Planar cell polarity: keeping hairs straight is not so simple.

The fur on a cat's back, the scales on a fish, or the bristles on a fly are all beautifully organized, with a high degree of polarization in their surface organization. Great progress has been made in understanding how individual cell polarity is established, but our understanding of how cells coordinate their polarity in forming coherent tissues is still fragmentary. The organization of cells in the plane of the epithelium is known as planar cell polarity (PCP), and studies in the past decade have delineated a genetic pathway for the control of PCP. This review will first briefly review data from the Drosophila field, where PCP was first identified and genetically characterized, and then explore how vertebrate tissues become polarized during development.