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Eukaryotic Cell, August 2009, p. 1106-1117, Vol. 8, No. 8
1535-9778/09/$08.00+0     doi:10.1128/EC.00025-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Dictyostelium discoideum CenB Is a Bona Fide Centrin Essential for Nuclear Architecture and Centrosome Stability {triangledown}

Sebastian Mana-Capelli,1 Ralph Gräf,2 and Denis A. Larochelle1*

Department of Biology, Clark University, 950 Main Street, Worcester, Massachusetts 01610,1 Institut für Biochemie und Biologie, ZELLBIOLOGIE, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, Haus 26, 14476 Potsdam-Golm, Germany2

Received 17 January 2009/ Accepted 13 May 2009

Centrins are a family of proteins within the calcium-binding EF-hand superfamily. In addition to their archetypical role at the microtubule organizing center (MTOC), centrins have acquired multiple functionalities throughout the course of evolution. For example, centrins have been linked to different nuclear activities, including mRNA export and DNA repair. Dictyostelium discoideum centrin B is a divergent member of the centrin family. At the amino acid level, DdCenB shows 51% identity with its closest relative and only paralog, DdCenA. Phylogenetic analysis revealed that DdCenB and DdCenA form a well-supported monophyletic and divergent group within the centrin family of proteins. Interestingly, fluorescently tagged versions of DdCenB were not found at the centrosome (in whole cells or in isolated centrosomes). Instead, DdCenB localized to the nuclei of interphase cells. This localization disappeared as the cells entered mitosis, although Dictyostelium cells undergo a closed mitosis in which the nuclear envelope (NE) does not break down. DdCenB knockout cells exhibited aberrant nuclear architecture, characterized by enlarged and deformed nuclei and loss of proper centrosome-nucleus anchoring (observed as NE protrusions). At the centrosome, loss of DdCenB resulted in defects in the organization and morphology of the MTOC and supernumerary centrosomes and centrosome-related bodies. The multiple defects that the loss of DdCenB generated at the centrosome can be explained by its atypical division cycle, transitioning into the NE as it divides at mitosis. On the basis of these findings, we propose that DdCenB is required at interphase to maintain proper nuclear architecture, and before delocalizing from the nucleus, DdCenB is part of the centrosome duplication machinery.

* Corresponding author. Mailing address: Department of Biology, Clark University, 950 Main Street, Worcester, MA 01610. Phone: (508) 793-7631. Fax: (508) 793-7174. E-mail: dlarochelle{at}clarku.edu

{triangledown} Published ahead of print on 22 May 2009.

Eukaryotic Cell, August 2009, p. 1106-1117, Vol. 8, No. 8
1535-9778/09/$08.00+0     doi:10.1128/EC.00025-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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