Differential modification of the C-terminal tails of different α-tubulins and their importance for microtubule functionin vivo

Abstract

Microtubules (MTs) are built from α-/β-tubulin dimers and used as tracks by kinesin and dynein motors to transport a variety of cargos, such as mRNAs, proteins, and organelles, within the cell. Tubulins are subjected to several post-translational modifications (PTMs). Glutamylation is one of them, and it is responsible for adding one or more glutamic acid residues as branched peptide chains to the C-terminal tails of both α- and β-tubulin. However, very little is known about the specific modifications found on the different tubulin isoforms in vivo and the role of these PTMs in cargo transport along MTs in vivo. In this study, we found that in Drosophila, glutamylation of the α-tubulin isoforms occurs specifically on the C-terminal ends of TBA1 and TBA3 in the ovaries. In contrast, the ovarian isoform TBA4 is not glutamylated. The C-terminal ends of TBA1 and TBA3 are glutamylated at several glutamyl side chains in various combinations. Drosophila TTLL5 is required for the mono- and polyglutamylation of ovarian TBA1 and 3. Furthermore, glutamylation of the α-tubulin is essential for the efficient localization of Staufen/osk mRNA and to give directionality to the fast ooplasmic streaming, two processes known to depend on kinesin-mediated processes during oogenesis. In the nervous system, the kinesin-dependent neuronal transport of mitochondria also depends on TTLL5. Additionally, α-tubulin glutamylation affects the pausing of the transport of individual mitochondria in the axons. Our results demonstrate the in vivo role of TTLL5 in differential glutamylation of α-tubulin isoforms and point to the in vivo importance of α-tubulin glutamylation for kinesin-dependent processes.