Slmb antagonises the aPKC/Par-6 complex to control oocyte and epithelial polarity

Abstract

The Drosophilaanterior-posterior axis is specified when the posterior follicle cells signal to polarise the oocyte, leading to the anterior/lateral localisation of the Par-6/aPKC complex and the posterior recruitment of Par-1, which induces a microtubule reorganisation that localises bicoidandoskar mRNAs. Here we show that oocyte polarity requires Slmb, the substrate specificity subunit of the SCF E3 ubiquitin ligase that targets proteins for degradation. The Par-6/aPKC complex is ectopically localised to the posterior ofslmbmutant oocytes, and Par-1 andoskar mRNA are mislocalised. Slmb appears to play a related role in epithelial follicle cells, as large slmbmutant clones disrupt epithelial organisation, whereas small clones show an expansion of the apical domain, with increased accumulation of apical polarity factors at the apical cortex. The levels of aPKC and Par-6 are significantly increased in slmb mutants, whereas Baz is slightly reduced. Thus, Slmb may induce the polarisation of the anteriorposterior axis of the oocyte by targeting the Par-6/aPKC complex for degradation at the oocyte posterior. Consistent with this, overexpression of the aPKC antagonist Lgl strongly rescues the polarity defects ofslmbmutant germline clones. The role of Slmb in oocyte polarity raises an intriguing parallel withC. elegansaxis formation, in which PAR-2 excludes the anterior PAR complex from the posterior cortex to induce polarity, but its function can be substituted by overexpressing Lgl. © 2014. Published by The Company of Biologists Ltd.