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Eukaryotic Cell, December 2002, p. 944-953, Vol. 1, No. 6
1535-9778/02/$04.00+0     DOI: 10.1128/EC.1.6.944-953.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Chromosome Localization Changes in the Trypanosoma cruzi Nucleus

Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo,¹ Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil,² Laboratory of Cellular and Tissue Biology, University of Liège, Liège, Belgium³

Received 19 April 2002/ Accepted 20 August 2002

Chromosome localization in the interphase nuclei of eukaryotes depends on gene replication and transcription. Little is known about chromosome localization in protozoan parasites such as trypanosomes, which have unique mechanisms for the control of gene expression, with most genes being posttranscriptionally regulated. In the present study, we examined where the chromosomes are replicated in Trypanosoma cruzi, the agent of Chagas' disease. The replication sites, identified by the incorporation of 5-bromodeoxyuridine, are located at the nuclear periphery in proliferating epimastigote forms in the early S phase of the cell cycle. When the S phase ends and cells progress through the cell cycle, 5-bromodeoxyuridine labeling is observed in the nuclear interior, suggesting that chromosomes move. We next monitored chromosome locations in different stages of the cell cycle by using a satellite DNA sequence as a probe in a fluorescence in situ hybridization assay. We found two distinct labeling patterns according to the cell cycle stage. The first one is seen in the G₁ phase, in hydroxyurea-arrested epimastigotes or in trypomastigotes, which are differentiated nondividing forms. In all of these forms the satellite DNA is found in dots randomly dispersed in the nucleus. The other pattern is found in cells from the S phase to the G₂ phase. In these cells, the satellite DNA is found preferentially at the nuclear periphery. The labeling at the nuclear periphery disappears only after mitosis. Also, DNA detected with terminal deoxynucleotidyl transferase is found distributed throughout the nuclear space in the G₁ phase but concentrated at the nuclear periphery in the S phase to the G₂ phase. These results strongly suggest that T. cruzi chromosomes move and, after entering the S phase, become constrained at the nuclear periphery, where replication occurs.

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