Cover legend: Ependymal cell basal bodies, labeled by γ-tubulin staining in red, are clustered in a patch on the apical surface of ependymal cells, outlined by β-catenin staining in green. The position of the basal body patch on the apical surface is planar-polarized, with neighboring cells having their basal body patch displaced to the same side, which corresponds to the downstream side with respect to cerebrospinal fluid flow. For more information, see the article by Mirzadeh et al. in this issue (pages 2600–2610).