Tracking Cell Fate with Synthetic Memory Circuits

Abstract

The capacity of cells to sense transient environmental cues and activate prolonged cellular responses is a recurring biological feature relevant to disease development and stem cell differentiation. While biologically significant, heterogeneity in sustained responses is frequently masked by population-level measurements, preventing exploration of cellular subsets. This thesis describes the development of tools for tracking the fate of subpopulations that differentially respond to DNA damage or hypoxia, illuminating how heterogeneous responses to these inputs affect long- term cell behavior and susceptibility to future dysfunction or disease. Taking a synthetic biology approach, I engineered genetic positive feedback loops that employ bistable, auto-regulatory transcription to retain memory of exposure to a stimulus. Strongly responsive cells activate these memory devices, while more weakly responsive cells do not, enabling the tracking and characterization of two subpopulations. Chapters 2 and 4 detail a yeast memory device used to track cells that differentially activate repair pathways after DNA damage. Chapter 3 describes a mammalian memory system used to follow subpopulations that uniquely respond to DNA damage or hypoxia. Both the yeast and mammalian systems capture subpopulations that differ in biological behavior for multiple generations, indicating a transmissible memory of the environmental perturbations that contributes toward distinct cell fates. Collectively, this work advances our understanding of the relationship between heterogeneous cell behavior and cellular memory in the context of disease development.