How is planar polarity coordinated between cells?
A characteristic property of planar polarity systems is that polarity information in one cell can be transmitted to adjacent cells, a property that helps to align cells with their immediate neighbors. As a result, disrupting the Frizzled system in one cell can cause polarity disruptions up to several cell diameters away. For example, wild-type wing cells point their hairs toward cells that lack Frizzled and away from cells that lack Van Gogh, suggesting that cells can monitor the activity of their neighbors and orient their polarity accordingly [2,3]. These results have led to the longstanding idea that Frizzled – a well-known receptor for Wnt ligands – is active in a large-scale gradient that organizes planar polarity across hundreds of cells. However, there is currently no direct evidence for a gradient of Frizzled expression or activity, and the obvious candidates for generating such a gradient, the Wnt ligands, do not appear to be required for planar polarity in Drosophila. In cont
