Thermo-sensing and argonaute-dependent transcriptome remodelling in trypanosomes

Abstract

Vector-borne parasites, such as African trypanosomes, experience temperature fluctuation due to fever symptomatic of infection, during developmental life cycle transitions, or due to diurnal shift. Mechanisms underpinning RNA-based thermo-sensing remain largely uncharacterised in these and other eukaryotic cells, however. Notably, trypanosomes exhibit almost exclusive polycistronic transcription, such that gene expression controls are dominated by post-transcriptional mechanisms mediated by mRNA-binding proteins and thousands of mRNA 3-untranslated regions (3-UTRs). Here, we quantify the transcriptomes and proteomes of bloodstream form Trypanosoma brucei following growth at 34{degrees}C, 37{degrees}C or 40{degrees}C for six hours. Approximately fifty genes encoding classical (co-)chaperones, with (UUA)n-rich 3-UTRs, display the expected heat-shock response. The expression of approximately 1,000 additional transcripts is also correlated with temperature, and these transcripts have relatively long 3-UTRs enriched in potentially complementary poly-purine tracts, poly-pyrimidine tracts, and palindromic sequences (P5-UTRs). To assess the potential impacts of mRNA secondary structure transcriptome-wide, we quantify mRNAs in cells lacking the central RNA interference nuclease argonaute (AGO1). Strains lacking AGO1 display increased retroposon expression, as expected, and strikingly abrogated thermo-regulation of transcripts with P5-UTRs. Thus, thermo-sensing involves argonaute-dependent transcriptome-remodelling in trypanosomes. We propose a post-transcriptional zipper hypothesis whereby access to regulatory motifs is controlled by temperature-sensitive mRNA secondary structure.