Biomedical subjects

K Weber

Publications and source records attributed to K Weber.

At least 595 records · Page 33Linked to original sources

PubMed1981

An immunofluorescence microscopical study of the neurofilament triplet proteins, vimentin and glial fibrillary acidic protein within the adult rat brain.

A collection of antibodies specific to different intermediate filament proteins were applied to frozen sections of adult rat brains. The relative distribution of these proteins was then studied using double label immunofluorescence microscopy. Antibodies specific to each of the neurofilament "triplet" proteins (of approximate molecular weight 68 K, 145 K and 200 K) stained exclusively neuronal structures. The distribution of these three antigens was in general identical, except that certain neurofilament populations such as those in the dendrites and cell bodies of pyramidal cells of the hippocampus and cerebral cortex, contained relatively little if any 200 K protein. Some neurone populations, such as the granule cells of the cerebellar cortex, could not be visualized by neurofilament antibodies, indicating that neurofilaments may not be essential for function of all neurones in vitro. Antibodies to GFA and vimentin stained an entirely different population of processes, none of which stained with any of the neurofilament antibodies. Vimentin antibody stained sheath material around the brain, a monolayer of ependymal cell bodies lining the ventricles, fibrous material associated within the choroid plexus, the walls of blood vessels and capillaries, and the processes of cells in certain regions. GFA antibody stained a second layer of sheath material under the vimentin layer, and numerous processes visible throughout the brain. Some specific populations of GFA-positive processes proved to stain also with vimentin. These included the processes of Golgi "epithelial" cells (Bergmann glial fibres), those of certain astrocytes in bundles of myelinated fibers. In addition, some processes apparently derived from ependymal cells proved to stain for both vimentin and GFA, whilst other could only be reliably visualized by vimentin alone. These results are discussed in terms of the previously described morphological characteristics of the various cell types of the brain.

Animals↗

PubMed1981

The cytoskeleton of blood platelets viewed by immunofluorescence microscopy.

Immunofluorescence microscopy has been used to characterize the morphological transitions that occur as platelets spread on a surface. Antibodies to the microfilament-specific proteins, actin, myosin, tropomyosin, alpha-actinin and filamin as well as antibodies to tubulin were used. Antibody to tubulin reveals the marginal band of microtubules as a bright fluorescent ring, the diameter of which decreases at a time coincident with pseudopod formation. The latter process is dictated by the assembly of microfilament bundles. Although the change in morphology of the platelet was not studied in detail, our data support the idea that microfilament reorganization influences the display of the marginal band of microtubules. A further conclusion is that the platelet in spite of its small diameter is a system suitable for immunofluorescence microscopy, a method which allows the rapid and simultaneous screening of many cells.

Actinin↗

PubMed1981

Actin rearrangement in living cells revealed by microinjection of a fluorescent phalloidin derivative.

A fluorescent derivative of phalloidin with a high affinity for F-actin was microinjected into tissue culture cells and its intracellular reorganization was followed by TV image intensification and video recording. When the F-actin stabilizing drug is used at concentrations, which do not inhibit cellular movement, rearrangement of fluorescently labelled microfilament bundles can be followed directly. We discuss the possibility that active ruffles are governed by structural rules different from those applying to stress fibers and raise the possibility that actin may be released from microfilaments in a form different from G-actin.

Actins↗

PubMed1981

Coiling of intermediate filaments induced by microinjection of a vimentin-specific antibody does not interfere with locomotion and mitosis.

Microinjection of polyclonal sheep anti-vimentin IgGs purified by affinity chromatography into a rat fibroblastoid line leads to a specific reorganization of the cytoskeleton. Immunofluorescence microscopy shows that cytoplasmic microtubules and microfilaments are unaffected by intermediate filaments collapse and are collected into a tight perinuclear cap containing antibody-crosslinked vimentin filaments. The crosslinking was further documented by electron microscopy after treatment with Triton X-100 and ferritin-labelled anti-sheep IgGs. Inspite of the presence of the caps, which are retained for about 30 h, cells show a normal morphology and are locomotive. The collapsed intermediate filaments do not interfere with subsequent mitosis or with cytokinesis. After mitosis the capped filaments can be distributed either to both daughter cells or to only one of the two daughter cells.

Animals↗

PubMed1981

Vimentin, the 57 000 molecular weight protein of fibroblast filaments, is the major cytoskeletal component in immature glia.

Comparison of cytoskeletal preparations obtained from newborn and adult rat brain showed similar patterns on SDS-PAGE. However, coelectrophoresis of the newborn and adult preparations revealed distinct differences in the mobility of 2 major bands in the molecular weight range of 50--70 000. In adult brain cytoskeletons, the main band in the 50 000 range co-migrated with purified rat GFA protein (apparent molecular weight 53 000). No major band co-migrated with purified rat vimentin (apparent molecular weight 57 000). The reverse was true for newborn brain cytoskeleton. In adult and newborn brain cytoskeleton a major band co-migrated with the 150 000 neurofilament polypeptide isolated from rat spinal cord by immunoaffinity chromatography. Another neurofilament polypeptide (apparent molecular weight 72 000) was prominent in adult but not in newborn brain cytoskeleton. Conversely, newborn brain cytoskeleton comprised a band trailing behind the 72 000 neurofilament polypeptide. This band was not present in adult brain cytoskeleton. The distribution of vimentin in newborn rat brain was studied by immunofluorescence microscopy and compared to the distribution of GFA protein. As previously reported, a relatively limited number of GFA positive cells are present in the brain at this stage compared to later in development. Conversely, the large number of vimentin positive cells in newborn brain was well in keeping with the presence of a prominent vimentin band in cytoskeletal preparations obtained from this tissue. With the exception of meninges and blood vessels, vimentin appeared to be mainly localized in immature glia: periventricular glia; glia in non-myelinated white matter; radial glia in cerebral cortex and basal ganglia; Bergmann glia in cerebellum (Bergmann glia are still GFA negative in newborn rat). The neuroblastic germinal layers in hippocampus and cerebellum did not stain with vimentin antisera.

Animals↗

PubMed1980

Calmodulin-binding proteins of the microfilaments present in isolated brush borders and microvilli of intestinal epithelial cells.

Isolated microfilament cores of intestinal microvilli are known to contain actin and four major associated proteins among which is calmodulin. Immunofluorescence microscopy reveals that calmodulin is present in the microvilli prior to biochemical fractionation of intestinal cells and thus is not bound artifactually during the isolation procedure. Identification of the major microvillus calmodulin-binding protein was achieved by the use of an [125I]calmodulin gel overlay technique. Proteins of microvilli or brush borders were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After removal of sodium dodecyl sulfate, direct binding of radiolabeled calmodulin to the separated polypeptides was assayed by autoradiography. Three calmodulin-binding polypeptides are detected in brush borders. Two polypeptides (apparent Mr = 280,000 and 140,000) show Ca2+ -dependent binding, whereas the third polypeptide (Mr = 110,000) can bind calmodulin in the presence or absence of Ca2+. Microvillus core filaments contain only the latter species. Microvillus cores treated with 25 mM Mg2+ retain calmodulin and the 110,000 polypeptide, whereas the other two associated proteins are greatly reduced, consistent with the hypothesis that the 110,000 protein is the major calmodulin-binding protein of the core filament structure. We discuss the currently documentable structure of the core filaments and evaluate the general usefulness of the calmodulin gel overlay technique.

Animals↗

PubMed1980

Different tubulin polymers are produced by microtubule-associated proteins MAP2 and tau in the presence of guanosine 5'-(alpha, beta-methylene)triphosphate.

Tubulin and the two microtubule-associated proteins MAP2 and tau were purified from pig brain. The ability of MAP2 and tau to induce tubulin polymerization in the presence of guanyl-5'-yl methylene diphosphonate was compared in parallel experiments. MAP2 at 0.2 mol/mol of tubulin induced the polymerization of tubulin exclusively into ribbons 0.45 +/- 0.05 micrometer long with an average of six protofilaments. At the same molar ratio, tau promoted the polymerizaton of tubulin exclusively into microtubules. These results strongly suggest that MAP2 and tau are functionally different proteins.

Animals↗

PubMed1980

Guanasone 5'-(alpha,beta-methylene)triphosphate enhances specifically microtubule nucleation and stops the treadmill of tubulin protomers.

Substitution of pp(CH2)pT for GTP in the polymerization of microtubular protein results in a marked enhancement of both the rate and the extent of microtubule nucleation. Comparison of the kinetics of microtubule polymerization and pp(CH2)pG hydrolysis reveals that massive microtubule nucleation occurs in the absence of pp(CH2)pG hydrolysis. The shortest microtubule nuclei formed in the presence of pp(CH2)pG are curled ribbons on three protofilaments 0.15 to 0.2 micrometer long. No specific effect of pp(CH2)pG on microtubule propagation is observed. Nucleotide chase experiments suggest that the rings of microtubular protein present at 4 degrees C are not incorporated directly into the microtubule. Microtubules polymerized by pp(CH2)pG do not show the treadmill of tubulin protomers characteristic of the microtubules polymerized by GTP. Nucleotide analysis of microtubules polymerized by pp(CH2)pG and GTP reveals that 95% of the exchangeable nucleotide contained in the microtubules is p(CH2)pG and GDP, respectively. pp(CH2)pG blocks the treadmill of tubulin protomers from microtubules assembled by GTP by suppressing depolymerization at the depolymerization end of the microtubule. On the other hand, GTP promotes the treadmill of tubulin from microtubules assembled by pp(CH2)pG by reactivating the depolymerization end of the microtubule.

Animals↗

PubMed1980

Vegetative Dictyostelium cells containing 17 actin genes express a single major actin.

Although actin is highly conserved between different eukaryotic species, six tissue-specific actins have been characterised in higher vertebrates by complete amino acid sequence analysis (two cytoplasmic actins, two smooth muscle actins and two sarcomeric actins). Their tissue specificity suggests they may differ in some important although unknown physiological property. Actin expression in lower eukaryotes seems to be a simpler process than in higher eukaryotes since biochemical experiments have indicated only one major type in purified preparations from various species. However, Firtel et al. have isolated several recombinant plasmids containing sequences of Dictyostelium discoldeum DNA complementary to actin messenger RNA and have suggested that this unicellular slime mould may have 17 actin genes potentially giving rise to several different actins. We have, therefore, determined the complete amino acid sequence of actin from vegetative Dictyostelium cells. This sequence is unique and agrees with the DNA sequences of four actin genes for that region of the DNA, which is currently known. The protein sequence does not agree with the three other 'genes' and we discuss the possible expression of minor actin species.

Actins↗

PubMed1980

[Q fever].

Explore the source record for details and available documents.

Adult↗

PubMed1980

Organization and spatial arrangement of fluorescein-labeled native actin microinjected into normal locomoting and experimentally influenced Amoeba proteus.

Fully polymerization-competent fluorescein-labeled actin from skeletal muscle was microinjected into both normal moving and experimentally treated Amoeba proteus. Its intracellular distribution was followed by integral image intensification of the fluorescence on a television screen and compared with controls injected with rhodamine-labeled serum albumin. The labeled actin was incorporated into the endogenous actin pool and exhibited a characteristic redistribution depending on the cellular morphology. Increased amounts of labeled actin could be detected within a thin layer separating the hyalo- and granuloplasm or running immediately beneath the plasma membrane when hyaloplasmic regions were absent. The topography of the fluorescent layer demonstrated in living cells is in agreement with the cortical microfilament layer described ultrastructurally recently in corresponding cells. The combined results emphasize the important role of the cortical filament layer in both morphogenetic processes (e.g., hyalo-granuloplasm separation or changes in cell shape) and motive force generation for cytoplasmic streaming and amoeboid movement.

Actins↗

PubMed1980

Pinocytosis and locomotion of amoebae. XV. Visualization of Ca++-dynamics by chlorotetracycline (CTC) fluorescence during induced pinocytosis in living Amoeba proteus.

The dynamics of Ca++ during induced pinocytosis were studied in Amoeba proteus using chlorotetracycline (CTC). The fluorescence of the Ca++ - CTC-complex was monitored by an image intensification system, which has certain advantages over standard equipment: (1) Living cells are not subjected to the damaging influence of intensive microscopic illumination, (2) fluorescent probes are not bleached during observation, and (3) the rapid dynamics of the Ca++ -fluxes can be recorded using short exposure times. The results demonstrate the existence of Ca++ bound to intracellular and extracellular sites of the cell membrane complex in normal locomoting and pinocytotic Amoeba proteus. The application of cations inducing pinocytosis causes a rapid decrease in the external CTC-fluorescence probably due to a release of Ca++ from the mucous layer. The degree of fluorescence intensity is correlated with the capacity of pinocytotic channel formation, i.e., the fluorescence decreases as the number of channels increases. During the phase of vesiculation a distinct fluorescence mainly restricted to the basal region of the channels is observed. Intracellular Ca++ was detected in close vicinity to the plasma membrane after both microinjection and external application of CTC. The internal CTC-fluorescence is slightly decreased during the induction phase of pinocytosis. The observations are in good agreement with previous results on the localization of Ca++ -binding sites at the plasma membrane of Amoeba proteus and demonstrate the important role of Ca++ -fluxes for the process of pinocytosis.

Amoeba↗

PubMed1980

[Influence of chloroquine on the hexachlorobenzene-induced porphyria. Investigations in the skin, liver, and urine (author's transl)].

Rats were fed with a diet containing hexachlorobenzene (HCB) for about 60 days. At this time the porphyria was manifst as shown by significantly elevated porphyrins. Thereafter, chloroquine (CQ) was additionally given over a period of at lest 6 weeks. At the end of the experiment the urinary porphyrin excretion and the porphyrin content in lijver and skin were diminished in HCB-CQ-treated animals by about 50% compared to the HCB controls. The relative porphyrin distribution pattern was not influenced by CQ. In a further investigation the prophylactic effect of CQ could be demonstrated. Rats given CQ simultaneously from the beginning of the HCB feeding showed a significantly delayed onset of porphyria. It is concluded from our results that CQ does not only form complexes with porphyrins during the treatment of th HCB porphyria. We rather assume an effect of CQ on the metabolism of iron.

Animals↗

PubMed1980