Planar Cell Polarity
Planar Cell Polarity is the ability of a cell within an epithelial sheet to develop asymmetry between cell surfaces in a direction that lies within the epithelial plane. Planar Cell Polarity contrasts with apico-basal polarity in that apico-basal polarity involves asymmetry between cell surfaces in an orthogonal direction to an epithelial plane.
Planar Cell Polarity is required for hair alignment, mammalian (vertebrate?) hearing, esophageal cilia, and neural tube closure.
Planal cell polarity typically results in the asymmetric production of a cell extension, such as a cilium in an esophageal epithelial cell, stereocillia in the ear (what are these cells called?), or an actin-rich projection in the Drosophila wing epithelia.
The most recent evidence suggests that planar cell polarity is brought about by asymmetrically localizing proteins within a cell. In the Drosophila wing, the proteins Frizzled and Disheveled localize to the distal faces of the cell, and the proteins Van Gogh and Prickled localize to the proximal faces. An actin-rich cell extension will then form in the area of highest Disheveled (correct?) concentration. Planar polarity information can be transferred between adjacent cells in an epithelium, and the polarity decision of one cells can influence its neighbors. In fact, recent evidence suggests that planar cell polarity is established through genetic feedback loops that exist between cells. (Cite the science paper here, or another of Jeff's papers.)
I am going to need to read more papers to write more here.
In Drosophila
In Mammals