FAP256A/B-KO tip defects and CCDC81 localisation. (A) Slices of FAP256A/B-KO tomograms along with cross-sections (dotted line) showing examples of the filamentous plugs in both CP microtubules. (B) Subtomogram average of FAP256A/B-KO tip CP (dark salmon). (C) FSC curve of the FAP256A/B-KO tip CP structure. (D) Measured twist angles for FAP256A/B-KO CP. The dotted line is drawn at the highest point of the curve fitted to the histogram. (E) Gallery of A-tubule plugs. The arrowheads point to the extremities of the plugs. (F) Gallery of bent A-tubules indicated by arrowheads. (G) Predicted structures of CCDC81 putative microtubule-binding domain (green) and EF-hand pair domains (purple). (H) Representative SR-SIM images of cells expressing CCDC81-GFP-mNeonGreen under the native promoter fixed and labeled with AXO49 anti-polyglycylated (polyG) tubulin monoclonal antibody that labels ciliary axonemes (green), anti-GFP polyclonal antibodies (red), and DAPI (Blue). Inset highlights CCDC81 enriched along the length of oral membranelles (arrowheads) and at the tips of anterior cilia (arrows). Scale bars, 10 μm; inset, 5 μm. (I) Slice through an example tomogram of demembranated CU428 showing that the cap complex is still present.