scholarly journals Mapping bilayer thickness in the ER membrane

2020 ◽  
Vol 6 (46) ◽  
pp. eaba5130 ◽  
Author(s):  
Rupali Prasad ◽  
Andrzej Sliwa-Gonzalez ◽  
Yves Barral
Keyword(s):  
Cleavage Plane ◽  
Lateral Diffusion ◽  
Physical Nature ◽  
Diffusion Barriers ◽  
Bilayer Thickness ◽  
Synthetic Membranes ◽  
Fluorescent Reporters ◽  
Discrete Domains ◽  
Lateral Organization ◽  
Er Membrane

In the plasma membrane and in synthetic membranes, resident lipids may laterally unmix to form domains of distinct biophysical properties. Whether lipids also drive the lateral organization of intracellular membranes is largely unknown. Here, we describe genetically encoded fluorescent reporters visualizing local variations in bilayer thickness. Using them, we demonstrate that long-chained ceramides promote the formation of discrete domains of increased bilayer thickness in the yeast ER, particularly in the future plane of cleavage and at ER–trans-Golgi contact sites. Thickening of the ER membrane in the cleavage plane contributed to the formation of lateral diffusion barriers, which restricted the passage of short, but not long, protein transmembrane domains between the mother and bud ER compartments. Together, our data establish that the ER membrane is laterally organized and that ceramides drive this process, and provide insights into the physical nature and biophysical mechanisms of the lateral diffusion barriers that compartmentalize the ER.

scholarly journals A sphingolipid-dependent diffusion barrier confines ER stress to the yeast mother cell

eLife ◽  
2014 ◽  
Vol 3 ◽  
Author(s):  
Lori Clay ◽  
Fabrice Caudron ◽  
Annina Denoth-Lippuner ◽  
Barbara Boettcher ◽  
Stéphanie Buvelot Frei ◽  
...  
Keyword(s):  
Er Stress ◽  
Diffusion Barrier ◽  
Mother Cell ◽  
Budding Yeast ◽  
Lateral Diffusion ◽  
Physical Nature ◽  
Diffusion Barriers ◽  
Yeast Cells ◽  
Misfolded Proteins ◽  
Dependent Manner

In many cell types, lateral diffusion barriers compartmentalize the plasma membrane and, at least in budding yeast, the endoplasmic reticulum (ER). However, the molecular nature of these barriers, their mode of action and their cellular functions are unclear. Here, we show that misfolded proteins of the ER remain confined into the mother compartment of budding yeast cells. Confinement required the formation of a lateral diffusion barrier in the form of a distinct domain of the ER-membrane at the bud neck, in a septin-, Bud1 GTPase- and sphingolipid-dependent manner. The sphingolipids, but not Bud1, also contributed to barrier formation in the outer membrane of the dividing nucleus. Barrier-dependent confinement of ER stress into the mother cell promoted aging. Together, our data clarify the physical nature of lateral diffusion barriers in the ER and establish the role of such barriers in the asymmetric segregation of proteotoxic misfolded proteins during cell division and aging.

The organization of cell surface membrane domains

1989 ◽  
Vol 47 ◽  
pp. 804-805
Author(s):  
Michael Edidin
Keyword(s):  
Cell Surface ◽  
Membrane Lipids ◽  
Surface Membrane ◽  
Lateral Diffusion ◽  
Cell Types ◽  
Membrane Domains ◽  
Membrane Biology ◽  
Morphological Polarity ◽  
Discrete Domains ◽  
Membrane Components

Cell surface membranes are based on a fluid lipid bilayer and models of the membranes' organization have emphasised the possibilities for lateral motion of membrane lipids and proteins within the bilayer. Two recent trends in cell and membrane biology make us consider ways in which membrane organization works against its inherent fluidity, localizing both lipids and proteins into discrete domains. There is evidence for such domains, even in cells without obvious morphological polarity and organization [Table 1]. Cells that are morphologically polarised, for example epithelial cells, raise the issue of membrane domains in an accute form.The technique of fluorescence photobleaching and recovery, FPR, was developed to measure lateral diffusion of membrane components. It has also proven to be a powerful tool for the analysis of constraints to lateral mobility. FPR resolves several sorts of membrane domains, all on the micrometer scale, in several different cell types.

scholarly journals Septin-dependent compartmentalization of the endoplasmic reticulum during yeast polarized growth

2005 ◽  
Vol 169 (6) ◽  
pp. 897-908 ◽  
Author(s):  
Cosima Luedeke ◽  
Stéphanie Buvelot Frei ◽  
Ivo Sbalzarini ◽  
Heinz Schwarz ◽  
Anne Spang ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Proteins ◽  
Diffusion Barriers ◽  
Yeast Cells ◽  
Dependent Manner ◽  
Protein Diffusion ◽  
Ultrastructural Studies ◽  
Bud Neck ◽  
Er Membrane

Polarized cells frequently use diffusion barriers to separate plasma membrane domains. It is unknown whether diffusion barriers also compartmentalize intracellular organelles. We used photobleaching techniques to characterize protein diffusion in the yeast endoplasmic reticulum (ER). Although a soluble protein diffused rapidly throughout the ER lumen, diffusion of ER membrane proteins was restricted at the bud neck. Ultrastructural studies and fluorescence microscopy revealed the presence of a ring of smooth ER at the bud neck. This ER domain and the restriction of diffusion for ER membrane proteins through the bud neck depended on septin function. The membrane-associated protein Bud6 localized to the bud neck in a septin-dependent manner and was required to restrict the diffusion of ER membrane proteins. Our results indicate that Bud6 acts downstream of septins to assemble a fence in the ER membrane at the bud neck. Thus, in polarized yeast cells, diffusion barriers compartmentalize the ER and the plasma membrane along parallel lines.

scholarly journals Deciphering the rules governing assembly order of mammalian septin complexes

2011 ◽  
Vol 22 (17) ◽  
pp. 3152-3164 ◽  
Author(s):  
Mikael E. Sellin ◽  
Linda Sandblad ◽  
Sonja Stenmark ◽  
Martin Gullberg
Keyword(s):  
Mammalian Cells ◽  
Temporal Order ◽  
Lateral Diffusion ◽  
Diffusion Barriers ◽  
Generic Model ◽  
Molecular Scaffolds ◽  
Domain Interactions ◽  
Ordered Assembly ◽  
A Minor ◽  
Combined Data

Septins are conserved GTP-binding proteins that assemble into lateral diffusion barriers and molecular scaffolds. Vertebrate genomes contain 9–17 septin genes that encode both ubiquitous and tissue-specific septins. Expressed septins may assemble in various combinations through both heterotypic and homotypic G-domain interactions. However, little is known regarding assembly states of mammalian septins and mechanisms directing ordered assembly of individual septins into heteromeric units, which is the focus of this study. Our analysis of the septin system in cells lacking or overexpressing selected septins reveals interdependencies coinciding with previously described homology subgroups. Hydrodynamic and single-particle data show that individual septins exist solely in the context of stable six- to eight-subunit core heteromers, all of which contain SEPT2 and SEPT6 subgroup members and SEPT7, while heteromers comprising more than six subunits also contain SEPT9. The combined data suggest a generic model for how the temporal order of septin assembly is homology subgroup-directed, which in turn determines the subunit arrangement of native heteromers. Because mammalian cells normally express multiple members and/or isoforms of some septin subgroups, our data also suggest that only a minor fraction of native heteromers are arranged as perfect palindromes.

scholarly journals Compartmentalization of the endoplasmic reticulum in the early C. elegans embryos

2016 ◽  
Vol 214 (6) ◽  
pp. 665-676 ◽  
Author(s):  
Zuo Yen Lee ◽  
Manoël Prouteau ◽  
Monica Gotta ◽  
Yves Barral
Keyword(s):  
Endoplasmic Reticulum ◽  
Cleavage Plane ◽  
Morphological Transition ◽  
Dependent Manner ◽  
Cell Lineages ◽  
C Elegans ◽  
Nuclear Envelope Breakdown ◽  
The One ◽  
Fate Determinants ◽  
Er Membrane

The one-cell Caenorhabditis elegans embryo is polarized to partition fate determinants between the cell lineages generated during its first division. Using fluorescence loss in photobleaching, we find that the endoplasmic reticulum (ER) of the C. elegans embryo is physically continuous throughout the cell, but its membrane is compartmentalized shortly before nuclear envelope breakdown into an anterior and a posterior domain, indicating that a diffusion barrier forms in the ER membrane between these two domains. Using mutants with disorganized ER, we show that ER compartmentalization is independent of the morphological transition that the ER undergoes in mitosis. In contrast, compartmentalization takes place at the position of the future cleavage plane in a par-3–dependent manner. Together, our data indicate that the ER membrane is compartmentalized in cells as diverse as budding yeast, mouse neural stem cells, and the early C. elegans embryo.

Lateral diffusion in synthetic membranes: models and experiments on protein influence

1991 ◽  
Vol 87 (13) ◽  
pp. 2039 ◽  
Author(s):  
Francis Baros ◽  
Abderrahim Naoumi ◽  
Marie-Laure Viriot ◽  
Jean-Claude Andre
Keyword(s):  
Lateral Diffusion ◽  
Synthetic Membranes

scholarly journals Tobacco mosaic virus (TMV) Replicase and Movement Protein Function Synergistically in Facilitating TMV Spread by Lateral Diffusion in the Plasmodesmal Desmotubule of Nicotiana benthamiana

2008 ◽  
Vol 21 (3) ◽  
pp. 335-345 ◽  
Author(s):  
Dana Guenoune-Gelbart ◽  
Michael Elbaum ◽  
Guy Sagi ◽  
Amit Levy ◽  
Bernard L. Epel
Keyword(s):  
Tobacco Mosaic Virus ◽  
Mosaic Virus ◽  
Protein Function ◽  
Fluorescent Protein ◽  
Lateral Diffusion ◽  
Integral Membrane Protein ◽  
Movement Proteins ◽  
Green Fluorescent ◽  
Cell Spread ◽  
Er Membrane

Virus spread through plasmodesmata (Pd) is mediated by virus-encoded movement proteins (MPs) that modify Pd structure and function. The MP of Tobacco mosaic virus (TMVMP) is an endoplasmic reticulum (ER) integral membrane protein that binds viral RNA (vRNA), forming a vRNA:MP:ER complex. It has been hypothesized that TMVMP causes Pd to dilate, thus potentiating a cytoskeletal mediated sliding of the vRNA:MP:ER complex through Pd; in the absence of MP, by contrast, the ER cannot move through Pd. An alternate model proposes that cell-to-cell spread takes place by diffusion of the MP:vRNA complex in the ER membranes which traverse Pd. To test these models, we measured the effect of TMVMP and replicase expression on cell-to-cell spread of several green fluorescent protein-fused probes: a soluble cytoplasmic protein, two ER lumen proteins, and two ER membrane-bound proteins. Our data support the diffusion model in which a complex that includes ER-embedded MP, vRNA, and other components diffuses in the ER membrane within the Pd driven by the concentration gradient between an infected cell and adjacent noninfected cells. The data also suggest that the virus replicase and MP function together in altering Pd conductivity.

scholarly journals Components of the plasma membrane of growing axons. I. Size and distribution of intramembrane particles.

1984 ◽  
Vol 98 (4) ◽  
pp. 1422-1433 ◽  
Author(s):  
R K Small ◽  
K H Pfenninger
Keyword(s):  
Plasma Membrane ◽  
Growth Cone ◽  
Freeze Fracture ◽  
Particle Diameter ◽  
Lateral Diffusion ◽  
Membrane Composition ◽  
Intramembrane Particles ◽  
Cellular Processes ◽  
Discrete Domains ◽  
Membrane Components

The plasmalemma of mature and growing olfactory axons of the bullfrog has been studied by freeze-fracture. Intramembrane particles (IMPs) of mature olfactory axons are found to be uniformly distributed along the shaft. However, during growth, a decreasing gradient of IMP density is evident along the somatofugal axis. The size histograms of axolemmal IMPs from different segments of growing nerve reveal regional differences in the particle composition. The distribution of each individual size class of particles along the growing nerve forms a decreasing gradient in the somatofugal direction; the slope of these gradients varies directly with particle diameter. These size-dependent density gradients are consistent with a process of lateral diffusion of membrane components that are inserted proximally into the plasma membrane. The membrane composition of the growth cone, however, appears to be independent of these diffusion gradients; it displays a mosaic pattern of discrete domains of high and low particle densities. The relative IMP profiles of these growth cone regions are similar to one another but contain higher densities of large IMPs than the neighboring axonal shaft. The shifting distributions of intramembrane particles that characterize the sprouting neuron give new insights into cellular processes that may underlie the establishment of the functional polarity of the neuron and into the dynamics of axolemmal maturation.

scholarly journals Endoplasmic Reticulum morphological regulation by RTN4/NOGO modulates neuronal regeneration by slowing luminal transport

2021 ◽  
Author(s):  
Tasuku Konno ◽  
Pierre Parutto ◽  
David M. D. Bailey ◽  
Valentina Davì ◽  
Cécile Crapart ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Transport System ◽  
Cortical Neurons ◽  
Intracellular Transport ◽  
Physical Nature ◽  
Bioactive Molecules ◽  
Cell Periphery ◽  
Neuronal Regeneration ◽  
Axonal Extension ◽  
Er Membrane

Cell and tissue functions rely on an elaborate intracellular transport system responsible for distributing bioactive molecules with high spatiotemporal accuracy. The tubular network of the Endoplasmic Reticulum (ER) constitutes a system for the delivery of luminal solutes it stores, including Ca2+, across the cell periphery. The physical nature and factors underlying the ER's functioning as a fluidics system are unclear. Using an improved ER transport visualisation methodology combined with optogenetic Ca2+ dynamics imaging, we observed that ER luminal transport is modulated by natural ER tubule narrowing and dilation, directly proportional to the amount of an ER membrane morphogen, Reticulon 4 (RTN4). Consequently, the ER morphoregulatory effect of RTN4 defines ER's capacity for peripheral Ca2+ delivery and thus controls axonogenesis. Excess RTN4 limited ER luminal transport, Ca2+ release and iPSC-derived cortical neurons' axonal extension, while RTN4 elimination reversed the effects.

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