Figure 9.

Planar polarity of cochlear-supporting cells directs peripheral axon turning. A, WNT signaling, perhaps acting in a gradient, promotes the asymmetric distribution of the core PCP proteins (green and magenta) within organ of Corti-supporting cells. This distribution is reinforced by intracellular feedback loops within individual cells (gray arrows) and intercellular signaling between neighboring cells (black arrows). This planar polarization mechanism may also direct the polarized subcellular distribution of membrane tethered axon guidance molecules, such as ephrins or semaphorins. B, As the growth cone of the peripheral axon enters this polarized environment, it is directed toward the cochlear base by the polarized array of proteins that it encounters before turning. Growth cone turning could occur in response to intercellular PCP signaling between supporting cells and the growth cone, or to the polarized distribution of axon guidance cues that are asymmetrically distributed through a PCP-dependent mechanism.