Project Summary Planar cell polarity (PCP) is a highly conserved pathway that regulates the coordination of polarity in cells along a single tissue plane, and is fundamental in development and tissue function. A defining feature of PCP is the asymmetric localization of its core components, which transition from uniform to asymmetric membrane distribution over time. Frizzled (Fz) localizes with Dishevelled (Dvl) on one side of the cell, while Vangl and Prickle (Pk) localize to the other. It is thought that transmembrane components Vangl and Fz recruit opposing complexes between cells while the cytoplasmic components, Dvl and Pk, mediate feedback interactions that amplify asymmetry within cells. Thus, both intercellular and intracellular core PCP protein feedback interactions are central to how we think PCP is established, however, the specific feedback interactions underlying PCP establishment, and whether they primarily occur within cells or between cells, are not well understood. The overall goal of this work is to determine how the core PCP proteins self-organize via feedback interactions to coordinate the establishment and propagation of polarity. What is needed to investigate these questions is a reductionist system that can uncouple intracellular feedback interactions from those that occur between cells, and isolate these interactions from the influence of tissue level polarizing cues. Our lab has established the murine skin as a powerful model system to investigate conserved mechanisms of PCP establishment. We have shown that primary keratinocytes isolated and cultured in vitro display spontaneous and locally aligned planar polarity in the absence of any global cue. I propose to further simplify this system using micropatterning and cell- mimicking interfaces to reconstitute the establishment and propagation polarity from its minimal components. Using a combination of live imaging, super-resolution microscopy, and genetic manipulation, I will determine the molecular mechanisms underlying the PCP protein interactions that drive polarity establishment and propagation. This study will provide new and innovative tools that will push the PCP field forward. Importantly, completion of the proposed aims will address an essential, but poorly understood question, by providing insight into the molecular mechanisms driving PCP establishment and revealing fundamental features of epithelial biology and tissue organization.