Planar cell polarity: one or two pathways?

Abstract

The prevailing view is that planar cell polarity is the outcome of one genetic pathway. On the basis of their observations in genetically mosaic adult flies, the authors challenge this assumption and discuss potentially far-reaching implications of their model. In multicellular organisms, cells are polarized in the plane of the epithelial sheet, revealed in some cell types by oriented hairs or cilia. Many of the underlying genes have been identified in Drosophila melanogaster and are conserved in vertebrates. Here we dissect the logic of planar cell polarity (PCP). We review studies of genetic mosaics in adult flies — marked cells of different genotypes help us to understand how polarizing information is generated and how it passes from one cell to another. We argue that the prevailing opinion that planar polarity depends on a single genetic pathway is wrong and conclude that there are (at least) two independently acting processes. This conclusion has major consequences for the PCP field.