‘Road network’ in nerve cell endings visualised in superresolution
20 nanometers, but still a big step forwards
For the first time, scientists have successfully managed to differentiate the ‘roads’ inside the thin endings of nerve cells using superresolution light microscopy. An international team of researchers under the leadership of cell biologists in Utrecht reported on their findings in a publication in the 11 August edition of Nature Communications. These ‘roads’, or microtubules, are responsible for the transport within the cell and are crucial for the proper functioning of the nervous system. Being able to differentiate these microtubules is therefore very important for research into the function of a nerve cell.
“Using our method, we were able to visualise microtubules using licht microscopy, with a resolution approaching that of electron microscopy”, explains Utrecht ľϸӰ cell biologist Dr. Lukas Kapitein. He led the study together with Dr. Helge Ewers from the Free ľϸӰ of Berlin. The main benefit to light microscopy is that it is easy to use fluorescent pigments to selectively differentiate various parts of the cell. This is much more complicated using electron microscopy.
Microtubules
In contrast to other cells, nerve cells have to last for the entire life of the organism. That means that their ability to grow and repair themselves is essential. Microtubules responsible for the transport of raw materials for growth and repair to the correct position within the cell. They are tube-shaped protein structures with a diameter of approximately 25 nanometres which form a living network: they grow and shrink constantly depending on where they are transporting something inside the cell. Little is known about how they organise themselves and their network.
Problem
For that reason, scientists around the world are searching for techniques that can be used to study microtubules and their organisation. This breakthrough, for example, is the result of work by the three research teams that were initially searching separately for a way to differentiate the microtubules in the ends of nerve cells using light microscopy. All three teams eventually realised that the problem lay with the antibodies that coupled the fluorescent pigments to the microtubules. These are so large in relation to the microtubules that they appeared so close together in thin ends of the cell that they were difficult to differentiate using a light microscope.
Breakthrough
The breakthrough in resolution came thanks to the cooperation with Utrecht ľϸӰ’s Dr. Paul van Bergen en Henegouwen, who is specialised in working with nanobodies. A nanobody is a binding element in certain antibodies that are common in llamas, camels and dromedaries. These nanobodies are unique in that they consist of only a single chain. The binding element in all other antibodies consist of two chains, and are therefore difficult to make smaller. A nanobody is only 4 nanometres long, or 2.5 times smaller than the antibodies that had been used until now.
Giant step forward
Thanks to the discovery of a suitable nanobody, researchers can now differentiate the microtubules in the ends of nerve cells. “I am extremely happy that we managed to do it”, says Kapitein. “It is only an improvement in resolution of 20 nanometres, but it is a giant step forwards for nerve cell research.”
