NuSAP regulates microtubule flux and Kif2A localization to ensure accurate chromosome congression

Sun et al. report that NuSAP regulates spindle length control and microtubule flux to ensure chromosome congression. They find that Aurora A-mediated phosphorylation of NuSAP at S240 promotes its interaction with Kif2A on the spindle body and reduces its localization on the spindle poles. Precise chromosome congression and segregation requires the 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 chromosome-dependent spindle assembly. However, its function in spindle dynamics remains unclear. Here, we demonstrate that NuSAP regulates the metaphase spindle length control. Mechanistically, NuSAP facilitates kinetochore capture and spindle assembly by promoting Eg5 binding to microtubules. It also prevents excessive microtubule depolymerization through interaction with Kif2A, which reduces Kif2A 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 with the spindle poles, thus maintaining proper spindle microtubule flux. NuSAP knockout resulted in the formation of shorter spindles with faster microtubule flux and chromosome misalignment. Taken together, we uncover that NuSAP participates in spindle assembly, dynamics, and metaphase spindle length control through the regulation of microtubule flux and Kif2A localization.