Valdez Venecia, Ma Meisheng, Gouveia Bernardo, Zhang Rui, Petry Sabine
Princeton University, Department of Molecular Biology, Princeton, New Jersey, United States.
Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine (St. Louis, Missouri, United States).
bioRxiv. 2023 Dec 18:2023.12.18.571906. doi: 10.1101/2023.12.18.571906.
In large vertebrate spindles, the majority of microtubules are formed via branching microtubule nucleation, whereby microtubules nucleate along the side of pre-existing microtubules. Hepatoma up-regulated protein (HURP) is a microtubule-associated protein that has been implicated in spindle assembly, but its mode of action is yet to be defined. In this study, we show that HURP is necessary for RanGTP-induced branching microtubule nucleation in egg extract. Specifically, HURP stabilizes the microtubule lattice to promote microtubule formation from γ-TuRC. This function is shifted to promote branching microtubule nucleation in the presence of TPX2, another branching-promoting factor, as HURP's localization to microtubules is enhanced by TPX2 condensation. Lastly, we provide a structure of HURP on the microtubule lattice, revealing how HURP binding stabilizes the microtubule lattice. We propose a model in which HURP stabilizes microtubules during their formation, and TPX2 preferentially enriches HURP to microtubules to promote branching microtubule nucleation and thus spindle assembly.
在大型脊椎动物纺锤体中，大多数微管是通过分支微管成核形成的，即微管沿着预先存在的微管侧面成核。肝癌上调蛋白（HURP）是一种与微管相关的蛋白，已被证明与纺锤体组装有关，但其作用方式尚未明确。在本研究中，我们表明HURP是卵提取物中RanGTP诱导的分支微管成核所必需的。具体而言，HURP稳定微管晶格，以促进γ-TuRC形成微管。在另一种促进分支的因子TPX2存在的情况下，该功能转变为促进分支微管成核，因为TPX2的凝聚增强了HURP在微管上的定位。最后，我们提供了HURP在微管晶格上的结构，揭示了HURP的结合如何稳定微管晶格。我们提出了一个模型，其中HURP在微管形成过程中稳定微管，而TPX2优先将HURP富集到微管上，以促进分支微管成核，从而促进纺锤体组装。
