The biosynthetic-secretory pathway, supplemented by recycling routes, determines epithelial membrane polarity

In prevailing epithelial polarity models, membrane-based polarity cues (e.g., the partitioning-defective PARs) position apicobasal cellular membrane domains. Intracellular vesicular trafficking expands these domains by sorting polarized cargo toward them. How the polarity cues themselves are polarized in epithelia and how sorting confers long-range apicobasal directionality to vesicles is still unclear. Here, a systems-based approach using two-tiered C. elegans genomics-genetics screens identifies trafficking molecules that are not implicated in apical sorting yet polarize apical membrane and PAR complex components. Live tracking of polarized membrane biogenesis indicates that the biosynthetic-secretory pathway, linked to recycling routes, is asymmetrically oriented toward the apical domain during this domain's biosynthesis, and that this directionality is regulated upstream of PARs and independent of polarized target membrane domains. This alternative mode of membrane polarization could offer solutions to open questions in current models of epithelial polarity and polarized trafficking.

Automated summary

A systems-based approach using two-tiered C. elegans genomics-genetics screens identified trafficking molecules that polarize apical membrane and PAR complex components without being involved in apical sorting. Live tracking of polarized membrane biogenesis revealed that the biosynthetic-secretory pathway, linked to recycling routes, is asymmetrically oriented towards the apical domain during its biosynthesis, independent of polarized target membrane domains and regulated upstream of PARs. This alternative mode of membrane polarization provides insights into current models of epithelial polarity and polarized trafficking.