Super-resolution Molecular Map of Basal Foot Reveals Novel Cilium in Airway Multiciliated Cells

Motile cilia are beating machines that play a critical role in airway defense. During airway cell differentiation, hundreds of motile cilia are templated from basal bodies that extend a basal foot, an appendage that links motile cilia together to ensure beating coordination. This assembly has thus far escaped structural analysis because its size is below the resolution limit. Here, we determine the molecular architecture and identify basal foot proteins using a super-resolution-driven approach. Quantitative super-resolution image analysis shows that the basal foot is organized in three main regions linked by elongated coiled-coil proteins. FIB-SEM tomography and comparative super-resolution mapping of basal feet reveal that, among hundreds of motile cilia of an airway cell, a hybrid cilium with features of primary and motile cilia is harbored. The hybrid cilium is conserved in mammalian multiciliated cells and originates from parental centrioles. We further demonstrate that this novel cilium is a signalling centre whose cellular position is dependent on flow.