Species-dependent immunological differences between vertebrate brain tubulins

Tubulins from different higher plant species are immunologically nonidentical and bind colchicine differentially

We have initiated immunological and drug-binding studies on the tubulins from different higher plant species. Antibodies were raised against electrophoretically separated rose (Rosa sp.) tubulin alpha- and beta-subunits and characterized by immunoblot autoradiographic assays. Each IgG preparation bound to its antigen and cross-reacted differentially with the respective tubulin subunits from an alga, sea urchin, rabbit, and cow. Antigenic determinants were shared more among the beta-subunits than among the alpha-subunits from these organisms. Tubulins were isolated from cultured cells of carrot (Daucus carota) and hibiscus (Hibiscus rosa-senensis). Immunoautoradiography and quantitation of cross-reactivity on blots showed nonidentity among homologous subunits from rose, carrot, hibiscus, and alga tubulins, with more antigenic differences among alpha-subunits than among beta-subunits. Comparative colchicine-binding assays showed that rose and hibiscus tubulins bound 33% and 65%, respectively, of the colchicine bound by carrot tubulin and that higher plant tubulins bound much less colchicine than bovine brain tubulin under identical conditions.

Monoclonal antibody that preferentially binds polylysine, polyarginine, and histones and selectively decorates nuclei and chromosomes

A monoclonal antibody, designated J-57, selectively and uniformly decorates the interphase nuclei and mitotic chromosomes of a variety of eucaryotic cells as determined by indirect immunofluorescence. As determined by enzyme-linked immunosorbent assay, however, this monoclonal antibody is not monospecific. It reacts weakly with cytochrome c, RNase A, and brain tubulin. By these tests monoclonal antibody J-57 has broad cross-reactivity similar to that of antisera directed against polylysine. The differential reactions of this monoclonal antibody suggest that it may be a useful immunohistochemical probe for nuclei and chromosomes in whole cells.

Extraction and immunochemical assays of a tubulin-like factor in cotton seedlings

Antibodies to tubulin were prepared in rabbits by immunization with reduced-carboxymethylated calf-brain tubulin. In immunodiffusion tests the antibodies showed full cross reactivity with the immunogen as well as with native calf-brain tubulin. The same antibodies showed cross reactivity with a factor in extract of cotton (Gossypium hirsutum L.) cotyledons but there was no full immunological identity between calf-brain tubulin and this factor. A solid-phase radioimmunoassay for quantitative estimation of this plant tubulin-like factor was developed. It measured the binding of antibodies to immobilized calf-native tubulin. Competition between the unknown soluble tubulin-like factor, and immobilized tubulin was assayed at serum dilution of 1:50. Extraction conditions which preserved the antigenic properties of the tubulin-like factor from cotton cotyledons were defined. The radioimmunoassay measured quantities of the tubulin-like factor in the range of 0.1-10 μg-equivalents of calf-brain tubulin. Immediately after homogenization of the tissue only 25% of the total amount of tubulin-like activity was present in soluble form, while most of it remained in the insoluble fraction. Apparent maximal solubilization was achieved spontaneously 10 h after homogenization or by treatment with guanidine hydrochloride. These results indicate that in this material, tubulin is not released immediately by homogenization but remains assembled in microtubules and-or in a bound or sequestered form.

Rat monoclonal antitubulin antibodies derived by using a new nonsecreting rat cell line

Hybrid myeloma cell lines secreting monoclonal antibodies to tubulin have been prepared using rat myelomas and spleen cells from rats immunized with yeast tubulin. A comparison between the results obtained with the rat myeloma Y3-Ag 1.2.3., which secretes a light chain, and a new line, YB2/O, which does not, shows that they are both excellent parental lines and that the second produces hybrids with no myeloma chain components. The antitubulin antibodies in the serum of rats bearing two of the hybrid myeloma tumors gave titers of up to 1:10(6) from which large amounts of monoclonal antibodies could be easily purified. They recognized tubulin from yeast as well as from birds and mammals. The two antibodies gave clear immunofluorescent staining of yeast mitotic spindles as well as the interphase microtubule network of tissue culture cells. Some difference in the pattern of immunofluorescence staining of yeast cells and nuclei was observed between the two antibodies. The purified antibodies could be conjugated to colloidal gold particles and used for direct labeling of yeast microtubules for electron microscopy.

Immunocytochemical study of microtubules in chromaffin cells in culture and evidence that tubulin is not an integral protein of the chromaffin granule membrane

Bovine adrenal chromaffin cells were maintained in culture in Dulbecco's modified Eagle's medium containing 20% foetal calf serum and 10 units per ml of Nerve Growth Factor. Under these conditions, chromaffin cells developed up to five neurites per cell. The neurites showed lateral branches and varicosities along their trunk which ended with thick growth cone-like structures. Cultures of chromaffin cells were stained by indirect immunofluorescence with antibodies against (a) chromogranin A to follow the distribution of chromaffin granules, the catecholamine-storing organelles, and (b) tubulin, to study the microtubular system during outgrowth of neurites. Chromogranin A antibodies showed a very intensely staining punctate pattern, not randomly distributed but localized in neurites. Chromaffin granules were found to migrate from the cell body to reach neurite endings where they were densely packed. Intense staining was also observed in varicosities; a linear arrangement of granules was evident along neurite trunks. Tubulin antibodies decorated a complex network, clearly visible at the cell periphery and also in the growth cone-like structures, in the palm region of the growth cone. Colchicine treatment effected retraction of neurites and disappearance of organized microtubule networks; chromaffin granules were found in the perinuclear region of the cell. Some tubulin (0.2% of total membrane proteins) was found in the purified chromaffin granule membrane preparation; however, this tubulin is probably associated with contaminating plasma membranes. By the criteria of morphology and staining with antitubulin antibodies, adult bovine chromaffin cells in culture display characteristics similar to those of sympathetic neurones. In addition, they showed an exaggerated transport of granules. Adult bovine chromaffin cells in culture offer an excellent model for studying the role of microtubules and the contractile apparatus in relation to cell morphological changes and neurosecretion.

Distribution of tubulin and actin in neurites and growth cones of differentiating nerve cells

Embryonic chick nerve cells, from dissociated dorsal root ganglia, were cultured on polylysine substrata and examined for tubulin and actin distribution by indirect immunofluorescence. Antibodies generated against chick brain tubulin produced specific fluorescence in growth cones, neurites, and cell bodies without revealing distribution differences or substructure in the nerve cells. However, at reduced antitubulin concentrations, differences were resolved. Tubulin fluorescence remained uniform and intense in neurites and cell bodies, but exhibited reduced intensity and patterning in growth cones. Nonneuronal cells in the cultures served as controls for typical cytoplasmic tubulin fluorescence distribution. Straining controls demonstrated that fluorescence resulted from tubulin-antitubulin binding. Analogous studies, using antibodies generated against chick brain actin, demonstrated distribution differences at reduced antiactin concentrations, including "hot spots" of intense fluorescence in growth cones and a paucity of fluorescence in neurites.

Effects of antibodies against tubulin on the movement of reactivated sea urchin sperm flagella

Antibodies binding to sea urchin flagellar outer-doublet tubulin have been isolated from rabbit sera by tubulin-affinity chromatography employing electrophoretically purified tubulin as the immobilized substrate. This procedure provides "induced" antitubulin antibody from immune sera and "spontaneous" antitubulin antibody from preimmune sera. These antitubulins were characterized in terms of their specificity, ability to bind to sea urchin axonemes, and effects on the motility of reactivated spermatozoa. Induced antitubulin antibody specifically reduced the bend angle and symmetry of the movement of demembranated reactivated spermatozoa without affecting the beat frequency. At identical concentrations, spontaneous antitubulin had no effect on motility. Affinity-purified induced antitubulins from three other rabbits all gave specific bend-angle inhibition, whereas their corresponding spontaneous antitubulins had no effect on the flagellar movement. The effects of antitubulin on microtubule sliding were examined by observing the sliding disintegration of elastase-digested axonemes induced by MgATP2+-. Affinity-purified induced antitubulin antibody, in quantities sufficient to completely paralyze reactivated flagella, did not inhibit microtubule sliding. The amplitude-inhibiting effect of induced antitubulin on reactivated spermatozoa may be caused by action on a mechanism responsible for controlling flagellar bending rather than by interference with the active sliding process. This is the first report of an antitubulin antibody having an inhibitory activity on microtubule-associated movement.

Immunological differences between actins from cardiac muscle, skeletal muscle, and brain

The antigenic similarities and differences between various actins were explored by use of antisera against purified bovine cardiac actin and chicken embryo brain actin. In double-antibody coprecipitation tests, purified iodinated actins from bovine cardiac muscle, rabbit skeletal muscle, chicken embryo brain, and bovine brain all bound to antiserum against chicken embryo brain actin. This result demonstrates the presence of shared antigenic determinants among these actins. Cardiac actin antiserum, on the other hand, bound cardiac and skeletal actin, but failed to bind significantly either brain actin. In radioimmunoassay, all four unlabeled actins were capable of some degree of inhibition of binding of (125)I-labeled chicken embryo brain actin to homologous antiserum. The results confirm the existence of shared or similar antigenic determinants, but also show that the molecules are not antigenically identical. In the cardiac actin radioimmunoassay, unlabeled cardiac and skeletal muscle actins inhibited the binding of (125)I-labeled cardiac actin to homologous antiserum, but neither brain actin inhibited the binding. Thus, the muscle actins possess at least one antigenic determinant not expressed by the brain actins, in addition to the shared determinants. Furthermore, cardiac actin and skeletal actin generated different inhibition curves in the cardiac actin radioimmunoassay, demonstrating that, although antigenically related, they are not identical. Correlations with existing sequence data imply that substitutions in only a few residues alter the antigenic properties of actin.

Studies on Chinese hamster ovary mutants showing multiple cross-resistance to oxidative phosphorylation inhibitors

Several stable Chinese hamster ovary (CHO) mutants were selected after ethylmethane sulfonate mutagenesis for resistance to oligomycin, ruatmycin, venturicidin, or antimycin. These mutants shared a number of common properties. They exhibited cross-resistance to those drugs which act on oxidative phosphorylation, irrespective of the structure and site of action of the drug. All the mutants showed a reduced ability to grow in suspension and to reach high saturation densities. They were also unable to use galactose as a carbon source. The short lag period required for selection (10-15 days), the similarity of the mutation rates for resistance to each of the four drugs, the high variance/mean ratios in fluctuation tests, and the recessive behavior of the resistance marker in hybrids suggest that the mutations responsible for resistance to oxidative phosphorylation inhibitors in CHO cells are coded by nuclear DNA. Segregation experiments indicated no linkage between the oligomycin-resistant marker (OLG) AND Thg (thioguanine resistance). Oxidative phosphorylation, as measured by the rate of respiration coupled to phosphorylation in whole cells remained as sensitive to the drugs in the mutants as in the parental cell line. Glucose transport and the overall Krebs' cycle activities also appeared similar in the mutants and the wild type. All the mutants had an increased rate of lactic acid production (up to twofold), associated with increased specific activities for several glycolytic enzymes when assayed in cell-free extracts.