Abstract:TX 75390-9111, USAThe Earth's rotation forced life to evolve under cyclic day and night environmental changes. In order to anticipate such daily cycles, prokaryote and eukaryote free-living organisms evolved intrinsic clocks that regulate physiological and behavioral 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 tha… Show more
“…Although no daily oscillation in parasite number has been detected in T . brucei -infected animals [25], we have recently shown that in culture, these extracellular parasites have intrinsic circadian rhythms in gene expression [27]. Such rhythms were identified by initially entraining the parasite population with temperature cycles followed by assessing the transcriptome by RNA-seq of samples every 4 hours for 2 days.…”
Section: What Did We Learn About Trypanosoma Brucei Circadian Rhythms?mentioning
confidence: 99%
“…brucei , transcription is believed to be constitutive and gene expression regulated mostly at the posttranscriptional level [38, 39]. The circadian clock in this parasite appears to also be driven mainly by posttranscriptional mechanisms because polycistronic units (PCUs) are not synchronous and individual transcripts within a PCU can be noncyclic or cyclic with different phases of transcript levels [27]. …”
Section: Are All Circadian Rhythms Dependent On a Transcription-transmentioning
confidence: 99%
“…We showed that T . brucei parasites (both mammalian-bloodstream and insect-procyclic forms) are able to entrain to temperature cycles differing by only 5°C, whereas the bloodstream forms do not appear to entrain to light/dark cycles [27]. It is possible, however, that—similar to peripheral clocks—other stimuli can also entrain these and other parasites, such as nutrient availability [49], hormones [50, 51], and perhaps even rhythmic immune pressure [52].…”
Section: Is Entrainment By Light Necessary To Establish Circadian Rhymentioning
confidence: 99%
“…brucei also has a circadian clock—it’s able to generate circadian rhythmic gene expression in the absence of host cells and in the absence of any stimuli [27]. What is this rhythm for?…”
Section: What Are the Selective Advantages For Parasites To Have A CImentioning
“…Although no daily oscillation in parasite number has been detected in T . brucei -infected animals [25], we have recently shown that in culture, these extracellular parasites have intrinsic circadian rhythms in gene expression [27]. Such rhythms were identified by initially entraining the parasite population with temperature cycles followed by assessing the transcriptome by RNA-seq of samples every 4 hours for 2 days.…”
Section: What Did We Learn About Trypanosoma Brucei Circadian Rhythms?mentioning
confidence: 99%
“…brucei , transcription is believed to be constitutive and gene expression regulated mostly at the posttranscriptional level [38, 39]. The circadian clock in this parasite appears to also be driven mainly by posttranscriptional mechanisms because polycistronic units (PCUs) are not synchronous and individual transcripts within a PCU can be noncyclic or cyclic with different phases of transcript levels [27]. …”
Section: Are All Circadian Rhythms Dependent On a Transcription-transmentioning
confidence: 99%
“…We showed that T . brucei parasites (both mammalian-bloodstream and insect-procyclic forms) are able to entrain to temperature cycles differing by only 5°C, whereas the bloodstream forms do not appear to entrain to light/dark cycles [27]. It is possible, however, that—similar to peripheral clocks—other stimuli can also entrain these and other parasites, such as nutrient availability [49], hormones [50, 51], and perhaps even rhythmic immune pressure [52].…”
Section: Is Entrainment By Light Necessary To Establish Circadian Rhymentioning
confidence: 99%
“…brucei also has a circadian clock—it’s able to generate circadian rhythmic gene expression in the absence of host cells and in the absence of any stimuli [27]. What is this rhythm for?…”
Section: What Are the Selective Advantages For Parasites To Have A CImentioning
“…Many parasite species exhibit daily rhythms in behaviour and/or development that are scheduled to optimally exploit periodicities in transmission opportunities and/or resource availability 8,9 . The parasitic protozoan Trypanosoma brucei, for example, possesses an intrinsic circadian clock that drives metabolic rhythms 10 . Malaria parasites complete their intra-erythrocytic developmental cycle (IDC) in 24h (or multiples of 24 h depending on the parasite species), suggesting a circadian basis to the asexual cell cycle 11 .…”
Malaria parasites complete their intra-erythrocytic developmental cycle (IDC) in multiples of 24 hours (depending on the species), suggesting a circadian basis to the asexual cell cycle, but the mechanism controlling this periodicity is unknown.Combining in vivo and in vitro approaches using rodent and human malaria parasites, we reveal that: (i) 57% of Plasmodium chabaudi genes exhibit 24 h "circadian" periodicity in transcription; (ii) 58% of these genes lose transcriptional rhythmicity when the IDC is out-of-synchrony with host rhythms; (iii) 9% of Plasmodium falciparum genes show circadian transcription under free-running conditions; (iv) Serpentine receptor 10 (SR10) has a circadian transcription profile and disrupting it in rodent malaria parasites shortens the IDC by 2-3 hours; (v) Multiple processes including DNA replication and the ubiquitin and proteasome pathways are affected by loss of coordination with host rhythms and by disruption of SR10. Our results show that malaria parasites are at least partly responsible for scheduling their IDCs explaining the fitness benefits of coordination with host rhythms.Daily fluctuations in environmental parameters such as light and temperature are assumed to select for the evolution of circadian clocks. In many organisms, circadian
RESULTSThe transcriptome of Plasmodium chabaudi responds to host circadian rhythms Transcriptome analyses of time series RNA sequencing datasets were performed with P.chabaudi parasites from infections that were in synchrony (phase aligned; "host rhythm matched") and out of synchrony (out of phase; "host rhythm mismatched") with host circadian rhythms (for details see methods section). Briefly, a controlled number of infected red blood cells (RBC) were sub-inoculated from donor mice into two groups of recipient mice (n = 43 per group) each housed under different light regimes (12 hours (h)
Temporal variations in the activity of arthropod vectors can dramatically affect the epidemiology and evolution of vector‐borne pathogens. Here, we explore the “Hawking hypothesis”, which states that these pathogens may evolve the ability to time investment in transmission to match the activity of their vectors. First, we use a theoretical model to identify the conditions promoting the evolution of time‐varying transmission strategies in pathogens. Second, we experimentally test the “Hawking hypothesis” by monitoring the within‐host dynamics of Plasmodium relictum throughout the acute and the chronic phases of the bird infection. We detect a periodic increase of parasitemia and mosquito infection in the late afternoon that coincides with an increase in the biting activity of its natural vector. We also detect a positive effect of mosquito bites on Plasmodium replication in the birds both in the acute and in the chronic phases of the infection. This study highlights that Plasmodium parasites use two different strategies to increase the match between transmission potential and vector availability. We discuss the adaptive nature of these unconditional and plastic transmission strategies with respect to the time scale and the predictability of the fluctuations in the activity of the vector.
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