FAP256 activity elongates the A-tubules while ARMC9 activity shortens the B-tubules. (A–C) Negatively stained whole cilia from a wild type (A) and cells overproducing either GFP-FAP256A (B; inset bar, 100 nm) or GFP-ARMC9B (C) after 6 h of exposure to cadmium chloride to induce the transgenes (green bracket, CP region; blue bracket, A-tubule region). (D and E) Quantifications of the length of CP-region (n = 50–60) and distal segment (n = 45–67) based on the images of negatively stained whole cilia in cells overexpressing either GFP-FAP256A (D) or GFP-ARMC9B (E) for 6 h (mean ± standard deviation; two-sided t test, P < 0.05). (F and G) SR-SIM images of a wild type (F) and a GFP-ARMC9B overproducing cell (in the ARMC9-KO background; G) after 6 h of exposure to cadmium chloride to induce the transgene overexpression (green, α-tubulin detected by 12G10 monoclonal antibody and GFP-ARMC9B; red, polyG antibodies; bars: 20 µm [main], 5 µm [inset]). The anti–α-tubulin 12G10 antibody labels more strongly the distal segment (as compared with the middle segment) likely due to increased accessibility of microtubules not covered by motility-related complexes. Color channels are shifted in magnified images, arrows point to the boundaries of the distal segment. (H) A summary of the functions of FAP256/CEP104, CHE-12/Crescerin, and ARMC9 uncovered in this study.