High-resolution mapping reveals topologically distinct cellular pools of phosphatidylserine

• DOI: 10.1083/jcb.201012028
• Publication Date: 2011-07-25T16:23:58Z
• Authors: Gregory D. Fairn; Nicole L. Schieber; Nicholas Ariotti; Samantha Murphy; Lars Kuerschner; Richard I. Webb; Sergio Grinstein; Robert G. Parton
• Keywords: 0301 basic medicine; 570; 571; Cells; Phospholipid-Bilayer; 612; Trans-Golgi Network; Endosomes; Phosphatidylserines; 3101 Biochemistry and Cell Biology; Endoplasmic Reticulum; Fluorescence; 1307 Cell Biology; Mice; 03 medical and health sciences; 3T3-L1 Cells; Chlorocebus aethiops; Animals; Humans; Tissue Distribution; anzsrc-for: 31 Biological Sciences; Rat-Liver; Endoplasmic-Reticulum; Research Articles; Cells, Cultured; Microscopy; Cultured; anzsrc-for: 3101 Biochemistry and Cell Biology; Cell Membrane; Freeze-Substitution; Mitochondria; anzsrc-for: 32 Biomedical and clinical sciences; anzsrc-for: 11 Medical and Health Sciences; Microscopy, Fluorescence; COS Cells; anzsrc-for: 06 Biological Sciences; Electron-Microscopy; 31 Biological Sciences; HeLa Cells; trans-Golgi Network

Phosphatidylserine (PS) plays a central role in cell signaling and in the biosynthesis of other lipids. To date, however, the subcellular distribution and transmembrane topology of this crucial phospholipid remain ill-defined. We transfected cells with a GFP-tagged C2 domain of lactadherin to detect by light and electron microscopy PS exposed on the cytosolic leaflet of the plasmalemma and organellar membranes. Cytoplasmically exposed PS was found to be clustered on the plasma membrane, and to be associated with caveolae, the trans-Golgi network, and endocytic organelles including intraluminal vesicles of multivesicular endosomes. This labeling pattern was compared with the total cellular distribution of PS as visualized using a novel on-section technique. These complementary methods revealed PS in the interior of the ER, Golgi complex, and mitochondria. These results indicate that PS in the lumenal monolayer of the ER and Golgi complex becomes exposed cytosolically at the trans-Golgi network. Transmembrane flipping of PS may contribute to the exit of cargo from the Golgi complex.