Coordinated beating of cilia in the trachea generates a directional flow of mucus required to clear the airways. Each cilium originates from a barrel-shaped basal body, from the side of which protrudes a structure known as the basal foot. We generated mice in which exons 6 and 7 of Odf2, encoding a basal body and centrosome-associated protein Odf2/cenexin, are disrupted. Although Odf2(ΔEx6,7/ΔEx6,7) mice form cilia, ciliary beating is uncoordinated, and the mice display a coughing/sneezing phenotype. Whereas residual expression of the C-terminal region of Odf2 in these mice is sufficient for ciliogenesis, the resulting basal bodies lack basal feet. Loss of basal feet in ciliated epithelia disrupted the polarized organization of apical microtubule lattice without affecting planar cell polarity. The requirement for Odf2 in basal foot formation, therefore, reveals a crucial role of this structure in the polarized alignment of basal bodies and coordinated ciliary beating.

The skin pigment pattern of zebrafish is a good model system in which to study the mechanism of biological pattern formation. Although it is known that interactions between melanophores and xanthophores play a key role in the formation of adult pigment stripes, molecular mechanisms for these interactions remain largely unknown. Here, we show that Delta/Notch signaling contributes to these interactions. Ablation of xanthophores in yellow stripes induced the death of melanophores in black stripes, suggesting that melanophores require a survival signal from distant xanthophores. We found that deltaC and notch1a were expressed by xanthophores and melanophores, respectively. Moreover, inhibition of Delta/Notch signaling killed melanophores, whereas activation of Delta/Notch signaling ectopically in melanophores rescued the survival of these cells, both in the context of pharmacological inhibition of Delta/Notch signaling and after ablation of xanthophores. Finally, we showed by in vivo imaging of cell membranes that melanophores extend long projections towards xanthophores in the yellow stripes. These data suggest that Delta/Notch signaling is responsible for a survival signal provided by xanthophores to melanophores. As cellular projections can enable long-range interaction between membrane-bound ligands and their receptors, we propose that such projections, combined with direct cell-cell contacts, can substitute for the effect of a diffusible factor that would be expected by the conventional reaction-diffusion (Turing) model.

Analysis of Odf2 deletion mutants reveals regions important for the formation of basal body transition fibers and centriole distal appendages and distinct regions required for basal feet and subdistal appendages.

The cytoskeleton is an essential cellular component that enables various sophisticated functions of epithelial cells by forming specialized subcellular compartments. However, the functional and structural roles of cytoskeletons in subcellular compartmentalization are still not fully understood. Here we identified a novel network structure consisting of actin filaments, intermediate filaments, and microtubules directly beneath the apical membrane in mouse airway multiciliated cells and in cultured epithelial cells. Three-dimensional imaging by ultra-high voltage electron microscopy and immunofluorescence revealed that the morphological features of each network depended on the cell type and were spatiotemporally integrated in association with tissue development. Detailed analyses using Odf2 mutant mice, which lack ciliary basal feet and apical microtubules, suggested a novel contribution of the intermediate filaments to coordinated ciliary beating. These findings provide a new perspective for viewing epithelial cell differentiation and tissue morphogenesis through the structure and function of apical cytoskeletal networks.

Determination of left-right asymmetry in mouse embryos is established by a leftward fluid flow that is generated by clockwise rotation of node cilia. How node cilia achieve stable unidirectional rotation has remained unknown, however. Here we show that brief exposure to the microtubule-stabilizing drug paclitaxel (Taxol) induces randomly directed rotation and changes the ultrastructure of node cilia. In vivo observations and a computer simulation revealed that a regular 9+0 arrangement of doublet microtubules is essential for stable unidirectional rotation of node cilia. The 9+2 motile cilia of the airway, which manifest planar beating, are resistant to Taxol treatment. However, the airway cilia of mice lacking the radial spoke head protein Rsph4a undergo rotational movement instead of planar beating, are prone to microtubule rearrangement, and are sensitive to Taxol. Our results suggest that the absence of radial spokes allows node cilia to rotate unidirectionally but, as a trade-off, renders them ultrastructurally fragile.