Functional Symmetry of Endomembranes

Abstract

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 compartment (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.

Arfs at a Glance

“…Arf6 functions in this plasma-membrane-endosomal membrane system (D'Souza-Schorey and Chavrier, 2006). These secretory and endosomal membrane systems intersect at the trans-Golgi network (TGN) and are maintained by recycling pathways (Saraste and Goud, 2007), in which Arf proteins play a major role.…”

Inherited hematological disorders due to defects in coat protein (COP)II complex

“…Less is known about the behavior of the secretory pathway within the context of the entire multicellular organism and how its malfunction might influence development and organ homeostasis. The increase in size of eukaryotic cell was accompanied by an increase in complexity of the molecular machinery of these transport routes, i.e., number and types of coat proteins, regulatory GTPases, fusion and recruitment factors [19]. One possible way in which evolution modifies function is to develop protein orthologues and isoforms, i.e., by gene duplication and/or by alternative mRNA splicing.…”

Considerations for Treatment Development in Rhabdomyosarcoma: In Vitro Assessment of Novel DNA Binding Drugs

“…Each vesicle differs not only in their function but also in their intravesicular pH and in the receptors they express. Early endosomes, which originate from clathrin coated pits (CCP) in the cell's plasma membrane, are an integral component in the endocytic uptake of extracellular material (Saraste et al, 2007). These vesicles, with an approximate pH of 6.2, express SNARE proteins, the GTPases Rab4 and Rab5 and the early endosome antigen 1 (EEA1) protein.…”