Abstract
BackgroundThe Trypanosoma cruzi genome was sequenced from a hybrid strain (CL Brener). However, high allelic variation and the repetitive nature of the genome have prevented the complete linear sequence of chromosomes being determined. Determining the full complement of chromosomes and establishing syntenic groups will be important in defining the structure of T. cruzi chromosomes. A large amount of information is now available for T. cruzi and Trypanosoma brucei, providing the opportunity to compare and describe the overall patterns of chromosomal evolution in these parasites.Methodology/Principal FindingsThe genome sizes, repetitive DNA contents, and the numbers and sizes of chromosomes of nine strains of T. cruzi from four lineages (TcI, TcII, TcV and TcVI) were determined. The genome of the TcI group was statistically smaller than other lineages, with the exception of the TcI isolate Tc1161 (José-IMT). Satellite DNA content was correlated with genome size for all isolates, but this was not accompanied by simultaneous amplification of retrotransposons. Regardless of chromosomal polymorphism, large syntenic groups are conserved among T. cruzi lineages. Duplicated chromosome-sized regions were identified and could be retained as paralogous loci, increasing the dosage of several genes. By comparing T. cruzi and T. brucei chromosomes, homologous chromosomal regions in T. brucei were identified. Chromosomes Tb9 and Tb11 of T. brucei share regions of syntenic homology with three and six T. cruzi chromosomal bands, respectively.ConclusionsDespite genome size variation and karyotype polymorphism, T. cruzi lineages exhibit conservation of chromosome structure. Several syntenic groups are conserved among all isolates analyzed in this study. The syntenic regions are larger than expected if rearrangements occur randomly, suggesting that they are conserved owing to positive selection. Mapping of the syntenic regions on T. cruzi chromosomal bands provides evidence for the occurrence of fusion and split events involving T. brucei and T. cruzi chromosomes.
Highlights
Trypanosoma cruzi is a protozoan parasite transmitted to vertebrate hosts by insect vectors causing Chagas disease, known as American trypanosomiasis
Several syntenic groups are conserved among all isolates analyzed in this study
The syntenic regions are larger than expected if rearrangements occur randomly, suggesting that they are conserved owing to positive selection
Summary
Trypanosoma cruzi is a protozoan parasite transmitted to vertebrate hosts by insect vectors causing Chagas disease, known as American trypanosomiasis. Natural populations of T. cruzi undergo clonal evolution with rare events of genetic recombination [6]. Hybrid lineages have been identified in natural T. cruzi populations [7,8,9,10]. On the basis of a number of genetic and biochemical markers, the strains of T. cruzi have been divided into six discrete typing units (DTU) designed as TcI to VI [11]. The Trypanosoma cruzi genome was sequenced from a hybrid strain (CL Brener). A large amount of information is available for T. cruzi and Trypanosoma brucei, providing the opportunity to compare and describe the overall patterns of chromosomal evolution in these parasites
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