title: Endoplasmosis and exoplasmosis: the evolutionary principles underlying endocytosis, exocytosis, and vesicular transport.
abstract: Eukaryotic cells are characterized by a multicompartmental structure with a variety of organelles. Vesicular transport between these compartments requires membrane fusion events. Based on a membrane topology view, we conclude that there are two basic mechanisms of membrane fusion, namely where the membranes first come in contact with the cis-side (the plasmatic phase of the lipid bilayer) or with the trans-side (the extra-plasmatic face). We propose to designate trans-membrane fusion processes as "endoplasmosis" as they lead to uptake of a compartment into the plasmatic phase. Vice versa we suggest the term "exoplasmosis" (as already suggested in a 1964 publication) for cis-membrane fusion events, where the interior of a vesicle is released to an extraplasmatic environment (the extracellular space or the lumen of a compartment). This concept is supported by the fact that all cis- and all trans-membrane fusions, respectively, exhibit noticeable similarities implying that they evolved from two functionally different mechanisms.
authors.affiliation: Center for Physiology and Pharmacology, Department of Vascular Biology and Thrombosis Research, Medical University Vienna, Schwarzspanierstraße 17, 1090, Vienna, Austria. Johannes.Schmid@meduniwien.ac.at.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Schmid
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004705:Endocytosis / Q000502:physiology*; D004721:Endoplasmic Reticulum / Q000502:physiology; D005057:Eukaryotic Cells / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D005110:Extracellular Space / Q000502:physiology; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology*; D022161:Transport Vesicles / Q000502:physiology*; D033921:Vesicular Transport Proteins / Q000502:physiology*
chemical_list: D008051:Lipid Bilayers; D033921:Vesicular Transport Proteins
keywords: Endocytosis; Eukaryotic Cells; Exocytosis; Extracellular Space; Lipid Bilayers; Membrane Fusion; Membranes