Extended Data Fig. 5: The central pair complex in mouse axoneme possesses more MIPs but the overall shape is similar to the one from sea urchin sperm.

a, Two longitudinal views of the MIPs inside the two singlet microtubules are shown. Periodic features (every 32 nm) are indicated (red empty arrowheads). b, The average of the central pair complex in mouse sperm axonemes is overlaid on the map for the central pair complex from sea urchin sperm (EMD-9385) and they are colored in grey and cyan, respectively²⁵. Note most of the protrusions are very similar and the sea urchin-specific protrusion 1f is indicated in the middle panel (red arrowhead). c, The average of the central pair complex in mouse sperm axonemes is overlaid on the map for the central pair complex from Chlamydomonas (EMD-31143)³⁵. Note the maps are aligned based on the similar C1 protrusions 1d. Other protrusions are generally less similar (1a, 1f and 2d) and there appears to be an 8-nm shift for the C2 protrusions. The Chlamydomonas C2 microtubule was recently shown to possess two possible registers with 8-nm longitudinal differences³³. d, The spatial relationship between the nine radial spokes and the central pair complex are determined by multibody refinement and the ‘average positioning’ of these two rigid bodies are shown (RS-CP1 denotes the interface between radial spokes from doublet 1 and the central pair.