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

The ras-related YPT1 gene product in yeast: a GTP-binding protein that might be involved in microtubule organization

The 23.5 kd protein product of the ras-related YPT1 gene of S. cerevisiae was found to be essential for cell growth. The loss of YPT1 function, studied in cells with the YPT1 gene on chromosome VI regulated by the galactose-inducible GAL10 promoter, led to arrested cells that were multibudded and exhibited a complete disorganization of microtubules and an apparent loss of nuclear integrity. The YPT protein binds GTP specifically. GTP binding of the protein is essential for its intracellular function. The Asn121----IIe substitution, generated by site-directed mutagenesis, had a dominant lethal phenotype, the expression of the mutant protein led to binucleated cells and abnormal spindles. In contrast to the S. cerevisiae RAS1 and RAS2 gene products, the YPT protein seems to be involved, directly or indirectly, in microtubule organization and function.

Ultrastructural colocalization of tyrosinated and detyrosinated alpha-tubulin in interphase and mitotic cells

Immunofluorescence with specific peptide antibodies has previously established that tyrosinated (Tyr) and detyrosinated (Glu) tubulin, the two species generated by posttranslational modification of the COOH-terminus of alpha-tubulin, are present in distinct, but overlapping, subsets of microtubules in cultured cells (Gundersen, G. G., M. H. Kalnoski, and J. C. Bulinski, 1984, Cell, 38:779-789). Similar results were observed by light microscopic immunogold staining in the two cell types used in this study, CV1 and PtK2 cells: most microtubules were stained with the Tyr antibody, whereas only a few were stained with the Glu antibody. We have examined immunogold-stained preparations by electron microscopy to extend these results. In general, electron microscopic localization confirmed results obtained at the light microscopic level: the majority of the microtubules in CV1 and PtK2 cells were nearly continuously labeled with the Tyr antibody, whereas only a few were heavily labeled with the Glu antibody. However, in contrast to the light microscopic staining, we found that all microtubules of interphase and mitotic CV1 and PtK2 cells contained detectable Tyr and Glu immunoreactivity at the electron microscopic level. No specific localization of either species was observed in microtubules near particular organelles (e.g., mitochondria or intermediate filaments). Quantification of the relative levels of Glu and Tyr immunoreactivity in individual interphase and metaphase microtubules showed that all classes of spindle microtubules (i.e., kinetochore, polar, and astral) contained nearly the same level of Glu immunoreactivity; this level of Glu immunoreactivity was lower than that found in all interphase microtubules. Most interphase microtubules had low levels of Glu immunoreactivity, whereas a few had relatively high levels; the latter corresponded to morphologically sinuous microtubules. Quantification of the relative levels of Tyr and Glu immunoreactivity in segments along individual microtubules suggested that the level of Tyr (or Glu) tubulin in a given microtubule was uniform along its length. Understanding how microtubules with different levels of Tyr and Glu tubulin arise will be important for understanding the role of tyrosination/detyrosination in microtubule function. Additionally, the coexistence of microtubules with different levels of the two species may have important implications for microtubule dynamics in vivo.

Colcemid inhibits growth during early G1 in normal but not in tumorigenic lymphocytes

Mitogenically stimulated human and mouse lymphocytes enter the cell cycle (G0, G1A, G1B, S, G2+M) via a newly recognized subphase, G1'. This subphase precedes G1A and is distinct from G0. The G1' subphase is absent in immortalized and tumorigenic lymphoblastoid cell lines (LCLs) by cytofluorimetric criteria. Furthermore, colcemid inhibits transition through the G0/G1' as well as G2 phases in mitogen-stimulated lymphocytes and in LCLs. Tumorigenic LCLs are not sensitive to growth inhibition by colcemid during early G1. These observations suggest that a progressive series of changes have occurred during G0/G1' which lead to deregulation of growth control.

The pattern of early neuronal differentiation in Drosophila melanogaster

Based on the staining of Drosophila embryos with neuron-specific monoclonal antibodies we describe the differentiation of the earliest neurons in the central nervous system. The metameric array undergoes a number of changes during development that distinguish several morphological units: metameres, neuromeres and ganglia. Neural landmarks in the CNS and the periphery are identified on the bases of their developmental history, axonal projection and segment specificity. A time sequence of differentiation starting in the posterior gnathal and anterior thoracic anlage has been found.

Caenorhabditis elegans morphogenesis: the role of the cytoskeleton in elongation of the embryo

During development Caenorhabditis elegans changes from an embryo that is relatively spherical in shape to a long thin worm. This paper provides evidence that the elongation of the body is caused by the outermost layer of embryonic cells, the hypodermis, squeezing the embryo circumferentially. The hypodermal cells surround the embryo and are linked together by cellular junctions. Numerous circumferentially oriented bundles of microfilaments are present at the outer surfaces of the hypodermal cells as the embryo elongates. Elongation is associated with an apparent pressure on the internal cells of the embryo, and cytochalasin D reversibly inhibits both elongation and the increase in pressure. Circumferentially oriented microtubules also are associated with the outer membranes of the hypodermal cells during elongation. Experiments with the microtubule inhibitors colcemid, griseofulvin, and nocodazole suggest that the microtubules function to distribute across the membrane stresses resulting from microfilament contraction, such that the embryo decreases in circumference uniformly during elongation. While the cytoskeletal organization of the hypodermal cells appears to determine the shape of the embryo during elongation, an extracellular cuticle appears to maintain the body shape after elongation.

2,4-Dichlorobenzyl thiocyanate, an antimitotic agent that alters microtubule morphology

A compound of simple structure, 2,4-dichlorobenzyl thiocyanate (DCBT), is an antimitotic agent with a number of unusual properties. The drug causes an extreme reorganization of microtubules in cells in culture. Most normal microtubules disappear, and remaining tubulin-containing structures appear to be bundled or aggregated. DCBT irreversibly inhibits in vitro polymerization of purified tubulin, but only after a prolonged preincubation of the protein with the drug. Binding of radiolabeled DCBT to tubulin similarly requires a long incubation time, with the reaction not being complete even after 6 hr at 37 degrees C. A specific interaction with tubulin is also shown by the crossresistance to DCBT of Colcemid-resistant cells with an altered beta-tubulin. A human KB carcinoma cell line and a Chinese hamster ovary cell line selected for crossresistance to multiple chemotherapeutic agents, including most antimitotic drugs, are sensitive to DCBT. Initial structure-function studies have demonstrated weak antimitotic and antitubulin activity with the parent compound benzyl thiocyanate. Chlorination at either position 2 or position 4 of the phenyl ring produces compounds of intermediate activity (4-chlorobenzyl thiocyanate is more active than 2-chlorobenzyl thiocyanate). The thiocyanate moiety appears to be essential for activity.

Alpha-tubulin is not detyrosylated during axonal transport

We have examined the question of whether alpha-tubulin is detyrosylated during axonal transport in retinal ganglion cell axons and axons of spinal motor neurons. The degree of tyrosylation of alpha-tubulin was estimated from immunocytochemistry and immunoblotting with two anti-alpha-tubulin monoclonals, one of which (YL1/2) recognizes only the tyrosylated form of alpha-tubulin. In the case of retinal ganglion cells, the axons were depleted of tyrosylated alpha-tubulin both in the retina and proximal region of the optic nerve. Distal regions of the axons, in the optic tract, gave a pattern of staining consistent with a reduction in the total level of alpha-tubulin at the expense of detyrosylated alpha-tubulin. Axons within the L5 ventral root, the sciatic nerve and tibial nerve were consistently unstained by YL1/2 indicating that these axons were depleted in tyrosylated alpha-tubulin in all 3 segments. The results indicate that alpha-tubulin destined for axonal microtubules is detyrosylated close to or in cell bodies and not progressively during its transport. Therefore the segregation of detyrosylated alpha-tubulin to axonal microtubules may occur at their site of assembly.

The dissociation of nuclear and centrosomal division in gnu, a mutation causing giant nuclei in Drosophila

We describe a recessive, maternal-effect lethal mutation of Drosophila, gnu. gnu uncouples nuclear division from many cytoplasmic events of mitosis in the Drosophila embryo. Embryos from homozygous females are defective in nuclear division, but not in DNA replication, and therefore develop a small number of giant nuclei. Centrosomes divide independently of nuclear division and migrate to the surface of the syncytial blastoderm. There they nucleate microtubules into asters, which appear normal at first but become very large. Only later, when the giant nuclei begin to break down, are spindles sometimes formed. The cortical actin of these embryos develops into a characteristic network.

Isolation and partial characterization of a 110-kD dimer actin-binding protein

Two Triton-insoluble fractions were isolated from Acanthamoeba castellanii. The major non-membrane proteins in both fractions were actin (30-40%), myosin II (4-9%), myosin I (1-5%), and a 55-kD polypeptide (10%). The 55-kD polypeptide did not react with antibodies against tubulins from turkey brain, paramecium, or yeast. All of these proteins were much more concentrated in the Triton-insoluble fractions than in the whole homogenate or soluble supernatant. The 55-kD polypeptide was extracted with 0.3 M NaCl, fractionated by ammonium sulfate, and purified to near homogeneity by DEAE-cellulose and hydroxyapatite chromatography. The purified protein had a molecular mass of 110 kD and appeared to be a homodimer by isoelectric focusing. The 110-kD dimer bound to F-actin with a maximal binding stoichiometry of 0.5 mol/mol of actin (1 mol of 55-kD subunit/mol of actin). Although the 110-kD protein enhanced the sedimentation of F-actin, it did not affect the low shear viscosity of F-actin solutions nor was bundling of F-actin observed by electron microscopy. The 110-kD dimer protein inhibited the actin-activated Mg2+-ATPase activities of Acanthamoeba myosin I and myosin II in a concentration-dependent manner. By indirect immunofluorescence, the 110-kD protein was found to be localized in the peripheral cytoplasm near the plasma membrane which is also enriched in F-actin filaments and myosin I.

Effects of low temperature and calcium on microfilament structure in flagellates of Physarum polycephalum

Microfilament structures of the ridge and the backbone in Physarum flagellates disintegrated selectively within a few minutes upon cooling by ice-water. The elongated cells concurrently rounded up to spherical or irregular and amoeboid shape. When such rounded cells were warmed to 25 degrees C, the microfilament structures were reconstructed within 1 min and cells subsequently returned to an elongated shape. Disruption of microfilaments by cytochalasin A also caused the rounding up of cells, indicating that the rounding up resulted from disintegration of microfilament structures. This transformation induced by the cold treatment was retarded by preincubation of the cells with EGTA for 15 min, but addition of EGTA immediately before the onset of the cold treatment was less effective. The effect of EGTA was cancelled by simultaneous addition of excess Ca2+. Addition of procaine also inhibited the transformation induced by the cold treatment, while caffeine inhibited the recovery of the elongated shape when returned to 25 degrees C. Furthermore, addition of A23187 at 25 degrees C in the presence of Ca2+ mimicked the effect of the cold treatment. Thus, intracellular release of Ca2+ was suggested to be involved in the transformation induced by the cold treatment. Lability of the microfilament structures at a high concentration of Ca2+ was directly proved using Triton-permeabilized cells. Therefore we concluded that low temperature disrupts microfilament structures that are necessary for the maintenance of the elongated cell shape by inducing intracellular Ca2+ release. However, microfilament structures in Physarum amoeba cells were affected neither by the cold treatment nor by high Ca2+ concentration.

Assembly and characterisation of a multi-component cytoskeletal gel from adrenal medulla

Incubation of bovine adrenal medullary cytoplasmic extracts results in the formation of three-dimensional supramolecular gels. Ultrastructurally, the gels display a network of fibres similar in appearance to the cytoskeleton within intact chromaffin cells. Analysis of the protein composition using both electrophoretic and immunoblotting techniques indicates that the gels are composed exclusively of cytoskeletal elements; microfilaments, microtubules and intermediate filament proteins have been identified as having a number of actin-associated proteins. Among the latter class of components the following polypeptides have been identified: filamin (300 kDa), fodrin (240 kDa), a 235 kDa polypeptide, myosin (200 kDa), caldesmon (70 kDa) and tropomyosins (39 kDa). All of these polypeptides co-sedimented with F-actin when gels were assembled in the absence of Ca2+. When gelation was performed in the presence of 10 microM Ca2+ actin, the 235 kDa polypeptide, 70 kDa caldesmon and tropomyosin were all absent from the gels. These results may suggest that the 235 kDa polypeptide, 70 kDa caldesmon and tropomyosins could act either individually or as a functional regulatory unit in controlling the Ca2+-activated reorganisation of the actin network in the cytoplasmic gels.

Transglutaminase and the neuronal cytoskeleton in Alzheimer's disease

Transglutaminase [EC 2.3.2.13, (R)-glutaminyl-peptide:amine gamma-glutamyltransferase], an enzyme that catalyzes the introduction of glutamine-lysine cross-links into proteins, was purified. Neurofilament and microtubule proteins were substrates for this enzyme but the insoluble neurofibrillary tangles (NFT) isolated from Alzheimer's disease brain were not substrates. In vitro cross-linking of neurofilaments and microtubules by the enzyme did not produce paired helical filaments (PHF), which are the major ultrastructural component of NFT. These results make it unlikely that PHF are formed by the straightforward cross-linking of neurofilaments or microtubules.

Localization and fine structure of a vaccinia virus gene encoding an envelope antigen

The major antigen on the envelope of extracellular vaccinia virus particles is a polypeptide with an apparent molecular weight of 37,000 (p37K; G. Hiller and K. Weber, J. Virol. 55:651-659, 1985). The gene encoding p37K was mapped in the vaccinia virus genome by hybrid selection of RNA followed by in vitro translation. p37K was then identified among the in vitro translation products by immunoprecipitation with a monoclonal antibody. The gene is located close to the right-hand end of the HindIII F fragment. The corresponding region of the DNA was sequenced, and an open reading frame encoding a polypeptide of 41,748 daltons was observed. The 5' end of the mRNA, as defined by nuclease S1 analysis, maps within only a few nucleotides of the translation initiation codon. Examination of the DNA sequence around the putative initiation site of transcription revealed a characteristic sequence, TAAATG, which includes the ATG translation initiation codon and which is conserved in all but one late gene so far analyzed. It is therefore likely that this sequence is an important regulatory signal for late gene expression in vaccinia virus.

Carboxy-terminal regions on the surface of tubulin and microtubules. Epitope locations of YOL1/34, DM1A and DM1B

Tryptic and cyanogen bromide peptides of pig brain alpha- and beta-tubulin reacting with monoclonal antibodies YOL1/34, DM1A and DM1B have been isolated and identified. They all correspond to parts of the C-terminal regions of either alpha- or beta-tubulin, and those peptides reacting with a given antibody have overlapping sequences. In the case of YOL1/34, its relatively high reactivity with small peptides suggests that many of the determinants for this antibody are within the overlapping region of these peptides comprising only nine amino acids in positions alpha 414 to 422. The smallest common region of peptides reacting with the other alpha-tubulin antibody DM1A corresponds to positions alpha 426 to 450, whereby amino acids within the positions 426 and 430 appear to be particularly important for reactivity. Since the last C-terminal residues of alpha-tubulin are also accessible to antibodies and enzymes, it seems that an extensive part (35 to 40 residues) of this very acidic C-terminal domain is exposed on the surface of native tubulin dimers. In microtubules, however, the amino-terminal end of this region appears to be less accessible, as YOL1/34 reacts poorly, if at all, with intact microtubules. All of the peptides reacting with beta-tubulin monoclonal antibody DM1B were derived from the acidic C-terminal domain and they overlapped in positions beta 416 to 430. This indicates that beta-tubulin is also positioned with at least part of its acidic C-terminal domain on the surface of microtubules, since DM1B reacts with unfixed microtubules after microinjection.

Pollen wall formation in Lilium: The effect of chaotropic agents, and the organisation of the microtubular cytoskeleton during pattern development

Using a combination of electron-microscopic and immunocytochemical techniques the behaviour of the microtubular cytoskeleton has been followed throughout microsporogenesis in Lilium henryi Thunb. Cells treated with colchicine at specific stages and then permitted to develop to near maturity were used to investigate any participation by microtubules in the regulation of pollen wall patterning. The microtubular cytoskeleton assumes four principal forms during the meiotic process; in pre-meiosis it resembles that characteristic of meristematic somatic cells, during meiotic prophase it becomes associated with a nuclear envelope and, perhaps, with the chromosomes and, as the nuclear and cell divisions commence, it takes the form of a normal spindle apparatus. In the young microspores, microtubules assume a radial organisation extending from sites at the nuclear envelope to the inner face of the plasma membrane. No firm evidence was found linking any one of these forms of cytoskeleton with the generation of patterning on the cell surface. Experiments with colchicine revealed that the drug would readily dislocate the colpus, but did not affect the general reticulate patterning. The radial cytoskeleton was present during the deposition of the early primexine, but evidence from these and other studies (J.M. Sheldon and H.G. Dickinson 1983, J. Cell. Sci. 63, 191-208; H.G. Dickinson and J.M. Sheldon, 1984, Planta 161, 86-90) indicates patterning to be imprinted upon the plasma membrane prior to the appearance of this type of cytoskeleton. These results are discussed in terms of a recent model proposed to explain pattern generation on the surface of Lilium pollen grains, based on the "self-assembly" of patterning determinants within the plasma membrane.

Components of microtubular structures in Saccharomyces cerevisiae

Most studies of cytoskeletal organelles have concentrated on molecular analyses of abundant and biochemically accessible structures. In many of the classical cases, however, the nature of the system chosen has precluded a concurrent genetic analysis. The mitotic spindle of the yeast Saccharomyces cerevisiae is one example of an organelle that can be studied by both classical and molecular genetics. We show here that this microtubule structure also can be examined biochemically. The spindle can be isolated by selective extractions of yeast cells by using adaptations of methods successfully applied to animal cells. In this way, microtubule-associated proteins of the yeast spindle are identified.

Cell shape and motility of oligodendrocytes cultured without neurons

Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), were cultured from newborn rat brain and optic nerve to study how they differentiate in vitro in the absence of neurons. By use of galactocerebroside (GC) as a reference marker, the development of the cell phenotype was studied with video-enhanced differential interference contrast microscopy, immunofluorescence and electron microscopy. After a few days in culture, oligodendrocytes extend 5 to 10 main processes that are very rich in microtubules, but they did not stain with a monoclonal antibody reacting with all known classes of intermediate filaments. The number of processes can vary with the substrate on which the cells are grown; fewer processes form on laminin than on polylysine coated glass. Oligodendrocytes, in a fashion similar to that of neurons appear to keep their body immobile while the long processes grow. However, while neurons display motile activities mostly at the end of the cell processes called growth cones, the oligodendrocytes display motile, actin rich filopodia and lamellipodia along the entire length of all processes. The outgrowth of motile processes from oligodendrocytes sometimes occurs preferentially towards neighboring astrocytes. Oligodendrocyte processes display intense bidirectional movement of cytoplasmic organelles. Movement of surface components also occurs since GC molecules cross-linked by antibodies move from the processes towards the cell body. Thus, oligodendrocytes cultured without neurons develop on schedule a complex phenotype similar to their in vivo counterpart. In addition, their processes are capable of specific motile activities which may function in vivo to find the target axon and to transport myelin membrane components at the site of myelin assembly.

Microtubule arrays present during the syncytial and cellular blastoderm stages of the early Drosophila embryo

The organization of microtubules within the surface caps of Drosophila embryos is described for the mitotic cycles of the syncytial blastoderm stage (particularly cycle 10), and for the subsequent cellularization process. Tubulin was labelled with the well characterized monoclonal antibody YL 1/2 (Kilmartin et al., J cell biol 93 (1982) 576). Each surface cap was found to contain an array of microtubules running around the nucleus. The microtubules originated at prominent centrosomes located close to the apical surface of each cap nucleus. During mitosis the spindle microtubules stained strongly for tubulin. A novel finding was that the spindle microtubules of the interzone region appeared to reduce their connections with the centrosomes at the end of anaphase. The spindle remnant remained in position during telophase but then became smaller in size, disappearing by interphase. At this phase of the cell cycle duplication of the aster centrosomes occurred. The cellular blastoderm stage was marked by a change in the main axis of microtubule orientation. The centrosomes of each cap separated somewhat and formed initiation centres for the development of a well developed basket of microtubules around each nucleus, but now perpendicular to the surface. The microtubule baskets were seen to extend in parallel with nuclear elongation, but not in concert with growth of the cell membranes, which extended some way beneath the bases of the nuclei.

Microtubule cycles in oocytes of the surf clam, Spisula solidissima: an immunofluorescence study

Oocytes of the surf clam, Spisula solidissima, underwent germinal vesicle breakdown and two meiotic divisions to give off polar bodies when they were fertilized or parthenogenetically activated with KCl. Fertilized eggs further proceeded to mitosis and cleaved, while parthenogenetically activated eggs remained uncleaved. We examined changes in microtubule-containing structures during meiotic divisions and subsequent mitotic processes by immunofluorescence. A monoclonal anti-tubulin antibody was applied to alcohol-fixed eggs from which the vitelline membrane had been removed by protease digestion. Up to the stage of second polar body formation, the pattern of microtubule organization in the first and second meiotic spindles was identical in both fertilized and parthenogenetically activated eggs. However, while fertilized eggs formed a sperm aster and mitotic spindles later, activated eggs formed only monaster- or ring-shaped microtubule-containing structures which underwent cycles of alternating formation and breakdown. Lactoorecin staining of parthenogenetically activated eggs revealed that the chromosome cycle could occur in these eggs, in phase with this microtubule cycle.

A chicken-yeast chimeric beta-tubulin protein is incorporated into mouse microtubules in vivo

The role of divergent primary sequences in restricting tubulin function was tested in vivo by a gene transfection experiment. A chicken-yeast chimeric beta-tubulin DNA was introduced into 3T3 cells using the transfection vector pSV2. The 5' end of this gene, from chicken, is similar but not identical with that of mouse beta-tubulins; the 3' end, from yeast, contains a carboxyl terminus that is very different from other known beta-tubulin sequences. The chimeric protein is incorporated efficiently into each of the microtubule structures and each of the microtubules in the host cells. The presence of the protein has no apparent effect on either growth rate or cell morphology. The results suggest that the divergent sequences in this chimeric tubulin molecule place no restrictions on its activities in mouse cells.

An immunofluorescent study of the microtubule organization in Trichomonas vaginalis using antitubulin antibodies

The flagellated protozoon Trichomonas vaginalis, parasite of the human urogenital tract, possesses a well developed microtubule system organized in highly differentiated structures. We have shown by immunoblotting that monospecific anti-sheep brain tubulin antibodies are able to react with the microtubular tubulin of T. vaginalis. These antibodies were used to study the microtubular system of T. vaginalis both in interphase and mitosis by indirect immunofluorescence. The interphase microtubular pattern, characterized by an axostyle, a pelta, four anterior flagella, and a recurrent flagellum, displayed remarkable changes at the onset of mitosis: the axostyle disappeared, and two pole bodies connected by a short spindle became evident; chromosomal fibers arose while pole-to-pole fibers elongated. The last phases of mitosis were marked by the disappearance of chromosomal fibers, the appearance of two small axostyles, and the depolymerization of the pole-to-pole bundle. At the end of mitosis, the normal interphase microtubule pattern was observed.

A gene required for the separation of chromosomes on the spindle apparatus in yeast

We describe the phenotypes caused by a cold-sensitive lethal mutation (ndc1-1) that defines the NDC1 gene of yeast. Incubation of ndc1-1 at a nonpermissive temperature causes failure of chromosome separation in mitosis but does not block the cell cycle. This defect results in an asymmetric cell division in which one daughter cell doubles in ploidy and the other inherits no chromosomes. The spindle poles are properly segregated to the two daughter cells. The primary visible defect is that the chromosomes remain associated with only one pole, and are thus delivered to one daughter cell. Meiosis II, but not meiosis I, is sensitive to the ndc1-1 defect, suggesting that NDC1 is required for some feature common to mitosis and meiosis II. ndc1-1 appears to define a new class of cell cycle gene required for the attachment of chromosomes to the spindle pole.

The use of submicroscopic gold particles combined with video contrast enhancement as a simple molecular probe for the living cell

We describe a new approach to probe the molecular biology of the living cell that uses small colloidal gold particles coupled to specific ligands. They are visualized in cells by bright-field, video enhanced contrast microscopy. We describe the basic aspects of the technique and provide examples of applications to intracellular motility, cell membrane dynamics, receptor translocation, internalization, and intracellular routing. We also provide examples of the use of this approach in immunospecific labelling of cells and tissue sections.

Decoration of microtubules by fluorescently labeled microtubule-associated protein 2 (MAP2) does not interfere with their spatial organization and progress through mitosis in living fibroblasts

Microtubule-associated protein 2 (MAP2) derivatized with iodoacetamidotetramethylrhodamine or with iodoacetamidofluorescein binds to microtubules after injection into living interphase cells [Scherson et al, 1984]. The binding of derivatized MAP2 stabilized microtubules in vitro; it was therefore important to check if the binding of MAP2 in vivo perturbed the dynamics and organization of the microtubule network. We have addressed these questions by studying the effect of the injection of derivatized MAP2 on mitosis in PtK 1 cells and on the recovery of the microtubule network from low temperature incubation in interphase cells. We found that the presence of derivatized MAP2 did not change the duration of any mitotic stage and that the injected cell normally completed mitosis. We subsequently showed that the injected MAP2 bound to the microtubules within 5 minutes after injection and remained bound throughout the course of mitosis. The reorganization of the microtubule network upon cooling and rewarming was studied in the cytoplasm of human foreskin fibroblasts (356 cells). During the recovery, the distribution of the fluorescent MAP2 in living cells was identical with the microtubule pattern visualized by immunofluorescence in lysed and fixed cells. In these experiments, the fluorescent MAP2 bound to microtubules can be considered as a nonperturbing reporter of the microtubule network. This result is discussed in terms of the role of MAPs in the dynamics and organization of microtubules in living cells.

Cytoskeletal architecture and motility in a giant freshwater amoeba, Reticulomyxa

Reticulomyxa is a large, multinucleated freshwater protozoan with striking intracellular transport. Cytoplasmic streaming and saltatory movements of individual organelles (at rates of up to 25 micron/sec) are observed within the naked cell body and the extensive reticulate peripheral network of fine cytoplasmic strands. As demonstrated by video-enhanced light microscopy, individual organelles move only when associated with cytoskeletal linear elements. The linear elements are composed of mixed colinear bundles of microtubules and actin filaments, which form the backbone of the reticulopodial network. The constant branching, sprouting, and fusion of network strands suggest unique membrane properties and an unusually dynamic cytoskeleton. The electrophoretic mobility of Reticulomyxa tubulins and the lack of crossreactivity with several antibodies known to react with many plant and animal tubulins suggest that they may differ from other tubulins more widely than might be expected. Reticulomyxa's large size, the rapidity and pervasiveness of the two forms of transport, and the simple and ordered cytoskeleton make the organism well suited for future studies on the mechanisms of intracellular transport.

Effects of colcemid and taxol on microtubules and intermediate filaments in chick embryo fibroblasts

Reports on how changes in microtubule (MT) distribution or polymerization affect the distribution of intermediate filaments (IFs) differ. Therefore, we have used cytoimmunofluorescence techniques and electron microscopy to systematically examine and compare the arrangements of MTs and IFs in cultures of chick embryo fibroblasts under the following conditions: at different times during the cell cycle, in the presence of Colcemid or of taxol, in the presence of both drugs in succession or simultaneously in varying ratios, and during recovery from treatment with Colcemid or taxol. We have found that depolymerization of MTs by 1 microM Colcemid resulted in the rapid formation of massive IF-cables, structures distinct from "collapsed IFs" or "juxtanuclear coils." Neither the rapid formation of IF-cables nor their dispersion during recovery required protein synthesis. Cells treated with 10 microM taxol rapidly formed MT-bundles, as well as aggregates of intertwining IFs, termed "IF-skeins." MT-bundles and IF-skeins displayed strikingly complementary distributions. This reciprocal distribution of packed MTs and IFs was also obvious in untreated anaphase and telophase cells. When 10 microM taxol and 1 microM Colcemid were applied simultaneously, the complementary distributions of MT-bundles and IF-skeins mimicked those in taxol alone. This ability of taxol to block Colcemid's effects was concentration dependent. Decreasing the taxol: Colcemid ratio allowed the depolymerization of MTs, which correlated with the formation of IF-cables.

Use of different hapten-protein conjugates immobilized on nitrocellulose to screen monoclonal antibodies to abscisic acid

The dot-immunobinding method for screening antibodies to proteins on sheets of nitrocellulose has been modified to allow monoclonal antibodies (McAb) to the hapten abscisic acid (ABA) to be screened. Several methods for conjugating ABA to proteins using new bifunctional coupling reagents, specific for hapten keto groups, are described. Hybridomas secreting McAb with a defined specificity for the hapten can be identified by screening supernatants against the carrier protein and other hapten-protein conjugates with different conjugation bridges or modified hapten structure. Inhibition of binding to conjugates by free hapten is used to determine the relative avidity of the McAb for free and bound hapten. All of these tests could be done with no more than about 50 microliter of antibody solution. Dot immunobinding is a useful alternative to radioimmunoassay for screening McAb to haptens.

Identification of a nuclear localization signal of a yeast ribosomal protein

To identify a signal involved in transporting a ribosomal protein to the nucleus, we constructed hybrid genes encoding amino-terminal segments of yeast ribosomal protein L3 joined to the amino-terminal end of the entire Escherichia coli beta-galactosidase molecule. The subcellular locations of the corresponding hybrid proteins in yeast were determined by in situ immunofluorescence. The first 21 amino acids of L3 were sufficient to localize beta-galactosidase to the nucleus. This region shows limited homology to portions of other nuclear proteins identified as essential for their transport. Larger fusion proteins were also localized to the nucleus. However, a hybrid protein containing all but the 14 carboxyl-terminal amino acids from L3 initially failed to localize; this defect was corrected by inserting a glycine- and proline-containing bridge between the L3 and beta-galactosidase moieties. The renovated protein was able to associate with ribosomes, suggesting that, in addition to entering the nucleus, this hybrid polypeptide was assembled into 60S ribosomal subunits that were subsequently exported to the cytoplasm.

Tubulin domains probed by limited proteolysis and subunit-specific antibodies

The substructure of the tubulin molecule was studied by limited proteolysis and high affinity polyclonal antibodies specific for alpha or beta-tubulin. Brief enzymatic cleavage separates the tubulin monomer into two domains of unequal size. Trypsin splits alpha-tubulin into components with Mr values of 36 X 10(3) and 14 X 10(3), chymotrypsin splits beta-tubulin into 31 X 10(3) Mr and 20 X 10(3) Mr fragments. The cleavage occurs at Arg339 (alpha) and Tyr281 (beta), as determined by sequencing several N-terminal residues of the small domains, i.e. the small domains are the C-terminal parts of the molecules, the large ones are the N-terminal parts. There is a second cleavage site of chymotrypsin within Mr 10(3) to 2 X 10(3) of the C terminus of beta-tubulin. The fragments can be separated only under denaturing conditions. They copolymerize into microtubules and incomplete microtubule walls joined by a wall junction, forming S-shapes and hooks in cross-section. The antibodies were raised against electrophoretically purified tubulin monomers. Those produced with alpha-tubulin are directed predominantly against the large domains; they are either specific for alpha-tubulin or cross-react with the large domain of beta-tubulin. Conversely, antibodies raised against beta-tubulin are directed predominantly against the small domains (beta-specific and beta-cross-reacting fractions). Thus the antibodies discriminate not only between the tubulin chains but also between the domains generated by the proteases. The complementary antigenicity correlates well with the stability of the domains. Potential sites of antigenic determinants are located within the polypeptide chains by comparing theoretical predictions with the pattern of immunoblots. Two epitopes of the alpha-cross-reacting antibodies have been located approximately. One is very close to the C terminus (within about 20 residues), the other is close to the N terminus (within about Mr 8 X 10(3) ). The epitope of the beta-cross-reacting antibody is also located within Mr 12 X 10(3) of the C terminus. The antibodies prevent microtubule assembly and cause disassembly of preformed microtubules. A variety of breakdown products are observed by electron microscopy. They include fibres of about 10 nm width, sheets with undefined substructure, thick tapered fibrous bundles and wispy filaments.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of monoclonal antibodies to analyse the expression of a multi-tubulin family

We have used a panel of monoclonal antibodies in a study of the expression of multiple tubulins in Physarum polycephalum. Three anti-beta-tubulin monoclonal antibodies, DM1B, DM3B3 and KMX-1 all reacted with the beta 1-tubulin isotypes expressed in both myxamoebae and plasmodia. However, these antibodies showed a spectrum of reduced reactivity with the plasmodial beta 2-tubulin isotype - the competence of recognition of this isotype was graded DM1B greater than KMX-1 greater than DM3B3. The anti-alpha-tubulin monoclonal antibody, YOL 1/34 defined the full complement of Physarum alpha-tubulin isotypes, whilst the anti-alpha-tubulin monoclonal antibody, KMP-1 showed a remarkably high degree of isotype specificity. KMP-1 recognises all of the myxamoebal alpha 1-tubulin isotypes but only recognises 3 out of the 4 alpha 1-tubulin isotypes expressed in the plasmodium (which normally focus in the same 2D gel spot). KMP-1 does not recognise the plasmodial specific alpha 2-tubulin isotype. This monoclonal antibody reveals a new level of complexity amongst the tubulin isotypes expressed in Physarum and suggests that monoclonal antibodies are valuable probes for individual members of multi-tubulin families.

Intermediate filaments in non-neuronal cells of invertebrates: isolation and biochemical characterization of intermediate filaments from the esophageal epithelium of the mollusc Helix pomatia

To screen invertebrate tissues for the possible expression of intermediate filaments (IFs), immunofluorescence microscopy with the monoclonal antibody anti-IFA known to detect all mammalian IF proteins was used (Pruss, R. M., R. Mirsky, M. C. Raff, R. Thorpe, A. J. Dowding, and B. H. Anderton. 1981. Cell, 27:419-428). In a limited survey, the lower chordate Branchiostoma as well as the invertebrates Arenicola, Lumbricus, Ascaris, and Helix pomatia revealed a positive reaction primarily on epithelia and on nerves, whereas certain other invertebrates appeared negative. To assess the nature of the positive reaction, Helix pomatia was used since a variety of epithelia was strongly stained by anti-IFA. Fixation-extraction procedures were developed that preserve in electron micrographs of esophagus impressive arrays of IFs as tonofilament bundles. Fractionation procedures performed on single cell preparations document large meshworks of long and curvilinear IF by negative stain. These structures can be purified. One- and two-dimensional gels show three components, all of which are recognized by anti-IFA in immunoblotting: 66 kD/pl 6.35, 53 kD/pl 6.05, and 52 kD/pl 5.95. The molar ratio between the larger and more basic polypeptide and the sum of the two more acidic forms is close to 1. After solubilization in 8.5 M urea, in vitro filament reconstitution is induced when urea is removed by dialysis against 2-50 mM Tris buffer at pH 7.8. The reconstituted filaments contain all three polypeptides. The results establish firmly the existence of invertebrate IFs outside neurones and demonstrate that the esophagus of Helix pomatia displays IFs which in line with the epithelial morphology of the tissue could be related to keratin IF of vertebrates.

Identification of molecular components of the centrosphere in the mitotic spindle of sea urchin eggs

Monoclonal antibodies were prepared to identify molecular components specific to the mitotic apparatus of sea urchin eggs. The mitotic apparatus or asters induced within unfertilized eggs by taxol treatment were isolated from Strongylocentrotus purpuratus and used for immunization of mice. After fusion with spleen cells, the supernatant of hybridomas were screened in two stages by indirect immunofluorescence staining, first on isolated sea urchin mitotic spindles in 96-well microtiter plates to identify rapidly potential positive hybridomas, and second, on whole mitotic eggs on coverslips to distinguish between spindle-specific staining and adventitious contamination. Two hybridomas, SU4 and SU5, secreted antibodies reactive to microtubule-containing structures in eggs during the course of development. They preferentially stained the centrosphere both in isolated mitotic apparatus and in whole metaphase eggs, which was further confirmed by staining the isolated centrospheres with these antibodies. SU4 recognized a major 190-kD polypeptide on immunoblots as well as a species at 180 and 20 kD, whereas hybridoma SU5 stained a species at 50 kD. Thus, these polypeptides may be components of the centrosphere.

Monoclonal antibodies to a higher-plant nitrate reductase: Differential inhibition of enzyme activities

A set of monoclonal antibodies has been raised against NADH-nitrate reductase (NR; EC 1.6.6.1) from spinach (Spinacea oleracea L.) leaves. Antibodies were screened by enzyme-linked immunosorbent assay and by their ability to inhibit various activities of the enzyme. The six monoclonals selected (AFRC MAC 74 to 79) are all gamma globulins; four (MAC 74 to 77) inhibit all terminal donating activities (NADH-NR; flavin mononucleotide, reduced form (FMNH2)-NR; and methyl viologen, reduced form (MV)-NR) and two (MAC 78 and 79) inhibit the acceptor activities (NADH-NR, and NADH-cytochrome c reductase). MAC 74 to 77 inhibit the NADH-NR activity of crude extracts of a variety of species (mono- and dicotyledoneae) while MAC 78 and 79 are effective against spinach and marrow, but not oil-seed rape, cucumber, oats, wheat and barley.

Microtubule nucleating sites in higher plant cells identified by an auto-antibody against pericentriolar material

Human scleroderma serum 5051, which is known to recognize the amorphous pericentriolar microtubule organizing center material of a variety of vertebrate cells, was found to immunostain spindle poles of meristematic higher plants from pre-prophase to late anaphase. Subsequently, during cytokinesis, staining was redistributed around the reforming telophase nuclei, but was not evident in the cytokinetic phragmoplast. At the transition between telophase and interphase, before the typical cortical interphase microtubule array was established, short microtubules radiated from the nucleus and in such cells the material recognized by 5051 was located around the daughter nuclei and not the cortex. These observations have led us to propose that the perinuclear region, or the nuclear surface, may function as a nucleation center for both spindle and interphase microtubules in higher plant cells.

Immunocytochemical demonstration of tubulin microheterogeneity within rat cortical and hippocampal pyramidal neurons

Rat cortical and hippocampal pyramidal cells were immunocytochemically investigated using the TU-01 monoclonal antibody recognizing alpha-tubulin. The isotypic specificity of this antibody is distinct from that of other available alpha-tubulin antibodies; therefore, an intracellular heterogeneity among neuronal microtubules could be revealed by observing intensely immunostained apical dendritic microtubules in the complete absence of staining of the microtubules in the basal dendrites and perikarya of the same pyramidal cells.

The small subunit of ribonucleotide reductase is encoded by one of the most abundant translationally regulated maternal RNAs in clam and sea urchin eggs

In both clam oocytes and sea urchin eggs, fertilization triggers the synthesis of a set of proteins specified by stored maternal mRNAs. One of the most abundant of these (p41) has a molecular weight of 41,000. This paper describes the identification of p41 as the small subunit of ribonucleotide reductase, the enzyme that provides the precursors necessary for DNA synthesis. This identification is based mainly on the amino acid sequence deduced from cDNA clones corresponding to p41, which shows homology with a gene in Herpes Simplex virus that is thought to encode the small subunit of viral ribonucleotide reductase. Comparison with the B2 (small) subunit of Escherichia coli ribonucleotide reductase also shows striking homology in certain conserved regions of the molecule. However, our attention was originally drawn to protein p41 because it was specifically retained by an affinity column bearing the monoclonal antibody YL 1/2, which reacts with alpha-tubulin (Kilmartin, J. V., B. Wright, and C. Milstein, 1982, J. Cell Biol., 93:576-582). The finding that this antibody inhibits the activity of sea urchin embryo ribonucleotide reductase confirmed the identity of p41 as the small subunit. The unexpected binding of the small subunit of ribonucleotide reductase can be accounted for by its carboxy-terminal sequence, which matches the specificity requirements of YL 1/2 as determined by Wehland et al. (Wehland, J., H. C. Schroeder, and K. Weber, 1984, EMBO [Eur. Mol. Biol. Organ.] J., 3:1295-1300). Unlike the small subunit, there is no sign of synthesis of a corresponding large subunit of ribonucleotide reductase after fertilization. Since most enzymes of this type require two subunits for activity, we suspect that the unfertilized oocytes contain a stockpile of large subunits ready for combination with newly made small subunits. Thus, synthesis of the small subunit of ribonucleotide reductase represents a very clear example of the developmental regulation of enzyme activity by control of gene expression at the level of translation.

A microtubule-associated protein (MAP1) which is expressed at elevated levels during development of the rat cerebellum

Monoclonal antibody (MAb) G10 labels a single high mol. wt. (HMW) band on Western blots of microtubule preparations from 2 day old rat brain. The G10 antigen is thermolabile and co-migrates with microtubule-associated protein (MAP)1 from young rat brain on low percentage (5%) polyacrylamide-SDS gels. The G10 antigen decreases by about five times from birth to adulthood in the rat cerebellum. The same single band is labelled on Western blots of homogenates of whole neonatal rat brain but no labelling is found using neonatal or adult kidney, lung or liver. We have therefore identified a brain-specific MAP1, designated MAP1(x). Immunofluorescence microscopy using MAb G10 on parasagittal sections of rat cerebella shows labelling of the newly formed molecular layer in 6 day old rats. Only a narrow band close to the pial surface is labelled in 18 day old animals, which disappears in the adult. Labelling of the cerebellar white matter found in young rats also disappears. Neurones but not flat cells in cerebellar cultures label with MAb G10. All staining patterns are consistent with an axonal distribution of the antigen. MAP1(x) may be part of a developmentally regulated microtubule structure.

A widely distributed nuclear protein immunologically related to the microtubule-associated protein MAP1 is associated with the mitotic spindle

A 280-kDa protein (p280) confined to the nucleus of interphase cells becomes associated with the mitotic spindle during cell division. p280 is immunologically related to the microtubule-associated protein MAP1, as shown by cross-reactivity with monoclonal (8D12) and polyclonal antibodies raised against MAP1. However, p280 is distinct from MAP1 as judged by its lower molecular size, proteolytic degradation products, presence in preparations of purified nuclei from which MAP1 is absent, and absence from the cytosol fraction that contains MAP1. Immunofluorescence microscopy of cells in interphase using 8D12 reveals punctate staining of the nucleus, cytoplasmic microtubules, and the microtubule organizing center. Dividing cells display strong staining of the spindle, centrioles, and mid-body. The only exception to this staining pattern is marsupial Pt k2 cells that contain p280 in the nucleus and lack MAP1. These cells exhibit fluorescent staining of the nucleus and the microtubule organizing center when in interphase, of spindle and centrioles in mitosis, and show no staining of cytoplasmic and mid-body microtubules.

Actin organization during the cell cycle in meristematic plant cells. Actin is present in the cytokinetic phragmoplast

The distribution and organisation of F-actin during the cell cycle of meristematic root-tip cells of Allium was investigated using a rhodamine-labelled phalloidin to stain F-actin in isolated cell preparations. Such preparations could, in addition, be stained for tubulin by immunofluorescence, enabling a comparison between F-actin and microtubule distributions in the same cell. In interphase, an extensive array of actin-filament bundles was present in the cytoplasm of elongating cells, the bundles generally following the long axis of the cell and passing in close proximity to the nucleus. In contrast, the interphase microtubule array occupied the cortex of the cell and was oriented at right angles to the actin bundles. In smaller, isodiametric cells, microfilament arrays were present but less well developed. During cell division, phalloidin-specific staining was seen in the cytokinetic phragmoplast, and co-distributed with microtubules at all stages of cell plate formation; however, neither the pre-prophase band nor the mitotic spindle were stained with phalloidin. Co-distribution of F-actin and microtubules only occurs, therefore, at cytokinesis. The relationship between microfilaments and microtubules is discussed, together with the possible role of actin in the phragmoplast.

Proteins closely similar to flagellar tektins are detected in cilia but not in cytoplasmic microtubules

Affinity-purified antibodies against Strongylocentrotus purpuratus sperm flagellar tektin polypeptides have been tested for cross-reactivity with microtubules isolated from various sources, using indirect immunofluorescent staining and antibody binding to nitrocellulose replicas of SDS polyacrylamide gels. The antitektins reacted with sperm tail axonemes from four genera of sea urchins and with cilia from sea urchin embryos. Antibody binding was observed only if the specimens were prefixed by methods that would not preserve them well at an ultrastructural level. However, even after such fixation regimes, no antibody binding was detected to cytoplasmic microtubule arrays in the same embryos, to mitotic spindles isolated from sea urchin eggs or to gill cilia from a mollusc. We conclude that, if tektins are present in sea urchin egg cytoplasmic microtubules, they are sufficiently different from the sperm tektins to have no common strongly antigenic determinants.