SMAUG MEMBRANELESS ORGANELLES REGULATE mRNAs THAT ENCODE MITOCHONDRIAL ENZYMES

PIMENTEL, J; PESSOA, J; GRECCO, H; THOMAS MG; PASCUAL M; CORBAT, A; CARMO-FONSECA; BOCCACCIO GL; BOSCAGLIA, L; AVIV M; PLESSIS, A; CASADO, M

CABA

Congreso; Congreso de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular; 2020

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Smaugis a conserved translational repressor thatbind transcripts that containspecific motifs termed Smaug recognition elements (SREs).We and othersreported that, among several target mRNAs, nuclear transcripts that encode mitochondrial enzymes are regulated by Drosophila Smaug (bruzzone et al EMBO R).We have previously shown that both insect and vertebrate Smaug orthologs form membraneless organelles (MLOs) dubbed Smaug-bodies (JBC  , Baez JCB). Smaug bodies are distinct from Processing Bodies (PBs), a well-known type of MLO alsoinvolved in mRNA regulation.The formation of MLOs and related molecular condensates is thought to involve liquid-liquid phase separation (LLPS) processes driven by multiple protein-protein interactions,and we found that a N-terminal deletion of mammalian Smaug1 seriously affect Smaug1 MLO formation.Loss of function of Smaug orthologs seriously affected mitochondrial function and this phenotype was rescued by full-length Smaug1 but not by Smaug1 deletion mutants with defective MLO formation (Fernandez Alvarez Biorxiv). In addition, pharmacological inhibition of complex I induced Smaug1-body dissolution whereas strong uncoupling by exposure to CCCP elicited no effect. Finally, we found that mammalian Smaug1 MLOs interact with nuclear mRNAs that encode mitochondrial enzymes. Specifically, single molecule FISH revealed that succinate dehydrogenase subunit B (SDHB) and ubiquinol-cytochrome C reductase core protein 1 (UQCRC1) mRNAs associated with Smaug1-bodies. Moreover, the formation of Smaug MLOs is important for mRNA binding. Deletion mutants with impaired MLO condensation show reduced mRNA binding and complex I inhibition reduces the presence ofUQCRC1 and SDHB mRNAs in Smaug MLOs. We propose that mitochondrial activity controls Smaug1 MLO dynamics, thus allowing for the regulated release of nuclear mRNAs that encode key mitochondrial proteins.