How do planar polarity pathways affect tissue structure?
During development, many tissues increase in length and simultaneously narrow in width through polarized cell movements, cell shape changes, and oriented cell divisions [3]. The Frizzled pathway is required for a subset of these elongation events, including elongation by mesenchymal cells in the Xenopus notochord and the zebrafish dorsal midline [15-17]. Frizzled and Fat are also required for elongation by epithelial cells during the development of the Drosophila wing, the mouse neural tube, and the mouse kidney [18-20]. Although planar polarity pathways regulate elongation in both mesenchymal and epithelial tissues, the cell behaviors that lead to elongation in these contexts appear to be different. Epithelial cells remain interconnected by adherens junctions throughout tissue elongation, while mesenchymal cells are less tightly adherent and display classical migratory behavior. Therefore, planar polarity mechanisms can regulate a range of cell behaviors that contribute to tissue stru
