Diversity Supplement R00 - Brianna Parrington

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Contact PD/PI: Rijo-Ferreira, Filipa Project Summary Malaria is a deadly parasitic disease. The parasite population coordinately ruptures the red blood cells (RBCs), reinvades new ones and replicates until their cycle is completed, and then a new burst of RBCs occurs. The result is a paroxysmal fever that recurs with the same periodicity as the parasite asexual cell cycle: 48h or 72h for human-specific Plasmodium species and 24h for rodent-specific Plasmodium species. The mechanism for parasite synchronicity, which is central to this phenomenon, remains unknown. Because the asexual cell cycle across Plasmodium species has a duration that is multiple of 24h, this led me to hypothesize that the mechanism for fever periodicity is an endogenous circadian clock of the parasite. Circadian clocks regulate multiple physiological functions, from gene expression to behavior. Having circadian clocks that anticipate rhythmic changes in the environment is an evolutionary advantage for organisms. From bacteria to humans, mutations in clock components or desynchrony between the clock and the environment (e.g. chronic jet-lag) leads to reduced fitness, metabolic disruption, and shorter lifespan. Similarly, it has also been shown that a mismatch between host and parasite rhythms is detrimental for malaria parasite infection success. We demonstrated the existence of an intrinsic circadian clock in malaria parasites. Even in hosts whose circadian rhythms are disrupted through clock gene mutations, the parasite gene expression rhythms persist. In a wildtype infections the parasite expresses rhythmically 80% of its genes, whereas in an arrhythmic mutant host infection the parasite maintains rhythmic the expression of 60% of its genes, strongly supporting the existence of an intrinsic mechanism in the parasites regulating this phenomena. My findings have also highlighted that parasites sense and adjust their intrinsic clock to the host rhythms, if those rhythms exist. In addition, my preliminary data shows that these gene expression rhythms are not only due to the cell cycle of the parasite as previously assumed, but the rhythms also persist when parasites are in a quiescent state. In this proposal, I will test a central hypothesis that malaria synchronicity is the result of both the integration of host signals and an intrinsic circadian clock. Through in vivo and in vitro experiments, I will determine whether malaria parasites have an intrinsic clock independent of cell cycle by testing if parasite rhythms persist in the mosquito stage of the infection, and whether such rhythms are indeed circadian rhythms by testing for temperature compensation. These studies will generate a comprehensive framework to resolve a long-standing question in the malaria field. More broadly, by dissecting whether the periodicity of fevers is driven by host signals alone or by both host signals and an internal parasite clock, these studies will guide strategies to disrupt the synchronicity of the parasite. This will not only provide lessons of host-parasite interactions as it will potentially provide complementary approaches to tackle this deadly disease. Project Summary