Coordinated assembly and release of adhesions builds apical junctional belts during de novo polarisation of an epithelial tube

We uncover the mechanisms allowing the generation of two opposing apical epithelial surfaces within the centre of an initially unpolarised, solid organ. Through functional inhibition of NOK/Pals1/Mpp5a and Rab11a we infer that Crumbs protein plays a dual role in coordinating the generation of ipsilateral junctional belts whilst simultaneously releasing contralateral adhesions across the centre of the tissue. We further suggest that Nok/Rab11a/Crumbs-mediated resolution of cell-cell adhesions is both necessary for midline lumen opening and contributes to later maintenance of epithelial organisation. In light of a recent conflicting publication, we also clarify the important role of cell division in aligning both ipsilateral and contralateral junctions at the midline of the tissue.