Midzone activation of aurora B in anaphase produces an intracellular phosphorylation gradient

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Abstract
Aurora B, a kinase important in mitosis, is now shown to generate a spatial gradient of phosphorylated substrates in anaphase with the highest concentration at the spindle midzone. Generation of this gradient involves a microtubule-dependent mechanism of aurora B activation. The gradient is proposed to provide important spatial information during mitosis. Aurora B is a kinase important for mitosis, and is shown to generate a spatial gradient of phosphorylated substrates in anaphase with the highest concentration at the spindle midzone. Generation of this gradient involves a microtubule-dependent mechanism of aurora B activation. The gradient is proposed to provide important spatial information during mitosis. Proper partitioning of the contents of a cell between two daughters requires integration of spatial and temporal cues. The anaphase array of microtubules that self-organize at the spindle midzone contributes to positioning the cell-division plane midway between the segregating chromosomes1. How this signalling occurs over length scales of micrometres, from the midzone to the cell cortex, is not known. Here we examine the anaphase dynamics of protein phosphorylation by aurora B kinase, a key mitotic regulator, using fluorescence resonance energy transfer (FRET)-based sensors in living HeLa cells and immunofluorescence of native aurora B substrates. Quantitative analysis of phosphorylation dynamics, using chromosome- and centromere-targeted sensors, reveals that changes are due primarily to position along the division axis rather than time. These dynamics result in the formation of a spatial phosphorylation gradient early in anaphase that is centred at the spindle midzone. This gradient depends on aurora B targeting to a subpopulation of microtubules that activate it. Aurora kinase activity organizes the targeted microtubules to generate a structure-based feedback loop. We propose that feedback between aurora B kinase activation and midzone microtubules generates a gradient of post-translational marks that provides spatial information for events in anaphase and cytokinesis.