Abstract
Trypanosoma cruzi the agent of Chagas disease is a monophyletic but heterogeneous group conformed by several Discrete Typing Units (DTUs) named TcI to TcVI characterized by genetic markers. The trans-sialidase (TS) is a virulence factor involved in cell invasion and pathogenesis that is differentially expressed in aggressive and less virulent parasite stocks. Genes encoding TS-related proteins are included in a large family divided in several groups but only one of them contains TS genes. Two closely related genes differing in a T/C transition encode the enzymatically active TS (aTS) and a lectin-like TS (iTS). We quantified the aTS/iTS genes from TcII and TcVI aggressive and TcI low virulent strains and found variable aTS number (1–32) per haploid genome. In spite of being low TS enzyme-expressers, TcI strains carry 28–32 aTS gene copies. The intriguing absence of iTS genes in TcI strains together with the presence of aTS/iTS in TcII and TcVI strains (virulent) were observed. Moreover, after sequencing aTS/iTS from 38 isolates collected along the Americas encompassing all DTUs, the persistent absence of the iTS gene in TcI, TcIII and TcIV was found. In addition, the sequence clustering together with T/C transition analysis correlated to DTUs of T. cruzi. The consistence of TS results with both evolutionary genome models proposed for T. cruzi, namely the “Two Hybridization” and the “Three Ancestor” was discussed and reviewed to fit present findings. Parasite stocks to attempt genetic KO or to assay the involvement of iTS in parasite biology and virulence are finally available.
Highlights
Chagas disease is a chronic disabling disease caused by the protozoon Trypanosoma cruzi
Primers that amplify the region containing the single nucleotide polymorphism (SNP) that determines the loss of enzymatic activity were used together with two probes that differ in only one base (T/C transition) and comprise the Tyr codon or His codon, respectively
Data obtained from the aggressive strains RA, Cvd, CL Brener and the clone Q501/3 and Br (TcII) indicated that both the active TS (aTS) and inactive TS (iTS) genes were present with high variability in the gene copy number (Table 1)
Summary
Chagas disease is a chronic disabling disease caused by the protozoon Trypanosoma cruzi. Because of the predominantly clonal evolution of the parasite, these DTUs are rather stable in space and time, constituting a useful framework for epidemiological and evolutionary analysis [5]. This genetic diversity seems to be correlated with a geographical distribution [3,6,7] and with biological characteristics of the parasite such as culture growth, pathogenicity in mice, evolution in the insect vector, susceptibility to antichagasic drugs and tissular tropism in animal and human infections. Heterogeneous geographical distribution of DTUs has been extensively described suggesting that the genetic composition of the parasite could be partly responsible for the different manifestations of Chagas disease. In Southern Cone countries, TcI is usually associated to the sylvatic cycle whereas TcII, TcV, and TcVI are relatively more abundant than
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