Spatio‐temporal mRNA dynamics in Stress Granules and Processing Bodies

Gene expression patterns are shaped by post-transcriptional processes such as mRNA splicing, export, localization, translation, and degradation. mRNA binding proteins regulate these processes and are assumed to function in microscopically visible cytoplasmic biological condensates, also called RNA-protein granules. These membraneless organelles form distinct cellular environments. How molecules are partitioned between these compartments and the surrounding cellular space and the functional consequences of this localization are not well understood. During this PhD project, the localization of mRNAs to two classes of RNA-protein granules, stress granules (SGs) and processing bodies (PBs), and the resulting effects on translation and mRNA degradation during the integrated stress response were investigated. Using single mRNA imaging in living human cells, we found that the interactions of mRNAs with SGs and PBs have different dynamics and that specific RNA binding proteins can anchor mRNAs within these compartments. During recovery from stress, we showed that mRNAs within PBs are selectively translationally repressed. Once SGs and PBs have dissolved, mRNAs that had been localized inside are translated and degraded at similar rates as their cytosolic counterparts. The work presented here, provides a framework for using single-molecule measurements to directly investigate local and temporal aspects of mRNA regulation in the context of biological condensates in their native cellular environment.