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At least 865 records · Page 48Linked to original sources

PubMed1987

Disassembly of the nucleus in mitotic extracts: membrane vesicularization, lamin disassembly, and chromosome condensation are independent processes.

We describe a stable cell-free mitotic extract derived from Xenopus eggs that contains activities necessary for nuclear envelope breakdown and chromosome condensation during mitosis. Using these cell-free extracts, we have demonstrated that nuclear envelope vesicularization, lamina solubilization, and chromosome condensation are independent and separable biochemical processes. We present evidence indicating that during mitosis nuclear membrane breakdown may involve the binding of a coating protein, lamin solubilization is enzymatically driven, and chromosome condensation involves both binding proteins and enzymatic activities including topoisomerase II. These results provide a coherent framework for investigating structural modification of the nucleus during mitosis at the biochemical level.

Animals↗

PubMed1987

DNA topoisomerase II is required for condensation and separation of mitotic chromosomes in S. pombe.

We show that DNA topoisomerase II (topo II) is continuously required for mitotic chromosome changes in Schizosaccharomyces pombe. We constructed cold-sensitive (cs) or temperature-sensitive (ts) strains mutated in the genes coding for topo II (top2) and beta-tubulin (nda3). The ATP-dependent activity of the top2cs gene product is cs in vitro. The cloned top2cs gene sequence predicts an amino acid substitution. A cs top2-cs nda3 double mutant at 20 degrees C shows long, entangled chromosomes, which condense and separate upon the shift to permissive temperatures. If spindle formation is prevented at permissive temperatures, the chromosomes condense but do not separate. Thus topo II is required for final chromosome condensation; moreover, pulse-shift experiments show that topo II is required for chromatid disjuction. Experiments with ts top2-cs nda3 cells show that topo II is also required for chromosome separation in anaphase: inactivation of topo II and activation of beta-tubulin allow normal spindle formation but result in "streaked" chromosomes.

Adenosine Triphosphate↗

PubMed1994

Effects of cycloheximide on chromatin condensations and germinal vesicle breakdown (GVBD) of cumulus-enclosed and denuded oocytes in cattle.

To determine if newly synthesized protein is imperative for the resumption of meiosis in bovine follicular oocytes collected from small antral follicles, cumulus-enclosed and denuded oocytes were cultured in TCM-199 both with and without various concentrations of the protein synthesis inhibitor, cycloheximide. After 11 h of culture in inhibitor-free medium, all oocytes had undergone germinal vesicle breakdown (GVBD). However, when concentrations of more than 1.0 mug/ml cycloheximide were added to the medium, the meiotic resumption of bovine oocytes was completely blocked. This inhibitory effect of cycloheximide was fully reversible after removal of the inhibitor from maturation media. Germinal vesicle breakdown following removal of cycloheximide occurred twice as fast as in the control medium. Nevertheless, when oocytes were arrested at the germinal vesicle (GV) stage by cycloheximide, a significantly higher proportion of chromatin condensation (40 to 57%) was observed in denuded oocytes than in cumulus-enclosed oocytes (11 to 22%). Thus the cycloheximide treatment could not prevent the chromatin condensation in only denuded oocytes. We conclude that protein synthesis is a prerequisite for GVBD in bovine follicular oocytes and that cumulus cells are responsible for the complementary regulation of the chromatin condensation at the GV stage, regardless of protein synthesis in the oocytes.

Journal Article↗

PubMed1991

Mitosis-arresting effects of cigarette smoke condensate on human lymphoid cell lines.

Whole-smoke condensates from the University of Kentucky reference cigarettes induced partial mitotic arrest in 4 human lymphoid cell lines. Treatment of cells for 3 h with 100 and 200 micrograms of cigarette-smoke condensate/ml of culture medium increased the frequency of metaphases and decreased the proportion of anaphases in the treated cell populations. Cytoskeletal studies using antitubulin immunofluorescence techniques and transmission electron microscopic studies demonstrated that in early stages of mitosis the formation of aster and the separation of centrosomes in condensate-treated cells were comparable to those of untreated control cells, but the poleward migration of centrosomes was inhibited. Arrested metaphases revealed two centrosomes surrounded by aggregated chromosomes in the center of each cell but the structure of the centrioles, microtubules and the kinetochores appeared normal. The results demonstrate the presence of antimitotic compounds in the tobacco-smoke condensate.

Analysis of Variance↗

PubMed1995

Cytotoxicity and genotoxicity of wood drying condensate from Southern Yellow Pine: an in vitro study.

We tested condensates from Southern Yellow Pine for potential cytotoxicity and genotoxicity in CHO-WBL and human peripheral blood lymphocytes (PBL) in the absence of S-9 activation. Cytotoxicity was evaluated by the Trypan blue exclusion assay, mitotic index (MI) and proliferative rate index (PRI). Genotoxicity was measured by the chromosome aberration (CA) assay and sister chromatid exchange (SCE) analysis. Both cytotoxic and genotoxic effects were observed. Laboratory-generated Southern Yellow Pine condensate reduced the viability of CHO-WBL cells. The number of viable cells was roughly inversely proportional to dosage over a range of 100% to 31% in treated groups, in both experiments, as compared to 2.6 x 10(5) (100%) in the control. The MI data in both CHO cells and PBL also showed an inverse correlation. The highest scorable dose limited by toxicity was determined to be 1 ml of Southern Yellow Pine condensate in 10 ml total of medium. Lastly, a dose response curve was observed in CHO cells, as well as in PBL, using the CA assay and also with the SCE analysis. The present findings corroborate the results from Ames testing and represent the only information currently available on the genotoxic potential of these chemicals.

Animals↗

PubMed1985

Double minutes in prematurely condensed chromatin of human tumor cells.

Comparative studies on the occurrence of double minutes (DMs) were performed on metaphases and prematurely condensed interphases (G1, G2) of cells from 28 cancerous effusions of 24 carcinoma patients. In 21 of these effusions, agreement between metaphase and prematurely condensed chromatin (PCC) data was obtained concerning occurrence or nonoccurrence of DMs (10 DM positive, 11 DM negative). In two cases, DMs were observed in metaphases only, whereas in five cases, they were found in interphases only. In normal cells, no DMs could be found, neither in metaphase nor in PCC. No causal correlation of the occurrence of DMs and cytostatic therapy was found. The data suggest that cytogenetic screening of prematurely condensed interphase cells from human tumors or cancerous effusions provides a valuable method for estimating the incidence of gene amplification in malignant cells, particularly in those with poor mitotic yield.

Adult↗

PubMed1987

Premature chromosome condensation in human cervical carcinoma.

Premature chromosome condensation was observed in 22 of 150 cases (15%) of cervical cancers studied with G-banding. The percentage of premature chromosome condensation in the tumors ranged from 1.5% to 8.9%. Premature chromosome condensation was present in greater frequency (16 of 22 cases) in tumors showing hyperdiploidy, suggesting that this could be a major mechanism of induction of polyploidy in addition to other operative mechanisms, such as endomitosis and endoreduplication. No relationship, either with the disease stage or prognosis, was evident.

Adult↗

PubMed1989

Simultaneous cell type identification and premature chromosome condensation analysis in a case of multiple myeloma.

The technique of premature chromosome condensation was combined with immunocytochemical techniques to determine the karyotype of the plasma cells in a patient with multiple myeloma. Although the patient's myeloma cells had a diploid DNA content, the mean chromosome number was 39. Multiple chromosome rearrangements were documented in the G- and C-banded G1 and G2 prematurely condensed chromosomes, and several of these involved telomeric regions resulting in dicentric chromosomes. That the aberrant karyotype was present in the kappa light chain positive plasma cells was proved by simultaneous chromosome analysis and immunocytochemical examination of the fused cells. Thus the combination of premature chromosome condensation and immunocytochemistry proved a powerful tool for cytogenetic analysis of a slow-growing, heterogeneous cell population.

Adult↗

PubMed1985

Condensation of the chromatin gel by cations.

Calf thymus chromatin gel, containing strongly bound nonhistone proteins, was used to study the effect of easily removable and tightly bound cations on the condensation of chromatin. The chromatin volume was found to be linearly dependent on the reciprocal square root of the concentration of easily removable cations (Tris X H+ + Na+ and Mg2+) except for the initial stages of condensation (up to 7-10 mM monovalent and 0.15-0.2 mM divalent cations). The effect of Mg2+ at the initial stage of condensation was not reproduced by Na+ and vice versa. At higher concentrations the effects of Na+ and Mg2+ were additive. The removal of tightly bound divalent cations by a treatment of the chromatin gel with 1,10-phenanthroline led to an approx. 50% increase in the volume of the chromatin gel, which was maintained at each concentration of easily removable cations. The 1,10-phenanthroline-caused decondensation of the chromatin gel was reversed by Ca2+ but not by Mg2+, Zn2+ and Cu2+. The chromatin gel pretreated with Ca2+ was not further decondensed by 1,10-phenanthroline.

Animals↗

PubMed1983

Surprising consequences of the tendency of pepsin to catalyze condensation reactions between small peptides.

Pepsin catalyzes numerous acyl-transfer reactions. Are peptic acyl-enzyme intermediates involved in such reactions? To start, we examine the cleavage of Leu-Trp-Met-Arg at pH 3.4-4.5 in the presence of 25 mM tryptophanamide. Substantial amounts of Leu-TrpNH2 are generated. However, the appearance of this acyl-transfer product cannot be attributed to the intervention of Leu-pepsin and its trapping by tryptophanamide. Experiment proves that Leu-Trp-Met-Arg affords Leu3, which, in turn, reacts with tryptophanamide to produce Leu-TrpNH2. Both the formation of Leu3 from Leu-Trp-Met-Arg and the conversion of Leu3 + tryptophanamide into Leu-TrpNH2 can potentially implicate the generation and trapping of a Leu-pepsin intermediate. Does experiment support either possibility? The answer is no. Our data show that most of the Leu3 derived from Leu-Trp-Met-Arg stems from an autocatalytic condensation process whereby Leu3 already present speeds the conversion of the leucine residues of unreacted Leu-Trp-Met-Arg into more Leu3. Technical problems have prevented us from determining whether the first Leu3 formed results from the trapping of an acyl-enzyme intermediate. The generation of Leu-TrpNH2 from Leu3 was studied primarily via a more tractable analogous reaction: Leu-Trp-Leu + tryptophanamide leads to Leu-TrpNH2. The mechanism governing these transformations is highly complex. Its major feature is an initial condensation between two molecules of substrate. All the examples investigated further illustrate the marked tendency of pepsin to catalyze condensation reactions between suitably constructed small peptides. The prevalence of these reactions complicates the interpretation of much data bearing on pepsin's mechanism of action.

Amino Acid Sequence↗

PubMed1985

Uncertainties of topodiagnosis of auditory nerve and brain-stem auditory evoked potentials due to rarefaction and condensation stimuli.

Auditory nerve and brain-stem auditory evoked potentials (AN and BAEP) were elicited after separate stimulation with rarefaction and condensation stimuli. There were only few persons with identical patterns in the two opposite phases. Rarefaction stimuli showed a tendency to evoke AN and BAEP with shorter latencies and better synchronization. In diseases of the auditory nerve and brain-stem the phase-dependent differences were even more prominent, indicating different topodiagnostic levels of lesions. The results point to the need for stimulus presentation with rarefaction and condensation stimuli separately and an evaluation of both curves. The alternating mode is the result of summating rarefaction and condensation stimuli.

Brain Stem↗

PubMed1993

Cross infection in an intensive care unit by Klebsiella pneumoniae from ventilator condensate.

Klebsiella pneumoniae serotype K28 was cultured from six patients over 5 weeks in a general Intensive Care Unit. Colonized condensate in the ventilator expiratory water traps was the probable source of the organism, and hand carriage the vehicle of transmission. Although the cross-infection hazard of ventilator tubing condensate is recognized, there is no report in the literature of an outbreak caused by such fluid. Ventilator tubing condensate should be viewed as contaminated clinical waste and dealt with accordingly.

Aged↗

PubMed1987

Prevention and reversal by a non-polar arotinoid (Ro 15-0778) of 3,4-benzpyrene- and cigarette smoke condensate-induced hyperplasia and metaplasia of rodent respiratory epithelia grown in vitro.

A non-polar arotinoid, Ro 15-0778, has been investigated for its effect on carcinogen-induced changes in rodent respiratory epithelia in organ culture. In neonatal rat tracheas and fetal mouse lungs grown in vitro, 3,4-benzpyrene and cigarette smoke condensate induce an increased proliferation of epithelial cells associated with a loss of secretory activity and of ciliary function. These changes persist in the absence of carcinogens in explants transferred to control medium. Ro 15-0778 alone has no influence on the normal epithelial growth rate or normal differentiation. However, if combined with either benzpyrene or smoke condensate, the arotinoid antagonizes the carcinogen-induced hyperplasia and metaplasia. During simultaneous treatment, it prevents the increase in mitosis and the loss of secretory activity or ciliary function. In explants pretreated with benzpyrene or cigarette smoke condensate, Ro 15-0778 reverses the high proliferation rate and restores secretory differentiation and ciliary function. The compound is of experimental and clinical interest, since--in contrast to most retinoids--it lacks the signs and symptoms of the classical hypervitaminosis A syndrome. It may be justified to consider it for the treatment of early precancerous changes of the bronchial tree.

Animals↗

PubMed1992

Effects of phenolic smoke condensates and their components on hepatic drug metabolizing systems.

Treatment of food with wood smoke is a long-established method of preservation and flavouring food. Recently, hardwood smoke condensates, purified of polycyclic hydrocarbons, have become of importance for direct flavouring of sausage-meat. The acute toxicity of the purified phenolic fraction in mice after intraperitoneal administration was therefore investigated. The LD50 was found to be 940 mg/kg body weight, which is about three times the LD50 of phenol (about 300 mg/kg). Only high concentrations of phenols or smoke condensate fractions are able to damage cytochrome P-450 by conversion to cytochrome P-420, whereas lower concentrations exhibit inhibitory effects on monooxygenase activity. Inductive properties of the phenolic fractions could not be demonstrated. Concentrations in vivo of free phenolic compounds do not reach inhibitory levels, since the hexobarbital-induced sleeping-time and 14CO2-exhalation after administration of p-[methoxy-14C] acetanilide are not altered. It is concluded that the phenolic compound intake with food regularly treated with smoke condensate fractions is below a toxicologically relevant level.

7-Alkoxycoumarin O-Dealkylase↗

PubMed1982

The tumourigenicity of smoke condensates from cigarettes containing different amounts of cytrel, as assessed by mouse skin painting.

Smoke condensates derived from cigarettes containing different amounts of the tobacco supplement Cytrel were painted onto the banks of mice 3 times a week for 104 weeks. Cigarette samples contained 0, 25, 50 or 100% Cytrel, blended with tobacco, and 3 dose levels were used for each sample. Statistical analyses were made of tumour incidence using a mathematical model based on the Weibull distribution. Good dose relationships were observed for each product; and for samples containing Cytrel there was a reduction in smoke condensate production and in tumourigenicity (per unit weight of smoke condensate) approximately proportional to the level of inclusion. Histopathological examinations of tumours indicated a reduction in malignancy of approximately 50% for all-Cytrel samples when compared with all-tobacco samples.

Animals↗

PubMed1992

The use of purified condensed tannin as a reference in determining its influence on rumen fermentation.

1. Tannins were purified from the leaves of trees forming part of giraffe's diet in the Kruger National Park. 2. In general, hydrolysable tannin formed less than 10% of the total purified crystal complexes, condensed tannin and possibly some non tannin phenols forming the balance. 3. Each tree species condensed tannin gave a different calibration curve and these were used in the assay. 4. Volatile fatty acid production during in vitro fermentation was greatly reduced when the substrate contained more than 6% condensed tannin.

Animals↗

PubMed1980

Induction of prematurely condensed chromosomes by mitoplasts.

The objective of this study was to obtain pure prematurely condensed chromosomes (PCC) by a fusion between mitoplasts and interphase G1 cells. The stabilization of mitoplasts with spermine (25 microM) and a modification of the Sendai virus-mediated fusion enabled us to obtain pure PCC without contaminating mitotic chromosomes. This study clearly suggests that the factors for premature chromosome condensation induction are present in the cytoplasm of the mitotic cells. Pure PCC obtained by this method may help us to understand the nature of the factors initiating chromosome condensation and cell division.

Cell Fusion↗

PubMed1992

Chromatin condensation: does histone H1 dephosphorylation play a role?

In this article we describe three distinct biological systems where histone H1 phosphorylation is uncoupled from mitosis and highly condensed chromatin is enriched in dephosphorylated forms of H1: the amitotic macronucleus of Tetrahymena, terminally differentiated avian erythrocytes and sea urchin sperm. Each system offers informative contrasts to the idea that H1 hyperphosphorylation is causally related to mitotic chromosome condensation. Assuming that higher order chromatin folding is primarily driven by electrostatic interactions between H1 and DNA, an alternative model is presented for the role of H1 phosphorylation in chromatin condensation.

Animals↗