(A) Paramecium showing 1 ciliated BB after control RNAi depletion (Ctrl). The TZ is characterized by 3 plates indicated by colored arrowheads: terminal plate (green), intermediate plate (blue), and axosomal plate (magenta). (B-E) Upon CEP90 depletion, undocked BB are detected close to the cell surface (C, E) or deep in the cytoplasm (B, D). Vestigial structures resembling the axosomal plate (magenta arrowhead) and intermediate plate (blue arrowhead) are detected on all internal BB (n = 63). (E) Example of rare BB displaying microtubule extensions on the free, uncapped side of the BB (white arrow). Scale bar = 200 nm. BB, basal body; RNAi, RNA interference; TZ, transition zone.