Supplemental Material

This article contains the following supporting material:

• Figure 1 - Simulated ipMT dynamics dominate recovery at the equator, but have little effect on recovery rates near the SPBs.
  (A) Recovery rates in the spindle zone with high kMT density (blue arrows) were not affected by the addition of robust ipMT dynamics to the simulation, assuming growth and shortening rates were similar between ipMTs and kMTs (range from 0.9 μm/min – 2.0 μm/min tested). Frequent depolymerization of ipMTs to the spindle equator does affect FRAP half-times towards the equator (red arrows). (B) Experimentally observed FRAP half-times at the equator limit theoretical ipMT plus-end excursion lengths, such that it is likely that ipMT plus-ends rarely visit the equator. The histogram shows the distribution of ipMT plus-end positions as a function of spindle position for (1) simulations where ipMTs are dynamic, and yet depolymerization to the equator is limited such that experimentally observed half-times are reproduced (blue and purple bars), and (2) for a simulation where ipMT dynamics result in a failure to reproduce experimental results because ipMT plus-end depolymerization leads to reduced FRAP half-times towards the equator (red and purple bars) (for ipMTs, k_c = 0.25 min^-1 , V _g = 1.2 µm/min, V _g = 1.2 μm/min). These simulation results indicate that if ipMTs are dynamic, they must have plus ends that are confined to be close to the opposite pole. Otherwise, they must be non-dynamic compared to kMTs.

• Movie 1 - Quantitative animation simulated via model-convolution of the GFP-Tub1 FRAP experiment in wild-type spindles. The movie is shown at six frames/second, with each frame representing 0.5 sec of real-time recovery. The total fluorescence recovery time depicted in the movie is 63 sec.

• Movie 2 - Quantitative animation simulated via model-convolution of the GFP-Tub1 FRAP experiment in •-tubulin mutant spindles. The movie is shown at six frames/second, with each frame representing 0.5 sec of real-time recovery. The total fluorescence recovery time depicted in the movie is 75 sec.