Department of Systems Biology, Harvard Medical School, Boston, MA 02115.
Marine Biological Laboratory, Woods Hole, MA 02543.
Mol Biol Cell. 2018 Feb 1;29(3):304-316. doi: 10.1091/mbc.E17-09-0540. Epub 2017 Nov 29.
The cleavage furrow in zygotes is positioned by two large microtubule asters that grow out from the poles of the first mitotic spindle. Where these asters meet at the midplane, they assemble a disk-shaped interaction zone consisting of anti-parallel microtubule bundles coated with chromosome passenger complex (CPC) and centralspindlin that instructs the cleavage furrow. Here we investigate the mechanism that keeps the two asters separate and forms a distinct boundary between them, focusing on the conserved cytokinesis midzone proteins Prc1 and Kif4A. Prc1E, the egg orthologue of Prc1, and Kif4A were recruited to anti-parallel bundles at interaction zones between asters in egg extracts. Prc1E was required for Kif4A recruitment but not vice versa. Microtubule plus-end growth slowed and terminated preferentially within interaction zones, resulting in a block to interpenetration that depended on both Prc1E and Kif4A. Unexpectedly, Prc1E and Kif4A were also required for radial order of large asters growing in isolation, apparently to compensate for the direction-randomizing influence of nucleation away from centrosomes. We propose that Prc1E and Kif4, together with catastrophe factors, promote "anti-parallel pruning" that enforces radial organization within asters and generates boundaries to microtubule growth between asters.
受精卵的分裂沟由两个从第一个纺锤体极生长出的大型微管星体定位。在这些星体在赤道相遇的地方，它们组装了一个盘状的相互作用区，由相互平行的微管束组成，这些微管束覆盖着染色体乘客复合物（CPC）和中央纺锤体，指导分裂沟的形成。在这里，我们研究了保持两个星体分离并在它们之间形成明显边界的机制，重点关注保守的胞质分裂中期区蛋白 Prc1 和 Kif4A。Prc1E，Prc1 的卵母细胞同源物，和 Kif4A 被招募到星体之间的相互作用区的相互平行的微管束中。Prc1E 对于 Kif4A 的募集是必需的，但反之则不然。微管正极的生长速度减慢并优先在相互作用区终止，导致阻止了星体之间的渗透，这取决于 Prc1E 和 Kif4A。出乎意料的是，Prc1E 和 Kif4A 也需要在孤立生长的大型星体中保持径向顺序，显然是为了补偿从中心体远离时对方向随机化的影响。我们提出 Prc1E 和 Kif4，连同崩溃因素，促进了“反平行修剪”，这加强了星体内部的径向组织，并在星体之间的微管生长之间产生了边界。
