Sperms don't use eel-like swimming strategy to reach egg, says study that might help diagnose infertility
'This discovery will revolutionize our understanding of sperm motility and its impact on natural fertilization'
Sperm's journey to the egg is a long and arduous one. You may have watched artistic visualizations of how these tiny cells swim like an eel to reach their destination. A new study has challenged that, suggesting that human sperms deploy a different swimming strategy. These findings, the researchers say, could help diagnose infertility.
About three centuries ago, a Dutch scientist, Antonie Philips van Leeuwenhoek, became the first person to observe sperms under a microscope. Describing it, he said, the sperm has a "tail, which, when swimming, lashes with a snakelike movement, like eels in the water". But observations from experts from the University of Bristol and Universidad Nacional Autonoma de Mexico have a different story to tell. Using a high-speed camera capable of recording over 55,000 frames in one second, these scientists reconstructed sperm's movements under a microscopic platform in 3D. They found that sperm spins, but only on one side. In other words, it swims in sidestroke, rolling in a circle to move forward. You can watch the video here.
Dr Hermes Gadelha, head of the Polymaths Laboratory at Bristol's Department of Engineering Mathematics, compares its movements with playful otters corkscrewing through the water. "The otter-like spinning of human sperm is however complex: the sperm head spins at the same time that the sperm tail rotates around the swimming direction. This is known in physics as precession, much like when the orbits of Earth and Mars precess around the sun," Dr Gadelha says.
And it does that at a fast and a highly synchronized pace, giving an illusion of wiggle. Under 2D microscopes, Gadelha explains, the tail symmetrically moves side-to-side, "like eels in the water", as described by Leeuwenhoek in the 17th century. "However, our discovery shows sperm has developed a swimming technique to compensate for their lop-sidedness, and in doing so, have ingeniously solved a mathematical puzzle at a microscopic scale: by creating symmetry out of asymmetry," he adds.
How does it change our understanding of infertility?
Doctors look at sperms' movements to diagnose infertility. A person is likely to be fertile if at least 40% of their sperm is moving. Experts test motility by visualizing them in 2D, similar to Leeuwenhoek's first microscope. This, they say, might not bring out the accurate picture. "With over half of infertility caused by male factors, understanding the human sperm tail is fundamental to developing future diagnostic tools to identify unhealthy sperm," adds Dr Gadelha. The experts hope their 3D technique might unravel more secrets about human reproduction. In the future, Dr Gabriel Corkidi from Universidad Nacional Autonoma de Mexico believes their technology might find a place in clinics.
"This discovery will revolutionize our understanding of sperm motility and its impact on natural fertilization. So little is known about the intricate environment inside the female reproductive tract and how sperm swimming impinges on fertilization. These new tools open our eyes to the amazing capabilities sperm have," Dr Alberto Darszon from the Universidad Nacional Autonoma de Mexico, explains.
The study is published in Science Advances.