E‐cadherin mediates apical membrane initiation site localisation during de novo polarisation of epithelial cavities

Abstract

Individual cells within de novo polarising tubes and cavities must integrate their forming apical domains into a centralised apical membrane initiation site (AMIS). This is necessary to enable organised lumen formation within multi‐cellular tissue. Despite the well‐documented importance of cell division in localising the AMIS, we have found a division‐independent mechanism of AMIS localisation that relies instead on Cadherin‐mediated cell–cell adhesion. Our study of de novo polarising mouse embryonic stem cells (mESCs) cultured in 3D suggests that cell–cell adhesion localises apical proteins such as PAR‐6 to a centralised AMIS. Unexpectedly, we also found that mESC clusters lacking functional E‐cadherin still formed a lumen‐like cavity in the absence of AMIS localisation but did so at a later stage of development via a “closure” mechanism, instead of via hollowing. This work suggests that there are two, interrelated mechanisms of apical polarity localisation: cell adhesion and cell division. Alignment of these mechanisms in space allows for redundancy in the system and ensures the development of a coherent epithelial structure within a growing organ. image Appropriate localisation of the apical membrane initiation site (AMIS) is critical for positioning a central and cohesive lumen during de novo polarisation of epithelial tubes and cavities. Here, our study of mouse embryonic stem cells (mESCs) reveals a cell division‐independent mechanism of AMIS localisation, which instead relies on Cadherin‐mediated cell‐cell adhesion. mESCs in Matrigel form a PAR‐3/ZO‐1 labelled AMIS between cells in the absence of cell division at the midpoint of cell‐cell contact. E‐cadherin is both necessary and sufficient for initiating AMIS localisation. In the absence of E‐cadherin and an AMIS, mESCs polarise later and form lumina via a ‘closure’ process, rather than by hollowing. Alignment of cell adhesion and cell division in space and time ensures development of a coherent apical domain within a proliferating organ primordium.