Models for the role of Yurt in epithelial polarity and terminal differentiation during Drosophila embryonic development. (A) Model illustrating regulatory interactions between Yurt and epithelial polarity proteins. (B) Top: Early during the polarity maintenance phase, apical aPKC prevents premature apical localization of Yurt by phosphorylating Yurt’s FA domain, disrupting Yurt oligomerization, preventing binding to Crumbs, and keeping Crumbs in an active state. Bottom: Later, during terminal differentiation, Yurt is recruited by Crumbs to the apical membrane, where it forms part of the Crumbs complex and negatively regulates Crumbs function. PDB, PDZ domain binding site.