Fig. 6

Electron microscopy cross-sections of sperm from Cfap44^−/− males reveal multiple structural axonemal defects. a Cross-section of the midpiece of a WT sperm, showing the arrangement of the ODFs around the axoneme. b Presence of extra ODFs in midpieces sections of sperm from Cfap44^−/− males. The orientation of ODFs is also defective, leading to an increase of the midpiece diameter. a, b Same scale bars = 250 nm. c Graph showing the increased number of ODF in the mutant. Data represent mean ± SD; the statistical difference was assessed with t test, P value as indicated. Twenty-one cross-sections in the midpiece region were analyzed for WT and 21 for Cfap44^−/−. d–f Various structural defects of the axoneme in sperm from Cfap44^−/− males. d Four DMTs (4–7) were missing. The central pair is shifted at the periphery (red arrowhead). e DMTs 5–7 were missing. Note the presence of a third longitudinal column (LC). f Irregular distribution of the DMTs associated with a rotation of the central pair (straight red line). Scale bars = 196 nm. g In WT sperm, the fibrous sheath is linked to the 3-central-8 complex by stalks emerging from the longitudinal columns (white arrowheads). h, i The presence of extra ODFs facing DMTs 3 and 8 (red arrowheads) prevents a normal anchoring of the fibrous sheath’s stalks on DMTs 3 and 8. Scale bars = 270 nm. j–o LCs are not aligned with 3–8 CPC axis. In contrast to WT, where the 3-central-8 complex is aligned with LC to form almost a straight line (j, red line), LC are misaligned in sperm from Cfap44^−/− males, leading to notable asymmetry of the structure (k, m, red lines). l, n The presence of a third LC increases asymmetry. Scale bars = 184 nm. o Bar graph showing the % of defects observed in the principal piece as described in g–n. One hundred cross-sections in the principal piece region were analyzed for WT and 50 for Cfap44^−/−