FIGURE 4:

CSC amiRNA mutants have reduced assembly and/or stability of the radial spokes. (A) Electron micrographs of cross- and longitudinal sections of chemically fixed axonemes isolated from CSC amiRNA mutants. Cross-sections show various numbers of doublet microtubules, which lack the radial spokes (red dots). In longitudinal sections, we observe both doublets with repeating pairs of radial spokes, as in wild type, and stretches of regularly repeating, single radial spokes (red arrows). Occasionally, a triplet of radial spokes was also observed (green arrowheads in 4A2 panel). (B) Histogram of the number of radial spokes missing in cross-sections of axonemes (n > 100 for each strain); ∼80% of cross-sections of wild-type axonemes (black bar) have spokes present on all nine doublets. In contrast, only ∼30% of cross-section for CSC amiRNA mutant sections have spokes present on all doublet microtubules. The majority of cross-sections for CSC amiRNA mutants have between one and five doublets that lack spokes. (C) Histogram indicating the specific doublet that lacked radial spokes in cross-sections (n > 20 for each strain). Doublet identity was determined by specific axonemal markers according to that established in Hoops and Witman (1983). In all strains, the distribution of doublets lacking radial spokes appeared random.