Differential modifications of the C-terminal tails of α-tubulin isoforms and their in vivo importance for kinesin function in Drosophila

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 acids 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 Drosophila TTLL5 is required specifically for the glutamylation of the α-tubulin isoforms TBA1 and TBA3 in ovaries, whereas the ovarian isoform TBA4 is not glutamylated. Furthermore, TTLL5 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 plays a role in controlling the pausing of the transport of individual mitochondria. 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. Summary Drosophila TTLL5 is required for: 1. α-tubulin glutamylation in vivo , specifically on the C-terminal domain of TBA1 and 3; the female germline isoform TBA4 is not glutamylated. 2. Kinesin-based localization of Staufen/ osk mRNA and ooplasmic streaming during oogenesis. 3. Kinesin-based transport of mitochondria in neurons. ### Competing Interest Statement The authors have declared no competing interest.