Concerning the universality of a microtubule antigen in animal cells

Anti-tubulin antibodies in rabbits before and after immunization with pig tubulin

Sera from rabbits before and after repeated injections of pig tubulin in complete Freund's adjuvant were examined for antibody activity against pig and rabbit tubulins and against a panel of antigens: actin, myosin, DNA, TNP/BSA. Antibody activity against all the antigens of the panel (PAg) increased moderately after the first but not after subsequent injections. Antibody activity against pig and rabbit tubulins strongly increased after the second immunization when the maximum was reached. Isolation of anti-tubulin antibodies from normal or immune sera on tubulin-immunoadsorbent demonstrated the presence of three different antibody populations: (1) polyspecific IgM reacting with the PAg and the tubulins, present in substantial amounts in normal sera and moderately increased in immune sera; (2) small amounts of polyspecific IgG detected only in immune sera; (3) high amounts of specific IgG reacting with pig and rabbit tubulins, present in immune but not normal sera. Western blot analysis of the specific IgG population showed that it contained antibodies reacting with both native pig and rabbit tubulins, as well as antibodies recognizing only the 30,000 proteolytic fragment of pig, but not that of rabbit tubulin. The results indicate that the immunization of rabbits with heterologous tubulin induced specific IgG anti-tubulin antibodies which recognize the self and non-self antigens differently.

Ultrathin cryosections in the plane of cell monolayers: evaluation of their potential for antibody localization studies of the cytoskeleton

In spite of the fact that the preembedding method is satisfactory for the ultrastructural localization of cytoskeletal proteins, there is a need for a localization method that retains the cells' ground substance, delicate filament arrangements, and membrane-filament interactions and provides a good delineation of ultrastructural detail. Ultracryomicrotomy, a resinless sectioning method, can combine good morphology with optimal antibody labeling. Until now, however, it has not been possible to section cell monolayers parallel to their plane of growth. This is a prerequisite for the localization of proteins along segments of filaments, contained within the section thickness. We describe such a method and give a first appreciation of its potential for antibody localization studies of cytoskeletal proteins. The method consists of seeding cells on a parallel 0.75-mm-thick gelatin substrate that can later be cut and used as a mounting block. An adapted negative staining has yielded a very useful delineation of the well-preserved structures within the cells, even in combination with immunogold labeling. The latter has been in its indirect version less satisfactory in dense microfilament bundles because of penetration problems, and more satisfactory on microtubules. Clearly, the penetration properties of gold probes will have to be improved before this method will become widely applicable. The availability of a sectioning method like this will provide the basis for further progress. There will be many cases which will justify the use of this relatively more difficult approach.

A monoclonal antibody to alpha tubulin recognizes host cell and Trypanosoma cruzi tubulins

A mouse monoclonal anti-alpha-tubulin antibody was used to investigate the disposition of the cytoskeletal microtubules of three tissue culture cell lines--J774 macrophages, BSC-1, and Vero cells--infected with the Brazil strain of Trypanosoma cruzi. Indirect immunofluorescence light microscopy was used to demonstrate the antigenic response in host cells and parasites, simultaneously. In all morphotypes of T. cruzi, the monoclonal antibody reacted with all subpopulations of microtubules, inclusively, the subpellicular, flagellar, cytopharyngeal, and mitotic. The host cell cytoskeletal microtubule framework was revealed and the redistribution and destruction of the microtubular lattice in response to parasite infection over a 120 h period recorded. Our results show that after the initial inoculation of tissue cultures with trypomastigotes, the parasites penetrate the cells and locate in the perinuclear region of the cell where they multiply. The number and distribution of host cell microtubules were altered during the infection. The normal radial distribution of microtubules extending from the center of the cell to the periphery was destroyed. The remaining microtubules were observed at the periphery encircling, but well removed from the proliferating parasites. The complete transformation of the parasites was monitored throughout the infection with the end result being the liberation of parasites and the near complete destruction of the microtubular framework of the host cell. A residual population of dividing spheromastigotes was observed in cells liberating trypomastigotes. Colloidal gold labeling of thin sections as seen in the electron microscope affirmed the specificity of our monoclonal antibody to all subpopulations of microtubules in T. cruzi.

Chlamydomonas alpha-tubulin is posttranslationally modified by acetylation on the epsilon-amino group of a lysine

Previous work has shown that the principal alpha-tubulin within Chlamydomonas reinhardtii flagellar axonemes differs from the major alpha-tubulin in the cell body. These two variants of alpha-tubulin are related to one another since posttranslational modification of the cell body form converts it to the axonemal form. When flagella are induced to assemble in the absence of de novo protein synthesis, tritiated acetate can be used to posttranslationally label alpha-tubulin in vivo, and under these conditions, no other flagellar polypeptides exhibit detectable labeling [L'Hernault, S. W., & Rosenbaum, J. L. (1983) J. Cell Biol. 97, 258-263]. In the present report, this labeling method has been used to provide material for chemical analysis of the tritiated moiety that is posttranslationally added to flagellar alpha-tubulin. This radioactivity was volatile after acid hydrolysis, suggesting that the posttranslational modification is the addition of neither an amino acid nor carbohydrate. Treatment of posttranslationally 3H-labeled alpha-tubulin with hydrazine yields radioactive acetylhydrazine, indicating that the moiety involved in posttranslational modification is an acetyl group. Analysis of complete proteolytic digests by thin-layer chromatography has revealed that this acetyl group is located on the epsilon-amino group of a flagellar alpha-tubulin lysine residue.

An immunocytochemical method for the visualization of tubulin-containing structures in the egg of Xenopus laevis

Tubulin can be isolated and purified from Xenopus laevis eggs through modification of Olmstedt's (1970) tubulin isolation method, viz. by repeating the vinblastin precipitation step after resuspension of the sediment in a detergent-containing stabilizing medium. By this we overcome the deleterious influence of the yolk granules in the isolation procedure. From 11 of Xenopus laevis eggs 25 mg VB-paracrystals can be obtained. The apparent molecular weight of the purified tubulin is 52,800. Antiserum against the purified Xenopus VB-paracrystals, raised in 2 Chinchilla rabbits, cross-reacts in immunodiffusion tests in agar gels with rat brain tubulin and with tubulin isolated from Xenopus laevis eggs by the described procedure. Specific indirect fluorescence staining and appropriate control reactions reveal that cilia of Tetrahymena pyriformis, cytoplasmic networks in cultured mouse Leydig cells, as well as mitotic spindles and nuclear regions in paraffin sections of Xenopus laevis blastulae, react with the antibodies against Xenopus laevis egg tubulin as well as with monoclonal antibodies against pig brain tubulin. These results provide additional evidence for the view that tubulin antibodies are neither species nor tissue specific and show that under appropriate conditions tubulin containing structures can be visualized in paraffin sections.

Radioimmunoassay for tubulin: a quantitative comparison of the tubulin content of different established tissue culture cells and tissues

A quantitative estimate of the cellular tubulin concentration can be obtained by the use of a radioimmunoassay based upon the competition between tubulin in cell extracts and a known amount of radioactively labeled homogeneous tubulin during binding to a limited amount of anti-tubulin antibodies. This assay shows that a variety of widely used tissue culture cells (mouse L cells, mouse 3T3 cells, chick embryo fibroblasts) have a tubulin content which corresponds to approximately 2.5--3.3% of their total protein. Transformation of mouse 3T3 cells by the DNA virus SV40, and of chick embryo cells by the RNA Rous sarcoma virus, does not change the intracellular tubulin concentration. Transformed cells of brain origin, such as some glia tumor cell lines and some neuroblastoma cell lines, have a much lower tubulin content than does normal brain tissue. The intracellular concentration of tubulin in mouse 3T3 cells is discussed in relation to the number of microtubules detected during interphase by immunofluorescence microscopy. These results are also discussed in view of a mechanism of microtubule elongation in vivo driven by self-assembly.

Concerning the localization of steroids in centrioles and basal bodies by immunofluorescence

Specific steroid antibodies, by the immunofluorescence technique, regularly reveal fluorescent centrioles and cilia-bearing basal bodies in target and nontarget cells. Although the precise identity of the immunoreactive steroid substance has not yet been established, it seems noteworthy that exogenous steroids can be vitally concentrated by centrioles, perhaps by exchange with steroids already present at this level. This unexpected localization suggests that steroids may affect cell growth and differentiation in some way different from the two-step receptor mechanism.

Quantitation of cytoplasmic tubulin by radioimmunoassay

A radioimmunoassay has been developed for the quantitation of crytoplasmic tubulin. It measures tubulin between 20 and 1500 nanograms and does so independently of decay in colchicine-binding activity. In addition, the state of tubulin as subunit or polymer does not alter the measurement.

Evidence suggesting the presence of common antigenic determinant between dynein and tubulin

The present experiments showed that the guinea pig antiserum prepared against the main polypeptides of 14 S dynein from Tetrahymena cilia reacted with sea urchin sperm flagellar dynein and with bovine brain high molecular weight protein to give rise to a precipitin line confluent with that formed between the antiserum and Tetrahymena dynein. Furthermore, it was found that this antiserum also reacted with tubulins from Tetrahymena cilia, sea urchin sperm flagella and bovine brain to give rise to the confluent precipitin line. Among muscle proteins, only actin preparation from rabbit skeletal muscle reacted with the anti-Tetrahymena dynein serum, whereas neither rabbit skeletal muscle myosin, chicken skeletal muscle tropomyosin nor chicken skeletal muscle troponin reacted with the antiserum. These results suggest that dynein and tubulin and probably actin share an antigenic determinant regardless of different protein species and of different animal species. The common antigenic determinant was detected only when the proteins denatured with urea/sodium dodecyl sulfate/beta-mercaptoethanol/N-ethylmaleimide were used, but it was not detected at all when the native proteins were used. This implies that a certain common antigenic determinant which is involved in the precipitin line formation exists in the primary structures of dyneins and tubulins and probably actin, and is hidden inside the tertiary structures of the native protein molecules.

Localization of tubulin in the mitotic apparatus of mammalian cells by immunofluorescence and immunoelectron microscopy

Antitubulin antibody was used as an immunofluorescent and immunoelectron microscopic probe to localize tubulin in components of the mitotic apparatus of rat kangaroo (strain PtK1) cells in vitro. In addition to the detection of tubulin in the spindle microtubules and centrioles, other structures were found to display specific staining including kinetochores, amorphous pericentriolar material and small virus-like particles associated with the centrioles. The kinetochores consisted of a densely stained outer layer about 400 A thick which is separated from an inner layer of the same dimension by a lightly staining middle layer. Microtubules were primarily associated with the outermost plate of the kinetochore but tubulin was uniformly distributed in both outer and inner plates. Colcemid treatment prevented the assembly of spindle microtubules and resulted in specific alterations of the kinetochore but failed to diminish the staining of the kinetochores. These observations suggest that tubulin molecules may comprise an important structural component of the kinetochore.

Fluorescent antibody localization of myosin in the cytoplasm, cleavage furrow, and mitotic spindle of human cells

We have studied the distribution of myosin molecules in human cells using myosin-specific antibody coupled with fluorescent dyes. Rabbits were immunized with platelet myosin or myosin rod. They produced antisera which precipitated only myosin among all the components in crude platelet extracts. From these antisera we isolated immunoglobulin-G (IgG) and conjugated it with tetramethylrhodamine or fluorescein. We separated IgG with 2-5 fluorochromes per molecule from both under- and over-conjugated IgG by ion exchange chromatography and used it to stain acetone-treated cells. The following controls established the specificity of the staining patterns: (a) staining with labeled preimmune IgG; (b) staining with labeled immune IgG adsorbed with purified myosin; (c) staining with labeled immune IgG mixed with either unlabeled preimmune or immune serum; and (d) staining with labeled antibody purified by affinity chromatography. In blood smears, only the cytoplasm of platelets and leukocytes stained. In spread Enson and HeLa cells, stress fibers stained strongly in closely spaced 0.5 mum spots. The cytoplasm stained uniformly in those cells presumed to be motile before acetone treatment. In dividing HeLa cells there was a high concentration of myosin-specific staining in the vicinity of the contractole ring and in the mitotic spindle, especially the region between the chromosomes and the poles. We detected no staining of erythrocytes, or nuclei of leukocytes and cultured cells, or the surface of platelets and cultured cells.

Heterogeneity of the alpha subunit of tubulin and the variability of tubulin within a single organism

When tubulins obtained from particular microtubules of the sea urchin (ciliary doublet A tubules, flagellar doublet microtubules, and mitotic microtubules) are analyzed by electrophoresis in a polyacrylamide gel system containing sodium dodecyl sulfate and urea, heterogeneity of the alpha subunit, and differences between the tubulins are revealed. The alpha subunit of tubulin from mitotic apparatus and from A microtubules of ciliary doublets is resolved into two bands, while the alpha subunit of flagellar doublet tubulin gives a single band. The mitotic and ciliary tubulins differ in the mobilities of their two alpha species, or in the relative amounts present, or both. The existence of differences between the tubulins has been confirmed by a preliminary analysis of their cyanogen bromide peptides.

Antisera against electrophoretically purified tubulin stimulate colchicine-binding activity

Several rabbit antisera have been prepared against reduced and alkylated, electrophoretically purified tubulin isolated from chick brain. These antisera give a single precipitin line in Ouchterlony double diffusion plates when tested against partially purified tubulin, and label specifically microtubule- and tubulin-containing structures, such as mitotic spindles, cilia, and vinblastine-induced crystals, in a variety of cells. The same antisera also display the unique ability to stimulate the colchicine-binding activity of tubulin preparations from chick brain and Chinese hamster ovary tissue culture cells. This specific stimulation of colchicine binding activity is also obtained with the gamma globulin fractions purified by ammonium sulfate precipitation of these antisera.

Immunofluorescence of mitotic spindles by using monospecific antibody against bovine brain tubulin

Monospecific antibody directed against bovine brain tubulin has been purified by affinity chromatography and tested against soluble tubulin and intact microtubules of brain and mitotic apparatus. Binding of the tubulin antibody to the mitotic spindle of rat kangaroo cells was demonstrated in all stages of mitosis by indirect immunofluorescence.

Antibody against tuberlin: the specific visualization of cytoplasmic microtubules in tissue culture cells

Cytoplasmic microtubules in tissue culture cells can be directly visualized by immunofluorescence microscopy. Antibody against tubulin from the outer doublets of sea urchin sperm flagella decorates a network of fine cytoplasmic fibers in a variety of cell lines of human, monkey, rat, mouse, and chicken origin. These fibers are separate and of uniform thickness and are seen throughout the cytoplasm. The fibers disappear either in a medium containing colchicine or after subjection of the cells to low temperature. The same treatments do not destroy the microfilamentous structures that are visualized by means of antibody against actin. When tryspin-treated enucleated cells are replated and then stained with antibody against tubulin, the fibers can be seen to traverse the entire enucleated cytoplasm.

Specific binding of nerve growth factor (NGF) by murine C 1300 neuroblastoma cells

Murine C 1300 neuroblastoma cells bind with high avidity on their membrane surface the nerve growth factor (NGF), a protein capable of inducing differentiation of sympathetic nerve cells. The total binding capacity of NGF by the cells was quantitatively measured by a radioimmunoassay technique, using (125)I-labeled NGF. An average number of about 10(6) molecules of NGF could be bound, at saturation, by each cell with an average relative association constant of about 10(7) liters/mol. Using synchronized cells, it was found, however, that either the number of molecules of ligand bound or the avidity of the binding interaction between NGF and cells varied depending upon their growth cycle, the maximal-binding occurring during the G(1) and early S phase. Binding of [(125)I]NGF was suppressed by trypsin treatment of the cells, however new receptor sites were rapidly replaced onto the membrane surface within 1-2 h. Cells exposed to 3 M KCl released into the supernate a protein product exhibiting similar high avidity for NGF. Acrylamide gel electrophoresis suggested a restricted molecular heterogeneity of this product, with a major component in the 52,000 mol wt region. Antibodies made specific to this protein were capable, in the absence of the complement, of inhibiting the binding of [(125)I]NGF by the cells and in the presence of the complement they killed them.

The fine structure and immunological labeling of the achromatic mitotic apparatus after disruption of cell membranes

After treatment of HeLa and L cells with vinblastine sulfate the material of microtubules (tubulin) was reorganized into (a) large paracrystals (PC) of tightly packed tubules; (b) smaller aggregates of tubules with greater diameter whose walls are constituted from well defined, helically arranged morphological subunits; and (c) microtubules associated with helices of polyribosomes of uniform size. All of these structures survived disruption of cellular membranes by means of a nonionic detergent. Following a thorough stripping of membranes there remained a subcellular fraction sedimenting at 1,500 g for 15 min, in which were contained nuclei, centrioles, and the above mentioned microtubular elements, maintained as a complex of organelles by an interconnecting network of 80 A microfibrils. As a result of membrane disruption it was possible to localize precisely in the electron microscope the binding of ferritin antibody conjugates. Specific labeling at the surface of PC and microtubule aggregates could be demonstrated. This result was substantiated by means of the immunoperoxidase method of labeling the PC. A concentrated deposit of ferritin was also found in the vicinity of centrioles and related structures, the annuli of the nuclear pore complex and the annulate lamellae. However, the specificity of the label on these organelles remains questionable because ferritin, albeit in lower concentration, was also present on them in control preparations reacted with preimmune sera.

Isolation and partial characterization of alpha and beta-tubulin from outer doublets of sea-urchin sperm and microtubules of chick-embryo brain

Two kinds of tubulin (alpha and beta) have been described in microtubules from many different systems. In this study a discontinuous acrylamide-gel system containing sodium dodecyl sulfate was used to separate milligram quantities of alpha- and beta-tubulin from microtubules of chick-embryo brain and from outer doublets of sea-urchin sperm. The isolated tubulins were characterized by peptide mapping and automated sequencing of the first 25 NH(2)-terminal amino acids. Our results show that alpha- and beta-tubulin are related but distinctly different proteins and that each one has been highly conserved in the course of evolution.