Abstract
Trypanosoma cruzi has been subdivided into seven Discrete Typing Units (DTUs), TcI-TcVI and Tcbat. Two major evolutionary models have been proposed to explain the origin of hybrid lineages, but while it is widely accepted that TcV and TcVI are the result of genetic exchange between TcII and TcIII strains, the origin of TcIII and TcIV is still a matter of debate. T. cruzi satellite DNA (SatDNA), comprised of 195 bp units organized in tandem repeats, from both TcV and TcVI stocks were found to have SatDNA copies type TcI and TcII; whereas contradictory results were observed for TcIII stocks and no TcIV sequence has been analyzed yet. Herein, we have gone deeper into this matter analyzing 335 distinct SatDNA sequences from 19 T. cruzi stocks representative of DTUs TcI-TcVI for phylogenetic inference. Bayesian phylogenetic tree showed that all sequences were grouped in three major clusters, which corresponded to sequences from DTUs TcI/III, TcII and TcIV; whereas TcV and TcVI stocks had two sets of sequences distributed into TcI/III and TcII clusters. As expected, the lowest genetic distances were found between TcI and TcIII, and between TcV and TcVI sequences; whereas the highest ones were observed between TcII and TcI/III, and among TcIV sequences and those from the remaining DTUs. In addition, signature patterns associated to specific T. cruzi lineages were identified and new primers that improved SatDNA-based qPCR sensitivity were designed. Our findings support the theory that TcIII is not the result of a hybridization event between TcI and TcII, and that TcIV had an independent origin from the other DTUs, contributing to clarifying the evolutionary history of T. cruzi lineages. Moreover, this work opens the possibility of typing samples from Chagas disease patients with low parasitic loads and improving molecular diagnostic methods of T. cruzi infection based on SatDNA sequence amplification.
Highlights
T. cruzi strains have been classified into seven Discrete Typing Units (DTUs), TcI-TcVI and Tcbat, which have been associated with different geographic distribution and transmission cycles
Two major evolutionary models have been proposed to explain the origin of hybrid lineages, but the phylogenetic relationships between the different T. cruzi DTUs are not completely understood
This study has been focused on the phylogenetic analysis of satellite DNA (SatDNA) sequences from DTUs TcITcVI aimed to clarifying the origin of T. cruzi lineages
Summary
Trypanosoma cruzi, the causative agent of Chagas disease, has been subdivided into seven Discrete Typing Units (DTUs), TcI-TcVI and Tcbat, which have been associated with different geographic distribution and transmission cycles [1,2,3,4]. After analyzing nine nuclear loci from 26 isolates representative of T. cruzi DTUs TcI-TcVI, Westenberger et al (2005) [12] postulated the hypothesis that an ancient fusion between TcI and TcII strains led, through a loss of TcI/II hybrid heterozygosity and independent clonal evolution, to the origin of TcIII and TcIV; later on a more recent hybridization event between TcII and TcIII strains generated TcV and TcVI by independent clonal evolution. On the other hand, following the analysis of five microsatellite loci and three mitochondrial genes from 75 TcI-TcVI stocks, Freitas et al (2006) [13] proposed the existence of at least three ancestral lineages (TcI-TcIII) and that two recent and independent genetic exchange events between TcII and TcIII strains resulted in TcV and TcVI; whereas the origin of TcIV could not be fully addressed due to the few isolates analyzed from this DTU
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