Sperm corkscrew towards eggs ‘like playful otters’

Fertility treatment may be improved after study finds cells rotate as they wriggle through fluids inside body

IT WAS long held to be true that sperm used their tails to propel themselves forwards in a snakelike movement, much like eels in water.

However, a pioneering 3D study has revealed that they rotate in a similar way to a spinning top or corkscrew as they wriggle through semen and vaginal fluids.

This unique action enables sperm to move towards an egg with maximum efficiency and its discovery could lead to better fertility treatment.

Previous notions of how sperm reached the egg were the result of an optical illusion created by 2D microscopes and originate in the discoveries of Antonie van Leeuwenhoek, a lensmaker, in 1678.

The Dutch scientist, regarded as the “father of microbiology”, was the first person to observe sperm cells under a microscope.

But his theories have now been upended by researchers from the University of Bristol and the National Autonomous University of Mexico, who, using state-of-the-art microscopy, reconstructed the true movement of sperm in astonishing detail.

The team used a camera that records more than 55,000 frames a second, and a “piezoelectric” scanner that generates its own energy through touch, to move the sample of sperm up and down at a high speed, so that they could be watched swimming freely in 3D. Dr Hermes Gadelha, the lead author, from the University of Bristol, said: “The sperm’s rapid and highly synchronised spinning causes an illusion when seen from above with 2D microscopes.

“The tail appears to have a side-toside symmetric movement, ‘like eels in water’, as described by Leeuwenhoek in the 17th century.

“However, our discovery shows sperm have developed a swimming technique to compensate for their lopsidedness, and in doing so have ingeniously solved a mathematical puzzle at a microscopic scale – by creating symmetry out of asymmetry.”

Dr Gadelha added: “Human sperm figured out if they roll as they swim, much like playful otters corkscrewing through water, their one-sided stroke would average itself out, and they would swim forwards. The otter-like spinning of human sperm is complex: the sperm head spins at the same time that the sperm tail rotates around the swimming direction.”

Better understanding of a sperm’s true movement, detailed in a study published in Science Advances, may provide fresh hope for couples struggling to conceive by helping clinicians pinpoint defective or weak specimens.

Dr Alberto Darszon, of the National Autonomous University of Mexico, said: “This discovery will revolutionise our understanding of sperm motility and its impact on natural fertilisation.

“So little is known about the intricate environment inside the female reproductive tract and how sperm’s swimming impinges on fertilisation.”