Planar cell polarity pathway in kidney development, function and disease

Planar cell polarity (PCP) refers to the coordinated orientation of cells in the tissue plane. Originally discovered and studied in Drosophila melanogaster , PCP is now widely recognized in vertebrates, where it is implicated in organogenesis. Specific sets of PCP genes have been identified. The proteins encoded by these genes become asymmetrically distributed to opposite sides of cells within a tissue plane and guide many processes that include changes in cell shape and polarity, collective cell movements or the uniform distribution of cell appendages. A unifying characteristic of these processes is that they often involve rearrangement of actomyosin. Mutations in PCP genes can cause malformations in organs of many animals, including humans. In the past decade, strong evidence has accumulated for a role of the PCP pathway in kidney development including outgrowth and branching morphogenesis of ureteric bud and podocyte development. Defective PCP signalling has been implicated in the pathogenesis of developmental kidney disorders of the congenital anomalies of the kidney and urinary tract spectrum. Understanding the origins, molecular constituents and cellular targets of PCP provides insights into the involvement of PCP molecules in normal kidney development and how dysfunction of PCP components may lead to kidney disease. Planar cell polarity (PCP) refers to the coordinated orientation of cells in the tissue plane and is important for several key morphogenetic and homeostatic processes. This Review describes the origins of PCP signalling, its activity and cellular targets, with an emphasis on the PCP pathway in kidney development, function and disease. Key points Planar cell polarity (PCP) refers to the coordinated organization of cells or cell components across a tissue plane as exemplified by the uniform patterns of scales on fish, trichomes (small hairs) on Drosophila wings or stereocilia in the mammalian inner ear. Evolutionarily conserved PCP proteins function in specialized signalling pathways to coordinate changes in cell shape and behaviour through processes that commonly involve actomyosin activation; these PCP-dependent changes in cell morphology control tissue morphogenesis. PCP proteins exhibit asymmetric subcellular localization along the tissue plane. Functions of vertebrate homologues of Drosophila PCP components in PCP signalling are often unclear owing to gene redundancy and/or their involvement in non-PCP-related processes. Given the ess