Spatial organization of spindle microtubules. (A, C, E, G, and I) Mode analysis of flux velocity distributions for representative individual spindles: the control spindle in Fig. 1 A (A), the DNA bead spindle in Fig. 2 A (C), the spindle treated with p50/dynamitin in Fig. 3 A (E), the spindle treated with 200 μM monastrol in Fig. 3 C (G), and the spindle treated with 200 μM monastrol and p50/dynamitin in Fig. 3 N (I). Red, fast mode; green, slow mode; cyan, mixture of both modes. (B, D, F, H, and J) Regional contribution of velocity modes. Averages of control spindles (B; N = 11), DNA bead spindles (D; N = 9), p50/dynamitin-treated spindles (F; N = 7), monastrol-treated spindles (H; N = 7), and monastrol and p50/dynamitin–treated spindles (J; N = 6). (K–O) Spatial distribution of speckle appearances of spindles analyzed in A, C, E, G, and I. Orange, speckles moving toward the left pole; blue, speckles moving toward the right pole. (P) Normalized distribution of average speckle intensity (average of 11 control spindles). (Q) Normalized speckle number along the pole-to-pole axis of nine control spindles. Gray, normalized speckle number of a spindle treated with 200 μM monastrol. (R) Model: two slow-fluxing polar microtubule arrays (green) are dynamically coupled via motors to a barrel array (red) with antiparallel microtubule polarity and faster flux velocities. Gray bands representing regions 1–2 and 22–23 define left and right poles in our analysis, respectively.