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The nuclear structure and the control of cell cycle and differentiation of Trypanosoma cruzi


The establishment of microbial infections depends of parasite adaptation and survival in their hosts. To survive, the Trypanosoma cruzi, a protozoan parasite, causative agent of Chagas disease, alternates between forms that divide in the insect vector intestinal lumen (epimastigote forms), or in mammalian cell cytoplasm (amastigote forms), to non-proliferative forms but capable of entering mammalian cells after being exposed to extreme conditions in the blood stream or insect feces. Transformation from one form the other involves complex mechanism poorly understood, by which the parasite sense the environmental conditions, progressing through the cell cycle, or undergoing differentiation. Identification of the signals and mechanisms that led to one or other process is therefore relevant to understand and control infection. In a previous project, our laboratory started studies about the nuclear organization of T. cruzi with the goal to understand the process involved in the gene expression control during the different developmental stages of the parasite. We found large changes in the nuclear structure by comparing replicative and non-replicative forms of this protozoan. These structural changes correlated with a general transcription shutdown [1] and changes in the chromatin structure and organization [2]. To further understand the meaning of these changes we localized the replication and transcription sites in the nuclei of this parasite. We found that DNA precursors were incorporated close to the nuclear envelope, and later moved to the nuclear interior [3], in agreement with the findings that they are in continuous movement and become restrained to the nuclear periphery to replicate [4]. By using antibodies specific for the RNA polymerase II large subunit of T. cruzi, characterized in our laboratory [5], we observed that transcription is also located in restricted domains, close to the nucleolus and that these domains disappeared when transcription was inhibited (in preparation). To understand these differential localization of replication and transcription, we started to investigate the structure and modifications in the chromatin, recognized to have a central role in the organization and coupling of nuclear events [6]. We found differential phosphorylation and acetylation of histones during the cell cycle and after differentiation of the parasite into non-replicative forms.Therefore, our main goal in this project is to further characterize these structural and functional changes in the T. cruzi nuclei during the cell cycle and differentiation. These studies may help us to understand how the parasite controls his life cycle. (AU)

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