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Results for “Cell Aggregation”

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At least 163 records · Page 9Linked to original sources

PubMed1998

Signet-ring cell aggregates simulating carcinoma in colon and gallbladder mucosa.

We describe three cases of benign signet-ring cell aggregates in the colon associated with pseudomembranous colitis, adenomatous polyp of the colon and ulcerated mucosa of the gallbladder excised for gallstones. In all cases, we found loose, benign signet-ring cell aggregates overlying the ulcerated mucosa surface, simulating signet ring-cell carcinoma. The most important sign of the benign signet-ring cell aggregates is that they are always confined to the surface of the mucosa of the intestine or gallbladder mucosa or crypts of the intestinal epithelium. In no case did we see an invasion of these cells into the lamina propria of the mucosa. In all cases, the benign signet-ring cell aggregates were immunohistochemically positive with antibodies to cytokeratins. The occurrence of benign signet-ring cell aggregates is a rare and very misleading diagnostic pitfall which must be differentiated from signet-ring cell carcinoma of the colon and gallbladder.

Adenomatous Polyps↗

PubMed1991

A catecholaminergic sensory neuron phenotype in cranial derivatives of the neural crest: regulation by cell aggregation and nerve growth factor.

Tyrosine hydroxylase (TH) is transiently detectable in cells distributed throughout cranial sensory ganglia during early stages of gangliogenesis [embryonic day (E) 10.5-15.5]. Although TH cells appear in embryonic ganglia of both neural crest and placode origin, mature cranial sensory neurons that express catecholaminergic properties are restricted to placode derivatives. The mechanism(s) underlying the loss of TH expression in crest-derived sensory ganglia is unknown, and the present study was undertaken to define the temporal regulation of this phenotype. Our data indicate that transient TH cells belong to a large subset of primary sensory neurons that exhibit the capability to express TH throughout development. The lack of TH expression after E15.5 appears to be due to modulation of this catecholaminergic potential. The phenotype reappears, however, when E16.5 and older ganglia are dissociated in culture into single cells, suggesting that factors associated with cell aggregation modulate TH expression. In support of this hypothesis, sensory neurons grown at high cell density exhibit lower levels of TH expression than low-density cultures. The decrease in TH levels seen at high density was associated with changes in sensory neuron morphology that are characteristic of ganglion cell maturation in vivo; therefore, modulation of TH expression may be only one facet of a more general program of sensory neuron differentiation associated with cell aggregation in developing ganglia. In contrast to the effects of cell aggregation, treatment with NGF increased the proportion of TH cells in dissociate cultures of E14.5 and E16.5 cranial sensory ganglia. Our findings indicate that sensory transmitter phenotype may be modulated by multiple factors during gangliogenesis, including cellular interactions intrinsic to the developing ganglionic microenvironment.

Animals↗

PubMed1989

Identification of a cell surface-associated protein involved in mouse neural cell aggregation by means of antibodies against the sponge aggregation factor.

Polyclonal antibodies were raised against the purified aggregation factor (AF) from the sponge Geodia cydonium to elucidate possible immunological relationships between adhesion molecules of lower multicellular eukaryotic systems (sponges) and those of vertebrates. This anti-AF recognized a series of polypeptides associated with the AF, among them also a polypeptide with a Mr of 47,000 (p47). The formation of the antibody-p47 immunocomplexes could be prevented by adsorbing the anti-AF with a brain extract from DBA/2J mice. Moreover, this brain polypeptide inhibited the AF-mediated aggregation of sponge cells. Interestingly, the anti-AF recognized a p37 molecule in the brains of 2- to 3-day-old mice; no reaction could be traced using brain extracts from animals older than 2 months. The anti-AF failed to interact with polypeptides from mouse liver or spleen. By indirect immunofluorescence staining the p37 was found to be localized on the plasma membranes of brain cells. Moreover, Fab' fragments of the anti-AF inhibited aggregation of mouse brain cells. These data indicate that the sponge anti-AF recognizes a p37 molecule in mouse brain cells which is either directly or indirectly involved in brain cell aggregation.

Animals↗

PubMed1981

On the importance of substrate adhesion and cell aggregation in the Con A-induced blastogenesis of lymphocytes.

The importance of substrate adhesion and cell aggregation for the Con A-induced blastogenesis of human peripheral lymphocytes was studied by flow cytometric methods. The percentage of lymphocytes responding to the mitogen by growth and DNA synthesis was approximately the same among non-adherent, single cells as among substrate-adherent and aggregated cells. However, the response of the former cells was delayed by about 10 h as compared with that of adherent and aggregated cells. This delay increased to about 20 h in monocyte-depleted cultures. Stimulation with succinyl-Con A, which caused negligible aggregation, produced a significant response. Blast cells appeared to be largely non-adherent. It is concluded that neither substrate adhesion nor cell aggregation are prerequisites for Con A-induced blastogenesis, although substrate adhesion seems to have a significant promotive effect that is probably associated with a direct contact of the lymphocytes with monocytes.

Cell Adhesion↗

PubMed2003

Human pancreatic precursor cells secrete FGF2 to stimulate clustering into hormone-expressing islet-like cell aggregates.

Development of the endocrine pancreas includes a series of early events wherein precursor cells cluster, that is migrate to form cell aggregates, which subsequently differentiate into islets of Langerhans. We show that PANC-1 cells, a human pancreatic cell line, differentiates into hormone-producing islet-like cell aggregates after exposure to a defined serum-free medium. These cells were used to provide the following evidence that fibroblast growth factor (FGF)2 is a paracrine chemoattractant during PANC-1 cell clustering: (i) FGF2 is secreted and remains bound to the extracellular matrix from where it may diffuse to form chemoattractive gradients; (ii) a subset of cells expresses FGF receptors (FGFRs) -1, -2, -3, and -4; (iii) inhibition of FGFR tyrosine kinase inhibits cell clustering; and (iv) FGF2 neutralizing antibody inhibits clustering. In addition, adult human islet-derived precursor cells, which cluster and differentiate in a manner similar to PANC-1 cells, also secrete FGF2 and express FGFRs. We conclude that FGF2, acting as a paracrine chemoattractant, stimulates clustering of precursor cells, an early step leading to islet-like cell aggregate formation. Similar processes may occur during development of the islet of Langerhans in humans.

Cell Aggregation↗

PubMed1996

Foamy cell aggregation in duodenal diverticula.

We have investigated 44 cases of duodenal diverticulum to delineate the pathological features. Foamy cell aggregations were observed in 24 (54.5%) of the cases. The foamy cells were located within the submucosa in all 24 cases and were found around the deepest portion of the diverticula in 14. There were no statistically significant differences between the depth of the diverticulum and the presence or degree of foamy cell aggregation. Lymphoid aggregates, focal thickening of the muscularis mucosae, submucosal fibrosis, intimal thickening of submucosal vessels and submucosal haemorrhage were also detected, but statistical analysis showed no significant associations between these pathological findings and the presence of foamy cell aggregates. We conclude that the foamy cell aggregates are a non-specific but frequent pathological finding in duodenal diverticula and which have not been described in previous studies.

Autopsy↗

PubMed1999

Dissection of the impact of various intracellular signaling pathways on stable cell aggregate formation of rat thymocytes after initial lectin-dependent cell association of using a plant lectin as model and target-selective inhibitors.

Bivalent lectins as bridging molecules between cells or cell surface lectins as docking points are involved in mediation of cell adhesion by specific recognition of suitable glycoconjugates on an opposing surface. The initial contact formation by a lectin can lead to intracellular post-binding events which effect stable cell association even in the presence of the haptenic sugar. To delineate the participation of intracellular signaling pathways in the cascade of reactions to establish firm association, reagents with proven inhibitory capacity on certain biochemical targets provide suitable tools. Using this approach with rat thymocytes and the galactoside-binding lectin from mistletoe (Viscum album L. agglutinin, VAA) as a model, a panel of 27 inhibitors with impact on e.g. several types of kinases, tyrosine phosphatases, NO synthases, G proteins, enzymes of arachidonate and cyclic nucleotide metabolism and calmodulin was systematically tested with respect to their capacity to impair the formation of lactose-resistant cell aggregates. In addition to the recently reported effectiveness of N-ethylmaleimide, nordihydroguaiaretic acid, and trifluoperazine the agents diacylglycerol kinase inhibitor II, emodin, D609, DPI, KT5720, KT5926, MK-886, bisindolylmaleimide I, and (+/-)methoxyverapamil were able to reduce aggregate stability in the presence of the haptenic sugar. Thus, various types of kinases including p561lck tyrosine kinase, lipoxygenases, phosphatidylcholine-specific phospholipase C as well as calmodulin and Ca(2+)-currents, but not modulators of the metabolism of cyclic nucleotides, NO synthases, MAP kinases, tyrosine phosphatases and phospholipase A (preferentially group II) and C can play a role in eliciting contact stability. More than one principal signaling pathway appears to be linked to the measurable parameter, since inhibitory substances show additive properties in co-incubation assays and differentially affect two lectin-elicited cellular activities, i.e. intracellular movement of Ca(2+)-ions and H2O2-generation, which can accompany cell adhesion and aggregation. Pronounced differences in the extent of modulation of H2O2-generation in human neutrophils by the same set of substances emphasizes that general conclusions on the post-binding effects for a certain lectin in different cell types are definitely precluded. In aggregate, the approach to employ inhibitors with target selectivity intimates an involvement of protein kinases A, C, Ca2+/calmodulin-dependent protein kinase II, p56lck tyrosine kinase, leukotrienes and/or hydroxyeicosatetraenoic acids, phosphatidylcholine-specific phospholipase C and Ca(2+)-fluxes in events following initial binding of a galactoside-specific plant lectin to rat thymocytes which establish firm cell contacts.

Animals↗

PubMed1990

Rheological aspects of red blood cell aggregation.

The rheological aspects of red blood cell aggregation include molecular phenomena, cell viscoelasticity, and bulk flow rheology. At the molecular level, rates at which bonds are formed and broken, the chemical energy liberation from bond formation, the elasticity of the cross-bridges and lateral mobility of cross-linking molecules must all be considered for a complete description of bond formation and distribution. Lateral migration of binding molecules occurs due to diffusion in the surface of the membrane but may also be influenced by the stresses in the membrane during separation of adhering cells. In red blood cell disaggregation, fluorescent probes have shown concentration of ligands in the region of contact close to the line of separation. The chemical potential decrement that occurs when a bond is formed provides the energy source that may deform red blood cells in the process of aggregation. The degree of aggregation and the extent of cell deformation depends on the viscoelastic properties of the cell as well as the dynamics of bond formation and repulsive potential of surface charges present, which is governed by an equation representing a balance of these energies. In flowing blood, the hydrodynamic forces applied by the plasma and surrounding cells must be added to the bond forces and elastic response of the cell. Under sufficiently strong aggregation, plug flow or large aggregates may result. At high shear rates, aggregation may be prevented due to the small contact time and high shear stresses so that no effects of aggregation may be observed. At intermediate shear stresses, transitory contact, adhesion and disaggregation may occur between neighboring cells. Such phenomena have not been analyzed in detail, but simplified models suggest that plug-like flow can occur due to hydrodynamic cell-cell interaction even when cells are not aggregated.

Erythrocyte Aggregation↗

PubMed1999

Reassemblage of primary cell aggregates and modulation of subcortical connections in the thalamic relay nucleus: effects of vibrissal damage in the developing whisker-to-barrel pathway in the mouse.

To investigate the mechanisms underlying the reorganization of barrels in the whisker-tobarrel pathway, the facial vibrissae of mice were damaged by electrocauterization at alternate positions on either postnatal day 0 (P0) or P3, before or after the onset of cell aggregation in the thalamus and cortex. Animals were subsequently killed on P8, topographical changes were examined by cytochrome C oxidase histochemistry, and afferent connections were identified using DiI tracer. The cytoarchitecture was characterized with bisbenzimide counterstain. Regardless of when damage was done, the reorganized barreloids and barrels in the thalamus and cortex, respectively, were integrated in an array that represented the topography of undamaged vibrissae. In the brainstem, although the original framework of the array was preserved, defective cell aggregates remained, possibly still in contact with damaged vibrissae. During normal development, on P0 cell aggregates are formed only in the brainstem, and begin to be organized at the other levels of the pathway on P3. Therefore, when damage is induced on P3, the primary cell aggregates are replaced by new, possibly recombined, cell aggregates in the thalamus and cortex to represent the new peripheral topography. The presumably recombined aggregates indicate that cell reassemblage occurred between neighboring cell aggregates. Concomitant with these changes, afferent fibers originating in the brainstem and thalamus extended their terminal arborizations to delineate the new cell aggregates in the thalamus and cortex, respectively. These findings indicate that activity-dependent competitive interactions of afferents may play a crucial role in organizing the topography of cell aggregation and reassemblage in response to vibrissal damage at each level of the pathway.

Afferent Pathways↗

PubMed1988

Developmental expression of glial fibrillary acidic protein and glutamine synthetase in serum-free aggregating cell cultures of fetal rat telencephalon.

Serum-free aggregating cell cultures of fetal rat telencephalon were examined by a combined biochemical and double-labeling immunocytochemical study for the developmental expression of glial fibrillary acidic protein (GFAP) and glutamine synthetase (GS). It was found that these two astroglial markers are co-expressed at different developmental stages in vitro. During the phase of cellular maturation (i.e. between days 14 and 34), GFAP levels and GS activity increase rapidly and in parallel. At the same time, the number of immunoreactive cells increase while the long and thick processes staining in early cultures gradually disappear. The present results demonstrate that in this particular cell culture system only one type of astrocytes develops which expresses both GFAP and GS and which attains a relatively high degree of maturation.

Animals↗

PubMedDate not supplied

Ultrasonic detection of red cell aggregation immediately preceding blood clotting.

High-resolution ultrasonic imaging of circulating blood was used to study the relation between red cell aggregation and blood clotting in vitro. A reversible increase in echogenicity produced by red cell aggregation occurred in moving heparinized blood as shear rate was decreased. We induced clotting of the heparinized blood by administration of protamine. At both low (1.6 sec-1) and moderate (22.6 sec-1) mean shear rates, transient homogenous increased echogenicity indicative of red cell aggregation preceded blood clotting. In separate experiments, we established that protamine can cause increased echogenicity due to red cell aggregation which can be reversed by adding heparin to circulating suspended red cells in the absence of clotting factors. Presumably, these effects of protamine and heparin are due to electrostatic bonding involving red cell surfaces. We conclude from these studies that red cell aggregation precedes clotting of heparinized blood by protamine at low and moderate shear rates.

Blood Coagulation↗

PubMed1994

Ectopic expression of NCAM in mouse fibroblasts stimulates self-aggregation, and promotes integration into primary cerebellum cell aggregates.

We have undertaken aggregation experiments using mouse LMTK(-)-fibroblasts transfected with various isotypes of the neural cell adhesion molecule, NCAM. We found that self-aggregation of NCAM-positive fibroblasts is enhanced compared to control-transfected cells. The aggregation properties are partly dependent on the expressed NCAM isotype. Fibroblasts expressing a NCAM 140 isotype with exons a3 and pi were further tested in primary cerebellum cell re-aggregation experiments. While control-transfected fibroblasts could not be found in forming aggregates, fibroblasts ectopically expressing NCAM were integrated into neural cell aggregates. Time-lapse photography indicated that the nascent primary cell aggregates actively participated in the integration process by migration and attachment to nearby NCAM-positive fibroblasts.

Animals↗

PubMed1999

Production of human CNS neurons from embryonal carcinoma cells using a cell aggregation method.

When treated with retinoic acid (RA), a human embryonal carcinoma (EC) cell line, NTera2 cl.D/1 (NT2), differentiates into several morphologically distinct cell types, which include terminally differentiated postmitotic central nervous system (CNS) neurons. Accumulating evidence has demonstrated the significant potential of NT2 cells in studies related to cancer therapy and neurodegenerative diseases. However, preparation of enriched NT2 neurons often requires a lengthy period (ca. five weeks) and depends largely on tedious techniques similar to those used for primary neuronal cultures. Here, we report a rapid protocol for the preparation of these human CNS neurons. Using the method of cell aggregation, enriched NT2 neurons can be obtained in approximately two weeks. We also demonstrated that cell aggregation reduced the time normally required for the induction of neuronal differentiation, as revealed by the early expression of neuronal markers. The period of RA treatment could also be reduced if NT2 cells were maintained as aggregates for a sufficient period of time. Taken together, our findings demonstrated that cell aggregation promoted RA-induced neuronal differentiation of NT2 cells and provided a rapid protocol for the efficient production of NT2 neurons. The ability to produce large quantities of human CNS neurons should facilitate future use of these neurons for basic research and applications in cell therapy.

Biomarkers↗

PubMed1986

Repolarization currents in embryonic chick atrial heart cell aggregates.

Outward membrane currents in aggregates of atrial cells prepared from 7-12-d-old chick embryonic hearts were measured with the two microelectrode voltage-clamp technique. Two outward current components, Ix1 and Ix2, were found in the plateau potential range of the action potential. The Ix1 component is activated between -50 and -20 mV; the Ix2 component is activated between -15 and +20 mV. The Ix1 component inwardly rectifies, whereas Ix2 has an approximately linear current-voltage relation. These preparations lack a time-dependent pacemaker current component, even though they beat spontaneously with an interbeat interval of approximately 1 s. A mathematical model of electrical activity is described based on our measurements of time-dependent outward current, and measurements in the literature of inward current components.

Animals↗

PubMed1982

The effects of stimulation rate on calcium-dependent action potentials recorded from chick embryo heart cell aggregates.

1. Action potentials were recorded from aggregates of heart cells prepared from 3- to 7-day chick embryos. At 3 days the maximum rate of rise (+ Vmax) was insensitive to TTX; at 7 days it was considerably reduced by TTX. 2. In the presence of TTX the action potential overshoot was dependent on [Ca]0; the results may be fitted using constant field theory and assuming that the membrane is over a hundred times more permeable to Ca than to Na or K. 3. An increase in stimulation rate in the range 0.2-2 Hz led to an increase in both overshoot and + Vmax. This effect was not seen after addition of 20 mM-tetraethylammonium ions, nor when Sr was substituted for Ca in the external medium. We suggest that these rate-dependent changes may result from partial inactivation of an outward K current.

Action Potentials↗

PubMed2002

A very late activating antigen-alpha4 (CD49d) monoclonal antibody, BU49 induces phosphorylation of a cAMP response element-binding protein (CREB), resulting in induction of homotypic cell aggregation and enhancement of interleukin-8 (IL-8) production.

A very late activating antigen-alpha4 (CD49d) monoclonal antibody (mAb), BU49 was found to induce phosphorylation of a cAMP response element-binding protein (CREB) in the human monocyte-like cell line, U937. This phosphorylation of CREB was completely inhibited by a protein kinase A (PKA) inhibitor H-89 with the optimum concentration (completely inhibits PKA). Furthermore, BU49 strongly and rapidly (within 5 hr) induced homotypic cell aggregation in the U937 cells accompanied by CREB phosphorylation. This cell aggregation was also completely inhibited by the addition of H-89. Interestingly, both of two mAbs (mAb13 and 4B4) recognizing different epitopes on the CD29 (beta1 integrin) completely inhibited this aggregation at the late phase (18 to 24 hr) but not at the early phase (5 hr) after cultured with BU49. On the other hand, BU49 significantly enhanced interleukin-8 (IL-8) production from the U937 cells into the culture supernatant. In addition, this IL-8 production was significantly blocked in the presence of H-89 with the optimum concentration. However, a CD29 mAb which inhibits homotypic cell aggregation could not block this IL-8 production. Taken together, these findings indicate that BU49 induces CREB phosphorylation mainly mediated by PKA, which finally results in the induction of homotypic cell aggregation and the enhancement of IL-8 production. Furthermore, these findings also indicate that the enhancement of IL-8 production from the U937 cells induced by BU49 partially depends on CREB phosphorylation mainly mediated by PKA.

Antibodies, Monoclonal↗

PubMed1992

The growth of Vero cells in suspension as cell-aggregates in serum-free media.

Vero cell lines, usually considered anchorage-dependent, could be grown as cell-aggregates in suspension culture with serum-free media. Several different combinations of base media gave growth results above 10(6) cells/ml (NCTC 135:SFRE 199-1; NCTC 135:Waymouth MB 752/1; NCTC 135:RPMI 1640). Insulin was not essential for growth and Bovine Serum Albumin could be diluted out of the media if linoleic acid was present. The size and density of the aggregates formed varied depending on the media used.

Animals↗

PubMed2006

In vitro self-assembly of proepicardial cell aggregates: an embryonic vasculogenic model for vascular tissue engineering.

Proepicardial/epicardial-derived cells are the main origin of the early embryonic coronary vascular bed. In vivo coronary vasculogenesis, which is a fast-occurring event, can be mimicked in vitro by culturing proepicardial tissue in different ways. The in vitro vasculogenic model presented in this study (a proepicardial suspension culture assay) partially reproduces coronary vascular development from its cellular precursors, a process known to be highly dependent on cell migration, cell differentiation, cell adhesion/sorting, and tissue fusion phenomena. The main aim of this study is to study the triggering signals and the cellular dynamics that regulate the differentiation of proepicardial cells into the angioblastic/endothelial lineage and their in vitro vasculogenic potential. Our results indicate that hanging drop-cultured proepicardia, which have an intrinsic vascular potential, behave like self-assembling cell aggregates or spheroids that can fuse to give rise to complex vascularized 3D structures. We believe that these self-assembling cell aggregates are an optimal choice to study the differentiation of coronary angioblasts, as well as a good method to reproduce vascular development in vitro. Finally, we propose the proepicardium as a suitable cellular source for vascular tissue engineering.

Animals↗