The establishment and maintenance of epithelial cell polarity is essential for animal development and physiology. In Drosophila, the scaffold protein Bazooka (Baz, the fly homologue of the mammalian and worm polarity protein PAR-3) forms apical polarity landmarks that establish epithelial polarity. But how is Baz recruited to the plasma membrane? On page , Tony Harris and co-workers propose that a multifaceted membrane-association mechanism assembles Baz polarity landmarks. Using a comprehensive structure-function approach, the authors dissect the roles of the Baz oligomerisation domain, its three PDZ domains and its atypical protein kinase C and phosphoinositide lipid binding regions in the cortical localisation of Baz in the Drosophila embryonic ectoderm. None of these protein domains is essential for cortical localisation, they report. Instead, Baz positioning depends on multiple redundant interactions. The authors also show that the specific downstream effects of Baz localisation include the promotion of epithelial structure, a positive-feedback loop that recruits other polarity proteins and a negative-feedback loop that regulates Baz. The authors propose that the recruitment of Baz to the plasma membrane through this new multifaceted membrane-association mechanism provides both plasticity and robustness to Baz polarity landmarks.
