Mathematical modeling of central spindle organization by Aurora B gradient. (A) A schematic image of the central spindle in the 2D model. Pairs of MTs form antiparallel MT overlaps, where they slide apart (red arrows). MT growth and shrinkage occur at plus ends (blue and pink arrow, respectively). The Aurora B gradient (orange) forms around the stem body and inhibits MT depolymerization at minus ends (purple arrows), depending on their distance from the stem bodies. L, length of the antiparallel overlap. S_l and S_r, lengths of nonoverlapping portions. The interchromosomal area is flanked by rigid chromosome walls (light blue), and MTs buckle when their length exceeds the interchromosomal distance (the top MTs). (B and C) Time plots of simulated MT length (sum of L, S_l, and S_r) with various MT growth rates (V_growth) or Aurora B gradient sizes (σ). The mean of 25 MT pairs from five independent simulations is shown for each condition. (D) Stem body distributions after 1,000-s simulations. Shown are 200 stem bodies from 40 independent simulations. Closed circles indicate outliers that exceeded the length limit (see Materials and methods). (E) Time plots of simulated stem body positions with or without the Aurora B gradient. A stem body (stem body #3) was misaligned at the beginning of the simulation in both cases. Alignment of stem body #3 was observed only when the Aurora B gradient was present. The mean of five independent simulations is shown for each condition. The parameter values used in each simulation are presented in Table S4.