title: Line tension at lipid phase boundaries regulates formation of membrane vesicles in living cells.
abstract: Ternary lipid compositions in model membranes segregate into large-scale liquid-ordered (L(o)) and liquid-disordered (L(d)) phases. Here, we show mum-sized lipid domain separation leading to vesicle formation in unperturbed human HaCaT keratinocytes. Budding vesicles in the apical portion of the plasma membrane were predominantly labelled with L(d) markers 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate, 1,1'-dilinoleyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate, 1,1'-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate and weakly stained by L(o) marker fluorescein-labeled cholera toxin B subunit which labels ganglioside GM(1) enriched plasma membrane rafts. Cholesterol depletion with methyl-beta-cyclodextrin enhanced DiI vesiculation, GM(1)/DiI domain separation and was accompanied by a detachment of the subcortical cytoskeleton from the plasma membrane. Based on these observations we describe the energetic requirements for plasma membrane vesiculation. We propose that the decrease in total 'L(o)/L(d)' boundary line tension arising from the coalescence of smaller L(d)-like domains makes it energetically favourable for L(d)-like domains to bend from flat mum-sized surfaces to cap-like budding vesicles. Thus living cells may utilize membrane line tension energies as a control mechanism of exocytic events.
authors.affiliation: Department of Dermatology, Copenhagen University Hospital, Bispebjerg, DK-2400 Copenhagen NV, Denmark. dv01@bbh.regionh.dk
authors.forename: Dina
authors.initials: D
authors.lastname: Vind-Kezunovic
authors.forename: Claus Hélix
authors.initials: CH
authors.lastname: Nielsen
authors.forename: Urszula
authors.initials: U
authors.lastname: Wojewodzka
authors.forename: Robert
authors.initials: R
authors.lastname: Gniadecki
mesh_terms: D000268:Adhesiveness / Q000187:drug effects; D055592:Biophysical Phenomena / Q000187:drug effects; D002232:Carbocyanines / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D022162:Cytoplasmic Vesicles / Q000737:chemistry* / Q000187:drug effects; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000648:ultrastructure; D008055:Lipids / Q000737:chemistry*; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: D002232:Carbocyanines; D008055:Lipids; D047392:beta-Cyclodextrins; C024286:3,3'-dioctadecylindocarbocyanine; C031215:betadex