Planar polarity establishment in an expansive epithelium: coordinating asymmetry across biological scales  

Planar cell polarity (PCP) is universal tissue property in which cellular structures and behaviors polarize and align with a tissue plane. Our lab uses the developing mouse epidermis as a model to investigate how planar polarity is established in an expansive and proliferative epithelium in which polarity is organized and coordinated across biological scales: from the molecular to junctional, cellular, appendage and organ scales. Planar polarity is, by definition, a multicellular phenomenon and yet, until recently, it was unknown whether asymmetry requires intercellular interactions at cell contacts, or if PCP proteins can intrinsically segregate within individual cells. Using mosaic approaches in mouse embryos we have reconstructed planar polarity in vivo, and determined the number of cells required for the establishment of junctional- and cellular-level asymmetries. Building on the finding that partitioning of PCP protein complexes is a strictly non cell-autonomous process, I will discuss recent work investigating how cell-cell contacts initiate planar polarization and restore it after cells divide.