In models of the female reproductive tract, bull sperm clump together in groups of 2 to 4, which seems to help them swim upstream
September 22, 2022
Swimming together in groups may help sperm propel upstream through thick vagina and uterus mucus That would wash away those who were swimming alone.
Sperm are often represented as individuals competing with each other to fertilize the eggs, But these descriptions are based on plan views of microscope slides and other laboratory environments and do not reflect their natural environment, says Chi Kanto at North Carolina A&S State University.
When placed in a three-dimensional model of the female reproductive tract, bull sperm, similar to human sperm, appeared to have groups of two to four cells.
When Tung and his team first noticed such clusters in their lab, they didn’t understand why it happened. “In biology, when [cells and structures] Do something, and they should probably get something out of it,” Dong said. “So it became the question we asked ourselves: What do these sperm get out of it? “
To solve the mystery, the researchers injected 100 million fresh bull sperm into a silicone tube that contained a fluid similar to cow cervical and uterine mucus — the consistency of melted cheese, Tung said. They then used a syringe pump to generate two flow rates.
When there is no flow, aggregated sperm swim straighter than single sperm. In an intermediate stream, clusters can go upstream, while individual sperm cannot. When the current is strong, clumps of sperm are much better at navigating through the oncoming current, whereas individual sperm are usually washed away by the thick water.
In all of these cases, Tung said, there was never a single “leader” sperm in the cluster that was supported by the others. Instead, these groups are very active, with individual sperm regularly joining and leaving their clusters and changing positions within them.Arrangements similar to Cyclists ride together in peloton Therefore they encounter less air resistance.
“It could be the mechanism that allows at least some of them to end up in the fallopian tubes,” Tung said. “Because without this, maybe none of them actually do, because the fluid in the uterus is so fluid.”
The clusters likely play an important role in the thick mucus that flows out of the vagina and cervix, as well as in the uterus, where contractions push fluid in multiple directions, he said. Beyond this point, by the time sperm reach the fallopian tube, where the fluid is thin and less mobile, they may begin to swim more independently.
These findings open up new avenues to aid in diagnosis Unexplained infertility, Dong said. Future analyses could include testing the extent of sperm aggregation or measuring the quality of a woman’s reproductive fluid.
Journal references: Frontiers in Cell and Developmental Biology , DOI: 10.3389/fcell.2022.961623
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