Genetic subdivisions within Trypanosoma cruzi (Discrete Typing Units) and their relevance for molecular epidemiology and experimental evolution

Abstract

BACKGROUND: This paper summarizes the main results obtained on Trypanosoma cruzi genetic diversity and population structure since this parasite became the theme of many genetic and molecular studies in the early seventies. RESULTS: T. cruzi exibits a paradigmatic pattern of long-term, clonal evolution, which has structured its natural populations into several discrete genetic subdivisions or "Discrete Typing Units" (DTU). Rare hybridization events are nevertheless detectable in natural populations and have been recently obtained in the laboratory. CONCLUSIONS: The DTUs and natural clones of T. cruzi constitute relevant units for molecular epidemiology and experimental evolution. Experimental mating opens the way to an in-depth knowledge of this parasite's formal genetics.

Figure 1

Neighbour joining dendrograms based on the analysis of 20 RAPD* primers (left) and 22 isoenzymatic* loci (right) showing the genetic relationships between 49 Trypanosoma cruzi stocks and T. cruzi marinkellei stock M1117. The scale indicates the Jaccard distance [39] along the branches. Six genetic clusters, or Discrete Typing Units (DTUs [14]), were distinguished and their names are given in the central column between the dendrograms. DTU 1 corresponds to the 1rst major lineage of T. cruzi, while the second major lineage is subdivided into DTUs 2a to e. Diagnostic RAPD fragments and isoenzymatic patterns, which were specifically observed in the stocks of a given cluster of the dendrograms (tags [14]), are indicated at the corresponding nodes (after [17]).