Microtubule glycylation promotes attachment of basal bodies to the cell cortex

Abstract

Motile cilia generate directed hydrodynamic flow that is important for the motility of cells and extracellular fluids. To optimize directed hydrodynamic flow, motile cilia are organized and oriented into a polarized array. Basal bodies (BBs) nucleate and position motile cilia at the cell cortex. Cytoplasmic BB-associated microtubules are conserved structures that extend from BBs. By using the ciliate, Tetrahymena thermophila, combined with EM-tomography and light microscopy, we show that BB-appendage microtubules assemble coincidently with new BB assembly and that they are attached to the cell cortex. These BB-appendage microtubules are specifically marked by post translational modifications of tubulin, including glycylation. Mutations that prevent glycylation shorten BB-appendage microtubules and disrupt BB positioning and cortical attachment. Consistent with the attachment of BB-appendage microtubules to the cell cortex to position BBs, mutations that disrupt the cellular cortical cytoskeleton disrupt the cortical attachment and positioning of BBs. In summary, BB-appendage microtubules promote the organization of ciliary arrays through attachment to the cell cortex.

Ciliary force-responsive striated fibers promote basal body connections and cortical interactions

“…The microtubule appendages consist of both the post-ciliary microtubule (pcMT) bundles, which project posteriorly from BBs, and the transverse microtubule bundles, which extend rightward (when viewed from the outside of the cell) to the adjacent ciliary row (Allen, 1967;Junker et al, 2019). SFs project anteriorly, to connect with anterior BBs by crossing the surface of the pcMT bundles (Allen, 1967;Junker et al, 2019;Pitelka, 1961). Ciliate cortical organization is promoted by both global and local polarity cues (Frankel, 1989;Frankel, 2008;Sonneborn, 1964).…”

C-terminal tail polyglycylation and polyglutamylation alter microtubule mechanical properties

“…Glycylation is present on the length of mature cilia and may contribute to overall cilia stability (22). In addition, glycylation is present on microtubule structures that anchor the basal bodies to the cell cortex (23). In contrast, glutamylation in cilia is important for early ciliary maturation (24) and proper ciliary beating (25).…”

Motile Cilia: Innovation and Insight From Ciliate Model Organisms

“…Identification and characterization of the TTLL family of tubulin modifying enzymes has also been carried out in Tetrahymena (Janke et al, 2005). From these studies we find that tubulin glutamylation and glycylation affect the stability and waveform of ciliary beating in Tetrahymena axonemes (Wloga et al, 2008, 2009, 2010; Suryavanshi et al, 2010; Junker et al, 2019). Overall, ciliates have been utilized to demonstrate how motile cilia beat and the molecular players that affect ciliary structure and function.…”

“…These studies highlight the power of ciliate reverse genetics approaches. Recent work has also made connections between the tubulin post-translational modification glycylation and attachment of Tetrahymena basal bodies at the cell cortex (Junker et al, 2019). The assembly, maintenance, and precise positioning of basal bodies remains an essential foundation for the building of a functional cilium and ciliates have, and will remain, at the forefront of basal body research.…”