Elucidating Dynamics and Heterogeneity in the Yeast Stress Response

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The goal of this project is to understand how some cells in a microbial population can survive environmental stress whereas other identical cells in the same environment cannot. This phenomenon is referred to as 'culture heterogeneity'. The goals of the project are to examine how much variation in stress response and survival exists in a culture of yeast cells, and to then understand the regulatory mechanisms that give rise to that variation. Using yeast as a model for free-living microbes, the project will use single-cell microscopy to study individual cells. Understanding both the sources and patterns of cell-to-cell variation in stress responses and survival will help society to understand how to control microbial cultures, which has benefits to human health, agriculture, and environmental remediation. In addition to this research, the project will develop an outreach program called 'Ask a Scientist', which aims to link K-6 elementary classrooms in the Madison, WI area with professional and student scientists who will serve as a science pen-pal for the class. The goal of the project is to provide teachers with a mechanism to increase young students' exposure to science and professional scientists. This project will combine past advances in network inference with single-cell investigations to understand the dynamics and heterogeneity in the yeast Saccharomyces cerevisiae stress response. Past work inferred a systems-level signaling network that controls the yeast transcriptomic response to salt stress. The network has proven powerful, but does not capture signaling dynamics or cell-to-cell signaling variation, both of which are important in microbial stress defense. This project will test network predictions through single-cell analyses designed to capture signaling dynamics and culture heterogeneity by: 1) performing single-cell microscopy in living cells before and after salt treatment to determine the localization dynamics of pairs of fluorescently tagged regulators of the yeast stress response to characterize the correlations in regulator localization patterns, and 2) follow dynamic changes in representative transcripts in single living cells that express a fluorescently tagged version of the responsible transcription factor. Results will relate the dynamics of transcription-factor localization to dynamics of target mRNAs and to the dynamics of cellular stress tolerance in single cells. Together, results of this research will increase understanding of the mode and mechanism of culture heterogeneity, which will in turn illuminate sources of variation in the upstream cellular signaling network.