Organization of stress fibrils in cultured fibroblasts studied by using an actin filament-fragmenting protein

Earlier we isolated a 1:1 complex of 90 kD-protein and actin from bovine brain. This complex was able to fragment actin filaments. Effects of this complex on the cytoskeleton of mouse and quail embryo fibroblasts are described. The cells were extracted with Triton X-100, and the resulting cytoskeletons were treated with the complex. Tetramethylrhodaminylphalloin and actin antibody staining failed to detect actin in preparations treated with the 90 kD protein-actin complex. Electrophoretic data confirmed actin solubilization upon this treatment. Immunofluorescent microscopy showed that actin solubilization was accompanied by extraction of vinculin and alpha-actinin from focal contacts and stress-fibers. In contrast, myosin distribution in treated cytoskeletons did not differ significantly from that in control extracted cells: in both the cases myosin was found mainly in the stress-fibers. Thus, myosin localization in stress-fibers does not depend on actin and is probably controlled by some other cytoskeletal component(s).     

NAD metabolism in Salmonella typhimurium: isolation of pyridine analogue supersensitive (pas) and pas suppressor mutants

Mutants of Salmonella typhimurium supersensitive to the nicotinic acid analogue 6-amino-nicotinic acid (6ANA) were isolated as unable to grow on what are normally subinhibitory concentrations of the analogue. The mutations were classified on the basis of their map positions as pasA (89-92 units), pasB (66-69 units), pasC (18-22 units), pasD (18 units) and pasE (55 units). The mutants exhibited a wide range of minimal inhibitory concentrations towards 6ANA, and several were affected in terms of growth. The data suggest that most of the mutations probably reside in genes whose products utilize nicotinamide adenine dinucleotide (NAD) as a cofactor, the altered gene products being more sensitive to internal 6-amino NAD concentrations. Secondary mutations which suppress the Pas- phenotype were found to reside in the following NAD-related loci; pncB, nadB and nadD. Two of the pncB mutants appear to be affected in the expression of NAPRTase while several of the nadB mutants are apparently insensitive to feedback inhibition by internal NAD concentrations.     

Identification of a yeast artificial chromosome clone spanning a translocation breakpoint at 7q32.1 in a Smith-Lemli-Opitz syndrome patient.

Smith-Lemli-Opitz syndrome (SLOS) is a mental retardation/multiple congenital anomaly syndrome. The gene(s) involved has not been mapped or cloned, but, recently, a biochemical abnormality in cholesterol biosynthesis has been shown to occur in most SLOS patients. The defect is suspected to occur in the penultimate step of the cholesterol pathway, involving the enzyme 7-dehydrocholesterol reductase, which has not been isolated. On the basis of the hypothesis that a de novo balanced translocation [t(7;20)(q32.1;q13.2)] in an SLOS patient directly interrupts the SLOS gene, positional cloning techniques are being employed to localize and identify the SLOS gene. We report the identification of a chromosome 7-specific YAC that spans the translocation breakpoint, as detected by FISH. This is the first study narrowing a candidate SLOS region and placing it on physical and genetic maps of the human genome.     

Down-Regulation of T-Cell Proliferation in Response to Soluble Anti-CD3 Antibodies through Development of Redirected Cytolytic Activity Eliminating Costimulatory Cells

CD4⁺ T-depleted spleen cells (CD8⁺ T cells) activated by anti-CD3 antibodies (aCD3) suppressed proliferation of CD8⁺ T-depleted spleen cells (CD4⁺ T cells) and fresh normal T cells in response to aCD3. Antigen-nonspecific cytolytic activity was induced in splenic CD8⁺ T cells by stimulation with aCD3 and showed the peak level on day 3, whereas cytolytic activity induced in CD4⁺ T cells was weak. Intact Ig but not F(ab')₂ of aCD3 induced and mediated cytolytic activity. Correspondingly, the cytolytic activity induced by aCD3 was directed against target cells bearing Ig-binding Fc-receptor activity and cytolysis was inhibited by the addition of free Ig into the assay system. We showed that aCD3-activated T cells carried a high level of aCD3 on their surface at the time after the peak proliferation when they attained high cytolytic activity. This raised the possibility that the anti-CD3-induced aCD3-redirected cytolytic activity eliminated Fc-receptor-bearing costimulatory cells in the culture for down-regulation of the T-cell proliferation. This view was supported by partial restoration of anti-CD3-induced low responsiveness of CD8⁺ T cells by the addition of fresh costimulatory cells. These results suggested a new pathway of down-regulation of T-cell proliferation by aCD3-activated cytolytic CD8⁺ T cells.     

C26-analogs of naturally occurring bile alcohols-II. Preparation of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrols (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrols (25R and 25S) by a hydroboration procedure

A convenient procedure for the synthesis of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrol (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12alpha,26-tetrol (25R and 25S) starting from 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,25-tetrol was developed. Dehydration of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha, 25-tetrol with glacial acetic acid and acetic anhydride yielded a mixture of 24-nor-5 beta-cholest-23-ene-3 alpha,7 alpha,12 alpha-triol and the corresponding delta 25 compound. Hydroboration and oxidation of the mixture of unsaturated nor-triols resulted in the formation of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,23-tetrols (23R and 23S) and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,26-tetrols (25R and 25S). In addition, smaller amounts of 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha,22 xi-tetrol and 24-nor-5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol were also obtained. The C26 bile alcohols epimeric at C-23 and C-25 were resolved by analytical and preparative TLC and characterized by gas-liquid chromatography and mass spectrometry. Provisional assignment of the configurations of the C-23 and C-25 hydroxyl groups were made on the basis of molecular rotation differences. These C26 alcohols will be used to test the stereospecificity of the hepatic enzymes that promote oxidation of the cholesterol side chain.     

Morphology of the microtubule system in mouse kidney epithelial cells]

The cultured mouse kidney cells forming epithelial sheets were studied using an indirect immunofluorescence microscopy with antibodies against tubulin. These cells, as well as fibroblasts, were found to contain a well developed microtubular system sensitive to colcemid. The assembly of microtubules after washing out of colcemid began from one or two perinuclear centers, associated with the cilium-like structure. There were certain differences between the microtubular systems in epithelial cells and fibroblasts: 1) Microtubules in the fibroblasts penetrated the whole cytoplasm including the peripheral lamella whereas in the epithelial cells the lamellar cytoplasm was often free from microtubules. 2) The orientation of microtubules in the epithelial cells, unlike in the fibroblasts, was not correlated with the stable or active state of the cell margin. A possible role of microtubular system in the epithelial cells and fibroblasts is compared and discussed.     

Processes determining changes in the shape of a cell following detachment from a substrate]

In contrast to living cells, glycerin extracted mouse embryo fibroblasts do not round up after detachment from the substrate. The addition of ATP makes these fibroblasts round up. Thus, the rounding of the detached cell occurs in result of active, ATP-requiring contractile forces rather than due to the action of elastic forces or of surface tension. The ATP-induced contraction of the glycerinated cell is accompanied with the loss of the parallel orientation of 50-70 A microfilaments. The loss is suggested to result from the attachment of different microfilaments of the same bundle to different points of the cell surface. Microtubules are not essential for the contraction: the rounding of living or glycerin-treated cells is not colcemide affected. Living cells treated with cytochalasine B (CH) reversibly lose their ability to round up after detachment. ATP is able to induce no contraction of glycerin-extracted cells treated with CH before extraction. In contrast, the addition of CH to the ATP-containing solution does not inhibit the contraction of glycerin-extracter normal cells. These results give reason to suggest that CH may inactivate contractile structures of the cell. It may be thought that some unknown additional factors, available in the living cell and not available in the glycerin-extracted one, are essential for this inactivation.