A computer model for reshaping of cells in epithelia due to in-plane deformation and annealing

Although cell reshaping is fundamental to the mechanics of epithelia, technical barriers have prevented the methods of mechanics from being used to investigate it. These barriers have recently been overcome by the cell-based finite element formulation of Chen and Brodland. Here, parameters to describe the fabric of an epithelium in terms of cell shape and orientation and cell edge density are defined. Then, rectangular "patches" of model epithelia having various initial fabric parameters are generated and are either allowed to anneal or are subjected to one of several patterns of in-plane deformation. The simulations show that cell reshaping lags the deformation history, that it is allayed by cell rearrangement and that it causes the epithelium as a whole to exhibit viscoelastic mechanical properties. Equations to describe changes in cell shape due to annealing and in-plane deformation are presented.

Pharmacological potential of embryonic stem cells

Established embryonic stem (ES) cell lines have been at the forefront of approaches to understand gene function during embryogenesis and in adult vertebrate organisms, principally due to exploitation of two essential attributes; their pluripotency or ability to contribute to all three germinal layers and germ line in mice and their ease of genetic modification. Endeavours to routinely establish ES cells from species other than mice have met with limited success, although with rapid progress being made in our understanding of their basic cell biology, the regular derivation of lines from pre-implantation embryos will become easier for many species including humans. With a recent growing awareness of how these cells can be made to grow in an unlimited, but regulated manner plus how their fate can be directed or manipulated into diverse, mature phenotypes in culture, it has become clear that the biological resource offers additional attractive features applicable for future biomedical research and therapy. Advanced mouse ES-based technologies are being used in the industry for pharmaceutical discovery and development, while it is also anticipated that human ES cell reagents will revolutionise aspects of regenerative medicine. This review will summarise the advantages, potential and great hope for ES cell based systems in these contexts.

Effects of silkworm paralytic peptide on in vitro hematopoiesis and plasmatocyte spreading

Bombyx mori paralytic peptide (BmPP), a multifunctional cytokine-like molecule, is expressed in the hematopoietic organ-wing imaginal disc complex, suggesting that BmPP is involved in both immune response and the hematopoietic process. We studied the effects of BmPP on plasmatocytes and hematopoietic organs of the silkworm. BmPP (1 microM) stimulated spreading of circulating plasmatocytes, but the percentage of spread plasmatocytes was only 20%. Over 10 nM of BmPP, however, elicited prominent spreading in 70% of young plasmatocytes discharged from cultured hematopoietic organs. Cells in hematopoietic organs that were enzymatically dispersed did not spread even after adding 100 nM of BmPP, indicating that plasmatocytes acquired BmPP-sensitivity immediately after discharge. When cultured in a medium containing larval plasma, hematopoietic organs grew markedly and discharged a large number of hemocytes, over 95% of which were morphologically plasmatocytes. The hemocyte discharge was blocked in the medium containing BmPP dose-dependently, although hematopoietic organ growth was not suppressed. These results suggest that BmPP plays important roles both in hematopoietic regulation and in the hemocyte immune reaction of the silkworm.

Co-occurrence in nature of different clones of the social amoeba, Dictyostelium discoideum

The social amoeba, Dictyostelium discoideum, produces a multicellular fruiting body and has become a model system for cell-cell interactions such as signalling, adhesion and development. However, unlike most multicellular organisms, it forms by aggregation of cells and, in the laboratory, forms genetic chimeras where there may be competition among clones. Here we show that chimera formation is also likely in nature, because different clones commonly co-occur on a very small scale. This suggests that D. discoideum will likely have evolved strategies for competing in chimeras, and that the function of some developmental genes will be competitive. Natural chimerism also makes D. discoideum a good model organism for the investigation of issues relating to coexistence and conflict between cells.

Surface engineering of living myoblasts via selective periodate oxidation

Cell surface molecules are vital for normal cell activity. To study the functions of these molecules or manipulate cell behavior, the ability to decorate cell surfaces with bioactive molecules of our choosing is a potentially powerful technique. Here, we describe the molecular engineering of living L6 myoblast monolayers via selective periodate oxidation of sialic acid residues and the application of this surface modification in the artificial aggregation of cells. The aldehyde groups generated by this reaction were used to selectively ligate a model molecule, biotin hydrazide, to the cell surfaces. Flow cytometry analysis after staining with fluorescently conjugated avidin revealed a concentration-dependent increase in fluorescence compared to untreated cells with a maximal shift of 345.1 +/- 27.4-fold and an EC(50) of 17.4 +/- 1.1 microM. This mild oxidation reaction did not affect cell number, viability, or morphology. We then compared this chemical technique with the metabolic incorporation of reactive cell surface ketone groups using N-levulinoylmannosamine (ManLev). In this cell line, only a 22.3-fold fluorescence shift was observed compared to untreated cells when myoblasts were incubated with a high concentration of ManLev for 48 hours. Periodate oxidation was then used to modify myoblast surfaces to induce cell aggregation. Crosslinking biotinylated myoblasts, which do not spontaneously aggregate in culture, with avidin resulted in the rapid formation of millimeter-sized, multicellular structures. These data indicate that sodium periodate treatment is an effective, noncytotoxic method for the in vitro molecular engineering of living cell surfaces with the potential for cell biology and tissue engineering applications.

Production of dopaminergic neurons for cell therapy in the treatment of Parkinson's disease

Dopaminergic cell therapy is a potential viable treatment for Parkinson's disease. However, lack of a well-characterized cell preparation of known phenotypic composition containing a high percentage of dopaminergic neurons, has prevented a definitive, controlled, pilot clinical trial from being conducted. We report the successful in vitro expansion of rat E12 mesencephalic progenitors to produce 5-fold the normal number of dopaminergic neurons. The expanded neurons (MAP2+) were detached, resuspended, and formed into small aggregates of 10-200 neurons containing 25-50% of dopaminergic neurons (TH+) that will likely be optimal for use in successful cell therapy. After storage in DPBS, in 0 mM Ca(2+) for up to 24 h at room temperature, aggregated cells were still 90% viable. These results demonstrate that it might be feasible to use a similar protocol to expand human dopaminergic progenitors in vitro. If successful, the requisite large numbers of dopaminergic neurons required to conduct a pilot clinical trial for Parkinson's disease will be produced in vitro. Indications are that the cells can be maintained at optimal viability for the duration of the neural transplantation procedure, under real operating conditions.

[The general theory of pathophysiological mechanisms of neurological and psychopathological syndromes]

Besides structural and functional deficits, central nervous system (CNS) damage causes another effect in the form of novel pathological integrations consisting of CNS primarily and secondarily changed structures. At the neuronal level, the integration presents as aggregation of hyperactive uncontrollable neurons, which produces enhanced uncontrolled impulse flow and acts as a generator of pathologically enhanced excitation, network type. At the system interrelation level, the integration is represented by a new pathodynamic organization including damaged CNS regions, which constitutes a pathological system (PS). The hyperactive CNS structure plays a role of a pathological determinant promoting PS formation may determine a type of PS activity. A clinical manifestation of PS activity is a corresponding neurological or psychopathological syndrome.

New information from cell aggregate compression tests and its implications for theories of cell sorting

In order to verify theories about the mechanics of cell sorting, tissue spreading and checkerboard pattern formation, it is necessary to measure certain cell properties such as surface tension and adhesiveness. The purpose of this work is to clarify the relationship between these two important properties and to use computer simulations and analytical calculations to extract additional information from parallel plate compression tests. This paper shows that compression tests can be used to determine not only the surface tension between the aggregate and the surrounding medium, but also the effective viscosity of the cell cytoplasm and the interfacial tension that acts between the cells that make up the aggregate. The findings reported here also support a novel, differential interfacial tension-based theory for cell sorting, tissue spreading and checkerboard pattern formation, and pose further challenges to current differential adhesion-based models.

Aluminum disrupts the pro-inflammatory cytokine/neurotrophin balance in primary brain rotation-mediated aggregate cultures: possible role in neurodegeneration

The etiology of human neurodegenerative diseases including Alzheimer's disease (AD) is exceedingly complex and our understanding of the mechanisms involved is far from complete. The experimental neurotoxicology of aluminum has been shown to recapitulate many of the pathophysiological features of AD and therefore represents a useful model to study the mechanisms involved in neurodegeneration. The present study investigated the effects of aluminum maltolate (Al-maltol) on the delicate balance that exists between pro-inflammatory cytokines and neurotrophins using primary brain rotation-mediated aggregate cultures. Aggregates were treated with Al-maltol (5-150 microM) on day 15 in vitro for 72 h. Cell death increased in a time- and concentration-dependent manner reaching significance in aggregates treated with 150 microM Al-maltol in 48 h and 50 microM by 72 h. Analysis of gene expression at 72 h revealed a concentration-dependent increase in tumor necrosis factor alpha (TNFalpha) and macrophage inflammatory protein-1alpha (MIP-1alpha) suggestive of a state of inflammation. In contrast, a dramatic concentration-dependent decrease in the expression of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) was observed. In fact, NGF expression could not be detected in aggregates treated with 50 and 150 microM Al-maltol. These changes in gene expression correlated with a decrease in aggregate size and an increase in neurodegeneration as indicated by Fluoro-Jade B staining. The results indicated a differential regulation of pro-inflammatory cytokines and neurotrophins in brain tissue following treatment with Al-maltol. Such findings provide insight into the possible involvement of deregulation of the cytokine/neurotrophin balance in the etiology of neurodegeneration.

Equilibrium shapes of erythrocytes in rouleau formation

A well known physiological property of erythrocytes is that they can aggregate and form a rouleau. We present a theoretical analysis of erythrocyte shapes in a long rouleau composed of cells with identical sizes. The study is based on the area difference elasticity model of lipid membranes, and takes into consideration the adhesion of curved axisymmetric membranes. The analysis predicts that the erythrocytes in the rouleau can have either a discoid or a cup-like shape. These shapes are analogous to the discoid and stomatocyte shapes of free erythrocytes. The transitions between the discoid and cup-like shapes in the rouleau are characterized. The occurrence of these transitions depends on three model parameters: the cell relative volume, the preferred difference between the areas of the membrane bilayer leaflets, and the strength of the adhesion between the membranes. The cup-like shapes are favored at small relative volumes and small preferred area differences, and the discoid shapes are favored at large values of these parameters. Increased adhesion strength enlarges the contact area between the cells, flattens the cells, and consequently promotes the discoid shapes.

Time course of hemorheological alterations after heavy anaerobic exercise in untrained human subjects

The time course of hemorheological alterations was investigated after heavy anaerobic exercise in untrained male human subjects. The Wingate protocol was performed by each subject, and blood lactate, red blood cell (RBC) deformability and aggregation, white blood cell (WBC) activation, and several hematological parameters were investigated during 24 h after the exercise and compared with preexercise values. Compared with the preexercise value, blood lactate level was found to be approximately 10-fold higher immediately after the exercise. There was a transient, significant increment of RBC and WBC counts immediately after exercise that was followed by a decrement of RBC count. There was a second increase of WBC count, accompanied with increased percentages of granulocytes and granulocyte activation, starting 45 min after exercise. RBC deformability was found to be impaired immediately after exercise and remained reduced for at least 12 h; RBC aggregation was also found to be decreased after exercise, with the onset of this decrease delayed by 30 min. The results of this study indicate that a single bout of heavy anaerobic exercise may induce significant hemorheological deterioration lasting for up to 12 h and thus suggest the need to consider such effects in individuals with impaired cardiovascular function.

Conjugation of heparin into carboxylated pullulan derivatives as an extracellular matrix for endothelial cell culture

A carboxylated pullulan, for use as a structural material for a number of tissue engineering applications, was synthesized and conjugated with heparin. By immobilization of heparin to pullulan, endothelial cells (ECs) attached on the heparin-conjugated pullulan were more aggregated than when attached to other pullulan derivatives. Attachments were 50, 45, 49, and 90% for a polystyrene dish, pullulan acetate, carboxylated pullulan, and heparin-conjugated pullulan, respectively. Heparin-conjugated pullulan inhibited the proliferation of smooth muscle cells (SMCs) in vitro. Heparin-conjugated pullulan material can thus be used for the proliferation of vascular ECs and to inhibit the proliferation of SMCs.

Relative aggregation state and hemolytic activity of amphotericin B encapsulated by poly(ethylene oxide)-block-poly(N-hexyl-L-aspartamide)-acyl conjugate micelles: effects of acyl chain length

We systematically altered the chemical structure of the core-forming poly(L-amino acid) block of an amphiphilic diblock copolymer series based on poly(ethylene oxide)-block-poly(N-hexyl-L-aspartamide), PEO-b-p(N-HA), acyl esters by varying the length of the attached acyl side chain. Drug-loaded micelles were prepared in good yield by a modified solvent evaporation procedure. In addition, the relative aggregation state and hemolytic activity of encapsulated amphotericin B (AmB) were analyzed by absorption spectroscopy. The length of the attached acyl side chain in PEO-b-p(N-HA) acyl ester micelles modulates the relative aggregation state of encapsulated AmB. Furthermore, acyl chain length appears to have a profound influence on the time-dependent hemolytic profile of encapsulated AmB toward bovine erythrocytes. For all acyl conjugate micelle-AmB formulations, the onset of hemolysis is delayed relative to free AmB. Particularly in the case of stearate ester micelles, the incomplete and gradual build-up of hemolysis might reflect the sustained release of drug over a period of 24 h. Based on the corresponding absorption spectrum, we speculate that encapsulated AmB may interact strongly with stearate side chains, resulting in sustained release. Via chemical manipulation of the core-forming region, it may be possible to fine-tune the release of encapsulated AmB from PEO-b-p(N-HA)-acyl ester micelles.

Cattaneo models for chemosensitive movement. Numerical solution and pattern formation

We derive models for chemosensitive movement based on Cattaneo's law of heat propagation with finite speed. We apply the model to pattern formation as observed in experiments with Dictyostelium discoideum, with Salmonella typhimurium and with Escherichia coli. For Salmonella typhimurium we make predictions on pattern formation which can be tested in experiments. We discuss the relations of the Cattaneo models to classical models and we develop an effective numerical scheme.

Cross-linked cell aggregates of Trigonopsis variabilis: D-amino acid oxidase catalyst for oxidation of cephalosporin C

Trigonopsis variabilis CBS 4095 was treated with alkali (pH 11, 30 min), heated (65 degrees C, 60 s) and immobilized. Glutaraldehyde, polyethyleneimine and a cross-linking reagent formed by reaction of polyethyleneimine with glutaraldehyde were used for stabilization of D-amino acid oxidase in the cells, as well as for aggregation and binding of the cells. A specific activity of 82-98 U of D-amino acid oxidase per g dry mass was produced with a yield of about 20%. The half-life time of 142 repeated conversion cycles corresponds to a productivity of 130 kg cephalosporin C oxidized per kg catalyst dry mass.

Characterization of proliferation and differentiation of EGF-responsive striatal and septal precursor cells

The epigenetic manipulation of precursors may provide data to elucidate the potential interactions among these cells in different brain regions. However, the response to epigenetic signals is modulated by the environment in which the cells are manipulated. Therefore, data regarding the action of a particular factor must be considered in the light of a specific system. To compare septal and striatal precursors, we have tested the effect of nerve growth factor (NGF) on the proliferation and neuronal differentiation of epidermal growth factor (EGF)-responsive cells from these brain regions. Precursors were cultivated as 'neuropheres' in serum free medium (SFM) to which NGF was added. NGF did not support the proliferation of EGF-generated precursors so that no differences in the cell magnitude with respect to control cultures were observed. Differentiation of precursors in SFM plus 1% fetal bovine serum (FBS) on poly-D-lysine showed that the neuron number was increased two-fold in septal cultures treated with NGF but not in those from striatum. A quantitative evaluation of the soma surface and the number of primary neurites showed differences between both populations of precursor-generated neurons. In addition, we also observed no influence of NGF on these parameters of cellular morphology. Thus, taken together these results seem to indicate that at this developmental stage in which these populations of precursors were isolated, heterogeneities exist between them, which is probably related to their origin and/or functional roles in vivo.

Conversion of embryonic stem cells into neuroectodermal precursors in adherent monoculture

Mouse embryonic stem (ES) cells are competent for production of all fetal and adult cell types. However, the utility of ES cells as a developmental model or as a source of defined cell populations for pharmaceutical screening or transplantation is compromised because their differentiation in vitro is poorly controlled. Specification of primary lineages is not understood and consequently differentiation protocols are empirical, yielding variable and heterogeneous outcomes. Here we report that neither multicellular aggregation nor coculture is necessary for ES cells to commit efficiently to a neural fate. In adherent monoculture, elimination of inductive signals for alternative fates is sufficient for ES cells to develop into neural precursors. This process is not a simple default pathway, however, but requires autocrine fibroblast growth factor (FGF). Using flow cytometry quantitation and recording of individual colonies, we establish that the bulk of ES cells undergo neural conversion. The neural precursors can be purified to homogeneity by fluorescence activated cell sorting (FACS) or drug selection. This system provides a platform for defining the molecular machinery of neural commitment and optimizing the efficiency of neuronal and glial cell production from pluripotent mammalian stem cells.

[Principles of changes of structural organization of cell membranes and functional properties of erythrocytes in neurotic disorders]

Investigation into structural, metabolic, and functional conditions of red blood cells was performed in 24 patients with a neurosis (neurasthenia, disturbance of asaptation) with the aid of electrophoretic division of proteins of the erythrocyte membrane, thin-layer chromatography, fluorescent probing of membranes, evaluation of peroxidative oxidation process, scanning and transmission electron microscopy, laser diphractometry, photometry. The patients with neurotic disorders at the early period after the influence of psychogenic factors (up to 3 months) revealed disorganization of lipid and protein composition of the red cell membrane, increase in microviscosity of its lipid phase, impairment of surface architectonics and ultrastructure of red cells, decrease of a deformation ability and increase of aggregate properties of erythrocytes. The authors treat stability of erythrocytes' homeostasis under the long-term influence of psychogenic factors from a viewpoint of adaptive changes in organism under the influence of neurogenic factors.

Primary cultures from the marine sponge Xestospongia muta (Petrosiidae, Haplosclerida)

In the context of the investigations on the origin and in vitro production of bioactive compounds, primary cultures were developed from ectosomal and choanosomal cell suspensions from the sponge Xestospongia muta. Dissociated cells aggregated and reorganized into a striking reticulated network of cells, typical for X. muta. Moreover, in some cultures an isotropic reticulation of small spicules, very similar to that found in the ectosome of adult sponges, was observed. Phytohaemagglutinin promoted aggregation and the reorganization of the cells. HPLC analyses revealed that straight-chain acetylenic compounds were recovered from short-term cultures and that they were synthesized during culture. Heterotrophic bacteria were assumed to be involved in the process. Together our results established that X. muta would be an excellent experimental model to study, in laboratory conditions, the differentiation of the skeleton and the in vitro biosynthesis of straight-chain acetylenic compounds.

Primmorphs from seven marine sponges: formation and structure

Primmorphs were obtained from seven different marine sponges: Stylissa massa, Suberites domuncula, Pseudosuberites aff. andrewsi, Geodia cydonium, Axinella polypoides, Halichondria panicea and Haliclona oculata. The formation process and the ultra structure of primmorphs were studied. A positive correlation was found between the initial sponge-cell concentration and the size of the primmorphs. By scanning electron microscopy (SEM) it was observed that the primmorphs are very densely packed sphere-shaped aggregates with a continuous pinacoderm (skin cell layer) covered by a smooth, cuticle-like structure. In the presence of amphotericin, or a cocktail of antibiotics (kanamycin, gentamycin, tylosin and tetracyclin), no primmorphs were formed, while gentamycin or a mixture of penicillin and streptomycin did not influence the formation of primmorphs. The addition of penicillin and streptomycin was, in most cases, sufficient to prevent bacterial contamination, while fungal growth was unaffected.

Optimizing the formation of in vitro sponge primmorphs from the Chinese sponge Stylotella agminata (Ridley)

The establishment and optimization of in vitro primmorph formation from a Chinese sponge, Stylotella agminata (Ridley), collected from the South China Sea, were investigated. Our aims were to identify the key factors affecting primmorph formation in this species and to optimize the technique for developing an in vitro primmorph culture system. The size of dissociated cells from S. agminata is relatively small, in the range between 5 and 10 microm. Round-shaped primmorphs of less than 100 microm were formed 3 days after transferring the dissociated cells into seawater containing Ca(2+) and Mg(2+). The effect of various cell dissociation conditions, inoculum cell density, concentration of antibiotics, pH, and temperature was further investigated upon the formation of primmorphs. The time required for primmorph formation, primmorph size distribution, and the proliferating capability were microscopically documented. Healthy sponge S. agminata, inoculum cell density and culture temperature play a critical role for the successful formation of primmorphs and that the microbial contamination will have to be controlled.

Cultivation of primmorphs from the marine sponge Suberites domuncula: morphogenetic potential of silicon and iron

Marine demosponges (phylum Porifera) are rich sources for potent bioactive compounds. With the establishment of the primmorph system from sponges, especially from Suberites domuncula, the technology to cultivate sponge cells in vitro improved considerably. This progress was possible after the elucidation that sponges are provided with characteristic metazoan cell adhesion receptors and extracellular matrix molecules which allow their cells a positioning in a complex organization pattern. This review summarizes recent data on the cultivation of sponges in aquaria and--with main emphasis--of primmorphs in vitro. It is outlined that silicon and Fe(+++) contribute substantially to the formation of larger primmorphs (size of 10 mm) as well as of a canal system in primmorphs; canals are probably required for an improved oxygen and food supply. We conclude that the primmorph system will facilitate a sustainable use of sponges in the production of bioactive compounds; it may furthermore allow new and hitherto not feasible insights into basic questions on the origin of Metazoa.

Epidermal growth factor receptor mediates increased cell proliferation, migration, and aggregation in esophageal keratinocytes in vitro and in vivo

Epidermal growth factor receptor (EGFR) overexpression is observed in a number of malignancies, especially those of esophageal squamous cell origin. However, little is known about the biological functions of EGFR in primary esophageal squamous epithelial cells. Using newly established primary human esophageal squamous epithelial cells as a platform, we overexpressed EGFR through retroviral transduction and established novel three-dimensional organotypic cultures. Additionally, EGFR was targeted in a cell type- and tissue-specific fashion to the esophageal epithelium in transgenic mice. EGFR overexpression in primary esophageal keratinocytes resulted in the biochemical activation of Akt and STAT pathways and induced enhanced cell migration and cell aggregation. When established in organotypic culture, EGFR-overexpressing cells had evidence of epithelial cell hyperproliferation and hyperplasia. These effects were also observed in EGFR-overexpressing transgenic mice and the esophageal cell lines established thereof. In particular, EGFR-induced effects upon aggregation appear to be mediated through the relocalization of p120 from the cytoplasm to the membrane and increased interaction with E-cadherin. EGFR modulates cell migration through the up-regulation of matrix metalloproteinase 1. Taken together, the functional effects of EGFR overexpression help to explain its role in the initiating steps of esophageal squamous carcinogenesis.

Cadherin-mediated cell adhesion and tissue segregation: qualitative and quantitative determinants

It is widely held that segregation of tissues expressing different cadherins results from cadherin-subtype-specific binding specificities. This belief is based largely upon assays in which cells expressing different cadherin subtypes aggregate separately when shaken in suspension. In various combinations of L cells expressing NCAM, E-, P-, N-, R-, or B-cadherin, coaggregation occurred when shear forces were low or absent but could be selectively inhibited by high shear forces. Cells expressing P- vs E-cadherin coaggregated and then demixed, one population enveloping the other completely. To distinguish whether this demixing was due to differences in cadherin affinities or expression levels, the latter were varied systematically. Cells expressing either cadherin at a lower level became the enveloping layer, as predicted by the Differential Adhesion Hypothesis. However, when cadherin expression levels were equalized, cells expressing P- vs E-cadherin remained intermixed. In this combination, "homocadherin" (E-E; P-P) and "heterocadherin" (E-P) adhesions must therefore be of similar strength. Cells expressing R- vs B-cadherin coaggregated but demixed to produce configurations of incomplete envelopment. This signifies that R- to B-cadherin adhesions must be weaker than either "homocadherin" adhesion. Together, cadherin quantity and affinity control tissue segregation and assembly through specification of the relative intensities of mature cell-cell adhesions.

Alpha5beta1 integrin mediates strong tissue cohesion

Integrins and cadherins are considered to have distinct and opposing functions. Integrins are traditionally cited for their role in cell-substratum interactions, whereas cadherins are thought to mediate strong intercellular cohesion. Together, these adhesion systems play crucial roles in a wide variety of cellular and developmental processes including cell migration, morphology, differentiation and proliferation. In this manuscript we present evidence that integrins possess the ability to mediate strong intercellular cohesion when cells are grown as 3D aggregates. Much of the data elucidating the role of integrins as mediators of cell-extracellular matrix (ECM) interactions have been generated using conventional cell culture techniques in which cells are plated onto ECM-coated 2D surfaces. In vivo, cells are embedded in a 3D meshwork of ECM proteins. We hypothesized that, within this meshwork, integrin-ECM interactions may impart cohesivity to an aggregate of cells by linking adjacent cells together. To test this hypothesis, we transfected Chinese hamster ovary (CHO-B2) cells to express alpha5beta1 integrin and found that these cells formed compact, spherical aggregates. We measured aggregate cohesivity using tissue surface tensiometry, a novel technique that quantifies cell-cell cohesivity of spheroids under physiological conditions. We determined that alpha5beta1 integrin is capable of conferring strong cohesivity (sigma=8.22+/-0.68 dynes/cm) to aggregates of alpha5-integrin-transfected cells. This cohesion was found to be independent of cadherin expression and was significantly greater than the cohesivity conferred onto CHO-B2 cells transfected with N-cadherin (sigma=3.14+/-0.20 dynes/cm, P</=0.0001), a more traditional cell-cell cohesion system. Fibronectin-null CHO cells that express alpha5beta1 integrin but do not secrete endogenous fibronectin do not form aggregates in fibronectin-depleted medium. Addition of increasing amounts of exogenous dimeric fibronectin to these cells resulted in a dose-dependent compaction. However, compaction failed to occur in the presence of fibronectin monomers. These data indicate that fibronectin is required for alpha5beta1-mediated compaction and that the dimeric structure of fibronectin is essential for this process. Additionally, aggregate formation of the alpha5 integrin transfectants was inhibited by an RGD peptide thus confirming alpha5beta1 integrin specificity. Collectively, these data confirm our hypothesis that alpha5beta1 integrin acts through fibronectin to link adjacent cells together, thus promoting strong intercellular cohesion in 3D cellular aggregates.