Stress granules and processing bodies oscillate in a circadian manner.

MALCOLM M; PENAZZI LG; GARBARINO PICO E

Congreso; LVI SAIB - XV SAMIGE ? Online Joint Meeting 2020; 2020

Stress granules (SG) and processing bodies (PB) are membrane-less organelles, responsible for storage and cytoplasmicprocessing of mRNA, which share some components such as mRNA and RNA binding proteins. SGs, which are alsoconstituted by translation initiation factors, the minor subunit of the ribosome 40S, and translation stalled mRNAs, are formedin response to different stress stimuli, typically through phosphorylation of the eIF2 factor. PBs, on the other hand, are enrichedin factors involved in mRNA degradation, translational repression, and RNA-mediated silencing, and they are constitutivemembrane-less organelles, although they increase in number with stress. In previous studies we found that SG formationpresents temporary changes in number and size in mouse fibroblast synchronized cultures (NIH/3T3). We wonder whether thecircadian clock controls these temporal changes. The cells were synchronized with dexamethasone and harvested every 4 hfor 68 h. We induced the formation of SGs with sodium arsenite (oxidative stress). On the other hand, we analyzed PBs in notstressed N2A cells (neuroblastome cell line). We also studied the temporal expression profile of p-eIF2α (factor involved inSG aggregation) and eIF3, the marker we used for detecting SGs, by Western blot. Cell cultures were arrested in order toprevent cell cycle progression, and we confirm their quiescence state by flow cytometry. We performed a doubleimmunolabeling of SGs (eIF3 and G3BP1) and PB (GE-1/HEDLS and DDX6) by immunocytochemistry. We observed thatNIH/3T3 and N2A cells show daily rhythms in SGs and PBs, respectively, for three variables: number, area, and signalintensity with the estimated parameters showing periods of approximately 24 h, for two cycles. The subtle differences that wefound between both translation initiation factors eIF3 and eIF2α, would not be responsible for generating the changes observedin SGs. These findings strongly suggest that the molecular circadian clock rhythmically controls SGs and PBs. The resultspresented here reveal new ways in which circadian clocks modulate mRNA translation, stability, and storage in the cytoplasm