It’s the same as swimming with one side of the body-but at the same time, it is very “witty” spinning around in the direction of swimming.

This offsets the asymmetry caused by the one-way swing, making it rotate forward like a wine corkscrew.

The sperm precesses strongly (frontal view of the head). The red track behind is the projection of a fixed point on the tail. |Polymaths Lab

From the reconstructed three-dimensional image, it can be seen that as the sperm rotates forward, its head is also rotating rhythmically (Although the analysis shows that there is no direct correlation between the rotation of the head and the rotation of the tail), the overall movement is very powerful and coordinated.

It’s almost like screwing a screw into wood. No wonder it can advance in such a high-viscosity environment.

PS: You should know that in the mucus of the female reproductive tract, the Reynolds coefficient of sperm swimming is as low as 0.0001, while the Reynolds coefficient of a child swimming in water is about 10,000. The Reynolds coefficient is used to reflect the relationship between inertial force and viscous force. The smaller the value, the greater the viscous resistance. 0.0001≈It’s difficult.

observe sperm swimming in all directions

Previously, people used 2D microscopes to observe sperm, creating the illusion of symmetrical tail wobble. This time, relying on advanced 3D microscope technology, we finally got a completely different image.

The microscope uses an ultra-high-speed camera that can record more than 55,000 frames per second. It also has a stage that can quickly move the sample up and down, allowing experimenters to shoot free-swimming sperm from different angles. The photos are processed digitally and finally turned into three-dimensional images.

Sperm swimming observed in a 3D microscope. |Polymaths Lab

The sperm of the test is placed in a physiological solution of lower viscosity artificially prepared, with a very high degree of freedom, and can be clearly observed from all directions. Through advanced mathematical analysis technology, more subtle details are displayed.

In fact, it was observed that this spiral progression is also asymmetric.

From different sides, you can see the projections of different poses, some of which originate from the unilateral wobble tail (like the distorted letter C), there is Represents the transmission of the rotation in the entire tail (like the letter S). This is very different from a well-proportioned wine opener, or spring. (Because the mathematics and mechanical analysis involved are more complicated, it is not shown here. For details, please read the original text)

Sperm swimming reconstructed by 3D microscope. |Polymaths Lab

Before, people were confused because sperms swim very fast. In experiments or medical observations, their tails are often fixed on a glass slide, so that the rotation of the head and tail is restricted, and sperm cannot be inferred. Scroll.

The two-dimensional motion is averaged over time, and it will show static symmetry. This symmetry is also used as an important indicator for judging sperm motility and has a significant relationship with fertility. No wonder people have been confused by it for more than 300 years.

More things you don’t know

This subversive discovery, let us see the difficulty of sperm swimming. And this is only part of the sperm “career”. In addition to the high resistance to swimming, it has to withstand many tests from the egg.

Some new studies have revealed the “dramatic” encounter of sperm and egg (or no encounter), which is amazing after reading.

For example, the egg is “eagle-eyed and sharp” and it will automatically exclude defective sperm even if it swims fast.

A 2017 study found that when healthy female mice are paired with male mice carrying oncogenic mutations, only 27% of the offspring carry the oncogene, which is much lower than the carrying rate of random sperm binding 75 %. This shows that the egg will actively choose sperm, running fast is not necessarily useful, and defects are still rejected. This was later called the “mysterious female choice” by scholars.

The egg will actively select sperm. |Public domain

Even if there is no defect, the egg will have its own unique preferences, which will make it difficult for the sperm to be “satisfied”.

2020A June study showed that human eggs use chemical signals to attract sperm from specific men. By observing the number of sperm accumulated in the follicular fluid sample, the researchers found that the female follicular fluid has its own preference for selection, it has a stimulating effect on the sperm of their choice, and can make the sperm swimming route straighter; Can use “delay magic” to reduce its movement speed.

What is puzzling is that this preference is tied to a specific person. In some infertile couples, the wife’s follicular fluid just “looks down on” the husband’s sperm, but is better at attracting the sperm of other men.

And in order to be favored by the egg, sperm is also working very hard. In addition to swimming hard, they also take the initiative to correct their mistakes.

In a study in January 2020, scientists found that during sperm maturation, they repair DNA damage through a biological mechanism called “transcription scanning” to reduce accumulation during proliferation and differentiation Genetic error. Under this mechanism, the coding error rate of activated genes is 15-20% less than that of inactivated genes. This adds a great guarantee to human genetic stability.

As for how the sperm meets the egg and grows into a new life, I believe there will be more new research in the future. The story of sperm and eggs is far from over.

At present, although we have observed the three-dimensional information of sperm swimming, we still lack understanding of the significance of this information in fertility; how to apply it to the diagnosis and treatment of reproductive problems needs further research.

New technical methods are constantly showing us new details. The mystery of life will one day be revealed, and a series of problems we are currently facing, including reproductive problems, will also be solved.


Reference material:

[1] Human sperm uses asymmetric andanisotropic flagellar controls to regulate swimming symmetry and cell steering[J]. Science Advances, 2020, 6(31): eaba5168.

https://advances.sciencemag.org/content/6/31/eaba5168

[2] Chemical signals from eggsfacilitate cryptic female choice in humans. https://royalsocietypublishing.org/doi/10.1098/rspb.2020.0805

[3] Bo Xia et al., (2020),WidespreadTranscriptional Scanning inthe Testis Modulates Gene Evolution Rates,Cell,DOI:https://doi.org/10.1016/j .cell.2019.12.015.

This article is from WeChat official account:Ten-point science (ID: Science_10) author: high Pei Wen, Chen naive