Planar cell polarity – the process whereby cellular structures within the plane of an epithelium are oriented in the same direction – has been well studied in flies; studies that have revealed the role of non-canonical Wnt signalling in this process. Now Dabdoub et al. report the first study of planar polarity development in a mammalian system: the cochlea, in which stereociliary bundles on mechanosensory hair cells in the sensory epithelium must be unidirectionally oriented to ensure unimpaired hearing. Their findings, on p. 2375, show that several Wnts, particularly Wnt7a, are highly expressed in developing mouse cochlea. Moreover, the application of Wnt7a, or Wnt signalling inhibitors, to cultured cochlear explants causes disrupted bundle orientation, indicating that the molecular basis of planar polarity might have been conserved between vertebrates and invertebrates.

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