PROJECT SUMMARY / ABSTRACT Coordination of gene expression across nuclear and mitochondrial genomes within a cell is crucial for the correct assembly of oxidative phosphorylation (OXPHOS) complexes that make up the electron transport chain and enable aerobic life. This mitonuclear balance must be tightly orchestrated by molecular players across cellular compartments and critically must adapt to a dynamic cellular milieu. Balanced gene expression across these genomes poses a unique challenge when we consider complex cellular states, for example aged cells that must deal with declining proteomes among other insults or long-lived, morphologically complex cells like neurons where this coordination could rapidly breakdown. Failure to maintain proper mitonuclear balance and the resulting mitochondrial dysfunction is implicated in a myriad of human diseases, including neurodegenerative diseases and cancer, as well as the aging process itself. Our lab has previously demonstrated that mitochondrial and nuclear genomes regulate coordinated gene expression programs on the translational but not transcriptional level for dual-origin OXPHOS genes required to build respiratory complexes during mitochondrial biogenesis. These studies utilized simultaneous cytosolic and mitochondrial ribosome profiling techniques, but to date have only been performed in healthy mid-log phase yeast. Our long-term objectives are now to understand how mitochondrial genomes are regulated across diverse cellular states and biological contexts. Our specific aims for this proposal that will help us attain these objectives are twofold: (1) to determine the effects of a deteriorating cellular environment during a cell’s lifespan on mitochondrial gene expression and mitonuclear coordination using replicatively-aged yeast and (2) determine how post-mitotic neurons which must have different mitochondrial demands in the soma compared to distal neurites can maintain proper mitonuclear coordination and appropriately regulate mitochondrial gene expression over the lifespan of this long-lived and morphologically complex cell. In summary this proposed research will advance our knowledge of mitochondrial gene regulation and mitochondrial biology in cellular states with relevance to human disease and aging.