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At least 19 recordsLinked to original sources
PubMed1992

Subcompartments of the endoplasmic reticulum.

The endoplasmic reticulum (ER) is the largest continuous endomembrane structure in the cytoplasm. It may be viewed as a series of unique subcompartments. In this review, we examine the rough ER, nuclear envelope and several smooth ER subcompartments. Consideration is given to the characteristic properties and functions of the ER and its domains, and to the formation and maintenance of subcompartments. Associations within the ER membrane bilayer, and with constituents of the cytoplasm and the ER lumen, contribute to the formation of domains and lead to the establishment of subcompartments that reflect specialized functions and vary according to the physiologic state and phenotype of the individual cell. Although the structural complexity of some ER subcompartments (such as the sarcoplasmic reticulum) is highly elaborate, the ER remains a dynamic organelle, subject to assembly and disassembly, capable of extensive remodelling and active in exchange with other organelles through mechanisms of membrane transport.

Animals↗
PubMedDate not supplied

Relationships between MR-imaged total amount of tissue removed, resection scores of specific mediobasal limbic subcompartments and clinical outcome following selective amygdalohippocampectomy.

Of 204 patients who underwent a selective amygdalohippocampectomy at our hospital, we studied 30 in whom special pre- and postoperative MR imaging was carried out and who were followed up for at least 1 year postoperatively. We measured the total size of the resection and the extent to which the following specific mediobasal temporal lobe structures had been removed: amygdala, hippocampus, pes hippocampi, dentate gyrus, parahippocampal gyrus, uncus and subiculum. Postoperative seizure control was correlated with the overall size of the resection as well as with the resection scores of the above mentioned limbic subcompartments. The mean size of the removed tissue was 7.2 cm3 (range: 2.1-17.7). The mean resection scores of the limbic subcompartments (in percentages) are: amygdala 92%, hippocampus 46%, pes hippocampi 92%, dentate gyrus 45%, parahippocampal gyrus 32%, uncus 92%, subiculum 40%. Although a small resection did not exclude a good outcome, the general tendency was that a better outcome was obtained from a larger resection. With regard to the resection scores of the limbic subcompartments, a positive correlation emerged between good postoperative outcome and the radicality of the removal of the parahippocampal gyrus (and the subiculum, which has been evaluated separately). These findings support our previously formulated amplifier hypothesis for the parahippocampal gyrus.

Adult↗
PubMed2025

esBAF and INO80C fine-tune subcompartments and differentially regulate enhancer-promoter interactions.

The genome is compacted in the nucleus through a hierarchical chromatin organization, ranging from chromosome territories to compartments, topologically associating domains (TADs), and individual nucleosomes. Nucleosome remodeling complexes hydrolyze ATP to translocate DNA and thereby mobilize histone proteins. While nucleosome remodeling complexes have been extensively studied for their roles in regulating nucleosome positioning and accessibility, their contributions to higher-order chromatin architecture remain less well understood. Here, we investigate the roles of two key nucleosome remodelers, esBAF and INO80C, in shaping 3D genome organization in mouse embryonic stem cells. Using Hi-C, we find that loss of either remodeler has minimal effects on global compartment or TAD structures. In contrast, subcompartment organization is notably altered, suggesting that esBAF and INO80C contribute to finer-scale chromatin topology. To overcome the limited resolution of Hi-C for detecting regulatory loops, we employed promoter capture Micro-C (PCMC), which revealed that the loss of esBAF or INO80C alters a subset of promoter anchored looping interactions. Although these changes occur at distinct genomic loci for each remodeler, the affected sites are commonly enriched for bivalent chromatin regions bound by OCT4, SOX2, and NANOG (OSN), as well as BRG1 and INO80 themselves. Together, our findings reveal that esBAF and INO80C selectively influence subcompartment identity and enhancer-promoter communication at key regulatory loci, highlighting a previously underappreciated role for nucleosome remodelers in higher-order chromatin organization.

chromatin↗
PubMed1992

Ca2+ stores in Purkinje neurons: endoplasmic reticulum subcompartments demonstrated by the heterogeneous distribution of the InsP3 receptor, Ca(2+)-ATPase, and calsequestrin.

The nature of second messenger-responsive intracellular Ca2+ stores in neurons remains open for discussion. Here, we demonstrate the existence in Purkinje cells (PCs) of endoplastic reticulum (ER) subcompartments characterized by an uneven distribution of three proteins involved in Ca2+ storage and release: the inositol 1,4,5-trisphosphate (InsP3) receptor, Ca(2+)-ATPase, and calsequestrin. Ca(2+)-ATPase and the InsP3 receptor have a widespread, although not identical, distribution throughout the ER. Calsequestrin is localized throughout the smooth ER and is particularly concentrated in pleiomorphic vesicles with a moderately electron-dense core, which appear to represent a subcompartment of the smooth ER. In double-labeling experiments many of these vesicles were unlabeled by InsP3 receptor antibodies. These results suggest a key role of the ER as an intracellular Ca2+ store and demonstrate a possible structural basis for distinct intracellular Ca2+ pools regulated by different second messengers.

Animals↗
PubMed1988

Organelle-specific antibodies: production of antibodies to Golgi subcompartments.

We have devised a strategy for producing Golgi subcompartment-specific antibodies that involves utilizing Triton X-114-phase separated membrane proteins derived from rat pancreatic Golgi subfractions as immunogens. When we tested the approach by immunizing rabbits with membrane proteins derived from heavy Golgi subfractions that are known to be enriched in cis Golgi elements, we succeeded in generating an antibody that recognized a 58 kD protein that was restricted in its distribution to cis Golgi cisternae in several cell types. Thus we have demonstrated the feasibility of the approach we devised for generation of Golgi subcompartment-specific antibodies, and we have also succeeded in identifying a heretofore unknown cis Golgi marker protein.

Animals↗
PubMed1992

Transport of proteins into the various subcompartments of mitochondria.

The import of proteins into mitochondria is an intricate process comprised of multiple steps. The first step involves the sorting of cytosolically synthesized precursor proteins to the mitochondrial surface. There precursor proteins are recognized by specific receptors which deliver them to the general import site present in the outer membrane. The second stage of import involves a series of complex intraorganelle sorting events which results in the delivery of the proteins to one of the four possible submitochondrial destinations, namely the outer and inner membranes, the matrix and intermembrane space. Here in this review, we discuss the current knowledge on these intramitochondrial sorting events. We especially focus on targeting of proteins to the intermembrane space. Sorting to the intermembrane space represents a particularly interesting situation, as at least three separate targeting pathways to this subcompartment are known to exist.

Biological Transport↗
PubMed1990

The inositol 1,4,5,-trisphosphate receptor in cerebellar Purkinje cells: quantitative immunogold labeling reveals concentration in an ER subcompartment.

The Ca2+ mobilization effect of inositol 1,4,5-trisphosphate, the second messenger generated via receptor-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate, is mediated by binding to intracellular receptors, which are expressed in high concentration in cerebellar Purkinje cells. Partially conflicting previous reports localized the receptor to various subcellular structures: elements of ER, both rough and smooth-surfaced, the nuclear envelope, and even the plasma membrane. We have now reinvestigated the problem quantitatively by using cryosections of rat cerebellar tissue immunolabeled with polyclonal monospecific antibodies against the inositol 1,4,5-trisphosphate receptor. By immunofluorescence the receptor was detected only in Purkinje cells, whereas the other cells of the cerebellar cortex remained negative. In immunogold-decorated ultrathin cryosections of the Purkinje cell body, the receptor was concentrated in cisternal stacks (piles of up to 12 parallel cisternae separated by regularly spaced bridges, located both in the deep cytoplasm and beneath the plasma membrane; average density, greater than 5 particles/micron of membrane profile); in cisternal singlets and doublets adjacent to the plasma membrane (average density, approximately 2.5 particles/micron); and in other apparently smooth-surfaced vesicular and tubular profiles. Additional smooth-surfaced elements were unlabeled. Perinuclear and rough-surfaced ER cisternae were labeled much less by themselves (approximately 0.5 particles/micron, two- to threefold the background), but were often in direct membrane continuity with heavily labeled, smooth-surfaced tubules and cisternal stacks. Finally, mitochondria, Golgi cisternae, multivesicular bodies, and the plasma membrane were unlabeled. In dendrites, approximately half of the nonmitochondrial, membrane-bound structures (cisternae, tubules, and vesicles), as well as small cisternal stacks, were labeled. Dendritic spines always contained immunolabeled cisternae and vesicles. The dendritic plasma membrane, of both shaft and spines, was consistently unlabeled. These results identify a large, smooth-surfaced ER subcompartment that appears equipped to play a key role in the control of Ca2+ homeostasis: in particular, in the generation of [Ca2+]i transients triggered by activation of specific receptors, such as the quisqualate-preferring trans(+/-)-1-amino-1,3-cyclopentamedicarboxylic acid glutamatergic receptors, which are largely expressed by Purkinje cells.

Animals↗
PubMed1991

Immunoelectron microscopic study of a new D-amino acid oxidase-immunoreactive subcompartment in rat liver peroxisomes.

We report the presence of a new subcompartment in rat liver peroxisomal matrix in which only D-amino acid oxidase is localized and other matrix enzymes are absent. By electron microscopic observation, the rat liver peroxisome has generally been considered to consist of a single limiting membrane, an electron-dense crystalline core, and a homogeneous matrix. Immunohistochemical staining for D-amino acid oxidase by the protein A-gold technique revealed the presence of a small area in the matrix that was immunoreactive for the enzyme and was less electron-dense than the surrounding matrix. The localization of D-amino acid oxidase in this small area of the peroxisomal matrix was confirmed by immunoelectron microscopy on freeze-substituted tissues processed without chemical fixation. To analyze the characteristics of the electron-lucent area, immunoreactivity for various peroxisomal enzymes, including catalase, acyl-CoA oxidase, enoyl-CoA hydratase/3-hydroxyacyl-CoA dehydrogenase bifunctional protein, 3-ketoacyl-CoA thiolase, L-alpha-hydroxy acid oxidase (isozyme B), and glycolate oxidase (isozyme A), was assayed. The electron-lucent area was negative for all of these. By double staining for D-amino acid oxidase and catalase, using colloidal gold particles of different sizes, these enzymes were shown to be located in separate areas in the matrix.

Animals↗
PubMed1989

Biochemical, kinetic and cytochemical approaches resolve Golgi subcompartments of IgM-secreting rat myeloma cells.

The rat myeloma cells chosen for study (IR202) are highly specialized toward the synthesis and secretion of immunoglobulin M (IgM). In [35S]methionine pulse-chase protocols the half-time for secretion of newly synthesized [35S]Ig at 37 degrees C is approximately 2 1/2 h. No degradation of [35S]Ig was detected in such experiments. Pulse-chase experiments with [3H]galactose show that addition of this terminal sugar occurs only approximately 2 min before discharge. The intracellular pool of Ig bearing mature oligosaccharides is therefore very small. Incubation at 20 degrees C stops secretion of the [35S]- and [3H]Ig. We describe a subcellular fractionation protocol for these cells which results in the recovery of a total microsomal fraction by gel filtration. This fraction includes approximately 1/4 of the galactosyltransferase and uridine diphosphatase (UDPase) of the homogenate. By employing two cytological Golgi markers (an "overosmicatable material" and UDPase), galactosyltransferase activity and [35S]methionine and [3H]galactose pulse-chase protocols with the chase at 15 degrees C we document the partial resolution of Golgi subcompartments in isopycnic sucrose gradients used to subfractionate the total microsomal fraction. Electron microscopic and enzymologic examination of the fractions resolved by these gradients confirm that rough microsomes are well separated from Golgi membranes and that the fractions most highly enriched in galactosyltransferase activity have a protein-based specific activity approximately 10 times that of the total microsomal fraction. These studies, therefore, form the basis for an analysis of the composition of the membranes of the Golgi Complex and document the location of proximal Golgi elements, as defined by cytological criteria, in isopycnic gradients.

Animals↗
PubMed1991

Subcompartment sugar residues of gastric surface mucous cells studied with labeled lectins.

We examined the intracellular localization of sugar residues of the rat gastric surface mucous cells in relation to the functional polarity of the cell organellae using preembedding method with several lectins. In the surface mucous cells, the nuclear envelope and rough endoplasmic reticulum (rER) and cis cisternae of the Golgi stacks were intensely stained with Maclura pomifera (MPA), which is specific to alpha-Gal and GalNAc residues. In the Golgi apparatus, one or two cis side cisternae were stained with MPA and Dolichos biflorus (DBA) which is specific to terminal alpha-N-acetylgalactosamine residues, while the intermediate lamellae were intensely labeled with Arachis hypogaea (PNA) which is specific to Gal beta 1,3 GalNAc. Cisternae of the trans Golgi region were also stained with MPA, Ricinus communis I (RCA I) which is specific to beta-Gal and Limax flavus (LFA) which is specific to alpha-NeuAc. Immature mucous granules which are contiguous with the trans Golgi lamellae were weakly stained with RCA I, while LFA stained both immature and mature granules. The differences between each lectin's reactivity in the rough endoplasmic reticulum, in each compartment of the Golgi lamellae and in the secretory granules suggest that there are compositional and structural differences between the glycoconjugates in the respective cell organellae, reflecting the various processes of glycosylation in the gastric surface mucous cells.

Animals↗
PubMed1992

The effect of changes in thiol subcompartments on T-cell colony formation and cell cycle progression: relevance to AIDS.

Recently, it has been shown that intra- and extracellular thiol levels are significantly lower than normal even in the relatively early stages of human immunodeficiency virus (HIV) infection. It is plausible that this deficiency could contribute both to the loss of T-cell function and the ability to replenish T cells associated with HIV infection. We had previously reported that the T-cell colony-forming cell (T-CFC) is impaired in HIV infection and that it can be enhanced with the thiol compounds 2-mercaptoethanol (2-ME) and N-acetylcysteine (NAC). In this study, the effect of the thiol-depleting reagents buthionine sulfoximine, cyclohexene-1-one, and copper phenanthroline on T-CFC formation and cell cycle progression was determined in HIV+ subject and/or controls. All three reagents inhibited T-CFC formation and cell cycle progression with a suggestion that colony formation by cells from HIV+ subjects was more sensitive to the effects of thiol depletion. 2-ME and NAC enhanced effect of NAC did not appear to involve increased protein kinase C translocation. Our results suggest that oxidation of membrane thiols, as well as depletion of intracellular glutathione, inhibits T-CFC formation as well as cell cycle progression for mitogen-stimulated cells in bulk culture.

Acetylcysteine↗
PubMed1988

Immunoelectron microscopic localization of synaptophysin in a Golgi subcompartment of developing hypothalamic neurons.

Synaptophysin, previously identified as an integral membrane glycoprotein (mol. wt 38,000) characteristic of presynaptic vesicles of mature neurons, provides a molecular marker to study the origin, formation and traffic of synaptic vesicles. Using the monoclonal antibody SY38 against this polypeptide we have localized synaptophysin by immunofluorescence and electron microscope immunoperoxidase methods in cultured mouse hypothalamic neurons taken from 16-day-old fetuses which achieve synaptogenesis after 10-12 days in vitro. We have compared the localization of synaptophysin in perikarya and nerve endings as a function of age (2-19 days in vitro) and of treatment of mature neurons with nocodazole. Using immunofluorescence microscopy, synaptophysin was already detected in neuronal soma at 2 days in vitro, where the initiation of neurite development is observed. At the electron microscope level, virtually all mature synaptic boutons and varicosities showed an extensive synaptophysin labeling of synaptic vesicles at 12-13 days in culture whereas neurites showed only very few labeled vesicles. In neuronal soma taken before synapse formation (6 days in vitro), synaptophysin was selectively localized in membranes of the innermost cisternae of the Golgi zone and in vesicles of variable size and shape in the core of the Golgi zone. In contrast, after synapse formation, synaptophysin labeling was barely detected in the Golgi zone of neurons but a very strong labeling of synaptic vesicles in synaptic boutons was observed. Treatment of mature neurons (12 days in vitro) with nocodazole (10(-5) M) resulted in a conspicuous synaptophysin staining of the innermost trans-Golgi cisternae and numerous vesicles in the cytoplasm. Furthermore, an accumulation of labeled synaptic vesicles on the presynaptic membrane of nerve terminals was found. The data suggest that synaptophysin is released from the Golgi apparatus in a vesicular form, after glycosylation, and is then transported to nerve endings by a mechanism which requires integrity of microtubules.

Animals↗
PubMed1992

Structure-function subcompartments of the mammalian cell nucleus as revealed by the electron microscopic affinity cytochemistry.

This electron microscopy review documents the in situ cytochemical localization of important nuclear structures and relates this to the important nuclear functions of RNA transcription and processing. With the help of specific probes (antibodies, nucleic acid probes), a comprehensive picture of nuclear subcompartmentalization is beginning to emerge.

3T3 Cells↗
PubMed1985

Proteoglycan biosynthesis in chondrocytes: protein A-gold localization of proteoglycan protein core and chondroitin sulfate within Golgi subcompartments.

The intracellular pathway of cartilage proteoglycan biosynthesis was investigated in isolated chondrocytes using a protein A-gold electron microscopy immunolocalization procedure. Proteoglycans contain a protein core to which chondroitin sulfate and keratan sulfate chains and oligosaccharides are added in posttranslational processing. Specific antibodies have been used in this study to determine separately the distribution of the protein core and chondroitin sulfate components. In normal chondrocytes, proteoglycan protein core was readily localized only in smooth-membraned vesicles which co-labeled with ricin, indicating them to be galactose-rich medial/trans-Golgi cisternae, whereas there was only a low level of labeling in the rough endoplasmic reticulum. Chondroitin sulfate was also localized in medial/trans-Golgi cisternae of control chondrocytes but was not detected in other cellular compartments. In cells treated with monensin (up to 1.0 microM), which strongly inhibits proteoglycan secretion (Burditt, L.J., A. Ratcliffe, P. R. Fryer, and T. Hardingham, 1985, Biochim. Biophys. Acta., 844:247-255), there was greatly increased intracellular localization of proteoglycan protein core in both ricin-positive vesicles, and in ricin-negative vesicles (derived from cis-Golgi stacks) and in the distended rough endoplasmic reticulum. Chondroitin sulfate also increased in abundance after monensin treatment, but continued to be localized only in ricin-positive vesicles. The results suggested that the synthesis of chondroitin sulfate on proteoglycan only occurs in medial/trans-Golgi cisternae as a late event in proteoglycan biosynthesis. This also suggests that glycosaminoglycan synthesis on proteoglycans takes place in a compartment in common with events in the biosynthesis of both O-linked and N-linked oligosaccharides on other secretory glycoproteins.

Animals↗
PubMed1989

Precursors of chondroitin sulfate proteoglycan are segregated within a subcompartment of the chondrocyte endoplasmic reticulum.

Immunocytochemical methods were used at the levels of light and electron microscopy to examine the intracellular compartments of chondrocytes involved in extracellular matrix biosynthesis. The results of our studies provide morphological evidence for the compartmentalization of secretory proteins in the ER. Precursors of the large chondroitin sulfate proteoglycan (CSPG), the major proteoglycan species produced by chondrocytes, were present in the Golgi complex. In addition, CSPG precursors were localized in specialized regions of the ER. Link protein, a separate gene product which functions to stabilize extracellular aggregates of CSPG monomers with hyaluronic acid, was segregated similarly. In contrast, type II procollagen, another major secretory molecule produced by chondrocytes, was found homogeneously distributed throughout the ER. The CSPG precursor-containing ER compartment exhibits a variable tubulo-vesicular morphology but is invariably recognized as an electronlucent, smooth membrane-bounded region continuous with typical ribosome-studded elements of the rough ER. The observation that this ER structure does not stain with antibodies against resident ER proteins also suggests that the compartment is a specialized region distinct from the main part of the ER. These results support recent studies that consider the ER as a compartmentalized organelle and are discussed in light of the possible implications for proteoglycan biosynthesis and processing.

Animals↗