ABSTRACT
Trypanosoma cruzi, the etiological agent of Chagas disease, has been widely studied, reflecting both its medical importance and the particular features that make this pathogen an attractive model for basic biological studies. The repression of transcripts by messenger ribonucleoprotein (mRNP) complexes is an important pathway of post-transcriptional regulation in eukaryotes, including T. cruzi. RBSR1 is a serine-arginine (SR)-rich RNA-binding protein (RBP) in T. cruzi that contains one RNA-recognition motif (RRM); this protein has a primarily nuclear localization and is developmentally regulated, not being detected in metacyclic trypomastigotes. RBSR1 interacts with other RBPs, such as UBP1 and UBP2, and the nuclear SR-protein TRRM1. Phylogenetic analysis indicated that RBSR1 is orthologous to the human splicing factor SRSF7, what might indicate its possible involvement in pre-RNA processing. Accordingly, ribonomics data showed the enrichment of snoRNAs and snRNAs in the RBSR1 immunoprecipiatation complex, hence reinforcing the supposition that this protein might be involved in RNA processing in the nucleus.
Subject(s)
Protozoan Proteins/genetics , RNA-Binding Proteins/genetics , Trypanosoma cruzi/genetics , Amino Acid Sequence , Phylogeny , Protozoan Proteins/metabolism , RNA-Binding Proteins/metabolism , Trypanosoma cruzi/metabolismABSTRACT
Asymmetric mRNA localization is a sophisticated tool for regulating and optimizing protein synthesis and maintaining cell polarity. Molecular mechanisms involved in the regulated localization of transcripts are widespread in higher eukaryotes and fungi, but not in protozoa. Trypanosomes are ancient eukaryotes that branched off early in eukaryote evolution. We hypothesized that these organisms would have basic mechanisms of mRNA localization. FISH assays with probes against transcripts coding for proteins with restricted distributions showed a discrete localization of the mRNAs in the cytoplasm. Moreover, cruzipain mRNA was found inside reservosomes suggesting new unexpected functions for this vacuolar organelle. Individual mRNAs were also mobilized to RNA granules in response to nutritional stress. The cytoplasmic distribution of these transcripts changed with cell differentiation, suggesting that localization mechanisms might be involved in the regulation of stage-specific protein expression. Transfection assays with reporter genes showed that, as in higher eukaryotes, 3'UTRs were responsible for guiding mRNAs to their final location. Our results strongly suggest that Trypanosoma cruzi have a core, basic mechanism of mRNA localization. This kind of controlled mRNA transport is ancient, dating back to early eukaryote evolution.
