Tiny messengers on behalf of life: constant movements of the tail drive sperm forward in their search for the egg – it was previously assumed. But now 3D analyzes reveal that their locomotion is characterized by asymmetry. Accordingly, the scourge does not move evenly, but with a list. This is compensated in a sophisticated way by the rotational movement of the sperm, so that a straight forward movement is possible. These new insights into sperm cell swimming technique could help better understand male fertility disorders, the researchers say.
Scurrying tiny things in his sights: around three hundred years ago, the Dutch naturalist Antoni van Leeuwenhoek first discovered sperm with one of the first microscopes and described how they move through a flapping tail. He assumed that the movement of the scourge was steady and worked like a meandering eel in water. To this day it was considered clear that the sperm cells swim forwards by moving their flagellum evenly back and forth. This was transferred to three-dimensional representations of movement: It was assumed that the flagellum performs a spiral movement due to the symmetrical drive. This also seemed to explain the observed head rotation of the sperm during locomotion.
A new look at the bustling tiny creatures
However, as the researchers working with Hermes Gadelha from the University of Bristol report, the previous models of the mode of locomotion of the sperm are still mainly based on two-dimensional observations. The scientists have therefore now targeted the tiny creatures using the most modern 3D microscopy methods: They combined a high-speed camera that can take over 55,000 images per second with a device that moves the sample up and down at a very high speed emotional. This enabled them to scan the movement behavior of freely swimming sperm in three dimensions in detail.
As the researchers report, the studies revealed that the sperm tail does not strike symmetrically at all, but crooked. This creates an asymmetrically wandering wave movement, the scientists discovered. This should actually result in the sperm swimming in circles. But this effect is offset by the rolling movement of the sperm, the researchers explain. So the list is constantly twisting and there is ultimately a steady forward movement. “Our discovery shows that sperm cells use their swimming technique to transform asymmetry into symmetry,” says Gadelha.
With corkscrew movements forward
The movement of the sperm can be compared to that of playful otters who swim through the water with a corkscrew movement, says the scientist: They drill their way through the liquid. “The otter-like rotation of the sperm is complex, however: the sperm head rotates at the same time as the sperm tail rotates around the swimming direction. This is called precession in physics, ”says Gadelha.
The traditional assumption that the sperm tail would move smoothly was ultimately based on an optical illusion, say the scientists. “If you look at them from above with 2D microscopes, the tail appears to have a symmetrical side-to-side movement, like an eel in water,” says Gadelha. “But this is an illusion that is caused by the fast and highly synchronized rotation of the sperm”. Co-author Gabriel Corkidi of the National Autonomous University of Mexico in Cuernavaca said: “That was a big surprise, and we believe that our state-of-the-art 3D microscope can reveal many more hidden secrets of nature. And one day this technology could also be available for clinical centers, ”said the scientist.
Potential for fertility medicine
With more than half of infertility due to male factors, understanding the human sperm tail is fundamental to developing future diagnostic tools for identifying unhealthy sperm, the scientists say. So far, however, computer-aided semen analysis systems in clinics still use 2D views. As with Leeuwenhoek’s first observations, this creates the illusion of symmetry, the researchers emphasize.
“Our discovery could revolutionize our understanding of sperm motility and its effects on natural fertilization. So little is known about the intricate environment within the female reproductive tract and how sperm swimming affects fertilization. The new tools could now open our eyes to the amazing abilities that sperm possess, ”concludes co-author Alberto Darszon of the National Autonomous University of Mexico.
Source: University of Bristol, Article: Science Advances, doi: 10.1126 / sciadv.aba5168
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