The Nup107-160 complex and γ-TuRC regulate microtubule polymerization at kinetochores

Abstract

The metazoan nuclear pore complex (NPC) disassembles during mitosis, and many of its constituents distribute onto spindles and kinetochores, including the Nup107-160 sub-complex1,2. We have found that Nup107-160 interacts with the γ-tubulin ring complex (γ-TuRC), an essential and conserved microtubule (MT) nucleator3,4, and recruits γ-TuRC to unattached kinetochores. Unattached kinetochores nucleate MTs in a manner that is regulated by the Ran GTPase5; such MTs contribute to the formation of kinetochore fibers (k-fibers)6, MT bundles connecting kinetochores to spindle poles. Our data indicate that Nup107-160 and γ-TuRC act cooperatively to promote spindle assembly through MTs nucleation at kinetochores: HeLa cells lacking Nup107-160 or γ-TuRC were profoundly deficient in kinetochore-associated MT nucleation. Moreover, co-precipitated Nup107-160/γ-TuRC complexes nucleate MT formation in assays using purified tubulin. While Ran did not regulate MTs nucleation by γ-TuRC alone, Nup107-160/γ-TuRC complexes required Ran-GTP for MT nucleation. Our observations collectively show that Nup107-160 promotes spindle assembly through Ran-GTP-regulated nucleation of MT by γ-TuRC at kinetochores, and reveal a novel relationship between nucleoporins and the MT cytoskeleton.