Retromer regulates apical-basal polarity through recycling Crumbs

Epithelial cells are characterized by an “apical–basal” polarization. The transmembrane protein Crumbs (Crb) is an essential apical determinant which confers apical membrane identity. Previous studies indicated that Crb did not constantly reside on the apical membrane, but was actively recycled. However, the cellular mechanism(s) underlying this process was unclear. Here we showed that in Drosophila, retromer, which was a retrograde complex recycling certain transmembrane proteins from endosomes to trans-Golgi network (TGN), regulated Crb in epithelial cells. In the absence of retromer, Crb was mis-targeted into lysosomes and degraded, causing a disruption of the apical–basal polarity. We further showed that Crb co-localized and interacted with retromer, suggesting that retromer regulated the retrograde recycling of Crb. Our data presented here uncover the role of retromer in regulating apical–basal polarity in epithelial cells and identify retromer as a novel regulator of Crb recycling.