ROLE OF CELL GEOMETRY AND CHROMATIN ARCHITECTURE IN MODULATING CELLULAR RESPONSE TO ENVIRONMENTAL STIMULI

Abstract

Cells in tissues integrate multiple mechanical and biochemical stimuli from their microenvironment to modulate gene expression patterns and thereby, their behavior. Recent advances in single cell technologies have revealed the vast variability in cellular response to extracellular signals. Identifying factors that characterize and contribute to such cellular heterogeneity remains an active area of research. In this thesis, we demonstrate that a cell’s geometric state contributes to the non-genetic origins of cell-to-cell variability in response to environmental stimuli using multiple model systems. First, using a 2D culture model, we show that fibroblasts produce a geometry-dependent transcriptional response to compressive forces as well as TNF-alpha. Next, we found that cancer cells selectively activate fibroblasts in primed geometric states using a 3D fibroblast-tumor coculture model. We also demonstrate that the proliferation efficiency of laterally confined cells was determined by their geometry. These results prompted us to modulate the efficiency of signal-induced cell state switches by targeting factors known to regulate cell geometry. Enriching the population with activation-primed cell geometric states by either increasing matrix rigidity or directly micropatterning primed cell shapes increased fibroblast activation levels. In addition, reducing actomyosin contractility influenced the direction and efficiency of cell state transitions induced by laterally confined growth. Collectively, our results reveal that a cell’s geometry modulates its perception and response to extracellular signals. Furthermore, in addition to differential gene and protein expression, we also demonstrate that features that describe the chromatin organization can be used to describe signal-induced cell state transitions. We further illustrate a potential application of our work by identifying pathogenic cells in human breast cancer tissues. Taken together, we demonstrate that cell geometry and chromatin organization can be used to trace and modulate cellular responses to environmental signals.