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Vol. 17, Issue 9, 3806-3818, September 2006

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The Nup107-160 Nucleoporin Complex Is Required for Correct Bipolar Spindle Assembly

Arturo V. Orjalo^*, Alexei Arnaoutov, Zhouxin Shen^*, Yekaterina Boyarchuk, Samantha G. Zeitlin, Beatriz Fontoura, Steven Briggs^*, Mary Dasso, and Douglass J. Forbes^*

Sections of *Cell and Developmental Biology and Molecular Biology, Division of Biological Sciences, University of California-San Diego Medical School, La Jolla, CA 92093-0347; Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-5431; and Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039

Submitted November 18, 2005; Revised June 9, 2006; Accepted June 19, 2006
Monitoring Editor: Karsten Weis

The Nup107-160 complex is a critical subunit of the nuclear pore. This complex localizes to kinetochores in mitotic mammalian cells, where its function is unknown. To examine Nup107-160 complex recruitment to kinetochores, we stained human cells with antisera to four complex components. Each antibody stained not only kinetochores but also prometaphase spindle poles and proximal spindle fibers, mirroring the dual prometaphase localization of the spindle checkpoint proteins Mad1, Mad2, Bub3, and Cdc20. Indeed, expanded crescents of the Nup107-160 complex encircled unattached kinetochores, similar to the hyperaccumulation observed of dynamic outer kinetochore checkpoint proteins and motors at unattached kinetochores. In mitotic Xenopus egg extracts, the Nup107-160 complex localized throughout reconstituted spindles. When the Nup107-160 complex was depleted from extracts, the spindle checkpoint remained intact, but spindle assembly was rendered strikingly defective. Microtubule nucleation around sperm centrosomes seemed normal, but the microtubules quickly disassembled, leaving largely unattached sperm chromatin. Notably, Ran-GTP caused normal assembly of microtubule asters in depleted extracts, indicating that this defect was upstream of Ran or independent of it. We conclude that the Nup107-160 complex is dynamic in mitosis and that it promotes spindle assembly in a manner that is distinct from its functions at interphase nuclear pores.

This article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E05-11-1061) on June 28, 2006.

Address correspondence to: Douglass Forbes (DForbes{at}UCSD.edu)

Abbreviations used: NPC, nuclear pore complex

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