Epithelial cells undergo coordinated changes in cell shape during tubulogenesis. On the other hand, in cell competition, epithelial cells eliminate a transformed cell from the epithelial sheet. Those phenomena suggest that epithelial cells communicate with their neighbor cells, but little is known about the ways of cell-cell communication.

The actin cytoskeleton, which is accumulated in the lateral surfaces, is connected between adjacent epithelial cells via cadherin-mediated adherens junction. Actin filaments provide cells with contractile force with myosin motor proteins and myosin-independent force by actin polymerization. In this research project, I hypothesize that competition of actin-dependent force between adjacent cells may function in epithelial cell-cell communication. The specific aims are: 1) To characterize dynamics of actin filament flow beneath the lateral membrane of epithelial cells. 2) To characterize response to pulling force in the actin network in adherens junction. 3) To investigate whether actin-dependent force is related to recognition of transformed cells by normal cells in cell competition.

To monitor actin dynamics in the lateral surfaces, we directly visualize individual actin filaments by the single-molecule speckle (SiMS) microscopy. Using cultured monolayer epithelial cells, I will quantify the velocity of the actin filament flow at the lateral surface and the movement of actin filaments in adherens junction. The quantified data will be compared between adjacent cells. These results will provide fundamental knowledge on dynamics of actin-dependent force in the lateral surface of epithelial cells. Based on the above results, I will characterize actin dynamics in the lateral surfaces between normal cells and transformed cells proceed and in cell competition.

While the actin-dependent force that mediated via cadherin-based adherens junction is a candidate for a means of cell-cell communication, it is challenging to monitor the intracellular force directly in cells. Instead, monitoring motion of the objects that receive the intracellular force may provide a clue estimate dynamics of the force. In this project, I will monitor motion of actin filaments for the purpose. We recently developed a new SiMS microscopy, which enables the SiMS imaging for actin with the finest spatiotemporal resolution. Our new method will enable dissect actin dynamics at the lateral surface and adherens junctions for the first time. This study will provide critical clues for understanding regulatory mechanisms of cell-cell communication via intracellular force.