bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of histone H2b as a heat-shock protein in Drosophila.
Authors: Sanders M M
Published: May 2004

Total cell polypeptides synthesized, in cultured Drosophila cells under control (25 degrees C) and heat-shock (37 degrees C) conditions have been compared in two different two-dimensional polyacrylamide gel electrophoresis systems which, together, resolve polypeptides having a wide range of isoelectric points, including the most basic polypeptides of the cell. The electrophoresis of basic proteins showed that the most prominent basic polypeptide synthesized in heat shock comigrated with histone H2b. This heat-shock polypeptide was identified as histone H2b by two criteria: (a) it comigrated with authentic histone H2b in Triton-urea-acetic acid acrylamide gel electrophoresis after solubilization from nuclei with acid; and (b) partial proteolysis peptide maps of the basic heat-shock protein and histone H2b were identical. The synthesis of histone H2b was induced threefold in heat shock, whereas synthesis of the other histones was reduced from two- to tenfold. The noncoordinate synthesis of histones in Drosophila in heat shock provides an interesting system in which to investigate transcriptional and translational controls of histone synthesis as well as assembly of histones into chromatin.
Immunoelectron microscope studies of membrane-microfilament interactions: distributions of alpha-actinin, tropomyosin, and vinculin in intestinal epithelial brush border and chicken gizzard smooth muscle cells.
Authors: Geiger B , Dutton A H , Tokuyasu K T , Singer S J
Published: May 2004

The ultrastructural localization of three cytoskeletal proteins, alpha-actinin, tropomyosin, and vinculin, in the brush border of epithelial cells of chicken small intestine and the smooth muscle cells of chicken gizzard was studied by immunofluorescence and immunonelectron microscope labeling of frozen sections of lightly fixed, intact tissues. In the immunoelectron microscope studies, a recently described new type of electron-dense antibody conjugate, imposil-antibody, has been successfully used, along with ferritin-antibody conjugates, in single and double immunolabeling experiments. In the intestinal brush border shows that vinvulin is sharply confined to the junctional complex close to the membrane region of the zonula adherens, in distinct contrast to the more diffuse distributions of the other two proteins. In the smooth muscle cells, the labeling patterns show that vinculin is sharply confined to the membrane-associated dense plaques, closer to the membrane than the alpha-Actinin is also present in the cytoplastic dense bodies, from which vinculin is absent. Tropomyosin is present diffusely distributed in the cytoplasm, but absent from both dense plaques and dense bodies. These findings with the muscle cells demonstrate, therefore, that the dense plaques and dense bodies are chemically and structurally distinct entities. The results with both tissues, along with those in previous papers (Geiger, 1979, Cell. 18:193-205.; Geiger et al., 1980, Proc. Natl. Acad. Sci. U. S. A. 77:4127-4131), suggest that vinculin may play an important and widespread role in the linkage of actin-containing microfilament bundles to membranes.
Polarity orientation of axonal microtubules.
Authors: Heidemann S R , Landers J M , Hamborg M A
Published: May 2004

The polarity orientation of cellular microtubules is widely regarded to be important in understanding the control of microtubule assembly and microtubule-based motility in vivo. We have used a modification of the method of Heidemann and McIntosh (Nature (Lond.). 286:517-519) to determine the polarity orientation of axonal microtubules in postganglionic sympathetic fibers of the cat. In fibers from three cats we were able to visualize the polarity of 68% of the axonal microtubules; of these, 96% showed the same polarity orientation. Our interpretation is that the rapidly growing end of all axonal microtubules is distal to the cell body. We support Kirschner's hypothesis on microtubule organizing centers. (J. Cell Biol. 86:330-334), although this interpretation raises questions about the continuity of axonal microtubules. Our results are inconsistent with a number of models for axonal transport based on force production on the surface of microtubules in which the direction of force is determined by the polarity of microtubules.
Factors influencing the release of proteins by cultured schwann cells
Authors: Carey DJ , Bunge RP
Published: May 2004

Cultured rat schwann cells grown in association with sensory neurons when labeled with [(3)H]leucinem, [(3)H]glucosamine, or [(35)S]methionine release labeled polypeptides into the culture medium. Analysis by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of the culture medium reveals a reproducible pattern of more than 20 polypeptides with molecular weights ranging from 15,000 to more than 250,000. Five major polypeptides (apparent molecular weights 225,000, 210,000, 90,000, 66,000, 50,000, and 40,000) account for approximately 40 percent of the leucine or methionine radioactivity in medium polypeptide. Schwann cells grown in a serum-free defined medium, in which schwann cells do not relate normally to axons, release approximately four times less labeled medium polypeptides tha cultures grown in medium supplemented with serum and chick embryo extract. In addition, there is a qualitative difference in the pattern of medium polypeptides resolved by SDS-PAGE, so that a single polypeptide (mol wt 40,000) accounts for nearly all of the label in medium polypeptides. Switching of cultures grown in defined medium to supplemented medium for 2 d results in a fourfold increase in the amount of labeled polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides appearing in the culture medium, and a return to the normal pattern of medium polypeptides as resolved by SDS-PAGE. This change in the pattern of polypeptides release by schwann cells is accompanied by changes in the association between schwann cells and axons. An early step in the establishment of normal axon-schwann cell relations appears to be an inward migration of schwann cells into axonal bundles and spreading of schwann cells along neurites. These changes are evident within 48 h after medium shift. Our results thus suggest that the release of proteins by schwann cells may be important for the development of normal axonal ensheathment.
Quantitative assay and subcellular distribution of enzymes acting on dolichyl phosphate in rat liver
Authors: Ravoet A , Amar-Costesec A , Godelaine D , Beaufay H
Published: May 2004

To establish on a quantitative basis the subcellular distribution of the enzymes that glycosylate dolichyl phosphate in rat liver, preliminary kinetic studies on the transfer of mannose, glucose, and N-acetylglucosamine-1-phosphate from the respective (14)C- labeled nucleotide sugars to exogenous dolichyl phosphate were conducted in liver microsomes. Mannosyltransferase, glucosyltransferase, and, to a lesser extent, N- acetylglucosamine-phosphotransferase were found to be very unstable at 37 degrees C in the presence of Triton X-100, which was nevertheless required to disperse the membranes and the lipid acceptor in the aqueous reaction medium. The enzymes became fairly stable in the range of 10-17 degrees C and the reactions then proceeded at a constant velocity for at least 15 min. Conditions under which the reaction products are formed in amount proportional to that of microsomes added are described. For N- acetylglucosaminephosphotransferase it was necessary to supplement the incubation medium with microsomal lipids. Subsequently, liver homogenates were fractionated by differential centrifugation, and the microsome fraction, which contained the bulk of the enzymes glycosylating dolichyl phosphate, was analyzed by isopycnic centrifugation in a sucrose gradient without any previous treatment, or after addition of digitonin. The centrifugation behavior of these enzymes was compared to that of a number of reference enzymes for the endoplasmic reticulum, the golgi complex, the plasma membranes, and mitochondria. It was very simily to that of enzymes of the endoplasmic reticulum, especially glucose-6-phosphatase. Subcellular preparations enriched in golgi complex elements, plasma membranes, outer membranes of mitochondira, or mitoplasts showed for the transferases acting on dolichyl phosphate relative activities similar to that of glucose- 6-phosphatase. It is concluded that glycosylations of dolichyl phosphate into mannose, glucose, and N-acetylglucosamine-1-phosphate derivatives is restricted to the endoplasmic reticulum in liver cells, and that the enzymes involved are similarly active in the smooth and in the rough elements.
Characterization of muscarinic acetylcholine receptors in the avian salt gland.
Authors: Hootman S R , Ernst S A
Published: May 2004

Electrolyte and fluid secretion by the avian salt gland is regulated by activation of muscarinic acetylcholine receptors (R). In this study, these receptors were characterized and quantitated in homogenates of salt gland from domestic ducks adapted to conditions of low (freshwater, FW) and high (saltwater, SW) salt stress using the cholinergic antagonist [3H]-quinuclidinyl benzilate (QNB). Specific binding of the antagonist to receptors in both FW- and SW-adapted glands reveals a single population of high affinity binding sites (KdFW = 40.1 +/- 3.0 pM; KdSW = 35.1 +/- 2.1 pM). Binding is saturable; RLmaxFW = 1.73 +/- 0.10 fmol/micrograms DNA; RLmaxSW = 4.16 +/- 0.31 fmol/micrograms DNA (where L is [3H]QNB and RL the high affinity complex). Calculated average cellular receptor populations of 5,800 sites/cell in FW-adapted glands and 14,100 sites/cell in SW-adapted glands demonstrate that upward regulation of acetylcholine receptors in the secretory epithelium follows chronic salt stress. The receptor exhibits typical pharmacological specificities for muscarinic cholinergic antagonists (QNB, atropine, scopolamine) and agonists (oxotremorine, methacholine, carbachol). In addition, the loop diuretic furosemide, which interferes with ion transport processes in the salt gland, competitively inhibits [3H]QNB binding. Preliminary studies of furosemide effects on [3H]QNB binding to rat exorbital lacrimal gland membranes showed a similar inhibition, although the diuretic had no effect on antagonist binding to rat brain or atrial receptors.
Purine nucleoside phosphorylase is associated with centrioles and basal bodies.
Authors: Oliver J M , Osborne W R , Pfeiffer J R , Child F M , Berlin R D
Published: May 2004

We have localized a fraction of the enzyme, purine nucleoside phosphorylase (PNP), to the centrioles and basal bodies of mammalian, avian, and protozoan cells. Two completely independent methods were used, one based on the ultrastructural cytochemistry of the enzyme activity and one based on immunofluorescence microscopy using an antibody raised in rabbit against purified human PNP. PNP catalyzes the reversible conversion of purine nucleosides and inorganic phosphate to the corresponding purine bases and ribose-1-phosphate. Its partial localization to centrioles and basal bodies raises the possibility that purine compounds are involved in centriole replication and/or in the regulation of microtubule assembly in vivo. No centriolar PNP could be detected in primary skin fibroblast from two infants with severe immunodeficiency disease associated with the absence of soluble PNP. This raises the possibility that defects in centriole function may contribute to the impaired division and maturation of T lymphoid precursor in this inherited disorder. Initially, the immunofluorescence analyses were complicated by a residual centriole-binding antibody that persisted in immunoglobulins from immune animals after complete removal of anti-PNP by affinity chromatography. Binding was abolished by exposure of cells to sodium periodate, indicating that this (and possibly other) "spontaneous" anticentriole antibodies in rabbit serum may be directed against carbohydrates.
Distribution of cells bearing receptors for a colony-stimulating factor (CSF-1) in murine tissues.
Authors: Byrne P V , Guilbert L J , Stanley E R
Published: May 2004

CSF-1 is a subclass of the colony-stimulating factors that specifically stimulates the growth of mononuclear phagocytes. We used the binding of 125I-CSF-1 at 0 degrees C by single cell suspensions from various murine tissues, in conjunction with radioautography, to determine the frequency of binding cells, their identity, and the number of binding sites per binding cell. For all tissues examined, saturation of binding sites was achieved within 2 h at 2--3 x 10(-10) M 125I-CSF-1. The binding was irreversible and almost completely blocked by a 2 h preincubation with 5 x 10(-10) M CSF-1. 125I-CSF-1 binding was exhibited by 4.3% of bone marrow cells, 7.5% of blood mononuclear cells, 2.4% of spleen cells, 20.5% of peritoneal cells, 11.8% of pulmonary alveolar cells and 0.4% of lymph node cells. Four morphologically distinguishable cell types bound 125I-CSF-1: blast cells; mononuclear cells with a ratio of nuclear to cytoplasmic area (N/C) greater than 1; cells with indented nuclei; and mononuclear cells with N/C less than or equal to 1. No CSF-1 binding cells were detected among blood granulocytes or thymus cells. Bone marrow promyelocytes, myelocytes, neutrophilic granulocytes, eosinophilic granulocytes, nucleated erythroid cells, enucleated erythrocytes, and megakaryocytes also failed to bind. The frequency distribution of grain counts per cell for blood mononuclear cells was homogenous. In contrast, those for bone marrow, spleen, alveolar, and peritoneal cells were heterogeneous. The monocytes in blood or bone marrow (small cells, with either indented nuclei or with N/C greater than 1) were relatively uniformly labeled, possessing approximately 3,000 binding sites per cell. Larger binding cells (e.g., alveolar cells) may possess higher numbers of receptors. It is concluded that CSF-1 binding is restricted to mononuclear phagocytic cells and their precursors and that it can be used to identify both mature and immature cells of this series.
An inhibitor of animal cell growth increases cell-to-cell adhesion.
Authors: Mannino R J , Ballmer K , Zeltner D , Burger M M
Published: May 2004

The interactions of both normal and transformed cells with their environment is mediated to a large extent by the cell surface. Succinylated concanavalin A (succinyl-Con A) is a nontoxic and nonagglutinating derivative of the jack-bean lectin concanavalin A. Succinyl-Con A, presumably through an interaction with the cell surface, reversibly inhibits the growth of normal cells and restores a normal growth phenotype to transformed cells. Whereas at high cell densities migration was inhibited, it turned out that at low cell densities where cells are not in contact with each other, cell movement was not affected by succinyl-Con A. Together with some additional observations, this suggests that this lectin derivative increases cell-to-cell adhesion in culture and thereby may influence cell migration. An increase in cell-to-cell adhesion by this lectin derivative may not be brought about simply by physically linking cells together. It occurs after a lag time, possibly by inducing surface changes. The relationship between cell adhesion in culture, cell movement, and cell growth is discussed.
Identification of gelsolin, a Ca2+-dependent regulatory protein of actin gel-sol transformation, and its intracellular distribution in a variety of cells and tissues.
Authors: Yin H L , Albrecht J H , Fattoum A
Published: May 2004

Antiserum prepared against gelsolin, a major Ca2+-dependent regulatory protein of actin gel-sol transformation in rabbit lung macrophages, was used to detect the presence of proteins immunologically related to gelsolin in a variety of cells and tissues. Cell extracts were electrophoresed on polyacrylamide gels, and replicas of the gels on cellulose nitrate paper were stained by an indirect immunohistochemical technique. A single band of crossreactive material which comigrates with macrophage gelsolin is found in at least nine different kinds of cells and tissues derived from rabbits and humans and in four lines of cultured cells from humans and rats. Gelsolin was also identified in human serum and plasma, raising the possibility that it may contribute to the clearance of actin from the circulatory system. Using this antiserum, we demonstrated, by indirect immunofluorescent staining of acetone-fixed macrophages and polymorphonuclear leukocytes, that gelsolin resides in the cortical cytoplasm and that during phagocytosis it is concentrated in pseudopodia engulfing particles to be ingested, an area of the cytoplasm actively engaged in movement. In longitudinal cryostat sections of contracted rabbit skeletal muscle, antigelsolin staining was associated with the I-band of the myofibril, suggesting that it may be involved, by an as yet undefined mechanism, in skeletal muscle function. In rabbit intestinal epithelial cells, gelsolin was associated with the cytoplasm and the terminal web region of the brush border, a localization distinct from that previously reported for villin, a structurally and functionally similar protein isolated from the brush borders of chicken intestinal epithelial cells. In conclusion, our findings support the idea that gelsolin is involved in the regulation of movement and suggest that gelsolin-mediated Ca2+-regulation of actin cytoskeletal structure, first characterized in macrophages, may be of general importance.
Membrane flow during nematode spermiogenesis.
Authors: Roberts T M , Ward S
Published: May 2004

Two distinct types of surface membrane rearrangement occur during the differentiation of Caenorhabditis elegans spermatids into amoeboid spermatozoa. The first, detected by the behavior of latex beads attached to the surface, is a nondirected, intermittent movement of discrete portions of the membrane. This movement starts when spermatids are stimulated to differentiate and stops when a pseudopod is formed. The second type of movement is a directed, continual flow of membrane components from the tip of the pseudopod to its base. Both membrane glycoproteins and fluorescent phospholipids inserted in the membrane flow backward at the same rate, approximately 4 micrometers/min, although their lateral diffusion coefficients in the membrane differ by at least a factor of 5. These observations suggest that pseudopodial membrane movement is due to bulk flow of membrane components away from the tip of the pseudopod.
Caenorhabditis elegans spermatozoan locomotion: amoeboid movement with almost no actin.
Authors: Nelson G A , Roberts T M , Ward S
Published: May 2004

The pseudopods of Caenorhabditis elegans spermatozoa move actively causing some cells to translocate when the sperm are dissected into a low osmotic strength buffered salts solution. On time-lapse video tapes, pseudopodial projections can be seen moving at 20-45 micrometers/min from the tip to the base of the pseudopod. This movement occurs whether or not the cell is attached to a substrate. Translocation of the cell is dependent on the substrate. Some spermatozoa translocate on acid-washed glass, but a better substrate is prepared by drying an extract of Ascaris uteri (the normal site of nematode sperm motility) onto glass slides. On this substrate more than half the spermatozoa translocate at a velocity (21 micrometers/min) similar to that observed in vivo. Translocating cells attach to the substrate by their pseudopodial projections. They always move toward the pseudopod; changes in direction are caused by changes in pseudopod shape that determine points of detachment and reattachment of the cell to the substrate. Actin comprises less than 0.02% of the proteins in sperm, and myosin is undetectable. No microfilaments are found in the sperm. Immunohistochemistry shows that some actin is localized in patches in the pseudopod. The movement of spermatozoa is unaffected by cytochalasins, however, so there is no evidence that actin participates in locomotion. Fertilization-defective mutants in genes fer-2, fer-4, and fer-6 produce spermatozoa with defective pseudopodial projections, and these spermatozoa are largely immotile. Mutants in the spermatozoa do not translocate. Thus pseudopod movement is correlated with the presence of normal projections. Twelve mutants with defective muscles have spermatozoa with normal movement, so these genes do not specify products needed for both muscle and nonmuscle cell motility.
Membrane fusion and glycosylation in the rat hepatic Golgi apparatus.
Authors: Paiement J , Rachubinski R A , Ng Ying Kin N M , Sikstrom R A , Bergeron J J
Published: May 2004

When purified Golgi fractions were incubated with UDP-[3H]galactose in the absence of Triton-X-100, radioactivity was incorporated into an endogenous lipid and several peptide acceptors. Electron microscope analysis of Golgi fractions incubated in the endogenous galactosyl transferase assay medium revealed extensive fusion of Golgi saccules. Systematic removal of constituents in the galactosyl transferase assay medium showed enhanced (minus beta-mercaptoethanol) or reduced (minus ATP, minus sodium cacodylate buffer or minus MnCl2) fusion of Golgi membranes compared to the complete medium, Stereologic analysis revealed a correlation between membrane fusion and galactosyl transferase activity (r = 0.99, P less than 0.001). Electron microscope radioautography was carried out after incubation of Golgi fractions with UDP-[3H]galactose. Silver grains were not observed over trans elements of Golgi but were revealed mainly over large fused saccules with the number of silver grains being proportionate to membrane fusion (r = 0.92, P less than 0.001). Bilayer destabilization at points of Golgi membrane fusion may act to translocate galactose across the Golgi membrane and thereby provide a fusion regulated substrate for terminal glycosylation.
Microtubule-associated proteins of HeLa cells: heat stability of the 200,000 mol wt HeLa MAPs and detection of the presence of MAP-2 in HeLa cell extracts and cycled microtubules.
Authors: Weatherbee J A , Sherline P , Mascardo R N , Izant J G , Luftig R B , Weihing R R
Published: May 2004

One of the major groups of microtubule-associated proteins (MAPs) found associated with the microtubules isolated from HeLa cells has a molecular weight of just over 200,000. Previous work has demonstrated that these heLa MAPs are similar in several properties to MAP-2, one of the major MAPs of mammalian neural microtubules, although the two types of proteins are immunologically distinct. The 200,000 mol wt HeLa MAPs have now been found to remain soluble after incubation in a boiling water bath and to retain the ability to promote tubulin polymerization after this treatment, two unusual properties also shown by neural MAP-2. This property of heat stability has allowed the development of a simplified procedure for purification of the 200,000 HeLa MAPs and has provided a means for detection of these proteins, even in crude cell extracts. These studies have also led to the detection of a protein in crude extracts of HeLa cells and in cycled HeLa microtubules which has been identified as MAP-2 on the basis of (a) comigration with calf brain MAP-2 on SDS PAGE, (b) presence in purified microtubules, (c) heat stability, and (d) reaction with two types of antibodies prepared against neural high molecular weight-MAPs, one of these a monoclonal antibody against hog brain MAP-2, although present in HeLa cells, is at all stages of microtubule purification a relatively minor component in comparison to the 200,000 HeLa MAP's.
Selective isoactin release from cultured embryonic skeletal muscle cells.
Authors: Rubenstein P , Ruppert T , Sandra A
Published: May 2004

The culture medium of embryonic quail myoblasts, labeled for 24 h with [35S]L-methionine, was analyzed by two-dimensional gel autoradiography. The major polypeptide observed had a 43,000 molecular weight and an isoelectric point of 5.4. This polypeptide could be specifically adsorbed to DNAse-I Sepharose. A tryptic peptide map of the [35S]methionine-labeled peptides of intracellular actin and the extracellular major polypeptide were virtually identical. These findings identify the released polypeptide as actin. A comparison of two-dimensional gel patterns of intracellular and extracellular labeled polypeptides showed a large number of differences indicating the actin release did not result from general cellular breakdown. The released actin was not filamentous as judged by its behavior during Bio-Gel A-5m chromatography (Bio-Rad Laboratories, Richmond, Calif.) The released actin did not originate solely from contaminating fibroblasts in the culture because actin was also observed in the medium in clonal myoblast cultures and in purified myotube preparations. Finally, the nonmuscle isoactins, as opposed to muscle alpha-isoactin, were released preferentially. These results indicate that within the developing muscle cell where both muscle and nonmuscle specific isoactins are simultaneously present, the different isoactins may be physically or functionally compartmentalized with the nonmuscle isoactins existing primarily at or near the cell surface.
Acetylcholine receptor: effects of proteolysis on receptor metabolism.
Authors: Hatzfeld J , Miskin R , Reich E
Published: May 2004

Previous studies (Miskin, R., T. G. Easton, and E. Reich, 1970, Cell. 15:1301-1312) have shown that sarcoma virus transformation and tumor promoters reduced the cell surface concentration of acetylcholine receptors (AChR) in differentiating chick embryo myogenic cultures. Both of these agents also induced high rates of plasminogen activator (PA) synthesis in myogenic cultures (Miskin, R., T. G. Easton, A. Maelicke, and E. Reich, 1978, Cell. 15:1287-1300), and the present work was performed to establish whether proteolysis might significantly affect receptor metabolism. Proteolysis in myogenic cultures was modulated by one or more of the following: stimulation of PA synthesis, direct addition of plasmin, removal of plasminogen, or addition of plasmin inhibitors. The results were: (a) When the rates of proteolysis were raised either by addition of plasmin or by stimulating PA synthesis in the presence of plasminogen, both the steady-state concentration and the half-life of surface AChR decreased, but the rate of receptor synthesis was unaffected. (b) The magnitude of these effects, and their dependence on added plasminogen, indicated that proteolysis initiated by plasminogen activation could account almost entirely for the reduction in receptor half-life produced by sarcoma virus transformation and phorbol ester. (c) The rate of receptor synthesis, which is also reduced by viral transformation and tumor promoters, was not modified by proteolysis; hence plasmin action may be responsible for a large part, but not all of the change in surface receptor under these conditions. (d) The plasmin catalysed changes in receptor parameters appear to occur in response to modified membrane metabolism resulting from proteolysis of surface components other than AChR itself.
Stable polymers of the axonal cytoskeleton: the axoplasmic ghost.
Authors: Morris J R , Lasek R J
Published: May 2004

We have examined the monomer-polymer equilibria which form the cytoskeletal polymers in squid axoplasm by extracting protein at low concentrations of monomer. The solution conditions inside the axon were matched as closely as possible by the extraction buffer (buffer P) to preserve the types of protein associations that occur in axoplasm. Upon extraction in buffer P, all of the neurofilament proteins in axoplasm remain polymerized as part of the stable neurofilament network. In contrast, most of the polymerized tubulin and actin in axoplasm is soluble although a fraction of these proteins also exists as a stable polymer. Thus, the axoplasmic cytoskeleton contains both stable polymers and soluble polymers. We propose that stable polymers, such as neurofilaments, conserve cytoskeletal organization because they tend to remain polymerized, whereas soluble polymers increase the plasticity of the cytoskeleton because they permit rapid and reversible changes in cytoskeletal organization.
Direct communication of homologous and heterologous endocrine islet cells in culture.
Authors: Meda P , Kohen E , Kohen C , Rabinovitch A , Orci L
Published: May 2004

The transfer of 6-carboxyfluorescein between islet cells in monolayer culture was observed by fluorescence microscopy, and the endocrine cells involved in this transfer were identified by immunohistochemistry and electron microscopy. The results show that carboxyfluorescein was directly exchanged between homologous B-cells and also between B- and A- or D-cells. Successive microinjections of the probe into different cells of the same cluster showed the existence of separate territories, each formed by 2-8 communicating cells. Intercellular communication was not observed after every dye microinjection, and communicating and noncommunicating islet cells were found to coexist within the same cluster. The data indicate that the exchange of exogenous cytoplasmic molecules occurs between different types of endocrine islet cells. However, within a single cluster, all islet cells are not metabolically coupled to one another, at a given time.
Quantitation of two endogenous lactose-inhibitable lectins in embryonic and adult chicken tissues.
Authors: Beyer E C , Barondes S H
Published: May 2004

Two lactose-binding lectins from chicken tissues, chicken-lactose-lectin-1 (CLL-1) and chicken-lactose-lectin-11 (CLL-11) were quantified with a radioimmunoassay in extracts of a number of developing and adult chicken tissues. Both lectins could be measured in the same extract without separation, because they showed not significant immunological cross-reactivity. Many embryonic and adult tissues, including brain, heart, intestine, kidney, liver, lung, muscle, pancreas, and spleen, contained one or both lectins, although their concentrations differed markedly. For example, embryonic muscle, the richest source of CLL-1 contained only traces of CLL-11 whereas embryonic kidney, a very rich source of CLL-11 contained substantial CLL-1. In both muscle and kidney, lectin levels in adulthood were much lower than in the embryonic state. In contrast, CLL-1 in liver and CLL-11 in intestine were 10-fold to 30-fold more concentrated in the adult than in the 15-d embryo. CLL-1 and CLL-11 from several tissues were purified by affinity chromatography and their identity in the various tissues was confirmed by polyacrylamide gel electrophoresis, isoelectric focusing, and peptide mapping. The results suggest that these lectins might have different functions in the many developing and adult tissues in which they are found.
Interaction of the cytoskeletal framework with acetylcholine receptor on th surface of embryonic muscle cells in culture.
Authors: Prives J , Fulton A B , Penman S , Daniels M P , Christian C N
Published: May 2004

To monitor the interaction of cell surface acetylcholine (AcCho) receptors with the cytoskeleton, cultured muscle cells were labeled with radioactive or fluorescent alpha-bungarotoxin and extracted with Triton X-100, using conditions that preserve internal structure. A significant population of the AcCho receptors is retained on the skeletal framework remaining after detergent extraction. The skeleton organization responsible for restricting AcCho receptors to a patched region may also result in their retention after detergent extraction.
Spectroscopic assays for measuring quantities of erythrocyte membrane "halves".
Authors: Fisher K A
Published: May 2004

The quantities of outer and inner"halves" produced by freeze-fracturing human erythrocyte membranes have been measured by visible and fluorescence spectroscopy. Assays have been developed that are based on the use of two membrane surface markers: hemoglobin (Hb), a native marker for the cytoplasmic side of the membrane, and fluoresceinated concanavalin A (FITC-Con-A), a marker for the extracellular side. Hb absorbance is proportional to the fraction of cytoplasmic "half" membranes, and FITC fluorescence is proportional to the fraction of extracellular "halves." A procedure is described for the preparation of surface-labeled, intact erythrocytes suitable for the formation of homogeneous, planar cell monolayers of square-centimeter dimensions on polylysine-treated glass (PL-glass). Cell monolayers were frozen and fractured, and the fractions of absorbance and fluorescence in each of the two split portions determined. The PL-glass portion of membrane contained a substantially higher ratio of fluorescence to absorbance than unsplit controls, and its paired portion, a complementary lower ratio, demonstrating that the PL-glass portion was significantly enriched in extracellular "half" membrane. Experiments investigating split membrane recovery show that the double labeled membrane splitting technique is well suited to analysis of the transmembrane distribution of membrane lipids and polypeptides using methods that do not require quantitation by electron microscopy.
Comparative analysis of the major polypeptides from liver gap junctions and lens fiber junctions.
Authors: Hertzberg E L , Anderson D J , Friedlander M , Gilula N B
Published: May 2004

Gap junctions from rat liver and fiber junctions from bovine lens have similar septilaminar profiles when examined by thin-section electron microscopy and differ only slightly with respect to the packing of intramembrane particles in freeze-fracture images. These similarities have often led to lens fiber junctions being referred to as gap junctions. Junctions from both sources were isolated as enriched subcellular fractions and their major polypeptide components compared biochemically and immunochemically. The major liver gap junction polypeptide has an apparent molecular weight of 27,000, while a 25,000-dalton polypeptide is the major component of lens fiber junctions. The two polypeptides are not homologous when compared by partial peptide mapping in SDS. In addition, there is not detectable antigenic similarity between the two polypeptides by immunochemical criteria using antibodies to the 25,000-dalton lens fiber junction polypeptide. Thus, in spite of the ultrastructural similarities, the gap junction and the lens fiber junction are comprised of distinctly different polypeptides, suggesting that the lens fiber junction contains a unique gene product and potentially different physiological properties.
Correlation between effects of 24 different cytochalasins on cellular structures and cellular events and those on actin in vitro
Authors: Yahara I , Harada F , Sekita S , Yoshihira K , Natori S
Published: May 2004

To compare the effects of cytochalasins on the cellular level with those on the molecular level, 24 cytochalasins, 20 natural compounds and 4 derivatives, were used. The following effects were tested for each of 24 cytochalasins; (a) four high dose (2-20 muM) effects on the cellular level: rounding up of fibroblastic cells, contraction of actin cables, formation of hairy filaments containing actin, and inhibition of lymphocyte capping; (b) a low dose (0.2-2 muM) effect: inhibition of membrane ruffling; and (c) two in vitro effects: an inhibition of actin filament elongation (the high affinity effect [low dose effect] in vitro) and an effect on viscosity of actin filaments(the low affinity effect [high dose effect] in vitro). These results indicated that there are almost the same hierarchic orders of relative effectiveness of different cytochalasins between low and high dose effects and between cellular and molecular effects. From the data obtained with the 24 cytochalasins, we have calculated correlation coefficients of 0.87 and 0.79 between an effect in vivo, inhibition of capping, and an effect in vitro, inhibition of actin filament elongation, as well as between inhibition of capping and another effect in vitro, effect on viscosity of actin filaments, respectively. Furthermore, a correlation coefficient between the high affinity effect and the low affinity effect determined in vitro was calculated to be 0.90 from the data obtained in this study. The strong positive correlation among low and high dose effects in vivo and those in vitro suggests that most of the effects caused by a cytochalasin, irrespective of doses or affected phenomena, might be attributed to the interaction between the drug and the common target protein, actin.

In the course of the immunofluorescence microscope study on cytochalasin-treated cells using actin antibody, we have found that aspochalasin D, a 10-isopropylcytochalasin, strongly induced the formation of rodlets containing actin in the cytoplasm of the treated fibroblasts. In contrast, the other cytochalasins, including cytochalasin B, cytochalasin C, cytochalasin D, and cytochalasin H, were found to induce the formation of nuclear rodlets. Both cytoplasmic and nuclear rodlets found in the cytochalasin-treated cells were similar in ultrastructures to those induced by 5 to 10 percent (vol/vol) dimethyl sulfoxide in the same type of cells.
Action of cytochalasin D on cytoskeletal networks.
Authors: Schliwa M
Published: May 2004

Extraction of SC-1 cells (African green monkey kidney) with the detergent Triton X-100 in combination with stereo high-voltage electron microscopy of whole mount preparations has been used as an approach to determine the mode of action of cytochalasin D on cells. The cytoskeleton of extracted BSC-1 cells consists of substrate-associated filament bundles (stress fibers) and a highly cross-linked network of four major filament types extending throughout the cell body; 10-nm filaments, actin microfilaments, microtubules, and 2- to 3-nm filaments. Actin filaments and 2- to 3-nm filaments form numerous end-to-side contacts with other cytoskeletal filaments. Cytochalasin D treatment severely disrupts network organization, increases the number of actin filament ends, and leads to the formation of filamentous aggregates or foci composed mainly of actin filaments. Metabolic inhibitors prevent filament redistribution, foci formation, and cell arborization, but not disorganization of the three-dimensional filament network. In cells first extracted and then treated with cytochalasin D, network organization is disrupted, and the number of free filament ends is increased. Supernates of preparations treated in this way contain both short actin filaments and network fragments (i.e., actin filaments in end-to-side contact with other actin filaments). It is proposed that the dramatic effects of cytochalasin D on cells result from both a direct interaction of the drug with the actin filament component of cytoskeletal networks and a secondary cellular response. The former leads to an immediate disruption of the ordered cytoskeletal network that appears to involve breaking of actin filaments, rather than inhibition of actin filament-filament interactions (i.e., disruption of end-to-side contacts). The latter engages network fragments in an energy-dependent (contractile) event that leads to the formation of filament foci.
Role of proteoglycans in endochondral ossification: immunofluorescent localization of link protein and proteoglycan monomer in bovine fetal epiphyseal growth plate.
Authors: Poole A R , Pidoux I , Rosenberg L
Published: May 2004

The hypothesis is widely held that, in growth plate during endochondral ossification, proteoglycans in the extracellular matrix of the lower hypertrophic zone are degraded by proteases and removed before mineralization, and that this is the mechanism by which a noncalcifiable matrix is transformed into a calcifiable matrix. We have evaluated this hypothesis by examining the immunofluorescent localization and concentrations of proteoglycan monomer core protein and link protein, and the concentrations of glycosaminoglycans demonstrated by safranin 0 staining, in the different zones of the bovine fetal cartilage growth plate. Monospecific antibodies were prepared to proteoglycan monomer core protein and to link protein. The immunofluorescent localization of these species was examined in decalcified and undecalcified sections containing the zones of proliferating and hypertrophic chondrocytes and in sections containing the zones of proliferating and hypertrophic chondrocytes and the metaphysis, decalcified in 0.5 M EDTA, pH 7.5, in the presence of protease inhibitors. Proteoglycan monomer core protein and link protein are demonstrable without detectable loss throughout the extracellular matrix of the longitudinal septa of the hypertrophic zone and in the calcified cartilage of the metaphysis. In fact, increased staining is observed in the calcifying cartilage. Contrary to the prevailing hypothesis, our results indicate that there is no net loss of proteoglycans during mineralization and that the proteoglycans become entombed in the calcified cartilage which provides a scaffolding on which osteoid and bone are formed. Proteoglycans appear to persist unaltered in the calcified cartilage core of the trabeculae, until at last the entire trabeculae are eroded from their surfaces and removed by osteoclasts, when the primary spongiosa is replaced by the secondary spongiosa.
Enzymatic basis for a lectin-resistant phenotype: increase in a fucosyltransferase in mouse melanoma cells.
Authors: Finne J , Burger M M , Prieels J P
Published: May 2004

In the search for the biochemical basis of the control of glycosylation of cell surface carbohydrates, revertant clones were isolated from previously characterized wheat germ agglutinin-resistant clones of B16 mouse melanoma cells by selection for resistance to Lotus tetragonolobus lectin or to ricin. Comparison of the wheat germ agglutinin-resistant clones with the parent and revertant clones indicated that this phenotype was correlated with an increased sensitivity to the Lotus lectin, a 60- to 70-fold increase in alpha 1 leads to 3 fucosyltransferase activity and a decreased sialic acid content of the N-glycosidic chains of glycoproteins. The results suggest a novel type of control mechanism for lectin resistance, an increase in a glycosyltransferase activity. The presence of alpha 1 leads to 3 bound fucose on N-acetylglucosamine residues would interfere with the addition of sialic acid by alpha 2 leads to 3 linkages to galactose residues in the carbohydrate units, and this change could explain the resistance to wheat germ agglutinin and the increased sensitivity to the Lotus lectin. A change in a regulatory gene for the fucosyltransferase as a possible primary cause for the changed phenotype is discussed.
Identification of phagocytosis-associated surface proteins of macrophages by two-dimensional gel electrophoresis.
Authors: Howard F D , Petty H R , McConnell H M
Published: May 2004

Two-dimensional PAGE (P. Z. O'Farrell, H. M. Goodman, and P. H. O'Farrell. 1977. Cell. 12:1133-1142) has been employed to assess the effects of antibody-dependent phagocytosis on the cell surface protein composition of RAW264 macrophages. Unilamellar phospholipid vesicles containing 1% dinitrophenyl-aminocaproyl-phosphatidylethanolamine (DNP-cap-PE) were used as the target particle. Macrophages were exposed to anti-DNP antibody alone, vesicles alone, or vesicles in the presence of antibody for 1 h at 37 degrees C. Cell surface proteins were then labeled by lactoperoxidase-catalyzed radioiodination at 4 degrees C. After detergent solubilization, membrane proteins were analyzed by two-dimensional gel electrophoresis. The resulting pattern of spots was compared to that of standard proteins. We have identified several surface proteins, not apparently associated with the phagocytic process, which are present either in a multichain structure or in several discretely charged forms. After phagocytosis, we have observed the appearance of two proteins of 45 and 50 kdaltons in nonreducing gels. In addition, we have noted the disappearance of a 140-kdalton protein in gels run under reducing conditions. These alterations would not be detected in the conventional one-dimensional gel electrophoresis. This evidence shows that phagocytosis leads to a modification of cell surface protein composition. Our results support the concept of specific enrichment and depletion of membrane components during antibody-dependent phagocytosis.
Functional angiotensin II receptors in cultured vascular smooth muscle cells.
Authors: Gunther S , Alexander R W , Atkinson W J , Gimbrone M A
Published: May 2004

To study cellular mechanisms influencing vascular reactivity, vascular smooth muscle cells (VSMC) were obtained by enzymatic dissociation of the rat mesenteric artery, a highly reactive, resistance-type blood vessel, and established in primary culture. Cellular binding sites for the vasoconstrictor hormone angiotensin II (AII) were identified and characterized using the radioligand 125I-angiotensin II. Freshly isolated VSMC, and VSMC maintained in primary culture for up to 3 wk, exhibited rapid, saturable, and specific 125I-AII binding similar to that seen with homogenates of the intact rat mesenteric artery. In 7-d primary cultures, Scatchard analysis indicated a single class of high-affinity binding sites with an equilibrium dissociation constant (Kd) of 2.8 +/- 0.2 nM and a total binding capacity of 81.5 +/- 5.0 fmol/mg protein (equivalent to 4.5 x 10(4) sites per cell). Angiotensin analogues and antagonists inhibited 125I-AII binding to cultured VSMC in a potency series similar to that observed for the vascular AII receptor in vivo. Nanomolar concentrations of native AII elicited a rapid, reversible, contractile response, in a variable proportion of cells, that was inhibited by pretreatment with the competitive antagonist Sar1,Ile8-AII. Transmission electron microscopy showed an apparent loss of thick (12-18 nm Diam) myofilaments and increased synthetic activity, but these manifestations of phenotypic modulation were not correlated with loss of 125I-AII binding sites or hormonal responsiveness. Primary cultures of enzymatically dissociated rat mesenteric artery VSMC thus may provide a useful in vitro system to study cellular mechanisms involved in receptor activation-response coupling, receptor regulation, and the maintenance of differentiation in vascular smooth muscle.