Super resolution microscopy reveals a turn within cells

If you want to understand the underlying mechanisms of cell motility and division, then the centriole is the organelle of interest. Each cell has a pair of centrioles that help segregate chromosomes during cell division. These special organelles are multimolecular machines made up of hundreds of proteins and have a hidden code of post-translational modifications (PTMs) that contribute to their stiffness or flexibility, which in turn can help explain how centrioles work.

Based on previous studies that mainly use electron microscopy, the basic structure of the centrioles is known. But PTMs are invisible to the electron microscope, so what do they look like?

Thanks to the improved super resolution fluorescence microscope technology developed by EPFL biophysicists, we now have a detailed picture of these nanoscale structures, both isolated and in situ. As expected, centrioles are shaped like fluted bullets, that is, they are cylindrical with nine longitudinal ridges and their diameter tapers at one end. Given this high degree of organization, scientists were surprised to discover that a PTM actually revolves around these ridges. The results are published today in Nature’s Methods.

“The symmetries of multimolecular machines often explain how they can perform various functions. PTMs can form a special code that tells proteins where to dock, but it can also stabilize the centriole as forces move during division. We don’t know yet. why the twist is there, but it offers a clue to how centrioles work. Our study highlights that superresolution microscopy is an important partner for electron microscopy for structural biology, “says biophysicist Suliana Manley, who directs the Laboratory for Experimental Biophysics (LEB).

Improved super resolution imaging techniques

Centrioles are approximately 100 times smaller than a mammalian cell and a thousand times smaller than human hair. Therefore, observing them inside living cells required improving the super resolution microscope technology that uses light to probe samples, as the methods tend to be too slow for structural studies. Dora Mahecic, Ph.D. A student at LEB, she improved the lighting design to increase the size of the images that her microscope could capture by delivering light more evenly across the entire field of view.

The microscope, a super resolution fluorescence microscope, is not at all the typical light microscope that would be seen in an introductory biology class. It is actually a complex configuration of carefully aligned mirrors and lenses that shape and deliver laser light to the sample. Biophysicists combined this setup with an advanced sample preparation that uses physical magnification of the sample and fluorophores to make proteins, the building blocks of life, re-emit light.

This new super resolution technology could be used to study many other structures within the cell, such as mitochondria, or to observe other multimolecular machines such as viruses.