The Earth's rotation forced life to evolve under cyclic day and night environmental changes. To anticipate such daily cycles, prokaryote and eukaryote free-living organisms evolved intrinsic clocks that regulate physiological and behavioural processes. Daily rhythms have been observed in organisms living within hosts, such as parasites. Whether parasites have intrinsic molecular clocks or whether they simply respond to host rhythmic physiological cues remains unknown. Here, we show that Trypanosoma brucei, the causative agent of human sleeping sickness, has an intrinsic circadian clock that regulates its metabolism in two different stages of the life cycle. We found that, in vitro, ∼10% of genes in T. brucei are expressed with a circadian rhythm. The maximum expression of these genes occurs at two different phases of the day and may depend on a post-transcriptional mechanism. Circadian genes are enriched in cellular metabolic pathways and coincide with two peaks of intracellular adenosine triphosphate concentration. Moreover, daily changes in the parasite population lead to differences in suramin sensitivity, a drug commonly used to treat this infection. These results demonstrate that parasites have an intrinsic circadian clock that is independent of the host, and which regulates parasite biology throughout the day.
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The authors thank M. Phillips for help with starting parasite cultures at UT Southwestern and advice on the suramin sensitivity experiments, P. Nakashe for the library preparations of the light/dark data sets, M. Broderick for help during the oxidative stress experiment, L. Pinho, I. Kornblum and G. Kilaru for technical support, J. Stubblefield for help during the blood collection, D. Barry, M. Phillips, C. Green and M. Vaz for reading the manuscript and C. Janzen for the GFP-PAD1utr cell line. The work was supported by an HHMI International Early Career Scientist award (55007419, to L.M.F.), EMBO Installation Grant (2151) to L.M.F., Fundação para a Ciência e Tecnologia awards (SFRH/BD/51286/2010 to F.R.-F. and IF/00595/2014 to N.L.B.-M.). J.S.T. is an Investigator in the Howard Hughes Medical Institute.
The authors declare no competing financial interests.
Supplementary Figures 1–10 and Supplementary Tables 1 and 2. (PDF 11397 kb)
List of genes, their RPKM counts and circadian algorithms analyses for bloodstream forms entrained with temperature. (XLSX 1626 kb)
List of genes, their RPKM counts and circadian algorithms analyses for insect procyclic forms entrained with temperature. (XLSX 1241 kb)
List of genes, their RPKM counts and circadian algorithms analyses for bloodstream forms entrained with light. (XLSX 382 kb)
GO term enrichment analysis of bloodstream and procyclic forms throughout the day. (XLSX 39 kb)
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Rijo-Ferreira, F., Pinto-Neves, D., Barbosa-Morais, N. et al. Trypanosoma brucei metabolism is under circadian control. Nat Microbiol 2, 17032 (2017). https://doi.org/10.1038/nmicrobiol.2017.32
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