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Vol. 20, Issue 8, 2146-2159, April 15, 2009

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Mlp1 Acts as a Mitotic Scaffold to Spatially Regulate Spindle Assembly Checkpoint Proteins in Aspergillus nidulans

Colin P. De Souza^*, Shahr B. Hashmi^*, Tania Nayak, Berl Oakley, and Stephen A. Osmani^*

*Department of Molecular Genetics, Ohio State University, Columbus, OH 43210; Columbia University, Department of Pathology and Cell Biology, New York, NY 10032; and Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045

Submitted August 27, 2008; Accepted February 11, 2009
Monitoring Editor: Mark J. Solomon

During open mitosis several nuclear pore complex (NPC) proteins have mitotic specific localizations and functions. We find that the Aspergillus nidulans Mlp1 NPC protein has previously unrealized mitotic roles involving spatial regulation of spindle assembly checkpoint (SAC) proteins. In interphase, An-Mlp1 tethers the An-Mad1 and An-Mad2 SAC proteins to NPCs. During a normal mitosis, An-Mlp1, An-Mad1, and An-Mad2 localize similarly on, and around, kinetochores until telophase when they transiently localize near the spindle but not at kinetochores. During SAC activation, An-Mlp1 remains associated with kinetochores in a manner similar to An-Mad1 and An-Mad2. Although An-Mlp1 is not required for An-Mad1 kinetochore localization during early mitosis, it is essential to maintain An-Mad1 in the extended region around kinetochores in early mitosis and near the spindle in telophase. Our data are consistent with An-Mlp1 being part of a mitotic spindle matrix similar to its Drosophila orthologue and demonstrate that this matrix localizes SAC proteins. By maintaining SAC proteins near the mitotic apparatus, An-Mlp1 may help monitor mitotic progression and coordinate efficient mitotic exit. Consistent with this possibility, An-Mad1 and An-Mlp1 redistribute from the telophase matrix and associate with segregated kinetochores when mitotic exit is prevented by expression of nondegradable cyclin B.

Address correspondence to: Stephen A. Osmani (osmani.2{at}osu.edu)

Abbreviations used: NE, nuclear envelope; NORs, nucleolar organizing region; NPC, nuclear pore complex; SAC, spindle assembly checkpoint; SPB, spindle pole body.

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Nucleolar Separation from Chromosomes during Aspergillus nidulans Mitosis Can Occur Without Spindle Forces

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