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51.
Using a model proposed earlier by Goel et al. and a set of plausible motility rules, a computer simulation of engulfment of two or more intact embryonic tissues is successfully carried out. The same motility rules are used to simulate the rounding up of a tissue, centralization of one tissue within another tissue (a phenomenon not yet observed), and phase inversion, a process which may have relevance to differentiation. The finnal structures bear a good resemblance to those observed experimentally. The software, in conjunction with an appropriate hardware configuration, allows a visual display of the dynamics of cellular movement. These simulations indicate that the range of inter-cellular interactions controlling these tissue rearrangements extends only one or two cell diameters. 相似文献
52.
The effect of the natural ATPase inhibitor and octylguanidine on the ATPase activity of soluble oligomycin-insensitive mitochondrial F1 were compared. Both compounds induced a maximal inhibition of 60–80% in various preparations of F1 studied. The inhibition was of the uncompetitive type with respect to MgATP, and the action of the compounds was partially additive. The data suggest that octylguanidine reproduces the action of the natural ATPase inhibitor. Alkylammonium salts also affect the ATPase activity in a similar form. F1 bound to Sepharose-hexylammonium is largely inactive, whilst free hexylammonium at higher concentrations induces only a partial inhibition of the activity. This suggests that the degree of immobilization of F1 is related to the magnitude of inhibition of ATPase activity induced by alkyl cations. The binding of F1 to Sepharose-hexylammonium is prevented by high concentrations of Na+ or K+. 相似文献
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55.
Various human Burkitt lymphoma and LCL lines established in vitro and their derived somatic cell hybrids were tested for their comparative EBV receptor levels in a virus binding assay. Their graded C3b and C3d complement receptor expression was estimated simultaneously by means of isotope labeled rosette marker cells. The receptor concentration of each cell line was related to Raji as the standard of comparison, K 562, P3HR-1, and YACUT were used as negative controls. In general, the charging curves for EBV and C3d receptors parallelled each other (r = 0.97) while C3b receptor charging showed no correlation (r < 0.60). In the Raji hybrids between the C3b receptor positive Raji parent and various patents that were negative for this receptor, C3b receptor expression was low or negative. In contrast, the C3d negative P3HR-1 line gave rise to hybrids, after fusion with receptor-positive cells, that were intermediate with regard to their C3d receptor expression. The host range restriction of the Epstein-Barr virus is determined at the receptor level. The close relationship between the EBV receptor and the C3d receptor, a B-lymphocyte-specific moiety, suggests that the moderate interaction with EBV with the B lymphocytes may have had a selective advantage, favoring the presence of EBV. Since EBV causes lytic infections after artificial introduction into nonnatural host cells, it may represent a B-lymphocyte-specific host range mutant, derived from an originally lytic herpesvirus with a much broader target cell range. 相似文献
56.
High dose tolerance to either bovine serum albumin (BSA) or fowl γ-globulin (FGG) was induced in CBA mice by neonatal injection. Tolerance to BSA lasted about 9 weeks, and that to FGG, about 18 weeks. Splenic B-cell function was analyzed using quantitative in vivo assays and in vitro limiting dilution analysis. Tolerogen-specific IgM- and non-IgM-producing B cells are depleted at least threefold in the spleens of tolerant mice. Tolerogen-specific T-helper-cell function was examined by immunization with haptenated antigens. Analysis of the recovery from tolerance indicates that the return to normal function in the tolerogen-specific B-cell and T helper fractions coincides with the return to normal responsiveness by the whole animal. 相似文献
57.
William R. Cullen Ann E. Erdman Barry C. McBride A.Wendy Pickett 《Journal of microbiological methods》1983,1(5):297-303
Candida humicola acts on benzenearsonic acid to produce dimethylphenylarsine, which was identified by mass spectroscopy following the chemofocusing of the volatile metabolite onto a mercuric chloride impregnated filter. The same technique established that trimethylarsine is the volatile metabolic product obtained from C. humicola treated with 4-NH2-2-OHC6H3AsO(OH)2 and (CH3)3AsO. Arsanilic acid, 4-NH2C6H4AsO(OH)2, is not metabolized to a volatile arsine. 相似文献
58.
Richard Beale David W. Beaton Volker Neuhoff Neville N. Osborne 《Neurochemistry international》1983,5(6):691-696
Cells dissociated from adult and neonatal rat retinas were separated by density gradient centrifugation. Previous work had shown that rat retinal cells labelled by an immunofluorescence assay for the Thy-1 antigen were chiefly or exclusively ganglion cells, and so the proportion of Thy-1 positive cells in the density gradient fractions was used as an index of the enrichment of ganglion cells. The proportion of Thy-1 positive neonatal cells was increased from about 0.4% in the initial dissociate to about 8% in the most enriched fraction of a Percoll step gradient. Amongst adult cells the initial 0.7% Thy-1 positive cells were increased to roughly 2% in the best fraction of a metrizamide step gradient.
The presence of relatively large numbers of Thy-1 positive cells in other fractions suggested that it would be difficult to further increase the proportion of rat ganglion cells by methods based on their sedimentation properties. These results demonstrate the importance of cell-type specific markers in attempts to purify cells from the central nervous system. 相似文献
59.
The hyaline layer (HL) surrounding the sea urchin blastula appears to dissolve in 1 M glycine. However, after this treatment, there persists over the surfaces of the blastomeres a layer of material, referred to here as the apical lamina (AL), that sloughs off as an adhesive convoluted bag upon gradual dissociation of the embryo. Isolated hyaline layers, referred to as HL-AL complexes, were analyzed by urea-SDS-polyacrylamide gel electrophoresis. A major protein of the HL-AL complex, hyalin, bands or precipitates in the stacking gel. Two other major proteins, both strongly PAS positive, migrate with apparent molecular weights of 175K and 145K daltons. As with intact embryos, the glycine wash removes the hyalin protein from the isolated HL-AL complex, leaving the undissolved AL which consists primarily of the 175K- and 145K-dalton proteins. The embryo's own perivitelline-localized cortical granule peroxidase heavily radioiodinates the proteins of the HL-AL complex, further verifying their apical, extracellular location. Unlike hyalin, the AL proteins do not precipitate with calcium ions. Compared to the entire HL-AL complex, the AL contains a greater percentage of carbohydrate. No sialic acid is associated with the HL-AL complex, but the AL contains some sulfate. In contrast to a published report based on ultrastructural staining, no biochemical evidence was found in this study for the presence of collagen or significant glycosaminoglycan within the HL-AL complex. No developmental differences were observed in AL proteins from 1-hr-old embryos compared to those from blastulae. However, there is evidence suggesting heterogeneity and developmental differences in hyalin. The possible organization of hyalin and the AL proteins into separate layers surrounding the embryo is discussed. The influence of the AL proteins in morphogenesis and cell adhesion is considered, and hypothetical roles attributed to the HL and hyalin are critically questioned. 相似文献
60.
Robert A. Schlegel Bonnie M. Phelps Gary P. Cofer Patrick Williamson 《Experimental cell research》1982,139(2):321-328
Mammalian erythropoiesis includes a step in which the nucleus is extruded through the cell membrane. We have investigated the relationship between concanavalinA (conA) plasma membrane receptors, which are known to leave the incipient reticulocyte during enucleation, and regions of the plasma membrane which bind merocyanine 540, a differentiation-specific marker of hematopoietic cells. The distribution of these two fluorescent probes was examined on living cells from the spleens of neonatal mice and on erythroleukemia cells induced to enucleate in culture. In both cases, the region of the membrane extruded with the nucleus preferentially binds conA and merocyanine 540, whereas the plasma membrane which is left behind retains the capacity to bind another lectin, wheat germ agglutinin (WGA). The implications of these findings are discussed with respect to the mechanism by which markers are eliminated from the erythrocyte cell surface. 相似文献