Fig. 7: Model: every outer doublet is surrounded by a different set of regulatory complexes in mammalian sperm.

Schematic of the (9 + 2) axonemes of mouse (a) and human (b) sperm. The doublets are numbered, and the sperm-specific regulatory complexes are labeled for each of the nine outer doublets. In particular, the components from the RSs are shown for each doublet and the N-DRCs are colored differently depending on the extra density (as in Figs. 4–6). Note that only the barrel distribution is different in mouse and human sperm axonemes. c, RSs from different doublets interact with specific stripes of protrusions of the central pair complex. Our multibody refinement is consistent with the sliding hypothesis, and potential longitudinal movements of dmt1 are indicated by the two red arrows. The model is analogous to ‘nine train moving on nine tracks’. d, Schematics showing gradual accumulations of offsets of periodic structure units between two filaments in a curved axoneme (left) and consistent offset between doublet 5–doublet 6 (right). e, The constant offset within tomograms and among tomograms (N = 63) would be consistent with limited horizontal bending in sperm flagella.