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A more recent version of this article appeared on January 1, 2006
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Submitted on July 29, 2005
Accepted on October 18, 2005
*Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109; Molecular and Cellular Biology Program, University of Washington, Seattle, WA 98195; Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan 11529
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.
These authors contributed equally to this study.
Address correspondence to:
Harmit S. Malik (hsmalik{at}fhcrc.org)
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