PRC1 and EB1 Binding Dynamics Reveal a Solidifying Central Spindle during Anaphase Compaction in Human Cells
During mitosis the spindle undergoes morphological and dynamic changes. It reorganizes at the onset of anaphase when the antiparallel bundler PRC1 accumulates and recruits central spindle proteins to the midzone. Little is known about how the dynamic properties of the central spindle change during its morphological changes in human cells. Using gene editing, we generated human cells that express from their endogenous locus fluorescent PRC1 and EB1 to quantify their native spindle distribution and binding/unbinding turnover. EB1 plus end tracking revealed a general slowdown of microtubule growth, while PRC1, similar to its yeast orthologue Ase1, binds increasingly strongly to compacting antiparallel microtubule overlaps. KIF4A and CLASP1 bind more dynamically to the central spindle, but also show slowing down turnover. These results show that the central spindle gradually becomes more stable during mitosis, in agreement with a recent bundling, sliding and compaction model of antiparallel midzone bundle formation in the central spindle during late mitosis.