More than three hundred years ago, Antonie van Leeuwenhoek used one of the earliest microscopes and observed human sperm as having a “tail, which, when swimming, lashes with a snakelike movement, like eels in water.” Up until now, it is believed that human sperm have been postulated to swim forward by merely moving their flagellum symmetrically from side-to-side.
Now, scientists from the Bristol and Mexico have made a breakthrough in fertility science by shattering the universally accepted view of how sperm ‘swim.’
Using state-of-the-art 3-D microscopy and mathematics, scientists developed the reconstruction of the true movement of the sperm tail in 3-D.
They used a high-speed camera to record over 55,000 frames within a second and a microscope stage with a piezoelectric device to move the sample up and down at an incredibly high rate, they were able to scan the sperm swimming freely in 3-D.
Their study reveals that sperm tail is, in fact, wonky and only wiggles on one side. Meanwhile, sperm’s one-sided stroke would have it swimming in circles; sperm have found a clever way to adapt and swim forwards.
Dr. Hermes Gadelha from the University of Bristol said, “Human sperm figured out if they roll as they swim, much like playful otters corkscrewing through water, their one-sided stoke would average itself out, and they would swim forwards.”
“The sperms’ rapid and highly synchronized spinning causes an illusion when seen from above with 2-D microscopes—the tail appears to have a symmetric side-to-side movement, “like eels in the water,” as described by Leeuwenhoek in the 17th century.”
“However, our discovery shows sperm has developed a swimming technique to compensate for their lop-sidedness and, in doing so, have ingeniously solved a mathematical puzzle at a microscopic scale: by creating symmetry out of asymmetry.”
“The otter-like spinning of human sperm is however complex: the sperm head spins at the same time that the sperm tail rotates around the swimming direction. This is known in physics as precession, much like when the orbits of Earth and Mars precess around the sun.”
This discovery, with its novel use of 3-D microscope technology combined with mathematics, may provide fresh hope for unlocking the secrets of human reproduction.
Dr. Alberto Darszon from the Universidad Nacional Autonoma de Mexico said, “This discovery will revolutionize our understanding of sperm motility and its impact on natural fertilization. So little is known about the complex environment inside the female reproductive tract and how sperm swimming impinges on fertilization. These new tools open our eyes to the amazing capabilities sperm have.”
- Human sperm uses asymmetric and anisotropic flagellar controls to regulate swimming symmetry and cell steering” Science Advances (2020). DOI: 10.1126/sciadv.aba5168