Planar Cell Polarity in Ciliated Epithelia

Ciliated epithelia have emerged as excellent models to identify cellular and molecular mechanisms of tissue and cell polarity. Ciliated epithelia harbor multiciliated cells (MCCs) at high density, each containing dozens to hundreds of cilia beating in a synchronized and directional manner to generate extracellular flow of biological fluids. This task requires coordination and transmission of planar polarity information at multiple scales. First, a global axis of polarity must be established in the developing epithelium that prefigures the direction of fluid flow. In response to this initial event, polarized membrane domains are established in individual epithelial cells, and polarity is coordinated between adjacent cells. Finally, in differentiating MCCs centrioles at the base of cilia are aligned with respect to polarized membrane domains, which allows directional cilia beating and generation of robust flow. Throughout this sequence of events and at all organizational scales, the planar cell polarity pathway plays a central role in tight interaction with the cellular cytoskeleton.