You may have thought you had seen it all when your high school health teacher projected phallic-looking sperm on the big screen, but scientists have uncovered something unexpected – a whole new structure on the wiggly guy's tip.
Researchers at the University of Gothenburg in Sweden and the University of Colorado found a teensy-weensy structure at the very end of the sperm’s tail that previously went unnoticed. It’s not clear exactly what it does, but the team think it could help us understand why some little swimmers are stronger than others.
What is clear is the imaging used to find the helix. It all started because researchers wanted to know what human sperm looks like in 3D to get a better idea of how sperm cells work.
Ask and you shall receive.
Using the Nobel prize-winning cryo-electron tomography method, they were able to produce 3D images of the extremely small cellular structures.
“When we looked at the first 3D images of the very end section of a sperm tail, we spotted something we had never seen before inside the microtubules: spiral that stretched in from the tip of the sperm and was about a tenth of the length of the tail.”
One little sperm tail has around a thousand types of building blocks that build up three sections: the mid-piece, the “propeller”, and a small terminus at the tip.
In the propeller are proteins called tubulins that form long tubes (microtubules) to make up more complex structures. Interactions in these proteins create the movement that sperm needs to “swim” through its environment.
Inside these microtubules is where researchers spotted a cellular structure wound into a left-handed helix. And because scientists think they’re funny, they dubbed it the “Tail Axoneme Intra-Lumenal Spiral”. Yeah, TAILS.
It turns out, a good TAIL is needed to help these little guys swim. The researchers published their findings in Scientific Reports.
“We believe that this spiral may act as a cork inside the microtubules, preventing them from growing and shrinking as they would normally do, and instead allowing the sperm’s energy to be fully focussed on swimming quickly towards the egg,” said Davide Zabeo, the lead author behind the discovery, in a statement.
As is often the case in science, the discovery brings about more questions than answers: what is it made of? What is it doing there? Does it really help some sperm swim stronger than others?
Is this why some sperm swim faster than others? We'll just have to wait and see.