Domestic researchers have captured the phenomenon of mouse sperm moving with a hook-like head that punctures the uterine wall.
Professor Park Jeong-hoon of the Ulsan National Institute of Science and Technology (UNIST) and his team analyzed the process of sperm movement in the reproductive organs of mice through joint research with Professor Kim Jae-ik's team at UNIST and researcher Ryu Heung-jin from Kyoto University, noting this on the 16th. The research results were published in the international journal eLife on Nov. 22.
So far, the hypothesis of sperm cooperation, which suggests that mouse sperm with hook-shaped heads connect like a train to increase their speed toward the egg, was prominent. This research was conducted to directly verify the hypothesis regarding the hook function of rodent sperm within living tissues.
The researchers mated genetically modified male mice, whose sperm heads emitted green fluorescence and parts of their tails emitted red fluorescence, with female mice, and then extracted the reproductive organs to observe sperm function. As a result, they verified the phenomenon of sperm moving rapidly by puncturing the uterus and oviduct walls with the hooks on their heads. This observation supports another hypothesis called the sperm and female reproductive organ interaction theory. The researchers believe that as sperm puncture the inner wall of the female reproductive organ with the hooks on their heads, they increase their straightness and can resist strong fluid flow.
Additionally, this study observed for the first time the phenomena where the heads of sperm align in one direction or where the tails of sperm synchronize like synchronized swimmers and move together. The researchers analyzed that due to the anchoring effect of the sperm hooks, the heads of the sperm are arranged in one direction while moving or can even perform synchronized swimming. They also proposed a new hypothesis that the hook on the mouse sperm head could be an evolutionary result of such behavior.
The researchers stated, "The sperm cooperation hypothesis has only been observed in a two-dimensional culture dish due to limitations in observational technology," adding, "In this experiment, we found a small cluster moving in a train-like formation while observing and analyzing the internal reproductive organs, but their speed was not faster compared to individual sperm." They emphasized that additional research is needed to secure statistically significant data to completely overturn the sperm cooperation hypothesis and noted that acquiring technology to quantitatively measure the speed and characteristics of sperm movement through the obtained videos is expected to help in developing sophisticated oviduct mimicry chips and infertility research.
Reference material
eLife (2024), DOI: https://doi.org/10.7554/eLife.96582.4