Abstract

Cytokinesis, the physical separation of a dividing cell into two daughter cells, is driven by the ingression of an actomyosin contractile ring. The mitotic spindle, which is composed of distinct populations of microtubules, dictates the location of the division plane. In particular, the central spindle, which forms between segregating sister chromatids recruits Ect2, the GEF leading to the activation of RhoA and the formation of the actomyosin ring in the equatorial plane. Anillin is a key regulator of cytokinesis that interacts with the core components of the division machinery including actin, myosin and their upstream regulator RhoA. Anillin also interacts with the membrane and proteins associated with the mitotic spindle. These numerous interactions stabilize the position of the ring to maintain the division plane. Consistent with this, anillin depletion causes lateral instability of the contractile ring and leads to mitotic failure. While the signalling pathway that activates RhoA from the central spindle is well understood, it is not known whether there is feedback from the cortex to the mitotic spindle to mediate changes in microtubule stability in response to cortical perturbations. Recently, C. elegans anillin was shown to directly interact with microtubules. Therefore, since anillin interacts with both cortical components and microtubules, it is a good candidate for mediating feedback from the cortex to the spindle to stabilize subsets of microtubules that position the contractile ring.
Here, we investigate anillin-microtubule interactions in human (HeLa) cells. Anillin localizes to microtubules during mitosis, and this localization is enhanced after treatments that stabilize microtubules or decrease RhoA activation. Anillin also directly interacts with taxol-stabilized microtubules in vitro. In anillin-depleted cells, there is a decrease in the proportion of centrally located spindle microtubules and a loss of bundled microtubules in monopolar cells. Live imaging of stably expressing EB1:2EGFP cells show that in the absence of anillin, a pool of long microtubules that emanate toward the equatorial cortex are missing. Together, these results suggest that anillin’s localization to microtubules could increase their stability, and supports a role for anillin in mediating feedback between the cortex and the mitotic spindle.