www.jcb.org/cgi/doi/10.1083/jcb.201408039 JCB 171

The collective alignment of cell polarity across the tissue plane is a phenomenon known as planar cell polarity (PCP). Exempli-fied by the uniform orientation of bristles covering the insect epidermis or of the hairs covering the mammalian body surface (Fig. 1 A), PCP patterns can align over thousands, even billions of cells. This phenomenon is controlled by the so-called PCP pathway, which integrates global directional cues to produce locally polarized cell behaviors. There has been a recent surge in interest in PCP after discoveries that various processes such as vertebrate gastrulation, mammalian ear patterning and hear-ing, and neural tube closure all require a conserved set of PC