Many epithelial tissues display planar cell polarity (PCP). This phenomenon has been best studied in Drosophila in which most epidermal cells produce hairs at one side that all point in the same direction. The molecular mechanisms underlying PCP establishment remain controversial. Key players are the transmembrane proteins Starry night (Stan; also known as Flamingo), Frizzled (Fz) and Vang Gogh (Vang, also known as Strabismus). Stan, a protocadherin, forms homodimeric bridges between cells. These bridges appear to link Fz and Vang on the abutting distal and proximal faces of adjacent cells, and their resulting asymmetric distributions polarise both cells to point the same way. Now, Struhl, Casal and Lawrence () report the surprising finding that Vang is not essential for cell polarisation. Instead, asymmetric interactions between Stan and Stan/Fz are sufficient to define polarity, and Vang plays an accessory role, probably by enhancing the capacity of Stan to interact with Stan/Fz. These results challenge current models of PCP, although the authors propose an alternative that may reconcile the data.
