Role of TbRRM1 in transcriptional regulation in T. brucei

SÁNCHEZ, DO; NÍTTOLO, AG; LEVY, GV; BAÑUELOS, C

Congreso; XXXI Molecular Parasitology Meeting; 2020

Genetics Society of America

Since transcription in trypanosomatids is polycistronic, regulation of gene expression occurs mainly at the post-transcriptional level mediated by RNA binding proteins (RBPs). In our lab we focus on elucidating the function of the RBP TbRRM1 of T. brucei. Previously, we have demonstrated that TbRRM1 is essential for survival in procyclic and bloodstream form stages since its silencing affects the parasite growth curve, produces aberrant phenotypes and promotes cell death by a mechanism compatible with apoptosis. On the other hand, RNA-Seq assays carried out in procyclic cells by Roditi´s lab showed that levels of 1/3 of the transcripts decreased after TbRRM1 depletion and many of them proceed from genes located in a particular region of chromosome 9. These authors also suggested that TbRRM1 could be a chromatin remodeler since the increase of H3 occupancy observed after TbRRM1 depletion. Results from our lab, indicated that TbRRM1 depletion affects RNA Pol II transcription-elongation rate and leads to compacted chromatin in a polycistronic transcription unit located in the same chromosome.In the present work we showed that TbRRM1 is both recruited to chromatin and to specific RNAs. In addition, we characterized TbRRM1 binding properties in the presence of RNAse A, RNAse H and Actinomycin D. Because our results suggested that TbRRM1 binds DNA-RNA hybrids, we decided to study the formation of R-loops in TbRRM1 depleted parasites by immunofluorescence with the S9.6 antibody. These experiments showed a significant increase in the number of positive intranuclear dots, thus suggesting that TbRRM1 prevents R-loops accumulation.Altogether, our results suggest that RNA Pol II transcription-elongation impairment, induced by TbRRM1 depletion, might be a consequence of R-loops accumulation.