Sperm cells are known to prefer cooler temperatures. 



For quite some time, a puzzling question for scientists has been: how do temperature-sensitive swimmers actually operate effectively within the warmer environment of the female reproductive system?



Scientists at Washington University School of Medicine have uncovered a fascinating answer. 



The warmer temperatures of the female reproductive tract act as a switch for sperm. 



This temperature increase triggers a signal that makes the sperm change their swimming style from a gentle glide to the vigorous thrashing and twisting required to break through to the egg.



Activation of sperm surface protein



Research on mice revealed that a particular protein, found in all mammals called CatSper, causes sperm to become hyperactive. This hyperactivation is crucial for fertilization.



It happens when the temperature around them reaches that of the female reproductive tract. 



“That hyperactive state in sperm is key for successful fertilization, and no one knew exactly how temperature triggers it. Our work has identified a temperature-controlled switch in sperm that triggers these increased movements precisely when they are needed during fertilization,” said Polina Lishko, a BJC Investigator and professor of cell biology and physiology at WashU Medicine.



This sperm surface protein regulates the flow of particles that fuel the powerful movements of the sperm’s tail. 



For a long time, scientists believed CatSper was activated by the pH levels in the female reproductive tract and, in primates, by the hormone progesterone.



However, this theory was incomplete because most mammalian sperm don’t respond to progesterone, suggesting another trigger for CatSper. 



The team suspected temperature as another crucial factor.









Better male contraceptive



The research revealed that as the temperature surrounding the sperm reaches that of the female reproductive tract, around 38 degrees Celsius or 100.4 degrees Fahrenheit, it triggers CatSper to open.



The team used micron-scaled tools to study individual sperm cells. This led to the observation of clear electrical signals, which indicated CatSper’s activation in sperm cells when the temperature rose above this threshold.



The temperature increase acts like an “on” switch, signaling the sperm to power up for fertilization.



Once CatSper is activated, sperm change their swimming style from a gentle, navigational movement to the vigorous, thrashing motions required to penetrate the egg.



The team says this new understanding creates promising new avenues for both male birth control and treating infertility. 



Since CatSper is found only in sperm, targeting it could lead to contraception methods that don’t interfere with other bodily processes.



As per the press release, previous attempts to create sperm-blocking contraceptives haven’t worked well. 



However, this new understanding of temperature’s role in activating CatSper could lead to more effective strategies for male contraception.



“Instead of creating inhibitors, it might be possible to activate CatSper with temperature thus, prematurely switching on this channel to drain the sperm of energy, so that by the time the sperm cell is ready to do its job and enter the egg cell, it is powerless,” the researcher noted.



The findings were published in the journal Nature Communications. 

Sperm cells use heat as a switch to power up for egg penetration, finds study