Overview of the ciliary tip. (A) Tomogram slice of a representative ciliary tip. 3D model of the same cilium generated with the subtomogram averages described in this study. The membrane is in brown, the CP is in dark salmon, doublets and singlet A-tubules are in gray, and the cap complex is in gold. The doublet and singlet at the front of the image were removed to allow the visualization of the CP. (B) Representative slice of a demembranated cilium showing the tip CP, the end of one B-tubule, the last radial spoke, the spike structure, and the axonemal doublet-zone CP. Scale bar: 100 nm. (C) 3D representation of the A-tubules (gray) from a representative tomogram. The central axis of the cilium (center of the CP) is in blue. (D) Length of A-tubules numbered from shortest to longest. The dotted line shows a linear trend line going through all points. Error bars show the standard deviation. n = 6 cilia. (E) Longitudinal slice through a representative tomogram at the narrowing zone. Orange dotted lines show cross-sections in panels a, b, and c. Orange arrowheads point toward the disassembling/incomplete B-tubule. Insets show a doublet with a disassembling/incomplete B-tubule. The CP microtubules are marked by a salmon diamond. Cartoons indicate what is shown in the insets. The purple arrowhead shows a filament capping the end of the B-tubule.