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 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 The FATP1–DGAT2 complex facilitates lipid droplet expansion at the ER–lipid droplet interface

2012 ◽  
Vol 198 (5) ◽  
pp. 895-911 ◽  
Author(s):  
Ningyi Xu ◽  
Shaobing O. Zhang ◽  
Ronald A. Cole ◽  
Sean A. McKinney ◽  
Fengli Guo ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Lipid Droplet ◽  
Mammalian Cells ◽  
Lipid Droplets ◽  
Molecular Mechanisms ◽  
Diacylglycerol Acyltransferase ◽  
Present Evidence ◽  
Evolutionarily Conserved ◽  
Subcellular Level

At the subcellular level, fat storage is confined to the evolutionarily conserved compartments termed lipid droplets (LDs), which are closely associated with the endoplasmic reticulum (ER). However, the molecular mechanisms that enable ER–LD interaction and facilitate neutral lipid loading into LDs are poorly understood. In this paper, we present evidence that FATP1/acyl-CoA synthetase and DGAT2/diacylglycerol acyltransferase are components of a triglyceride synthesis complex that facilitates LD expansion. A loss of FATP1 or DGAT2 function blocked LD expansion in Caenorhabditis elegans. FATP1 preferentially associated with DGAT2, and they acted synergistically to promote LD expansion in mammalian cells. Live imaging indicated that FATP1 and DGAT2 are ER and LD resident proteins, respectively, and electron microscopy revealed FATP1 and DGAT2 foci close to the LD surface. Furthermore, DGAT2 that was retained in the ER failed to support LD expansion. We propose that the evolutionarily conserved FATP1–DGAT2 complex acts at the ER–LD interface and couples the synthesis and deposition of triglycerides into LDs both physically and functionally.

scholarly journals ATP increases within the lumen of the endoplasmic reticulum upon intracellular Ca2+release

2014 ◽  
Vol 25 (3) ◽  
pp. 368-379 ◽  
Author(s):  
Neelanjan Vishnu ◽  
Muhammad Jadoon Khan ◽  
Felix Karsten ◽  
Lukas N. Groschner ◽  
Markus Waldeck-Weiermair ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Single Cells ◽  
Cell Types ◽  
Additional Energy ◽  
Intracellular Ca ◽  
A Cell ◽  
Specific Regulation ◽  
Amp Activated Protein Kinase ◽  
Different Cell Types

Multiple functions of the endoplasmic reticulum (ER) essentially depend on ATP within this organelle. However, little is known about ER ATP dynamics and the regulation of ER ATP import. Here we describe real-time recordings of ER ATP fluxes in single cells using an ER-targeted, genetically encoded ATP sensor. In vitro experiments prove that the ATP sensor is both Ca2+and redox insensitive, which makes it possible to monitor Ca2+-coupled ER ATP dynamics specifically. The approach uncovers a cell type–specific regulation of ER ATP homeostasis in different cell types. Moreover, we show that intracellular Ca2+release is coupled to an increase of ATP within the ER. The Ca2+-coupled ER ATP increase is independent of the mode of Ca2+mobilization and controlled by the rate of ATP biosynthesis. Furthermore, the energy stress sensor, AMP-activated protein kinase, is essential for the ATP increase that occurs in response to Ca2+depletion of the organelle. Our data highlight a novel Ca2+-controlled process that supplies the ER with additional energy upon cell stimulation.

Study of the Molecular Architecture of Keratin Filaments by Electron Microscopy

1982 ◽  
Vol 40 ◽  
pp. 118-119
Author(s):  
U. Aebi ◽  
P. Rew ◽  
T.-T. Sun
Keyword(s):  
Electron Microscopy ◽  
Structural Organization ◽  
Cell Types ◽  
Structural Features ◽  
Molecular Architecture ◽  
The Past ◽  
Keratin Filaments ◽  
Different Types ◽  
10 Nm Filaments ◽  
Different Cell Types

Various types of intermediate-sized (10-nm) filaments have been found and described in many different cell types during the past few years. Despite the differences in the chemical composition among the different types of filaments, they all yield common structural features: they are usually up to several microns long and have a diameter of 7 to 10 nm; there is evidence that they are made of several 2 to 3.5 nm wide protofilaments which are helically wound around each other; the secondary structure of the polypeptides constituting the filaments is rich in ∞-helix. However a detailed description of their structural organization is lacking to date.

scholarly journals Permeabilization of rat hepatocytes with Staphylococcus aureus alpha-toxin.

1985 ◽  
Vol 100 (6) ◽  
pp. 1922-1929 ◽  
Author(s):  
B F McEwen ◽  
W J Arion
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Rat Hepatocytes ◽  
Alpha Toxin ◽  
Cellular Functions ◽  
Transmembrane Channel ◽  
Selective Permeability ◽  
Treatment Conditions ◽  
Transmission Electron ◽  
A Cell

Pathogenic staphylococci secrete a number of exotoxins, including alpha-toxin. alpha-Toxin induces lysis of erythrocytes and liposomes when its 3S protein monomers associate with the lipid bilayer and form a hexomeric transmembrane channel 3 nm in diameter. We have used alpha-toxin to render rat hepatocytes 93-100% permeable to trypan blue with a lactate dehydrogenase leakage less than or equal to 22%. Treatment conditions included incubation for 5-10 min at 37 degrees C and pH 7.0 with an alpha-toxin concentration of 4-35 human hemolytic U/ml and a cell concentration of 13-21 mg dry wt/ml. Scanning electron microscopy revealed signs of swelling in the treated hepatocytes, but there were no large lesions or gross damage to the cell surface. Transmission electron microscopy indicated that the nucleus, mitochondria, and cytoplasm were similar in control and treated cells and both had large regions of well-defined lamellar rough endoplasmic reticulum. Comparisons of the mannose-6-phosphatase and glucose-6-phosphatase activities demonstrated that 5-10 U/ml alpha-toxin rendered cells freely permeable to glucose-6-phosphate, while substantially preserving the selective permeability of the membranes of the endoplasmic reticulum and the functionality of the glucose-6-phosphatase system. Thus, alpha-toxin appears to have significant potential as a means to induce selective permeability to small ions. It should make possible the study of a variety of cellular functions in situ.

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 THE SARCOPLASMIC RETICULUM IN MUSCLE CELLS OF AMBLYSTOMA LARVAE

1956 ◽  
Vol 2 (4) ◽  
pp. 163-170 ◽  
Author(s):  
Keith R. Porter
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Sarcoplasmic Reticulum ◽  
Constant Width ◽  
Muscle Cells ◽  
Cell Types ◽  
Thin Sections ◽  
System A ◽  
Structural Relationships ◽  
Complex Membrane

Electron microscopy of thin sections of muscle fibers in myotomes of Amblystoma larvae has revealed the presence of a complex, membrane-limited system of canaliculi and vesicles which form a lace-like reticulum around and among the myofibrils. This seems to correspond to the sarcoplasmic reticulum of the earlier light microscopists and the endoplasmic reticulum of other cell types. The elements constituting the reticulum are disposed in a pattern which bears a constant relation to the bands of the adjacent myofibrils and is therefore repeated in each sarcomere. At the H band the system is transversely continuous but not so at other levels. Longitudinally continuity is interrupted at the Z bands where large vesicles belonging to adjacent sarcomere segments of the system face off on opposite sides of the band. The opposing faces of these vesicles are flat and separated by a space of more or less constant width, in which are located small, finger-shaped vesicles. In view of these and other close structural relationships with the myofibrils it seems appropriate to assign to the system a role in the conduction of the excitatory impulse.

scholarly journals A conserved family of proteins facilitates nascent lipid droplet budding from the ER

2015 ◽  
Vol 211 (2) ◽  
pp. 261-271 ◽  
Author(s):  
Vineet Choudhary ◽  
Namrata Ojha ◽  
Andy Golden ◽  
William A. Prinz
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Lipid Metabolism ◽  
Caenorhabditis Elegans ◽  
Lipid Droplet ◽  
Lipid Droplets ◽  
De Novo ◽  
Fat Storage ◽  
Higher Eukaryotes ◽  
Er Membrane

Lipid droplets (LDs) are found in all cells and play critical roles in lipid metabolism. De novo LD biogenesis occurs in the endoplasmic reticulum (ER) but is not well understood. We imaged early stages of LD biogenesis using electron microscopy and found that nascent LDs form lens-like structures that are in the ER membrane, raising the question of how these nascent LDs bud from the ER as they grow. We found that a conserved family of proteins, fat storage-inducing transmembrane (FIT) proteins, is required for proper budding of LDs from the ER. Elimination or reduction of FIT proteins in yeast and higher eukaryotes causes LDs to remain in the ER membrane. Deletion of the single FIT protein in Caenorhabditis elegans is lethal, suggesting that LD budding is an essential process in this organism. Our findings indicated that FIT proteins are necessary to promote budding of nascent LDs from the ER.

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