level of active RAC1,’ said paper author and molecular geneticist Alexandra Amaral.

‘Either reduced or excessive RAC1 activity affects effective forward movement,’ she said.

Aberrant RAC1 activity, estimated by the team, could also describe some types of male fertility in humans – meaning the findings could pave the way for new types of treatment fertility.

‘Our data make it clear that sperm cells are ruthless competitors,’ said Dr Herrmann, adding that the haplotype also provides a demonstration of how some genes ‘use’ dirty tricks’ to get on.

‘Genetic differences can benefit individual sperm in the race for life, thus promoting the transmission of specific gene changes to the next generation.’

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