Progressive alignment of basal bodies in multiciliated cell : Dynamic motion of basal bodies revealed by long-term live imaging

Title Progressive alignment of basal bodies in multiciliated cell: Dynamic motion of basal bodies revealed by long-term live imaging (多繊毛細胞における繊毛基底小体の配列形成:長時間ライブイメージングによるダイ ナミクス解析) Introduction Multiciliated cells (MCCs) are uniquely polarized to drive fluid transport in tissues by the synchronous beating and metachronal waves of hundreds of motile cilia on the apical membrane. A differentiating MCC contains hundreds of basal bodies (BBs), which are short cylindrical structures at the base of mature cilia, and are docked at the apical membrane. In most types of MCCs, the orientation of the BBs, identified by their asymmetrically associated basal feet (BFs), is precisely coordinated to support efficient mucociliary transport. The positional distribution of BBs (BB array) in the apical plane of MCCs depends on the cell type. For example, the BBs of ependymal MCCs in the brain exhibit unipolar clustering in the apical plane while those of Xenopus larval skin MCCs are evenly distributed throughout the entire apical region. Cytoskeletons are involved in regulating these systems, in which microtubules (MTs) are thought to synchronize BB orientation downstream of the planar cell polarity (PCP) core-protein functions. Sub-apical actin is required for the proper distance between neighboring BBs, and myosin II activity plays a role in the unipolar migration of BB clusters. However, the mechanisms involved in correctly assembling and maintaining the proper distribution of BBs on the cell surface remain to be fully elucidated. Objective How multiciliated basal bodies are highly polarized after docking to the apical membrane needs further clarification. Especially, the spatiotemporal information on the cellular process remains largely unknown. In the present study, mouse tracheal MCCs was examined in which the BBs are linearly aligned, a pattern also found in oviduct MCCs. This striking pattern prompted me to address the mechanism by which these BBs become regularly aligned in the apical membrane. By employing a newly developed long-term live imaging method, this study focuses on the cellular process how basal bodies of multiciliated cell achieve their alignment pattern. This study is also aimed at elucidating the underlying mechanism of basal body alignment. Results The dynamics, sequential changes in ciliary patterns that occurred during the maturation of mouse tracheal MCCs were quantified in this study. The process occurred through four stereotypical changes in the BB array. These changes in BB patterns were positively correlated with the refinement of ciliary orientation, indicating that ciliary alignment may have stabilized the unidirectionality of the BBs, to enhance the function of MCCs. Furthermore, this study demonstrated that the genetic loss of BFs in Odf2ΔEx6,7ΔEx6,7 MTECs prevented BBs from achieving the “Alignment” pattern, and drug-induced apical MT disruption caused the “Alignment” pattern to change to a “Floret-like” pattern, suggesting that a self-organization mechanism involving the associated apical cytoskeleton could give rise to these patterns.