Figure 7.

Antiparallel microtubules in the middle of MII spindles show a preferred packing distance. Neighbor density analysis (see Figure 4F) of spindle midzone microtubules was examined in three size classes of MII spindles (1.47–1.62 μm, A and B; 1.7–2.0, C and D; >2.0 μm, E and F) and plotted as histograms showing the density of microtubules (x-axis) at given distances from the reference microtubule (y-axis, the reference microtubule is the one in the center in the Figure 4F schematic). The data for each microtubule in the models being used as the reference microtubule is summed. No significant preferred packing was detected between microtubules from the same SPB (parallel) in the shorter spindles (A and C), but a peak of ∼35 nm was seen in the longest spindles (E). A preferred distance of ∼40 nm is observed between microtubules from opposite SPBs (antiparallel) at all spindle lengths (B, D, and F). This distance of 40 nm is particularly apparent in longer spindle lengths (D and F). Such organization is not apparent in MI spindles (see text; our unpublished data).