Microtubule dependant autoactivation in the spindle midzone generates a gradient of Aurora B activity. (A), control; (B), brief exposure of HeLa cells to Nocodazole causes loss of midzone microtubules, displacement of Aurora B from the midzone, and loss of the histone H3 (S10) phosphorylation gradient. Similarly, inhibition of Aurora B activity by treatment with Hesperadin in (C) results in displacement of Aurora B (arrow), loss of midzone microtubule organization, and loss of the histone H3 (S10) phosphorylation gradient. (D - F), microtubules and Aurora B kinase activity are required for full activation of Aurora B in the spindle midzone. Brief exposure of Xenopus S3 cells to Nocodazole (E), or Hesperadin (F) results in disruption of midzone microtubules and loss of INCENP S850 phosphorylation; (D), control. (G), Aurora B and midzone microtubules physically interact. Proximity-ligation assay (P-Lisa) was used to detect physical interaction between Aurora B and microtubules in anaphase Xenopus S3 cells. Tubulin is stained green, the kinetochore marker Ndc80 is stained blue and P-Lisa product, demonstrating contact between Aurora B and microtubules in the midzone, is shown in red (C, G reproduced with permission from Fuller et al,  NPG).