Kinetochore structure, duplication, and distribution in mammalian cells: analysis by human autoantibodies from scleroderma patients

Characterization of a polypeptide associated with coated vesicles and the cytoskeleton which is recognized by a CREST serum

Serum from an individual with the CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dismotility, sclerodactyly, telangiectasia) reacts not only with kinetochores, but also with a cytoplasmic, phosphorylatable polypeptide, which is shown by immunofluorescence in whole cells and immunoelectronmicroscopy in sections to be associated with actin stress fibres in cultured mammalian cells. The antigen shows some variation in molecular weight between species, estimated by immunoblotting to range from 68 to 76 kD between mouse, Chinese hamster, sheep and human cells. Much of the polypeptide copurifies with coated vesicles, of which approx. 5% bound antibody from the serum, as detected by immunogold electronmicroscopy.

Direct evidence for the non-random localization of mammalian chromosomes in the interphase nucleus

Indirect immunofluorescence staining with human anti-centromere autoantibodies from a patient (LU 851) suffering from the CREST form of scleroderma was used to analyse chromosome topology in interphase nuclei of rat-kangaroo (PTO) and Indian muntjac (IM) cells. In some cells, centromeres were arranged in pairs suggesting association of homologous chromosomes. Clustering of centromeres at one pole of the nucleus (Rabl configuration) and other patterns suggesting higher order organization were also observed. In one fifth of the IM cells it was possible to identify the intranuclear location of each single chromosome on the basis of the morphology of the immunostained centromeres. In 30% of the IM cells in which centromeres could be identified, homologous chromosomes occupied adjacent territories within the interphase chromatin.

Arrangements of kinetochores in mouse cells during meiosis and spermiogenesis

Antibodies from the serum of patients with the autoimmune disease scleroderma CREST were used to investigate the association and distribution of kinetochores in mouse cells during meiosis and spermiogenesis. The pattern of indirect immunofluorescent staining in pachytene nuclei indicated that each autosomal bivalent contains one fluorescent spot. Throughout pachytene, the kinetochores were arranged non-randomly into several clusters and distributed around the periphery of the nucleus. In subsequent stages of meiotic prophase I, distribution was random and the number of fluorescent spots increased from 21 to 40 corresponding to the diploid chromosome number and the number of halfbivalents oriented to the spindle poles at the metaphase I. Twenty pairs of kinetochores were observed at metaphase II. During spermiogenesis, the number of kinetochores correlated with the haploid chromosome number in early spermatids but tandem association of centromeres and clustering into a conspicuous chromocenter corresponded to a significant reduction in the number of fluorescent foci in mid-spermatid nuclei. The number of stained sites per nucleus continued to decrease during sperm maturation and total absence of staining was apparent in mature spermatozoa. Immunoblotting of proteins extracted from mature sperm however, indicated that a kinetochore antigen of Mr 80,000 was still present. Therefore, the absence of kinetochore staining in mature spermatozoa is probably due to the blockage of epitopes during chromatin condensation.

Characterization of kinetochores in multicentric chromosomes

Long-term cultures of certain rat and mouse cell lines carry several dicentric and some multicentric chromosomes. Using antikinetochore antibodies obtainable from serum of scleroderma (var. CREST) patients we studied the number of kinetochores formed along the length of these chromosomes. The rat cells displayed as many kinetochores as there were centromeres. However, mouse cells showed the synthesis of only one kinetochore in dicentric and multicentric chromosomes which had been in the culture for a period of 1 year or more. When translocations were induced by bleomycin in mouse L cells, the newly formed dicentric chromosomes showed the formation of two kinetochores. It is not known when the accessory centromeres lose their capacity to assemble kinetochore proteins. Possibly, in the rat the 'latent' kinetochore lack a specific component which renders them ineffective for microtubule binding. The reason for the formation of only one kinetochore in mouse multicentric chromosomes is not clear. It may be due to the accumulation of mutations, modification of the kinetochore protein so that it lacks the antibody binding component, or a more effective regulatory gene than in the rat.

Sequence of centromere separation: a mechanism for orderly separation of dicentrics

Stable dicentric chromosomes from three mouse cell lines (viz., SEWA Rec4, brain tumor, and L-cells), as well as a human t(9;11) line were analyzed for the sequence in which the two centromeres separate. At prometaphase, as well as in many cells at midmetaphase, the dicentrics express the two centromeres in the form of two primary constrictions. As the cell advances to late metaphase, one of the constrictions loosens the two chromatids so that eventually there is no connection between them. The other centromere stays intact during this period and separates into two units at the metaanaphase junction along with the rest of the genome. The centromere that separates prematurely (out-of-phase) usually is the same in a given dicentric. It is proposed that such a prematurely separating centromere does not function as active element during chromatid migration. Apparently, in dicentrics some sort of control is exerted to eliminate the functioning of one centromere. The nature of such control is not understood at this time. The mouse dicentrics "synthesize" only one kinetochore as definable by antikinetochore antibody studies.

Topoisomerase I identified by scleroderma 70 antisera: enrichment of topoisomerase I at the centromere in mouse mitotic cells before anaphase

Antibodies derived from scleroderma patients positive for the extractable 70-kDa antigen were shown to react with topoisomerase I. Topoisomerase I was identified by molecular size and by antibody inhibition of the topoisomerase I-specific relaxation of supercoiled plasmid DNA. By using in situ localization by indirect fluorescence, we found topoisomerase I preferentially located in the centromeric regions of the mouse G2-phase cells and chromosomes, while the distribution in human cells is much more dispersed. Moreover, comparison of a published consensus sequence for topoisomerase I binding with mouse satellite DNA revealed a high degree of homology. The localization of topoisomerase I in the centromeres of mouse cells in the later part of the cell cycle and prior to anaphase suggests functional involvement in mitosis.

Organization within the mammalian kinetochore

The organization within the mammalian kinetochore was examined using whole-mount electron microscopic techniques on chromosomes digested with restriction enzymes or micrococcal nuclease. These preparations revealed that a portion of the kinetochore is highly resistant to nuclease digestion and can be visualized as a discrete structure. The relationship of this structure to the remainder of the chromosome suggests that it represents the outer kinetochore plate. The plate is composed of a series of fibrillar loops that are arranged in a parallel array along the plane of the plate. These fibers are 25-30 nm in diameter. The morphology, particulate substructure, and ultimate susceptibility to nuclease digestion suggest that these fibers contain DNA. A model is presented that suggests that the outer plate contains the apexes of chromatin loops that originate within the body of the primary constriction.

Spontaneous recurrent fetal wastage and autoimmune abnormalities: a study of fourteen cases

Case records of 14 women with spontaneous recurrent fetal wastage were analyzed. Venous and/or arterial thrombosis developed in nine patients and vasospastic symptoms in eight. Every patient had some kind of autoantibodies: prothrombin activation inhibitor was present in seven cases, anticardiolipin in five, and, antimitochondrial antibodies in two. Antinuclear antibodies were present in seven cases, and significant titer of antibodies to single-stranded DNA in nine cases. With a mean follow up of 6.5 years no patient developed systemic lupus erythematosus. It is suggested that such women have a peculiar form of vasculitis.

Preservation of chromosome integrity during micronucleation induced by colchicine in PtK1 cells

Colchicine induces the formation of small nuclei called micronuclei which contain limited parts of the genome. Some of them exhibit a DNA content equivalent to that of a single chromosome. Our purpose was to study the preservation of chromosome integrity during this micronucleation in PtK1 cells. Observation of karyotypes obtained after 3 days of cell cycle restoration revealed that micronucleation did not affect chromosome integrity or the presence of each chromosome pair in the surviving cells. In 'early restoration' cells, all the chromosomes included a centromere and were represented in the karyotype, but at variable rates. Furthermore, flow cytometry analysis of micronucleated cells, intermediate in DNA rate between control PtK1 cells in G1 and those in G2/M phases, led us to consider the possibility of selective replication of some chromosomes during micronucleation. Using antibodies against the kinetochore proteins, we derived the presence of one centromeric region (1-2 spots) in the smallest micronuclei. Therefore, these data (karyotypes, number of chromosomes, DNA content and kinetochore proteins) seem to indicate that micronucleation does not induce chromosome damages or translocations. Micronuclei are a convenient tool for investigation of the role of the different chromosomes in the organization of the interphase nuclei.

Fractionation and initial characterization of the kinetochore from mammalian metaphase chromosomes

We have partially isolated the kinetochore and associated centromeric structures from mammalian metaphase chromosomes. Human autoantibodies from scleroderma CREST (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia) patients were used as immunofluorescent probes to monitor fractionation. The procedure includes digestion of total chromosomal DNA with micrococcal nuclease, dehistonization with heparin, and dissociation of the remaining material with detergent and urea. We used a density gradient (metrizamide) to obtain an enriched fraction of stained material (kinetochore). When examined by electron microscopy, the kinetochore fraction is seen to contain numerous small immunoperoxidase-positive masses which are morphologically similar to the centromere/kinetochore region of intact metaphase chromosomes. The particulate fraction that contains kinetochore components represents less than 5% of total chromosomal proteins and contains less than 1% of total DNA. Two polypeptides of 18 and 80 kD were identified as kinetochore antigens by immunoblotting with CREST antiserum. In this paper we discuss the distribution of these kinetochore polypeptides with the associated centromeric chromatin.

Genetic change may be caused by interference with protein-protein interactions

Several aprotic polar solvents were shown to induce mitotic aneuploidy in yeast: diethyl ketone, gamma-valerolactone, pyridine, pivalinic acid nitrile, phenylacetonitrile and fumaric acid dinitrile. Only fumaric acid dinitrile also strongly induced other types of genetic effects including mitotic crossing-over, mitotic gene conversion and point mutation. The other substances only induced aneuploidy and this only over a very narrow dose range. The treatment protocol used suggested that these chemicals acted via interference with tubulin assembly and disassembly causing a malfunctioning of spindle fiber microtubules. This hypothesis was tested using twice recycled porcine brain tubulin. Diethyl ketone, gamma-valerolactone, pyridine and phenylacetonitrile inhibited GTP-promoted assembly of porcine brain tubulin in vitro in the concentration range needed for the induction of mitotic aneuploidy in yeast. Pivalinic acid nitrile accelerated tubulin aggregation whereas fumaric acid dinitrile had no effect even at concentrations 18 times higher than the lowest tested concentration effective in yeast. The in vitro experiments with porcine brain tubulin further suggest that genetic change can result from interference with specific protein-protein interactions. Fumaric acid dinitrile was the only exception since it did induce aneuploidy but had no effects on the assembly of porcine brain tubulin. This could be caused either by interference with protein-protein interactions other than between molecules during assembly and disassembly of microtubules or species-specific differences in susceptibility between yeast spindle and porcine brain tubulin.

Indications of centromere movement during interphase and differentiation

Mouse and human DNA sequences from centromeric and ribosomal domains were labeled with biotinylated deoxynucleotides and hybridized in situ to paraformaldehyde-fixed tissue culture cells. Centromeres were widely dispersed in most of these interphase nuclei. At late G2 phases of the cell cycle, centromeres appeared to coalesce and then to align in an orderly pattern, with discrete positional assignments for individuals chromosomes in metaphase and anaphase. Ribosomal cistrons were also organized in an orderly and defined fashion during mitosis. As soon as the nuclear membrane forms in early G1, centromeres rapidly disperse throughout the nucleus. Centromere patterns during G1 and S were indistinguishable in cultured cells, as determined by double-labeling experiments. Antibodies that bind to centric chromosomal proteins revealed the same patterns in cultured cells as those obtained with DNA sequence-specific probes. Large differentiated neurons display reproducible collections of centromeres in interphase that are very different from those seen in cultured cells. Neurons in widely divergent mammalian species, despite large differences in centromeric DNA sequences, maintain similar nuclear positions for these chromosomal segments. Similarly, ribosomal cistrons are positioned in comparable nuclear locales in neurons of divergent species. It is suggested that such arrangements reflect, or are necessary for, the function of a given cell type. Studies of large cerebellar neurons at critical times in development indicated a relative "movement" of centromeric domains, away from the nuclear membrane and toward the central nucleolar region. It is possible that the orderly and temporal positioning of centromeric, as well as of other chromosomal regions, is based on protein-nucleic acid interactions. Implications for trisomy 21 and other disorders involving chromosomal rearrangements, such as transposition, are considered from this perspective.

Kinetochore components recognized by human autoantibodies are present on mononucleosomes

We have developed a competitive enzyme-linked immunosorbent assay for solubilized kinetochore components, using human CREST (calcinosis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, telangiectasia) scleroderma autoimmune antibodies specific for these kinetochore elements. Using this quantitative assay, we found interphase persistent or "pre-kinetochore" components in low- and moderately high-salt (375 mM salt) extracts of micrococcal nuclease-digested rat liver and chicken erythrocyte nuclei. The release of antigen activity from nuclei under these conditions has been correlated with loss of pre-kinetochore foci as determined by immunofluorescence microscopy. Combined biochemical and competition assay analysis of chicken erythrocyte nuclear extracts indicates that pre-kinetochore components are tightly bound to chromatin of mononucleosome size. The conclusions based on competition assay data are supported by a direct binding assay, which confirms that antigens recognized by CREST sera are present on chromatin. These results raise the possibility that the kinetochore-specific chromosomal antigen(s) we have detected substitutes for "standard" mononucleosome components, such as histone H1. Furthermore, they suggest approaches to the isolation of kinetochore-specific DNA sequences from higher eucaryotes.

Fluorescence microscopy with antisera against specific cellular structure: double photography method for cell identification in populations of multiple cell types

Immunofluorescent staining techniques using antitubulin antibody have been difficult to apply to meiotic tissue (testis) because of the large number of cell types present. Such techniques customarily use a fluorescent dye to counterstain nuclei, and this counterstain is hard to distinguish because of the fluorescence of the antitubulin. By counterstaining with dilute hematoxylin, we can photograph the same field using UV and then conventional illumination. This double photography allows us to identify precisely the many types of cells present, and it will be a useful tool for reexamining the staging of spermatogenesis.

Anti-kinetochore antibodies: use as probes for inactive centromeres

Application of a modified immunofluorescence technique using an anti-kinetochore serum enables cytogeneticists to obtain quality metaphase spreads and to localize kinetochores. In a patient with a 45, XX, -9, -11, tdic (9p;11p) constitution, we found that the dicentric marker chromosome has an intensely fluorescent kinetochore (no. 11), the functional centromere, and a less intensely fluorescent kinetochore (no. 9), the inactive centromere. The data suggest that in the process of tandem fusion (telomere-telomere between 11p and 9p), the centromere of chromosome 9 was not deleted, but, rather, inactivated.

Kinetochore components recognized by human autoantibodies are present on mononucleosomes

We have developed a competitive enzyme-linked immunosorbent assay for solubilized kinetochore components, using human CREST (calcinosis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, telangiectasia) scleroderma autoimmune antibodies specific for these kinetochore elements. Using this quantitative assay, we found interphase persistent or "pre-kinetochore" components in low- and moderately high-salt (375 mM salt) extracts of micrococcal nuclease-digested rat liver and chicken erythrocyte nuclei. The release of antigen activity from nuclei under these conditions has been correlated with loss of pre-kinetochore foci as determined by immunofluorescence microscopy. Combined biochemical and competition assay analysis of chicken erythrocyte nuclear extracts indicates that pre-kinetochore components are tightly bound to chromatin of mononucleosome size. The conclusions based on competition assay data are supported by a direct binding assay, which confirms that antigens recognized by CREST sera are present on chromatin. These results raise the possibility that the kinetochore-specific chromosomal antigen(s) we have detected substitutes for "standard" mononucleosome components, such as histone H1. Furthermore, they suggest approaches to the isolation of kinetochore-specific DNA sequences from higher eucaryotes.

Aneuploidy and health risk assessment: current status and future directions

The U.S. Environmental Protection Agency (EPA) recently sponsored a workshop to discuss the contribution of aneuploidy to human disease and disability, the development of tests for detecting chemicals that induce aneuploidy and the relevance of these tests to human risk, and the current understanding of mechanisms by which aneuploidy arises. This summary is based on the presentations given at the workshop. It is hoped that this summary will stimulate thinking in this vitally important area of risk assessment and contribute to the establishment of priorities for basic research, development of new test methods, and validation of existing test approaches. Such research is needed to enhance the scientific basis of risk assessment for aneuploidy-producing chemicals.

The kinetochore of mammalian chromosomes: structure and function in normal mitosis and aneuploidy

The kinetochore is a structurally differentiated site on mitotic chromosomes to which spindle microtubules (MTs) are attached. In mammalian cells, the kinetochore is organized into a trilamellar plate and is morphologically distinct from the centromere. Although kinetochores and centromeres are morphologically and biochemically distinct regions, they are functionally linked and necessary for normal chromosome movement and segregation. Recent biochemical and immunocytochemical studies suggest that the kinetochore is composed of several polypeptides, DNA, and possibly RNA. The kinetochore plates are composed of tubulin and two antigens of 17 Kd and 80 Kd, as detected by scleroderma CREST antiserum. Colcemid, a MT inhibitor, also causes reversible rearrangements of kinetochore structure. Mitomycin C binds to heterochromatin and causes the trilamellar plates to become detached from the chromosome. Diethylstilbestrol (DES), a synthetic estrogen, inhibits mitosis in mammalian cells and causes chromosome lagging or malorientation during recovery. Electron microscopy indicates that DES causes disruption of the mitotic spindle, centriole elongation, and unusual chromosome associations due to interkinetochore microtubules. No apparent damage to kinetochores was noted in lagging or maloriented chromosomes.

Compound kinetochores of the Indian muntjac. Evolution by linear fusion of unit kinetochores

The chromosomes of the Indian muntjac (Muntiacus muntjak vaginalis) are unique among mammals due to their low diploid number (2N = 6 female, 7 male) and large size. It has been proposed that the karyotype of this small Asiatic deer evolved from a related deer the Chinese muntjac (Muntiacus reevesi) with a diploid chromosome number of 2n = 46 consisting of small telocentric chromosomes. In this study we utilized a kinetochore-specific antiserum derived from human patients with the autoimmune disease scleroderma CREST as an immunofluorescent probe to examine kinetochores of the two muntjac species. Since CREST antiserum binds to kinetochores of mitotic chromosomes as well as prekinetochores in interphase nuclei, it was possible to identify and compare kinetochore morphology throughout the cell cycle. Our observations indicated that the kinetochores of the Indian muntjac are composed of a linear beadlike array of smaller subunits that become revealed during interphase. The kinetochores of the Chinese muntjac consisted of minute fluorescent dots located at the tips of the 46 telocentric chromosomes. During interphase, however, the kinetochores of the Chinese muntjac clustered into small aggregates reminiscent of the beadlike arrays seen in the Indian muntjac. Morphometric measurements of fluorescence indicated an equivalent amount of stained material in the two species. Our observations indicate that the kinetochores of the Indian muntjac are compound structures composed of linear arrays of smaller units the size of the individual kinetochores seen on metaphase chromosomes of the Chinese muntjac. Our study supports the notion that the kinetochores of the Indian muntjac evolved by linear fusion of unit kinetochores of the Chinese muntjac. Moreover, it is concluded that the evolution of compound kinetochores may have been facilitated by the non-random aggregation of interphase kinetochores in the nuclei of the ancestral species.

The anticentromere antibody: disease specificity and clinical significance

Serum samples from 539 subjects were screened for the presence of the anticentromere antibody on a human laryngeal carcinoma (HEp-2) cell line (Antibodies, Inc.). The antibody was present in 61 patients (11%), most of whom had features of limited scleroderma or the CREST syndrome (calcinosis cutis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia), either independently or in association with primary biliary cirrhosis. The antibody was rarely found in patients with rapidly advancing or diffuse scleroderma. The anticentromere antibody is therefore a useful prognostic indicator in patients with early scleroderma, as it may help to predict what pattern of scleroderma will evolve. Screening for this antibody should be conducted in all patients with Raynaud's phenomenon, primary biliary cirrhosis, and scleroderma. Other previous studies have indicated a similar disease specificity and prognostic importance of this antibody.

Antitubulin immunofluorescence studies of spermatogenesis in the mouse

Immunofluorescence staining techniques, using antibodies against tubulin molecules, have been successfully used with somatic tissue culture cells. Their application to gametogenesis, however, has been more difficult, largely due to the presence of many different cell types in such a preparation. We have circumvented this problem by counterstaining with dilute hematoxylin, a biological stain that shows excellent cellular morphology without affecting the fluorescence of the antibody. We can then photograph the same field, using either ultraviolet light or conventional bright-field microscopy. Using this approach, we have examined the entire progression of murine spermatogenesis, from spermatogonial cells through mature spermatozoa. This technique has been especially valuable in the visualization of the manchette, and has allowed a reassessment of the staging of spermatid development. In the future, the antibody/hematoxylin double-staining approach will allow a more informative examination of the effects of tubulin-active mitotic poisons on mammalian germline cells.

Anticentromere antibodies bind to trout testis histone 1 and a low molecular weight protein from rabbit thymus

Antibodies directed against centromeric chromatin characteristically occur in the sera of patients with the CREST variant of scleroderma. We have studied the in situ enzymatic sensitivity and solubility of the centromeric antigen and have isolated an antigenic moiety that reacts with anticentromere antibodies. The centromeric antigen in the human epithelial cell line, HEp-2, was sensitive to DNAase I and micrococcal nuclease but not affected by RNAase A, trypsin or amylase. It was insoluble in 0.15-4 M NaCl but was extracted from the HEp-2 cells by 4 M urea/2 M NaCl. Antigenic activity in a 4 M urea/2 M NaCl extract of rabbit thymus was demonstrated by immunoabsorption. Indirect immunofluorescence of the extract separated by polyacrylamide gel electrophoresis revealed a fluorescent band with a mol. wt of 33,000. Calf thymus and trout testis histone preparations were fractionated by gel electrophoresis and transferred by blotting techniques to diazobenzyloxymethyl cellulose paper for autoradiography. Anticentromere antibodies bound to and were absorbed by trout testis histone 1. We propose that the centromeric antigen may be a variant of histone 1 that is associated with condensed chromatin.

NuMA protein is a human autoantigen

Routine examination of sera from patients with suspected or confirmed connective tissue disease has revealed the presence of autoantibodies directed against an unusual nuclear antigen. As characterized by immunofluorescence studies, the antigen is found exclusively in the nuclei of interphase cells, but appears to be part of the spindle pole in mitotic cells. Similar distributions in interphase and mitotic cells have been reported for the recently discovered nuclear mitotic apparatus (NuMA) protein. Using immunoblot analysis we have demonstrated that the autoantibodies that decorate the mitotic spindle poles are specific for the NuMA protein. Therefore, we conclude that the NuMA protein is a human autoantigen.

Phosphoproteins are components of mitotic microtubule organizing centers

Protein phosphorylation has been suggested as an important control mechanism for the events leading toward the initiation and completion of mitosis. Using a monoclonal antibody recognizing a class of phosphoproteins abundant in mitotic cells, we demonstrated the localization of a subset of these phosphoproteins to several discrete mitotic structures. Patchy immunofluorescence was present in the interphase nuclei, but a significant increase in nuclear immunofluorescence was apparent at prophase. Subsequent mitotic stages demonstrated that immunoreactive material was particularly apparent at microtubule organizing centers, namely, centrosomes, kinetochores, and midbodies. Intense centrosomal localization occurred at the prophase-prometaphase transition and persisted until the reformation of the nuclear membrane in early G1. The cytoplasm of mitotic cells also contained immunoreactive material in sharp contrast to interphase cells that exhibited no cytoplasmic fluorescent staining. Much of the diffuse immunofluorescent cytoplasmic material was removed by a brief lysis of the cells with 0.15% Triton X-100 prior to fixation. The localization of the remaining immunoreactive material after detergent lysis to mitotic microtubule organizing centers suggests that they contain phosphoprotein structural components important, perhaps, in the mitotic phase-interphase transition.

Clinical and laboratory associations of anticentromere antibody in patients with progressive systemic sclerosis

Anticentromere antibody (ACA) was found in the serum of 4 (3%) of 120 patients with progressive systemic sclerosis with diffuse scleroderma and in 69 (49%) of 141 with progressive systemic sclerosis with the CREST syndrome variant. The 69 CREST syndrome patients with ACA were compared with the 72 CREST syndrome patients without ACA. The former were older at the onset of symptoms and significantly more frequently female (97% versus 78%, P less than 0.01). Those with ACA more often had telangiectasiae of the digits (93% versus 75%) and calcinosis (55% versus 22%). These differences were also present after the groups were stratified according to duration of disease. Cutaneous involvement was similar in both degree and extent in the 2 groups; 20% of CREST patients both with and without ACA had forearm skin thickening. Pulmonary interstitial fibrosis on chest roentgenogram and restrictive disease on pulmonary function testing were significantly less frequent in the ACA patients. Gastrointestinal involvement, pulmonary arterial hypertension, and cardiac abnormalities were similar in both groups, and there has been no difference in survival between CREST syndrome patients with and without ACA. Tissue typing studies revealed a significant association between ACA and HLA-DR1.

The kinetochore is part of the metaphase chromosome scaffold

We used antisera from patients with the CREST syndrome of scleroderma (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia) to show that an antigenic component of the kinetochore present in metaphase chromosomes is also present in nonhistone chromosome scaffolds isolated following extensive digestion of the DNA and extraction of the bulk of chromosomal protein. All sera from 12 scleroderma CREST patients previously shown by immunofluorescence microscopy to have circulating antikinetochore antibodies recognise a protein of Mr 77,000 (CREST-77) in an immunoblotting assay. 9 of the 12 sera also recognise an antigen of Mr 110,000 (CREST-110). These proteins are present in isolated chromosomes and nonhistone scaffolds derived from them by two different procedures. Sera of five scleroderma CREST patients who are antikinetochore negative (by immunofluorescence) bind to neither protein in immunoblots. These data suggest that CREST-77 (and possibly CREST-110) is a component of the human kinetochore, and that the kinetochore is an integral part of the mitotic chromosome scaffolding.

Human anticentromere antibodies: distribution, characterization of antigens, and effect on microtubule organization

Properties of human anticentromere autoantibodies were analyzed. In intact cells or isolated cell fractions, these sera stain the centromeres of mitotic chromosomes and discrete speckles (prekinetochores) in nuclei. Staining is also retained in matrix preparations from nuclei or chromosomes. Immunoprecipitation or immunoblotting demonstrates protein antigens of 14, 20, 23, and 34 kd in HeLa nuclei and chromosomes; immunoprecipitates of nuclei also contain a protein of 15.5 kd. Matrix preparations contain only the 20, 23, and 34 kd species. Absorption of the anticentromere serum with any one of the four nuclear antigens immobilized on nitrocellulose is sufficient to eliminate centromere staining. Using a lysed cell model for microtubule nucleation, anticentromere sera are shown to inhibit specifically the organization of microtubules at the kinetochore.

Cytoplasmic microtubules in polymorphonuclear leukocytes: effects of chemotactic stimulation and colchicine

Indirect immunofluorescent (IIF) techniques employing antitutulin and anticentrosome antibodies were modified for studies of migrating polymorphonuclear (PMNs) leukocytes exposed to gradients or uniform concentrations of chemotactic factor (CF). No significant changes in microtubule (MT) number per cell occurred with chemotactic activation. Significant increases in average MT length per cell occurred upon exposure to gradients or uniform concentrations of CFs. Elongation of MT parallel to the direction of cell migration occurred coincident with shortening of other sets of MTs perpendicular to the direction of cell migration. MT extended radially from a single microtubule organizing center (MTOC) in greater than 99.9% of cells. Following chemotactic activation, the location of the MTOC was observed between nuclear lobes in 65% of fully polarized cells, "posterior" to the nucleus in congruent to 34% and "anterior" in less than 1%. Thus alterations of MT array occur coincident with cell orientation or migration in response to chemotactic stimuli.

A dependent pathway of gene functions leading to chromosome segregation in Saccharomyces cerevisiae

Methyl-benzimidazole-2-ylcarbamate (MBC) inhibits the mitotic cell cycle of Saccharomyces cerevisiae at a stage subsequent to DNA synthesis and before the completion of nuclear division (Quinlan, R. A., C. I. Pogson, and K, Gull, 1980, J Cell Sci., 46: 341-352). The step in the cell cycle that is sensitive to MBC inhibition was ordered to reciprocal shift experiments with respect to the step catalyzed by cdc gene products. Execution of the CDC7 step is required for the initiation of DNA synthesis and for completion of the MBC-sensitive step. Results obtained with mutants (cdc2, 6, 8, 9, and 21) defective in DNA replication and with an inhibitor of DNA replication (hydroxyurea) suggest that some DNA replication required for execution of the MBC-sensitive step but that the completion of replication is not. Of particular interest were mutants (cdc5, 13, 14, 15, 16, 17, and 23) that arrest cell division after DNA replication but before nuclear division since previous experiments had not been able to resolve the pathway of events in this part of the cell cycle. Execution of the CDC17 step was found to be a prerequisite for execution of the MBC-sensitive step; the CDC13, 16 and 23 steps are executed independently of the MBC-sensitive step; execution of the MBC-sensitive step is prerequisite for execution of the MBC-sensitive step; execution of the MBC-sensitive step is prerequisite for execution of the CDC14 and 23 steps. These results considerably extend the dependent pathway of events that constitute the cell cycle of S. cerevisiae.

Production and characterization of an antibody to myosin light chain kinase and intracellular localization of the enzyme

A specific precipitating antibody against chicken gizzard myosin light chain kinase (MLCK) has been produced in rabbits. The antibody inhibited enzyme activity in a dose-dependent manner with 11 moles of antibody required to inhibit 80% of the activity of one mole MLCK. Crude homogenates from various chicken tissues were analyzed by SDS-polyacrylamide gel electrophoresis, and the proteins were transferred onto nitrocellulose sheets and reacted with antibody. In each case, the antibody bound to only one protein with a molecular weight of approximately 130,000. These data suggest the MLCK present in all types of muscle as well as non-muscle tissues is of the same molecular weight. Indirect immunofluorescent microscopy of non-muscle tissue culture cells revealed MLCK to be localized in the spindle apparatus and midbody of mitotic cells and on the stress fibers and in the nucleolus of interphase cells. The nucleolar localization was confirmed by electron microscopy and shown to be restricted to the fibrillar region. In myofibrils isolated from skeletal and cardiac muscle, anti-MLCK decorated the actin-containing I bands of the sarcomere. These results are consistent with the suggestion that MLCK and calmodulin are intermediates in the regulation of cell motility by calcium.