Genome Evolution of Trypanosoma cruzi

Abstract

Abstract The protozoan parasite Trypanosoma cruzi is the etiologic agent of Chagas disease which is a major public health problem in Latin America. T. cruzi isolates have been classified into six main lineages (TcI–TcVI) based on genetics, phylogeographical and epidemiological studies. Its genome is complex, with a high variability among isolates, mainly as result of differences in the amount of repetitive sequences such as multigenic families encoding surface proteins and retrotransposons. Despite genome size variation and karyotype polymorphism, T. cruzi exhibits high conservation of chromosome structure with large syntenic groups conserved among all isolates. Comparison between Trypanosoma brucei and T. cruzi genomes suggests the occurrence of fusion and split events involving the chromosomes of these two species. Key Concepts: Trypanosoma cruzi chromatin is poorly condensed during cell division, which precludes the use of conventional cytogenetic analysis. Chromosomal bands can be separated by Pulsed‐Field Gel Electrophoresis (PFGE). A chromosomal band may contain co‐migrating chromosomes, which are not necessarily homologous. The exact number of chromosomes remains unknown. T. cruzi is essentially diploid, although some larger aneuploid fragments have been described. Six distinct T. cruzi lineages have been proposed on the basis of geographical, phylogenetic and epidemiological studies. Large syntenic regions are conserved among T. cruzi isolates and also between trypanosomatids. T. cruzi lineages exhibit a striking conservation of chromosome structure. The T. cruzi centromeric region consists of a GC‐rich strand‐switch domain composed mainly of degenerated retrotransposons. T. cruzi telomeres are composed of tandem repeats of the hexamer TTAGGG followed by a 189 bp species‐specific sequence. The subtelomeric region is enriched with members of surface protein gene families and could be a site of generation of new variants of surface antigens. The mapping of the syntenic regions on T. cruzi chromosomal bands provides evidence of the occurrence of fusion and split events involving T. brucei and T. cruzi chromosomes.