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At least 19 recordsLinked to original sources

PubMed1978

A three-dimensional study of organelle interrelationships in regenerating rat liver. 2. Transient connections with luminal continuity between thin- and thick-membraned organelles.

Luminal continuities can be established between thin- and thick-membraned structures, and serve the transfer of their contents. The abrupt change in membrane thickness at the site of connection suggests that exchange of membrane constituents is very limited. This enables retrograde separation of the connected organelles. sER (endoplasmic space) makes up such continuities with exoplasmic structures (mature Golgi cisterna, GERL-system, occasionally MVB). Transfer tubules, possessing a thiny membrane but nevertheless belonging to the exoplasmic space, take up endocytized material from large coated vesicles or from coated plasma membrane loops and carry it to MVB. They offer the possibility to recycle the internalized plasma membrane.

Animals↗

PubMed1979

A three-dimensional study of organelle interrelationships in regenerating rat liver. 3. Organelles related to bile.

A number of cell structures are described which show a morphological relationship to the bile canaliculi. Two types of peribiliary vesicles are identified: osmication positive ones occurring between the bile canaliculi and the osmicated immature Golgi cisternae and probably deriving from the latter, and osmication negative ones related to MVB, on which they appear as buds. Small coated vesicles are seen attached to this second type. Large lacunae may originate from MVB, as suggested by the MVB-like internal vesicles they may contain. Some stay in luminal continuity with the bile canaliculi. Canalicular coated vesicles are seen as parts of the canalicular plasma membrane and free in the cytoplasm.

Animals↗

PubMed1978

Velocity sedimentation of organelles at low centrifugal force in an isokinetic gradient.

Mast-cell granules and polystyrene microspheres (0.600 and 1.011 micrometer in diameter) were sedimented in a previously described [Pretlow (1971) Anal. Biochem. 41, 248--255] isokinetic gradient in a low-speed centrifuge. For the analytical velocity sedimentation of organelles, this gradient offers several advantages over gradients that are commonly used for the sedimentation of organelles: (a) the density gradient (0.0008 g.ml-1.cm-1) is small, and the effective densities of organelles will change relatively little during sedimentation; (b) the densities at all points in the gradient (1.017--1.027 g/ml) are less than those in gradients commonly used for the sedimentation of organelles, the effective densities of sedimenting organelles are consequently relatively large, and the effect of density as a determinant of velocity of sedimentation is less limiting than in conventional gradients; (c) the small slope of the gradient is associated with a relatively slow increase in the viscosity encountered by the sedimenting organelle; (d) the iso-osmotic gradient is not significantly affected by the gradient medium (Ficoll), and the osmolarity can be adjusted to the desired value by the selection of an appropriate salt solution as the solvent for the Ficoll; (e) the gradient will be isokinetic for particles of densities similar to most organelles. An ultracentrifuge is not required for work with this gradient.

Centrifugation, Density Gradient↗

PubMed2025

A molecular census to elucidate the demixing mechanism of membraneless organelles.

BACKGROUND: Cells contain membraneless organelles that have been proposed to form via phase separation involving dense networks of multivalent intermolecular interactions. As it is notoriously difficult to experimentally distinguish punctate structures formed by phase separation from those formed by other mechanisms, this issue is controversial. To complement experimental assays, we present a computational by-the-numbers approach to phase separation. We mine publicly available datasets to perform a molecular census of prominent subnuclear organelles in mouse embryonic stem cells: nucleoli, transcriptional condensates, heterochromatin foci, and Polycomb bodies. We estimate copy numbers and intermolecular distances and compare the latter to the Debye length, which is the characteristic distance over which intermolecular interactions typically occur. RESULTS: We find that none of the organelles studied here contain any protein species that shows intermolecular distances below the estimated Debye length if molecules in the organelles are randomly distributed, which disfavors the classical one-component phase separation scenario. Considering multiple species based on databases of phase-separating proteins, we find that nucleoli and transcriptional condensates are compatible with multi-component phase separation driven by proteins and RNAs, while heterochromatin foci and Polycomb bodies are better explained by a model in which proteins bind to chromatin without phase-separating via dense multivalent interaction networks. We also provide an interactive tool that allows testing of alternative multi-component scenarios. CONCLUSION: We introduce a computational by-the-numbers approach to benchmark different demixing models that may explain the assembly of membraneless organelles. Our results suggest that cells use different mechanisms to form subnuclear organelles with different biophysical properties.

Animals↗

PubMed1975

Computer analysis of organelle translocation in primary neuronal cultures and continuous cell lines.

Organelle translocation in a number of cell types in tissue culture as seen by high-resolution Zeiss-Nomarski differential interference contrast optics was filmed and analyzed by computer. Principal cell types studied included primary chick spinal cord, chick dorsal root ganglion, ratbrain, and various clones of continuous cell lines. Organelle translocations in all cell types studied exhibited frequent, large changes in velocity during any one translocation. The appearance of particles as seen with Nomarski optics was correlated with their fine structures in one dorsal root ganglion neurite by fixing the cell as it was being filmed and obtaining electron micrographs of the region filmed. This revealed the identity of several organelles as well as the presence of abundant neurotubules but no neurofilaments. Primary cell cultures exhibited more high-velocity organelle movements than continuous cell lines. The net progress of an organelle in a given direction was greater in primary neuronal cells than in fibroblasts or continuous cell lines. These findings are correlated with the literature on organelle translocation and axoplasmic transport.

Animals↗

PubMed1977

The influence of reserpine and ethylenediaminetetraacetic acid (EDTA) on serotonin storage organelles of blood platelets.

The present investigation has evaluated the influence of reserpine on the serotonin-rich organelles bodies) in platelets from dogs, rabbits, and humans. Reserpine markedly depresses the levels of stored serotonin in human and animal platelets, accompanied by a small decrease in platelet ATP but no change in platelet ADP content. Thin sections of human platelets showed no change in the number or morphology of serotonin storage organelles during reserpine therapy, whereas a profound decrease in the size and number of dense bodies occurred in platelets from rabbits treated with reserpine. Dog platelets also showed a decrease in the number and density of serotonin storage organelles after reserpine therapy. The basis for the difference between rabbit and human platelets was explored by fixing platelets in glutaraldehyde and osmium in the presence or absence of the chelating agent ethylenediaminetetraacetic acid (EDTA). Most of the dense bodies in fixed human platelets were removed by EDTA while rabbit platelet dense bodies remained essentially intact. The results suggested that the opacity of rabbit platelet dense bodies following fixation with glutaraldehyde and osmium relate primarily to their serotonin content, while the electron density of human serotonin storage organelles in fixed cells is due primarily to their calcium content. Further confirmation of this concept came from studies of platelets using the whole mount technique. Rabbit platelet serotonin storage organelles were found to lack the inherent opacity of the human dense bodies, a finding consistent with the lower concentration of calcium in the rabbit organelles.

Animals↗

PubMed1979

Hybrid pigment organelles in an invertebrate.

Observations of a number of vertebrate chromatophores have revealed the presence of more than one type of pigment organelles, suggesting that the different types are all derived from an equipotential organelle able to differentiate into any of the major pigment-containing organelles (Bagnara, 1972). Observations are presented concerning the occurrence of hybrid pigment inclusions, i.e., all kinds of intergrades between melanosomes, pterinosomes, and reflecting platelets in pigment cells of the daddy-long-legs. It therefore seems possible that pigment organelles in some invertebrates may also be derived from a common pluripotential primordial organelle.

Animals↗

PubMed1976

Lipids found in pulmonary lavage of patients with alveolar proteinosis and in rabbit lung lamellar organelles.

Lipids from the insoluble material obtained by pulmonary lavage of 6 patients with alveolar proteinosis and from lamellar organelles of normal rabbit lungs were isolated and characterized. In both types of samples, dipalmitoylphosphatidylcholine was the predominant lipid. Phosphatidylethanolamine, phosphatidylglycerol, lysophosphatidylglycerol, and 2 glycolipids, GM3 and GL1 were also present in both types of preparations. Sphingomyelin, lysophosphatidylcholine, lysophosphatidylethanolamine, phosphatidyl-N, N-dimethylethanolamine, phosphatidylserine, and lyso(bis)phosphatidic acid were found in the sedimented lavage material from humans but were not detected in lamellar organelles from rabbits. Significant quantities of neutral lipids were present in the lavage material, but only trace amounts, mainly as cholesterol and triglycerides, were detected in lamellar organelles. Phosphatidylcholine and the 2 glycolipids contained mostly saturated fatty acids and essentially no polyunsaturated fatty acids. Sphingomyelin, lysophosphatidycholine, and phosphatidyl-N, N-dimethylethanolamine, found only in the lavage, were also highly saturated. In addition to the fact that several phospholipids found in the lavage were not present in lamellar organelles, another striking difference between the lipids from these 2 sources was that phosphatidylglycerol of lamellar organelles contained predominantly palmitic acid, whereas the phosphatidylglycerol obtained by lavage of humans contained large amounts of stearic and oleic acids.

Animals↗

PubMed1975

[Changes in protein metabolism following irradiation. 1. Activity of protease, protease pattern, protein and free amino acids in cytoplams and cell organelles of the rat spleem following 600 R whole-body X-ray irradiation].

The protease activity of cytoplasm and cell organelles of the rat spleen against spleen protein and hemoglobin as a substrate increases during an initial reaction phase of the organism on the first day after 600 R whole body X-irradiation. The alkaline proteases in the cytoplasm and the acid proteases in the cell organelles increase, whereas the protease activity against externally added hemoglobin as substrate decreases below the initial values. The protein, the protease activity and the free amino acids of the cytoplasm and the cell organelles decrease during the disease phase on day 3 and 4 after irradiation. The protein loss of the spleen is therefore not explained by an increased protease activity. Acid proteases appear in the cytoplasm which derive probably from the cell organelles. The protease activity and the free amino acids are increased in the cytoplasm and the cell organelles during the regeneration phase of the organism between day 15 and 18 after irradiation.

Amino Acids↗

PubMed1978

Microtubules and organelle movements in the rust fungus Uromyces phaseoli var. vignae.

Direct visual observation and time lapse films of in vitro differentiating infection structures of the cowpea rust fungus Uromyces phaseoli var. vignae revealed three categories of movement: a) general movement of cytoplasm, plus organelles, into the developing portions of the fungus during which the nuclei, in particular, maintained their characteristic position with remarkable constancy, b) relatively slow movements of various organelles such that they became displaced relative to one another and to the growing fungal tip, and c) erratic, rapid, saltations of small organelles over short distances. Serial section ultrastructural analysis showed that microtubules were typically orientated parallel to the direction of cytoplasm migration. Simple statistical analyses showed that the microtubules were non-randomly associated with mitochondria but only rarely associated with lipid droplets or microbodies. All microtubules were typically short (less than 2 micrometer) and, in various parts of the cell, were often intimately associated with 3 to 6 nm diameter filaments of unidentified material. Interphase nuclei characteristically lacked microtubules emanating from their variously laterally or posteriorly located NAOs (nucleus associated organelle) but were associated with groups of laterally placed microtubules. The correlations between the observed types of movement and the ultrastructure of the cells discussed in terms of various models for organelle motility.

Basidiomycota↗

PubMed1978

Peripheral nerve ischemia: Part 2. Accumulation of organelles.

Following simultaneous ligation of the aorta and femoral artery in the cat, organelles accumulated in distal portions of the sciatic nerve and in lower portions of the tibial and peroneal nerves. The accumulations were located in the proximal and distal ends of the nerve infarction and delineated the borders of the necrotic area. Topographical analysis of the necrosis and organelle accumulations following ligation of these main arteries showed the larger nerve fascicles to be more sensitive to ischemia than the smaller ones. The center of a nerve fascicle was more sensitive than the periphery. The organelles accumulated in ischemic nerves during the first hours after arterial ligation, presumably as a result of lack of energy for fast axoplasmic transport. Later accumulations reflected mechanical block of axoplasmic transport due to focal necrosis of the nerve. The content of organelle accumulations was similar to that found in lesions resulting from transection except for the presence of 60 to 70 A filaments at the distal end of the infarction.

Animals↗

PubMed1977

Phospholipids of subcellular organelles isolated from cultured BHK cells.

Mitochondrial and nuclei were purified from cultured hamster fibroblasts (BHK21 cells) by centrifugation in sucrose gradients. The phospholipid compositions of the preparations were compared to those of the previously purified plasma membranes, endoplasmic reticulum and lysosomes. The mitochondria had a characteristically high content (approx. 16% of lipid phosphorus) of cardiolipin, which was practically absent from the other purified organelles. The nuclei were enriched in phosphatidylcholine and phosphatidylinositol (approx. 68% and 5% of lipid phosphorus, respectively). Lysobisphosphatidic acid was almost absent from the mitochondria and nuclei, as well as from the plasma membrane and endoplasmic reticulum, which suggests that this phospholipid is confined to the lysosomes of the BHK cell. The nuclei and the mitochondria contained relatively little sphingomyelin, a characteristic lipid of the plasma membrane. The distributions of the total cellular phospholipid and protein between the various organelles were calculated and compared to the corresponding data estimated for the rat liver. The BHK cell contained relatively more phospholipids in the nucleus and the lysosomes than the liver. All the organelles of the BHK cell contained less protein per phospholipid than the equivalent organelles of the liver.

Cell Fractionation↗

PubMedDate not supplied

Accumulation of basic drugs in 5-hydroxytryptamine storage organelles of rabbit blood platelets.

The subcellular distribution of basic substances such as mepacrine, chloroquine, chlorpromazine and imipramine was studied in rabbit blood platelets exposed to these compounds in vitro and to some in vivo. All the drugs showed a preferential concentration in the 5-hydroxytryptamine (5HT) storage organelles (5HT vesicles). Chloroquine and mepacrine accumulated more specifically in the organelles than did chlorpromazine and imipramine. After osmotic shock of the 5HT vesicles chlorpromazine sedimented mostly with the vesicular membranes, whereas the other compounds preferentially went into the supernatant. It is concluded that (a) fluorescent basic compounds such as mepacrine are rather specific markers for the 5HT storage organelles in live platelets and (b) drugs such as chlorpromazine and imipramine also have a considerable affinity for these organelles.

Animals↗

PubMed1975

The role of the Golgi complex in the isolation and digestion of organelles.

The origin of the membranes and lytic enzymes involved in autophagy has been studied in metamorphosing insect fat body. The Golgi complex has two functions in the organelle destruction which takes place when fat body cells change their activities. (1) It gives rise to envelopes which extermalize organelles scheduled for destruction. Microbodies, mitochodria and rough endoplasmic reticulum are sequentially removed from the cytoplasm by investment in isolation membranes. During the isolating phase, isolation membranes have the same osmiophilia as the outer saccular and microvesicular components of the Golgi complex, they do not contain lytic enzymes and they are specific in their adhesion to organelles scheduled for destruction. (2) The Golgi complex gives rist to lytic enzymes. Primary lysosomes which contain acid phosphatase fuse with the isolation bodies formed from invested organelles to become autophagic vacuoles. During this lytic phase, acid phosphatase is present in the inner saccules and microvesicular components of the Golgi complex, in the primary lysosomes seen fusing with isolation bodies and in autophagic vacuoles.

Acid Phosphatase↗

PubMed1975

Ultrastructural description of a "cylinder organelle" in the outer plexiform layer of human retinas.

A cylinder-like organelle ("cylinder organelle") present in the outer plexiform layer of the retina and apparently confined to the horizontal cell processess is described. This structure was studied in detail in three normal human retinas from eyes enucleated for ciliary body melanomas. The cylinder organelle, when cut longitudinally, showed an electron-lucent area bound by two bands of electron-dense filaments. In transverse section, the cylinder organelle revealed a circular profile of electron-dense crisscrossing filaments about an electron-lucent matrix. Since this structure was only found in the rod spherule synaptic complex, it is hypothesized that it may be involved in transmitting impulses.

Aged↗

PubMed1977

Human platelet storage organelles. A review.

Platelets contain numerous electron-dense subcellular organelles which have been referred to in the literature by various names such as alpha-granules, electron-dense and very electron-dense granules, lysosomes, dense bodies, etc. Most of the organelles are secretory granules, since induction of secretion by appropriate stimuli causes degranulation of platelets and the appearance of the granule contents in the extracellular medium. Among the substances that are known to be stored and secreted by platelets are: serotonin, ATP, ADP, calcium, pyrophosphate, acid hydrolases, fibrinogen, vascular permeability factor, beta-thromboglobulin, platelet factor 4 and growth factor. The recent literature concerning the localization of the secreted substances within specific platelet organelles is reviewed here. Results from electron microscopy and microprobe analysis, selective secretion experiments, subcellular fractionation studies and studies on platelets from patients with storage pool deficiency indicate that there are as many as four types of storage organelles in human platelets.

Blood Platelet Disorders↗

PubMed1979

Phospholipid exchange between subcellular organelles of rabbit lung.

A soluble protein fraction (PLEP) prepared from rabbit lung can catalyze the exchange of phospholipids between subcellular organelles of the lung and between these subcellular organelles and synthetic liposomes. Phospholipid exchange between microsomes and synthetic liposomes and between mitochondria and synthetic liposomes was stimulated 8-fold and 2.5-fold, respectively, in the presence of the protein fraction. Lung exchange protein could also catalyzed phospholipid exchange between subcellular organelles of the liver and synthetic liposomes. Phospholipid transfer between microsomes and lamellar bodies of the lung was stimulated 2-fold by the exchange protein. Both radiolabeled phosphatidylcholine (PC) and phosphatidylinositol (PI) were transferred from 32P-labeled microsomes to lamellar bodies, but the exchange protein exhibited no transfer activity for phosphatidylglycerol (PG) and that for phosphatidylethanolamine (PE) was insignificant compared to the transfer activity for phosphatidylcholine and phosphatidylinositol. While the physiological role of the phospholipid exchange proteins in the lung is unknown, it is possible that they participate in the distribution of the newly synthesized phospholipids from the site of synthesis to lamellar bodies and other membrane compartments of cells.

Animals↗

PubMed1977

Axonal transport of organelles visualized by light microscopy: cinemicrographic and computer analysis.

Rapid movements of intra-axonal organelles in acutely isolated single myelinated fibers from bullfrog sciatic nerve were visualized by dark-field microscopy. The movements were recorded by cinemicrography, and analyzed by computer-based methods. The movements are saltatory and bidirectional, but each particle moves mainly in a single direction. For more than 90% of the particles, the predominant movement direction is retrograde, i.e. toward the cell body. Quantitative measurements on a variety of parameters of the organelle movements are presented. Different particles in the same axon show a broad range of mean speeds. The average mean speed of movement in the retrograde direction at 28 degrees C was 1.08 micrometer/sec (S.D. - 0.41), equivalent to an axonal transport rate of 93 mm/day. Disperse distributions were also found for other parameters such as the instantaneous velocities of individual particles. Quantal velocities, periodic movement patterns, and specific 'channels' were not detected. When the data from a population of particles is treated statistically, the average mean speed, the distribution of velocities, and other statistical parameters are found to be similar in different axons studied at the same temperature. Direct microscopical observation of axonal organelle movement is a technique which provides information about axonal transport which is different from and complementary to that obtained from enzyme accumulation of radioactive tracer methods.

Animals↗