Epithelial polarity is an essential process occuring during organisms developpment. Here we focus on the C. elegans intestinal and epidermal epithelial tissue to better understand how the cell maintains its polarity by definining an apical and a basolateral membrane. The establishment and the maintenance of this polarity is ensured by polarity determinants proteins and among this, the PAR3/PAR-6/aPKC and CDC-42 are essential components to specify apical polarity. We have shown that the clathrin adaptor complex AP-1, an essential regulator of intracellular traffic, is involved in that process. We confirmed that AP-1 is indeed implicated in basolateral cargo sorting, consistent with mammalian AP-1 function but surprisingly AP-1 also controls the apical sorting of a transmembrane protein as well as the asymetric localisation of PAR-6 and CDC-42. The AP-1 loss of function induces a conversion of the lateral membrane into apical identity and eventually the formation of ectopic lumens. The AP-1 inhibition also causes an embryonic lethality which may be explained by the phenotype observed within the epidermis. In that context, AP-1 controls the cell junction integrity and interestingly the apical sorting of E-cadherin. Together our data demonstrate an essential function for AP-1 in apical sorting that directs epithelial polarity maintenance.
