Estudo sobre o reparo por recombinação homóloga em diferentes linhagens de Trypanosoma cruzi

Abstract

Trypanosoma cruzi is the etiological agent of Chagas Disease. The variety of symptoms of Chagas disease can be associated with the genetic variability of different strains of Trypanosoma cruzi. Studies of infection with different mixtures of different parasite strains demonstrated difference in tropism among them, demonstrating that the genetic variability among parasite populations result in different phenotypes. Despite the uncertainty about the position of certain populations of Trypanosoma cruzi and their phylogenetic relationships, phylogeny studies recently subdivided T. cruzi into six discrete taxonomic units, named T. cruzi I to T. cruzi VI. Even though reports the occurrence of recombination events are rare in the literature, it is known that they occur between populations, creating a division between hybrid and non-hybrid populations of the parasite. The Trypanosoma cruzi DNA metabolism is focus of study of our group. Repair by homologous recombination is one of the major DNA repair pathways. This pathway is responsible for dealing with breaks in the double strands of DNA, generated by external agents or the metabolism of organisms. While other organisms have other pathways, such as non-homologous end joining to deal with double strand breaks, Trypanosoma cruzi relies only on repair by homologous recombination to deal with this kind of damage, since major proteins on the non-homologous endoining pathway could not be identified. In view of this fact, we studied the response to ionizing radiation, an agent capable of causing double strand breaks, in different strains of Trypanosoma cruzi. Although the parasite does not face high doses of radiation on his life cycle, it can resist to doses as high as 500Gy of ionizing radiation. It was observed, after the exposure to ionizing radiation, that non-hybrid lineages have a distinct phenotype from hybrid lines in response to this kind of damage. The analysis of genes involved in the repair revealed differences in the sequence of certain proteins between strains, and the prediction of the impact of these changes made on HADDOCK software, showed that the interaction between the proteins of each strain could be different. Also, the basal levels of transcripts of the proteins BRCA2 and Rad51, essential to the process, are different between the strains could mean the difference in observed phenotype. We also demonstrate that cell signaling is quick and important to the repair process, since the inhibition of signaling pathways is able to delay the resumption of growth after irradiation