Planar cell polarity signaling in the development of left-right asymmetry.

The planar cell polarity (PCP) signaling pathway, principally understood from work in Drosophila, is now known to contribute to development in a broad swath of the animal kingdom, and its impairment leads to developmental malformations and diseases affecting humans. The 'core' mechanism underlying PCP signaling polarizes sheets of cells, aligning them in a head-to-tail fashion within the sheet. Cells use the resulting directional information to guide a wide variety of processes. One such process is lateralization, the determination of left-right asymmetry that guides the asymmetric morphology and placement of internal organs. Recent evidence extends the idea that PCP signaling underlies the earliest steps in lateralization and that PCP is invoked again during asymmetric morphogenesis of organs including the heart and gut.