Epithelial polarization by the core planar cell polarity complex is exclusively non-autonomous

For cells to polarize collectively along a tissue plane, asymmetrically
localized planar cell polarity (PCP) complexes must form intercellular
contacts between neighboring cells. Yet, it is unknown whether asymmetric
segregation of PCP complexes requires cell-cell contact, or if cell-
autonomous, antagonistic interactions are sufficient for polarization. To
test this, we generated mouse chimeras consisting of dual PCP-reporter
cells mixed with unlabeled cells that cannot form PCP bridges. In the
absence of intercellular interactions, PCP proteins failed to polarize
cell autonomously. Rather, PCP-mediated contacts along single cell-cell
interfaces were sufficient to sort PCP components to opposite sides of the
junction, independent of junction orientation. Thus, intercellular binding
of PCP complexes is the critical step that initiates sorting of opposing
PCP complexes to generate asymmetry.