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At least 19 recordsLinked to original sources

PubMed1979

Regulation of surface topography of mouse peritoneal cells. Formation of microvilli and vesiculated pits on omental mesothelial cells by serum and other proteins.

The mesothelial cells of the mouse omentum provide an in vivo model for the study of the mobilization of labile microvilli on the cell surface. These mesothelial cells are sparsely covered with microvilli and large pits 150--400 nm in diameter, termed vesiculated pits. On the unstimulated cell, the microvilli average 44/100 microns2 and pits, 30/100 microns 2 of surface and they are rapidly induced to increase in number by the intraperitoneal injection of isologous mouse serum. After 2 min, microvilli increase threefold, continue to sevenfold at 30 min, and decrease to fourfold at 90 min. Vesiculated pits increased with similar kinetics. Bovine serum albumin and gamma globulin also stimulate the microvilli and pits to form, but the response is a slow, gradual rise to five- or sixfold the normal value at 90 min. Evidence indicates that multiple factors, possibly including insulin and immunoglobulins, are involved in the effect of serum. The close physical and temporal relationship between microvilli and pits suggests that a correlation exists in their mobilization by the cell and it is hypothesized that microvilli function in the regulation of the cortical microfilament network in effecting this mobilization.

Animals↗

PubMed1992

Lectins bind differentially to cilia and microvilli of major and minor cell populations in olfactory and nasal respiratory epithelia.

Binding of colloidal gold-conjugated lectins was studied in cilia and microvilli of rat olfactory and respiratory epithelia. This was done in sections of rapidly frozen, freeze-substituted specimens embedded in Lowicryl K11M or, for wheat germ agglutinin (WGA) alone, in deep-etched replicas. Olfactory dendritic endings and cilia labeled with WGA and faintly with soybean agglutinin (SBA); olfactory supporting cell microvilli bound only Dolichos biflorus agglutinin (DBA). Microvilli of an infrequent cell bound peanut agglutinin (PNA), SBA, and WGA. These microvilli labeled more strongly with the last two lectins than the olfactory cilia. Respiratory cilia bound WGA and, somewhat more weakly, PNA; microvilli of ciliated respiratory cells bound all four lectins. Visualization of specific labeling improved after preincubation of sections with neuraminidase, except for DBA where lectin binding was abolished. PNA labeling was seen only after neuraminidase preincubation. The densities of membrane surface particles that labeled with WGA corresponded with those of fracture plane particles in a quantitative freeze-fracture, deep-etch analysis. Therefore, a considerable fraction of the WGA-bound particles could reflect transmembrane proteins in olfactory dendritic endings and cilia and in respiratory cilia. The possible nature of these particles is discussed.

Acrylic Resins↗

PubMed1992

A quantitative and morphological study of ectodermal microvilli in ten areas in the control and experimental prenatal rat.

This study provides a baseline of mainly quantitative morphologic information in relation to the ectodermal microvilli in ten areas in the control and experimental prenatal rat with special reference to the period of neural tube closure. Embryos from six litters were used and ten areas were examined mainly with the scanning electron microscope. Statistical analysis showed no significant difference between litters nor between the ten areas examined. In the 376 hr (day 15.6) fetus only the ectodermal cells of the nostril region demonstrated a rich population of microvilli, a fact possibly associated with late maturation of that region. Some evidence is provided to show that there is an increase in the population of microvilli in the 276 hr (day 11.5) embryo following experimentally induced zinc deficiency and introduction of nicotine in the culture medium. The possible mechanisms underlying the increase in ectodermal microvilli are i) an attempt by ectodermal cells to absorb nutrients, ii) a reflection of cells under stress, iii) failure of early embryonic ectodermal cells to shed microvilli normally associated with developmental changes, and iv) a generalized developmental delay rather than some cellular response to a trace element nutritional deficiency and a teratogen.

Animals↗

PubMed1978

A thin-section and freeze-fracture study of microfilament-membrane attachments in choroid plexus and intestinal microvilli.

Choroid plexus and intestinal microvilli in thin sections have microfilaments in the cytoplasm adjacent to the membranes, and in replicas have broken strands of filaments in both cytoplasm and on E faces of plasm membranes. The microfilaments contain actin as indicated by their binding of heavy meromyosin (HMM). In sections of choroid plexus, the microfilaments are 7-8 nm in diameter and form a loose meshwork which lies parallel to the membrane and which is connected to the membranes both by short, connecting filaments (8 times 30 nm) and dense globules (approximately 15-20 nm). The filamentous strands seen in replicas are approximately 8 nm in diameter. Because they are similar in diameter and are connected to the membrane, these filamentous strands seen in replicas apparently represent the connecting structures, portions of the microfilaments, or both. The filamentous strands attached to the membrane are usually associated with the E face and appear to be pulled through the P half-membrane. In replicas of intestinal brush border microvilli, the connecting strands attaching core microfilaments to the membrane are readily visualized. In contrast, regions of attachment of core microfilaments to dense material at the tips of microvilli are associated with few particles on P faces and with few filamentous strands on the E faces of the membranes. Freeze-fracture replicas suggest a morphologically similar type of connecting strand attachment for microfilament-membrane binding in both choroid plexus and intestinal microvilli, despite the lack of a prominent core bundle of microfilaments in choroid plexus microvilli.

Animals↗

PubMed1992

The upright position of brush border-type microvilli depends on myosin filaments.

We have studied the correlation between the actomyosin organization and microvillar position in an epithelial cell line derived from the proximal pig kidney tubule (LLC-PK1). When grown on glass, these cells are approximately 5-6 microns in height and develop numerous microvilli that project from the dorsal membrane. A fairly homogeneous distribution of microvilli was achieved by synchronization of the cell cycle. These microvilli are of the brush border type, as defined by their content of villin and their anchorage in a myosin-rich terminal web-like structure. When LLC-PK1 cells were injected with two monoclonal antibodies against pig brain nonmuscle myosin, in concentrations yielding a 1:1 ratio of antibody to myosin, neither microvillar number nor length was affected. However, when we examined the cells by scanning electron microscopy 1-3 h after microinjection, we found that one of the antibodies (a-PBM 4) had a profound effect on microvillar position: more than 50% were seen tilted or lying prone on the plasma membrane. The microvilli of cells injected with the other antibody (a-PBM 9) were not significantly different from those of cells injected with control antibodies. This difference correlates with in vitro properties of the antibodies: a-PBM 4 decreases the actin-activated Mg(2+)-ATPase of pig brain nonmuscle myosin quite substantially, while a-PBM 9 affects it only moderately. These differential effects are probably a consequence of the different epitope location as determined for both antibodies, not of differences in antibody affinity. Our data are compatible with the hypothesis that a-PBM 4 also interferes with the actomyosin interaction in situ, thus decreasing the effective cross-linking of microvillar rootlets by myosin filaments in the terminal web. On the basis of this model, we suggest that myosin filaments are essential for the upright position of brush-border type microvilli.

Antibodies, Monoclonal↗

PubMed1976

The correlation of plasma membrane microvilli and intracellular cyclic AMP content in a rat epitheloid kidney cell line.

Modulation of the intracellular concentration of cyclic AMP has been associated with a regulatory role in cell division, cell morphology, and physical properties of the plasma membrane. Untransformed rat kidney cells in culture exhibit epitheloid morphology, high intracellular cyclic AMP levels, and contact inhibition of growth. Untransformed rat kidney cells transformed with the Kirsten murine sarcoma virus exhibit a low cyclic AMP content, rapid growth rate, and a loss of contact inhibition. Scanning electron microscopy reveals a distinctive difference in the surface structure of the two cell types during Gl of the cell cycle. The surface of the transformed cell is covered with microvilli while its untransformed counterpart is devoid of microvilli. The presence of microvilli can be controlled as a function of temperature by two temperature-sensitive mutants of the Kirsten sarcoma virus (ts6t6 and ts371 cl 5). In the ts6t6 mutant, growth at 32 degrees C results in a low cyclic AMP content and the presence of microville, while growth at 39 degrees C results in a high cyclic AMP content and a decrease in microvilli. The opposite effect is seen with the ts371 cl 5 mutant. Correlation of cyclic AMP content with the presence of microvilli suggests that this surface phenomenon is a function of cyclic AMP concentration.

Cell Division↗

PubMed1975

Carbohydrate cytochemistry of the intestinal epithelium of Ascaris suum. Nature of the microvilli glycocalyx and basal lamella.

Results of various cytochemical tests demonstrate large deposits of glycogen within the intestinal absorptive cells of Ascaris suum. Carbohydrate material is also associated with the microvilli surface and basal lamella. Staining produced by the periodate-thiocarbohydrazide-osmium procedure was abolished by analine or m-aminophenol. Diastase digestion did not alter the staining on the microvilli surface. Similar results were seen using the silver methenamine procedure. A positive reaction was noted on the microvilli surface, vesicles in both the apical and basal cytoplasm, Golgi apparatus, and basal lamella. Lanthanum nitrate stained the microvilli surface and intercellular spaces between absorptive cells. Alcian blue or cetylpyridinium chloride in combination with lanthanum enhanced the staining produced by lanthanum alone. These results suggest the presence of acidic glycans on both the microvilli surface and basal lamella.

Animals↗

PubMed1976

Topographical relationship between sucrase and leucine beta-naphthylamidase on the microvilli membrane of rabbit intestinal mucosal cells.

The topographical relationship between sucrase [EC 3.2.1.26] and leucine beta-naphthylamidase (LNAase) on the microvilli membrane of rabbit small-intestinal mucosal cells was studied assuming that where enzymes with different antigenicities, A and B, are situated in close proximity on the surface of microvilli vesicles, the agglutination of vesicles by anti-A antibody is inhibited by the previous binding of monovalent fragments of anti-B antibody to enzyme B on the surface of vesicles. Like anti-sucrase antibody, anti-LNAase antibody quantitatively agglutinated microvilli vesicles. It inhibited the membrane-bound LNAase activity in the same manner as the detergent-solubilized activity. This inhibitory effect of anti-LNAase antibody was not interfered with by monovalent fragments of anti-sucrase antibody. However, the monovalent fragments inhibited vesicle agglutination by anti-LNAase antibody as well as by anti-sucrase antibody. These results indicate that LNAase is located on the outer surface of microvilli vesicles and suggest that LNAase and sucrase are situated in close proximity on the membrane surface of microvilli vesicles.

Agglutination↗

PubMed1976

Patching, microvilli, and the agglutination of normal and transformed cells.

Transmission and scanning electron microscopy were used to study possible structural correlates in the process of agglutination of several types of normal and transformed cells by Concanavalin A. In parallel studies we found that post-confluence inhibition of cell division and agglutiniability of cells by Concanavalin A were not correlated with patching of surface bound lectin molecules as determined with a hemocyanin marker. Transformed cells growing in monolayer cultures were found to have many more microvilli than the corresponding normal cells. However, when cells were brought into suspension with EDTA, all cells developed numerous microvilli and we were not able to distinguish between agglutinable and nonagglutinable cells on the basis of morphological appearance. Cells agglutinated by Concanavalin A had numerous interdigitated microvilli at points of cell-cell contact. The appearance of spontaneously agglutinated cells and lectin agglutinated cells was very similar with respect to the involvement of microvilli in cell-cell attachments, and labeling studies with hemocyanin indicated that Concanavalin A bound to microvilli is rapidly cleared from these surface specializations in a manner analogous to that observed with patching of surface bound lectin. Several lines of SV-40 transformed fibroblasts were shown to be considerably more spontaneously agglutinable than untransformed cells. These results indicate that Concanavalin A may amplify an intrinsic membrane property common to many transformed cells that is expressed as an increase in the rate of adhesion of suspended cells. It is proposed that the membrane change detected by the agglutination reaction may also be involved in the loss of post-confluence inhibition of cell division and growth of transformed cells in semisolid media, due to a surface interaction that allows transformed cells to use each other as growth substrata.

Agglutination↗

PubMed1991

Simulation of cell rolling and adhesion on surfaces in shear flow. Microvilli-coated hard spheres with adhesive springs.

The adhesion of cells to ligand-coated surfaces in viscous shear flow is an important step in many physiological processes, such as the neutrophil-mediated inflammatory response, lymphocyte homing, and tumor cell metastasis. This article describes a calculational method that allows simulation of the interaction of a single cell with a ligand-coated surface. The cell is idealized as a microvilli-coated hard sphere covered with adhesive springs. The distribution of microvilli on the cell surface, the distribution of receptors on microvilli tips, and the forward and reverse reaction between receptor and ligand are all simulated using random number sampling of appropriate probability functions. The velocity of the cell at each time step in the simulation results from a balance of hydrodynamic, colloidal, and bonding forces; the bonding force is derived by summing the individual contributions of each receptor-ligand tether. The model can simulate the effect of many parameters on adhesion, such as the number of receptors on microvilli tips, the density of ligand, the rates of reaction between receptor and ligand, the stiffness of the springs, the response of springs to extension, and the magnitude of hydrodynamic stresses. By varying these parameters, the model can successfully recreate the entire range of expected and observed adhesive phenomena, from completely unencumbered motion, to rolling, to transient attachment, to firm adhesion. Also, the model can provide meaningful statistical measures of adhesion, including the mean and variance in velocity, rate constants for cell attachment and detachment, and the frequency of adhesion. We find a critical modulating parameter of adhesion is the fractional spring slippage, which relates the extension of a bond to its rate of breakage; the higher the slippage, the faster the breakage for the same extension. Changes in the fractional spring slippage can radically change the adhesive behavior of a cell. We show that stiffer springs will only serve to increase adhesion if the fractional slippage remains small. In addition, our simulations emphasize the importance of reaction rates between receptor and ligand, rather than affinity, as being the key determinant of adhesion under flow. These results suggest reaction rates and response to stress of adhesion molecules must be independently measured to understand how adhesion is controlled at the molecular level.

Animals↗

PubMed1978

An analysis of Con A-mediated agglutination in a Chinese hamster ovary subclone which responds morphologically to growth in dibutyryl cyclic AMP. III. The role of microvilli in the agglutination process.

We have used the H-7w subclone of a Chinese hamster ovary cell line (K1) to investigate the role of cell surface architecture (specifically microvilli, blebs, and sheets) in determining the relative agglutinability of a cell line with Con A. Our evidence clearly demonstrates that no specific, immediately recognizable surface architecture is associated with the agglutinable or non-agglutinable phenotype. Our data suggest that the expression of microvilli on the cell surface is neither necessary to nor sufficient for the phenotype described by enhanced agglutinability with Con A. Furthermore our work demonstrates that cells covered with blebs are as agglutinable as cells covered with microvilli thereby suggesting that the intertwining of microvilli may not be an essential facet of the agglutination phenomenon.

Agglutination↗

PubMed1991

Relationship between development of microvilli on tumor cells and growth or metastatic potential of tumor cells.

The present study was undertaken to elucidate the ultrastructural differences between tumor cell clones with high growth or highly metastatic potential and those with low growth or weakly metastatic potential. Transmission, scanning and immuno-electron microscopy revealed a remarkable variance of surface microvilli between these two types of tumor cell clones. Greater numbers of microvilli appeared on the tumor cells which possess high growth or highly metastatic potential than on those of tumor cells with low growth or weakly metastatic potential. In contrast, gap junctions and desmosomes were more occasionally seen on the weakly metastatic tumor cells than the highly metastatic tumor cells. Immuno-electron microscopy revealed that epidermal growth factor (EGF) receptor and c-neu oncogene product, which is closely related to the EGF-receptor, were positively stained on the microvilli of tumor cells with high growth potential, whereas the tumor cells with low growth potential showed almost no staining. Western blot analysis also revealed that in the tumor cells with high growth potential, positive expression of c-neu at 185 kDa was stronger than in the tumor cells with low growth potential. The findings suggest that increased numbers of microvilli are closely related to the growth and metastatic potential of tumor cells.

Animals↗

PubMed1976

Schistosoma mansoni: the occurrence of microvilli on the surface of the tegument during transformation from cercaria to schistosomulum.

Microvilli are developed on the surface of Schistosoma mansoni schistosomula during penetration of the host skin; they form rapidly but are lost approximately 90 min after penetration. Identical microvilli are also formed on schistosomula which have penetrated a mouse skin preparation in vitro, and on schistosomula prepared by mechanical separation of the tail from the body of the cercaria. The microvilli, which are limited by the trilaminate tegumental membrane of the cercaria, eventually degenerate and are cast off from the surface of the tegument. There is little change in the surface area of the schistosomulum at this time, and the formation and loss of microvilli coincides with the replacement of the cercarial tegumental membrane by the new heptalaminate membrane. It is suggested that during the cercaria/schistosomulum transformation, some intramembraneous components of the original cercarial membran e may migrate into the new heptalaminate membrane and thus be retained, while other peripheral components such as the glycocalyx are almost certainly lost.

Animals↗

PubMed1975

Role of microvilli in surface changes of synchronized P815Y mastocytoma cells.

The surface morphology of synchronized P815Y mastocytoma cells has been examined by scanning electron microscopy. Early G1 cells are comparatively smooth or light villated, whereas at later stages the surface becomes progressively more villated. In G1 cell most microvilli have a uniform diameter, whereas in S and G2 cells, many microvilli show branching and often originate from much larger surface protuberances. Small "blebs" are seen on the surface of many cells but these structures do not appear to be a characteristic feature of cells at any one stage of the cycle. The presence of microvilli increases the total surface of the cell to such an extent that the ratio of volume to surface area remains constant throughout the cell cycle. The mechanism of cytokinesis is thus a physical one, involving the unfolding of previously accumulated microvilli.

Cell Division↗

PubMed1975

Localization of alkaline phosphatase activity of the small intestinal microvilli in various vertebrates from mammalia to fishes.

The localization of alkaline phosphatase activity in the small intestinal microvilli of the duodenum, jejunum, and ileum in various mammalia, birds, reptilia, amphibia and fishes has been investigated and compared both by light and by electron microscopes. When the incubating medium is intravitally perfused into the small intestine of living animals, deposition of azo-dye is found on the microvilli in the epithelium. Enzyme activity in the duodenal epithelium is strong in all 14 species. No appreciable differences in phosphatase activity are found among the species. In the birds and mammalia except rat, the microvilli of the jejunal and ileal epithelium shows strong alkaline phosphatase activity. In the amphibia and fishes, the jejunal epithelium of the striated border shows weak phosphatase activity. Ileal epithelium of the reptilia, amphibia and fishes shows weak or trace activity. In the glutaraldehyde-fixed material, the phosphatase activity of the duodenum in mammalia is similar in activity to that found in the intravitally perfused animal. But no azo-dye deposit can be seen on the microvilli in the jejunum of amphibia and fishes, nor the ileum of reptilia, amphibia and fishes. Furthermore, the effect of EDTA-inhibition for alkaline phosphatase in the small intestinal surface was also viewed in glutaraldehyde-fixed sections.

Alkaline Phosphatase↗

PubMed1991

The secretion-stimulated 80K phosphoprotein of parietal cells is ezrin, and has properties of a membrane cytoskeletal linker in the induced apical microvilli.

Stimulation of gastric acid secretion in parietal cells involves the translocation of the proton pump (H,K-ATPase) from cytoplasmic tubulovesicles to the apical membrane to form long, F-actin-containing, microvilli. Following secretion, the pump is endocytosed back into tubulovesicles. The parietal cell therefore offers a system for the study of regulated membrane recycling, with temporally separated endocytic and exocytic steps. During cAMP-mediated stimulation, an 80 kDa peripheral membrane protein becomes phosphorylated on serine residues. This protein is a major component, together with actin and the pump, of the isolated apical membrane from stimulated cells, but not the resting tubulovesicular membrane. Here we show that the gastric 80 kDa phosphoprotein is closely related or identical to ezrin, a protein whose phosphorylation on serine and tyrosine residues was recently implicated in the induction by growth factors of cell surface structures on cultured cells [Bretscher, A. (1989) J. Cell Biol., 108, 921-930]. Light and electron microscopy reveal that ezrin is associated with the actin filaments of the microvilli of stimulated cells, but not with the filaments in the terminal web. In addition, a significant amount of ezrin is present in the basolateral membrane infoldings of both resting and stimulated cells. Extraction studies show that ezrin is a cytoskeletal protein in unstimulated and stimulated cells, and its association with the cytoskeleton is more stable in stimulated cells. These studies indicate that ezrin is a membrane cytoskeletal linker that may play a key role in the control of the assembly of secretory apical microvilli in parietal cells and ultimately in the regulation of acid secretion. Taken together with the earlier studies, we suggest that ezrin might be a general substrate for kinases involved in the regulation of actin-containing cell surface structures.

Actins↗

PubMed1991

Effect of diazinon on freeze-fracture images of microvilli of intestinal epithelial cells of Tilapia nilotica.

The effect of the organophosphate insecticide, diazinon on the intramembranous particles (IMPs) of the microvilli of the intestinal epithelial cells of Tilapia nilotica fish was studied using freeze-fracture technique. Exposing fish to different repeated concentrations of diazinon (1/2LC50) caused a significant decrease in population density of IMPs in P- and E-faces. IMPs of microvilli found in intestinal epithelial cells are thought to represent many kinds of proteins including enzymes. In the present work, it is suggested that diazinon induced a reduction in enzymatic content of the membrane which was accompanied by a decrease in IMPs density of the microvilli.

Animals↗

PubMed1992

Responses of enterocyte microvilli in experimental diabetes to insulin and an aldose reductase inhibitor (ponalrestat).

The small intestine of 12-week-old streptozotocin-diabetic rats was examined by light and transmission electron microscopy in order to study the effects of alternative treatments on microvillous morphology. Four groups were examined: untreated diabetic rats, insulin-treated diabetics and rats treated with an aldose reductase inhibitor (ponalrestat) given with and without insulin. Numbers and dimensions of microvilli at the apex of columnar absorptive epithelial cells (enterocytes) were estimated using stereological principles. Values were obtained for the organ as a whole as well as for different sites along its length. In the untreated diabetic intestine, the mean (standard error of mean) number of microvilli was 4.5 (0.8) x 10(12) with a total surface area of 1.9 (0.50) m2. On average, the microvilli were 1.1 (0.08) microns long, 104 (3.8) nm in diameter and packed on the villous surface at a density of 3400 (50) per 100 microns 2. Their length at least varied with intestinal location. Significant effects of insulin therapy were detected. In contrast, the study failed to find any significant effect of aldose reductase inhibition on any variable except microvillous packing density.

Aldehyde Reductase↗