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Vol. 17, Issue 1, 485-497, January 2006
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* Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109;
Molecular and Cellular Biology Program, University of Washington, Seattle, WA 98195; and
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529
Submitted July 29, 2005;
Accepted October 18, 2005
Monitoring Editor: Kerry Bloom
Ciliated protozoans present several features of chromosome segregation that are unique among eukaryotes, including their maintenance of two nuclei: a germline micronucleus, which undergoes conventional mitosis and meiosis, and a somatic macronucleus that divides by an amitotic process. To study ciliate chromosome segregation, we have identified the centromeric histone gene in the Tetrahymena thermophila genome (CNA1). CNA1p specifically localizes to peripheral centromeres in the micronucleus but is absent in the macronucleus during vegetative growth. During meiotic prophase of the micronucleus, when chromosomes are stretched to twice the length of the cell, CNA1p is found localized in punctate spots throughout the length of the chromosomes. As conjugation proceeds, CNA1p appears initially diffuse, but quickly reverts to discrete dots in those nuclei destined to become micronuclei, whereas it remains diffuse and is gradually lost in developing macronuclei. In progeny of germline CNA1 knockouts, we see no defects in macronuclear division or viability of the progeny cells immediately following the knockout. However, within a few divisions, progeny show abnormal mitotic segregation of their micronucleus, with most cells eventually losing their micronucleus entirely. This study reveals a strong dependence of the germline micronucleus on centromeric histones for proper chromosome segregation.
The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).
These authors contributed equally to this work.
Address correspondence to: Meng-Chao Yao (mcyao{at}fhcrc.org) or Harmit S. Malik (hsmalik{at}fhcrc.org).
This article has been cited by other articles:
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  K. Mochizuki, M. Novatchkova, and J. Loidl DNA double-strand breaks, but not crossovers, are required for the reorganization of meiotic nuclei in Tetrahymena J. Cell Sci., July 1, 2008; 121(13): 2148 - 2158. [Abstract] [Full Text] [PDF]
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B. Cui, Y. Liu, and M. A. Gorovsky Deposition and Function of Histone H3 Variants in Tetrahymena thermophila Mol. Cell. Biol., October 15, 2006; 26(20): 7719 - 7730. [Abstract] [Full Text] [PDF]
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B. Cui and M. A. Gorovsky Centromeric Histone H3 Is Essential for Vegetative Cell Division and for DNA Elimination during Conjugation in Tetrahymena thermophila Mol. Cell. Biol., June 15, 2006; 26(12): 4499 - 4510. [Abstract] [Full Text] [PDF]
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M. D. Cervantes, R. S. Coyne, X. Xi, and M.-C. Yao The Condensin Complex Is Essential for Amitotic Segregation of Bulk Chromosomes, but Not Nucleoli, in the Ciliate Tetrahymena thermophila Mol. Cell. Biol., June 15, 2006; 26(12): 4690 - 4700. [Abstract] [Full Text] [PDF]
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