Dr Johanna Höög
AcademiaNet member Johanna Höög and her team have identified a completely new nanostructure inside sperm tails, thanks to the use of cryo-electron tomography. The method, which won its creators a Nobel Prize in 2017, produces 3D images of cellular structures. “Since the cells are deep-frozen without the addition of chemicals which can obscure the smallest cell structures, even individual proteins inside the cell can be observed” Dr Höög explains, “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.”
A highly effective tail is needed for a sperm to be able to swim so that it can reach and fertilise the egg cell. The tail is a complex machine that consists of around a thousand different types of proteins. The most important of these are called tubulins, which form long tubes, called microtubules. These are found inside the sperm tail. Motor proteins – molecules that convey movement – are attached to these tubes. By being fixed to one microtubule and “walking on” the adjacent microtubule, the motor proteins enable the sperm to swim.
“It’s actually quite incredible that it can work,” Dr Höög adds. “The movement of thousands of motor proteins has to be coordinated in the minutest of detail in order for the sperm to be able to swim.”
What the spiral is doing there, what it consists of and whether it is important in order for sperms to move are questions that the research team will now focus on answering. “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,” says Davide Zabeo, the lead PhD student behind the discovery.
(© Carina Eliasson / University of Gothenburg / AcademiaNet)