CADHERIN mediated AMIS localisation

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 mESCs suggest that cell-cell adhesion directs the localisation of apical proteins such as PAR-6 to a centralised AMIS. Unexpectedly, we also found that mESC cell clusters lacking functional E-CADHERIN were still able to form a lumen-like cavity in the absence of AMIS localisation and 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 allows for redundancy in the system and ensures the localisation of a coherent epithelial structure within a growing organ.