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At least 19 recordsLinked to original sources
PubMed1986

Effects of cell division, cell density, and cyclic nucleotides on choline acetyltransferase activity in a cholinergic neuroblastoma cell line (S-20Y).

We investigated the effects of a number of experimental perturbations on choline acetyltransferase (ChAT) in a cholinergic mouse neuroblastoma cell line (S-20Y). ChAT specific activity increased by 4.5-fold during growth, suggesting that enzyme activity is dependent on increased cell density. This was confirmed by assessing enzyme activity at differential initial seeding densities. ChAT activity was also markedly enhanced by 1 mM dibutyryl cyclic-3',5'-AMP (dBcAMP), an effect that was blocked by cycloheximide. Confirmation of the dBcAMP effect was achieved with forskolin, a compound known to enhance intracellular cyclic AMP; forskolin (100 microM) caused a significant increase in ChAT activity. After a 20-h latent interval ChAT activity was also enhanced significantly by cytosine arabinoside. The common element in these diverse effects on ChAT activity may be cessation of cell division, although cell-cell interactions at the level of the cell membrane may also be important in the control of ChAT in S-20Y.

Animals↗
PubMed1978

Cell division, cell elongation and the co-ordination of crystallin gene expression during lens morphogenesis in the rat.

A quantitative analysis of cell division and cell elongation was carried out during lens morphogenesis in the rat. At 13 days of development elongating cells in the posterior part of the lens vesicle (presumptive fibre cells) have a lower mitotic activity than cells in the anterior vesicle. By 14 days these elongating cells do not divide. Thus at 14 days of development the lens can be separated into two compartments; a proliferation compartment in the anterior lens and an elongation compartment in the posterior lens. The three main groups of lens-specific proteins, alpha-, beta- and gamma-crystallins, were localized by immunofluorescence. alpha-crystallin is the first crystallin to be detected and is localized in some lens pit cells at 12 days of development. By 14 days all lens cells contain alpha-crystallin. beta- and gamma-crystallins are detected later at 12 1/2 days and are localized in some cells situated primarily in the posterior part of the lens vesicle. At later stages of development these crystallins are restricted to cells of the elongation compartment, i.e. presumptive fibre and fibre cells. Possible mechanisms that govern the temporal and spatial distribution of crystallins are discussed.

Animals↗
PubMed1986

Effects of asbestos fibers on cell division, cell survival, and formation of thioguanine-resistant mutants in Chinese hamster ovary cells.

The ability of crocidolite fibers to induce point mutations and mitotic abnormalities in Chinese hamster ovary (CHO) cells was examined in cell cultures. The purpose has been to study the possibilities for establishing in vitro test methods to quantify genetic damage induced by asbestos and other mineral fibers. Results obtained with the CHO/hypoxanthine guanine phosphoribosyl transferase system indicated that crocidolite fibers per se do not significantly increase the number of thioguanine-resistant mutants. Crocidolite fibers also failed to potentiate the mutagenicity of benzo[a]pyrene. Time-lapse cinematography and microscopy showed that asbestos (crocidolite) fibers were markedly cytotoxic. Among surviving cells some underwent abnormal cell divisions which resulted in multi- and micronucleate cells. Many cells that contained a few asbestos fibers, however, underwent mitosis and successfully formed two mononucleate daughter cells capable of further divisions. Individual, fiber-containing cells were examined by time-lapse television recordings for 4-5 days. During this time period some cells underwent six divisions and generated an almost normal number of daughter cells. Cells which contained fibers that were longer or equivalent to the diameter of the mitotic cell (20 microns), showed different forms of mitotic abnormalities. The frequency of multinucleate cells was drastically increased following exposure to asbestos fibers. Only rarely, however, did these cells divide to produce viable daughter cells capable of continued cell multiplication. The frequency of multinucleate cells was dependent on the dose of exposure to asbestos fibers and could possibly be used as an index of the degree of mitotic disturbances induced by mineral fibers.

Animals↗
PubMed1989

Structural similarity among Escherichia coli FtsW and RodA proteins and Bacillus subtilis SpoVE protein, which function in cell division, cell elongation, and spore formation, respectively.

The Escherichia coli cell division gene ftsW (2 min) was cloned and sequenced. It encodes a hydrophobic protein(s) with 414 and/or 384 amino acid residues. The deduced amino acid sequence and the hydropathy profile of the protein showed high homology with those of the E. coli RodA protein functioning in determination of the cell shape and the Bacillus subtilis SpoVE protein functioning in spore formation. Probably similar functional membrane proteins are involved in these three cell cycle process.

Amino Acid Sequence↗
PubMed1987

Effect of pseudopterosin A on cell division, cell cycle progression, DNA, and protein synthesis in cultured sea urchin embryos.

Pseudopterosin A is a diterpene riboside isolated from Pseudopterogorgia bipinata, a soft coral of the order Gorgonacea. Pseudopterosin A inhibits the first cleavage in fertilized sea urchin eggs (Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, and Lytechinus pictus) with an IC50 of 25 microM. In time of addition studies, Pseudopterosin A (4 X 10(-5) M) progressively blocked the first cleavage when added within the first 50 min post fertilization; when added after 50 min the first division occurred normally. Cell cycle studies show that Pseudopterosin A had to be in continuous contact with the sea urchin eggs during the initial 45 min post fertilization to significantly inhibit the first cleavage. Shorter drug contact time progressively reduced the degree of inhibition, suggesting that inhibition of cytokinesis by Pseudopterosin A was correlated with mitosis. Pseudopterosin A (4 X 10(-5) M) inhibited the uptake and incorporation of [3H]thymidine during the S2 phase. This concentration of Pseudopterosin A also inhibits protein synthesis as measured by the uptake and incorporation of [3H]phenylalanine. In this case the inhibition started before the S1 phase. Cytological examination revealed that sea urchin embryos did not progress beyond early prophase. Notably, the nuclear envelope remained intact and chromatin was condensed into chromosomes in the arrested embryos. These synchronously dividing embryos did not show any abnormalities such as lysis, swelling, or morphological changes different from control embryos.

Animals↗
PubMed1986

Control of shoot apical development via cell division.

Cell division in plants not only partitions the protoplast but also provides the architectural framework for plant form. The shape of the shoot apical meristem is produced and maintained by gradients in the rate and plane of cell division, from the summit to the base of the apical dome, which also determine the region in which primordia can be formed. In Pisum leaf initiation is mainly the result of changes in the frequency of periclinal divisions at the leaf site whereas in Silene an increase in the rate of cell division seems more important since periclinal divisions are always present. Periclinal divisions may be permissive of primordium initiation rather than causal and may define the maximum area over which primordia can form. The occurrence in Pisum and Silene of periclinal divisions which do not seem to be related to concurrent outward growth suggests that the plane of division and the direction of growth may be controlled separately and in different ways. The control of outward growth during primordium initiation may lie in the epidermis, which necessarily grows faster at the leaf site. The initial orientation of epidermal growth at the primordial site, inferred as being normal to the plane of cell division, is predominantly longitudinal in Pisum but transverse in Silene. Longitudinal growth becomes dominant later in leaf development in Silene, as in Pisum. Several lines of evidence suggest a crucial role for the epidermis in the initial stages of primordium formation although the initial orientation of division planes in it may be concerned more with the shape of the young leaf than with initiation itself. In flower initiation primordial size becomes reduced, and in Silene there are alternations of higher and lower rates of cell division in successively initiated primordial types. A fuller understanding of the role of cell division in apical growth depends on better knowledge of the functional relationships between the plane of cell division, the orientation of microtubules and wall microfibrils, and the effect that division in one cell has on its neighbours.

Cell Division↗
PubMed1976

On the mode of action of 5-diazouracil on bacterial cell division.

Cell division by strains of Escherichia coli and Salmonella typhimurium is inhibited by 5-diazouracil (5-DU). Division recovers in the presence of the inhibitor after a period which is temperature-dependent. Recovery is probably due to breakdown of 5-DU and the rate of this breakdown is apparently increased at alkaline pH. Growth with 5-DU caused only a slight reduction in the rate of murein synthesis and no alteration in the properties or composition of membranes of S. typhimurium. The agent caused chaining in Streptococcus fecalis and inhibition of the penicillin-induced lysis of S. typhimurium. These effects may have been due to direct inhibition of lysin activity but an indirect effect seems more likely. The most marked effect of 5-DU on S. typhimurium was to cause a transient inhibition of DNA synthesis. Since 5-DU did not stop uncoupled cell division (i.e. division occurring independently of DNA replication) and since lon- strains were more sensitive to 5-DU than lon+ strains, it was concluded that 5-DU acts on cell division via an inhibitory effect on DNA replication.

Azo Compounds↗
PubMed1977

Epigenetic variation of cultured somatic cells: evidence for gradual changes in the requirement for factors promoting cell division.

Cells of higher plant species in culture sometimes lose their requirement for an exogenous supply of a cell division factor that, thereafter, they are able to produce. This heritable change, known as cytokinin habituation, appears to be an epigenetic one rather than a classical mutation because it is directed, potentially reversible, leaves the cell totipotent, and involves the expression of a latent differentiated function. By using cloned cell lines derived from pith parenchyma of tobacco, we have obtained evidence that the habituation process is gradual rather than all-or-none and leads to progressively more autotrophic tissues. Cells in culture show reversible shifts among a range of habituated states but remain totipotent and can be induced to regain their requirement for a cell division factor. Thus, it appears that habituation involves epigenetic changes in a quantitative cellular phenotype. Our findings support the hypothesis that tumor progression in crown gall, a neoplastic disease of higher plants, can be accounted for by heritable changes in the pattern of gene expression.

Cell Differentiation↗
PubMed1990

Evidence for autoregulation of cell division and cell transit in keratinocytes grown on collagen at an air-liquid interface.

Oral and epidermal rat keratinocytes when cultured on a matrix of type I collagen fibrils at the interface between the gaseous and liquid phases of a culture form a highly ordered stratified squamous epithelium. Autoradiographic studies of cells labeled by tritiated thymidine indicate that the keratinocytes are capable of autoregulating cell division. Early confluent cultures exhibit 51% of basal cells labeled, a percentage that decreases to 18% when a full differentiated stratified squamous epithelium is formed. Such a decrease in labeling occurs in cultures where the mitotically active basal cells have unimpeded access to culture medium supplied from below and when no cell type other than the keratinocyte is present in the culture. Additionally, the transit of keratinocytes from the basal cell layer through other viable cell strata to the layer of terminally differentiated cells can be followed by tracking cells labeled with tritiated thymidine. In cultures of oral keratinocytes, cells move from the basal cell layer to the cornified layer at a maximum rate of 7 days, while virtually all labeled cells (91%) are localized in the terminally differentiated cell layer 14 days following labeling. Keratinocyte cultures grown in culture at an air-liquid interface exhibit tissue organization that closely resembles the native, parent tissue. Such cultures can be useful in studying the effects of pharmacologic mediators of cell division and cell transit.

Air↗
PubMedDate not supplied

Slit scanning of Saccharomyces cerevisiae cells: quantification of asymmetric cell division and cell cycle progression in asynchronous culture.

Slit scanning flow cytometry has been applied to the analysis of the cell cycle and cell-cycle-dependent events in Saccharomyces cerevisiae, yielding information on the low-resolution spatial distribution of cellular components in single cells of unperturbed cell populations. Because this process is rapid, large numbers of cells can be analyzed to give distributions of parameters in a given population. To study asymmetric cell division and cell cycle progression, forward-angle light scattering (FALS) signals together with fluorescence signals from acriflavine-stained nuclei have been measured in cells from exponentially growing yeast populations. An algorithm has been developed that assigns the position of the bud neck in the FALS signals so that both FALS and DNA signals can be analyzed in terms of the contributions from the mother cell and the cell bud. The data indicate that mother cell FALS, on average, remains constant while FALS due to the cell bud increases as a cell progresses through the cell cycle. By identifying mitotic cells and measuring their properties, we have found that the coefficient of variation for the distribution of FALS is smallest within the dividing cell population and largest within the newborn cell population, in accordance with the critical size control mechanism of yeast cell growth. The use of this experimental approach to provide data for statistical population models is discussed.

Acriflavine↗
PubMed1974

The effects of isopropyl N-phenyl carbamate on the green alga Oedogonium cardiacum. I. Cell division.

Cell division in vegetative filaments of the green alga Oedogonium cardiacum is presented as an experimental system. We report on how we have used this system to study the effects of isopropyl N-phenylcarbamate (IPC) on the mitotic apparatus and on the phycoplast, a planar array of cytokinetic microtubules. Polymerization of microtubules was prevented when filaments, synchronized by a light/dark regime and chilled (2 degrees C) while in metaphase or just before phycoplast formation, were exposed to 5.5 x 10(-4) M IPC and then returned to room temperature. Spindles reformed or phycoplasts formed when these filaments were transferred to growth medium free of IPC. However, the orientation of both microtubular systems was disturbed: the mitotic apparatus often contained three poles, frequently forming three daughter nuclei upon karyokinesis; the phycoplast was often stellate rather than planar, and it sometimes was displaced to the side of both daughter nuclei, resulting in a binucleate and an anucleate cell upon cytokinesis. Our results suggest that IPC (a) prevents the assembly of microtubules, (b) increases the number of functional polar bodies, and (c) affects the orientation of microtubules in O. cardiacum. High voltage (1,000 kV) electron microscopy of 0.5-microm thick sections allowed us to visualize the polar structures, which were not discernible in thin sections.

Carbamates↗
PubMed1978

Mutants altered in the control co-ordinating cell division with cell growth in the fission yeast Schizosaccharomyces pombe.

The control co-ordinating cell division with cell growth has been investigated in the fission yeast Schizosaccharomyces pombe. Twenty-five mutants altered in this control have been isolated which have the same growth rate as wild type but divide at a smaller cell size. The mutants define two genes wee 1 and wee 2, both of which are involved in a control initiating mitosis when the cell attains a critical size.

Cell Count↗
PubMed1978

Cell division and cell allocation in early mouse development.

Cell division was observed in intact and dissociated mouse embryos between the 2-cell stage and the blastocyst in embryos developing in culture. Division to the 4-cell stage was usually asynchronous. The first cell to divide to the 4-cell stage produced descendants which tended to divide ahead of those cells produced by its slow partner at all subsequent stages of development up to the blastocyte stage. The descendants of the first cell to divide to the 4-cell stage did not subsequently have short cell cycles. The first cell or last cell to divide from the 4-cell stage was labelled with tritiated thymidine. The embryo was reassembled, and it was found that the first pair of cells to reach the 8-cell stage contributed disproportionately more descendants to the ICM when compared with the last cell to divide to the 8-cell stage.

Animals↗
PubMed1975

Control of cell division and cell differentiation by deoxynucleotides in the early embryo of Xenopus laevis.

It is proposed that the deoxyriboside triphosphates present in the egg of Xenopus laevis support the synchronous cell divisions occurring during the earliest phase of embryonic development and that, as long as synchrony prevails, the cells are prevented from undergoing differentiation. This hypothesis has been tested by injecting deoxyribonucleotides into fertilized eggs. The following effects were observed: 1) the duration of synchrony is prolonged, 2) the morphological development is suppressed, an effect which is greatest when four nucleotides are injected together and 3) the synthesis of all kinds of RNA is inhibited, including the mRNA required for differentiation to occur.

Adenosine Triphosphate↗
PubMed1989

Inhibition of growth of ftsQ, ftsA, and ftsZ mutant cells of Escherichia coli by amplification of a chromosomal region encompassing closely aligned cell division and cell growth genes.

Amplification of a 2.6-kilobase chromosomal fragment of the mra region of Escherichia coli encompassing the ftsI(pbpB) gene and an open reading frame upstream with lethal to E. coli strains with mutations of the flanking cell division genes ftsQ, ftsA, and ftsZ. A shortened fragment in which the major portion of ftsI was deleted also had lethal effects on ftsQ and ftsZ mutants.

Bacterial Proteins↗