Processing bodies are dynamically localised and associate with multiple organelles throughout the replicative lifespan of the yeast cell

Processing bodies (p-bodies) are cytoplasmic messenger ribonucleoprotein granules containing components of the mRNA degradation machinery, that form during stress conditions in the budding yeast Saccharomyces cerevisiae. P-bodies are conserved in eukaryotes and are related to other mRNP granules such as stress granules and neuronal granules. mRNP granules and their components self-assemble through a process of liquid-liquid phase separation, facilitated by protein-protein interaction by low complexity regions. Errors in this assembly process can cause a build-up of aggregated protein and have been implicated in the pathology of human neurodegenerative diseases such as amyotrophic lateral sclerosis. The exact role of p-bodies in normal cellular function is not known, but p-bodies are induced in conditions of stress, and can store mRNA that later re-enters translation, leading to the theory that they are sites of mRNA storage. A contrasting theory suggests them as sites of mRNA decay, due to the presence of deadenylation, decapping and exonuclease complexes within p-bodies. In this work, time-lapse fluorescence microscopy, using optimised high brightness, low photobleaching fluorescent protein fusions, was used to allow long term imaging of p-body localisation throughout the cell cycle of S. cerevisiae. Imaging was combined with microfluidic dissection of mother and daughter cells, to track single mother cells over their entire replicative lifespan (RLS) while continuing to monitor p body localisation. P-bodies were found to be localised in proximity to multiple different organelles with changes to localisation occurring through the cell cycle. Advanced replicative aged altered the profile of p-body localisation causing p-bodies to localise heavily to the mitochondria. P-bodies were also found to be inherited by daughter cells in a process dependent on the mRNA transport machinery and the p-body protein Dcp1. This inheritance was multigenerational with a single p-body moving between multiple daughter cells and was not lost in cells of advanced replicative age.