title: ER-to-Golgi carriers arise through direct en bloc protrusion and multistage maturation of specialized ER exit domains.
abstract: Protein transport between the ER and the Golgi in mammalian cells occurs via large pleiomorphic carriers, and most current models suggest that these are formed by the fusion of small ER-derived COPII vesicles. We have examined the dynamics and structural features of these carriers during and after their formation from the ER by correlative video/light electron microscopy and tomography. We found that saccular carriers containing either the large supramolecular cargo procollagen or the small diffusible cargo protein VSVG arise through cargo concentration and direct en bloc protrusion of specialized ER domains in the vicinity of COPII-coated exit sites. This formation process is COPII dependent but does not involve budding and fusion of COPII-dependent vesicles. Fully protruded saccules then move centripetally, evolving into one of two types of carriers (with distinct kinetic and structural features). These findings provide an alternative framework for analysis of ER-to-Golgi traffic.
authors.affiliation: Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, 66030 Santa Maria Imbaro, (Chieti), Italy.
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Mironov
authors.forename: Alexander A
authors.initials: AA
authors.lastname: Mironov
authors.forename: Galina V
authors.initials: GV
authors.lastname: Beznoussenko
authors.forename: Alvar
authors.initials: A
authors.lastname: Trucco
authors.forename: Pietro
authors.initials: P
authors.lastname: Lupetti
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Smith
authors.forename: Willie J C
authors.initials: WJ
authors.lastname: Geerts
authors.forename: Abraham J
authors.initials: AJ
authors.lastname: Koster
authors.forename: Koert N J
authors.initials: KN
authors.lastname: Burger
authors.forename: Maryann E
authors.initials: ME
authors.lastname: Martone
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Deerinck
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ellisman
authors.forename: Alberto
authors.initials: A
authors.lastname: Luini
mesh_terms: D015082:2,2'-Dipyridyl / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000494:pharmacology; D022181:COP-Coated Vesicles; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D022081:Cell Surface Extensions; D002614:Chelating Agents / Q000494:pharmacology; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D020756:Coatomer Protein / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D006153:Guanosine Diphosphate / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins / Q000378:metabolism; D008845:Microinjections; D016253:Microscopy, Immunoelectron; D008954:Models, Biological; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D011347:Procollagen / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D013997:Time Factors; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: D000975:Antioxidants; D002352:Carrier Proteins; D002614:Chelating Agents; D020756:Coatomer Protein; C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D011347:Procollagen; C106113:SEC31 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins; D006153:Guanosine Diphosphate; D015082:2,2'-Dipyridyl; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae; D001205:Ascorbic Acid