scholarly journals Mitofusin 2 ablation increases endoplasmic reticulum–mitochondria coupling

2015 ◽  
Vol 112 (17) ◽  
pp. E2174-E2181 ◽  
Author(s):  
Riccardo Filadi ◽  
Elisa Greotti ◽  
Gabriele Turacchio ◽  
Alberto Luini ◽  
Tullio Pozzan ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Morphological Analysis ◽  
Cell Types ◽  
Mitofusin 2 ◽  
Electron And Fluorescence Microscopy ◽  
Microscopy Data ◽  
Key Aspects ◽  
Different Cell Types ◽  
Close Contacts

The organization and mutual interactions between endoplasmic reticulum (ER) and mitochondria modulate key aspects of cell pathophysiology. Several proteins have been suggested to be involved in keeping ER and mitochondria at a correct distance. Among them, in mammalian cells, mitofusin 2 (Mfn2), located on both the outer mitochondrial membrane and the ER surface, has been proposed to be a physical tether between the two organelles, forming homotypic interactions and heterocomplexes with its homolog Mfn1. Recently, this widely accepted model has been challenged using quantitative EM analysis. Using a multiplicity of morphological, biochemical, functional, and genetic approaches, we demonstrate that Mfn2 ablation increases the structural and functional ER–mitochondria coupling. In particular, we show that in different cell types Mfn2 ablation or silencing increases the close contacts between the two organelles and strengthens the efficacy of inositol trisphosphate (IP3)-induced Ca2+ transfer from the ER to mitochondria, sensitizing cells to a mitochondrial Ca2+ overload-dependent death. We also show that the previously reported discrepancy between electron and fluorescence microscopy data on ER–mitochondria proximity in Mfn2-ablated cells is only apparent. By using a different type of morphological analysis of fluorescent images that takes into account (and corrects for) the gross modifications in mitochondrial shape resulting from Mfn2 ablation, we demonstrate that an increased proximity between the organelles is also observed by confocal microscopy when Mfn2 levels are reduced. Based on these results, we propose a new model for ER–mitochondria juxtaposition in which Mfn2 works as a tethering antagonist preventing an excessive, potentially toxic, proximity between the two organelles.

scholarly journals STUDIES ON MICROPEROXISOMES V. ARE MICROPEROXISOMES UBIQUITOUS IN MAMMALIAN CELLS?

1973 ◽  
Vol 21 (8) ◽  
pp. 737-755 ◽  
Author(s):  
ALEX B. NOVIKOFF ◽  
PHYLLIS M. NOVIKOFF ◽  
CLEVELAND DAVIS ◽  
NELSON QUINTANA
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Cell Types ◽  
Malignant Cell ◽  
Zymogen Granules ◽  
Novikoff Hepatoma ◽  
A Cell ◽  
Different Cell Types

A variety of mammalian cell types has been studied by electron microscopy following incubation in a 3,3'-diaminobenzidine medium at pH 9.7 and containing a high H2O2 concentration. This medium visualizes the recently described anucleoid microperoxisomes as well as the nucleoid-containing peroxisomes. All 24 cell types contain 3,3'-diaminobenzidine-positive microperoxisomes but none shows nucleoid-containing peroxisomes. The number of microperoxisomes within a cell varies greatly among different cell types. There are huge numbers in some cell types; in others microperoxisomes are common, few or rare. Such differences imply varying functional significance of these organelles in the metabolism of different cell types. Whether the endoplasmic reticulum (ER) is abundant or scarce or whether its membrane is studded with numerous ribosomes or not, ribosomes are lacking where the ER is connected to the microperoxisomes by slender channels. It may be presumed that molecular interchange occurs between these two organelles. Such interchange may occur between microperoxisomes, ER and lipid droplets, as previously suggested, and between zymogen granules of guinea pig pancreas and ER and microperoxisomes. Two rapidly growing malignant cell types were studied (HeLa and Novikoff hepatoma) and both show moderate numbers of microperoxisomes.

scholarly journals Divergent Mitochondrial and Endoplasmic Reticulum Association of DMPK Splice Isoforms Depends on Unique Sequence Arrangements in Tail Anchors

2005 ◽  
Vol 25 (4) ◽  
pp. 1402-1414 ◽  
Author(s):  
René E. M. A. van Herpen ◽  
Ralph J. A. Oude Ophuis ◽  
Mietske Wijers ◽  
Miranda B. Bennink ◽  
Fons A. J. van de Loo ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Kinase ◽  
Myotonic Dystrophy ◽  
Mammalian Cells ◽  
Cell Types ◽  
Unique Sequence ◽  
Protein Isoforms ◽  
Mitochondrial Outer Membrane ◽  
Splice Isoforms ◽  
Triplet Repeat Expansion

ABSTRACT Myotonic dystrophy protein kinase (DMPK) is a Ser/Thr-type protein kinase with unknown function, originally identified as the product of the gene that is mutated by triplet repeat expansion in patients with myotonic dystrophy type 1 (DM1). Alternative splicing of DMPK transcripts results in multiple protein isoforms carrying distinct C termini. Here, we demonstrate by expressing individual DMPKs in various cell types, including C2C12 and DMPK −/− myoblast cells, that unique sequence arrangements in these tails control the specificity of anchoring into intracellular membranes. Mouse DMPK A and C were found to associate specifically with either the endoplasmic reticulum (ER) or the mitochondrial outer membrane, whereas the corresponding human DMPK A and C proteins both localized to mitochondria. Expression of mouse and human DMPK A—but not C—isoforms in mammalian cells caused clustering of ER or mitochondria. Membrane association of DMPK isoforms was resistant to alkaline conditions, and mutagenesis analysis showed that proper anchoring was differentially dependent on basic residues flanking putative transmembrane domains, demonstrating that DMPK tails form unique tail anchors. This work identifies DMPK as the first kinase in the class of tail-anchored proteins, with a possible role in organelle distribution and dynamics.

scholarly journals A Fresh Look at the Structure, Regulation, and Functions of Fodrin

2020 ◽  
Vol 40 (17) ◽  
Author(s):  
Jamuna S. Sreeja ◽  
Rince John ◽  
Dhrishya Dharmapal ◽  
Rohith Kumar Nellikka ◽  
Suparna Sengupta
Keyword(s):  
Posttranslational Modifications ◽  
Mammalian Cells ◽  
Structural Integrity ◽  
Cell Function ◽  
Cell Types ◽  
Erythroid Cell ◽  
Structural Variations ◽  
Neuronal Tissues ◽  
Different Cell Types ◽  
Neuronal Disorders

ABSTRACT Fodrin and its erythroid cell-specific isoform spectrin are actin-associated fibrous proteins that play crucial roles in the maintenance of structural integrity in mammalian cells, which is necessary for proper cell function. Normal cell morphology is altered in diseases such as various cancers and certain neuronal disorders. Fodrin and spectrin are two-chain (αβ) molecules that are encoded by paralogous genes and share many features but also demonstrate certain differences. Fodrin (in humans, typically a heterodimer of the products of the SPTAN1 and SPTBN1 genes) is expressed in nearly all cell types and is especially abundant in neuronal tissues, whereas spectrin (in humans, a heterodimer of the products of the SPTA1 and SPTB1 genes) is expressed almost exclusively in erythrocytes. To fulfill a role in such a variety of different cell types, it was anticipated that fodrin would need to be a more versatile scaffold than spectrin. Indeed, as summarized here, domains unique to fodrin and its regulation by Ca2+, calmodulin, and a variety of posttranslational modifications (PTMs) endow fodrin with additional specific functions. However, how fodrin structural variations and misregulated PTMs may contribute to the etiology of various cancers and neurodegenerative diseases needs to be further investigated.

scholarly journals Reticulon 4a promotes exocytosis in mammalian cells

2019 ◽  
Vol 30 (18) ◽  
pp. 2349-2357 ◽  
Author(s):  
Richik Nilay Mukherjee ◽  
Daniel L. Levy
Keyword(s):  
Cell Surface ◽  
Protein Trafficking ◽  
Mammalian Cells ◽  
Cell Types ◽  
Vesicular Trafficking ◽  
Secreted Proteins ◽  
Mammalian Cell Lines ◽  
Rough Er ◽  
Different Cell Types ◽  
Functional Output

Endoplasmic reticulum (ER) tubules and sheets conventionally correspond to smooth and rough ER, respectively. The ratio of ER tubules-to-sheets varies in different cell types and changes in response to cellular conditions, potentially impacting the functional output of the ER. To directly test whether ER morphology impacts vesicular trafficking, we increased the tubule-to-sheet ratio in three different ways, by overexpressing Rtn4a, Rtn4b, or REEP5. Only Rtn4a overexpression increased exocytosis, but not overall levels, of several cell surface and secreted proteins. Furthermore, Rtn4a depletion reduced cell surface trafficking without affecting ER morphology. Similar results were observed in three different mammalian cell lines, suggesting that Rtn4a generally enhances exocytosis independently of changes in ER morphology. Finally, we show that Rtn4a levels modulate cell adhesion, possibly by regulating trafficking of integrins to the cell surface. Taking the results together, we find that altering ER morphology does not necessarily affect protein trafficking, but that Rtn4a specifically enhances exocytosis.

scholarly journals S100A6 and Its Brain Ligands in Neurodegenerative Disorders

2020 ◽  
Vol 21 (11) ◽  
pp. 3979
Author(s):  
Anna Filipek ◽  
Wiesława Leśniak
Keyword(s):  
Mammalian Cells ◽  
Brain Structures ◽  
Cell Types ◽  
Cytoskeletal Organization ◽  
High Level ◽  
S100a6 Protein ◽  
Different Cell Types ◽  
The Brain ◽  
Lateral Sclerosis

The S100A6 protein is present in different mammalian cells and tissues including the brain. It binds Ca2+ and Zn2+ and interacts with many target proteins/ligands. The best characterized ligands of S100A6, expressed at high level in the brain, include CacyBP/SIP and Sgt1. Research concerning the functional role of S100A6 and these two ligands indicates that they are involved in various signaling pathways that regulate cell proliferation, differentiation, cytoskeletal organization, and others. In this review, we focused on the expression/localization of these proteins in the brain and on their possible role in neurodegenerative diseases. Published results demonstrate that S100A6, CacyBP/SIP, and Sgt1 are expressed in various brain structures and in the spinal cord and can be found in different cell types including neurons and astrocytes. When it comes to their possible involvement in nervous system pathology, it is evident that their expression/level and/or subcellular localization is changed when compared to normal conditions. Among diseases in which such changes have been observed are Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), epileptogenesis, Parkinson’s disease (PD), Huntington’s disease (HD), and others.

scholarly journals TAPping into the treasures of tubulin using novel protein production methods

2018 ◽  
Vol 62 (6) ◽  
pp. 781-792
Author(s):  
Nuo Yu ◽  
Niels Galjart
Keyword(s):  
Mammalian Cells ◽  
Gene Families ◽  
Cell Types ◽  
Cellular Functions ◽  
Tubulin Isotypes ◽  
Associated Proteins ◽  
Cytoskeletal Elements ◽  
Different Cell Types ◽  
Β Tubulin

Microtubules are cytoskeletal elements with important cellular functions, whose dynamic behaviour and properties are in part regulated by microtubule-associated proteins (MAPs). The building block of microtubules is tubulin, a heterodimer of α- and β-tubulin subunits. Longitudinal interactions between tubulin dimers facilitate a head-to-tail arrangement of dimers into protofilaments, while lateral interactions allow the formation of a hollow microtubule tube that mostly contains 13 protofilaments. Highly homologous α- and β-tubulin isotypes exist, which are encoded by multi-gene families. In vitro studies on microtubules and MAPs have largely relied on brain-derived tubulin preparations. However, these consist of an unknown mix of tubulin isotypes with undefined post-translational modifications. This has blocked studies on the functions of tubulin isotypes and the effects of tubulin mutations found in human neurological disorders. Fortunately, various methodologies to produce recombinant mammalian tubulins have become available in the last years, allowing researchers to overcome this barrier. In addition, affinity-based purification of tagged tubulins and identification of tubulin-associated proteins (TAPs) by mass spectrometry has revealed the ‘tubulome’ of mammalian cells. Future experiments with recombinant tubulins should allow a detailed description of how tubulin isotype influences basic microtubule behaviour, and how MAPs and TAPs impinge on tubulin isotypes and microtubule-based processes in different cell types.

scholarly journals Growth of mammalian cells on substrates coated with cellular microexudates. I. Effect on cell growth at low population densities.

1975 ◽  
Vol 64 (1) ◽  
pp. 135-145 ◽  
Author(s):  
L Weiss ◽  
G Poste ◽  
A MacKearnin ◽  
K Willett
Keyword(s):  
Mammalian Cells ◽  
Cell Types ◽  
Cell Populations ◽  
Growth Enhancement ◽  
Plastic Substrates ◽  
Embryo Cells ◽  
Cell Layers ◽  
Feeder Cell Layers ◽  
Different Cell Types ◽  
Macromolecular Composition

Mammalian and avian cells cultured on glass or plastic substrates produce microexudates of cellular macromolecules which remain bound to the substrate when the cells are detached. The gross macromolecular composition of microexudates from a range of diploid, heteroploid, and virus-transformed cells was determined with cells labeled with radioisotopes. Significant differences in the amounts of cellular glycoproteins, proteins, and RNA present in microexudates were found between different cell types and between cells of the same type at different stages of growth. Inoculation of cells onto substrates "coated" with microexudates altered their growth behavior. Microexudates from exponentially growing subconfluent homotypic and heterotypic cell populations enhanced the growth of mouse and chick embryo cells seeded at very low densities, but similar microexudates had no effect on the proliferation of cells seeded at higher densities. The enhanced growth of low-density cell populations seeded on microexudates was compared with the growth enhancement produced by feeder cell layers and conditioned medium.

scholarly journals STUDIES ON THE ENDOPLASMIC RETICULUM

1955 ◽  
Vol 1 (6) ◽  
pp. 567-582 ◽  
Author(s):  
George E. Palade
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Membrane ◽  
Cell Types ◽  
Three Dimensions ◽  
Mature Erythrocyte ◽  
Nuclear Membranes ◽  
Membrane Bound ◽  
Different Cell Types

A survey of a large number of different cell types has indicated the presence of a network of membrane-bound cavities (the endoplasmic reticulum) in the cytoplasm of all cell types examined, with the exception of the mature erythrocyte. In its simplest form, encountered in seminal epithelia and in leucocytes, the reticulum consists mainly of interconnected strings of vesicles and appears to be randomly disposed in three dimensions. Local differentiations occur within the endoplasmic reticulum of all the cell types studied. The membrane limiting the cavities of the endoplasmic reticulum appears to be continuous with the cell membrane and the nuclear membranes.

scholarly journals The endoplasmic reticulum adopts two distinct forms of tubules

2021 ◽  
Author(s):  
Ke Xu ◽  
Bowen Wang ◽  
Zhiheng Zhao ◽  
Michael Xiong ◽  
Rui Yan
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Super Resolution ◽  
Cell Types ◽  
Membrane Curvature ◽  
Calcium Storage ◽  
Complex Membrane ◽  
Functional Implications ◽  
Different Cell Types ◽  
Super Resolution Microscopy

Abstract Being the largest and most expansive organelle in the cell, the endoplasmic reticulum (ER) carries diverse key functions from protein and lipid synthesis, protein folding and modification, transport, calcium storage, to organelle interactions1-6. The shaping mechanism of this complex, membrane-bounded organelle is thus of fundamental significance7-21. Using super-resolution microscopy, we uncover the coexistence of two distinct, well-defined forms of ER tubules in the mammalian cell. Whereas an ultrathin form, R1, is consistently covered by the membrane curvature-promoting protein Rtn4, in the second form, R2, Rtn4 curiously appears as two parallel lines at a conserved separation of ~105 nm over long ranges. The two tubule forms together account for ~90% of the total tubule lengths, with either one being dominant in different cell types. The R1-R2 dichotomy and the final tubule geometry are both co-regulated by Rtn4 and the ER sheet-maintaining protein Climp63, which respectively define the edge curvature and lumen height of the R2 tubules to generate a ribbon-like structure of well-defined width. The R1 and R2 tubules undergo active remodeling in the cell as they differently accommodate proteins, with the former effectively excluding ER-luminal proteins and ER-membrane proteins with large intraluminal domains. We thus unveil a dynamic ER-tubule structural dichotomy with intriguing functional implications.

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