How human sperm really swim: New research challenges centuries-old
assumption

Date:
July 31, 2020
Source:
University of Bristol
Summary:
A breakthrough in fertility science has shattered the universally
accepted view of how sperm 'swim'.



FULL STORY ==========================================================================
A breakthrough in fertility science by researchers from Bristol and
Mexico has shattered the universally accepted view of how sperm 'swim'.


==========================================================================
More than three hundred years after Antonie van Leeuwenhoek used one
of the earliest microscopes to describe human sperm as having a "tail,
which, when swimming, lashes with a snakelike movement, like eels in
water," scientists have revealed this is an optical illusion.

Using state-of-the-art 3D microscopy and mathematics, Dr Hermes Gadelha
from the University of Bristol, Dr Gabriel Corkidi and Dr Alberto Darszon
from the Universidad Nacional Autonoma de Mexico, have pioneered the reconstruction of the true movement of the sperm tail in 3D.

Using a high-speed camera capable of recording over 55,000 frames in one 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 3D.

The ground-breaking study, published in the journal Science Advances,
reveals the sperm tail is in fact wonky and only wiggles on one
side. While this should mean the sperm's one-sided stroke would have
it swimming in circles, sperm have found a clever way to adapt and
swim forwards.

"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," said Dr Gadelha, head of the Polymaths Laboratory at Bristol's Department of Engineering Mathematics
and an expert in the mathematics of fertility.



==========================================================================
"The sperms' rapid and highly synchronised spinning causes an illusion
when seen from above with 2D microscopes -- the tail appears to have a side-to-side symmetric movement, "like eels in water," as described by Leeuwenhoek in the 17th century.

"However, our discovery shows sperm have 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," said Dr Gadelha.

"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." Computer-assisted semen analysis systems in use today, both in clinics and for research, still
use 2D views to look at sperm movement. Therefore, like Leeuwenhoek's
first microscope, they are still prone to this illusion of symmetry
while assessing semen quality. This discovery, with its novel use of 3D microscope technology combined with mathematics, may provide fresh hope
for unlocking the secrets of human reproduction.

"With over half of infertility caused by male factors, understanding the
human sperm tail is fundamental to developing future diagnostic tools to identify unhealthy sperm," adds Dr Gadelha, whose work has previously
revealed the biomechanics of sperm bendiness and the precise rhythmic tendencies that characterise how a sperm moves forward.

Dr Corkidi and Dr Darszon pioneered the 3D microscopy for sperm swimming.

"This was an incredible surprise, and we believe our state-of the-art 3D microscope will unveil many more hidden secrets in nature. One day this technology will become available to clinical centres," said Dr Corkidi.

"This discovery will revolutionize our understanding of sperm motility
and its impact on natural fertilization. So little is known about the
intricate environment inside the female reproductive tract and how sperm swimming impinge on fertilization. These new tools open our eyes to the
amazing capabilities sperm have," said Dr Darszon.


========================================================================== Story Source: Materials provided by University_of_Bristol. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Hermes Adelha et al. Human sperm uses asymmetric and anisotropic
flagellar controls to regulate swimming symmetry and cell steering.

Science Advances, 2020 DOI: 10.1126/sciadv.aba5168 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200731145140.htm

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