Researchers have developed a
mathematical formula based on the rhythmic movement of a sperm's head and tail,
which significantly reduces the complexities of understanding and predicting
how sperm make the difficult journey towards fertilizing an egg.
Researchers
at the Universities of York, Birmingham, Oxford and Kyoto University, Japan,
found that the sperm's tail creates a characteristic rhythm that pushes the
sperm forward, but also pulls the head backwards and sideways in a coordinated
fashion.
Successful
fertility relies on how a sperm moves through fluid, but capturing details of
this movement is a complicated issue.
The
team aim to use these new findings to understand how larger groups of sperm
behave and interact, a task that would be impossible using modern observational
techniques. The work could provide new insights into treating male infertility.
Dr
Hermes Gadêlha, from the University of York's Department of Mathematics, said:
"In order to observe, at the microscale, how a sperm achieves forward
propulsion through fluid, sophisticated microscopic high precision techniques
are currently employed.
"Measurements
of the beat of the sperm's tail are fed into a computer model, which then helps
to understand the fluid flow patterns that result from this movement.
"Numerical
simulations are used to identify the flow around the sperm, but as the
structures of the fluid are so complex, the data is particularly challenging to
understand and use. Around 55 million spermatozoa are found in a given sample,
so it is understandably very difficult to model how they move simultaneously.
"We
wanted to create a mathematical formula that would simplify how we address this
problem and make it easier to predict how large numbers of sperm swim. This
would help us understand why some sperm succeed and others fail."
By
analysing the head and tail movements of the sperm, researchers have now shown
that the sperm moves the fluid in a coordinated rhythmic way, which can be
captured to form a relatively simple mathematical formula. This means complex
and expensive computer simulations are no longer needed to understand how the
fluid moves as the sperm swim.
The
research demonstrated that the sperm has to make multiple contradictory
movements, such as moving backwards, in order to propel it forward towards the
egg.
The
whip-like tail of the sperm has a particular rhythm that pulls the head
backwards and sideways to create a jerky fluid flow, countering some of the
intense friction that is created due to their diminutive sizes.
Dr
Gadêlha said: "It is true when scientists say how miraculous it is that a
sperm ever reaches an egg, but the human body has a very sophisticated system
of making sure the right cells come together.
"You
would assume that the jerky movements of the sperm would have a very random
impact on the fluid flow around it, making it even more difficult for competing
sperm cells to navigate through it, but in fact you see well defined patterns
forming in the fluid around the sperm.
"This
suggests that to achieve sperm stirs the fluid around in a very coordinated way
locomotion, not too dissimilar to the way in which magnetic fields are formed
around magnets. So although the fluid drag makes it very difficult for the
sperm to make forward motion, it does coordinate with its rhythmic movements to
ensure that only a few selected ones achieve forward propulsion."
Now
that the team has a mathematical formula that can predict the fluid movement of
one sperm, the next step is to use the model for predictions on larger numbers
of cells. They also believe that it will have implications for new innovations
in infertility treatment.
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