Planar polarity of hair cells in the chick inner ear is correlated with polarized distribution of c-flamingo-1 protein.

Hair cells of the vertebrate inner ear are directional mechanosensors: they have a polarity, defined by a vector in the plane of the sensory epithelium. It has been suggested that this polarity might be controlled by genes homologous to those that control planar cell polarity (PCP) in Drosophila, and vertebrate homologues of the Drosophila PCP genes Van Gogh/strabismus and flamingo/starry night are indeed essential for normal hair cell PCP. The underlying molecular mechanism is unclear, however. Although the PCP protein Flamingo shows a polarized intracellular distribution in the fly, it is unknown whether this is necessary for its function. Here, we describe the expression pattern of a flamingo homologue, c-flamingo-1 (c-fmi-1), in the developing chick ear and show that its protein product, like that of flamingo in the fly, has a polarized distribution in each hair cell, defining an axis that corresponds to the structural PCP axis. This conservation between fly and vertebrate suggests that the polarized protein localization is functionally important. In the basilar papilla, the same localization is seen in supporting cells also, suggesting that supporting cells are cryptically polarized, despite having no overt structural polarity; they may thus participate in PCP signal transmission across the sensory patch.