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At least 559 records · Page 31Linked to original sources
PubMed1984

Effect of parathyroid hormone and calcitonin on the cytoplasmic spreading of isolated osteoclasts.

Osteoclasts, the major agents of bone resorption, were isolated from neonatal rat bone, and the cytoplasmic spreading of these cells was measured after incubation in the presence or absence of hormones or other cell types. Salmon calcitonin, which inhibits osteoclastic bone resorption, reduced spreading in a dose-dependent manner and caused significant inhibition at concentrations as low as 6.7 pg/ml. Parathyroid hormone (PTH) had no effect on the spreading of isolated osteoclasts but if osteoblasts and osteoclasts were co-cultured the addition of PTH caused a marked increase in spreading at concentrations of 0.025 i.u./ml and above. The results suggest that while calcitonin is a direct inhibitor of osteoclastic activity, PTH may stimulate osteoclasts through a primary action on osteoblasts.

Animals↗
PubMed1996

Class II antigen processing compartments and the function of HLA-DM.

The DM alpha and DM beta genes encode a nonpolymorphic, class II-like molecule which functions by an, as yet, undefined mechanism in the assembly of Major Histocompatibility Complex class II-peptide complexes. Indeed, mutant cells which express class II molecules but fail to express DM are unable to process and present native protein antigens. A striking phenotype of the mutation is class II molecules that contain almost exclusively a nested set of invariant chain peptides, termed CLIP, for class II associated Ii peptides, instead of the normal array of endogenously and exogenously derived peptides. Thus, DM appears to be required for the correct assembly of processed antigen-class II complexes. Recently, the subcellular compartments that contain DM and in which functional processed antigen-class II complexes are first formed have been described. Here, the evidence for the function of DM in the antigen-processing compartments is reviewed.

Antigen Presentation↗
PubMed1982

Rheological properties of echinoderm eggs during cell division.

Mechanical properties of the cell before and during cleavage in sea urchin eggs (a typical equal symmetrical cytoplasmic division) and polar-body formation (a typical unequal cytoplasmic division) are reviewed with special reference to the mechanism of cell division. Both in sea urchin eggs and starfish oocytes, the tension at the cell surface gradually increases before the onset of cytoplasmic division. The tension gradually decreases during division in starfish oocytes and in some sea urchin eggs. Some other sea urchin eggs display two peaks of the tension, one just before the onset of division and the other during division. The cleavage furrow is formed by the active contraction of a layer formed in the equatorial cortex of the cell in sea urchin eggs and of a ring-shaped layer formed in the cortex around the animal pole of the cell in starfish oocyte.

Animals↗
PubMed1975

Cinemicrographic studies on beta granule movement in monolayer culture of islet cells.

Monolayer cultures of adult rat islets were used for cinemicrographic studies on the movement of beta granules in the cytoplasm of beta cells. Stimulation of insulin release by glucose produced a significant increase in the amount of beta granule movement in the cultured cells. Disruption of the microtubular system with vinblastine or stabilization of microtubules with deuterium oxide inhibited the induction of granule movement by glucose. Incubation of the cultures in the absence of calcium inhibited glucose-induced movement of beta granules, whereas the subsequent addition of calcium permitted movement to occur. The addition of epinephrine also inhibited glucose-induced beta granule movement. In the presence of nonstimulating levels of glucose, movement of beta granules was present. The amount of movement varied from cell to cell suggesting a difference in base line activity of individual beta cells. The movement of individual beta granules was saltatory in type, and the average rate of movement was 1.5 mum. per second. The study demonstrated that directed movement of beta granules occurs following stimulation with glucose and adds further support to the hypothesis that the microtubular-microfilamentous system is involved in the intracellular translocation of beta granules to the cell surface where they are released by emiocytosis.

Animals↗
PubMed2001

Leukocyte-specific gene 1 protein (LSP1) is involved in chemokine KC-activated cytoskeletal reorganization in murine neutrophils in vitro.

Leukocyte-specific gene 1 protein (LSP1) is a cytoskeletal-associated protein of leukocytes that in vitro cross-links F-actin into extensively branched bundles of mixed polarity. In this study, we examined chemotaxis and superoxide production in neutrophils prepared from wild-type (WT) and Lsp1 knockout mice. Compared to WT neutrophils, Lsp1-/- neutrophils showed impairment in both migration speed and chemotaxis direction during chemokine KC-directed chemotaxis. When examined by confocal microscopy, chemotaxing Lsp1-/- neutrophils showed abnormal morphologies. They had discontinuous primary actin-rich cortexes and large membrane protrusions. When stimulated by phorbol 12-myristate 13-acetate (PMA), Lsp1-/- peritoneal neutrophils produce more superoxide than WT. The data presented suggest that LSP1 plays important roles in the regulation of neutrophil morphology, motility, and superoxide production.

Actins↗
PubMed1997

Cytochalasin D does not inhibit gravitropism in roots.

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments. These results indicate that an interaction between amyloplasts and the actin cytoskeleton is not critical for gravity sensing in higher plants and weaken the current statolith hypothesis.

Actin Cytoskeleton↗
PubMed1986

Gravisensitivity of the acellular slime mold Physarum polycephalum demonstrated on the fast-rotating clinostat.

The acellular slime mold Physarum polycephalum was used to investigate a postulated general gravisensitivity of cells. Physarum was subjected i) to a rotation on the fast-rotating clinostat, which enables the simulation of weightlessness (0 g), and ii) to single horizontal turns of 180 degrees. On the fast-rotating clinostat the response consists of a frequency increase in radial contractile activity, an oscillation of the mean values (frequency regulation phenomena) and an increase in standard deviation. A combination of 0 g and respiration impediment inhibits the response to 0 g, i. e., the frequency increase in radial contractile activity during weightlessness simulation. Turning the specimens horizontally about 180 degrees in a normally positioned light microscope also leads to a frequency increase in radial contractile activity, but the temporal pattern of the frequency increase differs in comparison to the experiments performed on the clinostat during weightlessness simulation. These results demonstrate the occurrence of gravisensitivity in Physarum polvcephalum. Regulation phenomena and the possible role of mitochondria in graviperception are discussed.

Animals↗
PubMed1975

Scanning electron microscopy of murine macrophages. Surface characteristics during maturation, activation, and phagocytosis.

The present report describes the surface architecture of critical point dried mouse peritoneal macrophages, after attachment and spreading on glass, and during maturation and active phagocytosis of rabbit erythrocytes and latex spheres. This study also compares the appearance of unstimulated cells with that of thioglycollate and endotoxin-stimulated cells. Activated cells, particularly thioglycollate-stimulated macrophages, showed more rapid and extensive spreading, a larger surface area, and more prominent ruffled membranes and filopodia. Many fine cytoplasmic pits were also evident and these may represent the sites of formation of numerous pinocytotic vesicles. The sequence of events during the various stages of phagocytosis was well visualized with the scanning electron microscope. Multiple large, round, and hemispherical craters were observed in these cells, and particles were engulfed through these structures and subsequently ingested. The findings are discussed in the light of current knowledge of the macrophage plasma membrane.

Animals↗
PubMed1977

Chronic acceleration in plants.

Since this subject was last reviewed (at the Symposium on Gravity and the Organism, 1967), relatively little new work on hypergravity effects on plants has appeared. Centrifugation has been used widely for separation of cellular components, but only occasionally as a primary environmental condition. With increasing magnitude of accelerative forces, the following effects have been reported by a number of authors working with many different plants. In the range 2-25 g, auxin transport and geotropic response in coleoptiles are increased and growth is stimulated. From 25 to 500 g, coleoptile growth is reduced and some morphological changes may be seen. At 1000-2500 g, root formation in willow cuttings increases. From 1000 g upward, cytoplasmic stratification occurs and seed germination decreases. Between 200 and 15000 g, chromosome damage has been observed. Algal cell polarity may be reversed at 5000 to 20000 g. Above 30000 g, the response of some cells to gibberellic acid is halted. Permanent morphologic changes in Escherichia coli are produced at 110000 g. Some plant cells have survived 176000 g for 20 hr.

Acceleration↗
PubMed2004

Cdc42p, GTP hydrolysis, and the cell's sense of direction.

The GTPase Cdc42p is essential for polarity establishment in animals and fungi.(1) Human Cdc42p can functionally replace yeast Cdc42p,(2) indicating a high degree of evolutionary conservation. Current models of Cdc42p action generally follow the signaling paradigm established for Ras, in which receptors responding to an initiating stimulus cause guanine nucleotide exchange factors (GEFs) to trigger GTP-loading of Ras, leading to engagement of downstream effectors and ensuing cell proliferation. Key support for the Ras paradigm came from the finding that oncogenic forms of Ras, unable to hydrolyze GTP and therefore constitutively GTP-bound, mimicked the effect of constitutive signaling by the upstream receptors even in the absence of stimuli. Attempts to assess whether or not this paradigm is valid for Cdc42p-induced polarization of yeast cells have yielded conflicting results.(3-6) Here, we discuss the available information on this issue and conclude that unlike Ras signaling, Cdc42p directed polarity establishment additionally requires cycling between GTP- and GDP-bound forms. We suggest that such cycling is critical for a little-studied "function" of Cdc42p: its ability to designate a unique portion of the cell cortex to become the polarization site, and to become concentrated at that site.

Animals↗