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A more recent version of this article appeared on April 1, 2007
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Submitted on October 19, 2006
Revised on December 21, 2006
Accepted on January 19, 2007
*Section of Anatomy and Cell Biology, Department of Biomedicine, University of Bergen, N-5009 Bergen, Norway;
Centre National de la Recherche Scientifique Unité Mixte de Recherche 144, Institut Curie, Section de Recherche, 75248 Paris Cedex 05, France
Monitoring Editor: Sandra Schmid
In higher eukaryotic cells pleiomorphic compartments composed of vacuoles, tubules and vesicles move from the endoplasmic reticulum (ER) and the plasma membrane to the cell center, operating in early biosynthetic trafficking and endocytosis, respectively. Besides transporting cargo to the Golgi apparatus and lysosomes, a major task of these compartments is to promote extensive membrane recycling. The endocytic membrane system is traditionally divided into early (sorting) endosomes, late endosomes and the endocytic recycling compartment (ERC). Recent studies on the intermediate compart-ment (IC) between the ER and the Golgi apparatus suggest that it also consists of peripheral ("early") and centralized ("late") structures, as well as a third component, designated here as the biosynthetic recycling compartment (BRC). We propose that the ERC and the BRC exist as long-lived "mirror compartments" at the cell center that also share the ability to expand and become mobilized during cell activation. These considerations emphasize the functional symmetry of endomembrane compartments, which provides a basis for the membrane rearrangements taking place during cell division, polarization and differentiation.