In Trypanosoma cruzi, the etiologic agent of Chagas disease, Rad51 (TcRad51) is a central enzyme for homologous recombination. Here we describe the different roles of TcRad51 in DNA repair. Epimastigotes of T. cruzi overexpressing TcRAD51 presented abundant TcRad51-labeled foci before gamma irradiation treatment, and a faster growth recovery when compared to single-knockout epimastigotes for RAD51. Overexpression of RAD51 also promoted increased resistance against hydrogen peroxide treatment, while the single-knockout epimastigotes for RAD51 exhibited increased sensitivity to this oxidant agent, which indicates a role for this gene in the repair of DNA oxidative lesions. In contrast, TcRad51 was not involved in the repair of crosslink lesions promoted by UV light and cisplatin treatment. Also, RAD51 single-knockout epimastigotes showed a similar growth rate to that exhibited by wild-type ones after treatment with hydroxyurea, but an increased sensitivity to methyl methane sulfonate. Besides its role in epimastigotes, TcRad51 is also important during mammalian infection, as shown by increased detection of T. cruzi cells overexpressing RAD51, and decreased detection of single-knockout cells for RAD51, in both fibroblasts and macrophages infected with amastigotes. Besides that, RAD51-overexpressing parasites infecting mice also presented increased infectivity and higher resistance against benznidazole. We thus show that TcRad51 is involved in the repair of DNA double strands breaks and oxidative lesions in two different T. cruzi developmental stages, possibly playing an important role in the infectivity of this parasite.

The Protist kingdom individuals are the most ancestral representatives of eukaryotes. They have inhabited Earth since ancient times and are currently found in the most diverse environments presenting a great heterogeneity of life forms. The unicellular and multicellular algae, photosynthetic and heterotrophic organisms, as well as free-living and pathogenic protozoa represents the protist group. The evolution of sex is directly associated with the origin of eukaryotes being protists the earliest protagonists of sexual reproduction on earth. In eukaryotes, the recombination through genetic exchange is a ubiquitous mechanism that can be stimulated by DNA damage. Scientific evidences support the hypothesis that reactive oxygen species (ROS) induced DNA damage can promote sexual recombination in eukaryotes which might have been a decisive factor for the origin of sex. The fact that some recombination enzymes also participate in meiotic sex in modern eukaryotes reinforces the idea that sexual reproduction emerged as consequence of specific mechanisms to cope with mutations and alterations in genetic material. In this review we will discuss about origin of sex and different strategies of evolve sexual reproduction in some protists such that cause human diseases like malaria, toxoplasmosis, sleeping sickness, Chagas disease, and leishmaniasis.

pela orientação deste trabalho, apoio, conselhos, amizade e paciência comigo. Muito Obrigada! À Profa. Dra.Catarina Satie Takahashi, pela simpatia, amizade e por nos proporcionar momentos de confraternização e muita descontração no laboratório. Ao Prof. Dr. Ademilson Espencer E. Soares, coordenador do Programa de Pós-Graduação em Genética da FMRP/USP pelo apoio, paciência e simpatia. Às Professoras Dra. Zilá Luz Paulino Simões e Dra. Márcia Maria Gentile Bitondi, por gentilmente disponibilizar o uso de alguns aparelhos de seus laboratórios. Às Secretárias do Departamento de Genética, Susie e Sílvia, pela atenção, simpatia e por sempre esclarecerem as minhas dúvidas. Aos professores membros da banca examinadora, pela disponibilidade em analisar este trabalho e pelas sugestões e críticas. Ao Departamento de genética e à Faculdade de Medicina de Ribeirão Preto, pela estrutura oferecida para o desenvolvimento desse projeto. Aos técnicos do Laboratório de Citogenética e Mutagênese do Departamento de Genética da FMRP/USP, Luís Augusto da Costa Junior e Sueli Aparecida Neves, pela amizade, pelas longas e filosóficas conversas, ensinamentos e ótimas gargalhadas que me proporcionaram. Á Dona Cleuza por cuidar sempre com muito amor de todos nós. À FAPESP, CNPq e CAPES, pelo auxílio financeiro, para a realização deste trabalho.