Cell polarity in myelinating glia: from membrane flow to diffusion barriers.
Myelin-forming glia are highly polarized cells that synthesize as an extension of their plasma membrane, a multilayered myelin membrane sheath, with a unique protein and lipid composition. In most cells polarity is established by the polarized exocytosis of membrane vesicles to the distinct plasma membrane domains. Since myelin is composed of a stack of tightly packed membrane layers that do not leave sufficient space for the vesicular trafficking, we hypothesize that myelin does not use polarized exocytosis as a primary mechanism, but rather depends on lateral transport of membrane components in the plasma membrane. We suggest a model in which vesicle-mediated transport is confined to the cytoplasmic channels, from where transport to the compacted areas occurs by lateral flow of cargo within the plasma membrane. A diffusion barrier that is formed by MBP and the two adjacent cytoplasmic leaflets of the myelin bilayers acts a molecular sieve and regulates the flow of the components. Finally, we highlight potential mechanism that may contribute to the assembly of specific lipids within myelin. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
Max-Planck-Institute of Experimental Medicine, Hermann-Rein-Str. 3, Göttingen, Germany. msimons@gwdg.de
Mikael
M
Simons
Nicolas
N
Snaidero
Shweta
S
Aggarwal
D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D016764:Cell Polarity; D003593:Cytoplasm / Q000378:metabolism*; D004058:Diffusion; D005089:Exocytosis; D006801:Humans; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D009186:Myelin Sheath / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000378:metabolism; D012583:Schwann Cells / Q000378:metabolism*; D022161:Transport Vesicles / Q000378:metabolism
D008565:Membrane Proteins