Quantitative and dynamic assessment of the contribution of the ER to phagosome formation.
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.
Touret
Nicolas
N
Programme in Cell Biology, University of Toronto, Ontario M5G 1X8, Canada.
Paroutis
Paul
P
Terebiznik
Mauricio
M
Harrison
Rene E
RE
Trombetta
Sergio
S
Pypaert
Marc
M
Chow
Amy
A
Jiang
Aimin
A
Shaw
James
J
Yip
Christopher
C
Moore
Hsiao-Ping
HP
van der Wel
Nicole
N
Houben
Diane
D
Peters
Peter J
PJ
de Chastellier
Chantal
C
Mellman
Ira
I
Grinstein
Sergio
S
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