Planar cell polarity (PCP) refers to the phenomenon of the coordinative alignment of cell polarity across the plane of the epithelial sheet. PCP regulates a variety of physiological processes including gastrulation development, neural tube closure and the patterning of hearing cells and skin hairs. PCP is regulated by a group of conserved core proteins and the key feature is that many of them, such as Frizzled6 (Fzd6) and Vangl2, asymmetrically localize on opposite cell boundaries. This unique localization is essential for the establishment and maintenance of PCP. However, the molecular mechanisms behind are poorly understood.

The trans-Golgi Network (TGN) is an important sorting station in the secretory transport pathway. Cargo proteins are packaged into specific vesicles for differen...[ Read more ]

Planar cell polarity (PCP) refers to the phenomenon of the coordinative alignment of cell polarity across the plane of the epithelial sheet. PCP regulates a variety of physiological processes including gastrulation development, neural tube closure and the patterning of hearing cells and skin hairs. PCP is regulated by a group of conserved core proteins and the key feature is that many of them, such as Frizzled6 (Fzd6) and Vangl2, asymmetrically localize on opposite cell boundaries. This unique localization is essential for the establishment and maintenance of PCP. However, the molecular mechanisms behind are poorly understood.

The trans-Golgi Network (TGN) is an important sorting station in the secretory transport pathway. Cargo proteins are packaged into specific vesicles for different downstream destinations at the TGN. To explore the molecular mechanisms that regulate TGN sorting of PCP proteins, in vitro vesicle formation assay was performed to reconstitute release of Fzd6- and Vangl2-enriched vesicles from the TGN. Immunoblotting of released vesicles indicated that Fzd6 and Vangl2 exit the TGN in separate compartments. Knockdown analysis showed Fzd6 export at the TGN requires Arfs and cargo adaptors epsinR and GGA2, while Vangl2 export at the TGN is dependent on Arfrp1 and AP-1. Biochemical analysis revealed that epsinR forms a stable complex with clathrin heavy chain (CHC) and interacts with a conserved polybasic motif on Fzd6 cytosolic domain. Purified epsinR-C-terminus stimulated vesicular release of Fzd6 from the TGN and Fzd6-epsinR binding disassociated epsinR from AP-1. Moreover, animal study showed epsinR homolog lpfR regulates PCP in Drosophila in vivo. In addition, ER membrane anchored GTPase Atlastin is important for both Fzd6 and Vangl2 exit from the ER. Our results demonstrated that Fzd6 and Vangl2 utilize different sorting machineries to be exported out of the TGN, which may contribute to their asymmetric localization.