Quantifying Mechanical Behavior and Coherence of Epithelial Cell Monolayers

Cells generate forces as a means of interacting with their environment, including other cellular partners. Further, cells are sensitive to mechanical changes which often alter force generation or transmission. Mis-regulation of signaling in mechanosensitive pathways results in a variety of defects or diseases, including many epithelial cell cancers. Understanding the transmission of force within epithelial cells is crucial to addressing diseased states, and delineating the downstream impacts on important phenomenon such as contact inhibition of proliferation, cell fate determination, and apoptosis. Single epithelial cells primarily exert tensile by pulling against the extracellular basal substrate via focal adhesion. However, as epithelial cells grow into monolayers, the emergence of cell-cell junctions interconnects cytoskeletal structures between cells and fundamentally alters force transmission across the cellular landscape and the cellular colony. In this work, I specifically probe transmission of force throughout the cell, the peripheral E-cadherin junctions and fully internalized at the nucleus and chromatin. Using engineering proteins at key regions in the cell, I tracked the transduction of force and the impact on chromatin energetics deep within the nucleus showing that despite the dynamic nature of the cytoskeleton, there is still mechanical integration from the plasma membrane to the chromatin. Importantly, epithelial cells attain mechanical coherence as the monolayer matures, reaching a homeostatic energy state for the monolayer. Often, treatments that modulate the ability of the cytoskeleton to generate force result in concomitant energetic changes derived from the motion of chromatin. Thus, mechanical integration that spans a single cell is also present in the cell collective, shedding new light on the poorly elucidated behaviors of epithelial cell monolayers.