Mapping the cellular stress responses that overseeRNA health in Saccharomyces cerevisiae
Cells must maintain an internal biochemical balance—homeostasis—to survive. Specific molecular mechanisms, globally known as stress responses, enable cells to reinstate homeostasis when facing biochemical imbalances. In my project, I am working in establishing a model system that would allow us to gain insights into the inner workings of a stress response responsible for protecting the RNAs of eukaryotic cells. This model exploits the molecular features of Huntington’s disease, a neurodegenerative disorder characterized by neuronal cell death due to the accumulation of toxic protein aggregates. These aggregates result from expression of expanded polyglutamine tracts encoded by CAG nucleotide repeat expansions (NREs) found in the HTT gene. Notably, such NREs also causes a profound structural change in the mRNA encoding HTT (hungtintin), which adopts a double-stranded conformation. We hypothesize that such RNA conformation may cause cellular harm. To test this hypothesis, I have introduced constructs encoding chimeric mRNAs consisting of the GFP coding sequence fused to HTT NREs into the baker’s yeast Saccharomyces cerevisiae. Expressing these constructs in wild type yeast as well as in a collection of candidate mutant strains revealed that deletion of the RNA helicase Ski2 increased the sensitivity to these constructs. This result suggests that Ski2 is part of a dedicated system to combat abnormal RNAs in eukaryotic cells. In the next step of my project, I will perform a focused genetic screen in yeast cells to identify additional genes in charge of protecting the cells from RNA health imbalances.