The mammalian cochlea offers a unique opportunity to study the effects of planar cell polarity signaling during vertebrate development. First, convergence and extension play a role in outgrowth and cellular patterning within the duct, and second, hair cell stereociliary bundles are uniformly oriented towards the lateral edge of the duct. Defects in convergence and extension are manifested as a shortening of the cochlea duct and/or changes in cellular patterning, which can be quantified following dissection from mouse mutants or observed directly using an in vitro outgrowth assay. Changes in stereociliary bundle orientation can be observed and quantitated using either fluorescent tags or scanning electron microscopy (SEM) to visualize individual bundles. The high degree of regularity in many aspects of cochlear anatomy, including cellular patterning and stereociliary bundle orientation, makes it possible to detect subtle changes in the development of PCP in response to either genetic or molecular perturbations.
