Biomedical subjects

D R McClay

Publications and source records attributed to D R McClay.

At least 19 recordsLinked to original sources

PubMed1996

Molecular cloning of the first metazoan beta-1,3 glucanase from eggs of the sea urchin Strongylocentrotus purpuratus.

We report the molecular cloning of the first beta-1,3 glucanase from animal tissue. Three peptide sequences were obtained from beta-1,3 glucanase that had been purified from eggs of the sea urchin Strongylocentrotus purpuratus and the gene was cloned by PCR using oligonucleotides deduced from the peptide sequences. The full-length cDNA shows a predicted enzyme structure of 499 aa with a hydrophobic signal sequence. A 3.2-kb message is present in eggs, during early embryogenesis, and in adult gut tissue. A polyclonal antibody to the native 68-kDa enzyme recognizes a single band during early embryogenesis that reappears in the adult gut, and recognizes a 57-kDa fusion protein made from a full-length cDNA clone for beta-1,3 glucanase. The identity of this molecule as beta-1,3 glucanase is confirmed by sequence homology, by the presence of all three peptide sequences in the deduced amino acid sequence, and by the recognition of the bacterial fusion protein by the antibody directed against the native enzyme. Data base searches show significant homology at the amino acid level to beta-1,3 glucanases from two species of bacteria and a clotting factor from the horseshoe crab. The homology with the bacteria is centered in a 304-aa region in which there are seven scattered regions of high homology between the four divergent species. These four species were also found to have two homologous regions in common with more distantly related plant, fungal, and bacterial proteins. A global phylogeny based on these regions strongly suggests that the glucanases are a very ancient family of genes. In particular, there is an especially deep split within genes taken from the bacterial genus Bacillus.

Amino Acid Sequence↗

PubMed1996

Regulative capacity of the archenteron during gastrulation in the sea urchin.

Gastrulation in the sea urchin involves an extensive rearrangement of cells of the archenteron giving rise to secondary mesenchyme at the archenteron tip followed by the foregut, midgut and hindgut. To examine the regulative capacity of this structure, pieces of the archenteron were removed or transplanted at different stages of gastrulation. After removal of any or all parts of the archenteron, the remaining veg 1 and /or veg 2 tissue regulated to replace the missing parts. Endoderm transplanted to ectopic positions also regulated to that new position in the archenteron. This ability to replace or regulate endoderm did not decline until after full elongation of the archenteron was completed. When replacement occurred, the new gut was smaller relative to the remaining embryo but the recognizable morphology of the archenteron was re-established. Long after the archenteron reveals territorial specification through expression of specific markers, the endodermal cells remain capable of being respecified to other gut regions. Thus, for much of gastrulation, the gut is conditionally specified. We propose that this regulative ability requires extensive and continuous short-range communication between cells of the archenteron in order to reorganize the tissues and position the boundaries of this structure even after experimental alterations.

Animals↗

PubMed1995

Characterization of moesin in the sea urchin Lytechinus variegatus: redistribution to the plasma membrane following fertilization is inhibited by cytochalasin B.

We have investigated the distribution and function of an ezrin-radixin-moesin-like (ERM) molecule in the sea urchin. A sea urchin homologue of moesin was cloned that shares 75% amino acid similarity in the conserved N-terminal region to other moesin molecules. A 6.3 kb message is transcribed late in embryogenesis and is present in adult tissues. Polyclonal antibodies were generated to proteins expressed by a bacterial expression vector, and affinity purified. These antibodies recognize a single 75 kDa protein that is present throughout development in approximately equal abundance, and specifically they immuno-precipitate a single protein. We show by immunolocalization that SUmoesin has two predominant patterns during development. First, SUmoesin is rapidly redistributed after fertilization from a location throughout the egg cytoplasm to a location in the egg cortex. Later in embryogenesis, SUmoesin is localized to the apical ends of cells in the regions of cell-cell junctions. We show that SUmoesin is present in actin-rich regions of the embryo. Finally, we show that the location of SUmoesin requires an intact actin-based cytoskeleton. SUmoesin fails to localize to the plasma membrane after fertilization in the presence of cytochalasin B. Furthermore, SUmoesin loses its apical position in the region of cell-cell junctions in the presence of cytochalasin B in later stages of embryogenesis. This effect is reversible, and the microtubule inhibitor colchicine has no effect. These results show that SUmoesin becomes associated with apical plasma membrane structures early in development, and that SUmoesin is both coincident with actin and requires the assembly of actin filaments to maintain its localization.

Amino Acid Sequence↗

PubMed1994

Quantitative switch in integrin expression accompanies differentiation of F9 cells treated with retinoic acid.

F9 embryonal carcinoma cells resemble epithelial cells when in monolayer culture. After treatment with retinoic acid these cells differentiate into fibroblastic-like cells in a sequence that has been modeled as the mammalian equivalent of the differentiation from stem cells of the inner cell mass to parietal endoderm. This study examined the changes in integrin subtypes that accompany retinoic acid-induced differentiation of F9 cells. Although several integrins were found to be present on the surface of F9 cells and retinoic acid-induced (RA) cells, the two dominant integrins were alpha 3 beta 1 and alpha 5 beta 1. Differentiation of F9 cells resulted in about 10- to 25-fold increase in the amount of alpha 3 beta 1 integrin protein as measured by immunoprecipitation of cell surface labeled material. There was a corresponding several-fold reduction of alpha 5 beta 1 protein. The concentration of alpha 3 mRNA was about the same in F9 and RA cells while the concentration of alpha 5 mRNA dropped several-fold after retinoic acid treatment. Thus alpha 3 regulation appeared to be largely posttranscriptional while the drop in alpha 5 protein may have been a result of transcriptional down-regulation. Quantitative measurement of adhesion suggested that most of the F9 and RA cell-substrate adhesion to fibronectin or laminin is mediated by these integrins. They are the dominant integrins present, and antibodies to either these integrins or to the substrate blocked the adhesion. Despite the large switch in integrin subtype protein expression there was little difference between the two cell types in initial cell interactions when adhesive affinities were measured quantitatively. Also there was no difference between the two phenotypes in rate of initial adhesive strengthening. The phenotypic difference was first observed with later events in the attachment and spreading of the RA-treated cells to the substrate. These results show that retinoic acid treatment alters the amounts of alpha 5 and alpha 3 integrin subunits during the F9 to RA phenotypic switch. The data show that these integrins are important in the cell-substrate adhesion to fibronectin and laminin. They show, however, that the phenotypic changes observed with differentiation are not associated with the initial preferential adhesions to the substrate, but rather with consequences that alter the cytoskeletal architecture of the cell.

Animals↗

PubMed1994

Skeletal pattern is specified autonomously by the primary mesenchyme cells in sea urchin embryos.

In the sea urchin embryo the primary mesenchyme cells (PMCs) produce a CaCO3 skeleton in a pattern that is species specific. To establish whether skeletal pattern is specified autonomously by the PMCs or through instructive interactions with the ectoderm, we have taken advantage of improvements in cell transplantation techniques to produce PMC/ectoderm chimeras between two species. It was found that the pattern of the skeletons produced in these chimeric embryos depended upon the source of the PMCs. Thus, skeletal pattern appears to be specified autonomously by the PMCs. In comparing this data with other information known about skeletogenesis, it is proposed that the ectoderm provides spatial and temporal information for the correct placement and timing of skeletogenesis, and that the PMCs then synthesize the skeleton according to an endogenous program. The ability of PMCs from one species to produce an appropriately patterned skeleton in the ectoderm of another indicates that the cues provided by the ectoderm are largely conserved between species.

Animals↗

PubMed1993

Cell-cell interactions regulate skeleton formation in the sea urchin embryo.

In the sea urchin embryo, the primary mesenchyme cells (PMCs) make extensive contact with the ectoderm of the blastula wall. This contact is shown to influence production of the larval skeleton by the PMCs. A previous observation showed that treatment of embryos with NiCl2 can alter spicule number and skeletal pattern (Hardin et al. (1992) Development, 116, 671-685). Here, to explore the tissue sensitivity to NiCl2, experiments recombined normal or NiCl2-treated PMCs with either normal or NiCl2-treated PMC-less host embryos. We find that NiCl2 alters skeleton production by influencing the ectoderm of the blastula wall with which the PMCs interact. The ectoderm is responsible for specifying the number of spicules made by the PMCs. In addition, experiments examining skeleton production in vitro and in half- and quarter-sized embryos shows that cell interactions also influence skeleton size. PMCs grown in vitro away from interactions with the rest of the embryo, can produce larger spicules than in vivo. Thus, the epithelium of the blastula wall appears to provide spatial and scalar information that regulates skeleton production by the PMCs.

Animals↗

PubMed1992

Deployment of extracellular matrix proteins in sea urchin embryogenesis.

The apical extracellular matrix of the sea urchin embryo, known as the hyaline layer (HL), is a multi-laminate organelle composed of at least 10 polypeptides. Although integrated into one ECM, HL proteins exhibit individual temporal and spatial dynamics throughout development. These molecules are stockpiled in the oocyte during vitellogenesis in at least four distinct vesicle populations. They are released onto the cell surface at fertilization in a specific order, and interact differentially with embryonic cells as development proceeds. Many experiments have suggested that the HL is vital for embryogenesis, but relatively little is known about the functions and interactions of its constituent molecules. The purpose of the present review has been to gather information on the basic characteristics of the known HL proteins together with data on their expression in the embryo, and where possible, their biological activities. Compiled, these observations may provide some insight into the workings of a uniquely embryonic organelle.

Animals↗

PubMed1992

On the ultrastructure of hyalin, a cell adhesion protein of the sea urchin embryo extracellular matrix.

Hyalin is a large (ca. 350 x 10(3) kD by gel electrophoresis) molecule that contributes to the hyalin layer surrounding the sea urchin embryo. In previous work a mAb (McA Tg-HYL), specific for hyalin, was found to inhibit cell-hyalin adhesion and block morphogenesis of whole embryos (Adelson, D. L., and T. D. Humphreys. 1988. Development. 104:391-402). In this report, hyalin ultrastructure was examined via rotary shadowing. Hyalin appeared to be a filamentous molecule approximately 75-nm long with a globular "head" about 12 nm in diameter that tended to form aggregates by associating head to head. Hyalin molecules tended to associate with a distinct high molecular weight globular particle ("core"). In fractions containing the core particle often more than one hyalin molecule were seen to be associated with the core. The core particle maintained a tenacious association with hyalin throughout purification procedures. The site(s) of McA Tg-HYL binding to the hyalin molecule were visualized by decorating purified hyalin with the antibody and then rotary shadowing the complex. In these experiments, McA Tg-HYL attached to the hyalin filament near the head region in a pattern suggesting that more than one antibody binding site exists on the hyalin filament. From the ultrastructural data and from the cell adhesion data presented earlier we conclude that hyalin is a filamentous molecule that binds to other hyalin molecules and contains multiple cell binding sites. Attempts were made to demonstrate the existence of lower molecular weight hyalin precursors. Whilst no such precursors could be identified by immunoprecipitation of in vivo labeled embryo lysates, immunoprecipitation of in vitro translation products suggested such precursors (ca 40 x 10(3) kD) might exist.

Animals↗

PubMed1992

Commitment along the dorsoventral axis of the sea urchin embryo is altered in response to NiCl2.

Few treatments are known that perturb the dorsoventral axis of the sea urchin embryo. We report here that the dorsoventral polarity of the sea urchin embryo can be disrupted by treatment of embryos with NiCl2. Lytechinus variegatus embryos treated with 0.5 mM NiCl2 from fertilization until the early gastrula stage appear morphologically normal until the midgastrula stage, when they fail to acquire the overt dorsoventral polarity characteristic of untreated siblings. The ectoderm of normal embryos possesses two ventrolateral thickenings just above the vegetal plate region. In nickel-treated embryos, these become expanded as a circumferential belt around the vegetal plate. The ectoderm just ventral to the animal pole normally invaginates to form a stomodeum, which then fuses with the tip of the archenteron to produce the mouth. In nickel-treated embryos, the stomodeal invagination is expanded to become a circumferential constriction, and it eventually pinches off as the tip of the archenteron fuses with it to produce a mouth. Primary mesenchyme cells form a ring in the lateral ectoderm, but as many as a dozen spicule rudiments can form in a radial pattern. Dorsoventral differentiation of ectodermal tissues is profoundly perturbed: nickel-treated embryos underexpress transcripts of the dorsal (aboral) gene LvS1, they overexpress the ventral (oral) ectodermal gene product, EctoV, and the ciliated band is shifted to the vegetal margin of the embryo. Although some dorsoventral abnormalities are observed, animal-vegetal differentiation of the archenteron and associated structures seems largely normal, based on the localization of region-specific gene products. Gross differentiation of primary mesenchyme cells seems unaffected, since nickel-treated embryos possess the normal number of these cells. Furthermore, when all primary mesenchyme cells are removed from nickel-treated embryos, some secondary mesenchyme cells undergo the process of "conversion" (Ettensohn, C. A. and McClay, D. R. (1988) Dev. Biol. 125, 396-409), migrating to sites where the larval skeleton would ordinarily form and subsequently producing spicule rudiments. However, the skeletal pattern formed by the converted cells is completely radialized. Our data suggest that a major effect of NiCl2 is to alter commitment of ectodermal cells along the dorsoventral axis. Among the consequences appears to be a disruption of pattern formation by mesenchyme cells.

Animals↗

PubMed1992

Pattern formation during gastrulation in the sea urchin embryo.

The sea urchin embryo follows a relatively simple cell behavioral sequence in its gastrulation movements. To form the mesoderm, primary mesenchyme cells ingress from the vegetal plate and then migrate along the basal lamina lining the blastocoel. The presumptive secondary mesenchyme and endoderm then invaginate from the vegetal pole of the embryo. The archenteron elongates and extends across the blastocoel until the tip of the archenteron touches and attaches to the opposite side of the blastocoel. Secondary mesenchyme cells, originally at the tip of the archenteron, differentiate to form a variety of structures including coelomic pouches, esophageal muscles, pigment cells and other cell types. After migration of the secondary mesenchyme cells from their original position at the tip of the archenteron, the endoderm fuses with an invagination of the ventral ectoderm (the stomodaem), to form the mouth and complete the process of gastrulation. A larval skeleton is made by primary mesenchyme cells during the time of archenteron and mouth formation. A number of experiments have established that these morphogenetic movements involve a number of cell autonomous behaviors plus a series of cell interactions that provide spatial, temporal and scalar information to cells of the mesoderm and endoderm. The cell autonomous behaviors can be demonstrated by the ability of micromeres or endoderm to perform their morphogenetic functions if either is isolated and grown in culture. The requirement for cell interactions has been demonstrated by manipulative experiments where it has been shown that axial information, temporal information, spatial information and scalar information is obtained by mesoderm and endoderm from other embryonic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Tissue-specific, temporal changes in cell adhesion to echinonectin in the sea urchin embryo.

Echinonectin is a dimeric, glycoprotein found in the hyaline layer of the developing sea urchin embryo. It was found that echinonectin supports adhesion of embryonic cells in vitro. Previous studies have shown that the protein hyalin also supports adhesion. The purpose of this study was to examine the specificity of cell-echinonectin interactions during sea urchin development. Primary mesenchyme cells (PMCs) ingress into the blastocoel during gastrulation. In the process the PMCs lose contact with the hyaline layer. It was found experimentally that differentiating PMCs decreased their adhesion to hyalin at the time of ingression. It was of interest, therefore, to determine whether there was a coordinate loss of adhesion to echinonectin at ingression as well. When cell-echinonectin interactions were quantified using a centrifugal force-based adhesion assay, it was shown that micromeres adhered well to echinonectin. At the time of ingression, PMCs displayed reduced adhesion to echinonectin just as had been found when hyalin was tested as a substrate. There was no change in adhesion of presumptive ectoderm or endoderm to echinonectin over the same time period. Early in gastrulation presumptive ectoderm and endoderm adhered to echinonectin only half as strongly as to equimolar concentrations of hyalin. After gastrulation endoderm cells were observed to retain the same relative affinity to hyalin and echinonectin, while ectoderm cells became equally adhesive for both hyalin and echinonectin. Quantitatively, this represents an overall increase in the affinity of ectodermal cells for echinonectin. Adhesion to combined substrata of echinonectin and hyalin was reduced but not abolished by monoclonal antibodies specific for echinonectin. The antibodies did not cross-react with hyalin. We conclude that both echinonectin and hyalin independently act as adhesive substrata for the developing sea urchin embryo. PMCs lose an affinity for echinonectin and ectodermal cells later increase their affinity for this substrate.

Age Factors↗

PubMed1991

Gastrulation.

At gastrulation, a single layer of cells is converted into an outer ectodermal covering, an inner ectodermal tube, and in triploblastic phyla, a middle mesodermal layer. This morphogenesis is driven by motility and directed by cell interactions, some of which involve adhesion and others that involve information transfer.

Amino Acid Sequence↗

PubMed1990

In vitro biological activities of echinonectin.

Echinonectin (EN) is a 230-kDa extracellular matrix glycoprotein found in the hyaline layer of sea urchin embryos. Dissociated embryonic cells attached strongly to EN-coated microtiter wells in a centrifugal-based in vitro adhesion assay, suggesting that EN is one of the hyaline layer proteins to which cells adhere in vivo (Alliegro et al., 1988). The present study examines the molecular properties of that adhesion using monoclonal antibodies as probes to block cell attachment, and also demonstrates that EN possesses lectin activity. EN binds tenaciously to agarose-based chromatography resins, such as Sepharose. The sugar-binding activity is associated with the polypeptide component of EN, and not with the carbohydrate moiety. Binding is inhibited with galactose and fucoidan, but not with glucose or locust bean gum. Although functional sites both for polysaccharide binding and for cell attachment are present on each subunit of the EN molecule, the sites appear to be functionally distinct because galactose and fucoidan are completely without effect on cell attachment in vitro. Proteolytic digestion of EN yields a highly limited set of immunoreactive peptides. Digestion with trypsin yields a 20-kDa fragment, chymotrypsin, a doublet at 20 kDa, and 20- and 23-kDa fragments with thermolysin. McAb's directed against these peptides block cell adhesion in vitro, suggesting that they possess the cell attachment domain of EN. This is supported by the observations that trypsin-digested EN is an effective substrate in adhesion assays and that adhesion to the tryptic fragments is also blocked by McAb's to the 20-kDa domain.

Animals↗

PubMed1990

Neuronal-glial interactions: complexity of neurite outgrowth correlates with substrate adhesivity of serotonergic neurons.

To study the interactions between neurons of known transmitter phenotype and non-neuronal cells of glial or fibroblastic origin, serotonergic (5-HT) neurons were tested for their strength of adhesion and neurite outgrowth patterns on substrates of astrocytes or fibroblasts using a cell adhesion assay for transmitter-identified neurons, and morphometry of immunocytochemically stained neurons in dissociated cell cultures. Both the strength of adhesion and the rate and complexity of neurite outgrowth by 5-HT neurons were significantly greater on substrates of astrocytes compared to fibroblasts. These results provide evidence that 5-HT neurons can interact selectively with glia via cell surface determinants, and that this process may be important for the development of complex (dendrite-like) neuritic arbors. The methods developed in this study will be useful for future studies of interactions between transmitter-identified neurons and glial cells during ontogeny of the embryonic brain.

Animals↗

PubMed1990

A hyaline layer protein that becomes localized to the oral ectoderm and foregut of sea urchin embryos.

An antigen is described which is a marker for the oral ectoderm and foregut of the sea urchin embryo. In Lytechinus variegatus, the antigen is first detectable by immunofluorescence on the surface of fertilized eggs, and remains globally distributed through the early stages of gastrulation. Thereafter the antigen is localized to the oral ectoderm and foregut, coincident with the morphogenesis of these regions. The antigen is a large, detergent-insoluble, filamentous glycoprotein associated with the tips of the microvilli in the hyaline layer. This glycoprotein is present in two forms, a approximately 350-kDa form that is maternally synthesized and a much larger form which is synthesized at late gastrula stage as a 350-kDa precursor before becoming modified and assembled into the hyaline layer. The timing of synthesis of the zygotic form of the molecule correlates precisely with the localized expression of the antigen. The antigen copurifies with intact hyaline layers and cosediments with hyalin in the presence of calcium, suggesting that it is a structural component of the hyaline layer.

Animals↗

PubMed1990

Target recognition by the archenteron during sea urchin gastrulation.

During sea urchin gastrulation filopodia are sent out by secondary mesenchyme cells (SMCs) at the tip of the archenteron in continual cycles of extension, attachment, and retraction. Eventually the archenteron ceases its elongation and its tip localizes to the animal pole region of the embryo (Gustafson and Kinnander, 1956, Exp. Cell Res. 11, 36-57; Dan and Okazaki, 1956, Biol. Bull. 110, 29-42). We have investigated the mechanisms and specificity of this localization by analyzing filopodial behavior and by experimental manipulation of the interaction of the archenteron with the animal pole region. When the tip of the archenteron nears the animal pole, some filopodia make contact with a well-defined locus within this region. Filopodia that make contact with the locus remain attached 20-50 times longer than attachments observed at any other site along the blastocoel wall. The SMCs bearing the long-lived filopodia eventually change their phenotype by flattening and spreading onto this region. Several lines of experimental evidence indicate that contact with the animal pole locus, or "target" region, is crucial for the change in phenotype of the SMCs: (1) the phenotypic change can be induced precociously by bringing the animal pole region within reach of the tip of the archenteron early in gastrulation. Precocious contact with other regions of the blastocoel wall does not induce a similar change. (2) The phenotypic change can be delayed by placing the animal pole out of reach late in gastrulation, resulting in artificial prolongation of exploratory behavior by filopodia. (3) Ectopic combinations of animal pole ectoderm and archenterons in fused multiple embryos and chimaeras result in attachment of archenterons to the nearest available target, and (4) freely migrating SMCs are observed to migrate randomly within the blastocoel, then stop at the animal pole and undergo the change in phenotype. Filopodia rapidly attach to the animal pole when the shape of early gastrulae is altered such that the animal pole is less than 35 microns from the tip of the archenteron, even though such attachments only occur in normal embryos at the 2/3-3/4 gastrula stage. Since it has previously been shown that the archenteron elongates autonomously to 2/3 of its final length (Hardin, 1988, Development 103, 317-324), it appears that autonomous extension of the archenteron is required to place filopodia close enough to the animal pole to allow them to interact with it.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Embryonic cellular organization: differential restriction of fates as revealed by cell aggregates and lineage markers.

Cleavage-stage Lytechinus variegatus embryos were dissociated and the cells were aggregated in an experimental system designed to address questions of embryonic organizational capability. Using monoclonal antibodies against stage- and structure-specific antigens, it was determined that germ-layer specific molecules were expressed in the expected locations in aggregates and that the germ layers differentiated in the normal temporal sequence, but the dorsoventral axis of the embryo was not reestablished properly. In other experiments individual rhodamine-labeled blastomeres were incorporated into unlabeled aggregates. Micromeres localized and differentiated normally. Mesomeres, however, which in normal embryos form only ectoderm, were found to change their specified fate and participate in gut formation. The sequence of aggregate organization revealed other properties of the embryo. Ectodermal and endodermal epithelia formed via two temporally distinct epithelialization events. Ectoderm separated from a mass of interior cells at about 12 hrs, and endoderm compacted from the interior cells at about 20 hr. A lathrytic agent that prevents gut formation in normal embryos also prevented gut formation in aggregates; however, it did not affect formation of the ectoderm. Hence, formation of the triploblastic structure in aggregates appears to be dependent upon developmentally regulated, distinct cell adhesion events.

Animals↗

PubMed1989

Cell adhesion to fibronectin and tenascin: quantitative measurements of initial binding and subsequent strengthening response.

Cell-substratum adhesion strengths have been quantified using fibroblasts and glioma cells binding to two extracellular matrix proteins, fibronectin and tenascin. A centrifugal force-based adhesion assay was used for the adhesive strength measurements, and the corresponding morphology of the adhesions was visualized by interference reflection microscopy. The initial adhesions as measured at 4 degrees C were on the order of 10(-5)dynes/cell and did not involve the cytoskeleton. Adhesion to fibronectin after 15 min at 37 degrees C were more than an order of magnitude stronger; the strengthening response required cytoskeletal involvement. By contrast to the marked strengthening of adhesion to FN, adhesion to TN was unchanged or weakened after 15 min at 37 degrees C. The absolute strength of adhesion achieved varied according to protein and cell type. When a mixed substratum of fibronectin and tenascin was tested, the presence of tenascin was found to reduce the level of the strengthening of cell adhesion normally observed at 37 degrees C on a substratum of fibronectin alone. Parallel analysis of corresponding interference reflection micrographs showed that differences in the area of cell surface within 10-15 nm of the substratum correlated closely with each of the changes in adhesion observed: after incubation for 15 min on fibronectin at 37 degrees C, glioma cells increased their surface area within close contact to the substrate by integral to 125-fold. Cells on tenascin did not increase their surface area of contact. The increased surface area of contact and the inhibitory activity of cytochalasin b suggest that the adhesive "strengthening" in the 15 min after initial binding brings additional adhesion molecules into the adhesive site and couples the actin cytoskeleton to the adhesion complex.

Animals↗