EMBO J (2013) 32 1, 30–44 doi:10.1038/emboj.2012.305; published online November302012
Cell polarisation in development is a common and fundamental process underlying embryo patterning and morphogenesis, and has been extensively studied over the past years. Our current knowledge of cell polarisation in development is predominantly based on studies that have analysed polarisation of single cells, such as eggs, or cellular aggregates with a stable polarising interface, such as cultured epithelial cells (St Johnston and Ahringer, 2010). However, in embryonic development, particularly of vertebrates, cell polarisation processes often encompass large numbers of cells that are placed within moving and proliferating tissues, and undergo mesenchymal-to-epithelial transitions with a highly complex spatiotemporal choreography. How such intricate cell polarisation processes in embryonic development are achieved has only started to be analysed. By using live imaging of neurulation in the transparent zebrafish embryo, Buckley et al (2012) now describe a novel polarisation strategy by which cells assemble an apical domain in the part of their cell body that intersects with the midline of the forming neural rod. This mechanism, along with the previously described mirror-symmetric divisions (Tawk et al, 2007), is thought to trigger formation of both neural rod midline and lumen.