FIG. 2. .

The bull sperm connecting piece. A) Image of a negatively stained sperm CP showing asymmetrical segmented organization. Projections of approximately 23 nm-thick sections from 3-D cryotomogram reconstructions of (B) CP of sperm with head (inset shows lower magnification view that includes the base of the head) and of (C) CP of headless sperm show similar architecture, indicating the absence of any dramatic effect of decapitation on the overall structure of the CP; c, capitulum; db, dense band; pb, pale band. Three of the segmented columns appear to be folded in order to form the proximal centriolar vault (PCV), suggesting a possible association of the segment peripheries with centrioles (arrowheads in B and C). Bar = 250 nm (A–C). D) Images of the banding pattern exhibiting clear alternating repeats of pale/dark segment bands were extracted from sections of tomographic reconstructions of both intact and headless sperm tails, n = 3 for each. The independent excised images containing an area covering six linear segment repeats were manually aligned and averaged to obtain the average periodic unit (68 nm). Scale bar = 250 nm. Density profiles of the aligned images are plotted in E. The results show no significant variation in the size of the pale bands observed in the tomograms (F), indicating that the structure determined in this work are likely of a quiescent state (n = 10).