Abstract
Pontin is a multifunctional protein having roles in various cellular processes including regulation of gene expression. Here, we addressed Pontin intracellular localization using two different monoclonal antibodies directed against different Pontin epitopes. For the first time, Pontin was directly visualized in nucleoli where it co-localizes with Upstream Binding Factor and RNA polymerase I. Nucleolar localization of Pontin was confirmed by its detection in nucleolar extracts and by electron microscopy, which revealed Pontin accumulation specifically in the nucleolar fibrillar centers. Pontin localization in the nucleolus was dynamic and Pontin accumulated in large nucleolar dots mainly during S-phase. Pontin concentration in the large nucleolar dots correlated with reduced transcriptional activity of nucleoli. In addition, Pontin was found to associate with RNA polymerase I and to interact in a complex with c-Myc with rDNA sequences indicating that Pontin is involved in the c-Myc-dependent regulation of rRNA synthesis.
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Acknowledgments
We would like to thank Pavel Draber, Marvin Fritzer and Kenneth M. Pollard for providing us with antibodies, Klaus Holzmann (University of Vienna, Vienna, Austria) for Pontin-GFP constructs and Jasper Manning for comments on the manuscript. This work was supported by grants from the Grant Agency of the Czech Republic 301/05/0601 (to D.S.), 304/05/0374 (to K.K.), the Czech Ministry of Education (MSM0021620806, 1K05009 and LC535 to I.R.), the Wellcome trust grant 075834/04/Z (to I.R.) and the institutional projects AV0Z50520514, AV0Z50110509 and AV0Z50390512 awarded by the Academy of Sciences of the Czech Republic. The work of O.H. was supported by grants SFB366/C12 and HU881/5-1 of the Deutsche Forschungsgemeinschaft, LOM grants of the Charité—Universitätsmedizin Berlin and the Sonnenfeld Stiftung. Z.C. was supported by a grant from the Grant Agency of the Czech Republic 303/03/H065 and A.L. by 204/07/0133.
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Communicated by G. Matera
Zuzana Cvačková and Kai F. Albring contributed equally to this work.
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Cvačková, Z., Albring, K.F., Koberna, K. et al. Pontin is localized in nucleolar fibrillar centers. Chromosoma 117, 487–497 (2008). https://doi.org/10.1007/s00412-008-0170-8
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DOI: https://doi.org/10.1007/s00412-008-0170-8