Cytokinesis links polarization and tube formation in liver

The liver is an essential organ, and its function is crucially dependent on epithelial cell polarisation. However, the mechanisms that underlie this process, as well as apical lumen formation, are not well understood. On page 2483, Erfei Bi and colleagues examine how hepatocytes become polarised. Using the rat hepatocyte cell line Can10, which polarises and forms bile canaliculi robustly in vitro, they find that hepatocyte polarisation and apical lumen formation appear to be spatially linked to cytokinesis. Examining this phenomenon at a molecular level, the authors show that a key polarity regulator, a tight-junction-associated protein and a bile canaliculus membrane marker localise to the site of cell division in distinct spatiotemporal patterns before abscission. Further study of bile canaliculus formation revealed that the assembly and opening of a disc-shaped tight junction at the division site is accompanied by the emergence of an apical lumen. Moreover, oriented cell division and asymmetric cytokinesis are associated during apical tube formation. The authors next examined the possibility that the polarity protein Par3 defines the molecular link between cytokinesis and apical lumen formation. Indeed, the authors show that Par3 is required for tight-junction assembly, as well as the emergence and expansion of an apical lumen. Therefore, the authors propose that hepatocyte polarisation and apical tube formation are spatially linked to cytokinesis, and this new mechanism appears to be conserved in diverse cell types.