title: Quantitative and dynamic assessment of the contribution of the ER to phagosome formation.
abstract: Phagosomes were traditionally thought to originate from an invagination and scission of the plasma membrane to form a distinct intracellular vacuole. An alternative model implicating the endoplasmic reticulum (ER) as a major component of nascent and maturing phagosomes was recently proposed (Gagnon et al., 2002). To reconcile these seemingly disparate hypotheses, we used a combination of biochemical, fluorescence imaging, and electron microscopy techniques to quantitatively and dynamically assess the contribution of the plasmalemma and of the ER to phagosome formation and maturation. We could not verify even a transient physical continuity between the ER and the plasma membrane, nor were we able to detect a significant contribution of the ER to forming or maturing phagosomes in either macrophages or dendritic cells. Instead, our data indicate that the plasma membrane is the main constituent of nascent and newly formed phagosomes, which are progressively remodeled by fusion with endosomal and eventually lysosomal compartments as phagosomes mature into acidic, degradative organelles.
authors.affiliation: Programme in Cell Biology, University of Toronto, Ontario M5G 1X8, Canada.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Touret
authors.forename: Paul
authors.initials: P
authors.lastname: Paroutis
authors.forename: Mauricio
authors.initials: M
authors.lastname: Terebiznik
authors.forename: Rene E
authors.initials: RE
authors.lastname: Harrison
authors.forename: Sergio
authors.initials: S
authors.lastname: Trombetta
authors.forename: Marc
authors.initials: M
authors.lastname: Pypaert
authors.forename: Amy
authors.initials: A
authors.lastname: Chow
authors.forename: Aimin
authors.initials: A
authors.lastname: Jiang
authors.forename: James
authors.initials: J
authors.lastname: Shaw
authors.forename: Christopher
authors.initials: C
authors.lastname: Yip
authors.forename: Hsiao-Ping
authors.initials: HP
authors.lastname: Moore
authors.forename: Nicole
authors.initials: N
authors.lastname: van der Wel
authors.forename: Diane
authors.initials: D
authors.lastname: Houben
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Peters
authors.forename: Chantal
authors.initials: C
authors.lastname: de Chastellier
authors.forename: Ira
authors.initials: I
authors.lastname: Mellman
authors.forename: Sergio
authors.initials: S
authors.lastname: Grinstein
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D003713:Dendritic Cells / Q000378:metabolism / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008264:Macrophages / Q000378:metabolism / Q000648:ultrastructure; D008561:Membrane Fusion / Q000502:physiology; D051379:Mice; D046529:Microscopy, Electron, Transmission; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure