Anillin interacts with microtubules and is part of the astral pathway that defines cortical domains

Cytokinesis occurs by the ingression of an actomyosin ring that separates the cell into two daughter cells. The mitotic spindle, comprising astral and central spindle microtubules, couples contractile ring ingression with DNA segregation. Cues from the central spindle activate RhoA, the upstream regulator of the contractile ring. However, additional cues from the astral microtubules also reinforce the localization of active RhoA. Using human cells, we show that astral and central spindle microtubules independently control the localization of contractile proteins during cytokinesis. Astral microtubules restrict the accumulation and localization of contractile proteins during mitosis, whereas the central spindle forms a discrete ring by directing RhoA activation in the equatorial plane. Anillin stabilizes the contractile ring during cytokinesis. We show that human anillin interacts with astral microtubules and that this interaction is competed by the cortical recruitment of anillin by active RhoA. Anillin restricts the localization of myosin to the equatorial cortex and that of NuMA (part of the microtubule-tethering complex that regulates spindle position) to the polar cortex. The sequestration of anillin by astral microtubules might alter the organization of cortical proteins to polarize cells for cytokinesis.