Dr. Philippe Bastin
Trypanosome Cell Biology Unit, Pasteur Institute, Paris, France

In search of mechanisms driving evolution of cilia and flagella

Cilia and flagella are landmark organelles of eukaryotic organisms and are remarkably well conserved across evolution. Nevertheless, they exhibit a diversity of structural variations around a common theme, which are related to diverging functions in motility, sensing or morphogenesis. This is encountered between species (for example between protists) but also between different cell types within the same organism (for example in animals).

To decipher the mechanisms driving evolution of cilia and flagella, we are investigating intraflagellar transport (IFT), the machinery responsible for their construction. IFT trains are protein complexes driven by molecular motors shuttling on microtubule tracks between the tip and the base of the flagellum. They transport flagellar components for incorporation at the distal end but also various signalling molecules.

While studying IFT in the protist Trypanosoma brucei, we discovered that trains were not using the 9 doublet microtubules for trafficking but were restricted to a few of them. We proposed that this restriction would facilitate addition of supplementary structures or the circulation of other motors, hence favouring flagella evolution. In this presentation, we will discuss the candidate mechanisms responsible for IFT restriction and the possible role of tubulin post-translational modifications as a mean to contribute to microtubule identity and function. Powerful tools such as expansion, super-resolution or volumetric microscopy are used in combination with various reverse genetics approaches.