Figure 2.

Microtubule Organization in Minimal Central Anaphase Spindles

(A) TIRF microscopy images of self-organization of minimal anaphase midzone bundles in the presence of 5-nM PRC1-Alexa546 (green), 10-nM KIF4A-mBFP (blue), and 12.5-μM Alexa647-tubulin (red). Times in minutes after initiating microtubule nucleation by a temperature shift to 30°C are shown.

(B) Image sequence showing an example of antiparallel midzone bundle fusion and alignment; condition as in (A).

(C) (Top) Kymograph of a representative microtubule growing in the presence of 50-nM KIF4A-mBFP only, as in Figure 1E. (Bottom) Boxplot shows the speeds of plus and minus ends from individual dynamic microtubules (n = 18). The box represents the interquartile range (IQR) and whiskers represent the range (-outliers); x = outliers (>1.5 × IQR); box line, median; square, mean.

(D) Kymographs (top) and corresponding boxplots (bottom) showing the growth speeds of microtubules growing outward in minimal midzone bundles assembled under conditions as in (A) (n = 32) and from bundles formed only in the presence of 5-nM PRC1-Alexa546 (n = 57).

(E) Schematic illustrating the microtubule orientations in PRC1-only bundles (as in Figure 1F).

(F) The inverted microtubule orientation in antiparallel bundles formed by both PRC1 and KIF4A (as in A and B and Figures 1C and 1D).