Understanding mRNA Condensation and Its Role in Translational Control during Stress

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Project Summary/ Abstract How cells dynamically control their proteome in response to stress is a fundamental aspect of understanding how organisms are able to react to changing environments. Two representative features of the cellular stress response, which is universally conserved across eukarya and occurs in response to a variety of different noxious environmental conditions, are 1) the upregulation of the cytoprotective heat shock proteins and 2) biomolecular condensation of RNA and protein into assemblies. Most translation is shut down, while proteins involved in the stress response are efficiently produced. How translation is reprogrammed to favor heat shock protein production post-transcriptionally is poorly understood, but biomolecular condensation has been linked to translational control. Basic questions are incompletely answered: 1) Which mRNAs condense in response to stress? 2) What cellular mechanisms are responsible for mRNA condensation? And 3) What is the functional relevance of mRNA condensation to translational control? Herein, we present unpublished work measuring mRNA solubility of >5,000 genes during temperature stress in S. cerevisiae by biochemical sedimentation followed by RNA-Sequencing. These data inform our hypothesis that blocking translation initiation triggers condensation of an mRNA through specific binding by unknown protein factor(s). We also predict that mRNA condensation during stress is an adaptive process contributing to the preferential translation of stress response messages. To test these hypotheses, we aim to confirm that blocking translation initiation triggers mRNA condensation both on a transcriptome-wide and individual message level, to determine protein factors required for mRNA condensation, and to test the role of mRNA condensation in translational reprogramming during stress. Preliminary data measuring the solubility of both native and reporter mRNAs support that blocking translation initiation triggers condensation. We have identified and will interrogate a set of the translation initiation factors as candidates putatively required for mRNA condensation. We will test whether the candidates are required for mRNA condensation and measure the translational effect of perturbing mRNA condensation during stress. Biomolecular condensates are intimately related to cellular RNA homeostasis, and their dysfunction has been linked to the pathogenesis of several neurodegenerative diseases including Alzheimer's and Parkinson's. Knowledge of how mRNAs condense and the functional role of condensation informs disease pathogenesis and may inform future treatments for those affected.