Reconstitution of aster movement and cell division plane positioning mechanisms in Xenopus egg extract

During early development, microtubule asters move through the cytoplasm to position microtubule organizing centers (MTOCs) near the centers of subsequent cells. Aster movement is thought to depend on pulling forces by cytoplasmic dynein opposed by hydrodynamic drag; however, it remains unclear what are the cytoplasmic anchors, and how other cytoplasmic networks such as actin facilitate or hinder aster movement. We reconstituted aster growth, interaction, and movement in an actin-intact Xenopus egg extract system under quasi-2D confinement. We imaged microtubules, actin, and candidate cytoplasmic anchors. Asters interacted to generate dynamic Voronoi tessellations with edges corresponding to division planes. MTOCs moved toward the center of each polygon, mimicking their movement in vivo. Dynein inhibition blocked inward transport of cytoplasmic anchors. Actin depolymerization increased the rate of inward transport of anchors, but decreased the rate of aster movement. Actin depolymerized at Voronoi edges due to AurkB activity, resulting in aster movement away from edges. Our experiments inform how dynamic cytoplasmic networks interact to drive aster movement by dynein-dependent and -independent mechanisms.