Ciona intestinalis notochord as a new model to investigate the cellular and molecular mechanisms of tubulogenesis

► A cytokinesis-like contractile ring drives cell elongation in post-mitotic cells. ► Notochord cells de novo form two apical domains each. ► Vesicle trafficking and osmolarity synergistically drive lumen expansion. ► Lumens connects through bidirectional cell crawling and junction remodeling. ► Bipolarity is a common principle for lumen connection within single files of cells.