Planar cell polarity and tissue design: Shaping the Drosophila wing membrane.

Planar cell polarity (PCP) describes the orientation of a cell within the plane of an epithelial cell layer. During tissue development, epithelial cells normally align their PCP so that they face in the same direction. This alignment allows cells to move in a common direction, or to generate structures with a common orientation. A classic system for studying the coordination of epithelial PCP is the developing Drosophila wing. The alignment of epithelial PCP during pupal wing development allows the production of an array of cell hairs that point towards the wing tip. Multiple studies have established that the Frizzled (Fz) PCP signaling pathway coordinates wing PCP. Recently, we have found that the same pathway also controls the formation of ridges on the Drosophila wing membrane. However, in contrast to hair polarity, ridge orientation differs between the anterior and posterior wing. How can the Fz PCP pathway generate a different relationship between hair and ridge orientation in different parts of the wing? In this Extra View article, we discuss membrane ridge development drawing upon our recent PLoS Genetics paper and other, published and unpublished, data. We also speculate upon how our findings impact the ongoing debate concerning the interaction of the Fz PCP and Fat/Dachsous pathways in the control of PCP.