Skip to main content

Self-organization of the cilium: the role of the tubulin code

Periodic Reporting for period 2 - CiliaTubulinCode (Self-organization of the cilium: the role of the tubulin code)

Reporting period: 2020-09-01 to 2021-07-31

CiliatubulinCode investigates how tubulin post-translational modifications (PTMs) contribute to self-organization, mechanics, and function of the cilium – a specialized motility and sensory organelle of tremendous importance for many basic functions of eukaryotic organisms, e.g. humans, where ciliary dysfunction can lead to a wide range of severe pathologies.

Obtaining a detailed picture of the roles of tubulin PTMs in cilia is a challenging task. In order to succeed, CiliatubulinCode combines a variety of state-of-the art cell biological, molecular, biochemical, and imaging approaches, including novel correlative light and electron microscopy methods, immuno-cryo-electron tomography, and in vitro reconstitution methods.

The main objectives of CiliatubulinCode are to:
-understand the role of the tubulin code in the regulation of the intraflagellar transport (IFT),
-understand the role of the tubulin code in the assembly of the ciliary axoneme, and in the regulation of the activity of axonemal components such as axonemal dyneins,
-create a high-resolution spatiotemporal map of the tubulin code in cilia and eukaryotic flagella.

The results of our work are of interest to a broad scientific audience, reaching from more specialized cilia and microtubule fields to the broader cell and molecular biology arena. Because we provide fundamental insight into how mutations that affect tubulin PTMs enzymes cause human diseases, our work also has clinical relevance.
In the first two years of CiliatubulinCode, we have made substantial progress in all three objectives we have proposed.

In one study we have recently published in Science (DOI: 10.1126/science.abd4914) we investigated the role of tubulin glycylation in axonemal assembly and flagellar beating in mice sperms. We found that loss of glycylation results in altered flagellar beating activities by compromising the coordination of the activity of axonemal dynein motors. We demonstrated that tubulin glycylation controls sperm motility, and thereby directly affects fertility by regulating dynein motor proteins.
Our findings also suggest that a perturbation of tubulin glycylation could be the reason for some forms of male infertility in humans.

Other two recently published studies, where we made use of cryo-electron tomography, show high resolution maps of the axonemal structure of motile (DOI: 10.1371/journal.pgen.1009388) and primary cilia (DOI: 10.1038/s41594-020-0507-4).
These maps are the required groundwork for future investigation on the effect of mutation of tubulin PTM enzymes on the assembly and function of motile and primary cilia.
The proposed research will teach us how the tubulin code sets up and organizes functional specificity of microtubules at nanometer resolution. Further, we will reveal how alterations of this functional specificity affects cilia assembly and function and how the resulting cilia dysfunction are linked to other human pathologies (beyond infertility).
The proposed work will, by design, elevate our understanding of axonemal organization, but we believe that the fundamental principles of tubulin PTMs will translate to other cytoskeletal systems.