NuSAP participates in metaphase spindle length control in mammalians

Precise chromosome congression and segregation require proper assembly of a steady-state metaphase spindle, which is dynamic and maintained by continuous microtubule flux. NuSAP is a microtubule-stabilizing and -bundling protein that promotes chromosomedependent spindle assembly. However, its function in spindle dynamics remains unclear. Here, we demonstrate that NuSAP regulates the dynamics and length control of the metaphase spindle. Mechanistically, NuSAP facilitates kinetochore capture and spindle assembly via promoting Eg5 binding with microtubules. It also prevents excessive microtubule depolymerization through interacting with Kif2A and reduces its spindle-pole localization. NuSAP is phosphorylated by Aurora A at Ser-240 during mitosis, and this phosphorylation promotes its interaction with Kif2A on the spindle body and reduces its localization to the spindle poles, thus maintaining the proper spindle microtubule flux. NuSAP knockout resulted in shorter spindle formation with faster microtubule flux and chromosome misalignment. Taken together, we uncover that NuSAP participates in spindle assembly, dynamics, and metaphase spindle length control via affecting microtubule flux and Kif2A localization.