Mechanism of spindle stability and poleward flux regulating spindle length during the metaphase.

During metaphase, the spindle stabilizes chromosomes and maintains its size despite continuous microtubule poleward flux. To investigate the mechanism of the spindle stability and how the poleward flux regulates the spindle size, we establish a minimal spindle model that incorporates kinetochores, microtubules, spindle poles, and microtubule sliding proteins such as kinesin-5, microtubule depolymerizing proteins such as kinesin-13, and microtubule crosslinking proteins such as NuMA. We find that the poleward flux stabilizes the spindle by regulating the spindle length and the length of antiparallel microtubule overlaps to achieve equal rates of microtubule sliding, plus-end polymerization, and minus-end depolymerization. We reveal the underlying mechanism of how the poleward flux rate scales linearly with the spindle length and microtubule overlap length in small cells and how microtubule nucleation affects spindle dynamics in large cells.