Motility defects of C1a-e-c mutants, and FAP92 is a C1a protein. (A) Average swimming velocities of WT and mutant cells and rescue strains fap76-1;BCCP::FAP76 (fap76-1res) and fap216;BCCP::FAP216 (fap216res). In the sequence as shown in the histogram n = 30, 30, 30, 30, 30, 30, 32, 40, and 34. *, Significant difference (Student’s t test, P < 0.01) compared with WT. Error bars indicate ± SEM. (B) Each colored line represents the swimming path of one cell recorded for 1 s. The swimming paths of mutants are curving. (C) The percentage of cells displaying photoshock response, i.e., that switched from forward swimming to backward swimming upon light stimulus, compared with WT. (D–K) Comparisons of tomographic slices (D–F and H–J) and isosurface renderings (G and K) between the averaged CA repeats of WT (D–G) and fap92 axonemes (H–K) viewed in cross-sectional (D and H), longitudinal (E, G, I, and K) and top-down (F and J) orientations, showing a sheet-like density that is present in the WT C1a projection (red arrowheads in D–G) but missing in fap92 (white arrowheads in H–K). Thin blue lines indicate the location of the tomographic slices shown in E and F (in D) and I and J (in H). Scale bar in B (WT), 50 µm (valid for all images in B); D, 20 nm (valid for D–F and H–J).