Extended Data Fig. 6: The 5-6 bridge of mouse sperm axonemes.

a-d, Four views of the composite map for 5-6 bridge in mouse sperm axonemes combining maps for local refinement of the doublet 5, doublet 6 and the bridge. The inner arm dyneins, radial spokes, the barrel, N-DRC and extra bridge densities are colored in pink, different shades of cyan, light blue, green and blue, respectively. Note that the radial spokes which repeat every 96 nm on doublet 5 and doublet 6 are resolved and there appears to be a ~20 nm offset between their longitudinal registers, as indicated in the staggering distance of RS1 and RS2 from doublet 5 and doublet 6 in d. e, f, Two cut-in views of a and c are shown. Bridge−specific densities are highlighted in blue. These densities extend from the inner arm dyneins of doublet 5 towards the microtubule of doublet 6. Direct contacts of the bridge-specific densities to doublet 6 is indicated by the solid red arrowhead while densities in close proximity of the base of radial spoke 2 in doublet 6 are indicated by the empty red arrowhead. g, h, Subvolumes for doublet 1 was aligned and equivalent views of doublet 1 and 2 are shown (as in panel a and b). The expected positions for dyneins and radial spokes on doublet 2 are circled by dashed and solid red ovals. These 96 nm-repeating structures on doublet 2 are not resolved even after local refinement, suggesting the offsets between doublet 1 and doublet 2 are not consistent. The microtubule from doublet 2 is nevertheless partially resolved since variant longitudinal mismatching would not smear a tube of ‘continuous densities’ compared to ‘discrete densities’ like dyneins and radial spokes through averaging.