A new study reveals how sperm change their swimming patterns to navigate to the egg, from a symmetrical movement that allows the sperm to move in a straight line to an asymmetrical movement that promotes more circular swimming
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This change in behavior is called "hyperactivity", and once the sperm is close to the egg, it will sweep across the area, increasing the chance that the sperm will find the area
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In an in vitro study, the researchers designed a microfluidic chip with micrometer-sized channels so that they can observe the sperm of cows with a microscope and a high-speed camera
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By revealing the mechanism, this research not only solves the mystery of how sperm navigate to the egg, but also has implications for human in vitro fertilization and cow reproduction, and provides new information for engineers to design miniature swimming robots
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"By understanding what determines the navigation mechanism, as well as the biophysical and biochemical cues for sperm to reach the egg, we can use these clues to treat infertile couples and choose the best strategy for in vitro fertilization
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" The senior of the paper Said Alireza Abbaspourrad, the author and assistant professor at the School of Agriculture and Life Sciences
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The research titled "Mammalian Sperm Hyperactivation Regulates Navigation Via Physical Boundaries and promotes Pseudo-Chemotaxis" was published in the online edition of the Proceedings of The National Academy of Sciences on October 29
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This paper illustrates how millions of sperm pass through the reproductive tract of female mammals, with only a few sperm reaching the fertilization point in the end
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The sperm clings to the side wall and swims in a straight line in a small amount of liquid flowing up and down the reproductive tract
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But once the sperm reaches the junction of the uterus, enters the fallopian tube and moves to the egg, calcium ions will flood into their flagella, causing hyperactivity and circulatory swimming
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More research is needed to understand exactly what triggers the calcium influx in the flagella
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Microfluidic chips enable researchers to control the environment
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The research team recorded the sperm swimming along the ventricular wall
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Then they tested compounds including caffeine, which can increase calcium ions in the cell cytoplasm
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They recorded the behavioral transition of sperm in the presence of calcium, from a symmetrical direct swimming to an over-activated circular swimming, which means that the sperm is no longer close to the cell wall
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Without this transformation, the sperm may fall into a dead end and get stuck
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"It turns out that this (swimming) state is necessary for fertilization," Abbaspourrad said
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He said that although these observations were made in an in vitro laboratory, it provides a sense of what might happen in the body
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Original title:
Mammalian Sperm Hyperactivation Regulates Navigation Via Physical Boundaries and promotes Pseudo-Chemotaxis
