Planar cell polarity signaling: coordination of cellular orientation across tissues.

Establishment of Planar Cell Polarity (PCP) in epithelia, in the plane of an epithelium, is an important feature of the development and homeostasis of most organs. Studies in different model organisms have contributed a wealth of information regarding the mechanisms that govern PCP regulation. Genetic studies in Drosophila have identified two signaling systems, the Fz/PCP and Fat/Dachsous system, which are both required for PCP establishment in many different tissues in a largely non-redundant manner. Recent advances in vertebrate PCP studies have added novel factors of PCP regulation and also new cellular features requiring PCP-signaling input, including the positioning and orientation of the primary cilium of many epithelial cells. This review focuses mostly on several recent advances made in the Drosophila and vertebrate PCP field and integrates these within the existing PCP-signaling framework.