Dynamic composition of stress granules in Trypanosoma brucei.

Stress granules (SGs) are stress-induced RNA condensates consisting of stalled initiation complexes resulting from translational inhibition. The biochemical composition and function of SGs are highly diverse, and this diversity has been attributed to different stress conditions, signalling pathways involved and specific cell types. Interestingly, mRNA decay components, which are found in ubiquitous cytoplasmic foci known as processing bodies (PB), have also been identified in SG proteomes. A major challenge in current SG studies is to understand the cause of SG diversity, as well as the function of SG under different stress conditions. Trypanosoma brucei is a single-cellular parasite that causes Human African Trypanosomiasis (sleping sickness). In this study, we showed that by varying the supply of extracellular carbon sources during starvation, cellular ATP levels changed rapidly, resulting in SGs of different compositions and dynamics. We identified a subset of SG components, which dissociated from the SGs in response to cellular ATP depletion. Using expansion microscopy, we observed sub-granular compartmentalization of PB- and SG-components within the stress granules. Our results highlight the importance of cellular ATP in SG composition and dynamics, providing functional insight to SGs formed under different stress conditions. Author summary: Stress granules (SGs) and processing bodies (PBs) are cytoplasmic RNA granules containing multiple proteins with functions in translation initiation and mRNA degradation. mRNA and proteins can move between SGs, PBs and translating polysomes, likely regulating gene expression under different cellular conditions. However, little is known about the cellular factors regulating the dynamic behaviour of these RNA granules. In the unicellular Trypanosome parasites, SGs are formed under starvation stress and during differentiation. In this study, we found that in starved T. brucei, the composition and the dynamics of the SGs are distinct, depending on the supply of extracellular carbon sources and subsequent cellular energy (ATP) levels. Using expansion microscopy and super-resolution microscopy, functionally-distinct protein components are found in different sub-granular compartments within the SGs. Our findings emphasized the dynamic changes in SG composition, organization, and potential functions, which are affected by cellular ATP levels that can fluctuate under various stress conditions. [ABSTRACT FROM AUTHOR]