Basal foot MTOC organizes pillar MTs required for coordination of beating cilia

Coordination of ciliary beating is essential to ensure mucus clearance in the airway tract. The orientation and synchronization of ciliary motion responds in part to the organization of the underlying cytoskeletal networks. Using electron tomography on mouse trachea, we show that basal bodies are collectively hooked at the cortex by a regular microtubule array composed of 4–5 microtubules. Removal of ​galectin-3, one of basal-body components, provokes misrecruitment of γ-tubulin, disorganization of this microtubule framework emanating from the basal-foot cap, together with loss of basal-body alignment and cilium orientation, defects in cilium organization and reduced fluid flow in the tracheal lumen. We conclude that ​galectin-3 plays a crucial role in the maintenance of the microtubule-organizing centre of the cilium and the ‘pillar’ microtubules, and that this network is instrumental for the coordinated orientation and stabilization of motile cilia

Tetrahymena

Basal bodies comprise nine symmetric triplet microtubules that anchor forces produced by the asymmetric beat pattern of motile cilia. The ciliopathy protein Poc1 stabilizes basal bodies through an unknown mechanism. In poc1∆ cells, electron tomography reveals subtle defects in the organization of intertriplet linkers (A-C linkers) that connect adjacent triplet microtubules. Complete triplet microtubules are lost preferentially near the posterior face of the basal body. Basal bodies that are missing triplets likely remain competent to assemble new basal bodies with nine triplet microtubules, suggesting that the mother basal body microtubule structure does not template the daughter. Our data indicate that Poc1 stabilizes basal body triplet microtubules through linkers between neighboring triplets. Without this stabilization, specific triplet microtubules within the basal body are more susceptible to loss, probably due to force distribution within the basal body during ciliary beating. This work provides insights into how the ciliopathy protein Poc1 maintains basal body integrity