Some sperm literally poison their competition in the race to fertilize an egg

Some sperm literally poison their competition in the race to fertilize an egg

The race for life, in which millions of sperm swim swiftly towards the ovum, is neither fair nor noble: rather in a ruthless race in which there are even manipulative sperm that are careful to poison their competition .

In what points out a new study published in PLOS Genetics by researchers at the Max Planck Institute for Molecular Genetics (MPIMG) in Berlin.

In the research they studied mouse sperm cells under the microscope to better understand the effects of a particular DNA sequence known as the t-haplotype. The team knew from previous research that sperm carrying this sequence tend to swim straighter (rather than in circles) and faster on average than competing sperm without it.

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The t haplotype is a series of linked genes that occupy chromosome 17 in domestic mice around the world. (Unlike humans, who have 23 pairs of chromosomes, mice only have 20). What happens is that sperm with the t haplotype manage to disable sperm without it.

Specifically, the t haplotype ‘poisons’ all sperm during the early stages of sperm production, injecting each cell with certain genes that inhibit its ability to regulate movement. It is not until a later stage, when each cell divides in half, that the ‘antidote’ comes into play. After dividing, half of the sperm inherit the t-haplotype genes on chromosome 17 .

For the lucky sperm, the t-haplotype provides new genetic variants that reverse the inhibitory effects of the ‘venom’ that all cells consumed during the previous phase of development. As explained by study co-author Bernhard Herrmann , Director of the MPIMG:

The trick is that the t-haplotype ‘poisons’ all the sperm, but at the same time it produces an antidote, which acts only on the t-sperm (those with the t-haplotype) and protects them. The result is a kind of marathon in which all participants are given poisoned drinking water, but only some of the runners have access to the antidote.

In their study, the researchers saw that many sperm without the antidote literally swam in circles to death, while their t-haplotype competitors swam straight ahead.