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Results for “Cytoplasmic Structures”

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PubMed1959

Abnormal intranuclear and cytoplasmic formations associated with a chemically induced, transplantable chicken sarcoma.

Thirty GRCH/15 tumors (a 1, 2, 5, 6-dibenzanthracene-induced chicken sarcoma) were examined in the light and the electron microscope. Associated with the sarcoma were two types of abnormal intranuclear lesions, one in the form of a vacuole, the other as an aggregate containing glycogen. In the electron microscope, one type of lesion observed showed an organized microfibrillar structure. Abnormal cytoplasmic formations occurred as massed clusters of thread-like or tubular material, which gave rise to small bodies with concentric shell structure; similar bodies were found associated with vacuoles.

Animals↗
PubMed1996

When is a carrier not a membrane carrier? The cytoplasmic transport of amphipathic molecules.

After entering the cell, small molecules must penetrate the cytoplasm before they are metabolized, excreted, or can convey information to the cell nucleus. Without efficient cytoplasmic transport, most such molecules would efflux back out of the cell before they could reach their targets. Cytoplasmic movement of amphipathic molecules (e.g., long-chain fatty acids, bilirubin, bile acids) is greatly slowed by their tendency to bind intracellular structures. Soluble cytoplasmic binding proteins reduce this binding by increasing the aqueous solubility of their ligands. These soluble carriers catalyze the transport of hydrophobic molecules across hydrophilic water layers, just as membrane carriers catalyze the transport of hydrophilic molecules across the hydrophobic membrane core. They even display the kinetic features of carrier-mediated transport, including saturation, mutual competition between similar molecules, and countertransport. Recent data suggest that amphipathic molecules cross the cytoplasm very slowly, with apparent diffusion constants 10(2) to 10(4) times smaller than in water. By modulating the rate of cytoplasmic transport, cytosolic binding proteins may regulate transport and metabolism of amphipathic molecules. Storage diseases may cause hepatocellular dysfunction by disrupting normal cytoplasmic transport.

Animals↗
PubMed1983

Mobilization of maternal mRNA in amphibian eggs with special reference to the possible role of membraneous supramolecular structures.

Current knowledge of the mechanism of mobilization of maternal mRNA is summarized herein and a working hypothesis has been constructed to explain the mechanism on the assumption that the mRNA enters the cytoplasm in association with the cytoplasmic membraneous structures and is then stored in the structures until liberation and relocation at the step of oocyte maturation. An extensive turnover of poly(A) sequences as well as the occurrence of repetitive sequences in the maternal mRNA may be relevant to mRNA activation.

Amphibians↗
PubMed2003

Tyrosine phosphorylation of the well packed ephrinB cytoplasmic beta-hairpin for reverse signaling. Structural consequences and binding properties.

Tyrosine phosphorylation of the 22-residue cytoplasmic region of ephrinB induces its binding to the SH2 domain of Grb4, thus initiating reverse signaling pathways controlling cytoskeleton assembly and remodeling. Recently, the region corresponding to this 22-residue motif was demonstrated to adopt a well packed beta-hairpin structure with a high conformational stability in the unphosphorylated cytoplasmic subdomain. However, because the binding to Grb4 is phosphorylation-dependent and the hairpin contains three conserved tyrosine residues that may be phosphorylated, the key events remain unknown as to how tyrosine phosphorylation affects the structure of this well packed beta-hairpin and which phosphorylation site is relevant to SH2 domain binding. By characterizing the structural and binding properties of six 22-residue SH2 domain-binding motifs with different phosphorylated sites, the present study reveals that, as shown by circular dichroism and NMR, the unphosphorylated 22-residue motif adopts a well formed beta-hairpin structure in isolation from the ephrinB cytoplasmic subdomain. However, this beta-hairpin is radically abolished by tyrosine phosphorylation, regardless of the relative location and number of Tyr residues. Unexpectedly, the peptides with either Tyr304 or Tyr316 phosphorylated show high affinity binding to SH2 domain, whereas the peptide with Tyr311 phosphorylated has no detectable binding. This implies that ephrinB with Tyr311 phosphorylated might have a currently unidentified binding partner distinct from the Grb4 protein, because Tyr311 is known to be phosphorylated in vivo. Based on the results above, it is thus proposed that the disruption of the tight side-chain packing by tyrosine phosphorylation in the well structured region of a signaling protein may represent a general activation mechanism by which a cryptic binding site is disclosed for new protein-protein interactions.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Regulation of ion channel expression by cytoplasmic subunits.

Neuronal and cardiac voltage-gated ion channels contain auxiliary subunits that can profoundly affect the gating of the pore-forming and voltage-sensing alpha subunits. Recent studies on the structurally similar cytoplasmic beta subunits of Ca2+ and K+ channels reveal that these subunits can also exert profound effects on the expression of the integral membrane protein channel components. The mechanisms by which these effects occur are now being elucidated through a combined approach that employs biophysical, pharmacological, cell biological and biochemical techniques.

Animals↗
PubMed1981

Sézary syndrome with unusual undifferentiated cells.

In this study a case of Sézary syndrome, the Sézary cells showed typical cytoplasmic fibrillar structures, and the nuclei had the characteristic serpiginous appearance. In addition, other unusual undifferentiated cells were found, These cells had round nuclei and few cytoplasmic organelles, and areas of the outer membrane of the nuclear envelope had hairy fine fibrillar projections protruding into the cytoplasm. It is postulated that these cells represent immature Sézary cells, and that as the cells mature, the fibrils become organized around the nucleus, leading to the development of the nuclear deformity.

Cell Differentiation↗
PubMed1988

Hypereosinophilic syndrome human eosinophil degranulation induced by soluble and particulate stimuli.

Eosinophil degranulation induced by the calcium ionophore A23187 and opsonized zymosan particles was examined ultrastructurally in peripheral blood cells obtained from patients with the hypereosinophilic syndrome. Unstimulated hypereosinophilic syndrome eosinophils contained altered, vacuolated cytoplasmic granules and large cytoplasmic crystalloid structures not seen in normal cells. By morphometric analysis of transmission electron micrographs, the hypereosinophilic syndrome eosinophils contained a larger percentage of smaller sized cytoplasmic granules than normal cells. The hypereosinophilic syndrome eosinophils, however, were capable of undergoing noncytotoxic degranulation after stimulation with either A23187 or opsonized zymosan. Hypereosinophilic syndrome eosinophil degranulation was characterized by fusion of the perigranular membranes of adjacent cytoplasmic granules and vesiculation of the fused granules. Granule contents were released intracellularly into vacuoles after ionophore stimulation and into phagosomes containing the ingested zymosan particles. Noncytotoxic extracellular release of eosinophil peroxidase (EPO) was also observed after cell stimulation by either A23187 or zymosan. The capacity of hypereosinophilic syndrome eosinophils to degranulate after appropriate stimulation with release of toxic granule constituents such as EPO and other basic proteins may be important in the tissue injury observed in this syndrome.

Calcimycin↗
PubMed1995

In situ effects of interferon on human glioma protein kinase C-alpha and -beta ultrastructural localization.

Transmission electron microscopy was used to determine how immunogold labeling of PKC-alpha or -beta is modulated by the antitumor drug IFN (HuIFN alpha-2b) in the cytoplasm, membrane structures, and nucleus of rapidly dividing and confluent human glioma U-373 cells. Results showed that except for nuclear localization, there were no specific cytoplasmic organelles that PKC-alpha or -beta translocated to following HuIFN alpha-2b treatment. Electron micrographs of PKC-beta in proliferating cells depicted 1.34-fold more PKC-beta in the nucleus than in the cytoplasm and a 1-min HuIFN alpha-2b (500 units/ml) treatment transiently increased PKC-beta immunoreactivity in the cytoplasm (1.95-fold) and nucleus (1.97-fold). In confluent cells, incubation with HuIFN alpha-2b for 2 min significantly decreased cytoplasmic PKC-beta immunoreactivity by 37%, and no change was observed in nuclear PKC-beta labeling. PKC-alpha labeling in proliferating cells showed similar immunoreactivity in both control cytoplasm and nucleus. Treatment of proliferating cells with HuIFN alpha-2b for 2 min decreased PKC-alpha in the cytoplasm (59%) and nucleus (44%). In confluent cells, cytoplasmic PKC-alpha labeling decreased 59% at 1 min, 61% at 2 min, and 76% at 10 min of HuIFN alpha-2b treatment. Nuclear PKC-alpha decreased by 65% at 1 min, 80% at 2 min, and 62% at 10 min after HuIFN alpha-2b treatment. Western blots of total PKC-alpha in proliferating and confluent cells and PKC-beta in confluent cells showed similar results. However, Western blots of total PKC-alpha and -beta in proliferating cells did not demonstrate any significant changes in either PKC-alpha or -beta immunoreactivity following 1-min HuIFN alpha-2b treatment. These results suggest that treatment of proliferating U-373 cells with HuIFN alpha-2b for 1 min unfolds and exposes PKC-beta antigenic sites (hinge region) and increases in situ PKC-beta immunogold labeling.

Amino Acid Sequence↗
PubMed2000

Improved recovery of highly enriched mitochondrial fractions from small brain tissue samples.

The investigation of mitochondrial abnormalities in brain commonly requires isolation of these organelles from small tissue samples. We have modified a mitochondrial isolation procedure based on Percoll density gradient centrifugation to increase the proportion of the total mitochondrial pool recovered while reducing contamination with synaptosomes and related structures containing cytoplasm. Initially, myelin was removed by centrifugation in 12% Percoll in isotonic buffer. The pellet was resuspended, treated with digitonin to break up synaptosomes and similar structures and subjected to discontinuous Percoll density gradient centrifugation. The mitochondrial fraction obtained from this procedure was highly metabolically active and well coupled, exhibiting respiratory control ratios above 5. The recovery of mitochondrial markers using a single rat forebrain as starting material was approximately 18% to 21%. When small tissue samples (approximately 50 mg wet weight) were used as starting material the recovery of the mitochondrial marker was approximately 16%. The ratio of recovery of a mitochondrial marker to the cytoplasmic marker lactate dehydrogenase exceeded 200 in preparations from a single rat forebrain. This is substantially greater than values reported for previously published procedures reflecting both an improved yield of mitochondria and a reduction in cytoplasmic contamination.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1987

Light and electron microscopic observation on the process of tissue calcification in a case of parathyroid adenoma.

Metastatic calcification in various organs in an autopsy case of parathyroid adenoma was studied by light and electron microscopy. Calcification was observed in kidney, lung, liver, heart, stomach, and thyroid. In the kidney, calcification was found in the tubules and glomeruli. In the liver, calcification was mainly found in Disse's space. The kidney, lung, liver, and heart were examined by electron microscopy. Four forms of early calcification were observed: 1) amorphous dense bodies within the mitochondria; 2) needle-shaped hydroxyapatite; 3) concentric laminated structure; and 4) cytoplasmic vesicles originating in hepatocytes. Calcium phosphate precipitates within the mitochondria were seen as amorphous dense bodies. When calcium phosphate precipitated in the cytoplasmic colloid gel, concentric laminated structures were formed due to Liesegang's phenomenon. Needle-shaped crystals in the amorphous dense bodies of the mitochondria were interpreted as a phenomenon of epitaxy. Calcification in Disse's space was thought to start in cytoplasmic vesicles which were derived from hepatocytes.

Adenoma↗
PubMed1989

Mycelium-yeast transition in Histoplasma capsulatum. Early ultrastructural changes.

The ultrastructural changes which occur during the first 24 h of mycelium to yeast transition have been studied in the dimorphic fungus Histoplasma capsulatum. A temperature shift controls mycelial to yeast transition. During the first 24 h respiratory rate, ATP and cytochrome concentration fall to very low levels. Ultrastructural observations showed that the plasma membrane became undulated and the cell wall lost its characteristic fibrous outer layer. At 8 h the ordered lamellar structure of the mitochondria was no longer apparent. 24 h after the temperature shift 70% of the cells were lysed. The remaining cells contained many cytoplasmic membrane structures; mitochondria were rarely observed. These changes are considered to be the morphological expression of the physiological events characteristic of stage one in mycelial to yeast transition.

Histoplasma↗
PubMed1990

[Ultrastructural study of the mycelium-yeast transition in Histoplasma capsulatum. I. Changes at 37 degrees C].

Ultrastructural changes observed during the first 24 hours of mycelium to yeast transition in the dimorphic fungus Histoplasma capsulatum are reported. During this period the plasma membrane becomes undulated and the cell wall loses its characteristic fibrous outer layer. At 8 h the ordered lamellar structure of the mitochondria is no longer apparent. 24 h after the temperature shift 70% of the cells are lysed. The remaining cells contain many cytoplasmic membrane structures; mitochondria are rarely observed. These morphological changes are probably correlated with the physiological events characteristic of mycelial to yeast transition.

Cell Wall↗
PubMed1983

Alteration of luminal membrane structure by antidiuretic hormone.

The final step in the action of antidiuretic hormone (ADH) is the insertion of aggregates of water-conducting particles into the luminal membrane of the receptor cell. The aggregates arise from cytoplasmic tubular structures that fuse with the luminal membrane. This review presents a number of questions about this process, along with current attempts to answer them. The following topics are addressed: 1) the exact role of the cytoskeleton in promoting tubular fusion, 2) the nature of the translocation process leading to fusion, 3) the point in the sequence at which ADH enters, 4) the composition and structure of the water-conducting particles. Some of the answers require a more complete understanding of the structure of the apical portion of ADH-sensitive cells; recent morphological studies are therefore included.

Animals↗
PubMedDate not supplied

[Cytoplasmic male sterility-associated structural variation of the mitochondrial genome regions containing rps3 and orf215 in sugar beet Beta vulgaris L].

Several 5'-degenerate primers were selected by computer analysis and used for mtDNA typing in sugar beet cultivars with cytoplasms of the S (typical for cytoplasmic male sterility) or N (normal) type. A number of N- or S-specific markers were found to correspond to transcribed mitochondrial genes. One was from the orf215 region of the N-type mtDNA. A physical map of the corresponding region was constructed for the S-type mtDNA, and a substantial difference observed for the two genome types. One N-specific marker proved to contain a rearranged rps3 region and a truncated atp9 copy. With the known nucleotide sequence of this marker, three-primer PCR was designed and showed that both variants of the rps3 region simultaneously take place in the mtDNA pool, the new one occurring in a substochiometric proportion.

Base Sequence↗
PubMed1992

Comparative effects of pollen and seed migration on the cytonuclear structure of plant populations. II. Paternal cytoplasmic inheritance.

We continue our study of the effects of pollen and seed migration on the cytonuclear structure of mixed-mating plant populations by analyzing two deterministic continent-island models under the critical assumption of paternal cytoplasmic inheritance. The major results of this study that contrast with our previous conclusions based on maternal cytoplasmic inheritance are (i) pollen gene flow can significantly affect the cytonuclear structure of the island population, and in particular can help to generate cytonuclear disequilibria that greatly exceed the magnitude of those that would be produced by seed migration or mixed mating alone; (ii) with simultaneous pollen and seed migration, nonzero cytonuclear disequilibria will be maintained not only when there is disequilibrium in the immigrant pollen or seeds, but also through a variety of intermigrant admixture effects when the two pools of immigrants differ appropriately in their cytonuclear compositions; (iii) either immigrant pollen or immigrant seeds can generate disequilibria de novo in populations with initially random cytonuclear associations, but pollen migration alone generally produces lower levels of disequilibrium than does comparable seed migration, especially at high levels of self-fertilization when the overall fraction of immigrant pollen is low; (iv) the equilibrium state of the island population will be influenced by the rate of pollen gene flow whenever there is either allelic disequilibrium in the immigrant pollen or simultaneous seed migration coupled with different cytoplasmic or nuclear allele frequencies in immigrant pollen and seeds or nonzero allelic disequilibrium in either immigrant pool. The estimation of pollen migration should therefore be facilitated with paternal cytoplasmic inheritance relative to the case of maternal cytoplasmic inheritance. These basic conclusions hold whether the population is censused as seeds or as adults, but with simultaneous pollen and seed migration, the relationship between census time and the ability to detect nonrandom cytonuclear associations is complex. When migration is through pollen alone, however, the cytonuclear structure of the island population is independent of the life stage censused.

Alleles↗
PubMed2002

Hepatitis C virus NS5A colocalizes with the core protein on lipid droplets and interacts with apolipoproteins.

The nonstructural protein 5A (NS5A) of the hepatitis C virus (HCV) has been shown to interact with a variety of cellular proteins and implicated in the regulation of cell growth, interferon resistance, and other cellular signaling pathways, but the role of NS5A in HCV pathogenesis has not been firmly established. To further characterize this multifunctional protein, we instigated the studies of the subcellular localization of NS5A in a hepatoma cell line. NS5A was localized to the perinuclear membrane structures, including the endoplasmic reticulum (ER) and the Golgi apparatus, by immunofluorescence staining and confocal microscopy. In addition, it was also associated with the surface of cytoplasmic globular structures when expressed alone or as a part of the NS3-5B polyprotein. Oil red O staining revealed that these globular structures were lipid droplets, where the HCV core protein was also localized. The association of NS5A with intracellular membrane was further confirmed by membrane flotation analysis. To determine whether NS5A interacts with any cellular lipid-binding protein, we performed yeast two-hybrid screening in both HepG2 and human liver cDNA libraries. Apolipoprotein A1 (apoA1), one of the protein components of high-density lipoprotein (HDL) particles, was identified by two independent screening processes. The interaction between NS5A and apoA1 was confirmed by both in vitro pull-down and in vivo coimmunoprecipitation experiments. Immunofluorescence staining revealed a significant colocalization of NS5A and apoA1 in the Golgi apparatus. Our results established an association of NS5A with lipid droplets and apoA1, suggesting that NS5A, together with the core protein, may play a role in the pathogenesis of the derangement of lipid metabolism, contributing to liver steatosis commonly observed in hepatitis C.

Animals↗