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Results for “Cytoplasmic Structures”

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At least 37 records · Page 2Linked to original sources

PubMed1975

Intracisternal polycylinders: a cytoplasmic structure in cells of the terrestrial slug Arion empiricorum Férussac (Pulmonata, Stylommatophora).

Study of the digestive organs of the slug Arion empiricorum with the electron microscopy has revealed cytoplasmic structures that we call intracisternal polycylinders (ICPC). They consist of cylinders of cytoplasm (about 550 A in diameter) arranged in sheafs within cisterns of the endoplasmic reticulum. They appear in different cell types, being most common in the digestive epithelium of the midgut. Their morphology and apparent association with other cytoplasmic organelles such as mitochondria, peroxisomes, multivesicular and residual bodies suggests that the ICPC might be involved in exchange, transport and oxidation processes, contributing to the excretory function at a subcellular level.

Animals↗

PubMed1987

Effects of inhibitors of the cytoplasmic structures and functions on the early phase of infection of cultured cells with simian virus 40.

To obtain information about cytoplasmic structures and functions involving the entry of simian virus 40 virions into cells, we examined whether the inhibitors that affect the functions and/or structure of lysosomes, cell membrane, and cytoskeletons inhibit expression of nuclear T antigen in the SV40-inoculated rat 3Y1 and monkey CV-1 cells. Chloroquine, methylamine, and butylamine did not inhibit T-antigen expression, suggesting that lysosomal acidification is not required for establishment of infection. Cytochalasin B had no effect, suggesting that microfilaments are not involved. Monensin, colcemid, and amantadine each inhibited T-antigen expression at doses causing no obvious cytotoxicity. Maximal inhibition was seen when these inhibitors were added to the cultures within 1 hr (monensin), within 4 hr (colcemid), or within 12 hr (amantadine) after virion adsorption to the cell surface. When the inhibitor was present in the virus-inoculated cultures for 24 hr and then removed, nuclear T antigen began to be expressed at 4 hr (monensin), 9 hr (colcemid), or 1 hr (amantadine) after removal of the inhibitors. Results of SDS-PAGE analysis of immunoprecipitated radiolabeled proteins of infected cells revealed that amantadine inhibited synthesis of large and small T antigens as well as general protein synthesis. Inhibition by colcemid may be due to disruption of microtubules, because other microtubule-disrupting agents (colchicine, vinblastine, nocodazole, and podophyllotoxin) also inhibited appearance of nuclear T antigen but lumicolchicine and taxol did not. Electron microscopy revealed that, in the presence of colcemid, although the adsorbed virions were readily internalized to form pinosomes, vectorial movement of the pinosomes to the nucleus appeared to be inhibited. Results of electron microscopy also suggest that inhibition by monensin may occur mainly in internalization of adsorbed virions and that the inhibition is leaky such that the early steps of infection proceed slowly in the presence of monensin. We conclude that monensin, colcemid, and amantadine interfere with mutually different early events of SV40 infection.

Amantadine↗

PubMed2001

Microtubule-dependent organization of vaccinia virus core-derived early mRNAs into distinct cytoplasmic structures.

Vaccinia virus (vv) early transcription can be reconstituted in vitro from purified virions; in this assay mRNAs are made inside the viral core and subsequently extruded. Although the in vitro process has been extensively characterized, relatively little is known about vv early transcription in vivo. In the present study the fate of vv early mRNAs in infected HeLa cells was followed by BrUTP transfection and confocal and electron microscopy. The extruded vv early mRNAs were found to be organized into unique granular cytoplasmic structures that reached a size up to 1 microm. By EM these structures appeared as amorphous electron-dense cytoplasmic aggregates that were surrounded by ribosomes. Confocal images showed that the RNA structures were located some distance away from intracellular cores and that both structures appeared to be aligned on microtubules (MTs), implying that MT tracks connected mRNAs and cores. Accordingly, intact MTs were found to be required for the typical punctate organization of viral mRNAs. Biochemical evidence supported the notion that vv mRNAs were MT associated and that MT depletion severely affected viral (but not cellular) mRNA synthesis and stability. By confocal microscopy the viral mRNA structures appeared to be surrounded by molecules of the translation machinery, showing that they were active in protein synthesis. Finally, our data suggest a role for a MT and RNA-binding viral protein of 25 kDa (gene L4R), in mRNA targeting away from intracellular cores to their sites of cytoplasmic accumulation.

Blotting, Western↗

PubMed1989

Assignment of estradiol-17 beta dehydrogenase and of estrone reductase to cytoplasmic structures of porcine endometrium cells.

Homogenates of porcine endometrium contain substantial activity for the dehydrogenation of estradiol-17 beta but little for estrone reduction. Both activities are associated with cytoplasmic structures. The dehydrogenase is characterized by a pH 7.7 optimum, Km 2.2 x 10(-7) mol/l for estradiol and Km 4.4 x 10(-5) mol/l for the cosubstrate NAD+. The corresponding figures for the reductase are pH 6.6, Km 1.1 x 10(-6) mol/l for estrone and Km 2.1 x 10(-5) mol/l for the cosubstrate NADPH. The (mitochondrial/lysosomal) 17,000 x g particulate fraction contains a 52-fold higher dehydrogenase than reductase activity. The (microsomal) 200,000 x g particulate fraction is only 16-fold richer in dehydrogenase. Isopycnic centrifugations of the two fractions in Percoll gradients reveal that estrone reductase and the coequilibrating marker enzyme cytochrome c reductase occur in constant proportions, whereas the dehydrogenase/cytochrome c reductase ratios are different. Both, the kinetic data and the structural assignments speak in favour of individual enzymes catalyzing the dehydrogenation of estradiol and the reduction of estrone. All gradient fractions exhibiting dehydrogenase activity feature small, electrodense vesicles of 0.15-0.20 microns in diameter as a common structural element which might harbour the dehydrogenase.

17-Hydroxysteroid Dehydrogenases↗

PubMed1998

Association of HAP1 isoforms with a unique cytoplasmic structure.

HAP1 is a neural protein and interacts with the Huntington's disease protein huntingtin. There are at least two HAP1 isoforms, HAP1-A and HAP1-B, which have different C-terminal amino acid sequences. Here we report that both HAP1 isoforms associate with a unique cytoplasmic structure in neurons of rat brain. The HAP1-immunoreactive structure appears as an inclusion that is an oval mass of electron-dense material, 0.5-3 microm in diameter, containing many curvilinear or ring-shaped segments, and often containing electron-lucent cores. This structure is very similar to those previously termed the stigmoid body, nematosome, or botrysome. Transfection of cell lines with cDNA encoding HAP1-A, but not HAP1-B, resulted in similar HAP1-immunoreactive inclusions in the cytoplasm, suggesting that HAP1-A is essential to the formation of this structure. Yeast two-hybrid and transfection studies show that both HAP1-A and HAP1-B can self-associate, implying that native HAP1 in the cytoplasmic inclusion may be a heteromultimer of HAP1-A and HAP1-B. Coexpression of HAP1-A and HAP1-B in human embryonic kidney 293 cells demonstrates that the ratio of the expressed HAP1-A to HAP1-B regulates the formation of HAP1-associated inclusions. We propose that HAP1 isoforms are involved in the formation of HAP1-immunoreactive inclusions in the neuronal cytoplasm.

Animals↗

PubMed1977

A unique cytoplasmic structure in papular histiocytoma.

Intracytoplasmic granules with a unique and highly complex ultrastructure, have been observed within the cellular infiltrate of the lesions of two patients with papular histiocytosis. Examination of serial sections has enabled construction of a three-dimensional model of these granules, which appear to be composed of an elaborate arrangement of membranes and vesicles. Two hypotheses (endocytosis and exocytosis) are proposed for the mode of formation of these unique cytoplasmic structures.

Adolescent↗

PubMed1993

Cytoplasmic structure in organotypic cultures of rat hippocampus prepared by rapid freezing and freeze-substitution fixation.

We have compared rapid freezing followed by freeze-substitution fixation with conventional aldehyde fixation as preparative methods for the electron microscopic study of organotypic cultures of neonatal rat hippocampus. Rapid freezing by contact with a copper block chilled by liquid helium was accomplished without mechanical distortion of superficial structures, and preserved structure to a depth of at least 20 microns without visible ice crystals. Freeze-substitution fixation in acetone/osmium tetroxide, followed by en bloc staining with tannic acid and uranyl acetate, provided satisfactory staining of cytoplasm and organelles. While both preparative techniques yielded generally satisfactory results, rapid freezing provided much better preservation of astrocytic lysosomal inclusions, and afforded new views of intermediate filament substructure. Rapid freezing and freeze-substitution fixation seemed especially well suited to the preservation of short filamentous proteins, such as those forming the membrane cytoskeleton of dendritic spines or those associated with synaptic vesicles. The combination of rapid freezing methods and organotypic culture provides an opportunity to examine cytoplasmic structure in tissue from deep regions of the brain which had previously been inaccessible to rapid freezing techniques.

Animals↗

PubMed1983

Improved preservation and staining of HeLa cell actin filaments, clathrin-coated membranes, and other cytoplasmic structures by tannic acid-glutaraldehyde-saponin fixation.

Fixation of HeLa cells with a mixture of 100 mM glutaraldehyde, 2 mg/ml tannic acid and 0.5 mg/ml saponin allows the tannic acid to penetrate intact cells without disruption of membranes or extraction of the cytoplasmic matrix. After subsequent treatment with OsO4 cytoplasmic structures are stained so densely that fine details are visible even in very thin (dark gray) sections. Actin filaments are protected from disruption by OsO4 so that straight, densely stained filaments are seen in the cell cortex, filopodia, ruffling membranes, and stress fibers. Stress fibers also have 15-18-nm densities similar in appearance to myosin filaments. Tannic acid staining reveals that the coats of coated vesicles, pits, and plaques have a 12-nm layer of amorphous material between the membrane and the clathrin basketwork. HeLa cells have very large clathrin-coated membrane plaques on the basal surface. These coated membrane plaques appear to be a previously unrecognized site of cell-substrate adhesion.

Actins↗

PubMed1980

[Temporal organization of the functioning of enterocyte cytoplasmic structures during the process of absorption].

The dynamic on fat and protein absorbtion was followed in epithelial cells of the small intestinal villi in mature and newborn rats. General and specific mechanisms participating in processes of marginal enterocyte absorbtion, duration of separate phases, participation of cytoplasmic structures in transporting the absorbed substances were stated. Temporal parameters in functioning enterocytic membrane structures were revealed. Coordinative activities of enterocytic organelles, structural-functional units of the organ, processes on absorbtion and secretion demonstrate close functional and anatomical interconnections existing between separate structures. Absorbtion, as one of the most essential biological processes, has an inherent property of alternate activity of the functioning structures, their continuity and intermittence depending on the level studied.

Animals↗

PubMed2000

The majority of duck hepatitis B virus reverse transcriptase in cells is nonencapsidated and is bound to a cytoplasmic structure.

The hepadnavirus reverse transcriptase binds cotranslationally to the viral pregenomic RNA. This ribonucleoprotein complex is then encapsidated into nascent viral core particles, where the reverse transcriptase copies the viral RNA into DNA. Here we report that 75% of the duck hepatitis B virus reverse transcriptase present in transfected LMH cells does not follow this well-known pathway but rather exists in the cell separate from the core protein or nucleocapsids. The nonencapsidated reverse transcriptase is also abundant in infected duck liver. The nonencapsidated reverse transcriptase exists as a complex set of isoforms that are most likely produced by posttranslational modification. Interestingly, only the smallest of these isoforms is encapsidated into viral core particles. The nonencapsidated reverse transcriptase is bound to a large cellular cytoplasmic structure(s) in a detergent-sensitive complex. The cellular distribution of the reverse transcriptase only partially overlaps that of the core protein, and this distribution is unaffected by blocking encapsidation. These observations raise the possibilities that the metabolic fate of the reverse transcriptase may be posttranscriptionally regulated and that the reverse transcriptase may have roles in the viral replication cycle beyond its well-known function in copying the viral genome.

Animals↗

PubMed1992

Nuclear and mitochondrial inheritance in yeast depends on novel cytoplasmic structures defined by the MDM1 protein.

The mdml mutation causes temperature-sensitive growth and defective transfer of nuclei and mitochondria into developing buds of yeast cells at the nonpermissive temperature. The MDM1 gene was cloned by complementation, and its sequence revealed an open reading frame encoding a potential protein product of 51.5 kD. This protein displays amino acid sequence similarities to hamster vimentin and mouse epidermal keratin. Gene disruption demonstrated that MDM1 is essential for mitotic growth. Antibodies against the MDM1 protein recognized a 51-kD polypeptide that was localized by indirect immunofluorescence to a novel pattern of spots and punctate arrays distributed throughout the yeast cell cytoplasm. These structures disappeared after shifting mdm1 mutant cells to the nonpermissive temperature, although the cellular level of MDM1 protein was unchanged. Affinity-purified antibodies against MDM1 also specifically recognized intermediate filaments by indirect immunofluorescence of animal cells. These results suggest that novel cytoplasmic structures containing the MDM1 protein mediate organelle inheritance in yeast.

Amino Acid Sequence↗

PubMed1964