Search

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 G, 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 G, 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 G, phase but concentrated at the nuclear periphery in the S phase to the G, 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. Universidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, Brazil Univ Fed Rio de Janeiro, Inst Biofis Carlos Chagas Filho, Lab Ultraestrutura Celular Hertha Meyer, BR-21941 Rio de Janeiro, Brazil Univ Liege, Lab Cellular & Tissue Biol, Liege, Belgium Universidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, Brazil Web of Science