(12b) Intercellular Forces Regulate Mitosis and Migration within Epithelial Tissues

Introduction: Cell-cell and cell-matrix interactions are crucial for proper embryonic development and tissue homeostasis. The forces generated by these adhesive interactions often transduce mechanical stimuli into changes in intracellular signaling and gene expression. In addition, the spatial distribution of mechanical stress, dictated by the geometry of the tissue and requiring intercellular adhesion, has been shown to define patterns of proliferation within multicellular tissues. However, it is unclear how forces generated locally by individual cells influence this collective behavior. Here, we examined how local cell-cell mechanical communication influences proliferation within an epithelial tissue.

Materials and Methods: To increase intracellular tension within individual cells, a photoactivatable RhoA construct was expressed in mouse mammary epithelial tissues cultured on microcontact printed islands of fibronectin. Blue light activates this optogenetic form of RhoA, which leads to a concomitant increase in actomyosin contractility. A control construct lacking the RhoA coding sequence was used for comparison. Timelapse imaging enabled real-time visualization of cellular responses to local activation of RhoA in individual cells within multicellular tissues.

Results and Discussion: Optogenetic stimulation of RhoA within epithelial cells led to increased actin polymerization and decreased projected cell area, consistent with activation of the downstream effectors of RhoA. Two-dimensional traction force microscopy confirmed that optogenetic stimulation increased contractility and force generation, compared to control cells. Interestingly, we found that activating RhoA in a subset of cells within the epithelial tissues controlled proliferation of neighboring cells, as determined by timelapse imaging and quantification of cell division frequency. This pattern of proliferation was distinct from the pattern of cell motility within the epithelial tissue, which was also affected by intercellular force transmission. These data suggest that distinct signaling pathways downstream of adhesion forces lead to different emergent phenotypes.