Megan N. McClean

University of Wisconsin-Madison

Single-cell measurement and control to unravel yeast gene expression

Abstract:  Cells live in diverse environments and cellular communities, from the cells in our bodies to single-celled organisms surviving in the soil. To navigate these complex environments, cells must be able to sense and respond to a variety of signals. This is done through biological signaling pathways, consisting of sensors and interacting proteins, which process external signals and transmit information. A key step in understanding the transmission of extracellular signal to cellular outcomes is understanding how the dynamic activities of intracellular effectors, such as transcription factors, are interpreted and decoded by promoters to determine gene expression outcomes. In different stress conditions, the yeast general stress-response transcription factor Msn2 shows distinct nuclear localization patterns, going from sustained localization to burst-like localization, and there is evidence that these activity patterns determine gene expression output. In order to understand how promoters decode transcription factor dynamics we have generated a light-controlled version of Msn2 (opto-Msn2) and opto-Msn2 mutants with known differences in affinity for the canonical Msn2-binding site. Localization of these opto-Msn2 transcription factors to the nucleus drives gene expression from natural Msn2 target promoters and promoters can be classified as low, mid, and high sensitivity. Using a model of promoter activation in conjunction with the opto-Msn2s we have found that both transcription factor affinity and promoter characteristics play a role in determining promoter decoding. The interplay between TF dynamics and affinity means that changes in transcription factor affinity can qualitatively change how a promoter interprets stimuli (e.g. switching a glucose responsive promoter to a salt responsive promoter). In addition, using these transcription factors we are working to resolve the relationship between bursts of transcription factor activity and gene expression that leads to population-level heterogeneity.

Biosketch: Dr. Megan N. McClean is an Associate Professor in the Department of Biomedical Engineering at the University of Wisconsin-Madison. She received her B.A. from the University of California-Berkeley and her Ph.D. from Harvard University, both in Applied Mathematics. During her thesis work with Dr. Sharad Ramanathan, she used computational modeling in combination with single-cell microscopy to understand the mechanisms of crosstalk prevention and signaling specificity in Saccharomyces cerevisiae MAP kinase pathways. Prior to joining UW-Madison, Dr. McClean was a Lewis-Sigler Fellow at Princeton University where she utilized optogenetics and synthetic biology to develop tools for controlling biological circuits. At UW-Madison, Dr. McClean’s research group employs systems and synthetic biology approaches to understand biological signal processing in fungi, including human fungal pathogens, with implications for improving treatment strategies. Dr. McClean holds a Career Award at the Scientific Interface from the Burroughs Wellcome Fund, a Maximizing Investigators’ Research Award from the National Institute of General Medical Sciences, and a National Science Foundation CAREER Award.