Chromosomal localization of seven cloned antigen genes provides evidence of diploidy and further demonstration of karyotype variability in Trypanosoma cruzi

The karyotype of Trypanosoma cruzi was studied by pulsed field gel electrophoresis (PFGE) in conditions that allowed 20–25 chromosome bands to be detected. However, several of these bands were present in non-equimolar amounts, suggesting that the total chromosome number is considerably higher. The patterns obtained with the different cloned and uncloned strains were unique, suggesting that the karyotype of T. cruzi is highly variable. The chromosomal localizations of seven cloned genes were determined by Southern blotting of PFGE-separated chromosomes. Three of the clones gave rise to similar patterns and mapped on a chromosome or a family of chromosomes larger than 1.6 Mb. Two clones mapped on either single or pairs of chromosomes, which in some cases differed considerably in size between the different strains tested, suggesting that extensive chromosome rearrangements occur in T. cruzi. Another clone hybridized to several chromosomes in most strains and probably represents a family of genes. Lastly, one clone hybridized to nearly all chromosomes. Many of the clones hybridized to pairs of restriction fragments in the different strains, suggesting that they are allelic. For one of the clones it was possible to provide further evidence for the allelic nature of the fragments by establishing detailed restriction maps around them and by showing that the two fragments in a pair hybridized to chromosomes which differed slightly in size. Taken together, the results infer that the genome of T. cruzi epimastigotes is diploid.