Divergent Single-Cell Trajectories in Homeostatic Control and Genome Instability during Aging

Abstract

The budding yeast has a long and storied history as a model organism for biological inquiry. Accordingly, experiments into the replicative aging of S. cerevisiae have yielded critical insights into evolutionarily conserved mechanisms of aging. Historically, replicative aging experiments have relied on labor-intensive techniques for lifespan measurement, and methods to observe physiological function across a cell’s lifespan were not available. Recently, novel microfluidic devices have been developed for the whole-lifespan monitoring of yeast cells during replicative aging. Using time-lapse microscopy, these devices allow researchers to measure replicative lifespan in much higher throughput and to quantitate various aspects of cell biology during aging, with single-cell resolution, across a cell’s entire lifetime. In this dissertation, I engineer a low-cost motorized light microscopy system with open-source software, aimed at increasing the accessibility this new technology. Recently, an early life decline in vacuolar/lysosomal acidity in the budding yeast has been found to underlie the aging process. I use our microfluidic device to investigate the consequences of lysosomal/vacuolar dysfunction during yeast replicative aging. I find that this loss acidity triggers an iron sulfur cluster deficiency and is associated with a age-associated genome instability. However, only a subset of cells mount the expected iron starvation gene expression program, leading to divergent single-cell trajectories of iron dyshomeostasis during aging. Cells which mount an iron starvation response during aging have limited iron sulfur cluster deficiency and extended survival and passage through periods of genome instability during aging.